diy circuit that measures voltage with relay to turn off power to the generator. Can it be done?

[farroffgrid]

I'm working on an Outback 48v system that currently has lead acid batteries. We're trying to use the Tesla model s batteries which are a lower voltage application. All the settings adjust correctly, i.e. the Low Battery cut out/cut in and Float, for this application with one exception, the Absorb/Bulk voltage on this unit will not let me go bellow 52 volts. We don't want to over charge these batteries and 50.3 is MAX so we need to be at 50v or less on this setting. The settings for the FELX Max 80 charge controllers are accommodating for the 50v settings. The concern is that the generator kicks in and the inverter allows it to charge up to 52v which could destroy these batteries, this is an off grid system so it's not grid tied. Any way to circumvent this issue or will we just have to go with more compatible inverters??? Is there a circuit that I could install that would measure the voltage with relay to turn off power to the generator at 50v or less?

 

[SolarForU2]

Get an adjustable voltage sensitive relay, use its internal switched contact to open a larger contactor that will handle the current\voltage out of the generator. Link Voltage Relay

Cheers
Mike

 

[farroffgrid]

Thanks Mike, the relay in that link looks to only go down to 65v but we need it to go below 50?

 

[SolarForU2]

Adjustment range for 48v version is 20-80V


Cheers
Mike

 

[LB3]

If you want to go the analog route, a voltage switch could be created using a voltage comparator with a 5v reference voltage and a voltage divider on the comparator input.

 

[John Frum]

I'm working on an Outback 48v system that currently has lead acid batteries. We're trying to use the Tesla model s batteries which are a lower voltage application. All the settings adjust correctly, i.e. the Low Battery cut out/cut in and Float, for this application with one exception, the Absorb/Bulk voltage on this unit will not let me go bellow 52 volts. We don't want to over charge these batteries and 50.3 is MAX so we need to be at 50v or less on this setting. The settings for the FELX Max 80 charge controllers are accommodating for the 50v settings. The concern is that the generator kicks in and the inverter allows it to charge up to 52v which could destroy these batteries, this is an off grid system so it's not grid tied. Any way to circumvent this issue or will we just have to go with more compatible inverters??? Is there a circuit that I could install that would measure the voltage with relay to turn off power to the generator at 50v or less?

Is this a 13s pack?
52 volts / 13 cells = 4.0 volts per cell.
I'm not sure of the exact chemistry of Tesla model s but most of the "explody" lithium chemistries have an hard upper bound of 4.2 volts.
4.0 volts is comfortably inside the envelope.
Is your chemistry limited to 3.869230769 volts per cell?

 

[John Frum]

Also if you bulk at 52 volts and terminate the charge when the battery hits 50.3 you won't have any absorption and your BMS will probably struggle to maintain top balance.

 

[welnat]

What inverter do you have? Why not get an inverter that is adjustable to exactly what you want?