RC Lipo pack inspection, series/parallel charging, and lifespan/safety tips

[mkollmer]

Thanks for tutorial. Was wondering how I can series packs on the bike. I want to leave the packs individual and series them as I put them on the bike. Do you know of anyone that done something like that? I like the idea of experimenting and adding packs, adding more for more time, ect. Where can I look for connectors that have a waterproof plug when not in use? Thanks in advance.

 

[pdf]

It is somewhat frustrating to me that these batteries can be made very reliable and safe for use in phones, laptops, tablets etc., but nobody has bothered to make a self-contained light EV battery system with comparable performance, reliability and safety-- even though the risks and consequences of failure are much greater.

My two cents (very US-centric, but I think can be generalized to most countries): Cell phones, laptops, etc. are sold by major US companies (Apple) or companies with major US divisions (Samsung). If an Apple computer catches on fire, it makes the news, and Apple falls all over itself to do damage control and possibly pays the family millions. So it has a major incentive to minimize these situations. Hobby King is a Chinese company. There are "warehouses" from where they ship, but to my knowledge, there is no US division and so as far as I know, you can't sue then if you burn up your house or car or just your $2000 bike. There are dozens of incidences where the fire was actually filmed while it was happening with RC LiPo. It is unknown how many cases there are in total. I don't think there is even an estimate. But ultimately, HobbyKing still sells (literally) megatons of LiPo, so why would they or the manufacturers seek to enforce strict manufacturing guidelines? There is no incentive.

The safety of every battery type varies tremendously with the manufacturing quality, design of electrodes, chemistry, packaging design, etc. As far as I know, all lithium batteries of significant size have some potential for fire. There are chemistries that have less intrinsic potential due to the material properties of the electrodes, but a very badly made and abused battery of a "safe" chemistry is more dangerous than one well-made and properly maintained of a "dangerous" chemistry. I do personally favor certain battery chemistries. I can afford to and the downside of a battery fire, for me, dwarfs nearly all other considerations. Part of that is the engineer in me. A well designed system has a high degree of fault tolerance, to the extent it is economically feasible. For me, paying even 50% more for bike batteries that are more likely to tolerate an electronics failure without catastrophic consequences is worth it. Plenty of people claim "this or that won't happen because there is system X in place to stop it". And as long as system X performs as designed, that is true. But all man made systems have error rates due either to inherent variations in the manufacturing process or to the life cycle of the device. There is an entire engineering discipline dedicated to "Reliability and Maintainability Engineering". You have to make up your own mind what level of risk you can tolerate for what level of benefit.

OK, so that was more like four cents worth. Still, worth what you paid. Stay safe out there! (Not trying to derail the discussion. I really like this tutorial. The only thing I might add is that there have been documented LiPo fires while balance charging. See the web pages of companies that sell the kevlar bags for charging. Charging on a wooden or plastic covered bench is probably not a good idea unless you are present.)

 

[friendly1uk]

I program the balancing charger(s) to terminate at say 4.10V, and program the BMS to terminate at.....

You don't use a balance charger with a bms.

Lipo is not 100% safe whatever you do with it. One RC seller claims about 1 in 200,000 cells buggers up. All found to be user error. Just like all the fires here. There was a whole run of nokia batteries that were defective and got through once. Distorting cases they got so hot, but no fires. It was about 3 weeks of production outside of china. No amount of being careful would of helped. They all failed on the charger or just after.

Presuming you have good cells to start with, there is no reason your wife can't just get on with it with the same level of involvement as charging her phone. I do no different myself. I wouldn't accept any different either.

I find balance charging quite ridiculous. It costs more to do it, It is more faffing about, and it leads to fires. On the plus side, there is nothing.

Find yourself an example of how to do it properly. Pick a manufacturer. Visit there site and pick a bike. Now tell me if the wife can charge it in the manner you expect. Of course she can. Nobody should be settling for less. Nobody is even being asked to. It is just an option open to you if you engineer it that way yourself. It is not something you can sell.

I wouldn't of posted this thread either. Why is there even a balance board present when you can buy a 2x5s - 10s convertor lead. It is typically over complicated and of a poor standard. People should not be accepting this. If they are incapable enough to need leading by people that can't do a great job themselves, you know where this is going.


Most of my cells have never had there voltage measured by anything other than the bms. Most proper packs are like this. I know it is a diy orientated forum, But it does not mean you have to do everything yourself (he says, banging it out on his morse key)


edit: Incidentally, thermal runaway starts from a temperature you would never reach if using a bms with pack temperature probes. You could perhaps involve such temperature sensing with balance or bulk charging. Many chargers are designed to do so. Even my $20 one. I have not seen one used properly though. Why would I... there is nothing proper about it

 

[agniusm]

Thank you Neptronix for this great guide. I'm just about to order coupke of packs for my winter lawnmower project and wasnt sure about paralleling balance wires on these. Thanks again

 

[adrock8519]

Hi, Thank you so much for this post I have a few questions I would like to ask before I build 2 packs. One for myself and one for a friend. We are both using BMC (p/n:14110-3) v3?

1. First of all I notice that 10awg wire is rated to 15 amps. However a 20 c battery with 5 amps will pull 100amps? And this battery will only have 10awg wire?

2. I plan to join 6 cell 5amp in series and then parallel to give 44.4v 15a. I will not draw more that 1665 Watts from the battery (2.5c?) to look after BMC. What awg cable should I be using for the series harness and what awg cable should I be using for the parallel harness? Is it a smaller gauge as the load now draws from across the packs? But what if I one day need to draw more from the packs?

3. For my frame I can fit 8 batteries and given my previous question in regards to amperage and awg gauge is it possible to have a 20amp pack?

4. If I use a parallel balance lead harness,will my cells be balanced with each other? Example if one cell is 3.6 and one 3.8, when I plug the lead in will then both average out?

Kr,
adam

 

[dnmun]

i thoght BMC was british motor company. where did you read that 10AWG can only handle 15A? i use 60A breakers on 10AWG romex, and i use 40A breakers on 12AWG. but they can handle more for short periods imo.

 

[izeman]

i thoght BMC was british motor company. where did you read that 10AWG can only handle 15A? i use 60A breakers on 10AWG romex, and i use 40A breakers on 12AWG. but they can handle more for short periods imo.

i guess he's talking about the bmc hub motors.
btw: my bike is made by bmc as well. still it's not made by a chinese nor a british motor company, but a swiss bike company. how can that be?!

 

[o00scorpion00o]

Hey Nep, great write up, I remember all the help you gave me just before I decided to take the lipo route.

I was glad I did because. I had wicked fun that lifeP04 couldn't have given me back then, or probably now.

I didn't blow up anything or burn the house down and I was never tempted to keep an LiPo in the house, ever.

In the end I gave up because when. I got to 24s 2p, it's just too much to manage with all the wiring and trying to balance now and again. Too much to try put on a bike.

But for up to 16 S it's terrific for making a really fun short distance bike, though even with 16S 8 ah, I was able to get 15-18 miles 18-20 mph max with a mac 8T.

 

[izeman]

Hi, Thank you so much for this post I have a few questions I would like to ask before I build 2 packs. One for myself and one for a friend. We are both using BMC (p/n:14110-3) v3?

1. First of all I notice that 10awg wire is rated to 15 amps. However a 20 c battery with 5 amps will pull 100amps? And this battery will only have 10awg wire?

2. I plan to join 6 cell 5amp in series and then parallel to give 44.4v 15a. I will not draw more that 1665 Watts from the battery (2.5c?) to look after BMC. What awg cable should I be using for the series harness and what awg cable should I be using for the parallel harness? Is it a smaller gauge as the load now draws from across the packs? But what if I one day need to draw more from the packs?

3. For my frame I can fit 8 batteries and given my previous question in regards to amperage and awg gauge is it possible to have a 20amp pack?

4. If I use a parallel balance lead harness,will my cells be balanced with each other? Example if one cell is 3.6 and one 3.8, when I plug the lead in will then both average out?

Kr,
adam

hi adam, welcome to the sphere

1) no worries. there are suggested value how much different strand can handle. they can handle much more but will get hot at some c-rate. and yes: a 20c 5000mah battery should be able to provide 100a, but as stated in the first post: you shouldn't trust those c numbers, and the less you stress the battery the longer it will live. and just because it could handle that load doesn't mean you will use it, as stated by you under 2)
2) first it's not 6 cell 5amp but 6cell 5ah (Ah to be precise). amp=current. ah=capacity. 1600w@44v equals around 40a which is around 2.5c for your battery. correct. which is an easy load. if you can run 10awg cable between battery and controller and then to the motor - do it. but 12awg is fine also.
3) sure. why not? same setup as above. doesn't change a thing. just more range and easier on the battery.
4) no. the balance wire would probably just melt or the connector would vaporize. imagine how much energy will be transfered between the batteries within a millisecond to bring them to the same level. as stated in post#1: all cells you want to put parallel must be the very same voltage!!! some 50mv are fine though.

 

[dnmun]

Hey Nep, great write up, I remember all the help you gave me just before I decided to take the lipo route.

I was glad I did because. I had wicked fun that lifeP04 couldn't have given me back then, or probably now.

I didn't blow up anything or burn the house down and I was never tempted to keep an LiPo in the house, ever.

In the end I gave up because when. I got to 24s 2p, it's just too much to manage with all the wiring and trying to balance now and again. Too much to try put on a bike.

But for up to 16 S it's terrific for making a really fun short distance bike, though even with 16S 8 ah, I was able to get 15-18 miles 18-20 mph max with a mac 8T.

i built up a 24S lipo pack using 40C HK 6S packs using a 24S D131 Bestechpower BMS and got it to balance initially under the BMS. it only needs a 100.8V bulk alloy charger to charge and i have both LVC and short circuit protection.

 

[o00scorpion00o]

i built up a 24S lipo pack using 40C HK 6S packs using a 24S D131 Bestechpower BMS and got it to balance initially under the BMS. it only needs a 100.8V bulk alloy charger to charge and i have both LVC and short circuit protection.

That setup looks good, but to be honest the triangle on my old bike was too small to begin with, even if it weren't, It's still too much to squeeze into a bicycle, too much can go wrong with that banging around on shit roads. I could see it working on scooter/motorbike conversions where you got a lot more space.

I think the 16-18S 2P is the sweet spot of bicycles, unless of course you're lucky enough to have a custom frame where you got loads of space.

 

[adrock8519]

i thoght BMC was british motor company. where did you read that 10AWG can only handle 15A? i use 60A breakers on 10AWG romex, and i use 40A breakers on 12AWG. but they can handle more for short periods imo.

I read it here > http://www.keywolf.com/American_Wire_Gauge.php
But i noticed this today too > http://www.powerstream.com/Wire_Size.htm

And this is about calculating voltage loss over a length of wire > http://forum.allaboutcircuits.com/showthread.php?t=21643

 

[adrock8519]

Thanks ezeman. Makes sense now. I checked out your mantra build nice job!

With my Pack Im going to have 18c so wont be able to plug all the balance connectors with 6x cell balance parallel, so should I just use four of the plugs from the balance parallel harness and use another 4 from a second parallel harness?

 

[izeman]

Thanks ezeman. Makes sense now. I checked out your mantra build nice job!

With my Pack Im going to have 18c so wont be able to plug all the balance connectors with 6x cell balance parallel, so should I just use four of the plugs from the balance parallel harness and use another 4 from a second parallel harness?

sorry. i dont understand your question. you plan to go 18s. ok. that's 3x 6s pack in series. there won't be any parallel connections. if you plan to do 18s2p. so 3x series of 2x parallel, you would parallel 2x 6s packs. make this 3 times. then put those 3 double packs in series. after you make this series pack those balance plugs never ever must touch. big sparks or molten balance wires will happen.
but i may not have understood your question.

 

[adrock8519]

Charging in series with a single balance charger.

Introduction


+ 2x celllog 8s's

Is it okay to leave my parallel balance leads on whilst riding the bike? If I can find or make a 8-1 balance lead it would be neat for just one cell log. Any advice for making ing one or sourcing one would be great : )

 

[adrock8519]

1.Ah sorry my mistake yes im making 2 packs first will be 6 batteries, x3 2 in series then parallel them up (12s 3p)?

2.second one for my bike 4x 2 in series and then parallel them up ( 12s 4p?)

 

[adrock8519]

Charging in series with a single balance charger.

Introduction


+ 2x celllog 8s's

Is it okay to leave my parallel balance leads on whilst riding the bike? If I can find or make a 8-1 balance lead it would be neat for just one cell log. Any advice for making ing one or sourcing one would be great : )

ah yes we would have to use two as they can only do up to 43 volts an im using lyen controller with low voltage cut off.

 

[izeman]

Charging in series with a single balance charger.

Introduction


+ 2x celllog 8s's

Is it okay to leave my parallel balance leads on whilst riding the bike? If I can find or make a 8-1 balance lead it would be neat for just one cell log. Any advice for making ing one or sourcing one would be great : )

ah yes we would have to use two as they can only do up to 43 volts an im using lyen controller with low voltage cut off.

ok. you still messed it up please read ALL i wrote about connecting balance leads.!! you MUST NOT connect balance leads of a pack in series!! so if you connect 2 6s packs 5000mah into one 6s2p parallel pack with 10000mah: yes connect the balance leads. but DO NOT connect these two combined balance leads to the second 6s2p pack which will be in series with your first one (making the whole thing a 12s2p pack).
i hope you got it know. if not prepare for kff (kentucky fried fingers).
really take this serious. if you are not 100% sure look for someone with r/c experience or some electronics knowledge.

 

[izeman]

1.Ah sorry my mistake yes im making 2 packs first will be 6 batteries, x3 2 in series then parallel them up (12s 3p)?

2.second one for my bike 4x 2 in series and then parallel them up ( 12s 4p?)

no. parallel first, then put them in series. it's safer (logic wise) to have individual bigger packs - regarding connection of them.

 

[adrock8519]

This is from hobby king
Here is AWG/Amp rating relation:
8AWG 200 amps
10AWG 140 amps
12AWG 90 amps
14AWG 60 amps
16AWG 35 amps
18AWG 20 amps
20AWG 12 amps
22AWG 10 amps

 

[adrock8519]

As for parallel/series cable, use 10AWG, it will handle all the power you may use, at just under 2kw you will have no problems at all.

In parallel balance environment the cells are all connected one to another, and 1 cell is impossible to have lower than others, as simply put- other battery with higher cell voltage will give it's energy to the rest of cells making them equal, charger will stop the charge when it sees same voltage through all sets of cells, physics do the rest to have the cells equal, so you are good to go!

 

[adrock8519]

Hhahah yeah thanks for the advice I dont want to end up with lipostick face either haah

I Didnt say I was going to join the balance leads in series. I will build the pack with all the cells within 0.05v of each other like mentioned. And then add the parallel balance lead to all the little packs so I can then just plug one plug into the battery medic or charger. ?correct?

If so can I just leave the parallel balance lead plugged into the individual packs whilst using the battery? As the cells are are paralleled, cell 1 will be equal to the other cell 1's and cell 2 with the other cell 2s etc. Then when the balance parallel lead is plug into the charger that will make cel one group equal with cell 2 group etc?

Yeah also I was going to start off with the little packs paralleled first until I saw this post I suppose starting off with paralleling is neater for the wiring as one plug can be used to join the blacks and another to join the reds from neighbour packs if just going to 10amp or 20amp. Ill draw a few diagrams first to suss out what what is best for my packs.

 

[izeman]

ah ok. you just want to connect a balance lead extendion to each battery and plug that into a balance charge to charge it? sure. but this only work with one charger i now of. only one charging through the balance leads.
a rc charger needs power plug and balance plugs connected to charge. off course it must only see the voltage of the little pack it can handle. so only 6s for a 6s charger. you must not connect the power of the series pack (44v) to the charger and then a single balance plug to the charger. you would need to cut/remove the serial connection first to make it 2 small voltage packs.
two more practical solutions: buy a 12s rc charger. it takes the whole packs input and has 12s balance port.
the other one: buy a bms (eg bestechpower) and charge through this. this is by far the most confortable solution.
for all solutions buy two if these and connect your parallel packs at cell level (you may need a 2x or 3x harness only depending of the sum of packs. for 12s2p you will need a 2x)

 

[adrock8519]

I see, so the charger will count the cells from the plug and if its only one plug it presume the battery pack is a 6 cell. I was planning on buying a 2000w duo charger and also some of these http://www.bmsbattery.com/alloy-shell/457-alloy-shell-900w-lifepo4li-ionlead-acid-battery-ev-charger.html set to the exact voltage. Im unsure of using a bms ill have to read into it but I have low volt cut off on my controller so I shouldn't need it? Really starting to look forward to building these packs now : ) thanks ezeman!!

 

[izeman]

nope. any RC balance charger NEEDS the balance plug do be connected to charge. otherwise it will refuse to charge a lipo chemistry.
those alloy chargers (which are the same i sold) only output a single voltage and don't care about anything. they pump whatever power they can give even into a single cell - letting it explode in the case
so a bms is fine to have anyway. it's nice because it takes care that the battery is not drained beyond a specific level on a cell level, but it also takes care of the charging process. discharging the battery is a bad thing as a too much empty cell can take damage and will be lost, but a too high charged cell may catch fire or explode burning down the battery box, the bike or even your house.
so yes: can can charge a lipo battery with a bulk charger. it will work if you know the state of your battery, and know that there are no dead or weak cells (but who REALLY knows??), and if you watch the charging process carefully, so no cell gets overcharged (maybe with cellogs connected to the balance plugs), and you can stop the charging by hand if necessary.
an rc charger will take care that NOT A SINGLE cell gets overloaded by watching each cell's voltage. and a bms does the same so you can bulk charge. think of an RC charger as a bulk charger and bms combined, communicating with each other to take care of the charging process.