Wiring a small solar battery bank

[melvin2345]

I have everything I need to install a solar system for my garage. Harbor Freight 45 watt kit, 3 12v 35AH batteries (in parallel) and a 750 watt inverter. I don't need to power much out there, just some lights and a radio mostly, with the occasional charger for the cordless tools. My question is on the best way to wire the charge controller and inverter to the battery bank.



Which of the above methods is the correct way to wire things up?

[Naptown]

Actually none of the above.
That harbor freight is only capable of supporting one of those batteries not three.
If you need 105AH of battery buy one battery. Batteries in parallel are never a good idea and will die in a short time. In your case shorter due to low charge current. You need another kit to maintain those batteries at minimum.
But to answer you directly D would be correct with fuses on both the charge controller and inverter. On both + and- terminals

[PNjunction]

Don't feel bad - nearly all new HF solar users grossly oversize the battery and undersize the panels. In addition, instead of a 750 watt inverter which will be grossly inefficient when just charging up small stuff, a 75 watt inverter would be more appropriate and more efficient.

Consider that a 45 watt HF panel puts out 2.5a under the very best of conditions. If you ran with only ONE of those batteries, and withdrew 50%, say 17.5ah from it, at 2.5a charge that would take 7 hours of charging just to reach absorb. Add an additional 3 hours to finish the absorb, and you are looking at 10 hours, which no place on earth has that much solar-insolation in one day since these hours differ a LOT from mere sunrise-to-sunset hours depending your location.

For now, just run with only one of those batteries. The other two can be kept as spares, say to hot-swap out when the weather is bad. Perhaps keep them alive by putting them on a small charger like a 6-amp Stanley BC-6809 one every 2 months or so.

In the meantime, check out the stickies in the forums to optimize what you have even further.

[SunEagle]

As PNjunction stated most people see those kits from HF and think this is the perfect system to learn about solar. Unfortunately those panels produce very little for the cost and won't keep their battieris properly charged.

My son in law bought one of those kits and it didn't perform anywhere near what he expected. I told him to return it for a credit. I sold him a 100 watt panel that I had as a spare. He installed it and is very happy with the performance of one panel as compared to the 3 that came with the HF system.

[PNjunction]

Those HF kits are everywhere. Thing is, you CAN learn from them, no doubt they function, (I have one for small needs) but the smart ones will visit the stickies and do the math to see what they can support in the real world.

The biggest mistake is oversizing the battery, underestimating your power load over time, and not taking into account solar-insolation hours for recharging, which differ from sunrise-to-sunset hours - see an online chart for your area and use the winter-hours if possible. Do that, and they work fine! Although the first thing one learns is that they probably want a *system* 3 times as big (and not just tripling the battery capacity!) .....

[melvin2345]

So, after reading a bunch over the last few days, I grabbed the receipt for the HF kit and HF 750/1500 inverter and headed back to the store. Both were unopened so I had no issues getting a refund.

I then got off Amazon:
2 70 watt panels (Vmp 18V, Imp 3.89A, Isc 4.18A, Voc 22V)
Sunsaver 10L with LVD
Wagan EL2601 Elite 400W Pro Pure Sine Inverter - Probably don't need pure sine, but it's a personal preference thing

I also decided to use a bus bar for hooking up the batteries. And to address a concern posted above, I'm using these 3 batteries instead of 1 because I got them brand new and free! That fits into my budget quite nicely, hehe.

Here is the "power center" I have started.



The Sunsaver will mount on the vertical face of the top shelf, and the inverter will go on top. I used 19" 4awg wires for the battery connections, and have the same for the inverter. I have 12awg wire and a 15A fuse for the run from the controller to the battery bank. The rest of the stuff should get here by the weekend or sooner, so I'll post more as I get things up and running. Assuming I don't find a way to blow myself up or start a fire anyway

[PNjunction]

The first thing I see here is that it lacks any sort of FUSE. Don't be in so much of a rush that you overlook safety. Many good threads on fusing here.

Still too much battery. Pull one. Those UPS-style agm batteries will typically handle a max of 0.25C current. Charge each one individually with your system at first to try and get a full charge for balance, and THEN put two in parallel at most. Keep the 3rd one on the shelf (after charging, and topped off every 3 months or so) for another project.

Make sure those are AGM batteries and NOT gel. For a Morningstar, the "flooded" setting/jumper is closer to what you want with agm. Sealed on a morningstar is usually meant for gel.

Critically, we don't know where you are located, and thus have no idea of your solar-insolation hours. These differ from sunrise-to-sunset hours, so this whole project could be a complete waste of time and resources.

You'll be wanting to pick up a DECENT quality voltmeter at least for agm battery maintenance. Look up the agm static battery voltages (at least 4 hours of rest with no charge / no load) to get a ballpark figure of what their SOC is.

You are on your way. Without knowing your load and solar-insolation hours, nothing here is optimal, but it will be fun nevertheless. Winging it here means keeping the wallet open.