I like DieBieMS a lot, even more now with the Metr Pro integration. It would be a go to solution for me if it wasn’t so bulky. I wish there was a charge only DieBieMS lite. You could then use it both inside the enclosure or outside (basically use it as a balance charger). I mean, you could use it as a balance charger even now. It would still be cheaper than getting a regular 12S balance charger. It would just be a complete waste of the nice features (e-switch, discharge protection) that you wouldn’t use at all.
I like that. I thought about doing something along those lines as well.
These cheap checkers use voltage dividers to get the individual cell voltage readings. If your switch is only on the negative lead and the other balance leads remain connected to the checker, I believe it will still discharge the cells a little bit. There will be a small current going across the resistors of the voltage dividers. Probably not a big problem, but still something to keep in mind.
After a little more thinking about this, I can’t see a good way of making it work with 13 relays/MOSFETs (switches) for 12 cells. I think I would need 24 switches, 12 of which would go to the negative of each cell and 12 to each positive. That’s still not a showstopper since both relays and MOSFETs can be found for very cheap.
What I see is a more serious problem, though, is that it would be pretty dangerous to wire things up in that way. If more than 1 switch in any of the 12-switch group got closed, that would create a short over the battery cells and destroy the battery. A bug in the controller would then be a disaster. I think I know how to make a hardware protection for this, but with that it’s already drifting away from the intended “simple solution”. I may still build this for science. At least for 3S to start with.
Not sure about that, I have a batterymedic from HK and I had to have a switch on the first 3 wires to cut the power, even then it was probably still drawing power
I didn’t say it would “measure” across the cell, but you would still have resistors between cells and small current would flow there, which would only be turned into heat.
With the negative connected you have something like this. Without it, you have this.
Maybe something like this would work for toggling between individual cells. Good old binary tree. For 8S, it would require 14 two-state relays, organized into three rows. Each row would be controlled with the same signal.
This would be pretty safe. It can never create a short across a battery cell, even if the relays in the same row don’t switch exactly at the same time. It could create a short across the charger, but that can certainly be dealt with.
12S would then require 22 relays organized into 4 rows.
Why not just using a smart bms and use it as „balance“ adapter on your charger.
Just route the balance leads out of your enclosure on the waterproof plug.
Than make an adapter plug from the bms to the enclosure and you good to go.
Brick charger - smart bms - battery
The smart charger is about 25€ and you can use it than on all 12s batteries you have.
I hope that’s working
As min it was my plan when the smart bms finally arrive.
I don‘t like to don’t monitor the individual cell voltage with a usual bms.
I don’t need the e-switch function of a discharge bms.
And a fuse in line is way much smaller.
Edit: i‘m not 100% sure yet, but I think with the smart bms you even can set the balance voltage to 4.1v per cell (or any other value you want).
This way you even can adjust the charge level and don’t need to worry that you hit your cells when „fully“ charged you need to hit the breaks
Yes, I thought about that too. Is there a smart BMS that you can interface with, though? Ideally one with a clearly documented communication protocol? I don’t want one that only sends data to my cell phone with a proprietary protocol. Plus, installing some Chinese app from an untrusted source on my phone would make me feel queasy.
You can buy bms modules from AliExpress that allow you to change all of the parameters from your phone or computer. I wanted to use one but it’s a little too big for my integrated deck
I‘ll get this one
Unfortunately it is not so much documtation about it and you will need an app which is luckily not only in Chinese. (iOS user so not sure how it is with apps you can get in the playstore and if you can trust them)
I know some guys here already use this bms and on endless sphere they also speak a lot about it and it seems to work pretty good.
As mine just on the way, so all I say is all I read here. Hope it will arrive next week.
I can hold you up to date how it’s working if you want.
Why charge only? It can handle more than most will be able to throw it it in regards to discharge too… You’re talking about bulk etc buy how many relays were you going to wire together??
@Friskies Bulky is only an issue if you were to put the thing inside the enclosure. That was never the intention.
The issue with DieBieMS is that either you put it inside the enclosure, in which case you have to make a lot of space for it, or you use it outside of the enclosure as a balance charger, in which case you’re wasting a nice product.
Meanwhile i use a 80A bestech BMS for daily use. it is so easy to use and trustable.
every 2 month I use my “frankenstein charger” to charge the cells independent from the bms.
therefor I have to open enclosure, unplug the BMS and plug the charger instead.
Not a big deal to do so…
It just seems a little counter intuitive. If you are that worried about unbalanced P groups then you are probably just better off finding a way to incorporate a discharge BMS. There are still some really compact 60a discharge units around.
LHB recommended one from batterysupports which seems to be pretty tiny…
This looks like a good option, especially with the link that @deucesdown has shared. I will get one too for experimenting. Which one are you getting? The cheapest one to bypass or the 60A one?
Sure the cheapest one.
I anyhow use it only in time of charging and I think I will not charge with more than 20a
I ordered a pc module too, but not sure if it’s really needed.
Sounds good. I just ordered the same. If it works, that’s an easy way to implement a 12S balance charger. If it doesn’t, I’ll just have to build my binary relay tree.
At least for 3S to start with.
For 8S, it would require 14 two-state relays, organized into three rows. Each row would be controlled with the same signal.
As min it was my plan when the smart bms finally arrive.
I ordered a pc module too, but not sure if it’s really needed.