Batruim as a PARTIAL BMS

Ok first the TL;DR - Looking for a way to NOT spend $600/USD+ on a 16s watchmon/blockmon kit right now if that's possible. So looking for a cheaper alternative.


So I have a PIP (not really "MPP solar" but some other brand of the same Voltronic inverter... it's basically identical). It's connected to a 48v LiFePO4 battery (16s4p Headway cells). And I already have a cheaper Chinese BMS but it doesn't really balance a battery of this size, so I only use it for voltage monitoring right now.

So I'm wondering if I can buy a Watchmon and SOME blockmons, (like say 5 of them) just to monitor my most troublesome cells and not the rest, for now. The idea is I go back later and buy the rest of the blockmons that I need, understanding that I won't have coverage of those cells. All I ask of such a solution is over/under voltage protection, and obviously ONLY FOR THOSE CELLS that I buy the mons for. I'm not worried about over current protection because the inverter and solar system I have is not large enough to charge/discharge my cells at more than .5 (or 1/2 if you prefer) C rate of the battery bank. Also I have breakers on the battery and they have never tripped before (even when I turn on my A/C which is max inrush current for me) so I'm doubting I'm stressing the cells too much on that front.

But what I do need is coverage for when I set my inverter to float charge at say 56.0v and most of my cells are at 3.42v but the weak ones are at like 3.9v or 4.0v (remember these are 3.2v not 3.7v Li-Ions) and thus getting cooked! The inverter doesn't have a way of backing off charge just because of weak cells, since it doesn't know which cells are weak.

So will this work? Can I do this piecemeal?

Also how does batrium handle overvoltage situation? Shut down the cells entirely or just burn off excess?

And if burn off excess how many Amp's (watts?) can it burn off? Will it work with my solar system at full throttle in other words.

Also how does it handle under voltage of a cell?




Thanks for the info ahead of time guys.

Not sure about any of hte Batrium stuff, but there might be single cell BMS / discharges out there that might work and run autonomously.

Would it be possible to obtain a few more cells and just replace the weak ones with better ones? That would be my first choice.
You can then use the B grade cells to make a smaller project or something.

If you arent looking for full BMS function long term it may be cheaper to go to a 1S style balancing system or a stand alone top burn off units.

Obviously if going with the S1 solution would need to get enough to include the highest and lowest cells as they need somewhere to balance the cells to.

Lots of Arduino based DIY top burners on YouTube.

Colin Hickey has an arduino based bms he's designed. I believe Brett Watley has expanded on it, or maybe it's the other way around. Adam Welch has several videos on the unit as he's incorporated it into his setup.

CrimpDaddy said:

Would it be possible to obtain a few more cells and just replace the weak ones with better ones? That would be my first choice.

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Yes it absolutely IS possible but... this is quite expensive since I have a very hard time finding used Headway cells, in good condition, that an owner wants to part with. So I'm forced to buy new from China via Alibaba, or use one of these ebike stores (that are just doing that themselves). So after about 5 or 6 cell group replacements I would have paid for the entire Batrium BMS anyway so... yeah... $100 a pop ain't fun!

Possible... but not my first choice (or even second, third or fourth).

I believe the economics of doing this with secondhand DIY powerwalls is/are completely different than doing this with new brick/prismatic powerwalls, and thus might require a different tactic to be successful.

Aside of self discharge, would it be possible, given 4p, to re arrange so capacities match.

I would be inclined to reduce to 3p and swap and test, until you can match them up. Also check for self discharge.

How old are these batteries? Some other thoughts include, that maybe they are just way out of balance, and if balanced manually, they would come good. LiFe batteries have a very flat discharge curve, so it is impossible to judge state of charge by voltage.

Geek said:

Aside of self discharge, would it be possible, given 4p, to re arrange so capacities match.

I would be inclined to reduce to 3p and swap and test, until you can match them up. Also check for self discharge.

How old are these batteries? Some other thoughts include, that maybe they are just way out of balance, and if balanced manually, they would come good. LiFe batteries have a very flat discharge curve, so it is impossible to judge state of charge by voltage.

Click to expand...

It's certainly possible and I the thought crossed my mind. But it's an ENORMOUS amount of work screwing and unscrewing cells and bus bars and would take my solar system offline for a while. Throw in that I have a full time job and this would kill all my free time. I'm one of those people with more money than time (not that I feel rich or anything lol, I'm just time poor).

The batteries are not old at all... maybe half a year. I'm clearly having an issue somewhere because I'm not trying to charge them to full or all the way to empty at all. I had my float set to 56.8 and empty set to 49.0... I've since changed that to 56.0 and 50.0 to be more conservative. These original batteries were all bought from Zhejiang Xinghai Energy Technology Co (https://zjxhny.en.alibaba.com/). Which I think is the real Headway. Apparently Alibaba is littered with fake companies trying to make their batteries look almost exactly like real Headway, Calb or Sinopoly cells but way lower quality.

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Korishan said:

Colin Hickey has an arduino based bms he's designed. I believe Brett Watley has expanded on it, or maybe it's the other way around. Adam Welch has several videos on the unit as he's incorporated it into his setup.

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Thanks I'll look at his channel.

nrm21 said:

Geek said:

Aside of self discharge, would it be possible, given 4p, to re arrange so capacities match.

I would be inclined to reduce to 3p and swap and test, until you can match them up. Also check for self discharge.

How old are these batteries? Some other thoughts include, that maybe they are just way out of balance, and if balanced manually, they would come good. LiFe batteries have a very flat discharge curve, so it is impossible to judge state of charge by voltage.

Click to expand...

It's certainly possible and I the thought crossed my mind. But it's an ENORMOUS amount of work screwing and unscrewing cells and bus bars and would take my solar system offline for a while. Throw in that I have a full time job and this would kill all my free time. I'm one of those people with more money than time (not that I feel rich or anything lol, I'm just time poor).

The batteries are not old at all... maybe half a year. I'm clearly having an issue somewhere because I'm not trying to charge them to full or all the way to empty at all. I had my float set to 56.8 and empty set to 49.0... I've since changed that to 56.0 and 50.0 to be more conservative. These original batteries were all bought from Zhejiang Xinghai Energy Technology Co (https://zjxhny.en.alibaba.com/). Which I think is the real Headway. Apparently Alibaba is littered with fake companies trying to make their batteries look almost exactly like real Headway, Calb or Sinopoly cells but way lower quality.

Click to expand...

Perhaps manually load the offending cells. Or even get a hobby charger to top off the cells that are low. Check all your connections too. It's odd that they came out of balance that quickly.

What BMS are you using? There are Battery Equalizers on AliExpress which claim up to 6a bypass. Another forum user was using them, however I cannot locate the post.

Yes you can run Batrium on just some of the cells but actually why not fix the problem instead?

Also the block or longmons is the cheap alternative in the whole. They are cheaper than 1s balancers that you dont know whats going on with at all!
For your questions about Batrium check out their FAQ and specifications page. You can configure it in many ways

One mon can do 1A continues burn and 2A burst kind of. You can have it to trip a shunt on issues but that disconnect the whole chain.
With Batrium and my software you can control the inverter and thus lower the charge when needed!

Geek said:

Perhaps manually load the offending cells. Or even get a hobby charger to top off the cells that are low. Check all your connections too. It's odd that they came out of balance that quickly.

What BMS are you using? There are Battery Equalizers on AliExpress which claim up to 6a bypass. Another forum user was using them, however I cannot locate the post.

Click to expand...

I have a hobby charger and that's what I do to balance. It definitely helps some but I need to take this to the next level, because I can't be sitting there all day. Also I really should NOT be needing to balance batteries bought from the same source at the same time (and thus I assume same factory and manufacturing batch). Especially when relatively new. Something else must be going on.

I will re-check the connections again. The BMS I'm using is the very one that Daniel Romer reviewed on YT as a cheap alternative to Batrium. It does a good job at telling me what the voltages are from a laptop that I keep connected. Well he reviewed a 14s I think, mine is the 16s version of that same one.

daromer said:

Yes you can run Batrium on just some of the cells but actually why not fix the problem instead?

Also the block or longmons is the cheap alternative in the whole. They are cheaper than 1s balancers that you dont know whats going on with at all!
For your questions about Batrium check out their FAQ and specifications page. You can configure it in many ways

One mon can do 1A continues burn and 2A burst kind of. You can have it to trip a shunt on issues but that disconnect the whole chain.
With Batrium and my software you can control the inverter and thus lower the charge when needed!

Click to expand...

Daniel,

When you say "fix the problem instead", do you mean buy the entire Batrium and all the mons that I need for all the cells or fix in some other way (like replacing weak cells with new cells)? It was a bit ambiguous how you said it, that's why I'm asking.

Also, the telemetry is the reason why I am still considering the BMS. Like yourself my prefered way to "view" solar and battery information is influx/grafana. And it's hard to find BMS's that are "code friendly" enough for me to extract the raw text (or hex) values for things like that so I can store it my way.

Fix the problem as in fixing the battery drifting The BMS or balancer is not there as a fix. its there to save you time to get it fixed and even do some protection in first hand.
But yes I also recommend getting the full Batrium since you will have a better overview but you should never get a BMS or balancer just because the cells are drifting alot.

Comparision: If your cars engine is smoking and sounding bad like hell its not a good sollution to just add some extra oil and put earplugs in your ears.. its better to repair the engine

daromer said:

Comparision: If your cars engine is smoking and sounding bad like hell its not a good sollution to just add some extra oil and put earplugs in your ears.. its better to repair the engine

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What?!? I've doing it wrong all along?! Doh!

So what likely causes battery drift? Loose connections yes? What else?

nrm21 said:

So what likely causes battery drift? Loose connections yes? What else?

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Batteries that are not at the same health & capacity as the rest of the ones in the pack is probably the primary reason things drift and come out of balance.

Health can be anything from internal resistance to a self-discharging cell.

CrimpDaddy said:

nrm21 said:

So what likely causes battery drift? Loose connections yes? What else?

Click to expand...

Batteries that are not at the same health & capacity as the rest of the ones in the pack is probably the primary reason things drift and come out of balance.

Health can be anything from internal resistance to a self-discharging cell.

Click to expand...

Put simply, no two batteries are perfectly identical. Over time they will drift apart. Once one drifts away from the next, overcharging, or over-discharging will further change the batteries characteristics. Eventually you will end up with batteries that are quite different.

Agreed with previous comments, Batrium is the best protection for batteries. Not only does it balance them, but it allows you to identify faults, such as poor connections, or a self discharging pack.