Using Lithium batteries in parallel?

[anotherkiwi]

You are over complicating and as d8veh and I tried to explain human error is where your LiPos will go wrong. 6 X 16 Ah should get you across the Atlantic nicely on one charge...

Parallel 4 x 16 Ah packs using your reinforced wiring balance board, plug your balance cables in, plug a LiPo alarm (set to 3.65 V) into the balance out socket.

There you have a nice 64 Ah battery that will return about 51 Ah if you charge to 4.15 V per cell that is 1895 Wh! Compare to the 450 Wh of a typical lead acid battery... It is capable of 640 Amps nominative at 10 C (about 120 real Amps) so don't go short circuiting anything - lots of sparks guaranteed.

When you need to charge unplug the LiPo alarm, plug the balance board output into the charger, plug the balance cable from the charger into the balance board and charge.

Use the other two packs as spares or on a second cruise ship...

What I would do (KISS method):

Parallel up 3 pairs of 16 Ah packs to make 3 x 32 Ah batteries with a simple parallel harness from HK or home made. Bang a LiPo alarm on each pack.
Put each battery in a nice puncture proof box (washing powder boxes are just the right size for 10 Ah) and put each in a separate waterproof bag.
Use one battery till the alarm goes off
Unplug and plug in another
Repeat
Enjoy

 

[T i m]

You are over complicating and as d8veh and I tried to explain human error is where your LiPos will go wrong.

.
So, if that's where I *will* go wrong (especially at the beginning), why would it be unreasonable for me to try to make things safer if if I choose to?

6 X 16 Ah should get you across the Atlantic nicely on one charge...

That would be a nice thought. ;-)

Parallel 4 x 16 Ah packs using your reinforced wiring balance board, plug your balance cables in, plug a LiPo alarm (set to 3.65 V) into the balance out socket.

Ok, just OOI, why would I *need* a balance board for say £25 (for XT90) when a balance harness is £1.65 and the XT90 plugs and some wire just a few quid? I mean what does a balance board give me that a couple of harnesses (where all the battery power leads join in a bigger plug) don't?

There you have a nice 64 Ah battery that will return about 51 Ah if you charge to 4.15 V per cell that is 1895 Wh!

So why only 4 of my 6 cells OOI?

Compare to the 450 Wh of a typical lead acid battery... It is capable of 640 Amps nominative at 10 C (about 120 real Amps) so don't go short circuiting anything - lots of sparks guaranteed.

No, no (big) sparks, resettable fuses mate. ;-)

When you need to charge unplug the LiPo alarm, plug the balance board output into the charger, plug the balance cable from the charger into the balance board and charge.

Yes, I know how I could do it ... but have you read how I suggested I could do it and ignoring the perceived 'complexity' (that is my problem not yours <g>), what have I suggested that is going to make anything worse or less safe?

Use the other two packs as spares or on a second cruise ship...

If this 96Ah solution works as well as you suggest it might I may go for another. ;-)

What I would do (KISS method):

Parallel up 3 pairs of 16 Ah packs to make 3 x 32 Ah batteries with a simple parallel harness from HK or home made. Bang a LiPo alarm on each pack.
Put each battery in a nice puncture proof box (washing powder boxes are just the right size for 10 Ah) and put each in a separate waterproof bag.
Use one battery till the alarm goes off
Unplug and plug in another
Repeat
Enjoy

Except ... what sort of power do I assume to have left when the pack suddenly alarms and I'm halfway under a tunnel or passing a weir etc?

Why wouldn't I have all 6 packs in parallel, after all, you can easily get Balance Boards, BMS's and power harnesses in combinations of 6, why wouldn't I have them all in place at one time?

Ok, the bottom line for me is to have a solution, however 'complicated' it may seem to those who may be more familiar with such things that gives me the most protection, the most feedback and the biggest capacity I can get for say 10kgs.

I like designing technical solutions ... I like wiring and soldering ... I like having the most feedback possible and all I'm asking from you guys (with respect) is to qualify if what I'm proposing to do (that will be good for me and part of the interest for me) won't make matters (in a functional sense) worse or less safe? I don't care how complex or complicated it may seem to others, it's what I want to do as part of my learning and fun and none of it is written in stone. ;-)

See, I didn't win a IEEE award for 'Technical Innovation' on my home made electric racing bike because I made it simple. What I did was used some new / innovative ideas to make a system that was considered 'good' by some independent observers and that made the system better / easier to monitor using simple stuff in a technical way (in comparison with the other competitors anyway). ;-) [1]

Cheers, T i m

[1] It was interesting walking round the pits and seeing the vehicles designed and built by others. The carpenters had beautifully crafted wooden machines but the wiring, transmission and steering often left a lot to be desired. Those who worked for high tech materials suppliers used some exotic and expensive materials for the body but often with huge compromises in the rest of the design. The engineering on the engineers machines was often exotic and precise but the wiring was a mess. The electrical engineers had lovely wiring but the (spoked) wheels collapsed on the first corner (etc etc). ;-)

I was a motorcyclist and so by running a two wheeler I didn't stress the wheels (spokes) on the corners like the three and four wheelers did. Cycle transmission parts were cheap, light and strong enough without me needing to do any complex engineering (although I did have to make a large sprocket (by hand) for the primary reduction stage). As an electronics support tech I was able to design and build all the telemetry gear using cheap and readily available parts (and ended up with a digital speedo that had a greater accuracy and resolution than a RADAR gun <g>). The lower half of the nose fairing was moulded by me in fibreglass using a bubble windscreen (used on the top half) as the mould. The steel (triangulated) frame with rear swinging arm suspension was once my old bench when I worked at BT, welded up by me in our spare (undecorated at the time) bedroom. ;-)

It all took a long time but it never let me down on any race and I enjoyed the building and fettling of it as much as I enjoyed the racing. ;-)

p.p.s And I could use my Sinclair C5 as a 'pit trike' for running about between the races. ;-)

 

[anotherkiwi]

I'm pretty sure I calculated Wh for a 36 V battery above - tired...

The balance board makes paralleling 4-5-6 packs as easy a plugging them in. I can't see you needing more than 32 Ah with 32 more as a backup but I may be wrong.

 

[T i m]

I'm pretty sure I calculated Wh for a 36 V battery above - tired...

Ok. ;-)

The balance board makes paralleling 4-5-6 packs as easy a plugging them in.

Yes, I know, but I'm trying to see how it makes it any 'easier' than using two harnesses mate? After all, electrically they are identical and with harness I don't have to find anywhere to stick the board?

I can't see you needing more than 32 Ah with 32 more as a backup but I may be wrong.

Well, assuming 32Ah (2x16) with 25Ah useable then just on speed 3 (without a PWM controller so 15A) would give me a run time of just over 1.5 hours. Now, that could be ok ... but on it's own it's less than we currently get with the single 60Ah LA. Being able to swap out to the next battery (of 3 total) could be a viable solution (compared with just one big one) or more logically with 6 packs, to have the 2 x 3 pack combo so I could use one battery 'out' and the other 'back' and giving me nearly 2.5 hours each way (5 hours run time total). We are getting there. ;-)

A disadvantage of not having one big battery is you would probably have to re-charge each 'battery' (say 3 x 16A) separately as it would probably take too long to equalise to charge in parallel and I think I understand that partial discharges are 'better' on the battery than full (for safety and lifespan)?

Subject to the maximum weight for any single 'battery' not wanting to exceed say 10kgs (inc any container be it a lunch bag or an ammo box <g>), the ultimate solution would be to have enough battery power in two batteries to be able to cruise all day (as we know we should be able to get back as long as we turn round as soon as the first battery is exhausted). ;-)

Don't forget, that is out or goal, We aren't into fishing or the sea (we like to go boating when we want, not when the water happens to be there) and 'spending a day on the water' means exactly that! ;-)

Now, it's very possible we might supplement the outboarding with rowing (as the eBikers would with straight pedalling) and possibly, with the outboard and battery stashed away in waterproof bags, some sailing.

The last trip we did like that was in the 14' sailing dinghy with a 2hp Yamaha 2/ outboard. We sailed for about 6 hours (Norfolk Broads) but were then becalmed and outboarded back. ;-)

Cheers, T i m

 

[T i m]

Two 4S batteries in parallel with LiPo alarms:

So, more of my bits have come though in the post and I've just soldered some XT90's on my power monitor (like yours). I've also found that there is probably a technique for soldering AWG12 cable into the XT90's to make a general purpose charge / discharge / test cable and practice for making a harness (getting all the strands into the receptacle).

I notice you have two monitor / alarms on your (parallel) setup and I thought I remember it being suggested that having a monitor on each pack to be an overkill and that the balance leads should also be paralleled and one monitor applied to that?

The only thing that still troubles me with that is then you are trying to use the 2 x 4S as a 4S2P, rather than hefty bus bars forming the 2P part, you just have skinny balance wires?

Now, I realise that if all cells are of the exact same capacity and performance, discharging them from the ends of the 4S should see all intermediate voltages of all cells decrease identically but I'm guessing that ITRW that's rarely the case (and hence why parallel cell groups are generally constructed with substantial bus bars)?

What I am thinking out loud is that whist I'm guessing I would be advised by some here that say 30A being drawn from across 3 x 4S 16000 mAh packs isn't likely to cause particularly high balancing currents within the balance leads ... but if that's an ideal situation I guess that's how they would wire all parallel LiPo packs of this size and I don't think they do?

Anyroadup ... I am still playing with the idea of going 2 x 3 packs over 1 x 6 (depending on the RW capacity of the packs etc) and have ordered 6 x fireproof pouches that should take one pack in each (so IF one goes up it might not take out the other 2 / 5) and it will also help me protect each pack physically as well.

Reading around further on Lithium chemistry batteries in general it seems that if you want to prolong the cycle life then restricting the maximum depths of charge and discharge can make a big difference. Now I can't see the number of cycles being an issue in my current application (electric outboard on a boat) so what voltage limits would the panel suggest would be a good compromise between (in order of importance to me) 1) safety 2) best capacity and 3) cycle life on these 16A LiPo packs please?

Cheers, T i m

p.s. Do I understand correctly that EV car battery packs (like say the Tesla) only give long cycle lives when running the cells between 20 and 80% charge? Take that to 25-75% and you are on the same range as a LA battery (100 - 50%)? However, with a LA it's called DOD but is it called something different when you don't start from 100% charge?

 

[Deleted member 4366]

I don't think anybody knows. Most people would say that 4.2v is 100% charged. Depending on who you ask, 100% discharged could be 2.5v, 3v or 3.1v.

Now, are we going to measure DOD in volts or charge. If we used 2.5v as 100% DOD, then 3.1v would be 65%, though others might call that 100%. There's virtually no difference in the amount of charge in the cells between 3.1v and 2.5v, so 3.1v could be 99.5% DOD and 2.5v would be 100%

Lipos fall off a cliff when they get down to about 3.5v, which some people would call 41% DOD, but others would call it 95% DOD because there's very little charge left in the cells.

A lot of that battery University stuff was done years ago, before the manufacturers found ingredient X to put in their batteries. Personally, I wouldn't worry about any of that old theory. It probably still holds true to an extent, but more likely, you'll brick your packs long before they ever wear out, so probably better to get every bit of enjoyment out of them while you can. Charge them to 4.2v and run them down to 3.5v. Don't set your alarms to 3.1v. By the time you hear the alarms, the batteries may already be bricked. They go down so quickly at that voltage.

 

[T i m]

I don't think anybody knows.

Ah, 'magic', (as some would see it) like WiFi or Bluetooth. ;-)

Most people would say that 4.2v is 100% charged.

Noted.

Depending on who you ask, 100% discharged could be 2.5v, 3v or 3.1v.

Looking as a range of (random) discharge graphs on the net it looks like at 1C, 3.5V could also be considered?

Now, are we going to measure DOD in volts or charge. If we used 2.5v as 100% DOD, then 3.1v would be 65%, though others might call that 100%. There's virtually no difference in the amount of charge in the cells between 3.1v and 2.5v, so 3.1v could be 99.5% DOD and 2.5v would be 100%

True.

Lipos fall off a cliff when they get down to about 3.5v, which some people would call 41% DOD, but others would call it 95% DOD because there's very little charge left in the cells.

If cutting off slightly early would be considered 'a good thing' then I'm happy to do it. ;-)

A lot of that battery University stuff was done years ago, before the manufacturers found ingredient X to put in their batteries. Personally, I wouldn't worry about any of that old theory. It probably still holds true to an extent, but more likely, you'll brick your packs long before they ever wear out, so probably better to get every bit of enjoyment out of them while you can.

Hmmm. ;-(

Charge them to 4.2v and run them down to 3.5v. Don't set your alarms to 3.1v. By the time you hear the alarms, the batteries may already be bricked. They go down so quickly at that voltage.

Understood and agreed. Do you think though that if I'm only discharging each pack at ~.3C (15A across 3 x 16A packs) that even 3.5V could be a little low?

Whilst waiting for the bits to do some experiments with these packs I've been testing some LiIon cells from an old Toshiba battery pack. Thy were wired 3S2P and the terminal voltages were all over the place and one below 1V. All seem to have recovered (all be it only giving ~1250 mAh down to 3V) and now I'm just doing a self discharge test. Is LiIon just more durable than LiPo?

Cheers, T i m

 

[anotherkiwi]

The only thing that still troubles me with that is then you are trying to use the 2 x 4S as a 4S2P, rather than hefty bus bars forming the 2P part, you just have skinny balance wires?

You parallel the discharge wires BEFORE you parallel the balance wires. You plug the discharge wires into your charger before you plug in the balance plug. etc. etc. It is in the manual, you read that?

p.s. Do I understand correctly that EV car battery packs (like say the Tesla) only give long cycle lives when running the cells between 20 and 80% charge? Take that to 25-75% and you are on the same range as a LA battery (100 - 50%)? However, with a LA it's called DOD but is it called something different when you don't start from 100% charge?

Tesla wants the battery pack to give about 80% of its capacity for many years. They can get away with that because there is space and carrying capacity for a huge battery.

There is no possible comparison between the energy density of a lithium battery and LA, LA gives heaps of current for a very short time where lithium gives heaps of current for hours on end.

I charge to 4.15 V and discharge to 3.65 V, your iCharger allows you to set the voltage per cell which is good news some of the cheaper chargers don't. So that is 0.05 V less than full and I stop at 0.15 V before recommended LVC. Does that help battery life? Don't know and really care with LiPo bought at sale price. In any case there is no noticeable difference in range and the 10 Ah battery gives over 8.7 Ah (haven't bothered counting lately) which is 87% of capacity on the label.

 

[T i m]

You parallel the discharge wires BEFORE you parallel the balance wires. You plug the discharge wires into your charger before you plug in the balance plug. etc. etc. It is in the manual, you read that?

Erm yes, I think you have misunderstood my question. ;-)

I was saying if you had say a pack that was (internally, like mine) 4S2P, the P's would be connected together by substantial capacity wires, certainly MUCH more substantial than the conventional balance leads you find hanging out of a battery pack. In fact, I'm not sure the balance leads on my 16Ah packs are any bigger than those I have seen on 1A packs?

So, if you make a 4S4P by doing what has been suggested here by paralleling both the power and balance leads, in the case of a large load placed on a big pack, the imbalance between the cells could be significant and so possibly overwhelm the capacity of the balance wires?

I noticed with your twin parallel pack, you *didn't* parallel the balance wires and had two monitors etc?

Tesla wants the battery pack to give about 80% of its capacity for many years. They can get away with that because there is space and carrying capacity for a huge battery.

Ok.

There is no possible comparison between the energy density of a lithium battery and LA, LA gives heaps of current for a very short time where lithium gives heaps of current for hours on end.

You mean for the same weight presumably? Millions of Milk floats, fork lift trucks and many submarines did / do very well with Lead Acid batteries for many years and a lot cheaper than Lithium (especially then)? ;-)

My 'expensive' traction LA is 60 Ah and assuming a 50% DOD gives me 30Ah over 1000 cycles for £200. 3 x 16Ah LiPo cost me about the same (more with p&p etc) and assuming a 'safe' DOD of 80% gives me 38 Ah.

http://www.phillipsmobility.co.uk/mk-gel-mobility-scooter-battery-m34-sldg-60ah-576-p.asp

The LA is pretty bomb proof and from what I've been reading here about the potential consequences of a single instance of user error on LiPo being 'bad' ... (ignoring the weight advantage of LiPo over LA), is that so great a revolution (for use in a boat specifically)?

Don't get me wrong here, I wouldn't have spent what I just have on 6 x 16Ah LiPos if I didn't hope it was to be a good solution ... but I'm yet to be convinced how good it will all pan out ITRW etc.

I charge to 4.15 V and discharge to 3.65 V, your iCharger allows you to set the voltage per cell which is good news some of the cheaper chargers don't.

Agreed and I have already played with that whilst testing these 18650 LiIon cells.

So that is 0.05 V less than full and I stop at 0.15 V before recommended LVC. Does that help battery life? Don't know and really care with LiPo bought at sale price. In any case there is no noticeable difference in range and the 10 Ah battery gives over 8.7 Ah (haven't bothered counting lately) which is 87% of capacity on the label.

Yup, then that's fair enough (you potentially treating them as consumables) and sounds a good compromise (lifespan / safety over capacity etc). ;-)

Given that I have at the smallest, 38 Ah's worth of LiPo in one pack (3 x 16Ah), would you consider the 1010B+ 'man' enough to manage such a capacity efficiently? Would charging said battery at .1C (3.8Ah) for ~10 hours be considered 'good practice' or should I go .2C or the full 10A (~.3C)?

https://hobbyking.com/en_us/multistar-high-capacity-4s-16000mah-multi-rotor-lipo-pack.html

I guess the question may be seen in two halves.One being the use of the charger for testing (charge / discharge logging and analysis) and a straight charger for use one I have used the batteries and just need to charge them up again (store or use etc).

Cheers, T i m

 

[anotherkiwi]

Erm yes, I think you have misunderstood my question. ;-)

I was saying if you had say a pack that was (internally, like mine) 4S2P, the P's would be connected together by substantial capacity wires, certainly MUCH more substantial than the conventional balance leads you find hanging out of a battery pack. In fact, I'm not sure the balance leads on my 16Ah packs are any bigger than those I have seen on 1A packs?

So, if you make a 4S4P by doing what has been suggested here by paralleling both the power and balance leads, in the case of a large load placed on a big pack, the imbalance between the cells could be significant and so possibly overwhelm the capacity of the balance wires?

I noticed with your twin parallel pack, you *didn't* parallel the balance wires and had two monitors etc?

Ok.

You mean for the same weight presumably? Millions of Milk floats, fork lift trucks and many submarines did / do very well with Lead Acid batteries for many years and a lot cheaper than Lithium (especially then)? ;-)

My 'expensive' traction LA is 60 Ah and assuming a 50% DOD gives me 30Ah over 1000 cycles for £200. 3 x 16Ah LiPo cost me about the same (more with p&p etc) and assuming a 'safe' DOD of 80% gives me 38 Ah.

http://www.phillipsmobility.co.uk/mk-gel-mobility-scooter-battery-m34-sldg-60ah-576-p.asp

The LA is pretty bomb proof and from what I've been reading here about the potential consequences of a single instance of user error on LiPo being 'bad' ... (ignoring the weight advantage of LiPo over LA), is that so great a revolution (for use in a boat specifically)?

Don't get me wrong here, I wouldn't have spent what I just have on 6 x 16Ah LiPos if I didn't hope it was to be a good solution ... but I'm yet to be convinced how good it will all pan out ITRW etc.

Agreed and I have already played with that whilst testing these 18650 LiIon cells.

Yup, then that's fair enough (you potentially treating them as consumables) and sounds a good compromise (lifespan / safety over capacity etc). ;-)

Given that I have at the smallest, 38 Ah's worth of LiPo in one pack (3 x 16Ah), would you consider the 1010B+ 'man' enough to manage such a capacity efficiently? Would charging said battery at .1C (3.8Ah) for ~10 hours be considered 'good practice' or should I go .2C or the full 10A (~.3C)?

https://hobbyking.com/en_us/multistar-high-capacity-4s-16000mah-multi-rotor-lipo-pack.html

I guess the question may be seen in two halves.One being the use of the charger for testing (charge / discharge logging and analysis) and a straight charger for use one I have used the batteries and just need to charge them up again (store or use etc).

Cheers, T i m

1. once you connect the packs in parallel via the discharge wires there will be no extra current flowing through the balance wires, nada, nothing, zilch...

2. I balance on charge so they don't need to be connected via balance wires on discharge. If I wanted to save 2.87 € I could connect the balance wires in parallel and use one alarm for the pair. Now that I know my different packs little quirks there is only one alarm and it is connected to the Multistar 4S which has shown some issues of unbalance on cell number 3. The good news is that since it has been paralleled with the Graphene 4S pack it is much better behaved.

3. yes energy density per kg

4. if you can, charge them at 1C, HK says they can be charged at up to 5C. I think you may be limited to 10 A? If you are going to charge in parallel use the maximum power of the charger, you will be hearing some fan noise... I charge 10 Ah packs at 10 A and bought two 300 W chargers and a 540 W power supply to cope. In normal use I see 18 V x 20 A (more like 23 A with the overhead) so about 410 W in all, well within the power available. I blew up the converted 360 W PC power supply I was using previously, it couldn't handle 18 A constant draw...

5. when charging LiPo you have to be there (see power supply issue above...) I can think of better things to do than babysitting charging LiPo for hours. I have the following charging strategy:

- after use charge to storage voltage, this usually takes just over an hour for the 4 packs (6S and 4S) I watch the news on TV or whatever with one eye
- before going out bring them up to 4.15 V per cell, this takes about 58 minutes. Time enough for breakfast and getting the gear ready to go out

So if you do the math 4 x 10000 mAh packs can be charged from "empty" (3.65 V/cell) to "full" (4.15 V/cell) in about 2 hours with 2 x 300W chargers. YMMV and all the usual disclaimers . You have a boat load of 16 Ah packs!

 

[Deleted member 4366]

I always join the balance wires when I use parallel packs. It helps keep the cells in balance, plus, it's necessary for monitoring. You can use a voltmeter for pack voltage to get an idea of the state of charge, but the primary safety controls must be at a cell level.

That means if you had four 6S packs in a 2S2P configuration, you only need two monitors with the balance wires joined, but if you leave them unjoined, you need four monitors.

 

[T i m]

1. once you connect the packs in parallel via the discharge wires there will be no extra current flowing through the balance wires, nada, nothing, zilch...

Yes, once they have balanced and assuming there is no charge or discharge activity going on etc. Because I understand that no two cells will ever have the exact same characteristics, there will always be *some* balancing current going on (however small etc).

2. I balance on charge so they don't need to be connected via balance wires on discharge.

Understood.

If I wanted to save 2.87 € I could connect the balance wires in parallel and use one alarm for the pair.

I didn't want to scrimp on such so bought 6 alarms for my 6 packs. ;-)

Now that I know my different packs little quirks there is only one alarm and it is connected to the Multistar 4S which has shown some issues of unbalance on cell number 3.

So how do you monitor for low voltage on the other packs (or do you mean when using it in parallel with other packs)?

The good news is that since it has been paralleled with the Graphene 4S pack it is much better behaved.

That's interesting. If you don't run the packs with the balance leads connected I wonder if it is better behaved because of the reduced load (load sharing)?

3. yes energy density per kg

Ok. ;-)

4. if you can, charge them at 1C,

Are you saying that's the *best* charge rate for a LiPo (generally) or that's the lowest starting point (up to maximum) simply to save charge time?

HK says they can be charged at up to 5C.

That brings me back to my question. Whilst I understand they 'can be' charged at 5C, is that better (for reliability, safety, cycle count) than say 1C?

I think you may be limited to 10 A?

On my 1010B+, I think you are right. In the manual it mentions:
"Note: The maximum charge power capacity is also limited by input current. The maximum input current of 1010B+ is about 24A,"
It also shows an optional PSU that is '15V 23A 350W'.

https://www.progressiverc.com/media/P350 Manual.pdf

If you are going to charge in parallel use the maximum power of the charger, you will be hearing some fan noise... I charge 10 Ah packs at 10 A

I have generally only charged batteries at a 'moderate' rate, other when racing 12th scale electric cars in the very beginning and using the same 4 x SubC 1.2Ah Nicads that were built into the car! ;-) I think I understand with some chemistries that charging slower creates a finer chemical formation that gives a higher energy density but a lower discharge rate (smaller crystals equal lower surface area).

and bought two 300 W chargers and a 540 W power supply to cope. In normal use I see 18 V x 20 A (more like 23 A with the overhead) so about 410 W in all, well within the power available.

So do you charge that hard simply to give a shorter charge time?

I blew up the converted 360 W PC power supply I was using previously, it couldn't handle 18 A constant draw...

I was considering the use of a PC PSU but I might just buy a dedicated one. I only have a 12V 4A laptop style 'brick' on there ATM but do have a 15A 'hobby' adjustable PSU somehere.

5. when charging LiPo you have to be there (see power supply issue above...) I can think of better things to do than babysitting charging LiPo for hours. I have the following charging strategy:

Ah, this may answer my previous questions then ...

- after use charge to storage voltage, this usually takes just over an hour for the 4 packs (6S and 4S) I watch the news on TV or whatever with one eye

Do you have them in any form of fireproof container when you are doing this?

- before going out bring them up to 4.15 V per cell, this takes about 58 minutes. Time enough for breakfast and getting the gear ready to go out

That sort of strategy would be fine for me as I generally know in advance when I / we might be going boating. So, as long as I have the time from when I know and when we leave that should be time (keeping in mind the need to keep the batteries attended whilst charging etc). [1]

So if you do the math 4 x 10000 mAh packs can be charged from "empty" (3.65 V/cell) to "full" (4.15 V/cell) in about 2 hours with 2 x 300W chargers. YMMV and all the usual disclaimers . You have a boat load of 16 Ah packs!

Quite!

Hmm, it looks like I'm going to have to get myself at least one more and potentially 'high power' charger. Funds permitting ... a single or dual (with dual you have all yours eggs in one basket)?

I guess much of the above could highlight another advantage (for me and this scenario) of lead acid ... as you can generally charge it unattended and it can be left with a maintaining charger connected 24/7 so it's always ready to go?

Thanks again for all your thoughts and feedback ... the 'bigger picture' is slowly emerging. ;-)

Cheers, T i m

[1] Because of the capacity of my LiPo packs I was just thinking of building a charge bunker / box and / or putting a steel charging garden store thing outside so I could leave it all running unattended. (I was also thinking of suspending a large bag of sand in the ceiling so that any excessive heat / flame would melt the bag and have it automatically dump the sand over everything. ;-)

 

[T i m]

I always join the balance wires when I use parallel packs.

Yes, you seem to differ with AK on that.

It helps keep the cells in balance,

Understood ... however, what are your thoughts re the potential of some fairly high balancing currents being carried over the often fairly thin balance wires, especially when high loads may be being drawn? I understand this may not be an issues in most cases and ITRW but my question still remains unanswered (e.g. That a parallel cell group would *normally* be joined using fairly heavy duty conductors)?

plus, it's necessary for monitoring. You can use a voltmeter for pack voltage to get an idea of the state of charge, but the primary safety controls must be at a cell level.

Understood, but if say you did have 6 x 4S2P running in parallel via their main cables, wouldn't you get a more granular monitoring if you had a monitor on each (empty) balance connector (and ignoring any perceived 'complexity' etc)? I know the 'All' value will be the same on all 6 monitors but the sub values might show / protect (alarm) any cell going high or low amongst the others? <shrug>

That means if you had four 6S packs in a 2S2P configuration, you only need two monitors with the balance wires joined, but if you leave them unjoined, you need four monitors.

Understood. It's just that (again, ignoring the complexity and only thinking out loud etc ...) the little monitor alarm modules are so cheap ... ? My thought may be that I would prefer to over than under-monitor, especially as I'm testing / learning etc?

I ran a storage charge on one pack last night (1.6A) and logged it on LogView. A couple of cells (pairs) were very close and the other two (pairs) were both down (and different). It looked like all the cells had levelled off (after about an hour) and the gap had closed but I don't think the balance function is in action on a storage charge (1010B+)?

Cheers and thanks also for the ongoing thoughts, advice and feedback. ;-)

T i m

p.s. I 'question' things, not because I don't trust or believe what you / people say, but because I want to better understand the subject in general (both theoretical and in practice etc). ;-)

 

[Deleted member 4366]

There's no significant balancing currents.

 

[T i m]

There's no significant balancing currents.

Playing devils advocate for a sec, how do you know ... have you actually monitored it in practice? Or maybe it's just because you have never melted any balance leads whilst doing so yourself (it may not be they that you 'vaporised'). ;-)

Background thoughts ... I believe I have read that you should get all series cells of a battery pretty close to that of another before you join them in parallel 'or excessive currents can flow'? AFAICS, there is little difference between the voltage (and therefore subsequent current) across the main terminals and the voltage difference between cells when brought together in parallel?

Now, I understand that once a pair of cells have been paralleled they will balance but those currents can be high?

Observation ... if the current between cells wired in parallel are never 'significant' why are they typically wired together using substantial sized conductors when assembled in the factory? After all, if they could get away with lighter conductors they would as they would be cheaper?

Question: If you were going to build a permanent 4S12P 96Ah pack from 6 x 4S2P smaller 16Ah packs, would you use the sort of gauge wire you typically see on balance leads used to join the parallel cells together to form each parallel group?

Interested minds etc ... ;-)

Cheers, T i m

 

[Deleted member 4366]

OK, you got me. I give up. You win.

 

[anotherkiwi]

Do you have them in any form of fireproof container when you are doing this?

Yes. It also doubles as an oven so I can't charge batteries and bake at the same time. It has a handy smoke extractor mounted above too!

Question: If you were going to build a permanent 4S12P 96Ah pack from 6 x 4S2P smaller 16Ah packs, would you use the sort of gauge wire you typically see on balance leads used to join the parallel cells together to form each parallel group?

No. Electricity like water will always take the path of least resistance and so the current will flow through the discharge leads. The balance lead is there to control the difference in voltage between individual cells within one pack, there is little to no current on those wires. As all your cells are balanced* to within 0.0xx V of each other before you connected them in parallel, the eventual "strong" ones are dragged down tenths or hundredths of a volt by the "weak" cells so if you do connect for whatever reason the balance leads in parallel too there will be no current on those wires. If there is current on those wires you have a bad cell and other problems on your hands. When you balance charge there are tiny, tiny, tiny currents flowing in or out to bring the cells to the same voltage.

Once you have charged and used the battery a few times it becomes very predictable which is why I only have a LiPo alarm on the pack(s) with the weakest known cells, the ones that will reach 3.65 V first. Or at least it has been doing so for over a year now. I do have a LiPo alarm for each pack and if I was doing serious long range mountain touring they might all be hooked up.

* For control I use a Battery Medic, my cells are mostly within 0.02 V of each other, I think those balance wires can handle >0.2 W heat in case of current flow...

 

[T i m]

OK, you got me. I give up. You win.

Nothing to do with winning or losing mate, it's just this tekky guy trying to get to grips with it all and make what you say fit with what others say, what I have experienced myself over 50 years playing with 'electricity' and what I read on the subject elsewhere? <shrug>

It's also a slightly different role to that on say an electric cycle. Like, at 4 knots I have all the time in the world to keep an eye on say 6 battery monitors but may not have the time to get to somewhere safe should the worst happen. Someone running an eBike daily, especially as a primary form of transport may not have the same requirements as someone using them in a boat .. and as part of a hobby rather than just 'transport' as such. Especially so if there are others sharing the same battery carrier (even compared to an eTandem). ;-)

They also say the value of advice is what you pay for it ... yet purely from taking advice from and listening to you (and others here) I have already invested a considerable amount of time and money in a energy technology that seems, compared to older solutions (like Lead Acid, Nicad or NiMh) to be quite 'needy' in both cost, time and equipment?

That said, I'm still very much looking forward to getting it all setup and running some tests and then seeing if those test make all the money and effort worth it when I'm on the water. I'm very hopeful that it will be the case. ;-)

Thanks again for all your help.

Cheers, T i m

 

[T i m]

Yes. It also doubles as an oven so I can't charge batteries and bake at the same time. It has a handy smoke extractor mounted above too!

Excellent. ;-)

No. Electricity like water will always take the path of least resistance and so the current will flow through the discharge leads.

Yes, agreed and whilst I don't disagree with that in general, it't doesn't tally with science and the concept of parallel resistance bridges / potential dividers that these cell combinations could be compared with.

e.g. Let's say the first R(esistor)4 string is made up of 1.2 ohm in series with .9 ohm, 1.1 ohm and say 1 ohm and that is parallel up with a similar network at all joints with a *different combination* but identical total resistance, the current (pre bonding the joints) will be *identical* in each leg but the voltages will not be the same at each joint. Therefore, when you also bond the joints (as with paralleling balance leads) whilst the primary current will still run though each leg, other currents *will* flow though the bonds as well.

The balance lead is there to control the difference in voltage between individual cells within one pack,

I agree with that 100%. ;-)

there is little to no current on those wires.

Carrying on being pedantic here (because I think it's important to my POV and hopefully your understand of what I'm on about), I would be happy to concede there would be no current in an ideal world but would inevitably be some current ITRW and the level of that current down to the power of whatever was managing that 'control'. e.g. What if you had a balancer that had the ability to balance at 10A, then wouldn't that 10A be passing though the balance leads?

As all your cells are balanced* to within 0.0xx V of each other before you connected them in parallel, the eventual "strong" ones are dragged down tenths or hundredths of a volt by the "weak" cells so if you do connect for whatever reason the balance leads in parallel too there will be no current on those wires.

'If connected once balanced and only when no other activity was taking place'?[/quote]

If there is current on those wires you have a bad cell and other problems on your hands.

Butbut isn't that assuming that 1) all cells are created and stay equal and therfore the reaction to load will be identical on each and every cell? Don't we accept that ITRW that is rarely the case (even with 'matched cells') so *even* if the balance wires are left connected all the time, some current will flow in tyhe balance leads all the time the packs are charging or discharging?

When you balance charge there are tiny, tiny, tiny currents flowing in or out to bring the cells to the same voltage.

.
Even when working with say a 16Ah pack that may have done some work (but still considered 'ok' as a pack)? Wouldn't that mean that it could take *ages* to balance charge a 16Ah pack at 10A and how then would it 'control' the charge into different cells and still charge at anything like that rate, without reasonable levels of current passing down the balance leads?

I get the 10A would be passing through the discharge leads but to have any influence on that per cell, wouldn't it have to boost or buck the voltages across each cell and so 'divert' some of that current around the highest cell(s)?

Once you have charged and used the battery a few times it becomes very predictable which is why I only have a LiPo alarm on the pack(s) with the weakest known cells, the ones that will reach 3.65 V first.

Understood 100% again. ;-)

Or at least it has been doing so for over a year now. I do have a LiPo alarm for each pack and if I was doing serious long range mountain touring they might all be hooked up.

Or if you were new to the game and were interested to see what was going on across 3 or 6 packs paralleled up etc? ;-)

* For control I use a Battery Medic, my cells are mostly within 0.02 V of each other, I think those balance wires can handle >0.2 W heat in case of current flow...

Hey, I didn't think there was any current flow in the balance wires!! ;-)

Just for the S&G's I'm going to rig up a bunch of ammeters in the paralleled balance leads and see what I get when I put the packs under some load. ;-)

I'll be very happy to report back that I saw nothing (of note) under any charge or discharge condition. ;-)

Keep an eye out for the smoke mate! ;-)

Cheers, T i m

 

[T i m]

Yes. It also doubles as an oven so I can't charge batteries and bake at the same time. It has a handy smoke extractor mounted above too!

Excellent. ;-)

No. Electricity like water will always take the path of least resistance and so the current will flow through the discharge leads.

Yes, agreed and whilst I don't disagree with that in general, it doesn't tally with science and the concept of parallel resistance bridges / potential dividers that these cell combinations could be compared with as I would know it?

e.g. Let's say the first R(esistor)4 string is made up of 1.2 ohm in series with .9 ohm, 1.1 ohm and say 1 ohm and that is paralleled up with a similar network at all joints with a *different combination* but identical total resistance, the current (pre bonding the joints) will be *identical* in each leg but the voltages would not be the same at each joint. Therefore, when you also bond the joints (as with paralleling balance leads) whilst the primary current will still run though each leg, other currents *will* flow though the cross bonds as well.

The balance lead is there to control the difference in voltage between individual cells within one pack,

I agree with that 100%. ;-)

there is little to no current on those wires.

Carrying on being pedantic here (because I think it's important to my POV and hopefully your understand of what I'm on about), I would be happy to concede there would be no current in an ideal world but there would inevitably be some current ITRW and the level of that current down to the power of whatever was managing that 'control'. e.g. What if you had a balancer that had the ability to balance at 10A, then wouldn't that 10A be passing though the balance leads?

As all your cells are balanced* to within 0.0xx V of each other before you connected them in parallel, the eventual "strong" ones are dragged down tenths or hundredths of a volt by the "weak" cells so if you do connect for whatever reason the balance leads in parallel too there will be no current on those wires.

'If connected once balanced and only when no other activity was taking place' ... yes. ;-)

If there is current on those wires you have a bad cell and other problems on your hands.

Yeahbut isn't that assuming that all cells are created and stay equal and therefore the reaction to load will be identical on each and every cell? Don't we accept that ITRW that is rarely the case (even with 'matched cells') so *even* if the balance wires are left connected all the time, some current will flow in the balance leads all the time the packs are charging or discharging?

When you balance charge there are tiny, tiny, tiny currents flowing in or out to bring the cells to the same voltage.

.
Even when working with say a 16Ah pack that may have done some work (but still considered 'ok' as a pack)? Wouldn't that mean that it could take *ages* to balance charge a 16Ah pack at 10A and how then would it 'control' the charge into different cells and still charge at anything like that rate, without reasonable levels of current passing down the balance leads?

I get the 10A would be passing through the discharge leads but to have any influence on that per cell, wouldn't it have to boost or buck the voltages across each cell and so 'divert' some of that current around the highest cell(s)?

Once you have charged and used the battery a few times it becomes very predictable which is why I only have a LiPo alarm on the pack(s) with the weakest known cells, the ones that will reach 3.65 V first.

Understood 100% again. ;-)

Or at least it has been doing so for over a year now. I do have a LiPo alarm for each pack and if I was doing serious long range mountain touring they might all be hooked up.

Or if you were new to the game and were interested to see what was going on across 3 or 6 packs paralleled up etc? ;-)

* For control I use a Battery Medic, my cells are mostly within 0.02 V of each other, I think those balance wires can handle >0.2 W heat in case of current flow...

Hey, I didn't think there was any current flow in the balance wires!! <ducks> ;-)

Just for the S&G's I'm going to rig up a bunch of ammeters in the paralleled balance leads and see what I get when I put the packs under some load / charge. ;-)

I'll be very happy to report back that I saw nothing (of note) under any charge or discharge condition. ;-)

Cheers, T i m

p.s. I'm firmly from the 'What you hear you forget, what you see you remember and what you do you understand' camp. Keep an eye out for the smoke mate! ;-)