I need help.

[Stephen Shreds]

I built a large battery in parallel series (4x double 100ah cells) so 400ah battery this past february to put in my van I have 900w of solar on top. my battery has been sitting around 12.8 volts when i check my mt-50. I ran my espar b5e heater last night to make sure things are running properly before winter hits. the heater worked great. bring my van from 45~ ish to 80F. I woke up and turned on my hot water kettle and half way through my water heating process my system starts beeping at me notifying the voltage is low on my battery. I looked at the voltage and it read 11.6v's. I looked up my w/h on my espar unit and its around 32-50w/h with a big 400ah battery 400ahx12=4800 of w/h to play with. 50x8hours is 400 watts. my water kettle is 120v 1000w's. would this really brig my battery that low? ( i know having a electric water kettle is a luxury item in a van and i could use a jetboil if need be but i like the convenience)

real question. am i overestimating my my battery should be able to handle or is there something i am not seeing here? if i have to run my heater 24 hours a day for -30f days am i screwed for winters here in alaska? its been pretty cloudy the past couple of days but i didn't think it would effect my panels that much.

 

[shavermcspud]

12.8 volts is on the low side if that's classed as fully charged.

 

[snoobler]

12.8V = 3.2V/cell... that's pretty low. You should be about 13.6 if fully charged.

Cloudy can have a massive effect on panels. When overcast but with a lot of ambient light, you're lucky to get 1/3 of your rated power.

1. Did the voltage bounce up when you turned off the kettle?
2. Do you have hefty cables between your battery bank and your inverter?
3. Are all of the connections tight?
4. Can you charge via alternator?
5. Do you have a battery monitor that counts current to establish a % SoC?

 

[Sojourner1]

You say sitting around and 12.8v on batteries. Is the solar connected and charging (floating) during this period? What are your settings for the solar?
As mentioned 12.8v at rest if it was disconnected is not full.

 

[Luthj]

From the LFP voltage thread. This is roughly the correlation between resting voltage and SOC. 12.8V is pretty low SOC.

 

[Stephen Shreds]

You say sitting around and 12.8v on batteries. Is the solar connected and charging (floating) during this period? What are your settings for the solar?
As mentioned 12.8v at rest if it was disconnected is not full.

Yeah it's floating around 12.8.
Ov disc: 14.3
Charge limit:14.2
Ov rec:14.2
Equal charge: 14.2
Float charge: 13.6
Boost charge: 14.2
Boost recconect: 13.3
Low volt reconnect: 12.6
Undervolt reconnect: 12.2
Undervolt warning: 12.1
Low volt disconnect 12.0
Discharge limit 12.0
Equalize time: 0
Boost time: 30 minutes

 

[snoobler]

You're not charging your battery.

 

[Stephen Shreds]

So I did another test last night to see if it was my water kettle. The panels got the battery back to 12.8v. I got up again to a super dead battery. Which was weird because every the heater and fan were still running but with a low volt warning in the espar heater. The battery was 10.6v I turned off everything and am going to let this charge for a couple of days as it's pretty overcast. Solar is the only way I can charge the battery. I thought about a separate battery just for the heater and use the renogy dual charger on a whole separate system. Needless to say I won't be using the battery for a minute.

 

[Stephen Shreds]

You're not charging your battery.

Wait what?

 

[snoobler]

You're staring the night with a nearly dead battery at 12.8V. If your battery is only getting to 12.8V, you're not charging it. You should be getting to 14.2 to get close to a full charge.

 

[Stephen Shreds]

You're staring the night with a nearly dead battery at 12.8V. If your battery is only getting to 12.8V, you're not charging it. You should be getting to 14.2 to get close to a full charge.

Could it just be it's overcast? Or are my charge settings messed up?

 

[snoobler]

I can't answer that, other than your charge settings look okay. I can tell you that when it's completely overcast, but still "bright" out (not dark gray clouds) here in AZ, I get about 900-1000W on my 3kW array. If it's a dark gray day, I get very little. I would assume you're getting substantially less than even the 1/3 due to your extreme latitude.

Only you can answer that based on what output you see from your solar controller. I assume it reports some or all of: battery voltage, current, wattage.

Not many choices in link #5 in my signature for Alaska, so I picked Fairbanks since it was the farthest north option (Juneau and Anchorage aren't much better):



Right now, you're only getting between 2.48 and 1.15 hours of full sun charging on your panels on the flat roof assuming a cloudless sky and the panels are in full sun all day with no shading.

This means that of the 4800Wh of battery capacity, you can only charge AT MOST 2.48h * 900W = 2.2kWh - not even half way full.

In December and January, you'll get essentially no sun at all.

I don't see how you'll make it through the winter without an alternate means of charging.

 

[Stephen Shreds]

I don't see how you'll make it through the winter without an alternate means of charging.

So what you're saying is I am f*cked.
Ok. I am glad we are finding this out now.
What can I do to change this? The inverter chargers that I looked at were pretty expensive. Is there a recommendation for a alternator charger for lithium?

 

[John Frum]

So what you're saying is I am f*cked.
Ok. I am glad we are finding this out now.
What can I do to change this? The inverter chargers that I looked at were pretty expensive. Is there a recommendation for a alternator charger for lithium?

Get a shunt based battery monitor.
Knowledge is power.

 

[Stephen Shreds]

Get a shunt based battery monitor.
Knowledge is power.

Yeah I was looking at one the other day. Guess I'ma pull the trigger on that.

 

[snoobler]

Will lists an alternator charger here:

https://www.mobile-solarpower.com/simplified-400-watt-fewer-wires-and-alternator-charging.html (also a solar charge controller)

Victron Orion units do the same:

https://www.victronenergy.com/dc-dc-converters (only an alternator charger)

You could also buy a small generator:

https://www.harborfreight.com/900-watt-max-starting-2-cycle-gas-powered-generator-epacarb-63025.html (700W max continuous)

and a AC-12VDC charger:

PM3 12V Series - PowerMax Converters in 12, 24 & 48 Volts

AC to DC Power Converters can be used for RV Converters, Car Audio Power Supplies and Battery Charging for 12, 24 & 48V - Lithium Compatible

powermaxconverters.com

The generator could run the 45A version.

 

[John Frum]

Yeah I was looking at one the other day. Guess I'ma pull the trigger on that.

Power + watts
Watts = volts * amps
And if we have all three, we can compute resistance in ohms.


?

 

[snoobler]

Also, the addition of the PM3-12V charger would give you an option for plugging into an external outlet and charging up kinda like "shore power."

 

[Stephen Shreds]

Will lists an alternator charger here:

https://www.mobile-solarpower.com/simplified-400-watt-fewer-wires-and-alternator-charging.html (also a solar charge controller)

Victron Orion units do the same:

How far can I run a cable between the batteries on the renogy charger? My house battery is on the back right and my car battery is on the front right. About 12 feet away.

 

[snoobler]

Depends on the wiring. 2awg welding cable could do you fine. 1.56% voltage drop for a 20' run. I'd install the Renogy close to the LFP battery so the losses will be on the alternator side, not the battery side.