Lipo battery charging and voltage

[brianw]

I have an e-mountain bike with Bafang BBSO2 500w motor. I built the bike in October last year with no prior experience of e-bike electrics.
I have had much help from Tony who sold me the Marin Wolfridge frame and reading Pedelecs Forum.
Like many others, I'm sure, I have had many problems with the batteries, much due to my lack of knowledge. I have read the Battery University Forum articles and have learnt a great deal but an area they don't seem to have covered is the use of the number of sets of batteries in parallel and to a less extent the depth of discharge before recharging. I use Lipo 5S 20C 21v /4.2v per cell
I'm looking for answers to the following situation.
My riding regime is to switch to '0'level power assist as much as possible and only use assist in lowest level to suit gradient or wind. I'm stating this because of relevance to my questions. I link two packs of 5C's in parallel and after a ride of 20 miles on relatively flat terrain the voltage varies from pack to pack.
Sometimes one set of packs show 'full charge' on connection to the charger, this I thing is most likely a bad connection. The voltage readings vary from 20..1v to 19.5v for 5C pack and 3.9v to 4.1v per cell.
So, question 1 How can tell if both series packs are connected.
And question 2 Should packs be charged no matter how little voltage drops after a ride.
If the answer is to discharge to a lower voltage, what percentage of nominal voltage is recommended and then would it be better to use only one pack down to this voltage and then switch to another.

I'd be interested to know other riders experience or experts views.
Thanks for taking the time to read my ramblings.

 

[anotherkiwi]

Your message is very scary @brianw...

Why are you using lipos?
What is the reason you are running at 21V and not 37V?
What brand are the lipos, they don't sound like very high quality ones?
How are you charging?

Lipo should be charged to storage voltage (3.85V) if you aren't using them and then to 4.15 V per cell just before going for a ride. I like to keep my lipos balanced to within about 0.05V.

 

[awol]

I link two packs of 5C's in parallel and after a ride of 20 miles on relatively flat terrain the voltage varies from pack to pack.

Don't you mean 5S's? and you are linking them in series to make a 10s pack?
Don't take them below 3.5v per cell.
Are you using a balance charger?

 

[Nealh]

BE VERY CAREFUL IF YOU DON'T FULLY UNDERSTAND HOW TO LINK PACKS OR HANDLE THEM CORRECTLY YOU COULD START AN INFERNO.

How many 5s pack's are you actually using ?

It appears from reading your op that you have 500w 36v BBSO2, if this is the case your pair of 5s packs should be connected in series for a nominal 37v battery pack and not in parallel.
If you have 4 packs then you need a pair of parallel strings wired up consisting of 2 packs, this would increase Ah (capacity) by 2 fold whilst maintaining voltage at a nominal 18.5v.
Once paralleled then the two strings need to be wired in series to double the voltage for a nominal 37v pack with the desired 2 fold .Ah (capacity).
Be very careful with the wiring get it wrong and there wIll be BOOM !!!

Charge to 4.1v or up to 4.15v however there is very little gain above 4.1v.
Discharge to minimum 3.5 v and never store above 3.85v for long periods.
Charge and discharge should be adhered to as well as careful handling and storage.

Better and safer to use Li-on with bms unless you fully under stand lipo implications

 

[Deleted member 4366]

How to wire up your lipos 5S is the same as 6S. this is for 4 bricks. if you're only using two, it's much simpler. with two bricks in series, you can't influence the voltage of each brick. it just depends on their quality and the accuracy of your charging:

 

[brianw]

Your message is very scary @brianw...

Why are you using lipos?
What is the reason you are running at 21V and not 37V?
What brand are the lipos, they don't sound like very high quality ones?
How are you charging?

Lipo should be charged to storage voltage (3.85V) if you aren't using them and then to 4.15 V per cell just before going for a ride. I like to keep my lipos balanced to within about 0.05V.

Thanks for your reply. Why lipo well as I said I knew nothing about e-bikes and took advice from Tony who sold me the Wolfridge and he has used them for some years. They are Turnigy 5000mAh
and the charger is GTPower X Drive 670
As I said I recharge after every ride back to 'full' on charger which is 21v and all 5 cells are 4.2v If each cell is not at 4.2 then I recharge that individual cell until it is/
Any thoughts on running parallel battery packs or not?

 

[anotherkiwi]

OK so you are running a 5 Ah 37 V battery composed of 2 X 5 Ah Turnigy LiPos in series.

1. LiPo marked as 20 C does not really give that much power, on ES the estimate is 20-25% so your battery is capable of only about 20-25 Amps. That isn't enough for a BBS02 motor in my opinion.
2. This and the quality of your cells probably explains why your battery goes out of balance so easily. Better batteries for e-bikes are the Multistar, I use those and the high end Graphene which are always within 0.02V between cells.
3. Always charge to "Storage" after your ride then top up the battery just before riding. I have 10 Ah packs and it takes about 45 minutes to top them up before going out.
4.That charger seems to be pretty basic it is better to use one that lets you set the final voltage per cell to 4.15 V max. It is able to charge your batteries at 1C (5 Amps) which is a good thing.
5. Never use the fast charge option, it shortens pack life

More reading, you can never read too much about LiPo...
https://endless-sphere.com/w/index.php/Lithium_Polymer_(LiPo)

If you want to continue with LiPo then yes, get two more 5 Ah packs. Connect two in parallel and then connect the 2 groups in series as per d9veh's schema above. That will give you a 10 Ah nominative (8 Ah real) 296 Wh battery capable of 40-50 Amp continuous output.

 

[Deleted member 4366]

I agree. 20C 5Ah lipo bricks are not enough. You need 35C or you need to use ones with more capacity.

 

[brianw]

Don't you mean 5S's? and you are linking them in series to make a 10s pack?
Don't take them below 3.5v per cell.
Are you using a balance charger?

Yes I meant 5S, I link two 5S's in parallel to make 10Ah for my 36v motor.
I use a G T Power charger and charge each 5S on balance charge at 2.5amps

 

[Deleted member 4366]

Yes I meant 5S, I link two 5S's in parallel to make 10Ah for my 36v motor.
I use a G T Power charger and charge each 5S on balance charge at 2.5amps

You're still confusing us. You need 4 x 5Ah 5Ss to get 10Ah 37v. Two in series makes 5Ah 37v. Two in paraĺel gives 10Ah 18.5v.

 

[brianw]

OK so you are running a 5 Ah 37 V battery composed of 2 X 5 Ah Turnigy LiPos in series.

1. LiPo marked as 20 C does not really give that much power, on ES the estimate is 20-25% so your battery is capable of only about 20-25 Amps. That isn't enough for a BBS02 motor in my opinion.
2. This and the quality of your cells probably explains why your battery goes out of balance so easily. Better batteries for e-bikes are the Multistar, I use those and the high end Graphene which are always within 0.02V between cells.
3. Always charge to "Storage" after your ride then top up the battery just before riding. I have 10 Ah packs and it takes about 45 minutes to top them up before going out.
4.That charger seems to be pretty basic it is better to use one that lets you set the final voltage per cell to 4.15 V max. It is able to charge your batteries at 1C (5 Amps) which is a good thing.
5. Never use the fast charge option, it shortens pack life

More reading, you can never read too much about LiPo...
https://endless-sphere.com/w/index.php/Lithium_Polymer_(LiPo)

If you want to continue with LiPo then yes, get two more 5 Ah packs. Connect two in parallel and then connect the 2 groups in series as per d9veh's schema above. That will give you a 10 Ah nominative (8 Ah real) 296 Wh battery capable of 40-50 Amp continuous output.

1 I have no problem with power from my setup. I use two packs to make 10s but is that preferable to using one set to low voltage and then switching to the other set?
2 The out of balance is very low for 4 out of the 5 cells' it's just the odd cell which is under charged on occasions.
3 The only way I could do this is to stand and watch but my voltages never go down below 3.85 anyway. This is part of my question, should I be using my setup for several rides until low voltage and what should this voltage be? What effect on battery life to these alternatives have?
4 What charger would you recommend and at what cost?
5 I have never used fast charge
Thanks for your help, it seems I'm doing my e-biking on the cheap and that was my intention from the outset

 

[brianw]

How to wire up your lipos 5S is the same as 6S. this is for 4 bricks. if you're only using two, it's much simpler. with two bricks in series, you can't influence the voltage of each brick. it just depends on their quality and the accuracy of your charging:

Thanks, yes that is how I setup to run on the bike but I only ever charge one 5S at a time on balance at 2.5amp

 

[brianw]

You're still confusing us. You need 4 x 5Ah 5Ss to get 10Ah 37v. Two in series makes 5Ah 37v. Two in paraĺel gives 10Ah 18.5v.

 

[brianw]

I connect 2x 5S in series and another two in parallel to give me 10Ah.
The questions are
How can I be sure I have the parallel link sucessfuly
And with low discharge as described Is it better for battery life to run on one 5Ah pack to low voltage and then connect the other pack, or run the 10Ah packs to less discharge?

 

[Deleted member 4366]

Use all 4 packs together. Use parallel balance leads like I show in my diagram. That will keep them balanced better. Also it means that you can charge them two at a time.

My favourite charger is the BC168. It charges each cell separately, so you get perfect balance and rapid balancing. It charges each channel at 5 amps. Everything is programmable.

 

[Nealh]

I connect 2x 5S in series and another two in parallel to give me 10Ah.
The questions are
How can I be sure I have the parallel link sucessfuly
And with low discharge as described Is it better for battery life to run on one 5Ah pack to low voltage and then connect the other pack, or run the 10Ah packs to less discharge?

To me and probably at least 3 others on this thread, it sounds like you are not connecting your 4 packs up correctly. Your statement above is either worded wrongly or not expressed properly.
You are best as in d8veh's diagram to connect the 4 packs up in parallel to give two separate packs of 10ah (18.5v nominal) then do the series connection for 37v nominal x 10ah.

Batteries perform better in parallel the more the better.
For my BBS if I wish to, I parallel 4 x 6s packs and 4 x 4s packs then I have one series connection at the end for a 26.4ah/10s single pack using 6.6ah multistars.

 

[brianw]

To me and probably at least 3 others on this thread, it sounds like you are not connecting your 4 packs up correctly. Your statement above is either worded wrongly or not expressed properly.
You are best as in d8veh's diagram to connect the 4 packs up in parallel to give two separate packs of 10ah (18.5v nominal) then do the series connection for 37v nominal x 10ah.

Batteries perform better in parallel the more the better.
For my BBS if I wish to, I parallel 4 x 6s packs and 4 x 4s packs then I have one series connection at the end for a 26.4ah/10s single pack using 6.6ah multistars.

Cor what size battery box have you got for that?
But again, how can you be sure the parallel connections are good before you ride? And how many miles do you ride before recharging and do you measure that by voltage check or just experience?
Thanks for bearing with me

 

[Deleted member 4366]

https://hobbyking.com/en_us/jst-xh-parallel-balance-lead-5s-250mm-2xjst-xh.html

 

[Nealh]

Cor what size battery box have you got for that?
But again, how can you be sure the parallel connections are good before you ride? And how many miles do you ride before recharging and do you measure that by voltage check or just experience?
Thanks for bearing with me

I either use rear panniers or a cross bar pannier bike bag.
I solder up my own leads as a 4 in to 1 or 2 in 1 for the series link I use HK XT60 premade. I know the P connection is good after a run as I all voltages will be pretty well matched on all cells, I quickly check these before a storage charge.
Mileage depends on the terrain I ride, Voltage and amps etc I monitor with an inline watt meter and some lipo alarms in case of an errant low cell.

 

[brianw]

I either use rear panniers or a cross bar pannier bike bag.
I solder up my own leads as a 4 in to 1 or 2 in 1 for the series link I use HK XT60 premade. I know the P connection is good after a run as I all voltages will be pretty well matched on all cells, I quickly check these before a storage charge.
Mileage depends on the terrain I ride, Voltage and amps etc I monitor with an inline watt meter and some lipo alarms in case of an errant low cell.

Thanks, sounds as you what you are doing, unlike me pushing my limited knowledge to the limit.
No idea what HK XT 60 premade' s are?
Like the watt meter idea, do you have a link to them?