New to the game. Want to build a small solar generator. Need battery advice

Hi all.

So my plan was to build a small power pack/solar generator out of a harbor freight "pelican case".. it's the mid size one. Mostly for taking camping and running small devices in a power outage, etc.

The goal was to run 1-2 110v outlets from a 500 or 750watt inverter (really the biggest I can find that will fit)...and then wire up some USB ports, a battery monitor display (for charge status etc), and some solar inputs.

I've been looking at 23ah Dakota lithium batteries for price point and physical size...but here's my question. For this kind of system, is that capacity battery way too small? If so, I was thinking about building a 50ah lifepo4 battery from Chinese cells but I'm not sure I want to dive that far into the build. However, the price is a WAY better bang for the buck. Really I'm just unsure how to go about the power source for this machine.

All the stuff I see or read deals with much bigger solar systems for RV type builds, or the battery packs are built from a ton of 18650 cells or weird smaller batteries and honestly I want a much safer alternative than the stuff I see people build on YouTube.

I have no experience building battery packs from cells but I'm an automotive technician with a good understanding of electrical operation. Just never have to deal with battery builds.

Thanks for the help guys!

I recommend 100Ah for 500 watt inverter, 150Ah for 750 watt inverter. This would be my minimum.

Eviper21 said:

I've been looking at 23ah Dakota lithium batteries for price point and physical size...but here's my question. For this kind of system, is that capacity battery way too small? If so, I was thinking about building a 50ah lifepo4 battery

Click to expand...

You did not specify but I'll assume you will be building a 12v (4S) battery...

23ah @12.8v = 294wh
294wh x .85 (inverter loss) /120v = 2h runtime

50ah @ 12.8v = 640wh
640wh x .85 / 120v =4.53h runtime

You be the judge of whether its enough or not.

Make sure you add up your other usage numbers too. Converting to watts and watt hours makes it easiest.

MisterSandals said:

You did not specify but I'll assume you will be building a 12v (4S) battery...

23ah @12.8v = 294wh
294wh x .85 (inverter loss) /120v = 2h runtime

50ah @ 12.8v = 640wh
640wh x .85 / 120v =4.53h runtime

You be the judge of whether its enough or not.

Make sure you add up your other usage numbers too. Converting to watts and watt hours makes it easiest.

Click to expand...

You need to consider what MisterSandals posted and determine your usage. If you can get by with these numbers, you will be OK.

The description of what you want to build sounds similar to the smaller capacity "solar generators" from Bluetti, Jackery, Renogy, etc. It could be fun to DIY your own system, but it would be larger and probably more expensive than something you could buy from one of these companies. You didn't list a battery management system (BMS) which is an additional cost to your build. If you want to charge with solar, you will also need a solar charge controller.

I built a 12V battery from four 3.7V, 50 amp hour cells and a cheap BMS that Will used in one of his videos. I bought the cells locally so they were more expensive than getting them shipped from China and I received them within days, not months. If you add the costs of an inexpensive MPPT solar charge controller and a 500W pure sine wave inverter, you would probably be better off buying a Bluetti AC50S or EB70, Jackery 500, or Renogy Phoenix.

I bought a Jackery 500 on sale at the beginning of the year for $419. It fulfills my need for a portable and immediate power solution but solar charging is very slow. Input from solar is capped at about 65 watts even though I have a 180 watt panel for it. If I was looking for another portable "solar generator" I would get something with faster charging capabilities. Also, these other units are not LiFePO4 cells so their cycle life is shorter, but they are Lithium based.

The run times that people have commented on assume your inverter is loaded to its rating. You have not shared the important details of your real load. If you want to run a mini-frig or something that is a constant load (other than tiny load) then your 23ahr battery is pretty small. But you could use more than one, if that would solve run time problems and avoid building a battery.

With a tiny 300 watt inverter I can run a 120v 4 foot LED light tube (2.2-ish amps at 12v) for more than 8 hours on a 20ahr battery. I have a 5 cup coffee maker (approx 550 watts) that will run off of a cheap 750 watt inverter. It takes only about 10 minutes to brew a pot of coffee. But questions like, "How many pots" or "How long do I leave the heater on" will have a great impact on how long my battery will last between charges.

So a better understanding of load over time periods will help you make better decisions on battery size.

Not sure how good these (Amazon) are.

Will review. edited...just watched that review again, not great but there are many battery options out there.

Sorry, 12v system, yes...
Hmm, I guess I didn't realize how fast stuff starts using power when you add the 120ac into the mix. This all started because I thought that the mini packs in a plastic ammo can were super cool. With the few USBs and led lights. But I thought it'd be even cooler with a 120 outlet and solar capability.

I was under the impression that anything I built would be cheaper than what I can buy, but I guess for this "carry case" size build that's not the case.

As far as usage, I'm not really sure to be honest. I know for a fact I can't run a fridge on this size for very long at all. So I probably wouldn't bother trying. However, all matters of device charging for sure. (Laptops phones etc) and possibly a small appliance or a modem/router in a power outage. I guess these are things that make determining capacity needs difficult for this project as I don't have a specific need for this unit. Just thought it'd be fun. But I also don't wanna spend $500 building something that will only last 1hr and take 8hrs to charge

MisterSandals said:

You did not specify but I'll assume you will be building a 12v (4S) battery...

23ah @12.8v = 294wh
294wh x .85 (inverter loss) /120v = 2h runtime

50ah @ 12.8v = 640wh
640wh x .85 / 120v =4.53h runtime

You be the judge of whether its enough or not.

Make sure you add up your other usage numbers too. Converting to watts and watt hours makes it easiest.

Click to expand...

Sorry, I don't understand how those run times are calculated with no specific load on the circuit.

DThames said:

Not sure how good these (Amazon) are.

Will review. edited...just watched that review again, not great but there are many battery options out there.

Click to expand...

These look super sketch hahah

DThames said:

Not sure how good these (Amazon) are.

Will review. edited...just watched that review again, not great but there are many battery options out there.

Click to expand...

I have one of these powering a gate, charged with what I believe is a 100 watt panel. I got tired of putting walmart lead acid batteries on it. It also powers a motion activated led light.

I think I'll go down and check out the voltage today but it is a low usage situation. After watching the review I'll never use them in anything but something like I'm doing.

Eviper21 said:

Sorry, I don't understand how those run times are calculated with no specific load on the circuit.

Click to expand...

Watt Hours is the run-time common denominator for comparing solar generators/ batteries, etc.. For a 500 Watt Hour battery/inverter system, you can run a 500 watt load for 1 hour or a 50 watt load for 10 hours, or any combination in between. In the real world batteries often only very loosely follow this.

Battery Hookup has 4 25amp cells for $59.00 will 8 fit in your case?

Link to the cells mentioned above.

I have 48 of these cells and they are fantastic. It seems like they are actually grade A cells, they stay PERFECTLY in balance. They are small, and can fit in just about any enclosure. For the price (especially considering that they are shipped quickly, domestically), they can't be beat.

Eviper21 said:

Sorry, I don't understand how those run times are calculated with no specific load on the circuit.

Click to expand...

Heh, you're right! That was nonsense what I wrote!

MisterSandals said:

23ah @12.8v = 294wh
294wh x .85 (inverter loss) /120v = 2h runtime

50ah @ 12.8v = 640wh
640wh x .85 / 120v =4.53h runtime

Click to expand...

This is just plain hideous, sorry. Without a load we can only compare 294Wh to 640Wh.