Battery voltage drop due to cold weather

[Ninjakitty]

So this morning I went to fire up the coffee maker and the alarm tripped on my inverter and turned itself off. After some poking around and reading manuals, I discovered it did this because of the low voltage cut off. Apparently the batteries were reading 10.5 volts this morning when I got up.

After some tooling around and the sun broke the horizon, the solar kicked in and so did the charger when I plugged in, batteries were back up to 13.7 ish while charging.

The only reason for the voltage drop that I can figure is that it got too cold in the electric room (which is located by the backdoor and not fully insulated).

With that said, I was thinking of adding some battery insulation to the batteries and this 150 watt heater for cold nights

Fdit PTC Car Air Heater 150W 12V Energy Saving Small Space Car Fan Heater Constant Temperature Heating Element Heaters(12V 150W)
https://www.amazon.com/dp/B07JKNKBXH..._XWrLCb3P7ST0Z

Any thoughts about this?

[Booyah45828]

You're in Florida I assume? What kind of temp did you see?

I assume you're using lead acid batteries? I don't think voltage drops due to the cold, but the capacity definitely drops. I'm talking below freezing cold. If you are using lead acid batteries, check the specific gravity of the acid in the cells and go from there.

If you're batteries were fully charged and it got cold out, you might notice a slight difference in capacity. However, if the battery is half dead and it gets cold, your lack of power will definitely be noticeable. Then again, it has to be at or below freezing. There isn't much difference to a battery whether it's 70 or 50 out.

If you're using Lithium batteries you can throw out all that I just said, those act entirely different.

[Ninjakitty]

Sorry, should.uave added they are AGM. It was in the 40's last night. It's been cold the last few nights and haven't had any problems. Everything is acting normal now...

[Jolly Roger bus 223]

That heater at 150w without a thermostat control would also be a significant battery drain in a low solar period.
In my mind anyway.
Do they make low watt/amp battery mats like the oil pan heaters?
Just a thought that's been in my head for my just setting batteries?

[Ninjakitty]

Maybe this thermostat with it? I'll look into battery mats

Inkbird Dual Stage 12V(DC) Digital Temperature Controller Fahrenheit Thermostat https://www.amazon.com/dp/B019I3YCFS..._EHsLCbKZPQ47B

[john61ct]

The voltage at rest is one thing.

Voltage while charging has little relevance.

10.5V at rest is very low SoC, in fact the definition of ZERO %, and very harmful to longevity to let an expensive bank get that low.

And the difference in the above due to a 40° ambient is vanishingly small.

Your setup needs an overhaul, and in the meantime cut back drastically on your consumption.

Try to stop discharging at 12.2V, an LVD would automate that, but a good BM SoC meter would be more accurate.

And get the bank recharging as soon as possible after hitting that low point.

[Ninjakitty]

Well, this all is the reason I was confused about everything. The bank was nearly full at 12:00 pm. I have a victron battery monitor, 1400 watts of solar on the roof and I've been plugging in every other day. I've been running this system for about 6 months and have never had this issue. There wasn't enough items running to pull that much out. All that was running overnight when I went to sleep was two 12 volt fans, the inverter, and the fridge.

My batteries are about a year old. They have only hit 50% discharge about 5 times. I've never let them get lower than that and the lowest is usually about 70% discharge. It supposed to be cold again tonight. I'm going to make sure the batteries are full before I go to bed and I'll check the voltage on the.monitor and the inverter before I turn anything on.

Thank you all for the info. I'll update in the morning.

[Ninjakitty]

Also forgot to mention, the GFCI on the side of the inverter had popped and when I plugged in, it popped the GFCI in the house. I can't find any traces of water anywhere either

[Ninjakitty]

Shot of the electric room

[Ninjakitty]

Dropping these pics at 4:09 pm for future reference. This is with a pot of coffee brewi g, which is what set this off this morning.

[Ninjakitty]

System info:

four 200 ah: 10hr rate (210 ah at 20 hr) for 840 ah/420 usable ah renogy AGM batteries wired in parallel

1400 watts solar (4x350 watts)

Midnite Classic 200 MPPT scc

3000 watt Aims pure sine Aims inverter/charger

Victron battery monitor (never sounded an alarm)

[Ninjakitty]

After coffee (for reference)

[john61ct]

Originally Posted by Ninjakitty

Victron battery monitor (never sounded an alarm)

Which model?

What sort of alarm did you program it for?

[Ninjakitty]

Bmv 702. I am busting out the manual and will reset the alarm

[john61ct]

Brewing coffee using electricity is a pretty big load IMO.

Originally Posted by Ninjakitty

1400 watts of solar on the roof and I've been plugging in every other day.

Why not just keep it plugged in?

What are the charge profile settings on the SC?

Can you link to the batt charging specs for that model?

Does the SC have a shunt / remote that measures trailing endAmps at the bank?

> All that was running overnight when I went to sleep was two 12 volt fans, the inverter, and the fridge.

The stuff running off the inverter is more relevant than the inverter's parasitic load. That you should IMO be turning on/off as needed.

> My batteries are about a year old. They have only hit 50% discharge about 5 times. I've never let them get lower than that and the lowest is usually about 70% discharge.

How do you know?

And never is not accurate. . .

How often do you reset the BMV to tell it the bank is at 100% Full?

> I'll check the voltage on the monitor and the inverter before I turn anything on.

Verify at the bank with your ammeter or DMM.

[Ninjakitty]

Brewing coffee using electricity is a pretty big load IMO.

Why not just keep it plugged in?

Yes, I should do that. The coffee is 1000 watts, yes a big load, but I have done it often enough I didn't think it was a big deal.

What are the charge profile settings on the SC?

I will have to look that up. It's been a minute since I have messed/looked it up.

Can you link to the batt charging specs for that model?

https://www.renogy.com/template/file...-AGM12-200.pdf


https://www.google.com/url?sa=t&sour...BeHpY4vTK8911m

Or

http://www.midnitesolar.com/pages/pa...?article_ID=14

Does the SC have a shunt / remote that measures trailing endAmps at the bank?

I don't believe so.

> All that was running overnight when I went to sleep was two 12 volt fans, the inverter, and the fridge.

The stuff running off the inverter is more relevant than the inverter's parasitic load. That you should IMO be turning on/off as needed.

Good point as well. I will start turning the inverter off overnight.

> My batteries are about a year old. They have only hit 50% discharge about 5 times. I've never let them get lower than that and the lowest is usually about 70% discharge.

How do you know?

And never is not accurate. . .

Good point. I'm new to all this. I can only go by the voltage and percentages my monitors are telling me. I'm not sure how to check an AGM another way.

How often do you reset the BMV to tell it the bank is at 100% Full?

Um.. I haven't. I will try to figure that now.

> I'll check the voltage on the monitor and the inverter before I turn anything on.

Verify at the bank with your ammeter or DMM.

Not sure what a dmm is, but I will look that up as well.

Thank you

[Ninjakitty]

Well, I think I got some reading to do

[Ninjakitty]

Ok. I'm plugged back in. In the morning, after it's charged all night, I am going to reset the bmv and the SC and reprogram them again according to battery specs

[david.dgeorge07]

Following. I have a very similar setup to yours. I agree, a coffee maker is no sweat for that inverter and bank. I’ve run two mini splits off of mine!

10.5v sounds like dead batteries. Maybe you just overlooked something that was using power...

It might be useful to disconnect and do a slow controlled discharge and slow trickle charge for each battery individually. I know your charging system is supposed to be a good one, but I have found taking the batts out of the bank for a couple of controlled drain/trickle cycles can improve the performance quite a bit.

Double check the accuracy of your voltage readout with a known good meter as well. My similar aims charger/inverter is a few tenths off of what my stand alone meter tells me.

[john61ct]

Battery Absorb V spec is 14.4-15V

A very wide range, likely higher would be better than lower.

They do not give an endAmps spec, so for a 200Ah batt, charging alone I'd use stop charging when current tapers to 1A.

That is the point until which the charge source should be holding Absorb V, before which should not be dropping to Float. Even with a high amps charger, rarely will that be less than 6-7 hours from start of the charge cycle.

It is very common for a mostly-solar setup to hardly ever get there, aka chronic PSOC abuse, drastically shortens bank longevity.

Of course, proportionally increase that 1A stopcharge setpoint, when bulk charging the whole bank at once. So 840Ah would be say 5A.

If the batts are so worn they take say over 10 hours at Absorb V to get there, you could use 10-15A instead, but then

you aren't **really** getting to 100% Full, which is needed at least a few times a week for good longevity, especially for AGM.

As a last resort, you could use Deka's endAmps spec:
Absorption End Point = "Current change over 1 hour period of less than 0.1A"

Note finally that I doubt Renogy (maybe Full River is the OEM?) makes a great quality true deep cycling AGM, at least not as good as Lifeline or Enersys / Odyssey, and

no AGM is as robust and long-lasting as quality FLA.