Minimal Battery Space, how much solar?

[DBJohn]

Hi team, and thanks for the add. We've got a small truck camper with very little room for battery or equipment. If I swap out the current Group 31 AGM 133AH with a 100AH lithium mini I can fit a 25A DC/DC charge controller with dual input MPPT, an upgraded disconnect, and buss bars in the compartment. Since I don't expect to ever have more battery capacity I'm thinking two 100W panels is all I need to plan for, and the max 32V MPPT will be enough. I'd appreciate any advice, including thoughts on the mini's with pouch cells. Bought your book Will!
Thanks,
John

 

[sunshine_eggo]

Hi team, and thanks for the add. We've got a small truck camper with very little room for battery or equipment. If I swap out the current Group 31 AGM 133AH with a 100AH lithium mini I can fit a 25A DC/DC charge controller with dual input MPPT,

Huh?

Dual MPPT or PV input + DC input from alternator?

an upgraded disconnect, and buss bars in the compartment. Since I don't expect to ever have more battery capacity I'm thinking two 100W panels is all I need to plan for, and the max 32V MPPT will be enough. I'd appreciate any advice, including thoughts on the mini's with pouch cells. Bought your book Will!
Thanks,
John

Max 32V? Link?

25A can utilize no more than 25A * 14.6V = 365W

 

[DBJohn]

Thanks for the reply. The Redarc dual input DC/DC 25A with MPPT for the solar input. Here's the link: https://www.redarcelectronics.com/u...7uZfvpRnqcExQ4wZS0At3JTjL-E4IXohoC_IUQAvD_BwE
Renogy makes them as well, but I like Redarc products and it seems like enough if I stick with the 200W. It's max 32V. Is it likely to ever see more than 32V if the panels are wired in series?

 

[sunshine_eggo]

Okay, so it's a DC-DC charger + PV MPPT. Gotcha.

Not a fan of Renogy. Redarc has a good reputation, and the 32V limit beats the shit out of the 25V renogy. Spendy, but it's the better choice.

IMHO, you can never have enough solar, so put as much as you can fit, but yes, use 100W panels and put them in parallel.

 

[DBJohn]

Excellent, thank you. Any opinion on the lithium minis? I saw Enduro has smaller prisatic cell lithium batteries at 2X the price of the pouch cell ones on Amazon.

 

[sunshine_eggo]

No opinion, but my nature demands that since LFP has a certain minimum density and volume, I'm dubious of anything that claims a smaller size.

 

[Rednecktek]

Ummm... have you thought about rolling your own? If you've got a Group 31 battery now, I know from personal experience that you can make a 304Ah 12v battery with a 200a BMS that fits into the Noco Group 24-31 battery box. I used the JBD BMS with the low temp protection for that build and the 304Ah cells and 280Ah cells are the same physical dimensions so they'll drop right in there nicely.

No opinion, but my nature demands that since LFP has a certain minimum density and volume, I'm dubious of anything that claims a smaller size.

Most of those seem to be pouch cells and the big space savings comes from NOT installing the 4" blocks of foam on every side of the cell.

 

[DBJohn]

Thanks for the thought, I haven't looked at building batteries at all. I'll check some threads here but it may be a bridge too far...

 

[Rednecktek]

Thanks for the thought, I haven't looked at building batteries at all. I'll check some threads here but it may be a bridge too far...

I was nervous the first time I built one, and when I was done all I could think was "Why was I so paranoid? That was easy!" If you're nervous and have a little extra cash you're willing to risk, go to Sirko batteries, grab some super cheap LFP cells, like 50ah or so, and a cheap 4s Daly BMS for $30 and build a little guy. When you see how simple that was you'll have no worries building a big-boy battery for the camper.

If push comes to shove I'm sure you could find someone here ( ) that would be willing to build & ship it to you for materials + shipping + pizza money. Watt per pound it's the best way to go.

Also, as for how much solar? As much as you can fit!!!

 

[Solarcabin Channel]

Are you able to keep LFP batteries above freezing in your truck camper?

If not a portable mid size power station with LFP batteries you can take in the house to stay warm and also charge might be a better option. Also eliminates the extra components and has ports for all your gadgets.

 

[MichaelK]

You are going to lay these panels flat on the roof of the camper? Keep in mind that at a less than optimal angle to the sun, the panels will never be at full output. Normally, I would de-rate flat-mounted panels to 60-70% output. Especially for up above the 45th parallel.

What that means in the real-world is that your two 100W panels might never put out more than 120W. To fully utilized the 365W your controller can handle, you would need 365W/75% = 487W of panels. Let's call that four 120W panels for simplicity.

BTW, though that is a nice controller, you could get far more capacity at a higher voltage limit, just shopping around.