Stay with AGM or go Lithium

[moorefc]

Originally Posted by 1der

Okay, looks like we have some Li gurus I can consult with based on a couple other threads. Suggestions for following scenario:

I would look at building a 200 to 400 AH Li bank as the replacement for the 2x175Ah batteries. The 400Ah level would provide a bit of extra capacity for water heating via 12v element.

Help me decide - stay with AGM or transition to Li ??

Tip of iceberg comments---

You increase the complexity and decrease the reliability of your house system. Do you go out back for long time periods?

Due to reliability (complexity) buy quality dcdc, bms, etc...
Decreased weight
Compromise high output >120A....Ie potentially limiting output or spending more on bms that can handle 2KW + inverters if you have 4S or one li batt...paralleling mitigates...
High temps are not an issue, only charging at low.
You may need a fancy/bigger alternator setup, since you have lots of ah needs, so want high amp charging..

A 200ah li is really like a 300+ah lead cell (people claim 2X, but don't agree since discharging generally is really low and the greater difference is at high discharge rates)


Li likes to be stored discharged....isn't that a paradigm...



As I have stated in other threads I'm on the fence and have built and tested ~300ah lifepo4.....Not sure if I will install..


Sound attractive?
If you want to build, this is where I had very good success-
https://diysolarforum.com/threads/in...26#post-259638
Lishen and EVE seem to be the cells of choice currently...


Have fun!

[kcshoots]

@1der-

Li-I has no appreciable reduction in output until below about below 0F (depending upon chemistry, with some that I worked on nearly 80% @ -40). Whereas an AGM will significantly reduce output by freezing temp, so yes, Li-I has much better cold weather output than any lead acid battery. Most Li-I do have a very reduced charge rate when below freezing, and again this varies by chemistry, with some that I worked on fine until -20, but most charge rates have significant reduction when the battery cells are below freezing.

I monitor 8 different temperatures in my van, including outside away from exhaust or other heat sources, and also at the battery positive (four batteries in total). Because there is always a load on the batteries, and the floor of the van is transferring a lot of heat (very little to no real insulation and it's massive in mass and size compared to other panels), and there is always residual heat from the engine, transmission, transfer case, even drive shafts (too warm to touch after mellow driving--just take a 30 minute drive and then try to grab onto any mechanical component), as well as heater, water heaters, etc., the batteries are always going to be warmer than outside air, and it's cell temp that matters which are inside a case with a bunch of them packed together putting off some heat as they provide load, so yes, they are about 5-10F warmer than outside temps when mounted under the van, and a charge from solar or heater running or engine running will warm them up. I have seen this thru actual use and my multiple sensors. You will not "hurt" an Li-i battery using it or charging it in the cold, and any decent Li-I battery pack as internal BMS to reduce or curtail charging when too cold and reduce or curtail output when too hot (>120F depending upon battery and chemistry but usually much higher). There is a lot of misinformation that lithium batteries are more sensitive to temperature than lead acid which is absolutely not the case. They work in space, they work in flight, they work on the moon, they work in our pockets which are darn hot and humid, they work in cars... I live in the Tahoe region with many Tesla's in my neighborhood, friends with them, etc., and they drive great in the snow and when below 0F. If those cars used AGMs they'd barely get out of the driveway when that cold.

[Scalf77]

I generally would have more concern with the heat and charging of a Lithium battery mounted under the van, than cold charging.

-greg

[1der]

I am super clear on the Li output characteristics, no issues there and our 480ah of AGM's have always been fine with cold weather output even though the 480 is down to about 300ah total capacity at 5F. But they accept lots of charge from the alternator and solar panel at that temperature and I do not have to worry about them.

I know it is below 32F right next to batteries because my holding tank drain pipe that is two inches away freezes solid if I do not leave the drain valve open. A hairdryer has become an essential tool, lol! Our floor is very well insulated as are the walls, windows, top. When we are parked at a ski resort for three days I might not run the engine for two days especially if the solar panel has had a chance to charge the bank.

I hear you about the Tesla's, my neighbor has three, but those battery banks have LOTS of safeguards and sophisticated environmental controls including heating and cooling circuitry/tubing as part of its BMS.

Is there a simple solution DIY Li capable of 0F charging off grid for weeks at at a time in temperatures from -5F to 120F?? I have not found it - yet.

[moorefc]

https://batteryuniversity.com/index...._temperatures/


There is a lot of test data out there re charging below freezing and the temp related lithium plating of the anode, dendrites, etc....using is not an issue at low temps..this can be mitigated by the bms programming via a temp sensor, or heaters...



They do work in space, and thermal management is a part of that...Work great in my volt, but it has heaters (and cooling thermal management) - the vehicle is not charging while driving, same is true of teslas........But cold charging heaters come on...



Great thing is thermal mass...for a while


I haven't seen simple thermal management beyond adding some typically blanket heater system

[posplayr]

Originally Posted by moorefc

https://batteryuniversity.com/index...._temperatures/



I haven't seen simple thermal management beyond adding some typically blanket heater system

The link states that which is obvious but at the same time not well defined.
What is clear is that there must be some thermal management to cool under hot conditions and heat under cold conditions (LOL some words of wisdom).

I'm working on a cold plate that does not allow "too" much heat to escape while heating.

You have to consider self-heating if heaters are applied as well as the gradual charging increase based on thermal profiles. I think they have computers for this?

Extreme cold and high heat reduce charge acceptance, so the battery must be brought to a moderate temperature before charging.

[Charliesmom]

Battle Born batteries now come with internal heating systems and I believe Relion offers them also. Since the LiFePO4 system you would require will use a smaller footprint and have significantly less weight, have you considered a redesign to bring the batteries inside the van. This would truly make your electrical system “four seasons” and simplify controlling the temperature regulation of lithium batteries. I also use temp monitors in and outside the van (Moat Technologies) and a temp probe on the battery + terminal (Victron 712 BMS). Both allow Bluetooth connectivity. We have a Truma Combi heating system in our van and have camped in some moderately cold temperatures over the last year (low 20’s). The van has the standard SMB insulation package (not Arctic). The battery temps stayed in the 50’s and 60’s similar to the inside temperature of the van. We haven’t tried 3 days in sub zero temps at a ski resort, but I would like try it. Our LiFePO4 system is an Expion 360 ah (no internal heating system). I have used a small ceramic space heater under our bed, near the battery cabinet during the winter months to maintain van temps >35 degrees.

[BCam]

Many newer LiFePO4 batteries, Battle Born for one, have built-in heaters for low temperatures. They are, however, more expensive:

https://battlebornbatteries.com/prod...h-12v-battery/