JK BMS intermittently won't accept charge

[manson79]

ok, i'm stuck, i've been reading forums, and changning settings, and it's Vodoo.

I have a 150a JKBMS, 280Ah, 15cell, LiFepo4 battery, that we swapped out for old Lead Acid, 8v x 6 cells.

I think we top balanced them, but not sure, but we did have them on an active balancer in the shop for a few weeks.

it seemed to work fine, but, 2 days ago, it didn't want to take a charge. We fiddled with some settings, unplugged, and plugged it in a few times, and it came up. But, to be hones, we couldn't recreate the problem. But, we were happy.

Now, after running it down a bit, we can't get it to take a charge any more. We are still using the original charger, which I think is 48v, (assuming it is slightly higher to get the old Lead Acid charged, and it worked before.

We noticed 3 cells are much lower than the others as well. 2,6, and 14 Which occured after 2 days of running. they originally were same.


And nothing I can do, to make it charge. I think i changed every setting I could that made sense. Nothing. I jiggled all the wires, made sure it is connected, turned on and off Charging/Balancing/Discharging. I'm at wits end. Other than no charge, the BMS seems to be working properly.

What am I missing? what should I check?

 

[Steve_S]

1) The JKBMS is designed for 4S/8S/16S NOT 15S with LFP !
2) The logs on that model are NOT rolling logs, you get 50 entries and it locks. This is changed with their new models (Inverter model BMS')
3) The wire resistance reported for the cells is HIGH ! These should be around 0.040 - 0.050 (+/- 0.010) *1
4) Start Balance (settings) is at 1.50V NO NO NO !!! Start Balance to be at 3.100 or 3.200 !!!
Settings:
OVP(V) set to 3.600
OVPR(V) set to 3.550
UVPR(v) set to 2.750
UVP(V) set to 2.700 * Set before the UVPR or it will generate an error.
Power Off Vol. set to 2.600
This will allow the BMS to remain awake to take a charge when depleted. If the cells drop to 2.50 the BMS shuts down and can only be awakened with the "emergency" function and that's not good ! doesn't always work.

*1 these values are with the standard wire harness as provided with "crimped" on terminals connected to the cells. It's generally suggested to fold the end of the wire so that when crimped you get a full contact crimp. Soldering with Silver Soldering is ok but with care & caution that no blobs etc exist. Soldering Not required nor recommended actually.

TEMP SETTINGS are Terribly OFF
Charge OTP(C) set to 50 (LFP cannot be charged above 50C temp see manufacturer spec sheets... chemistry limit)
Charge OTPR(C) set to 45
Charge UTP(C) set to 0 (LFP cannot take charge below 0C)
Charge UTPR(C) set to 5 (@ 5C temp cells can take charge safely.)

A note on Active Balancing.
Active does NOT waste power, it only moves power from High Cells to Low Cells "WHEN" the cell differential exceeds the set limit and WHEN it is above the trigger voltage. Otherwise it sits and does nothing. The best starting point is at the LFP Nominal Voltage of 3.200v.

As an FYI, I am the same Steve_S that edited & wrote the English JKBMS manuals.

Please get another cell and make it a proper 16S or you will continue to have peculiar issues. In fact you are lucky that worse things haven't happened so far. Please understand that such a shortcut (cheaping out & skipping a cell) could cost you the entire battery pack and that's an unacceptable waste. Remember the old English Saying, "Penny Wise & Dollar Foolish" which is terribly true when it comes to this tech.

Hope it helps, Good Luck.

 

[Alarchist]

Also Manson79 could change continuous charge current from 18A to 140A for 280Ah cells, there were a few alarms from that as it was so low? Maybe set the balance trigger voltage to start at a lower differential like 0.005v too.

I like Off Grid Andy's logic for only setting balance to start at the target charge voltage I.e. 3.45v / 51.75v for 15s. I'd guess the unbalancing has been because it's been on permanently from 1.5v which would have just been unbalancing the battery at such a low start voltage.

 

[manson79]

Ok, wow, that was very interesting. I spent 2 full days bent over this golf cart that I'm trying to retrofit. I have also made a few changes to some wrong things I did, like not putting all the data wires on the + terminal side. But ok, I'll change all those things.

To be fully honest here though, I did learn the hardway about the workings of golf cart charging system. And found that there were other issues, one, namely, was the wire that went into the main contactor box, there was a connector there that was super brittle, and fell apart in my hand. I cleaned it, and reconnected it, and the Charger started charging fine.

It seems the existing charger was only 17.5amps, so, i was thinking that if I had it too high on the BMS, that it somehow affected the lack of charge. I realize now, this was stupid.

Now, my question is, Do I need to buy a LiFEPO4 charger? or can I get away with using this same one that charged the old 48v Lead Acid battery pack (6 cells, 8volts each)

Oh, regarind the 15s, vs 16s, I was also afraid of making the battery pack to high V, just in case it affected the Golf Carty system, like Inverter, and or existing charger

 

[manson79]

1) The JKBMS is designed for 4S/8S/16S NOT 15S with LFP !
2) The logs on that model are NOT rolling logs, you get 50 entries and it locks. This is changed with their new models (Inverter model BMS')
3) The wire resistance reported for the cells is HIGH ! These should be around 0.040 - 0.050 (+/- 0.010) *1
4) Start Balance (settings) is at 1.50V NO NO NO !!! Start Balance to be at 3.100 or 3.200 !!!
Settings:
OVP(V) set to 3.600
OVPR(V) set to 3.550
UVPR(v) set to 2.750
UVP(V) set to 2.700 * Set before the UVPR or it will generate an error.
Power Off Vol. set to 2.600
This will allow the BMS to remain awake to take a charge when depleted. If the cells drop to 2.50 the BMS shuts down and can only be awakened with the "emergency" function and that's not good ! doesn't always work.

*1 these values are with the standard wire harness as provided with "crimped" on terminals connected to the cells. It's generally suggested to fold the end of the wire so that when crimped you get a full contact crimp. Soldering with Silver Soldering is ok but with care & caution that no blobs etc exist. Soldering Not required nor recommended actually.

TEMP SETTINGS are Terribly OFF
Charge OTP(C) set to 50 (LFP cannot be charged above 50C temp see manufacturer spec sheets... chemistry limit)
Charge OTPR(C) set to 45
Charge UTP(C) set to 0 (LFP cannot take charge below 0C)
Charge UTPR(C) set to 5 (@ 5C temp cells can take charge safely.)

A note on Active Balancing.
Active does NOT waste power, it only moves power from High Cells to Low Cells "WHEN" the cell differential exceeds the set limit and WHEN it is above the trigger voltage. Otherwise it sits and does nothing. The best starting point is at the LFP Nominal Voltage of 3.200v.

As an FYI, I am the same Steve_S that edited & wrote the English JKBMS manuals.

Please get another cell and make it a proper 16S or you will continue to have peculiar issues. In fact you are lucky that worse things haven't happened so far. Please understand that such a shortcut (cheaping out & skipping a cell) could cost you the entire battery pack and that's an unacceptable waste. Remember the old English Saying, "Penny Wise & Dollar Foolish" which is terribly true when it comes to this tech.

Hope it helps, Good Luck.

In addition to my comments above, here are some pics, in case it brings it home. FYI i'm in the phillippines.

 

[MisterSandals]

here are some pics,

Is your battery going to be secured or will it just bounce around? Do you have plans to constrain/compress the cells?

 

[Steve_S]

A 48V Lead Acid / AGM battery tops out at 57.6 to 58.8 volts.
A 48V LFP tops out at 56V when cells are just above the Working Voltage range @ 3.500 Volts per cell. LFP once in operation never needs to be charged above that and the chemistry will "Naturally & Normally" settle to 3.400 Volts per cell after being fully charged which is 54.4V. This is for a Standard & Proper 16S Battery Pack.

Note you indicated a serious RED FLAG ! Wires being crispy & crunchy is VERY BAD ! They have been overheated & "cooked" without failure (which was not far behind) so you got lucky. That wire CANNOT be trusted, it needs to be replaced with a fresh wire that can actually handle the duty cycle & amperage. Wires should never get HOT, warm is okay and if you can hold it without discomfort your good, if it's hot, that is dangerous.

 

[Alarchist]

Now, my question is, Do I need to buy a LiFEPO4 charger? or can I get away with using this same one that charged the old 48v Lead Acid battery pack (6 cells, 8volts each)

That depends on the charger settings, if you can set it to your desired absorption voltage i.e. for 15s 3.45v x 15 = 51.75v or 52v @ 3.46v per cell? But if the charger has float or equalise settings that you can't change, you can easily cook your cells.

 

[Steve_S]

FLOAT is Variable Current and won't cause any harm as it won't ever push over voltage.
EQUALIZE IS a KILLER ! That can whomp a Lithium Based battery really fast.

 

[manson79]

A 48V Lead Acid / AGM battery tops out at 57.6 to 58.8 volts.
A 48V LFP tops out at 56V when cells are just above the Working Voltage range @ 3.500 Volts per cell. LFP once in operation never needs to be charged above that and the chemistry will "Naturally & Normally" settle to 3.400 Volts per cell after being fully charged which is 54.4V. This is for a Standard & Proper 16S Battery Pack.

Note you indicated a serious RED FLAG ! Wires being crispy & crunchy is VERY BAD ! They have been overheated & "cooked" without failure (which was not far behind) so you got lucky. That wire CANNOT be trusted, it needs to be replaced with a fresh wire that can actually handle the duty cycle & amperage. Wires should never get HOT, warm is okay and if you can hold it without discomfort your good, if it's hot, that is dangerous.

Yeah, that is a good point about the wires, I was thinking the same about changing it. I've never seen a clip become that brittle. It was the one of wires that came out of the charger, and into the contactor, and possibly a relay, that I could hear click when I bypasse it before I cleaned it.

Is your battery going to be secured or will it just bounce around? Do you have plans to constrain/compress the cells?

Yeah, this is mainly for testing purposes, and agreed I don't love it like this, we don't have a case at this point, and putting a strap around them in that small area is not easy. so we may take them out and put them in with at least a strap

 

[manson79]

To help clarify some mystery, and put my mind at easy while I wait for a proper charger to arrive from my supplier, I'm assuming that that 60v picture is the inverter that is powering the motor in the picture attached. That is from the original manufacturer 13 years ago. The client is complaining that the inverters and contactors and chargers do go bad. I'm sure the salt air doesn't help, but I'm wondering if it's also not the best matched system overall. Either way, continuing on, the little whie sticker shows to me, that i'm getting 210v input, and I can have 18A, Which co-incides with the BMS readout of 17.5A. so I'm happy. What is confusing me now, is that I can charge the battery higher, as can be seen by the higher voltage. how is that possible? Does it have something to do with that second line on the white sheet? the 14.5A @ 100v? If yes, then I ask, why haven't i killed the battery by charging it to 100v? Is something else in the golf cart controlling the max voltage? and why can't I use this charger if the BMS would be limiting it to 3.600 anyways? Sorry for all the dumb questions, but, I love this stuff, and I've learned more in the past 4 days than most of my life about this stuff.