Stay with AGM or go Lithium

[1der]

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

Usage environment is true four season. Sub zero F winters to 100F plus summer days. Solar 360w fixed plus 200w supplemental. Alternators 2 x 110amp. Draws are typically 40 to 50 amps overnight for two fridges, lights, water pump, Espar heater if needed. If using the microwave I usually start the engine and high idle to compensate for the draw but w Li I would probably just run the microwave. Spec was/is to provide enough Ah capacity to operate two to three days w minimal solar input due to weather and not starting the engine gif charging.

Current setup is 2x175sh AGM plus 2x65Ah AGM for total 480ah bank mounted under on frame. The 175Ah batteries are doing okay but are going on 4.5 years of well cared for use. Resting voltage of around 12.6 at 60 deg F.

IF there is a legit viable Li setup I would be up for creating an insulated underfloor compartment w a little heat from the Espar, plus possible AC cooling from rear engine driven compressor. I would love to build a Li battery bank or is the SOK 200Ah units. The benefit of building my own Li bank is the format could be a non-standard size that is flat and wide vs Group 31/4D format.

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 ??

[BCam]

I'm no expert but, if your current setup is working, I suggest waiting until it was time to replace some or all of your current batteries. Prices of LiFePO4 batteries will probably continue to decrease and the quality will improve so waiting a year or so might not be a bad plan. You can also use the time to educate yourself on LiFePO4 battery installs.

Subscribe to Will Prowse's DIY Solar Youtube channel. He has a ton of videos on DIY builds, battery tests, teardowns and the like.

https://www.youtube.com/channel/UCoj...q8kmJme-5dnN0Q

There's also a companion forum:

https://diysolarforum.com/

Things are evolving quickly so try to stick to Will's more recent videos, especially with respect to product evaluation/testing. The older videos still are valuable for educating yourself on the basics of the technology and DIY builds.

One of the downsides of DIY builds for vehicles and especially with respect to Sportsmobiles will be the effects of vibration and other physical jolts.

[arctictraveller]

Originally Posted by 1der

I would love to build a Li battery bank or is the SOK 200Ah units. The benefit of building my own Li bank is the format could be a non-standard size that is flat and wide vs Group 31/4D format.?

Sounds like you have plenty of charging capacity, can you regulate the voltage suitable for Li? If you build your own bank, how would you incorporate the battery management system?

[BCam]

This thread has some posts on DIY LiFePO4, starting at post #13:

https://www.sportsmobileforum.com/fo...r-28623-2.html

[posplayr]

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:

Usage environment is true four season. Sub zero F winters to 100F plus summer days. Solar 360w fixed plus 200w supplemental. Alternators 2 x 110amp. Draws are typically 40 to 50 amps overnight for two fridges, lights, water pump, Espar heater if needed. If using the microwave I usually start the engine and high idle to compensate for the draw but w Li I would probably just run the microwave. Spec was/is to provide enough Ah capacity to operate two to three days w minimal solar input due to weather and not starting the engine gif charging.

Current setup is 2x175sh AGM plus 2x65Ah AGM for total 480ah bank mounted under on frame. The 175Ah batteries are doing okay but are going on 4.5 years of well cared for use. Resting voltage of around 12.6 at 60 deg F.

IF there is a legit viable Li setup I would be up for creating an insulated underfloor compartment w a little heat from the Espar, plus possible AC cooling from rear engine driven compressor. I would love to build a Li battery bank or is the SOK 200Ah units. The benefit of building my own Li bank is the format could be a non-standard size that is flat and wide vs Group 31/4D format.

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 ??

I started on the DIY LiFePO4 route before seeing these off-the-shelf lithiums. They are quoted at $575 for 100 Amp-Hr.

https://www.sokbattery.com/products/...f=h-cvbzfahsek

In contrast to the DIY route the going popular config duration is a 280 Amp-hr 4S battery with ha single BMS single battery set.
https://www.aliexpress.com/item/1005...%2315616%23728

You could easily double this by paralleling cells and still keep a 12V 4S configuration. Alternatively, you could double a smaller size like the 130 Amp-Hr. Looks like there is also 310 amp-hr set without needing to double up.

Obviously, Li is available and doable the question of how much time you want to spend making a DIY setup work. You can probably do a Victron setup but much more expensive. Are you electrically inclined?

The first problem is building the battery bank. If you but that off the shelf about of 1/2 the problem go away if you can trust the product.

The next set of hurdles is the alternator charging usually has done with a DC to DC converter as being discussed in the hood-mounted solar thread. Given the capacity you are talking about you can get into a situation of stressing the alternator trying to push 40-60 amps to the battery bank at idle.

Finally, you have compatibility of these things with your existing system From the issues I'm hearing you want a solar charge controller that has independent connections for solar, battery, and load.

As far as environmental concerns, you have to keep the batteries from freezing. I think a little air circulation for the BMS will be sufficient for 100 degF. A DIY setup would lend itself better to this than the 100 Amp-Hr standard configuration.

Anyway, these are not an exhaustive set of considerations but at the forefront of my consciousness because that is what I'm finding out as I design my DIY system and interact in the various threads.

[posplayr]

https://www.youtube.com/watch?v=RxMIs0PXrBw

https://www.youtube.com/watch?v=gCmwBfIk9Gs

[posplayr]

https://www.youtube.com/watch?v=MDdN3HiBf3w

[larrie]

My system is described in this thread.

[kcshoots]

Lithium-ion will have as good if not better low temperature and way better high temperature performance than AGM...by a long shot. The only thing lithium-ion won't do as well as AGM is charge as fast when cold but will way out provide power over AGM hot or cold. A lithium-ion with integrated BMS will regulate to get 3-10 times the life than from AGM. I used to run battery cell manufacturing engineering at Tesla and those cells are ramped up and down across a wide range of temps in a very short period as part of their final testing, and I have my lithium-ion's mounted underneath the van--they've kept the power flowing and charge with exterior temps from -5 to over 110 F--well within their operating specs. There is a lot of heat transfer from van floor to below van.

[1der]

kcshoots -
Our last year's 10 week ski trip saw no outside temp above 25F for 8 weeks straight. The van floor heat transfer from inside to under the van?

You are saying a Li bank mounted under the van, parked in 10F temp( let alone -5F) will accept enough charge (in 3.5 hrs) from the solar panel?? While simultaneously providing enough current to power two fridges and an Espar heater that have been running overnight and during the day?

Your post seems to contradict virtually everything I have read about cold temperature charging of Li as well as the specs on nearly every Li battery I have looked at.

What battery and BMS are you running?