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Errant shutoff with chargery DCC

ndrober

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Oct 24, 2020
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Has anyone had problems with their chargery DCC disconnecting without an alarm on the BMS?

I have 16 eve 280ah batteries mounted under my rv connected to an 16t bms with 600 amp shunt and DCC. Twice the DCC has cutout while all the cell voltages and temperatures are in in the acceptable range. (3.3v and 35c) . I have also checked the cell difference voltage, temperatures difference settings and charge limits. It will be a couple days limping home before I can pull the battery pack and get back to the BMS to see what signal is being sent.

It seemed to work fine on the bench but now the solar is charging it at 45 amps on solar vs 2amp of my benchtop supply.
 
As a temporary bandaid, consider lowering your absorption voltage to 55.2V (3.45V/cell). This will permit you to attain 98%+ state of charge over a longer period, and it may prevent a disconnect if it's cell or dV based.
 
I had such occur and realized there is a BMS setting that was tripping cutoff. See my BMS8T settings (identical to 16T)

SettingDefaultMy settingsNOTES
Over charge P Voltage3.653.65
Over charge R Voltage3.553.55
Over charge Current5086A / 150A0.5C rate for 174AH / 280AH
Over Discharge P Voltage3.002.65CUTOFF Trigger
Over Discharge R Voltage2.002.75Release @ this V.
Over Discharge Current300175A / 250A1.0C Rate for 174AH / 280AH
Low SOC cutoff20%0%forces cutoff @ % (faulty)
High Temp cutoff50C70C
Diff of Batt Temp1015C
Diff of cell Voltage30mv200mvUnmatched cells drift,
Temp UnitCC
Key BeeperONON
LCD Backlight1010min
Cut off Delay Time1010S
Current Calibration-SET-
Temp AlarmONON
Cell Empty Voltage2.502.50
Cell Full Voltage4.20?3.65
Default SettingEnable
Balance Parameter-SET- (OFF)*Passive is ON charge only, start at 3.40V, 30mv diff.
Battery Capacity AH1174 | 280Label Value of cells
Battery Power WH10004554 | 7168FORMULA (NominalVolts * #ofCells * RatedAH) (3.2*8*280=7168)
Low Temp cut off in Charge2C2C
Low Temp cut off in Discharge-10-10C

The Charging profile also has to be just right, so I'll post my charge profile from my Midnite Classic-200 which is also identical to my Inverter/Charger. The tweaks are subtle.

All equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT) see link in my signature on how to do it.
Divide Values X2 for 12V. Multiply X2 for 48V.
Absorb: 28.2 for 15 minutes (3.525vpc) (some call this boost)
Equalize: OFF
Float 27.9V (3.4875vpc)
MIn Volts: 22.0 (2.750vpc)
Max Volts: 28.7 (3.5875vpc)
Rebulk Voltage: 27.7 (3.4625vpc)
End Amps: 14A (*1)

This get's the bank charged to full with high amps (Constant Current) and then float (Constant Voltage) tops off so the cells are on average between 3.475-3.500. I am running 7/24/365 so float is used up by the Inverter + provides whatever the packs will take to top off.
(*1): End Amps is calculated from the Highest AH Battery Pack in a Bank. IE: 200AH X 0.05 = 10A 280AH X 0.05 = 14A.
** Coulumbic Efficiency for LFP is 99%

Hope it helps Good Luck.
Steve
 
I had such occur and realized there is a BMS setting that was tripping cutoff. See my BMS8T settings (identical to 16T)

SettingDefaultMy settingsNOTES
Over charge P Voltage3.653.65
Over charge R Voltage3.553.55
Over charge Current5086A / 150A0.5C rate for 174AH / 280AH
Over Discharge P Voltage3.002.65CUTOFF Trigger
Over Discharge R Voltage2.002.75Release @ this V.
Over Discharge Current300175A / 250A1.0C Rate for 174AH / 280AH
Low SOC cutoff20%0%forces cutoff @ % (faulty)
High Temp cutoff50C70C
Diff of Batt Temp1015C
Diff of cell Voltage30mv200mvUnmatched cells drift,
Temp UnitCC
Key BeeperONON
LCD Backlight1010min
Cut off Delay Time1010S
Current Calibration-SET-
Temp AlarmONON
Cell Empty Voltage2.502.50
Cell Full Voltage4.20?3.65
Default SettingEnable
Balance Parameter-SET- (OFF)*Passive is ON charge only, start at 3.40V, 30mv diff.
Battery Capacity AH1174 | 280Label Value of cells
Battery Power WH10004554 | 7168FORMULA (NominalVolts * #ofCells * RatedAH) (3.2*8*280=7168)
Low Temp cut off in Charge2C2C
Low Temp cut off in Discharge-10-10C

The Charging profile also has to be just right, so I'll post my charge profile from my Midnite Classic-200 which is also identical to my Inverter/Charger. The tweaks are subtle.



Hope it helps Good Luck.
Steve
Thanks. I Appreciate the SOC note
 
Thanks. I lowered the charge profile from Victrons LiFepo4 default on the solar charger(it was 56v bulk and 54 float) based on snobbery comment.

I appreciate the note on the faulty SOC shutoff and have turned that off. I tweaked the rest of the setup like yours( adjusted for 48 v 280 ah)

We will see if she behaves any better today.
 
I am missing something. I see nothing that would cause the DCC to open..

All the cells are about 3.3 volts with a spread of 41mV. Other than it being hot, but I have the thermal alarms off and set at 70C with 30C difference. ... its about 100F out in the Southwest today so they are only a couple degrees above ambient.

Is there any way to see what limit is causing it to be open?
 
"snobbery" :(

Seriously though, it's not clear what's causing it to trip. Worth checking all connections.
 
I got home last night and plugged the RV into a 15amp circuit, with my Charger (Quattro) off. Woke up this morning and the solar charging the batteries.... The only difference I can see if the ground provided by the 120 circuit. Looks like I will be chasing a grounding issue.
 
I got home last night and plugged the RV into a 15amp circuit, with my Charger (Quattro) off. Woke up this morning and the solar charging the batteries.... The only difference I can see if the ground provided by the 120 circuit. Looks like I will be chasing a grounding issue.
I found the connection between dc negative and vehicle chassis was 36 M ohms. Also the connection that was not firing was the charging relay. Checked all the connections and it seems ok.

I fixed that and the BMS seemed to be better. Let it run on solar for an day and then I let it charge on float for a day off the house. Took it out today and again in the afternoon it disconnected again. About 92% charged and the worst case balance was 41mv and it is triggering a disconnect
 
Nothin worse than chasing electrical gremlins, says the guy who used to restore antique cars which in some cases included rebuilding the harnesses to factory specs, AND getting it all to work as it should... oivey... and that wasn't puterized putput's either, Thank God for that.
 
Did
I found the connection between dc negative and vehicle chassis was 36 M ohms. Also the connection that was not firing was the charging relay. Checked all the connections and it seems ok.

I fixed that and the BMS seemed to be better. Let it run on solar for an day and then I let it charge on float for a day off the house. Took it out today and again in the afternoon it disconnected again. About 92% charged and the worst case balance was 41mv and it is triggering a disconnect
you raise the cell difference setting to like 75mv. Factory default is 30mv. Your cells are drifting more than 30mv
 
Did

you raise the cell difference setting to like 75mv. Factory default is 30mv. Your cells are drifting more than 30mv
Yep checked that one. Temp limits are off. Voltage limits 1000mV.

The weird behavior continued with the troubled BMS. It dies a couple more times and I was on the side of the road trying to reach the on off switch and despite the power cycling it the DCC status light was out and the batteries disconnected. I removed the battery cover one night and both BMS to DCC cables show 12 volts while the status light was out. I went to get some bigger wrenches to bypass the DCC for the rest of the trip and magical it started working.

I had a 2nd set of batteries and git those installed with their own BMS. That one seems to be behaving as expected.

The following day we are driving down the road and the troubled BMS alarms again. Now it's drawing 350 amps and tried the high current alarm. I was watching it slowly go down for a few seconds before I disconnected it. Now I have a 300amp fuse and 250 amp breaker before my main loads, both of which should have tried if it was real. Since I had a second battery pack at that point I left it disconnected. I reconnect it yesterday. SOC is all goofed up but it seems to be working. I am at an RV park hooked into power so it is not being stressed... at least untill tomorrow. I suspect I have a bad DCC as all these disconnects do not have a visual indicator on the screen.

I emailed Jason and will see where that goes.
 

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voltages, temps all that looks fine on the screen image.
now you are saying this is mobile and occurs also while in motion... That leads me back to a loose connection, bad crimp, or broken connection (possibly internal to the DCC) or the FET Rail got buggered up maybe (where the batt terminals are attached)

To check the DCC use a DMM/DVOWM and measure the resistance between two terminals, if it is 7.5K ohm, means the DCC is ok.
Must be powered OFF, best to have everything off to be safe.
 
Not sure this got resolved but when I was having disconnect issues I found it to be the Diff of cell Voltage setting like mentioned above post #4. Not sure if you extended this range?
 
The DIFF of Cell Voltage has to change at 30MV it will trip even with a deep Load Sag (that was a bugger to figure out as my powerhouse is 50' from the house) so it's tough to watch when in different buildings. Have a look at my BMS settings - I didn't post it just for fun but because it works broadly and those who have used those settings are quite happy without the issues.

My Air Express package arrived yesterday, 3 days before the expected date (DHL has gotten better !) which included the latest generation of DCC-300 and some other goodies, so now I can tell you for certain the lugs got changed longer & more spacing between, everything else appears the same but I am not cracking it open to mod it as it does not need it. There is now lots of clearance so that got sorted as well... BUT I am running a fleet of 1st issue DCC's.
 
The DIFF of Cell Voltage has to change at 30MV it will trip even with a deep Load Sag (that was a bugger to figure out as my powerhouse is 50' from the house) so it's tough to watch when in different buildings. Have a look at my BMS settings - I didn't post it just for fun but because it works broadly and those who have used those settings are quite happy without the issues.

My Air Express package arrived yesterday, 3 days before the expected date (DHL has gotten better !) which included the latest generation of DCC-300 and some other goodies, so now I can tell you for certain the lugs got changed longer & more spacing between, everything else appears the same but I am not cracking it open to mod it as it does not need it. There is now lots of clearance so that got sorted as well... BUT I am running a fleet of 1st issue DCC's.
I noticed if he left it at default and his photo was showing the drift at 44MV then it would have disconnected. Figured that might had something to do with some of the issues he was having. I had that going on with mine until I believe I seen you post your settings somewhere way long ago and changed mine to 300mv
 
I noticed if he left it at default and his photo was showing the drift at 44MV then it would have disconnected. Figured that might had something to do with some of the issues he was having. I had that going on with mine until I believe I seen you post your settings somewhere way long ago and changed mine to 300mv
Actually, the "unwritten rule" for a pack (especially bulk cells) is 1mv per AH of capacity as Bulk cells can drift that much, especially when pushed hard. So for a 280AH cell up to 280mv differential is quite possible. I do not suggest exceeding that because beyond 1mv difference other issues will rear their heads and none of them are good for the cells or your investment.

The matched cells never drift like that, I've seen 50mv with hard 200A pulls, I can see 200mv with the Bulk cell packs @ 200A pull.
Just another difference between Bulk & Properly Matched cells. But pennies override common sense for some and then they whine when they got the Chevette they paid for, rather than the Cadilac they wanted & expected, at which point blame is spread like manure on the field.
 
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