Keeping Batteries Charged

Not uncommon for 5% antimony batteries to discharge <1% month at -20c

Hi,

On Dec 21 I receive 17 amp-hours of charging in a day from 256 watts of solar. That is way beyond the self discharge rate of any healthy battery bank.

Solar harvest with six inches of snow at solar noon for most of the winter is approximately 2 to 3 amps. Again--enough to keep the battery bank topped up in storage.

YMMV.

Harvey51 wrote:

No problem with freezing in northern Alberta, either.
But solar panels don't work well in winter here due tomorrow snow and the sun low in the sky. I just check the voltage once a month and put a charger on when it's a bit low.

Lynnmor wrote:
Yes, get a battery switch to stop any draws during storage, use it whenever you are disconnected from power.

A fully charged battery will not freeze. most should be charged about once a month to be safe.

You have a good plan with the solar charger, Battery Tender has well controlled solar chargers, but they are a bit pricey. Just Google "Battery Tender Solar", and choose the one that fits your needs.

X2
No problem with freezing in northern Alberta, either.
But solar panels don't work well in winter here due tomorrow snow and the sun low in the sky. I just check the voltage once a month and put a charger on when it's a bit low.

This project is growing and gaining momentum. First we are charging a battery in storage and suddenly we have four batteries, monitor, and need capacity to charge in use.

Now it is just roof space to consider. Are you going large 24v panels and MPPT or smaller 12v in parallel into PWM controller?

I assume you are looking at 200 to 500 watts of solar. Could go 2x 250w 24v panels for $325 and 30 amp tristar MPPT controller $330.

Or maybe 3x 160w 12v panels $345 into a 45 amp PWM controller $165

https://www.solarblvd.com/
The PWM seems more cost effective and can still expand a bit if needed.

smkettner wrote:
Are you adding solar just for storage or while in use?

For while in use.

westend wrote:
How far are you with the solar installation? Depending on what you have installed, you may have the charging solution right there. If it's not underway, you'll need at least 40W->60W of solar to keep the batteries charged. It might even be better to use a 100W panel and a controller, saving the 100W panel for portable/fixed deployment in the future. The smaller solar panels sell at a premium for what they put out.

So far I only have 2 of the 4 batteres that are installed, the battery monitor and shunt that are not yet installed.

allen8106 wrote:
I had considered that but charging will keep the batteries warm and much less likely to freeze. I know from experience what happens when a battery freezes, they die.

Batteries with a reasonable charge (90 percent) won't freeze down to about -40 F so you really don't have to worry about that.
Being cold actually slows the self discharge process.

Do you have an on-board generator ?
If so, can you run it for a half hour or so once a month ?

You don't need a special switch to disconnect the batteries; removing one of the cables works fine. A LOT of RVs come with a switch though.

Fully charged and totally disconnected, healthy batteries should be OK for 3 months or so in a cold environment......but would be better if kept fully charged.

Yes, if you are parked in a sunny location solar is a good option. There are several solar "experts" on here. I'm sure they can supply some recommendations.

We don't rely on any mechanical means for keeping our batteries fully charged while in our 6-month dry storage cycle. I disconnect the fully charged batteries (switch) and check them once a month. Most winters I don't need to charge them up at all. And yes, it does freeze in CA.

Lynnmor wrote:
Yes, get a battery switch to stop any draws during storage, use it whenever you are disconnected from power.

A fully charged battery will not freeze. most should be charged about once a month to be safe.

Good advice.

The OPs battery has a self discharge rate of 3.5%/week at 80F which is excellent. Still my calculations show that it will self discharge to 50% SOC in 19 weeks at 80F, less I assume in lower temperatures. This will shorten battery life.

I would want a temperature compensated charger that maintains the battery per the Crown specification.