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Using Lithium batteries in parallel?
- Thread starter T i m
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If they are in an adequate enclosure, sanely wired and correctly charged/discharged - yes as safe. I have seen a leaking Lead Acid eat through its support and fall to the ground (Italian car...) I have seen one boil on charge and spit acid all over an engine bay... Nowadays we have gel Lead Acid which eliminates many of those problems.
I have a flat dinghy racer style jacket which I sit on when rowing. I have accidentally found myself in breaking waves twice (concentrated on fishing, not the ocean, once and cleaning my catch in a place where there is never surf - except that time...) and often row in +4 metre swells - record +6 metres, that was a lot of fun.
Twice on beaching I have been rolled by surf - I was avoiding swimmers on the dinghy beach, you know, the one with the big "No Swimming" sign at the entry... LOL! Yes, we have seen the picture of your hand! ;-)
Another tech paralleling question if I may ... I'm guessing you shouldn't really leave the balance wires connected (in parallel) when running (S4) batteries in parallel? The reason why I am thinking you shouldn't (but again could be wrong etc) is that the balance wires aren't typically 'man' enough to carry any current that could exist between cells in different packs when under load? <shrug>
If they were man enough you would just affectively be running a S/P battery?
(Without anything in the balance connector you could also have a cell monitor / alarm on each pack, rather than the battery as a whole (so greater granularity to the monitoring)?)
Cheers, T i m
Hmm, there are quite as few provisos there in comparison with a lead acid and in general though eh (well, two more than lead acid). ;-)
I think you might find that was just condensation on very thin Italian car metal mate. <ducks> ;-)
But charge risks aren't something you typically experience at point of use though in an electric boat are they (same with LiPo charging risks of course)? That said ... it sounds like *you* might get some regen charging with your electric outboard when surfing ...!
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By 'many' you mean (re using a gel LA traction battery in a boat for an electric outboard) none (as in if you over-discharge a LA battery ... 'nothing bad happens' for example) ;-) The only real risk I see re using my MK LA battery in the boat is getting a hernia carrying it or dropping it though the boat! ;-(
Yup, we do that also. ;-)
I bet (for a particular meaning of the word 'fun'). ;-)I have accidentally found myself in breaking waves twice (concentrated on fishing, not the ocean, once and cleaning my catch in a place where there is never surf - except that time...) and often row in +4 metre swells - record +6 metres, that was a lot of fun.
Don't you just love the general public. Why are there never sharks about when you want them ... ;-(Twice on beaching I have been rolled by surf - I was avoiding swimmers on the dinghy beach, you know, the one with the big "No Swimming" sign at the entry...
Cheers, T i m
Having the balance leads connected as well in a parallel board will depend on the amps being drawn. The balance leads will get warm more then 5/6 amps each but if you have 5 /6 batteries connected then the amps are divided and the leads will be fine.
You can use a parallel balance lead and use only one LiPo alarm plugged into the end. I would suggest one LiPo alarm for every two packs.
Neat. Observation though if I may. The gauge of the (XT90?) plugged harness wire looks smaller than that of the batteries (one especially, although it could just be thicker insulation)?Two 4S batteries in parallel with LiPo alarms:
Is this intentional so that the harness melts before the battery wiring?
I ask because I need to make my own 6 x 16000mAh 4S harness (from 6 x XT90 to 50A PowerPoles probably because that's what I've already got on the LA battery and outboard) so need to gauge the harness wire appropriately.
FWIW, because I am only running 12V and aware that resistance can waste a load of power (even at only ~15A) ... and because I wanted the heavy (17.5kg) LA battery up the bow of the boat ... I wired my LA battery with *very* substantial (200A?) and reasonably long cable so I effectively see the full battery terminal voltage in the stern of the boat, even under full load. [1]
Depending on how I use my packs ... 2 x 3 or 1 x 6, I might just have the battery in the stern near the outboard and the spare up the bow or if all one one box, keep it up the bow (as it's still going to be around 10kg (cased)). If it works as hoped (as a 1 x 6) I might invest in a duplicate and then with a PWM controller we may be able to cruise all day. ;-)
Cheers, T i m
[1] When I designed my electric racing (endurance) 'motorbike' it ran from 25kg (max) and in my case, 2 x 12V SLI lead acid batteries. I had a small DVM acting as my 'dash' and via a couple of toggle switches could display battery A volts, battery B volts, total volts, speed and total current. The speed was a magnetic transducer set over the final drive gear that was coupled to a F to V converter and to the dash (calibrated to MPH using an oscillator and wheel circumference calculations). The current was measured via the voltage drop over the main battery cable so that saved adding a shunt. ;-) My basic efforts one an IEEE award for 'Technical Innovation' but it was a long time ago. ;-)
p.s. You may have heard of Cedric Lynch of the 'Lynch motor' fame? I was one of the few to beat him but that wasn't because my machine was better or faster (far from it), I just caught him on the hop. ;-)
Thanks for that.
The idea was to have as large a capacity battery as would still be an advantage weight wise (so ~10kg V 17.5 kg of the LA). The positive spin off was the (as you say) the overall current per pack would be reduced so in my case with the outboard at max speed would be 30/6= 5A / battery? I'm not sure how (or if) you could predict the current between the cells / batteries via the balance leads ... only if you assume a worst case low / high voltage condition on series groups ... ?
On speed 3 of 5 the outboard draws 15A and for the same speed I'm hoping to improve that with PWM speed controller (so let's hope 10A). 6 x 16Ah packs in parallel = 96Ah, at 80% DOD gives me ~75Ah and so potentially nearly 7.5 hours continuous running (if my math(s) and understanding are correct)? ;-)
So, given that (low) load, would just one voltage monitor be ok (I've ordered 6 as part of the experiment)?
Cheers, T i m
If 15a was max draw, each set of balance leads theoretically would only see 2.5a between them. How ever they will only need to be monitoring voltage as the least resistance for the draw will be through the main power lead/connector.
If all six ports are used then you will need to monitor all the packs separately though being in parallel you should find that the cells will stay within 0.02- 0.03v, though now and then you do get some errant cells with the HK packs and from time to time some may wander by 0.1v.
If all six ports are used then you will need to monitor all the packs separately though being in parallel you should find that the cells will stay within 0.02- 0.03v, though now and then you do get some errant cells with the HK packs and from time to time some may wander by 0.1v.
Those are XT60s and the parallel lead is stock from HobbyKing and 16 AWG. The serial ones are 12 AWG. There is less current over the parallel connections than over the serial ones if I have been following correctly? So long since I did High School Physics I'm afraid, lucky me there is always someone to correct me on here!
;-)Those are XT60s and the parallel lead is stock from HobbyKing and 16 AWG. The serial ones are 12 AWG. There is less current over the parallel connections than over the serial ones if I have been following correctly? So long since I did High School Physics I'm afraid, lucky me there is always someone to correct me on here!
I was just thinking the current though each leg of the harness (between each battery and the output Y connector) would be limited by the harness, rather than the battery lead (therefore the harness wiring would be the weakest link, all be it only by a tiny amount)?
eg.(and this is just for S&G's etc) Let's say the harness wiring is 12 AWG and that is rated at 10A and the battery leads (between the battery and harness) are 10 AWG (rated at 15A) then you will drop more volts between the harness and the Y joint than the battery and the harness?
I think the bit you were talking about was from there to the load (serial bit) so that would, to get the best out of the batteries need to be able to support at least 30A and so 6 AWG?
However, in your case the total load would be limited by 2 x the harness so 2 x 10 = 20A (8 AWG).
We are probably just at cross purposes though ... ;-)
Cheers, T i m
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Correct AK, the current flow is at it's mightiest when in series.
Though if all cells are within 0.5v equalising current flow should be ok and not cause to much heat.
Though if all cells are within 0.5v equalising current flow should be ok and not cause to much heat.
In an ideal world (with all cells identical and all wiring paths equal resistance), I'm not sure you should see anything flowing though the balance leads should you?
Ok.
That was my thought. The more balanced everything is, (by definition) the less current will be flowing within the balance leads and (again, by definition), the voltage across each parallel link will be the same?
Without the balance leads keeping everything in balance, the more chances there are for different cells in each (now isolated, all but the terminal voltage) pack to drift out of line and therefore the greater need for multiple pack and cell voltage monitoring?
If the balance leads were of the same capacity as the main output leads you would have a straight S/P pack. So, rather than 6x 4S in parallel, you would have a single 4S6P solution. Well, that's if I've understood it all correctly! ;-)
Cheers, T i m
p.s. I intend to make up a harness where the harness cable gauge was at least as large as the individual battery leads and all 6 cables would join where it goes off to the load. The load cable would be at least 6x the CSA of the singles (probably a lot lot more). ;-)
I guess the problem could exist then if a cell starts to go bad / weak and surrounding cells try to pick up the slack via the balance lead wiring?
It might therefore be more sophisticated (for those reasons at least) to have individual monitors, assuming they will alarm for both over and under voltage on each cell?
ie. (Without the balancing leads all paralleled up via a balancing board or harness) ... If one cell in one series string starts to go lower voltage, the voltage from the other packs will try to lift it though the good cells in the same string and may over charge them? <shrug>
Cheers, T i m
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There's no current between parallel cells because the voltage is always the same, so you leave them permanently connected.
No need for a monitor on each pack because they're all in parallel. There's 6 positions to connect packs on the balance board plus a position on the end, where you can fit the monitor. you can connect them up like that, charge through the end balance connector and the power leads, so for all use, the only thing you need to change is to disconnect the monitor for charging, although some boards have double connectors on the end, so you could leave it on permanently; however, the monitor will eventually run down the pack because it takes power.
'In an ideal world' I'm guessing or I'm not sure what the point of the balance leads would be? e.g. If all cells always charged and discharged equally ... ?
Understood.
Understood. I've not ordered the balance board yet but did order a balance harness (JST-XH Parallel Balance Lead 4S 250mm (6xJST-XH)) but will order the board soon.
Understood
If the recommendation was not to leave all the balance leads hooked up when not being charged I was considering presenting all the ends (so 6 x 3 + the pos and neg = 20) on a DB25F and then 'remote' 6 monitor / alarms in a small enclosure that I could keep in front of me. Not because I thought it was needed, just that it might be interesting (to me anyway) and could highlight a weak cell?
Cheers, T i m
Correction: Weak cell group if you have a weak cell it will drag all the others in the same parallel group down. I have a weak cell in the 4S multistar pack in the photo above. It hasn't given me any trouble but I watch it. It is 0.2 V off the other cells, the RC guys say 0.3 V is too much and as they are the ones with batteries on fire I take their word for it.
Qualification: 'When balance wires are interconnected'. ;-)
As you might! ;-)
Cheers, T i m
Thinking again and please bear with my 'outsider' thoughts on all this (someone who has never played with LiPo or multiple packs in parallel but has been using rechargeable batteries of all sorts for over 40 years etc).
On my LA battery I have a 50A resettable fuse on the cable as it leaves the +ve battery terminal. Having a controlled 'weak link' is normally considered a 'good thing' in such situations, especially where the is the potential of very large currents, should a mistake be made or something go wrong.
So, I'm replacing a single (as in presentation) 12V monoblock (that I know is made up of 6 x 2V cells in series) with 6 x 16000mAh LiPo packs in parallel that are each made up of 4 cells in series but where the voltage / charge on each cell (< ideally), needs close attention.
It has been suggested that I run this new 'battery' with all the power leads connected in parallel (XT90, 6 > 1 harness or XT90 balance board etc) *and* the balance leads in parallel (harness or balance board).
Now, I would feel safer adding a resettable fuse in each battery leg [1] (say 30A each) and possibly a 50A jobby in the main output lead (as per the lead acid battery). This would protect both us and the boat and potentially one LiPo pack from the others, should something go wrong. However, if I also have all the balance leads connected in parallel all the time, even if one trip trips, the balance leads may still try to supply fault current and potentially cause other issues (melted balance wires being the least dramatic).
So, my (possibly OTT / outsider idea) would be to not run the balance wires in parallel all the time but (as touched upon elsewhere) have them brought out individually to say a DB25F on the outside of whatever container I put the packs in and then I could have different DB25M plug / leads plugged into it, depending on what I'm doing ...
1) Would be a cable connected to a remote box containing 6 x voltage monitor / alarms so I can monitor the performance of each cell as (sort of*) a subset of the entire pack (* all the packs would still be connected in parallel by their main terminals).
2) A 'balance plug' that could contain suitable resistors to allow me to balance the parallel cell groups pre re-charging (as they will all be re-charged in parallel anyway).
3) A charging / balance plug / lead that connects all the balance wires back in parallel and connects to the balance port on my 1010B+ charger. So, once charged I could either disconnect the plug and allow the cells to do their own thing (within the constraints of them still being connected in parallel by the main terminals etc) or leave it plugged in and just disconnect it from the charger (whatever the panel deem the best).
I appreciate much of this may be considered OTT by some of the 'old skool' here but I am actually as interested in the monitoring, management and safety of this as a solution as I am it being a solution etc. I feel I would both lean more about how this solution behaves in the real world and maybe prevent some bad situation before it becomes an issue.
So, what I would like is confirmation that what I outlined above is in itself not making matters worse (battery function or lifetime) or more dangerous please?
I actually *like* wiring stuff up and having flexibility so none of what I have suggested would be a chore to me. ;-)
Cheers, T i m
[1] As you get on some of the 'better' balance boards?