diy solar

diy solar

Heltec BMS' (up to 350A) with Active Balancing & Independent Active Balancers

I just measured it, they seem to be 2.5 mm. I measured across 10 pins for accuracy. It looks like a JST connector. It even has the small retaining tabs like the XH series. I am looking in a DigiKey catalog and comparing the pictures of the connectors.
The lower first 14 cells is a 15 pin. The upper one is an 11 pin.
So it looks like we need an XHP-11 and an XHP-15 housings. The temp sensors are on a 4 pin. I think it is the same series.
Then we need the pins. I am only using 16, but I will order at least 30 to have a few spares. They normally come on a reel but they will sell small quantity. There are 3 possible pins. Standard ones are Phosphor Bronze with tin plating. Gold plated has to be special ordered. I think the pin we want is part number SXH-001 T-P0.6 which is the standard tension for 22-28 awg wire.

I can find pins on Amazon, but not the 11 and 15 pin housings. I think I want to get name brand quality, and not the cheap copies. The pins in the BMS do not look like gold plating, so the tin plated is probably the right way to go.
 
Here is an update...

My system is back up and running with the current back going through the JK BMS. I used the leads for cells 23 and 24 to replace the poor connection leads that were in the cell 3 and 4 positions. I tested the wire harness at about 2 amps of current and saw between 60 and 66 millivolts of drop on all the leads now. And it is working perfectly. There was nothing wrong with the actual BMS, just bad crimps on the balance lead harness. I tugged pretty good on all the leads and the rest all seem fine, but I will still build a new harness when I get the new pins. So the JK (Heltec) BMS still gets a good rating from me. I was very worried when it cut out, but the board actually did it's job. The cell voltages were out of range, so it shut down the system. The bad pins look like they were partially crimped on the wire insulation. My guess is that one of the cells went just enough out of balance that it tried to pull the 2 amps on the bad lead, and with a tiny contact point and maybe a little corrosion, the connection failed.
 
Heat and/or corrosion...

That’s the reason I prefer soldered leads - if there is no movement involved, once a soldered connection is validated, there is little short of corrosion if the underlying wire itself that can lead to change in resistance...

[edit: see it is on the BMS side of the harness, so not a DIY crimp connector on the battery side. A poorly-made crimp connector by the supplier can easily result in non-stable resistance...]
I have wondered if crimp-then-solder could be problematic. Since the wire and connector must be somewhat dissimilar metals, couldn't heating up the both of them to add solder decrease the contact area (from the crimp), and increase resistance? I don't really know of course and admit I am an expert at none of this; it's only a guess since I was thinking about (and have been told) that crimp-then-solder is the best way to make a 'gas-tight' permanent connection. And I'm getting ready to make a bunch of them! :) Solder only is not as low resistance as crimping, I'm pretty sure. But like you say, it seems the best way to prevent corrosion. Sorry, I know this is off topic and you can refer me elsewhere etc.

--
Stevelk
 
I have wondered if crimp-then-solder could be problematic. Since the wire and connector must be somewhat dissimilar metals, couldn't heating up the both of them to add solder decrease the contact area (from the crimp), and increase resistance? I don't really know of course and admit I am an expert at none of this; it's only a guess since I was thinking about (and have been told) that crimp-then-solder is the best way to make a 'gas-tight' permanent connection.
The advantage of crimp is purely mechanical protection of the wire. The weak point about soldered connections is that the folder invariably flows back up the wire for a length and results in a solid/rigid section after which all movement/flex eventually wears through the wire.

Crimp connectors have no rigid soldered section and support the flexible wire with a short section of plastic, much better distributing the stress of any movement.

And if you crimp a soldered connection (or solder a crimped connection), you will have the vulnerability of a rigid soldered section but it will be much better protected by the plastic support housing/casing of the crimp connector.

If your wires are never moving, there is not much reason crimping in addition to soldering improves the connection...

And I'm getting ready to make a bunch of them! :) Solder only is not as low resistance as crimping, I'm pretty sure. But like you say, it seems the best way to prevent corrosion. Sorry, I know this is off topic and you can refer me elsewhere etc.

--
Stevelk
Pretty sure that is not correct (though I’m interested in any reference you find showing that I’m wrong),
 
I have wondered if crimp-then-solder could be problematic. Since the wire and connector must be somewhat dissimilar metals, couldn't heating up the both of them to add solder decrease the contact area (from the crimp), and increase resistance? I don't really know of course and admit I am an expert at none of this; it's only a guess since I was thinking about (and have been told) that crimp-then-solder is the best way to make a 'gas-tight' permanent connection. And I'm getting ready to make a bunch of them! :) Solder only is not as low resistance as crimping, I'm pretty sure. But like you say, it seems the best way to prevent corrosion. Sorry, I know this is off topic and you can refer me elsewhere etc.

--
Stevelk
Extensive discussion about corrosion on terminals here.
 
Pretty sure that is not correct (though I’m interested in any reference you find showing that I’m wrong),
The important part is to get the right crimp tool. The automotive industry is pretty much crimp only, and I there are few places with a harsher environment.
 
The advantage of crimp is purely mechanical protection of the wire. The weak point about soldered connections is that the folder invariably flows back up the wire for a length and results in a solid/rigid section after which all movement/flex eventually wears through the wire.

Crimp connectors have no rigid soldered section and support the flexible wire with a short section of plastic, much better distributing the stress of any movement.

And if you crimp a soldered connection (or solder a crimped connection), you will have the vulnerability of a rigid soldered section but it will be much better protected by the plastic support housing/casing of the crimp connector.

If your wires are never moving, there is not much reason crimping in addition to soldering improves the connection...


Pretty sure that is not correct (though I’m interested in any reference you find showing that I’m wrong),
I believe this because crimping presses the conducting metals together with great force, while soldering may "bridge the gap" between the conductors if not crimped, and the solder itself can end up as the conductor, and is a relatively poor conductor.
 
Extensive discussion about corrosion on terminals here.
Thanks.?
 
Should you ever end up just having it sit there after a refund or something, let me know. I'd like to have a look and do a post-mortem (if you're not) and see if I can fix it or even play with a different set of mosfets.
I'll pay for shipping it over...
I am getting a replacement for one of my BMSs from Heltec. If they don't ask me to send back the old one, you are welcome to it.
It gets a CPU warning that I can't clear. The balancer still works but it won't allow me to turn on charging or discharging.
 
A quick update on mine. Since repairing the balance lead harness, my JK BMS has been working perfectly. I have been watching it very closely, and I started to notice a trend. While all cells are staying within 0.006 volts (my balance threshold setting), I noticed that cells 10 and 11 were reporting as the high cells. But then another time it was the same cells 10 and 11 reporting as the low cells. All of the other cells were always within 0.002 volts. Sure, this is just a 4 millivolt error, which means nothing, but I was curious why I was seeing it. As I checked the cells with my Fluke meter, right at the cell tabs, they were dead on within 1 or 2 millivolt to the neighboring cells. But I did see a 3 mv difference at the balancer harness, but not always, and sometimes they were high, and sometimes low. Then I put it together in my head. Those cells were low when discharging, high when charging, and balanced at rest. My Chevy Bolt packs all have identical buss bar plates between them, with the balance lead at the center of the buss bar, except for the connection from cell 10 to 11. There I have two #2 awg cables, about a foot (30 cm) long bridging from the 10 cell packs to the 4 cell groups. The balance lead is effectively at the center of those cables. Under my 30 amp charge current, the cables are dropping about 6 mv more than the buss bar plates. Half of that difference is added to cells 10 and 11 in the balancer measurements. That means the resistance of the cables are about 0.0002 ohms more than the buss bar plates. That is so crazy close. That is also a testament to how accurate the balancer is and how incredibly well matched these cells are. Had I been seeing balance activity across other cells, I never would have seen this. As long as the balance leads are good, I am now very confident that the balancer is accurate well beyond what we need to monitor the cells. It is a shame that they supplied JST connector cables have caused issues with at least 3 people on this forum. I was very close to ordering a different BMS.

Is there anyone else on here that had the error of 2 adjacent cells showing very low readings and shutting down? I questioned the balance leads when I saw the first report, but don't remember hearing what the remedy was in that case.
 
Then I put it together in my head. Those cells were low when discharging, high when charging, and balanced at rest. My Chevy Bolt packs all have identical buss bar plates between them, with the balance lead at the center of the buss bar, except for the connection from cell 10 to 11.

I noticed the same when I was testing these half a year ago or so. That's why it's important to make sure your connections are as perfect as you can get them (not directed to you personally, just to everyone else reading this and using the BMS with their cells). I've not had any issues with that JST connector, but since I'll be taking apart my pack soon, I'll double check all the connections or even just make an extra connector and replace them preemptively.
 
Thanks mmdb.
I am not sure what armor 6 is. Is that for Apple? I saw the Apple store link still works but the link for Play Store just starts a download.
The APK I downloaded from JK is called - enjpower-3
I think the phone I am trying to use is too old for the APK. I tried the APK from Heltec and got the same error. Something to do with unable to parse file.
I have a few other androids laying around I'll keep trying to hack my way in.
Eventually I'd like to leave an unused phone or two near the batteries. I have an android tablet too that I never use.

My regular phone is working fine so I can still see everything..
I get the same errors on my samsung 8 on the heltec bms app. The victron app installs no problem for the shunt. I was able to install the xiaoxiang app from the play store version 3.1.1014. Hoping that works with the Heltec BMS.
 
I measured the voltage drop at 20, 35 and 80 amps, in each case it was very close to 1 mOhm or 0.001 ohm . So yes, it was about 80 vm across the BMS leads at 80 amps. And I suspect a fair bit of the resistance is actually the wires. The two #7 awg wires seem a bit light for 200 amps.
Speaking of amps, does anyone know why Tesla max charge amps is limited to 12 amps? Would that be a good charge limit for these 280Ah cells? Just wondering how they came to that number. They seem to have some pretty good engineers.
 
I have a Chargery and I have to say I'm extremely pleased with it - and I VERY much like it having a remote control and display screen I can put at the end of a 80 foot phone cable to see whats going on while in the main house and not having to find my phone or fire up a computer.

It uses external relays or SSRs for separate control of charging.

Personally I wouldnt trust chinese mosfets of unknown provenance with anything more than 40 amps, maybe even down to 30. I'm using Gigavac contactor relays on both the charge and discharge current paths, the discharge is a 400A contactor and the charge is a 150A contactor and they barely get above ambient temp. They use about 8 watts each to stay energized and have integrated flyback diodes. I can't recommend gigavac enough, they're a awesome value.

I also like knowing that if it fails it fails in a safe condition and the contactors open. Mosfets fail closed so you could be in a situation where you have no ability to do a emergency over/under voltage shutdown only to discover the hard way that the mosfets failed.

There's a reason industry uses contactors for high amperage loads and its a pretty good one. The only time we use SSRs is to drive contactors.
Thats interesting. Blue Sea Systems support sent me to Gigavac for a battery cutoff switch for a 48V system. They said theirs are rated at MAX 48V, but Gigavac uses a different design that can support cutoff during high current load.
 
Not sure. I guess 240V. I noticed it while watching off-grid Garage on Youtube.
 
Not sure. I guess 240V. I noticed it while watching off-grid Garage on Youtube.

Yes, so at 240V and 12A that's 2880W. For a typical 48V 280Ah pack, that would be equivalent to 60A charge current.
The reason it's limited to that amount as well is that you'll blow a fuse if you go much higher (16A fuses in a home).
 
Yes, so at 240V and 12A that's 2880W. For a typical 48V 280Ah pack, that would be equivalent to 60A charge current.
The reason it's limited to that amount as well is that you'll blow a fuse if you go much higher (16A fuses in a home).
Ah, now that makes sense! Thanks!
 
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