diy solar

diy solar

Need some advice on a potenial solar system

Ri_not

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Jun 17, 2022
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I'am in the starting phase of putting together a backup solar system. I have a 4000 watt pure sine wave inverter 12vdc input 120 vac out put. 6 100ah deepcycle gell batteries and 4 200 watt solar paels rated 12vdc , I have not put it together , Im looking for a good controler and not sure what amp I should use i was thing 100 amp controler. Any one have any advice.
 
4 200W panels is of course 800W. 800W / 13V is about 60A. So at most you need a 60A SCC. If you think you might add more solar later then you could start with a higher amperage controller or start with the 60A now and add a 2nd controller in the future if needed.

BTW - A 4000W 12V inverter is a bit much. That's up to 400A being pulled from the batteries. That will require some serious wiring and fusing. You really should be looking at 24V or 48V systems.
 
Second what RM says. Skip 12V and move up to 24 or 48V. With 600Ah at 12V, you need 60-80amps of charge to keep the batteries happy. That will require a more expensive charge controller than wiring the same six batteries to 24V. Then you only need 30-40A of charging current.

I can tell you from personal experience that higher voltage just works better. And you'll also save money on thinner copper wire that doesn't have to convey as many amps. It will also allow you at add more panels in the future, so expansion will be easier.
 
Guys thank you very good info, ill deep six the 12 volt and try to pick up a 24v,
 
Guys thank you very good info, ill deep six the 12 volt and try to pick up a 24v,
Do you already have the 12V batteries? Switching to 24V means little else than changing the wiring, 2S3P instead of 1S6P. In terms of off-grid batteries, there are many, many choices, including 2V, 4V, 6V, 8V, and 12V, which can all be wired in series. Only Li batteries controlled via a BMS need to stay in parallel.

Before you start buying stuff, you really should first conduct a power audit, and list out what it is you expect to power, and how many watts each item consumes, and for how long. We're glad to help.
 
Guys thank you very good info, ill deep six the 12 volt and try to pick up a 24v,
You'll need a new inverter but you can keep the batteries.

800W of solar on a 24V system means you only need a 30A SCC instead of 60A. But again, you might want a bigger SCC if you plan to add more solar in the future, or add a 2nd SCC when needed.
 
Good Morning Guys, I have another question, I will be using the 4 x 100 ah batteries , to feed a 24vdc inverter , I will put 2 of the battries in series and the other 2 in parrallel to obtain the required 24vdc for feed. Where would i hook up the charging wires coming from the SCC for best results? (being a Newbie want to get it right) The new inverter I will be getting is 3000 watt 24VDC to 120VAC. I figured a 200 amp inline fuse on the battery feed side. My Panels are rated at 4 x 200 watts at 12 VDC , will this lenghten the charge time on a 24vdc system?
 
I will be using the 4 x 100 ah batteries , to feed a 24vdc inverter
Your OP states you have 6 batteries. You can still use all 6 for a 24V setup. Wire them in 2S3P.

I will put 2 of the battries in series and the other 2 in parrallel to obtain the required 24vdc for feed.
Just to be clear, you take 2 and put them in series. You take 2 more and also put them in series. You then connect those two series pairs in parallel. This is 2S2P. It will give you a 24V 200Ah battery bank. Create 3 sets of series pairs and put all three pairs in parallel for 2S3P. This will use all 6 of your batteries and give you a 24V 300Ah battery bank.

Where would i hook up the charging wires coming from the SCC for best results?
Use bus bars. Connect the positive wire from first series pair to the positive bus bar. Connect the negative wire from the last series pair to the negative bus bar. Then you can connect the SCC and the inverter (and anything else) to the bus bars.

The new inverter I will be getting is 3000 watt 24VDC to 120VAC. I figured a 200 amp inline fuse on the battery feed side.
3000W / 24V / 85% = 150A. Wire for 150A (1AWG minimum, 1/0AWG better). Then use a 200A fuse for the main battery fuse between the battery and positive bus bar. BTW - why did you drop from a 4000W inverter to a 3000W inverter? Changing system voltage wouldn't change the size inverter you need.

My Panels are rated at 4 x 200 watts at 12 VDC , will this lenghten the charge time on a 24vdc system?
No since your battery bank is still the same amount of Wh. 6 x 12V x 100Ah = 7200Wh. That's true whether they are in 6P for a 12V system or 2S3P for s 24V system. Depending on the SCC you get you will want the 4 panels in either 2S2P or 4S. A 30A controller will easily handle the 800W on a 24V system.
 
Hey Rmaddy,
Been working all day, The reason i ent to a smaller inverter is the 4000 one I have only feeds with 12 VDC not auto switching, so Now I have the brand new 4000 w 12 vdc I will sell it at help pay for the 3000 w 24 vdc inverter. My wife thinks I'm nuts , just another project
 
I should have been more clear. If you needed a 4000W inverter before, why do you only need a 3000W inverter now? Changing system voltage doesn't change the amount of watts you need in your inverter. So either you should have started with a 12V 3000W inverter (which is doable) or you should be getting a 24V 4000W inverter.
 
No Worries , You have been incredably helpfull , I'm sure I will have more questions
 
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