heated FLA battery enclosure

[dalek]

Does anyone heat your batteries in a battery box? What is your setup like? I'm looking for examples and ideas.

I have two big forklift 48v batteries built into a box in an unheated garage. The system is from a set of DC Solar trailer parts.

The battery box is vented across the top of the cells. It should work passively by gravity and heat exchanged inlet & exhaust flow, and certainly does work with the exhaust fan controlled by the inverter/charger. The exhaust fan draws primarily across the top of the cells through two 1-1/2" copper tubes, but there's also a smaller tube down to the bottom to remove heavier than air gases. The batteries are insulated on the sides and bottom. There's airspace underneath where I can add a heater, and I could seal around the top edge of the insulation, keeping the venting on top separate from the heated bottom and sides.

For the lead, it should not have any potential ignition source. So a relay contact thermostat is out, and small incandescent bulbs are an equally bad idea. Maybe an old mercury thermostat would be fine, not sure about using that at 48v DC or 120v AC. A heater could run off either power source. I have some heater plates from a Nissan Leaf battery, they could work. And a remote temperature probe controller I'd need to buy.

Another item on my list is to get a lithium bank set up, and that will do most of the daily energy cycling. The lead would be there just for short term power draws and wouldn't cycle very deep most of the time. That would reduce the need for keeping the lead warm in winter. They would always be full, and the reduced capacity at lower temp shouldn't matter as they won't cycle too deep. So maybe I should get started on the lithium bank instead of a lead heater. The most elegant heater may be none. And, well, I'll definitely need one for the lithium in the cold garage, so hey I can still set up a heater.

Thanks!

[Mike90250]

What is your climate like, in the unheated garage ? Would a gallon jug of water freeze there ?

Flooded LA batteries produce some self-heating, you don't need to suck all the heat from the battery bank. Do you have enough solar in the winter to complete Absorb several days a week ?

Li bank. That should be in it's own box, and you can insulate the heck out of it in the winter. Self-heating will help it some, you might need a small heater mat, but nothing exotic. Your BMS may even have a heater relay contact. You do want to keep the Li above 40F. Below 40F, it will start to struggle.

but what's the rational of having 2 battery banks, FLA & Li ? The charge settings are going to be different for each, and reprogramming each time you change over.. That will be a fun mistake to discover a week later. As I hear it, Li blows FLA away (except for cost)

[Sunking]

Now that is some funny stuff, I don't care who you are. How much more moronic can it get from the Green Mafia. You take a battery system with a negative EROI, and make it even more negative by heating batteries. Stupid is what stupid does.

[dalek]

Glad I could entertain. Thanks for your other posts, they're informative and food for thought.

EROI: I generally try not to charge & discharge the FLA bank, especially winter. The reason as SK eludes, there is a large amount of charge & discharge loss for FLA. Especially at higher SOC where you want to be for good long life. Sure, adding a heater is throwing away that much more energy. But, it's in an insulated box, except for the top venting, which does lose heat out the top.

I'm in lower Michigan. This winter, I did use about 50w, sometimes, just manually watching the temperature and plugging or unplugging heater under the battery, to keep it from getting colder than about 10dC. On sunny days, especially, I would plug it in, as the only other thing to do with the extra power is to run resistance heaters in the basement. Safety police will riot, but I used a couple strings of mini christmas lights under the batteries. There is good venting on the top, the airspace below is sealed mostly around the top edge of the batteries. Pictures of the battery box & system.

$ROI: the forklift batteries were basically free, and seem to have label capacity, so I didnt' try to sell them or whatever. I wouldn't have chosen FLA to start, but they were free. They're a great match for a pair of SMA SI inverters, run the whole house no drama.

Why think about heating: A cold FLA has lower capacity, keeping it a little warm would help the capacity if it was needed for an outage. If there was a power outage for several days, the larger capacity would be of use. In the winter especially, the FLA is mostly on float, I don't draw it down overnight since solar production is less than house needs generally in winter. The battery runs the house during on-peak to not buy on-peak power if it's cloudy, otherwise the solar runs the house.

Why 2 banks, FLA + Li: FLA is free and great for high power to the inverters, and it was free, so I'll keep it. No BMS on FLA is simple too. FLA is not optimal for energy storage, want's to be always full for good life, and roundtrip energy losses are relatively high. Li is better for energy and power. I'll try to have most of daily energy cycling go through the Li, mostly charged direct from solar to the Li banks. Overnight, the Li banks discharge at the average house consumption, with old enphase microinverters AC coupled behind the main inverters. So far I'm doing this manually with a bank of Nissan Leaf modules & BMS in an Electrak tractor. So until the FLA is no longer useful, the main inverters are just on the FLA. No changing back and forth, no paralleling the FLA & Li directly. Yes, some claptrap and extra controls, but raspberryPi w/ nodered is not too hard and completely flexible.

[Weldman]

The energy spent heating the batteries will offset what you are trying to gain by keeping them above said temperature. Want to keep them warm, just put insulation around them. Though if you ever run across another free forklift battery I sure would come take it off your hands or whoever is getting rid of them.