Solar Panels Dual Use

[fw12]

I have four 300W solar panels for charging my battery bank.

I am thinking of getting a DC pump, which also requires about 1200W to run.

Is it possible to use the same four solar panels for both purposes? By that I mean to charge the battery, and run the pump.

Maybe there is a way to switch between each use. If so, how?

The pump will only need to run for about 1 hour daily. After that, the battery can be charged the rest of the day.

[J.P.M.]

For starters, 1,200 STC W of solar panels will not produce 1,200 W most all of the time. About the best you can expect under ideal conditions is maybe 900 - 1,000 W. Then, if they have not been taken into account in the 1,200 W the motor requires, and also not considering starting requirements, there are P.F. losses in the motor .

[fw12]

Fore starters, 1,200 STC W of solar panels will not produce 1,200 W most all of the time. About the best you can expect under ideal conditions is maybe 900 - 1,000 W. Then, if they have not been taken into account in the 1,200 W the motor requires, and also not considering starting requirements, there are P.F. losses in the motor .

That is true. But that is not a problem here.

[azdave]

There is plenty you have not told us yet to make a better suggestion but for starters, why would you not wire the pump to the battery bank and put the pump on a timer to run 1 hour per day? When the pump is not running, the panels would charge the batteries. When the pump is running, the batteries would assist the pump if the panels don't quite produce enough energy for the pump alone.

[fw12]

There is plenty you have not told us yet to make a better suggestion but for starters, why would you not wire the pump to the battery bank and put the pump on a timer to run 1 hour per day? When the pump is not running, the panels would charge the batteries. When the pump is running, the batteries would assist the pump if the panels don't quite produce enough energy for the pump alone.

Good idea. But the last time I did that, the battery died a premature death.
As you know, pumps pull a lot of amps on start up. Sometimes up to 5x the running amp. That means you have to oversize your battery bank by a lot, just to run a pump.

Currently, I connect the pump directly to the solar panels. No battery required. That saves me a lot of money.

[fw12]

I have come up with something I believe will work, as the diagram shows.
solar-panel-dual-use.png
The key are the Timers. They will be configured to run at mutually exclusive times.

[SunEagle]

I have come up with something I believe will work, as the diagram shows.
solar-panel-dual-use.png
The key are the Timers. They will be configured to run at mutually exclusive times.

I would make sure the contacts on those timers are rated for the DC amp currents going through them and that they have the ability to open under load. If not then you can melt those contacts via high DC currents or from arching when they open.

[Ampster]

......... That means you have to oversize your battery bank by a lot, just to run a pump.

It depends on the batteries. Many Lithium chemistries can handle short surges of 5 times their Amphour rating.

Currently, I connect the pump directly to the solar panels. No battery required. That saves me a lot of money.

I am glad that has worked for you. I did not realize you already had the pump. Solar panels do not handle surge so you may want to explain what kind of pump you have so that other readers can expect the exact same results. There are pumps that are soft start and perhaps that is what you purchased.

[fw12]

It depends on the batteries. Many Lithium chemistries can handle short surges of 5 times their Amphour rating.

Yep. You can get any battery if you're prepared to spend the money. Batteries generally are not cheap.

Solar panels do not handle surge so you may want to explain what kind of pump you have so that other readers can expect the exact same results. There are pumps that are soft start and perhaps that is what you purchased.

https://www.aliexpress.com/item/4000738115260.html

It's a DC pump. Pumps 800 gallons per Hour from 400ft borehole.
Power: 850W. I run it with 4x 300W solar panels.
It has built-in controller, maybe also soft start capacitor. So you just connect the solar panels directly.

I bought one before which lasted 2yrs. I hope the tech has improved now. I think it died because someone ran it dry. We're being more careful this time.

[fw12]

I would make sure the contacts on those timers are rated for the DC amp currents going through them and that they have the ability to open under load. If not then you can melt those contacts via high DC currents or from arching when they open.

I was told they measured about 77V.
Assuming the upper limit of 1,200W.
1200/77 = 16A.

I'll keep it in mind to get a timer designed for such amp draw.

[SunEagle]

I was told they measured about 77V.
Assuming the upper limit of 1,200W.
1200/77 = 16A.

I'll keep it in mind to get a timer designed for such amp draw.

Most relays only have contacts rated for 10amps along with not being able to clear a DC arc. Just make sure you look at the specifications of the relay before you purchase it.