storage

penrosefred · November 2010

I have a 135w 7 a panal on my camper, What do I do with it when I am not going to use it for 2 or 3 months? I have a on off switch I us when I am traviling. Di I turn it off or do I leave it on do I leave acouple of lights on . Please help. and thanks.

Fred

stevend · November 2010

Re: storage

You don't have to leave any lights on. The only concern I can think of is if the temperature where the batteries are located will get below freezing. If the battery is not fully charged then the chemical composition includes water and water will turn to ice, expand, and potentially crack the battery case (I've seen it.) A battery that is fully charged will not freeze because the chemical composition is different.

The problem is you can't just charge up the batteries at the beginning of the 2-3 month period and leave them. A battery will lose around 2% of it's charge every day, even if there is nothing turned on.

So if freezing is a possibility, make sure your solar panels are where they will get some sun and your switches are such that they will charge up the batteries. Turn off your inverter if you can so that nothing is using up battery power, including the inverter.

Since the batteries will be charging, there will be some water loss in them. So top up the water in the batteries too. If they're going to be exposed to freezing conditions right away, run some loads or do some charging for a few hours to mix the water and the acid in the batteries.

If your panels won't be in a place where they can get sunlight then arrange some other form of charging. Leave the camper connected to shore power and the inverter turned on so the inverter can keep the batteries topped up.

If there will be no chance of freezing then top up the water level, shut off the inverter, make sure there are no loads, but keep the solar panels able to charge. If they can't then I don't think it matters.
-Steve

BB. · November 2010

Re: storage

Do you have a solar charge controller on the system? And what size battery (bank) do you have (amp*hour rating and voltage).

If the charge controller has a float stage--then just check the battery electrolyte levels once per month. Boiling a battery such that the levels are below the top of the plates will ruin a battery.

Also, leaving a battery with full charging voltage of 14.5 volts or higher can shorten the life of a battery bank.

If you do not have a charge controller--the panel can overcharge the battery bank if there are no loads.

-Bill

penrosefred · November 2010

Re: storage

Thanks very much. Now is it right to turn the solor off when I am traveling, again I have a switch between the panel and controler. Thanks again.

BB. · November 2010

Re: storage

Leaving the solar on when traveling is not a problem...

The questions for me: Do you have a solar charge controller between the panel and the battery bank, and what size battery bank do you have?

There are other details to worry about too (how much power you use per day, type of batteries, is the RV battery tied to the tow vehicle battery, how deeply do you cycle the battery bank, etc.).

If you don't have a proper solar charge controller--it is much easier to overcharge the battery bank and cause damage--especially during storage/low power use.

-Bill

penrosefred · November 2010

Re: storage

I have 2-12 volt deep cycle battries. I have a sunsaver 10 amp cortroler between the panal and the battries, I have been told I shoulden't have the panal on when I am traviling as the truck would be charging to. Does that make sence? Thank you.

BB. · November 2010

Re: storage

There can be an issue between solar and vehicle power systems.

Vehicles charge around 13.8 to 14.2 volts.

A typical solar system may charge around 14.5 to 15.5 volts (charging, equalization).

Charging a 12 volt car or truck above 14.5 volts is that can cause lights and electronics in the vehicle to fail.

I believe your controller is not going above 14.5 volts except in cold weather, so your setup may be less of an issue.

-Bill

icarus · November 2010

Re: storage

you don't have to leave any lights on. The only concern I can think of is if the temperature where the batteries are located will get below freezing. If the battery is not fully charged then the chemical composition includes water and water will turn to ice, expand, and potentially crack the battery case (I've seen it.) A battery that is fully charged will not freeze because the chemical composition is different.

The problem is you can't just charge up the batteries at the beginning of the 2-3 month period and leave them. A battery will lose around 2% of it's charge every day, even if there is nothing turned on.

Sorry, but much of this is not quite correct. Yes, dead batteries will freeze and crack, but even a battery with 50% charge will not freeze until well below 0F. A fully charged FLA battery won't freeze until nearly -60F. A sitting battery will loose charge over time, but not 2-3% per day, more like maybe 10% per month. Unless the battery is nearly junk anyway.

I suggest that everyone read and understand the following links regarding the "care and feeding of batteries".

http://www.batteryfaq.org/
http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

As for the OP's question, buy a simple PWM controller, like a morningstar, wire it up, and the battery will be perfectly happy over the winter. Just make sure the water is topped up before you start. We have remote site battery banks, sitting on 70 watts of PV for up to 9 months at a time, through -40 temps, and the batteries are just happy to see us when we return.

Tony

stevend · November 2010

Re: storage

icarus wrote: »

Sorry, but much of this is not quite correct. Yes, dead batteries will freeze and crack, but even a battery with 50% charge will not freeze until well below 0F. A fully charged FLA battery won't freeze until nearly -60F. A sitting battery will loose charge over time, but not 2-3% per day, more like maybe 10% per month. Unless the battery is nearly junk anyway.

I was speaking from experience. I'm also speaking from Ottawa, Ontario, Canada where we do sometimes get below 0F (-17C). penrosefred didn't say where he's from so it may or may not be a factor for him. And no, I don't know what temperatures were involved or what the customer's battery state of charge was. It was a cottage system and he'd left it over the winter with no charging and if I recall correctly, the inverter on. Reread penrosefred's initial post - he asked if he should leave some lights on, which, unless they're DC lights, also implies leaving the inverter on so my cautions were valid.

As for the 2% number, that's just a rule of thumb I was told by a fellow who's worked with deep cycle batteries and has been in the solar business for around 15 years. It's not something I've measured.
-Steve

Kamala · November 2010

Re: storage

FLA or AGM? FLA is so often assumed. The difference is significant.

stevend · November 2010

Re: storage

Kamala wrote: »

FLA or AGM? FLA is so often assumed. The difference is significant.

FLA (if it was me you were asking.) Surrette S-460s or S-530s, don't recall which.
-Steve

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