Low Voltage Disconnect alarm DOD change from 6v to LifeP04 12V

[68camaro]

Hello, I plan to go from 2 - 6V AGM batteries in a 12V system to two LifeP04 heated Lithium batteries in a 2001 camper, since lithium has a much greater allowable DOD (depth of discharge), do I need to reset my existing Low Voltage Disconnect alarm to not kick-in once I go lower than 50% DoD, or do I need to get new Low Voltage Alarm that is preset for lower DOD? I currently have the Shure Model but not sure sure what it is set at, I think 50% (12.1v).

Also, I am looking at Battle Born and they have internal BMS, does this act as Low Voltage Alarm allowing me bypass existing Alarm?


Thanks

 

[68camaro]

I found my current LVD and it is Sure Model 135001, set at 20% DoD (11.8v) but I do not think it is set at 20%. It's seems much higher but I guess I need to check.

 

[CMARJEEP]

You can take LiFePO4 down to 0% no problem and pretty much every LiFePO4 has an internal BMS that will cut it off automatically when it gets to a minimum voltage including the Battle Born batteries. Also voltage isn’t a good way to measure LiFePO4 charge remaining because it has such a flat voltage curve. You might want to get something like a shunt that will be able to measure charge remaining a lot more accurately.

 

[68camaro]

You can take LiFePO4 down to 0% no problem and pretty much every LiFePO4 has an internal BMS that will cut it off automatically when it gets to a minimum voltage including the Battle Born batteries. Also voltage isn’t a good way to measure LiFePO4 charge remaining because it has such a flat voltage curve. You might want to get something like a shunt that will be able to measure charge remaining a lot more accurately.

Thanks, I do have a shunt already with 6 volt batteries, so with LifeP04, I can just bypass LVD?

 

[jonyjoe101]

according to the 135001 manual the LVD is set to 11.8 volts. The lifepo4 BMS will disconnect long before it reaches that voltage. A 4S lifepo4 resting voltage (no load) will be 13.1 volts from about 10 percent to 100 percent. Once the resting voltage drops to around 12.8 volts your at about 10 percent and it won't be long before it shuts down, any large load will usually trigger the BMS to shutdown.
A coulombmeter with a shunt that can count amps in/out of the lifepo4 is the only way to make sure what the SOC of the battery is at all times.

This is the tk15 coulombmeter I been using on my 220ah lifepo4. It only has a 50A shunt but its all I ever needed.

 

[68camaro]

according to the 135001 manual the LVD is set to 11.8 volts. The lifepo4 BMS will disconnect long before it reaches that voltage. A 4S lifepo4 resting voltage (no load) will be 13.1 volts from about 10 percent to 100 percent. Once the resting voltage drops to around 12.8 volts your at about 10 percent and it won't be long before it shuts down, any large load will usually trigger the BMS to shutdown.

I was a bit confused as your reference about the LifeP04 cut off at around 12.8v, but I think I realized the lithium has different voltage levels than 12v. I have been using the following chart, but will I need to replace with a LifeP04 such as one below it?

So based on what you said and chart below, i can just leave my LVD alone since the lithium batteries BMS will shut it down before my LVD does at 11.8v?

Battery Voltage Chart - 12v
% of Full Charge	Voltage
100 % charged	12.7 volts
90 % charged	12.6 volts
80 % charged	12.5 volts
70 % charged	12.3 volts
60 % charged	12.2 volts
50 % charged	12.1 volts
40 % charged	12.0 volts
30 % charged	11.9 volts
20 % charged	11.8 volts
10 % charged	11.7 volts
completely discharged	11.6 volts or less

LifeP04

 

[Alloy]

I was a bit confused as your reference about the LifeP04 cut off at around 12.8v, but I think I realized the lithium has different voltage levels than 12v. I have been using the following chart, but will I need to replace with a LifeP04 such as one below it?

So based on what you said and chart below, i can just leave my LVD alone since the lithium batteries BMS will shut it down before my LVD does at 11.8v?

Battery Voltage Chart - 12v
% of Full Charge	Voltage
100 % charged	12.7 volts
90 % charged	12.6 volts
80 % charged	12.5 volts
70 % charged	12.3 volts
60 % charged	12.2 volts
50 % charged	12.1 volts
40 % charged	12.0 volts
30 % charged	11.9 volts
20 % charged	11.8 volts
10 % charged	11.7 volts
completely discharged	11.6 volts or less

LifeP04

I haven't come across an assembled Lithium that doesn't have a low cut off at 20% (for warranty) SOC.

There are many that don't have a low (I don't mean heating) temp cutoff if that's important.

Lithium operating temp is 0C to 45C . People are finding it best to stay well below 45C for longevity. Tesla batteries are kept between 15C and 27C.

 

[CMARJEEP]

I was a bit confused as your reference about the LifeP04 cut off at around 12.8v, but I think I realized the lithium has different voltage levels than 12v. I have been using the following chart, but will I need to replace with a LifeP04 such as one below it?

So based on what you said and chart below, i can just leave my LVD alone since the lithium batteries BMS will shut it down before my LVD does at 11.8v?

Battery Voltage Chart - 12v
% of Full Charge	Voltage
100 % charged	12.7 volts
90 % charged	12.6 volts
80 % charged	12.5 volts
70 % charged	12.3 volts
60 % charged	12.2 volts
50 % charged	12.1 volts
40 % charged	12.0 volts
30 % charged	11.9 volts
20 % charged	11.8 volts
10 % charged	11.7 volts
completely discharged	11.6 volts or less

LifeP04

Check the specs of the specific battery you are looking at. Battle Born lists the low voltage disconnect of their 12v 100ah LiFePO4 as 10.6 volts. In any case you probably don’t need the LVD between your battery and load unless you want it to cut out before the built in BMS disconnects it.

If you charge your camper battery off your vehicle alternator when driving you could repurpose your LVD so it doesn’t drain your vehicle battery.