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Battery needs to be jumped if drained

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Wael

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Nov 21, 2021
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Hi all, I'm not sure if that's normal or not but when the batteries in my tiny house drain overnight (which is rare) I have to use a car battery charger to jump my solar batteries for them to start getting charged by my solar panels. Is that normal? In my van, if they get drained, they automatically start recharging themselves once it's sunny. Could I have done something wrong with the wiring or need some sort of sensor or something?

My setup in the tiny house is: 1200W solar panels, (2x) 60A MPPT charge controllers by renogy, (2x) CHINS LiFePO4 12V 300Ah with 200A BMS.
 
Wael said:
Hi all, I'm not sure if that's normal or not but when the batteries in my tiny house drain overnight (which is rare) I have to use a car battery charger to jump my solar batteries for them to start getting charged by my solar panels. Is that normal? In my van, if they get drained, they automatically start recharging themselves once it's sunny. Could I have done something wrong with the wiring or need some sort of sensor or something?

My setup in the tiny house is: 1200W solar panels, (2x) 60A MPPT charge controllers by renogy, (2x) CHINS LiFePO4 12V 300Ah with 200A BMS.
Click to expand...

When you run LFP batteries to empty, the BMS cuts them off and shows 0V or some other arbitrary very low voltage. Chargers require power and need to see some voltage to begin charging.

I suspect the van drain may be less severe than the house, or the batteries in the van are lead-acid.
 
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@sunshine_eggo ahh I see. Thank you. I have a 170ah Lithium battery in the van. But yeah, the house definitely uses more power day and night.
 
@Supervstech Thank you I'll have to look into it! Inverter? You mean the charge controller? I have a 2 Renogy Rover Series 60A. I hope I can set it to not drain the batteries that'd be amazing
 
@sunshine_eggo Ohh my bad yeah I wasn't thinking about "that" inverter ?‍♂️ Yes, I do have one. It's a Giandel 4000W/8000W, draws about 3amps with no load. With my fridge running through the night and the inverter it draws about 12.
 
Unfortunately, I don't think those are programmable. If a 12A overnight draw is all you're powering, your batteries must start the night at a very low state of charge. If you really have no additional loads, then your 600Ah of batteries should be able to power the fridge for 50 hours.
 
That inverter uses
Wael said:
@sunshine_eggo Ohh my bad yeah I wasn't thinking about "that" inverter ?‍♂️ Yes, I do have one. It's a Giandel 4000W/8000W, draws about 3amps with no load. With my fridge running through the night and the inverter it draws about 12.
Click to expand...
I bet the inverter pulls more than 3 amps standby, a fridge shouldn't pull that bank down overnight.
My fridge lasts all day and night on a 160Ah12V...
3A@24V is around 72W in 24 hours that would be 1728Wh... by itself. If ALL you are powering is the fridge overnight, I'd get a smaller more efficient inverter for that load.
 
Wael said:
@sunshine_eggo Ohh my bad yeah I wasn't thinking about "that" inverter ?‍♂️ Yes, I do have one. It's a Giandel 4000W/8000W, draws about 3amps with no load. With my fridge running through the night and the inverter it draws about 12.
Click to expand...
My fridge running pulls about 4A @120V that's a lot more at 12V likely around 50A if your fridge is like mine. I'm guessing you are on 24V of course.
 
@Supervstech I'm running a 12V system. Would it be more efficient if it was 24V? I'm not sure that I can switch it to 24V at this point without having to replace the charge controllers. Having a dedicated inverter for the fridge alone would need some serious remodeling to run the wire from inverter to fridge without tripping over wires :/ I have a 120V Insignia mini fridge/freezer 4.9 cu. ft. It says the "rated current is 1.5A". But when everything is turned off at night but the inverter and fridge I get a reading between 9-12 on my monitor. I needed that big of an inverter to power my water heater and mini split during the day (it's a Mr.Cool 12k BTU) but I usually turn it off a couple hours before sunset to top off the batteries. I thought it was odd that 600ah bank would discharge overnight for just a the both on. Could it be losing power because of my wires? I thought I got them thick enough to handle it?
I have 1/0 gauge wires going from batteries to inverter with a 300A ANL fuse.
4 AWG from battery to charge controllers with 60A ANL fuse
 
sunshine_eggo said:
Is this a fridge that can also run on propane?
Click to expand...
No :/ the fridge is 120V only. Yeah I don't think the inverter is programable, it just has an on/off button. I emailed Giandel we'll see. When I wake up to a dead battery, it's usually at 85% or below and hovering between 11.9V to 12.3V around sunset. But even with that I didn't think the fridge and inverter would drain the batteries so fast
 
The BMS on my lithium battery needs a jumpstart if it is drained. I don’t know if you can adjust the chins, but on mine you can lower the minimum voltages to allow charging to start.

i have not seen an inverter that has an adjustable low voltage cutout, I’m surer they exist.

600 ah at 12 volts is about the same as 50 amp hours at 120 volts taking into account inverter losses. You probably get about 80% of that before your BMS trip. I recommend plugging the fidge in with a kilawatt meter to see how much power in watt hours your fridge is actually using.

To figure out the voltage loss on the wire, you’d need an amperage requirement, wire size, and wire length run. In what I build, 1/0 AWG is too skinny for a 300 amp fuse. I use 4/0. It really is how many amps going through the wire.
 
Wael said:
No :/ the fridge is 120V only. Yeah I don't think the inverter is programable, it just has an on/off button. I emailed Giandel we'll see. When I wake up to a dead battery, it's usually at 85% or below and hovering between 11.9V to 12.3V around sunset. But even with that I didn't think the fridge and inverter would drain the batteries so fast
Click to expand...

Good. Some folks buy those for the redundancy, and what they don't realize is how horribly inefficient they are in terms of AC consumption.

Where are you getting the 85% number? If it's from the charge controller, it's complete junk and unreliable. Ignore it. Get a legitimate battery monitor.

11.9-12.3V around sunset means your battery is nearly depleted. That is an extremely low state of charge, and it's very likely that you're repeatedly using more than your solar can provide.
 
chrisski said:
The BMS on my lithium battery needs a jumpstart if it is drained. I don’t know if you can adjust the chins, but on mine you can lower the minimum voltages to allow charging to start.

i have not seen an inverter that has an adjustable low voltage cutout, I’m surer they exist.

600 ah at 12 volts is about the same as 50 amp hours at 120 volts taking into account inverter losses. You probably get about 80% of that before your BMS trip. I recommend plugging the fidge in with a kilawatt meter to see how much power in watt hours your fridge is actually using.

To figure out the voltage loss on the wire, you’d need an amperage requirement, wire size, and wire length run. In what I build, 1/0 AWG is too skinny for a 300 amp fuse. I use 4/0. It really is how many amps going through the wire.
Click to expand...
Gotcha thanks for tips! Hmm sounds like I have some research / math to do. I honestly thought I was going overboard with my wires but it doesn't seem like it. The wire going from battery to inverter does get somewhat hot when running the AC and water heater at the same time. The wire run is just about 18".
 
sunshine_eggo said:
Good. Some folks buy those for the redundancy, and what they don't realize is how horribly inefficient they are in terms of AC consumption.

Where are you getting the 85% number? If it's from the charge controller, it's complete junk and unreliable. Ignore it. Get a legitimate battery monitor.

11.9-12.3V around sunset means your battery is nearly depleted. That is an extremely low state of charge, and it's very likely that you're repeatedly using more than your solar can provide.
Click to expand...
Yes I'm getting my battery readings from the charge controllers. Good to know! I thought I could rely on "renogy's" charge controllers for that. I'll invest in some actual battery monitors. I don't think I'm using more than what my solar panels are providing. At peak sun hours I get anywhere between 750-900W from them and the batteries are usually at "100%" even when my AC is on. My AC pulls about 90W. I live in the High Desert of CA, the sky is almost always clear with scorching sun.
Happened again! Around sunset yesterday I had about 13V at "90%" and woke up to dead batteries :/
 
Wael said:
I live in the High Desert of CA, the sky is almost always clear with scorching sun.
Happened again! Around sunset yesterday I had about 13V at "90%" and woke up to dead batteries :/
Click to expand...
Do you Run the AC at night?

IME, my 2500 watts of panels with a 1700 watt to 2000 watt load will provide enough energy to keep up with AC while the sun is shining between about 9 am to 4 pm, after that most of the energy comes from the batteries. Very little charging.

After that, the battery has to take up the slack, which would give me 7 hours until it’s dead. Would be dead before morning and it has 10 kWh useable.
 
chrisski said:
Do you Run the AC at night?

IME, my 2500 watts of panels with a 1700 watt to 2000 watt load will provide enough energy to keep up with AC while the sun is shining between about 9 am to 4 pm, after that most of the energy comes from the batteries. Very little charging.

After that, the battery has to take up the slack, which would give me 7 hours until it’s dead. Would be dead before morning and it has 10 kWh useable.
Click to expand...
No, I turn off the AC at least a couple hours before sunset to be able to top off the batteries. I just have the fridge and inverter on at night and a couple 12v lights. I'd probably get ~3 hours past sunset if I left the AC on.
 
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