Best way to connect 4 separate 12s packs?

[jcampbell3d]

I have 4 Honda Clarity packs that I'm looking to combine to put in an electric dune buggy conversion. Individually they are 44.4v in a 12s configuration. I'd like to combine in them in series and parallel to get double the voltage and double the ah. I've been reading a lot on the forum of what people have done in the past when combining multiple packs but most everything I have read deals with packs that total 72v or below. I'd like to keep it as simple as possible and of course not purchase any unnecessary parts. I'd like to charge the system together if possible as well. What do you think is the best way to configure the packs?

- Should I combine 2 in series first with a 24s bms and then parallel?
- Or should I combine 2 in parallel first and then series connect? If I did that method, would it require a bms on each pack or 1 bms for the whole system?
- Most bms I see on the market for 24s seem to be rated for just 72v. Will they have a problem handling 90v or are these ratings typically strict?
- Which configuration is the best for charging all 4 packs at the same time?

Thanks for your help.

 

[pwd]

Those vehicle EV packs are great for the type of build you are doing. There are many BMS that can handle 24S + of lithium ion. I'm using an ANT BMS for my Grom Clone build which is 24S (used ev modules too).

I cannot answer your question with confidence about the best way to connect them but I think in an ideal scenario; you would combine the cells in parallel first so you would only need one BMS. It would be more difficult to do with 12S modules though. I'd wait for someone else to chime in on that question.

 

[AdR]

Make parallel modules connection first then series paralleled modules. Importantly "Equalize all cell voltages before making parallel connections". For this setup only one 24S BMS is needed

 

[harrisonpatm]

Make parallel modules connection first then series paralleled modules. Importantly "Equalize all cell voltages before making parallel connections". View attachment 353031 For this setup only one 24S BMS is needed

This is how I agree it should be done.

There will be a difficulty, however, in making said parallel connections. I googled a pic of the packs you're planning to use. Essentially, you would need 25 individual cables interconnecting the 4 packs (not including balance wires). This isn't impossible, but it will certainly need planning and cable management. You're looking in the area of 10-14AWG cables needed for each of those parallel connections.

 

[jcampbell3d]

Thanks for the help.

If I do parallel first and series second and use 1 24s BMS, how does that BMS know the voltage of all cells sense there's technically 48 total. Or does that not matter? Do I just connect the leads to just 12 out of the 24 on each 2p?

Why 25 individual cables? I couldn't connect in parallel through just the positive and negative posts?

 

[E-HP]

I googled a pic of the packs you're planning to use.

I did the same thing and came to the same conclusion. It looks easy on paper, but once you throw in how the packs will be physically located, it quickly becomes a nightmare.

 

[E-HP]

Why 25 individual cables? I couldn't connect in parallel through just the positive and negative posts?

You are essentially making the four packs into one big pack by paralleling each group, so 24 groups in series requires 25 parallel connections. Since your subject asks for “the best way”, maybe define what best means. You can either deal with the headaches up front and have an easy charging routine, or do something simpler up front and deal with ongoing charging hassles on the back end.

 

[harrisonpatm]

If I do parallel first and series second and use 1 24s BMS, how does that BMS know the voltage of all cells sense there's technically 48 total.

If cells are in parallel, it's electrically the same cell, same voltage. A BMS doesn't care how many cells you have in parallel. You only need a balance lead for each series connection.

Why 25 individual cables? I couldn't connect in parallel through just the positive and negative posts?

In the drawing above by @AdR , count the number of lines he's drawn for parallel connections. Each of those represents one cable you need to have between paralleled cells.

And he's actually drawn 26 lines, but the parallel connection between the last cell group of the first pack, and the first cell group of the second pack in series, can technically be one cable. Though for redundancy I would personally make that cable anyway, so yeah, 26.


If you parallel between just the positive and negative posts, the packs as a whole would be paralleled, but the cells won't be. And whatever BMS you end up using would presumably only be reading cell voltages for one of the paralleled packs. So it could potentially be showing a perfectly balanced pack, while the one it's paralleled to may be way out of balance, and you'd have no way of knowing.

Again, let me reiterate that while this would be a headache to wire, if you can manage it and do it correctly, and you can tidy the wires in a way that won't be electrically dangerous, you would have a pretty nice battery as a result.

 

[jcampbell3d]

Since your subject asks for “the best way”, maybe define what best means. You can either deal with the headaches up front and have an easy charging routine, or do something simpler up front and deal with ongoing charging hassles on the back end.

Thanks for the help, I don't mind the work up front with wiring if that's what needs to be done. On this pack, would the wires need to be spot welded? That would be the only difficulty for me, haven't done that before. With that said, I also don't mind charging packs separately if needed. This is a recreational vehicle and not used on a daily basis.

If I did them in series first with a 24s BMS for each 2S and then in parallel, when I make the parallel connect could I just do it through the battery terminal posts? Would it then be better to charge the two 2S packs separate or could I safely charge all 4 packs in the 2S2P configuration?

Also, these packs are rated for 200amp continuous and 400amp peak. For the parallel connections, I don't need beefier wires than 10-14awg? I would just need them for the final positive/negative discharge?

 

[harrisonpatm]

If I did them in series first with a 24s BMS for each 2S and then in parallel, when I make the parallel connect could I just do it through the battery terminal posts?

Yes, you could do it this way. Because that way, each paralleled pack would have its own BMS. If you do it, you'd probably want to rate each BMS to handle the full current (even though in theory they'd each only provide half current), or a fuse between the two. Or both.

Which is why I would probably do it the first method, if it were my project. 2 BMSs are twice as expensive as one.

Would it then be better to charge the two 2S packs separate or could I safely charge all 4 packs in the 2S2P configuration?

You would still be able to charge all 4 packs as if they were 1 large battery, as long as the 2 paralled BMS's are correctly working. Again, as long as you're staying within the ratings of everything.

Also, these packs are rated for 200amp continuous and 400amp peak. For the parallel connections, I don't need beefier wires than 10-14awg?

Parallel connections don't carry the full current of the pack; series connections do that. What parallel connections do is help equalize current and voltage between paralleled cells. If you have well-matched and healthy cells, then you won't see much current moving on your paralleled connections. But that doesn't mean you can get away with just laying a 28awg wire between cells. Imagine you have two paralleled cells suddenly dumping a 200A load, like on rapid acceleration from zero (a plausible situation for your planned build). If the cells aren't completely identical, the "healthier" cell may contribute more to the load, which could cause it to sag in voltage faster than the other. Since they're paralleled, they'll attempt to equalize in voltage, and the only way for them to do so is via the paralleled connections you make. If your cables are too thin, you'll either get mismatched cells wasting current trying to equalize, or melted cabling. Or both.

If you do end up doing the paralleled connections as we discussed, my suggestion of using 10-14AWG was, frankly, a guess. 10awg is good for like 40 amps, so you'd probably be fine. If you can manage thicker wire than 10awg for parallel connections, do it. But as discussed, it's going to be a maze and you need it to be manageable.

On this pack, would the wires need to be spot welded?

You could probably solder 10awg to the connections, based on the pic I googled. If it were me, I would also want to secure the balance cables elsewhere after the solder point, so you're not just relying on solder as the mechanical connection as well as electrical.

 

[E-HP]

Just gathering info for future reference. Do these packs regularly go out of balance? It seems like that would be problematic for a EV when it comes to charging due to the extra time for balancing. Or, do they use an active balancing circuit? If it were me, I’d run them without a BMS for a while, while monitoring the groups before and after charging to see how well matched they are, then decide what type of protection, or maintenance routine you’ll need. If you don’t charge to 100% or discharge to zero, then you have room for a little imbalance.
Also, what is the max charge rate on these types of batteries?

 

[jcampbell3d]

Do these packs regularly go out of balance? It seems like that would be problematic for a EV when it comes to charging due to the extra time for balancing. Or, do they use an active balancing circuit?

I checked the voltage of each cell of each pack when they arrived. All 4 packs were perfectly balanced. There is a part of me that has considered not running a BMS but just an inline fuse to protect the system and then ever so often pull the packs and balance them if needed.

Also, what is the max charge rate on these types of batteries?

Not sure, haven't seen any info on it. I purchased from Jag35 and they only give the charge voltage of 50.4vdc, not the charge rate.

 

[jcampbell3d]

Yes, you could do it this way. Because that way, each paralleled pack would have its own BMS. If you do it, you'd probably want to rate each BMS to handle the full current (even though in theory they'd each only provide half current), or a fuse between the two. Or both.

Which is why I would probably do it the first method, if it were my project. 2 BMSs are twice as expensive as one.


You would still be able to charge all 4 packs as if they were 1 large battery, as long as the 2 paralled BMS's are correctly working. Again, as long as you're staying within the ratings of everything.

Parallel connections don't carry the full current of the pack; series connections do that. What parallel connections do is help equalize current and voltage between paralleled cells. If you have well-matched and healthy cells, then you won't see much current moving on your paralleled connections. But that doesn't mean you can get away with just laying a 28awg wire between cells. Imagine you have two paralleled cells suddenly dumping a 200A load, like on rapid acceleration from zero (a plausible situation for your planned build). If the cells aren't completely identical, the "healthier" cell may contribute more to the load, which could cause it to sag in voltage faster than the other. Since they're paralleled, they'll attempt to equalize in voltage, and the only way for them to do so is via the paralleled connections you make. If your cables are too thin, you'll either get mismatched cells wasting current trying to equalize, or melted cabling. Or both.

If you do end up doing the paralleled connections as we discussed, my suggestion of using 10-14AWG was, frankly, a guess. 10awg is good for like 40 amps, so you'd probably be fine. If you can manage thicker wire than 10awg for parallel connections, do it. But as discussed, it's going to be a maze and you need it to be manageable.

You could probably solder 10awg to the connections, based on the pic I googled. If it were me, I would also want to secure the balance cables elsewhere after the solder point, so you're not just relying on solder as the mechanical connection as well as electrical.

Thanks for all this info. This has really filled in the gaps of what I have learned so far. You've definitely given me some things to think about. Really appreciate it.

 

[jcampbell3d]

You could probably solder 10awg to the connections, based on the pic I googled. If it were me, I would also want to secure the balance cables elsewhere after the solder point, so you're not just relying on solder as the mechanical connection as well as electrical.

One these packs, the balance cables are pre-wired into a single connector that you connect leads to.

 

[harrisonpatm]

One these packs, the balance cables are pre-wired into a single connector that you connect leads to.

Yes, for the balance leads. The potential parallel connections we've been discussing are a separate thing, which I suggested have both a mechanical and soldered connection for all 25 or 26 cables at both ends. Even if its just zip ties.

 

[E-HP]

I’m wondering if using an active balancer on each of the four packs, then two volt meters to monitor the voltage of the two 12S series portions to ensure they stay at about the same voltage would be sufficient.

Amazon.com

 

[jcampbell3d]

I’m wondering if using an active balancer on each of the four packs, then two volt meters to monitor the voltage of the two 12S series portions to ensure they stay at about the same voltage would be sufficient.

100Balance Active Balancer - I've considered a 24s active balancer like this with 2 of the packs in series and forgoing a BMS. If I'm not mistaken, you can view the voltages in the app with the balancer and not need any type of volt reader.

 

[harrisonpatm]

100Balance Active Balancer - I've considered a 24s active balancer like this with 2 of the packs in series and forgoing a BMS. If I'm not mistaken, you can view the voltages in the app with the balancer and not need any type of volt reader.

An active balancer has no way to disconnect input or output in case of overcharge, undercharge, overcurrent, one cell going way out of balance, overtemp, undertemp... all it does is balance. It's all well and good to have a device that can show you all your voltages, but if it doesn't do anything in case of an issue, then you have to be the BMS, meaning you have to monitor voltages and current all the time and take action when there's a problem. The saying someone once told me is: "If you don't use a BMS, then you're the BMS."

JKBMS 24s 200A does all of that, plus active balance (at 2A, instead of 1.2A from the device you linked), plus you can access and change parameters with your phone.

Furthermore, you don't really need an active balancer, 99% of the time. Cells go out of balance because they're old, used, reaching the end of their life, weren't assembled correctly in the first place, ect. If you have well-matched cells, in a healthy pack, that isn't abused, that were put together in balance in the first place, then you shouldn't need to balance. Once, maybe twice a year. When I make a new pack, I top balance once, then turn off the balance function on my BMS. They shouldn't drift. And if they do drift, that's the sign of a problem, or age.

Which is another reason not to just use an active balancer. If your cells do start to age differently, or if one gets damaged and underperforms, and you have an active balancer on 24/7, then it will hide the symptoms of a problem that you'd otherwise see if you weren't balancing.