25 bucks

[mike3113]

Hello All
Unlike other threads I Pay for real advice.

I will send via Venmo 25 bucks to the first person who can answer this question.

I have 3
250 Watt solar panels that are tied in tandem and that i am using to maintain the charge on a 12 volt lead acid battery used to power a washer.

I have been told in need to place a "battery charge controller" between the solar panels and the battery to prevent over charging.

the question WHAT SIZE (charge controller) DO I NEED??

additional information on the panels I'm using.
max power --- 250 watt
open circut voltage --- 37.6 volts
voltage at pmax ---- 30.3 volts
short - circuit current --- 8.85 amps
current at Pmax --- 8.27 amps
max system voltage --- 600 volts
fuse rating --- 15 amps

 

[Porch]

3 x 250watts = 750 watts
3 x 8.27 = 24.81 amps.

So bigger then the above. I would go with a 12v controller rated for at least 30 amps or more.

 

[mike3113]

3 x 250watts = 750 watts
3 x 8.27 = 24.81 amps.

So bigger then the above. I would go with a 12v controller rated for at least 30 amps or more.

thanks any product recommendations you could make?

also send me a privet message so I can pay you for your advice

 

[rmaddy]

Save your $25. Go to the Victron MPPT calculator. Go to the custom panel tab and enter the specs for your panels and system voltage (12V). Try entering the panels in 3S and in 3P and see which size controllers it recommends. You don't need to buy a Victron controller but it will at least give you an idea on size.

MPPT Calculator - Victron Energy

MPPT Calculator - Victron Energy

www.victronenergy.com

But with those 3 panels in series I bet it recommends a 150/45 or 150/60. In parallel it probably recommends 100/50.

 

[rmaddy]

3 x 250watts = 750 watts
3 x 8.27 = 24.81 amps.

So bigger then the above. I would go with a 12v controller rated for at least 30 amps or more.

Too small. 750W / 12V = 62.5A. You want a controller rated for about 60A output battery current.

 

[mike3113]

Thanks will do

 

[Porch]

Too small. 750W / 12V = 62.5A. You want a controller rated for about 60A output battery current.

You are very correct. I made the incorrect assumption that if it was wired to a 12V battery, it was a 12V panel. Looks like he has a 24V panel wired to a 12V battery. I don't see that everyday. A proper MPPT controller is needed to correct the 2 issues he has.

 

[rmaddy]

You are very correct. I made the incorrect assumption that if it was wired to a 12V battery, it was a 12V panel. Looks like he has a 24V panel wired to a 12V battery. I don't see that everyday. A proper MPPT controller is needed to correct the 2 issues he has.

First, I'm assuming an MPPT controller. Second, in that case there really isn't any such thing as "12V" or "24V" panels. The Voc of the panel is what matters. The idea of "12V" and "24V" panels is just marketing and doesn't apply when using an MPPT controller.

Just to make it clear, I have a 24V battery. I have 3 panels in series each with a Voc of 42V. That's 126V going into my controller. But the controller's job is to convert that to the 24V of my battery at the appropriate amperage.

 

[Texas-Mark]

The idea of "12V" and "24V" panels is just marketing and doesn't apply when using an MPPT controller.

Not entirely true. A single 100W "12V" panel (or if in parallel) will not work well with a MPPT controller. And will not work with a 24V battery.

 

[rmaddy]

Not entirely true. A single 100W "12V" panel (or if in parallel) will not work well with a MPPT controller. And will not work with a 24V battery.

True. I didn't mention that in most cases you need a Voc at least 5V higher than system voltage for the MPPT to actually be able to charge a battery.

 

[Porch]

First, I'm assuming an MPPT controller. Second, in that case there really isn't any such thing as "12V" or "24V" panels. The Voc of the panel is what matters. The idea of "12V" and "24V" panels is just marketing and doesn't apply when using an MPPT controller.

Just to make it clear, I have a 24V battery. I have 3 panels in series each with a Voc of 42V. That's 126V going into my controller. But the controller's job is to convert that to the 24V of my battery at the appropriate amperage.

Correct-ish. It 12V panel will not work on a 24V battery bank even with MPPT, unless the MPPT can also boost up the voltage, and most can't.

The panel listed above, is designed to have a high enough voltage, at high wattage, to charge a 24v battery, using a simple PWM controller. That is why I called it a 24v panel. And why panels like it are listed as 24v in solar websites.

 

[HRTKD]

I'm going to put in a vote for rmaddy as the winner here. The context is three 250 watt panels, so 12v or 24v panels isn't germane to this discussion. It's relevant in a general sense, but it's becoming more and more a corner case as panels get bigger and bigger.