For lithium users

[VanKitten]

What are you doing about temperature and battery health?

Knowing that charging in high temperature or discharging in low temperatures will be damaging and /or dangerous ....what are you doing?

I have a thermometer with sensors in the battery compartment.  Master cut off switch.   Fans, and ability to open/close additional external venting.  Plus, I do not plan on spending time in hot or cold places...but sometimes it happens.

I would be happier if I had a system to automatically cut off charging at 105 f.   And shut down discharge at 35 f.     That would leave me with a bit of room for slop.

Since I am forced to hang out day after day doing nothing .....I have been thinking about improvements I could get parts for now and just add it to the list anyway.

What do you do?

 

[John61CT]

My understanding is charging below freezing is what's harmful, discharging can continue lower, just less output just like lead.

There are low-wattage 12V DC flexible heat elements, can set to run from thermostat.

Heat hurts longevity, but I don't think usage in bearable to humans range is an issue?

Do you keep your LFP bank outside the living space?

 

[VanKitten]

The batteries are in a separate compartment with venting to the outside. But..outside the insulation of the RV. I have an additional vent I can open .... and I can close the vents entirely. I can open the compartment to the interior of the RV if I needed to. Don't plan on being in freezing temps....but...I could open it right up.

I have fans inside the compartment as well. I didn't want to use any heating in there...like a heating pad...because I do not actually know the internal temps in the cells themselves...so don't want to have a heat source conducting heat to the cells themselves.

The spec on the batteries says high cut off charge at 113 f. Low cut off discharge at 32 f. But that is internal temp. So just figured to set battery room temp settings so that it does not get too close.

 

[John61CT]

My plan for external mounted LFP is a heating pad with high cutoff built-in of 50°F at the pad.

To be controlled by external ambient thermostat within the insulated box between 40° and 70°.

I think the pad used 20w and would just lie at the bottom, maybe some wool between it and the cells, not in direct contact.

About $35 made custom to spec.

 

[VanKitten]

Do you happen to have a link for that? Heating pad and thermostatic control?

Since the cells are aluminum wrapped...heat transfer will be more efficient.... surrounding air temp might not be a good clue. Thinking maybe if there was a way to set the temp of the pad? Just worry about over heating them

 

[John61CT]

That's why I spec'd the high cutout be built in, measures the pad itself internal temp.

Can't look up now, but they sell on eBay from China, color orange.

 

[DLTooley]

I've seen a suggestion for cold - just place the battery in a sealed container and it will keep itself warm enough. My plan is to put the LFP in a waterproof pelican style case.

 

[John61CT]

My scenario is batts in an external box under the chassis, vehicle parked outside long-term in sub-zero conditions no shore power.

Yes box is insulated but that's no help in those conditions until *after* they're warmed up.

Need to get them up to 35+°F before drawing, 45+ before applying a charge.

BTW I haven't come across any of those fancy BMS-included systems costing thousands that take care of this issue.

 

[VanKitten]

John...

If you cannot draw till above 35... where is the power to heat them? Best to set low temp to 40 so that the heat can be safely run. I want am alarm on the system. I can close vents and open access doors to the interior to help keep them warm if I am doing a cold night.

I did find a 12v low voltage heating pad. It isn't thermostaticly controlled...I guess I will have to handle it manually till I figure out a more automated system.

I remember several hobbyists who built their own BMS.

Issue I have with the BMS the hobbyists were offering was that it only takes current up to 100amps. I have 400 amps constant possible.
By wiring the two contactors (one normally open, one normally closed) I solve the issue of cut off high and low voltage. The balancer solve the issue with keeping the cells/batteries balanced. But, the temp still remains.

I simply could not figure out how to wire the BMS and the Contactors together in the same system. Guys at electriccarparts were baffled too...decided to eliminate the BMS and solve the temperature control issue separately.

I would not feel comfortable buying a "plug-n-play" lithium system. After learning a lot about what is built in and what is not, I think those systems are too costly in two ways... initial up front costs way more than build it yourself...and long term cost in shortened battery life from poor or no battery management. A few people I talk with bought the PnP systems because they didn't want to have to learn all this sh*t. I guess that is great if you can afford it!

 

[John61CT]

Johnny Tang | Sales Department
Mobile:+86 186 1635 0189

Keenovo International Group Limited
T:+86 21 3126 3395 
F:+86 21 3387 9551 
E: [email protected]|[email protected]
W: www.keenovo.com

This is their generic eBay listing

https://m.ebay.com/itm/281744712285

Tell him your specs and they create it custom, once-off or large qty.

Mine was $25 per pad for four.

 

[John61CT]

If you cannot draw till above 35... where is the power to heat them?

My Reserve (also usually running essentials, engine / starter / safety / navigation loads) bank is lead.

The LFP bank is for "auxiliary" House loads only, so usually in deep-freeze conditions, lead gets the vehicle running, then some time later House is warmed up and ready.

Either load circuit can if needed be switched to either bank.

Charging circuit also, in normal use all charging goes to house, Reserve topped up via VSR. But in very cold weather this is reversed.

 

[John61CT]

I remember several hobbyists who built their own BMS.

Issue I have with the BMS the hobbyists were offering was that it only takes current up to 100amps. I have 400 amps constant possible.
By wiring the two contactors (one normally open, one normally closed) I solve the issue of cut off high and low voltage. The balancer solve the issue with keeping the cells/batteries balanced. But, the temp still remains.

I simply could not figure out how to wire the BMS and the Contactors together in the same system. Guys at electriccarparts were baffled too...decided to eliminate the BMS and solve the temperature control issue separately.

I see BMS as functionality, not off the shelf hardware.

Balancing is as needed, manual, if gentle House usage, bank properly coddled, maybe once every couple years.

Multiple levels of LVD / OVD I think are a good idea, but can be done with generic OTS devices, until a flexible open-hardware design comes on the market.

I also can't come at the pricing of proprietary "system solutions".

Plus all seem to have setpoints way too high, I don't charge past 3.45 Vpc.

 

[DLTooley]

My 120v heating pad, used for Kombucha brewing, has a safety timer feature. It works good enough. Changing the battery location to a conditioned space seems like the only other option.

 

[Kevin Carney]

I've used Lithium for years. It's done wonders for my bi-polar ... oh, wait ...

 

[John61CT]

Changing the battery location to a conditioned space seems like the only other option.

Which in my case, and many others, just doesn't exist.

It's just not practical to keep the living space warm when you're not in the vehicle, and even a half-day can freeze everything solid.

 

[Weight]

I like Lead Acid.

 

[blars]

Charging at low temperatures is the problem, not discharging. Discharging may be less efficient, but that will cause self-heating and correct itself. Low-rate charging at low temperatures should also not be a problem. Some brands (formulations) can handle low temperature charging better.

The problem with charging or discharging at high temperatures is the self-heating makes the problem worse. Heat, even with no use, reduces battery lifetime.

 

[WanderingCanuck]

It's just not practical to keep the living space warm when you're not in the vehicle, and even a half-day can freeze everything solid.

Really? I'm new to this, but I was under the impression that I'd need to do this to keep moisture at bay and prevent my water supply from freezing. I'm also working under the assumption that with very good insulation, the energy to maintain even a lower temperature when away from the vehicle will be less than it would take to reheat from a very low temperature.

I realize maintaining temperature is another topic entirely, but I'm considering the feasibility of having some heat storage in the form of water, wax or oil as well. Perhaps I'll find out soon that it isn't practical, but if it is it will help with interior temperature and thus the battery temperature.

Feel free to dispel my misconceptions.

 

[John61CT]

I have not seen data that low-rate charging is OK, my plan is no input at all below 32°F bank temp.

My plan is to put the LFP bank in a well insulated box with efficient 12V heating pads underneath, similar to those used for fuel lines, propane tanks etc

External thermostat turns on based on low temp, pads have a built-in cutoff so they don't get too hot.

When not in use, discharge to 20-30% and let them freeze.

Starting a day or two before use, get them warming up, either via the pads fed by lead starter/Reserve bank or something more powerful if available, active heating sources like from running the engine, Webasto type combined HWS / hydronic space heating, all can be put to use once systems in use, Reserve is big enough to delay use of LFP bank if an unplanned startup is required.

But the built in heating pads are always available integral to the LFP powerpacks, just like temp protections built into the "DIY BMS". My goal is to keep the packs portable and self-contained, can use in another vehicle / trailer, on a boat, off-grid cabin.

 

[John61CT]

prevent my water supply from freezing. I'm also working under the assumption that with very good insulation, the energy to maintain even a lower temperature when away from the vehicle will be less than it would take to reheat from a very low temperature.

Depends on relative time periods. Vehicle parked off-grid for months vs in a motel overnight vs weekender in the driveway.

I don't plan on designing water systems where pipes can freeze.

heat storage in the form of water, wax or oil as well. Perhaps I'll find out soon that it isn't practical, but if it is it will help with interior temperature and thus the battery temperature.

When not in use, heating the whole space just for the bank is wasteful.

If you want thermal mass for buffering, use an already existing HWS tank or the engine block, adding additional weight for just that purpose is IMO impractical.