What minimum size battery for startup off grid solar array

[Rascal]

I'm slowly acquiring components and have not yet ordered any solar panels for the 400 watt off grid camper system I will build. I have a 35 amp/hr AGM, a 20 amp/hr LiFePo from Bioenno Power, and a 50 amp/hr LiFePo, also from Bioenno. I'm a ham radio operator who trains for disasters so my 50 amp battery has a 180 watt, 3 panel solar array and is dedicated to my mobile radio station. The camper system will be 400 watts but I can't afford to order the panels yet. I have a 40 amp EPEver Tracer MPPT charge controller, just ordered a 3000 watt pure sine wave inverter, a DC circuit breaker, and fuses. I'm acquiring stuff in bits. BTW, the camper is a 6 x 12 enclosed cargo trailer I'm converting to be a mobile radio station.

So a couple of questions: should my panels all be of the same vintage or can I order them one at a time as I have cash? What is the minimum battery size for a 100 watt panel? I don't want to kill my battery. I plan to buy 2 Battle Born 100 amp/hr batteries when I have enough cash. In the meantime I want to assemble my system and get it into at least partial service as I acquire parts.

Thanks!

 

[Craig]

It makes life easier if they are of same voltage and amp ratings. Scour craigslist and maybe you can find a good deal on some used or extra panels.

A 100 watt panel will produce about 500 watts a day so that will only charge a battle born battery less than half.

 

[MisterSandals]

You are going about this in an unconventional way. First you should determine your power needs. Then get batteries to supply the power. Then panels matched to a charge controller capable of recharging the power you use daily (more ideally).
Then an inverter.
Your 3000w inverter will require at least 2x 100ah LiFePO4 batteries. And even the discharge is 1.25C.
3000w is around the level you should have a 24v battery bank.

The math:
Assuming 12v system: 3000/12=250amps.
Discharge 200ah at 250a is 1.25C.

 

[Rascal]

You are going about this in an unconventional way. First you should determine your power needs. Then get batteries to supply the power. Then panels matched to a charge controller capable of recharging the power you use daily (more ideally).
Then an inverter.
Your 3000w inverter will require at least 2x 100ah LiFePO4 batteries. And even the discharge is 1.25C.
3000w is around the level you should have a 24v battery bank.

The math:
Assuming 12v system: 3000/12=250amps.
Discharge 200ah at 250a is 1.25C.

I agree with you. It's a matter of cash flow. The difference between the 2200 watt inverter and the 3k inverter is actually negative so thinking of a potential future, I bought the bigger one. I currently have a 35 amp/hr AGM battery, have not yet purchased the LiFePo 100 amp/hr batteries... those are on the want list at the moment waiting for cash to fulfill that want. I also need solar panels. I will have to be careful not to over draw from the system with the larger inverter. I have a low voltage cutoff device to protect the battery in case I'm not paying attention. I'm not doing this on credit although I could. Trying to stay within a budget as I prepare for retirement in 3 years.

So my real question is, can I bring my budding system online with one 100 watt panel (when I get one) and the 35 amp battery without killing it. The other two LiFePo batteries are dedicated to my radio station, not for luxury items like running a laptop (although I could make a case for the laptop being part of the station running digital modes).

I camped in my trailer for 7 days in January in Quartzsite (QuartzFest 2020). For that trip I bought an el cheapo 100 watt system from Harbor Freight (for expediency). That ran lights and my MaxxAir exhaust fan and kept my Surface Pro charged. For a small trailer like mine I chose Will's classic 400 watt configuration. I expect over time that may evolve.

So, what do you think about the 35 amp battery? Will I ruin it?

 

[MisterSandals]

So my real question is, can I bring my budding system online with one 100 watt panel (when I get one) and the 35 amp battery without killing it.

Your EPEver should control charging safely. If you don't discharge more than 50% you should be fine. Its a small panel, a small battery and a big SCC. Plenty of room to grow with more panels and batteries.

 

[Rascal]

Thanks! I was more concerned about overcharging the battery. I bought a low voltage disconnect after a power outage killed the AGM battery that was backing up my radio station. That was also a 35 amp/hr battery. It would charge but was dead in 15 minutes ever after that. I love that LiFePo batterys have a BMS to manage over and under voltage.

After watching Will's battery teardown videos I've decided that I'm going with Battle Born. Others may be cheaper but you get what you pay for. Buy once, cry one!

 

[MisterSandals]

I bought a low voltage disconnect after a power outage killed the AGM battery

A low voltage disconnect wouldn't kill an AGM battery. It should do the opposite (disconnect before the power gets to a damaging level). If you leave a highly discharged battery in a discharged state, especially an elderly battery, it will be compromised.

Ah, a Battleborn. That's LiFePO4, good choice. I've never heard a bad outcome with that choice and the 10yr warranty will help one sleep easier.

 

[Rascal]

I acquired the low voltage disconnect after the power outage killed that battery and I replaced it. At that time I had a BBS up and running on packet radio (2 meters) and the battery supported that.

From what I hear, Battle Born has spectacular customer service as well. Be safe!