ANT BMS shuts down

[Callinger]

I hope someone can help with this quickly since I am on the mountain at the transmitter site with a BMS issue. When the batteries were depleted overnight the BMS shut down the power as expected but then the BMS unit itself shut off after a few minutes. Thus, when the sun came back to the panels, the LV6548 did not re-establish connection to the batteries because the BMS was down and did not let the amps flow back into the batteries. HELP!

 

[sunshine_eggo]

This is normal behavior. You should likely raise the inverter cut-off voltage to a higher level to insure the BMS does not trigger.

You likely need to "jump" start the 48V with a charger or other source to get the voltage up.

 

[sunshine_eggo]

Do you have a pre-charge circuit?

If you have access to the individual cells and a 12V source, you could put the source on the 4S groups.

IIRC, the LV should PV charge even with the inverter off, so starting efforts with the inverter off may help.

 

[Callinger]

Sorry, I dont know if I have a pre-charge circuit, do you mean for the BMS or the LV6548? The PV would charge but it does not "see" the batteries because the BMS has them cut off.
Can I permanently attach a AA battery to the BMS so it never shuts itself down?

 

[sunshine_eggo]

Sorry, I dont know if I have a pre-charge circuit, do you mean for the BMS or the LV6548? The PV would charge but it does not "see" the batteries because the BMS has them cut off.

When batteries are first connected to an inverter, there is a MASSIVE but brief surge in current as the capacitors charge. A pre-charge circuit involves a resistor in series to limit the current flow. Failure to do this may cause the BMS to enter short circuit protection. A BMS disconnecting the battery from the inverter often results in the surge and repeated shut down.

Concept:

A #2 pencil sharpened at both ends makes a great resistor.

Can I permanently attach a AA battery to the BMS so it never shuts itself down?

No. The BMS draws its power from the cell sense wires. A AA battery would prevent it from properly sensing the cell voltage if it didn't have otherwise catastrophic effects.

Do you have a generator?

While not recommended for normal operation, can you bypass the bms by connected on the battery side of the BMS just long enough to get a little current into the battery?

 

[Callinger]

thank you so much for your advice. Without the help of this forum I don't think we could have gotten this far. When "those who know" sacrifice their time, energy and experience for "those who don't" it gives me hope for humanity!

Our project is powering a small radio station on a mountain, 2 1/2 hours from home and inaccessible for several months except by snowmobile and sometimes not even then. It needs to be able to "re-start" itself after a 3 day snow event or similar situation. Yes, we have a propane generator but the tanks wont carry us through several days of no sun or of snow cover. eventually we hope to have a bigger tank and a wind turbine to carry us through but for now we just need it to be able to handle an occasional outage.

The system does fine as long as the BMS does not shut itself down after low power cut-off. Why would it do this? Is there a better BMS out there or is it a settings issue?

 

[sunshine_eggo]

Desired operation:

Inverter hits cut off voltage and shuts down.
BMS stays active providing battery voltage and discharge ability to inverter while inverter is in standby waiting for sun.
PV charging begins in the morning.
Inverter turns on and resumes normal function.

Undesired operation:

BMS cuts off discharge.
Batteries effectively disconnected from inverter. It can receive no power whatsoever to engage PV in the morning.
Manual intervention required.

The BMS should only be seen in a catastrophic situation. All equipment should operate INSIDE the cut-off parameters of the BMS, so the BMS is never triggered. You need to adjust the LV6548 cut off so that it shuts down well before the BMS triggers low voltage protection.

What is the power requirement of the radio station? The LV6548 is a very hungry inverter that consumes a lot of power even without loads. It alone is probably consuming about 100W 24/7 or 2.4kWh/day of energy.

Do your batteries have heating? If not, how can you be sure the batteries will get above freezing to allow charging?

 

[TomC4306]

As Sunshine said above, "This is normal behavior. You should likely raise the inverter cut-off voltage to a higher level to insure the BMS does not trigger."

The settings of the inverter should determine when to stop using the battery.
NOT the BMS

 

[TomC4306]

Dup post

 

[acdoctor]

Inverter could have shut down approximately and a low cell disconnected BMS around the same time.
But still raising the inverter cut off should help.
The more you absolutely have to rely on something. The more unreliable they seem to become.

 

[Callinger]

Thank you for this advice. This is very helpful. I will try to apply this as soon as I can.

 

[Ellcon123]

The OP is saying the BMS shut down completely, not just disconnected from the load. Check the logs and any low voltage settings.

 

[Callinger]

Ellcon123 - please explain - what is "OP"?

 

[Ellcon123]

Original Poster, ie you.

 

[Callinger]

to answer sunshine_eggo: at full power (1000 watts output from the transmitter plus a few other pieces of equipment) it draws about 1700 watts, 24/7. Our 30 kWH bank of batteries can't get through the night at 1000 watts transmit power so we have been lowering power to 200 watts at night. We are currently shopping for more batteries.
We have a warm water (antifreeze) system to keep the batteries warm if the transmitter room gets close to freezing and a generator backup that can run about a day on the propane tank we have currently.

 

[Ellcon123]

Check the low voltage settings. I'll have to check mine but think there is a setting at which the BMS will shut down.

 

[Ellcon123]

The ANT BMS logs errors so this should point you towards the issue.

 

[sunshine_eggo]

to answer sunshine_eggo: at full power (1000 watts output from the transmitter plus a few other pieces of equipment) it draws about 1700 watts, 24/7. Our 30 kWH bank of batteries can't get through the night at 1000 watts transmit power so we have been lowering power to 200 watts at night. We are currently shopping for more batteries.
We have a warm water (antifreeze) system to keep the batteries warm if the transmitter room gets close to freezing and a generator backup that can run about a day on the propane tank we have currently.

Wow. That's a beastly load. Add the 100W idle load of the inverter, and that makes it worse.

1800W * 24h = 43.2kWh usable capacity.

I hope you get fantastic insolation and have the PV absolutely maxed out on that unit. It's essentially impossible to hit the claimed 4000W MPPT output due to the 250V/18A input limits. Getting 3500W/MPPT is tough. My system is in the AZ high desert, and we get fantastic insolation. 7kW of solar won't reliably generate 43.2kWh for me. On average it will, but a lot of my days aren't average.

Does the warm water system use power?

Good call on dialing back the transmit power. I don't think there's any way to get through the night with 1800W 24/7 in the existing configuration. I would be looking hard at expanding the solar to 10-12kW total with an additional MPPT.

Have you simulated your system at https://pvwatts.nrel.gov/ ?

100# propane bottle?

 

[Callinger]

Yes, the warm water system uses power and that is a concern if we become snow-covered for several days or something like that. We are still working on making the system bullet-proof but it is getting more and more complex.

We have 12 kW of solar panels and 32 kWH of battery capacity with 2 LV6548 controllers set to split-phase to give us 240 volts to the transmitter.

There is about 18 hours when the sun is not hitting the panels so we need 30 kWH from the batteries to carry us through the dark. We should be able to do that (at least on a best-case scenario) Our batteries are not even coming close to that so I am wondering if it is a matter of getting the settings wrong in the charge cycle or if the batteries are just old. (we got them used from military surplus).