Greetings from MD

[lucasd05]

Hi! I've been monitoring the forum for a while, but I figured I might as well join since my projects are beginning to manifest in physical forms instead of just existing as lots of spreadsheets. I've done hobby electronics and household electrical work for many years, so I'm not a total noob with project planning, but I've yet to build a full scale power system.

I live in Maryland. (Within a decent driving distance of the batteryhookup.com warehouse, oddly enough.) My current project is an old 1977 Dodge RV I've been restoring. I've got 1500w of solar panels for the project, an mppt charger, and I'm debating what size and type of battery bank to go with for it.

I'm currently undecided between the savings involved with using salvaged 18650 cells and the far less manual labor involved with just grabbing some of the currently available spim08hp 7s3p units that are available on batteryhookup, throwing a 7s BMS on each pack, and calling it good.

I'm planning for a 24v battery system, so I suppose I could just grab four lead acid 6v Costco golf cart batteries and call it a day, but that feels like accepting defeat. I would know there are better solutions... and it would haunt my dreams. lol

 

[floydR]

welcome
For a RV I would go with LiFePo4. The SAB 60280 cells are good but bulky. 20Ah LiFePo4 pouch cells from Battery clearing house are another option. Unfortunately neither are available in a prebuilt battery.
Later floyd

 

[italianuser]

Welcome Lucas! Nice project. I have a similar panel capacity (6x280W) and I'm going for a 4x 44Ah batteries (second hand 18650). The manual of the Inverter (inverter includes MPPT controller, charger and inverter) suggest at least 200Ah 48V battery. Considering the 5/5.5 hours of sun a day a 180-220Ah battery does make sense. Do create a new post with the project details!

 

[lucasd05]

welcome
For a RV I would go with LiFePo4. The SAB 60280 cells are good but bulky. 20Ah LiFePo4 pouch cells from Battery clearing house are another option. Unfortunately neither are available in a prebuilt battery.

Thanks for the welcome and the suggestions. You're right, those 20ah LiFePo4 pouches are decently priced, assuming they are in good condition. They may not be available as a prebuilt unit, but they do have nice big tabs on them, so they don't look too bad to work with. The folks over on endless-sphere.com seem to have been using that style of battery for years and have a ton of design examples.

They're going on my list to consider. Being LiFePo4 chemistry is definitely a plus. The shipping's not even too bad for those.

 

[lucasd05]

Welcome Lucas! Nice project. I have a similar panel capacity (6x280W) and I'm going for a 4x 44Ah batteries (second hand 18650). The manual of the Inverter (inverter includes MPPT controller, charger and inverter) suggest at least 200Ah 48V battery. Considering the 5/5.5 hours of sun a day a 180-220Ah battery does make sense. Do create a new post with the project details!

Thanks for the welcome, and yeah, sounds like a similar size project. When you say that your inverter recommends a 200ah 48v battery, is that a total bank size recommendation based on a lead acid safe depth of discharge limit? Or is it saying you should size your bank to have 9.6kWh of actual available capacity? Just curious, since a recommendation based on the total label rating of your bank would be completely different depending on the chemistry you're using.

 

[italianuser]

Thanks for the welcome, and yeah, sounds like a similar size project. When you say that your inverter recommends a 200ah 48v battery, is that a total bank size recommendation based on a lead acid safe depth of discharge limit? Or is it saying you should size your bank to have 9.6kWh of actual available capacity? Just curious, since a recommendation based on the total label rating of your bank would be completely different depending on the chemistry you're using.

That's the recommanded nominal battery spec for my model (it's a 5KW offgrid inverter). Battery type is programmable and for lithium you can set all parameters. It should work with smaller batteries, too, maybe if you just want to switch it on. But the reason for that (big) battery size is also for the power inverter needs to run (manual says <55W with no load, which is quite a bit).

 

[lucasd05]

That's the recommanded nominal battery spec for my model (it's a 5KW offgrid inverter). Battery type is programmable and for lithium you can set all parameters. It should work with smaller batteries, too, maybe if you just want to switch it on. But the reason for that (big) battery size is also for the power inverter needs to run (manual says <55W with no load, which is quite a bit).

Ok, makes sense. That is a sizable idle consumption. I have a little 1500w (3000w peak) inverter, but I'm only looking at a handful of AC appliances. As long as the fridge runs, the rest is gravy. Water, heat, and lights all run off DC directly.