strip heaters underneath SLA batteries

[sunbelt56]

I'm building an insulated wooden box to house my T-104's, I was either going to have 3 or 4 banks of 8 in series. I have some 120v strip heaters that I will have on a thermostat. My question is: is it ok to have the batteries sit right on top of the heat strips or should I have an air gap between the strip and the battery?

[bigrockcandymountain]

I have to ask, why are you heating batteries?

[Scruff]

They're very fashionable BigRock. You can get one for the low-low price of a golf cart battery that can operate in -20°C unassisted.

They're especially good at adapting your LFP from effectively useless to highly inefficient.

[bigrockcandymountain]

Did you mean t-105's by chance? Those would be golf cart size trojan 6v batteries. 

If so, don't worry about heaters.  Worry more about getting the heat out while charging them.  Lead batteries will handle -40 no problem, it is the heat that will kill them. 

The exception is if they are way low on charge and it gets extremely cold.  Then they freeze and bad things happen. 

I would also go with bigger batteries and less parallel strings,  unless you have a good reason for using smaller ones.

[bigrockcandymountain]

Wow i just checked out your link scruff.  For $220 i get a device that not only doesn't add to my battery, but actually applies a load to it.  Now how do i calculate the payback on this wonderful unit.......

[Scruff]

Including the €1000 100Ah 12v battery it's designed for?

Payback = Never ²


The return of invested power to heat lead exceeds the losses associated with cold temperature operation many times over. Put them somewhere cosy, insulate them and use temperature compensated charging.

[Bruce S]

I'm building an insulated wooden box to house my T-104's, I was either going to have 3 or 4 banks of 8 in series. I have some 120v strip heaters that I will have on a thermostat. My question is: is it ok to have the batteries sit right on top of the heat strips or should I have an air gap between the strip and the battery?

As you can see from the current replies, it's not a good idea to do this.
A well charged Lead-based battery can survive some very cold temps. AND heat from them charging will help too.

If it's the type of strip heater that normally wraps around water pipes, then it could be even worse! These are designed for metal pipes and if left unchecked could end up melting or warping the battery containers :-(.

Seeing that you will be insulating the area where the batteries will be located , then it would be best to add some cross ventilation to keep the hydrogen  vapors from accumulating.  Most storage areas posted on here in the past, used old muffins fans from computers, they're easy to mount and can be powered by just about anything.

Hope this helps
Bruce S

[sunbelt56]

Yes, I meant T-105's. Yeah, I heard that if they freeze, they are ruined. Here in WY it can get really cold. Thanks for the replies, all.

[Bruce S]

Yes, I meant T-105's. Yeah, I heard that if they freeze, they are ruined. Here in WY it can get really cold. Thanks for the replies, all.

That is very true, but even as cold as it does there. They'll handle it while charged, gotta get to a Day-After-tomorrow (Movie ) type cold for them to freeze  .

The Ruined part is due to the crystallization of the water. Depending on the severity of the freeze, the water well swell and push the plates into failure.
During my short stay in Germany, we would see this on old trucks that sat with no chargers on the batteries.

 Hope this helps

Bruce S

[DamonHD]

I've seen a number of practical experiences written up as suggested above.  If you don't let them get to too low a charge, they really are not going to freeze, not even in the Arctic.

A very quick search for example brought up this:

https://www.sciencedirect.com/science/article/abs/pii/S0378775302006997

You might have to allow a higher absorption voltage (maybe even over 15V) if things get very cold.

Rgds

Damon

[Mary B]

They sell a battery blanket heater, I had one on my truck. It would sit 2 weeks at a time in the cold before I built the garage and having a warm battery meant more starting energy at -20f.