Wiring and charging advice please


Can I get a bit of advice? I’ve just bought 6 5s LiPo batteries and plan to buy a BMS, hopefully this one: -

I’m not fantastic at electrical circuitry, so i’m playing it safe and posting how I’m going to do it here. Below is how i’d like it: -

Can anyone see any issues with it?

My real question is about the charger. As up until now I’ve balanced charged my previous 2 6S batteries every time, but now that I’ve almost tripled my WH, I need a temporary easier solution. Until I get the BMS wired in, which’ll be in a month or so I’m guessing, I’d like to charge using just a basic charger that lobs power back into the circuit. Ideally I’d like one that just charged to 41V (for safety and battery health), but can’t find one that’ll do this, could anyone recommend a good charger that allows voltage adjustment?

*Could i use the Imax B6 charger?

Thanks for all replies :slight_smile:

You have Lipos - they should be balanced everytime! Also that BMS will not help much as you have parallel packs. Ideally you would balance each pack individually and not in a parallel config.

@Maxid I don’t like that answer, give me another one :slight_smile:

Best practice dictates that I stay near the charger and balance charge them one by one. Seeing as that would take about 7 hours charging at about 3.5A I’m not that keen. I like to charge at a relatively low amperage, and to max 4.1V per cell. I’d also check their balance after every charge (I have a nifty portable balance check thingy) which I think is pretty safe practice…

I’ve got no choice with the BMS parallel charging, there’s no better alternative (at least to my knowledge), but again i’d only charge to 4.1V and discharge to 3.55ish.

well it also will be a pain to set up as you will have to connect the balance wires to the BMS in parallel. Make sure to double and triple check polarity. I already plugged my two 3S balancer cables together the wrong way - big spark but luckily nothing broke.

Shouldn’t be difficult to set it up in parallel, and I’d only have to do it once then I’d (hopefully) be set for a long time. Thing is, in theory should it work? I hope so.

Most lipo/li-ion balance charging threads I’ve read say that connecting batteries in parallel will balance them to a point. I’m thinking that if I check balances after every charge, only charge to 41V and occasionally balance charge (1 in 5 or 7 charges) I should be fine. I’m also considering having 3 10s voltage displays on the side of the box. Largely useless but great for a control freak like me.

@Namasaki @longhairedboy @sl33py @whitepony (virtual tap on the shoulder for you all) Please tell me Maxids being overly cautious, will my diagram and plan work?

he is not being overly cautious. It would be easy to make an alarmingly hot and vibrant mistake here.

This is something i wouldn’t even want to try. doing three series groups in parrallel… i’m not 100% but im’ pretty sure involving a BMS here with parallel balance leads going to each pack in parrallel is going to cause a short.

For Li-Ion sure, but for Lipo - i balance charge every single time.

I also like to pull and inspect them, and usually throw a thermal probe on them when charging so even if i’m not 100% paying attention it’ll auto shut off before any thermal issue…

And lipos (or at least the inexpensive ones i have) drift frequently so should be balanced every time.

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I agree with @Maxid Lipos should be balanced at every charge Cycle. Lipos are great for high power in a small package but, you better give them a healthy amount of respect.

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So I’m going to get a darwin award then…Least i have all you lot to help me live a bit longer.

@!£$^%…So is it possible (and safe) to get a 500+ Wh Lipo pack? I’d settle for about 400Wh Ideally one that isn’t too fat, Either the width or height needs to be under 44mm so I can get it in a good case and be high enough off the ground.

Since I’ve bought 6 of these batteries I could just run 2 at a time I suppose…Carry the rest in a backpack maybe. But that’s not living the dream of having all connected and charging easily.

I could have 3 of these in series: -

Not the best C rating but the high capacity makes it un-necessary i think.

How would all you guys do it?

Others have tried those packs with poor results. The C rating is too low regardless of the capacity

so you have two 5S in series and 3 in Parallel? making one 10S3P? I see no problems here at all. why is everyone saying don’t do it? did I miss something?

so I have read through this again and again. I see no problems. I say do it. I do this everyday. have done for years. parallel up the balance leads and terminate to two 5S JST connectors and charge with two imax B6 balance chargers.

job done.

also you are right about the multistars. the 10C rating is quite adequate given the 10000mah capacity. infact here is a video of my mate on a board powered by 10C multistars smoking my 30C zippys

remember the C rating is multiplied by the mAh to give current output.

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It does work in principle. If he is cautious when setting it up it can work. But personally I am overly suspicious of anything related to lipos so just want to tell him to be really careful. He seems not too experienced with this type of thing (otherwise he would not ask in the first place right?) so the potential for failure is high. Also when hooking the packs up in parallel permanently (like with a BMS) then you will not notice when a single cell goes bad (the same is true with Liion packs but when a Liion vents it is not as bad as when a Lipo burns).

@riva_00 as soon as you hook any of these packs up in parallel you should have more than enough current at your disposal :smiley:

I was thinking about going for it anyway, however ignoring the advice of a few veterans would be tremendously stupid. I asked for everyone’s advice for good reason. No I’m not especially experienced, but I’m careful and doing the most intelligent thing I could think of, which is asking all of you. If i want experience, I have to do stuff.

I’ll test using a 5s-6x jst parallel charging cable, and use an IMAX b6 (or 2 5s-3x jst cables with 2 chargers). I have a safe area to charge and store the batteries (LiPo bags and steel boxes).

I may actually downgrade to a 10s2p setup, depends if the extra Wh makes a difference when I’m out riding.

I’m also wondering if i said i was using Li-Ion packs, lets say 10s3p, would you give the same advice of uber caution? Or is it just because of the fact I’m using LiPo’s?

Lastly (sorry for all the questions) can you tell me if there’s something similar to this: - https://www.ebay.co.uk/i/291766384982?chn=ps&dispItem=1&adgroupid=41767405657&rlsatarget=pla-327666158629&abcId=1129006&adtype=pla&merchantid=115010295&poi=&googleloc=1007138&device=c&campaignid=861364981&crdt=0 But shows a balanced display (individual cell voltage, not combined voltage)

I actually have this: - http://alexnld.com/product/skyrc-lipopal-self-voltage-balancer-2-6s-lipo-for-battery-voltage-checker/?gclid=Cj0KEQjwnPLKBRC-j7nt1b7OlZwBEiQAv8lMLP6E5d78pQqLmNTNiMzE4-7eIZtVm4XiZS2Z_0Xyh6AaAlVW8P8HAQ But I have to open up the battery case and plug it into each battery’s balance connector individually. Not the worst, but I’d like to make my board show a ridiculous amount of info on the outside if i can, just for fun (nothing to do with my OCD that means I have to check the back doors locked several times every night)

It’s just lipos mate. If you said 10S3P li ion every one would have been “hell yeah do that man”

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I used 2 of those in series didn’t see a big problem with the amperage drop but I also didn’t really use them for long (also light and not in a hilly area). I had a cell in one pack go too low and after that it never came back fully so basically had to abandon that pack and ran 6S for a short while waiting on some replacement 5S 5Ah 20C but those have been fine for quite a while (I set very conservative cut off voltage on the VESC)

I think the hard and fast rule is DON’T OVER DISCHARGE. i have been running my lipos on about 10 or mor boards for 3 years now and never have any problems with them balancing.

I usually only run them down to around 3.8v per cell.

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3.8V :scream: That is still above their nominal voltage which means you are barely using half the energy in your pack. You could have just used smaller batteries.

My cut-offs are going to be 3.7 initially, then 3.6 if the packs look fine after a few weeks. Plenty of time to fine-tune everything, just need to make sure i walk to the goal.

I normally open the pack up several times when riding and check how their doing during the initial rides

yeah or I could use the batteries that I have and regularly ride short trips and recharge and still have the juice to take a longer trip if I want to. so much better to over engineer than under engineer. less stress on everything.