Chargery bms8t caution

[Craigmck]

I have found out the hard way that when the Chargery bms shuts down because of a low cell voltage event. It only shuts down the discharge relay only. It does not shut down the charge relay, so when the bms shuts the battery pack down because one cell discharging down to 2.5v ( as the bms is programmed to). The charge relay is still active and is still pulling that 2.5v cell voltage lower. I discovered this problem this morning when one cell had dropped to 2.1v. When i unplugged the 8 cell wires from the bms the charge relay click off. Emailed Jason at Chargery today and he confirmed that in the event of an over discharge shut down, only the discharge relay is shut down. The charge relay is still active and consuming power.
I'm running 8 cell 3.2v 580ah lifepo4 from xuba in12v configuration. I believe 4s2p, 2 cells in parallel and 4 cells in series. I was doing a capacity test with 10 amp discharge rate. i only got 220 ah when the pack shut down because #2 cell bottomed out at 2.5v. the other 3 cell packs were at 3.00, 2.99, 2.98. Before this test i had done a proper parallel top balance. difference of .35mv.
Is there a better or more efficient way to build a 560 ah battery, or is it better to run two 12v 280ah packs then parallel for 560ah.
Thanks for any information.

 

[Bob B]

Yes .... that's the way it is designed so that the charge and discharge disconnect independently. The idea is that you will still be able to charge the battery. I would use some of the SSR relays that @Craig has tested so the relay coil won't pull much current.

 

[legacyturbo]

That is the point of a separate port bms, the charging relay should stay on so that the battery can be recharged. Therefore relays with low power consumption should be installed.

 

[legacyturbo]

Yes .... that's the way it is designed so that the charge and discharge disconnect independently. The idea is that you will still be able to charge the battery. I would use some of the SSR relays that @Craig has tested so the relay coil won't pull much current.

ahh, im to slow, and bobs english is better. ?

 

[Craig]

I have found out the hard way that when the Chargery bms shuts down because of a low cell voltage event. It only shuts down the discharge relay only. It does not shut down the charge relay, so when the bms shuts the battery pack down because one cell discharging down to 2.5v ( as the bms is programmed to). The charge relay is still active and is still pulling that 2.5v cell voltage lower. I discovered this problem this morning when one cell had dropped to 2.1v. When i unplugged the 8 cell wires from the bms the charge relay click off. Emailed Jason at Chargery today and he confirmed that in the event of an over discharge shut down, only the discharge relay is shut down. The charge relay is still active and consuming power.
I'm running 8 cell 3.2v 580ah lifepo4 from xuba in12v configuration. I believe 4s2p, 2 cells in parallel and 4 cells in series. I was doing a capacity test with 10 amp discharge rate. i only got 220 ah when the pack shut down because #2 cell bottomed out at 2.5v. the other 3 cell packs were at 3.00, 2.99, 2.98. Before this test i had done a proper parallel top balance. difference of .35mv.
Is there a better or more efficient way to build a 560 ah battery, or is it better to run two 12v 280ah packs then parallel for 560ah.
Thanks for any information.

I think at that size of a pack 2 would be better because there is so much energy to move around.

I'm more concerned though that your cell is.. 5 lower than the rest. I think you also helped show that bottom balancing would be an important first step to a full pack capacity test.

Looks like that cell has less capacity than the rest.

But thanks for the warning probably best to unhook charge relay during cap test.

 

[DW SD]

Hey Craig,
I see the issue and am slow to reply.

Another option is to wire the charge / discharge relays in series to the contactor control circuit. Or just allow one small relay driven by one BMS relay output to interrupt the 12V+ control signal for the other to the large contactor control circuit.

My circuit diagram posted on the chargery thread shows this.

That way, ANY BMS event would disable the contactor and then its current draw. Think of this circuit as a boolean operator "OR".
I think in the latest Chargery manual, this is called "common port" configuration.

Doug

 

[Craig]

Hey Craig,
I see the issue and am slow to reply.

Another option is to wire the charge / discharge relays in series to the contactor control circuit. Or just allow one small relay driven by one BMS relay output to interrupt the 12V+ control signal for the other to the large contactor control circuit.

My circuit diagram posted on the chargery thread shows this.

That way, ANY BMS event would disable the contactor and then its current draw. Think of this circuit as a boolean operator "OR".
I think in the latest Chargery manual, this is called "common port" configuration.

Doug

Have you tried wiring the leads in series?

I have considered thus but am afraid it could create some sort of a short. I want to try but don't want to toast another unit.

 

[DW SD]

Craig,
I'm wiring them in series via relays!! I found the photo I posted elsewhere.

Don't wire them directly in series. Sorry for the confusion.

So red and black from charge controller relay circuit to 85 / 86 on relay (Bosch cube, at least has these pins). That relay then either interrupts ground or positive of the control side of the load controller relay circuit. (pick one!)

Doug

 

[Craig]

Craig,
I'm wiring them in series via relays!! I found the photo I posted elsewhere.

Don't wire them directly in series. Sorry for the confusion.

So red and black from charge controller relay circuit to 85 / 86 on relay (Bosch cube, at least has these pins). That relay then either interrupts ground or positive of the control side of the load controller relay circuit. (pick one!)

Doug

Ok that makes more sense.

 

[Cal]

Craig,
I'm wiring them in series via relays!! I found the photo I posted elsewhere.

Don't wire them directly in series. Sorry for the confusion.

So red and black from charge controller relay circuit to 85 / 86 on relay (Bosch cube, at least has these pins). That relay then either interrupts ground or positive of the control side of the load controller relay circuit. (pick one!)

Doug

The Bosch relay will still consume power during a low voltage shutdown. And... you have no capability to automatically recharge the battery.

 

[DW SD]

The Bosch relay will still consume power during a low voltage shutdown. And... you have no capability to automatically recharge the battery.

Craig,
True.
Note, I'm actually using (and would advocate for) an SSR for the charge relay. It does draw, but <10mA. So, it would take longer for the scenario Craig (OP) exposed. The Bosch relays draw about 150mA. If Craig was using the Chargery OE relay, probably more like >1000mA (IE >1 amp).

Doug

 

[grizzzman]

Does anyone know if the chargery relay delay board come with the connections?

 

[Craigmck]

i have decided to change from a Chargery bms8t 300a to Electrodacus sbms0 bms. I will be putting the chargery bms's up for sale. I have 2 chargery bms8t 300a bms going to put up for sale for what they cost me. one is brand new and the other has maybe 30 days of operating. The used Bms will be sold with the 2 relays and relay chip board. The Sbms0 bms is what i was looking for. Discovered it from a fellow on you tube who i follow called everlanders. They are overlanders who travel north america. He and his wife completely built a truck to travel with all his electrical appliances automated from his phone. Super smart guy.