Heltec (JK) 200A Smart BMS with 2A Active Balance

[UV-PWRD]

Odd one for you all. Short version, no battery percentage or AH info and logs are too small. Bonus, maybe 1 bad cell.

I went to bed at 1030, battery was 60-70%, at around 3am the hot water element came on (1800w) on a schedule. I've run this before for a few hours at a time, but usually when the battery is in the top end (dumping excess solar into hot water) without any issues.

It ran for 10mins and then the inverter switched off (can see off time from MPP inverter logs) I assume because the BMS disconnected the battery. Now as the MPP has tried to restart, the BMS sees that as a short so it's filled the logs with short circuit protection errors until I've gotten up and plugged in a power supply on the output side of the BMS to give the inverter a chance to charge its caps and everything was back up and running. But logs don't go far enough back for me to tell what happened. I immediately tested the hot water element again, ran it for 20mins, had no issues then switched it off.

Since then, there's no capacity or AH info in the BMS screen, see screen shot.

Do I need to fully reboot the BMS? It's been up for over 40 days. If I do need to reboot it, what's the process as I've heard horror stories about disconnecting/reconnecting the wrong ends at the wrong time.




As for why it switched off, I think cell 14 might be an issue, as per my other thread it's hitting HVD well before others, I thought maybe it was not balanced and have switched on balancing sooner (but the pack was paralleled for almost 2wks before commissioning), but now I am seeing it is also dropping much further under load. In these 2 screen shots You can see it dipping well below pack average voltage and then in the next image, being close to the others (but I think it's because in the image where it's not as far below, the balance current is positive and likely going into that cell).

I have started chatting with Ali about the cell.







Since restarting the inverter I also see this Eeprom fault but logs do not go far enough back for me to tell if that was there last time I switched the inverter on. Ignore the line in fault, that was me turning AC input off.

I have ordered a USB/RS485 setup so I can put a PC in there and log properly from the watch power app for the inverter and maybe Grafan for the BMS.

All help appreciated

 

[ArthurEld]

I would check and clean the connections to cell 14.
Check and clean the connections on both sides of the busbars.
So, you clean the connection on the cells next to cell 14.

Your BMS could have gone bad but you could try cleaning all of the balance connections.

The only reset I know of is on the last page on the app. If you select factory reset it will reset the BMS after you turn it off.

 

[UV-PWRD]

When I say reset I mean reboot it to get battery percent info back.

So power it down and back up, I assume to do that I need to disconnect the header connectors from the BMS, but I recall seeing something about cooking BMS doing that or doing it in the wrong order. Or do I just remove main pack neg and pos to reboot the BMS?

I have double stacked bus bars and used new studs washers and nuts, not what came with the cells so I doubt the connections are "dirty" after a month in a sealed cabinet with a filtered fan/vent setup but I can try it.

I am also going to move cell 14 to a different spot and see if the low readings follow it.

 

[ArthurEld]

I suggest that you at least scratch up the terminals and busbars with scotchbrite or fine sandpaper. New cells often have tape residue on the terminals. It doesn't take much to cause a bad connection.

Un plug the balance wire harnesses first. Then you can disconnect anything.

 

[UV-PWRD]

OK so it's just the 2 harnesses with the balance wires that need to come out before disconnecting a main pos or neg? As I want to reboot the BMS so a main pos or neg will need to be disconnected.

 

[ArthurEld]

OK so it's just the 2 harnesses with the balance wires that need to come out before disconnecting a main pos or neg? As I want to reboot the BMS so a main pos or neg will need to be disconnected.

Yes, unplug 2 harnesses. Then disconnect the main negative and the BMS should turn off.
When you turn it on you will have to set the correct number of cells and select lifepo4 battery type.

 

[UV-PWRD]

- Unplug both harnesses
- Disconnect main neg


To repower, last time I had both harnesses plugged in first, then made last main neg connection to the pack.

I will also move Cell 14 location to see if the low voltage follows it.


I am still assuming the pack turned off last night because cell 14 hit LVD.

 

[UV-PWRD]

I have moved cell 14, re-checked the bars/connections and cleaned up anything unusual.

I did find this washer, which is odd as I bought new washers for this install so I've either missed it or its degraded like this in 6 weeks. I have made a very conscious effort to centre the washers/balance lead terminals on the studs when tightening.

The pack is charging currently, JK tell me the battery percentage may not read correctly until the battery has been fully charged or discharged.

I have confirmed the system log shows "boot" so it did restart yet it kept all my settings.

It's only charging at low current and I know from yesterday it won't be near the top yet so at the moment all cells look even.

 

[upnorthandpersonal]

Question: do you have your cells compressed, and what bus bars are you using?
Reason I ask is that maybe your cells expanded while charging/discharging and this action put pressure on your bus bars and moved them, possibly giving a bad connection.

What material are those washers?

 

[UV-PWRD]

The washers are zinc coated steel.

Cells are compressed with ratchet straps on the upper and lower edge areas, wood boards at both ends to ensure no cell damage where straps rest. IKEA chopping boards between cells.

Bus bars are tinned copper Xuba tells me.

 

[UV-PWRD]

Here we go.

I've pulled 40a from it for a hour this evening and I'm not seeing the single cell drop.

I'll keep monitoring.

 

[Choco]

Guys, I'm close to pulling the trigger on one of these 16s 2A models, do you still recommend, any regrets or wish you had gone for say an OverKill?

 

[UV-PWRD]

I've been re-assessing a few things since seeing that washer, and I note I have used 304 grade stainless M4 studs, and the terminals are aluminium.

Does anyone have experience with corrosion in this instance? My only experience is with cars and it tends to not be a good outcome.

 

[Bob B]

I've been re-assessing a few things since seeing that washer, and I note I have used 304 grade stainless M4 studs, and the terminals are aluminium.

Does anyone have experience with corrosion in this instance? My only experience is with cars and it tends to not be a good outcome.

Do a search for the galvanic corrosion thread .... more info that you want.

 

[UV-PWRD]

This one?

Galvanic Corrosion

Hi, everyone. How significant is galvanic corrosion in a portable DIY system? Like when soldering an aluminum wire to a copper XT60 terminal. Or soldering a copper wire to a circuit board. Or just soldering or crimping copper and aluminum wires together. Thanks.

diysolarforum.com

 

[Bob B]

This one?

Galvanic Corrosion

Hi, everyone. How significant is galvanic corrosion in a portable DIY system? Like when soldering an aluminum wire to a copper XT60 terminal. Or soldering a copper wire to a circuit board. Or just soldering or crimping copper and aluminum wires together. Thanks.

diysolarforum.com

There a bigger one ... I'll see if I can find it.

 

[Bob B]

This one has more reading material ... https://diysolarforum.com/threads/avoiding-galvanic-corrosion.10947/

 

[lonertic]

Guys, I'm close to pulling the trigger on one of these 16s 2A models, do you still recommend, any regrets or wish you had gone for say an OverKill?

I've got 3 of these... they're on 200Ah cells.. I am so grateful to have gone with this one as it's the only one on the market with 2A balancing. everything else is in the mA's... I saw Will's YT video on why he thinks you don't need more than a few mA's for balancing but the reality is, if we're buying DIY cells, especially the high capacity LFP's (as opposed to tiny 18650 cells), the tiniest variation in manufacturing, even with "new" cells, is enough to create a variation between cells that size... I can monitor the BMS and at no point during any part of the day is the balancer working below 1.9A - ie: it's CONSTANTLY balancing all the cells as best as it can during charge/discharge..

since the overall capacity of the bank is determined by the weakest cell, in my case, the weakest cell is 178Ah (cell 6/16).. and what I find happening overnight is that, as cell 6 drops below UVP (under voltage protection) threshold, BMS stops discharge as it should.. but then the balancer works hard to replenish cell 6 from the rest of the cells, and it normally only takes a few minutes (cos there's 15 cells charging 1), before Cell 6 is charged above UVPR threshold again.. in which case discharge is re-enabled again... for a while.. until cell 6 hits UVP again.. and the process repeats, giving me a kind of square wave output throughout the night... ie: it's effectively giving me access to the remaining missing 22Ah that's in the rest of the cells. That would not happen with a BMS with a lower balancing current as it would take hours to bring up a 200Ah cell back above UVP release voltage.

I wish there was a 5 or even 10A balancing option, cos on my 200A cells it can accept a charge rate of up to 100A... so the BMS balancing is only scratching 2% of that in the above overnight scenario... I just haven't figured out if I can run an active balancer in parallel with this BMS yet but that would be my only "regret"

 

[Sanwizard]

I've got 3 of these... they're on 200Ah cells.. I am so grateful to have gone with this one as it's the only one on the market with 2A balancing. everything else is in the mA's... I saw Will's YT video on why he thinks you don't need more than a few mA's for balancing but the reality is, if we're buying DIY cells, especially the high capacity LFP's (as opposed to tiny 18650 cells), the tiniest variation in manufacturing, even with "new" cells, is enough to create a variation between cells that size... I can monitor the BMS and at no point during any part of the day is the balancer working below 1.9A - ie: it's CONSTANTLY balancing all the cells as best as it can during charge/discharge..

since the overall capacity of the bank is determined by the weakest cell, in my case, the weakest cell is 178Ah (cell 6/16).. and what I find happening overnight is that, as cell 6 drops below UVP (under voltage protection) threshold, BMS stops discharge as it should.. but then the balancer works hard to replenish cell 6 from the rest of the cells, and it normally only takes a few minutes (cos there's 15 cells charging 1), before Cell 6 is charged above UVPR threshold again.. in which case discharge is re-enabled again... for a while.. until cell 6 hits UVP again.. and the process repeats, giving me a kind of square wave output throughout the night... ie: it's effectively giving me access to the remaining missing 22Ah that's in the rest of the cells. That would not happen with a BMS with a lower balancing current as it would take hours to bring up a 200Ah cell back above UVP release voltage.

I wish there was a 5 or even 10A balancing option, cos on my 200A cells it can accept a charge rate of up to 100A... so the BMS balancing is only scratching 2% of that in the above overnight scenario... I just haven't figured out if I can run an active balancer in parallel with this BMS yet but that would be my only "regret"

I think DanF is just using the Heltec 5 amp balancer as his BMS. I have one of those also, and if the 2Amp balancer in my BMS does not do the trick, I will be adding the additional 5 amps in parallel.
Heltec seems to make some decent stuff.

5A Capacitive active equalization/Active Balancer

<h5 class="product-title-text" data-spm-anchor-id="a2g0o.detail.1000016.i2.6230fb43MzlDtd">3S 4S 5S 6S 7S 8S 3S-21S 5A Active Equalizer Balancer Lifepo4 Lithium Lipo LTO Battery Energy active equalization Capacitor</h5>

heltec-bms.com

I like the black case on my 200/amp 2/amp active balance BMS they put out, and that it has built in bluetooth.
Hoping my other 16 cells I ordered from the group buy (Michael Caro) in Feb get here before the summer is over!

 

[UV-PWRD]

I think DanF is just using the Heltec 5 amp balancer as his BMS. I have one of those also, and if the 2Amp balancer in my BMS does not do the trick, I will be adding the additional 5 amps in parallel.
Heltec seems to make some decent stuff.

5A Capacitive active equalization/Active Balancer

<h5 class="product-title-text" data-spm-anchor-id="a2g0o.detail.1000016.i2.6230fb43MzlDtd">3S 4S 5S 6S 7S 8S 3S-21S 5A Active Equalizer Balancer Lifepo4 Lithium Lipo LTO Battery Energy active equalization Capacitor</h5>

heltec-bms.com

I like the black case on my 200/amp 2/amp active balance BMS they put out, and that it has built in bluetooth.
Hoping my other 16 cells I ordered from the group buy (Michael Caro) in Feb get here before the summer is over!

No I'm using the full BMS with the additional 2a active balancer function built in.