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Low Voltage Cutoff For LiFePo4

ChukLee

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Jan 10, 2022
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What I thought would be a simple search for an appliance to cut off my lithium batteries as turned into a rabbit hole. I'm looking at these Victron low voltage cutoff devices and reading that they can't take current going to the batteries. So I thought about replacing my inverter with one of the xantrax models that has a programmable cut off, but I can't find one. My current cheap 3000 watt 24 volt pure sine wave inverter is doing fine except for not having a low voltage cutoff high enough to handle the 24 volt lithium battery. All I need is something to cut off the power at, say, 26 volts, and I really could use a recommendation.

3 sets of 3 300W panels, wired in series-parallel to output 120VDC @ 24A through a Midnite Solar Combiner.

The current passes through 66 meters of 8 Gauge wire to a Midnite Solar Classic 150,

Which goes into two Ampere Time 12v 200ah batteries wired in series to make a 24v 200ah battery.

They output to a 3000w Pure Sine Wave inverter.

Handling the backup charging is a predator 4375 watt generator hooked up to an aims power 24v 37.5A charger.
 
Please provide a link to the product details for your inverter.
Do you have any significant pure dc loads that also need to be disconnected?
My inverter has a remote switching feature that allows me to control it via a victron battery protect without running all that current through the battery protect.
 
I'm looking at these Victron low voltage cutoff devices and reading that they can't take current going to the batteries
LVD -> relay -> big loads?

In this model the only power running through the LVD is the power it requires to run itself. I use

solar charge controller LVD setpoint -> LOAD output -> relay -> opportunity loads
 
3V/cell

Design a system that is unlikely to need it.

Most 12V batteries' BMS will cut off at 10V.

Personally, I wouldn't worry about it.
I wasn't worried about it until I exhausted the batteries, but when the battery was discharged down to the 20 volt level, it took the entire system out. It shut off my inverter, my charger, and my charge controller. When I put the system back on LED batteries, it fired right back up. I'm currently trickle-charging the lithium batteries.
 
I wasn't worried about it until I exhausted the batteries, but when the battery was discharged down to the 20 volt level, it took the entire system out. It shut off my inverter, my charger, and my charge controller. When I put the system back on LED batteries, it fired right back up. I'm currently trickle-charging the lithium batteries.

Yep, it is pretty annoying.

I can't find it, but Will did a video where he used a battery protect to shut off the mechanical switch of a MPP Solar AiO.
 
Could use a voltage based relay to cut the load from the inverter. At least that would put you down to idle.
If this happens a lot I would look at 2x battery capacity. Or if you are not getting fully charged then 2x solar.
 
I tend to spend a little more money to buy programmable equipment so I can keep the system a bit more simple - at least at first glance. My old inverter was not programmable, so I had to keep an eye on it. The new inverter/charger (Victron Multiplus 12/3000) has a user defined low voltage cutoff. I'll set that value to be above where the BMS low voltage disconnect is set.

I'll be implementing one of those Victron Smart Battery Protect devices soon that will cut off power to my RV's main distribution panel (the DC side).
 
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