huh…is it just a space-saving strategy? Save the space on the inside you’d be using for a BMS? What’s the point? It’s really cool regardless.
2 Likes
Yea, save the space where the BMS would be.
You just can’t charge your board without it and it makes the charger a little clunkier.
Unless you also have a port for charging. Because you can charge without a BMS.
I’m actually not sure what’s involved. If you are checking the cells on the BMS frequently this is fine. But if you get some drift, charging without a BMS has the potential to way overcharge a cell.
Would love to hear how you’re working with this @BenjaminF
It looks like a GX20 connector. You need to run all of the balance leads and a positive lead.
3 Likes
good deal, thanks for explaining =)
Does it mean the current (say 8a) is split amongst each balance lead? Am I understanding this setup right?
It seems like a lot of heckmeck and potential failure points just to save a few square inches of space
Nah, all the charge current still runs through the (+) and (-) leads. The balance wires just bleed off cells that are higher until they match the rest
3 Likes
Depending on the enclosure I have gotten whole p groups to fit by ditching the BMS.
5 Likes
There is no more failure points than having the bms installed (assuming charge only bms).
There is even the advantage that the bms will definitely not drain your pack to 0V with this method 
I did charge my packs like this before I had a proper 12s hobby balance charger.
The only down side is that you need to plug in 2 plugs (charge barrel and balance wire plug) instead of just the one barrel plug.
One more plus, you need only one bms for X packs with the same voltage.
2 Likes
Ohh so there’s a plug for balancing and a separate one for normal charging?
Hm, ok I do not understand this connections.
I would make the balance wires directly long enough that they reach from the cell till the 13pin plug.
1 Like
Yea some can config can add more P groups because of it.
Just look how much work I’m doing to the bustin just to get the BMS to fit with the heatsink.
1 Like
Woof ok, looks like I sparked quite a conversation haha.
I made a really janky balance charger! Rather than put the BMS inside the enclosure, I combined it with my charger, and wired up everything to a GX20-14 Aviation connector. The way I have it wired, I have the GX20, and I have a normal barrel jack, and both operate independently of the other. So I can balance charge with just the GX20, or I can fast charge with the barrel jack and a different, unmodified charger.
Saves space inside the enclosure, and removes the BMS from a really high vibration environment that could cause a catastrophic failure. Also removing the risk of a BMS failure draining your pack, like Andy mentioned. And a bunch of other reasons that I’m having trouble remembering right now lol. Basically its the #FuckBMS Lifestyle that @glyphiks introduced me to. Maybe he has some more words on reasons to do this. I mostly did it as a proof of concept 
Yes i can 
No I dont
Nah, everything works exactly the same as when the BMS is inside the enclosure. Think of this as just making really long wires running from the pack to the BMS. So long, in fact, that your BMS is now outside of your enclosure
For sure. Though its also removing some potential failure, like I was saying. And it gives me the freedom to use a really big BMS (LLT SmartBMS) without worrying about how much space it takes up in the enclosure. Cus as awesome as that BMS is, its fucking huge.
Yep. With a BMS this big, some layouts you could probably fit 2 extra groups! @bwahl602 and you have been answering all of these questions better than I could have hoped to lol. Nice!
Another great point! I didnt even think about that. Nice!
True, that adds a bunch of solder joints to potentially fail. But I trust a good solder joint to stand up to high vibrations a lot more than I trust a PCB with lots of delicate parts.
If I did that, then I would not be able to remove the port from the enclosure. I would have to solder it with the port in the enclosure, and cut the wires if I ever wanted to get it out. This way I can remove the port, and it also made soldering much easier. Though I will be the first to admit that bullet connectors numbered in pen is not the best solution haha. Its just what I had.
@iamasalmon, @bwahl602 and @Andy87 can I quote/credit you guys in the tutorial I’m going to be writing on this topic? Y’all have brought up some really insightful stuff that I didnt even consider! Thanks!
6 Likes
Yes Im not proud.
No impacts so far. Even with a huge gasket on the enclosure, I still have lots of ground clearance 
4 Likes
Of course.
Do you have anything between the DC jack and the battery when fast charging without the BMS?
Any behaviors you adopted for that? Like not letting it charge to full or anything that worries you about sending a P group way over.
That means you can snag a buddies charger to fill up right?
Hmmmmmm. GX20 is so big though
1 Like
Not all BMSs remove charge from each pack though, right? Some move voltage around to even it out too I think…(?) This is really cool and I’d love to try something like this, I’m wondering what BMSs would work in the way you’ve described
@BenjaminF, The biggest issue that I see is that, the voltage measurements might not be accurate with that long of a balance wire. The reported voltage will be less than what it actually is. I am apprehensive about the whole setup.
1 Like
Just a fuse 
Nope lol. I think im going to default to Balance charging, and only fast charge on rare occasions as needed. And check my pack regularly to make sure it is staying in balance on its own.
Yep! Or my 6A fast charger haha.
It really isnt. Only a 23mm hole. Only a bit bigger than a regular barrel jack. This is a great connector for this application. Kudos to @glyphiks for pointing me to it.
3 Likes
Thats possible, though I haven’t noticed any problems yet. Ill keep an eye on it. The cable length here is still pretty short. Less than 1m total from BMS to cell.
1 Like