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Charge Controller Help Needed

Huffman38

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Nov 18, 2021
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I have three 300 watt / 44 volt panels that I would like to install on pre existing 12 volt system. I've been trying to figure out what size of charge controller that's required.
I have found a few online calculators but everyone makes me doubt the other. Hooking them up in series makes sense to me to keep the voltage down but I may be wrong. Would a 150/60 charge controller work the best?
Any suggestions would be great. Thanks.
 
in series you add the voltage, in parallel you add the amperage. So hooking them up in series increases the voltage and keeps the amperage down.

Post the full specs for the panels.

Do note that 3 300W panels is 900W. On a 12V system that would be about 75A max output to the battery. Choosing a 60A controller would limit you to about 800W or so depending on the current battery voltage.

Let's assume for the moment that the 44V you posted is the Voc of the panels. In series that would be 3 x 44V = 132V. But Voc goes up in the cold. Depending on where you are the Voc could get to be a bit over 150V in very cold conditions. You never want to exceed the max input voltage of a charge controller.

Since you mention a 150/60 charge controller, that sounds like a Victron designation. You might want to play around with their MPPT calculator. It allows you to enter the specs and configuration of your own custom panels. You can enter a temperature range as well. It will then show the best matching charge controller. When entering temperatures, enter absolute min and max temps, not typical temps.

 
in series you add the voltage, in parallel you add the amperage. So hooking them up in series increases the voltage and keeps the amperage down.

Post the full specs for the panels.

Do note that 3 300W panels is 900W. On a 12V system that would be about 75A max output to the battery. Choosing a 60A controller would limit you to about 800W or so depending on the current battery voltage.

Let's assume for the moment that the 44V you posted is the Voc of the panels. In series that would be 3 x 44V = 132V. But Voc goes up in the cold. Depending on where you are the Voc could get to be a bit over 150V in very cold conditions. You never want to exceed the max input voltage of a charge controller.

Since you mention a 150/60 charge controller, that sounds like a Victron designation. You might want to play around with their MPPT calculator. It allows you to enter the specs and configuration of your own custom panels. You can enter a temperature range as well. It will then show the best matching charge controller. When entering temperatures, enter absolute min and max temps, not typical temps.

Thanks for the info. I only mentioned the Victron number because I’m a newb lol. Definitely not brand loyal at all.

Do you want to have a high amperage vs a high voltage? Of course I’d like to use the three panels but if it makes sense to use only two, I’m fine with that.

Here’s the label off of a panel.
 

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You could put the panels in parallel and easily use all 3. With a Voc of 44.6V and a 12V system you have plenty of voltage, even in parallel, to charge the batteries.

Even if you don't plan to buy a Victron controller, their MPPT calculator will still give you a good idea of what works and what doesn't. Make sure you lookup the real voltage temperature coefficient from the spec sheet for your panel so you can determine the real max Voc you will see for your temperatures.
 
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The possible issue might be how far the panels are from the charger .... there is abit of loss in cable runs. 300' of double ought cable from the panels probably cost more than the panels and charger
 
Sorry to ask a side question.

@rmaddy Are you finding your solar is enough for your needs year round? (and what do you power?)
 
You could put the panels in parallel and easily use all 3. With a Voc of 44.6V and a 12V system you have plenty of voltage, even in parallel, to charge the batteries.

Even if you don't plan to buy a Victron controller, their MPPT calculator will still give you a good idea of what works and what doesn't. Make sure you lookup the real voltage temperature coefficient from the spec sheet for your panel so you can determine the real mas Voc you will see for your temperatures.
I will have a look at their calculator, thanks again.
 
Use a string calculator like this one. https://www.midnitesolar.com/sizingTool/index.php
With three of these panels in series, you'll hit 150Voc at about 10 degreesF. One cold morning, and your system is fried! Don't buy a controller with a 150V limit. Buy one with a 200V limit.
1637510726187.png

In terms of amperage, 60A will most likely meet your needs. The system only makes 900W in a test chamber, in the real-world it is most likely only 85% of that value. So, in real sun, expect (900W/13V charging) X 0.85 (85%) = 59A. On those rare occasions that the panels put out more, the peak just gets clipped off. Exceeding voltage is far more important in your system design then exceeding amperage.
 
Use a string calculator like this one. https://www.midnitesolar.com/sizingTool/index.php
With three of these panels in series, you'll hit 150Voc at about 10 degreesF. One cold morning, and your system is fried! Don't buy a controller with a 150V limit. Buy one with a 200V limit.
View attachment 73085

In terms of amperage, 60A will most likely meet your needs. The system only makes 900W in a test chamber, in the real-world it is most likely only 85% of that value. So, in real sun, expect (900W/13V charging) X 0.85 (85%) = 59A. On those rare occasions that the panels put out more, the peak just gets clipped off. Exceeding voltage is far more important in your system design then exceeding amperage.
So according to this calculator, if I chose to put them in parallel I'd see 52 volts at -30c (-22f) and 62.5 amps. Would this setup be better?
 
What are these panels on - an RV, shed, etc. How long of a wire run (approx) from the panels to the SCC(solar charge controller) and from SCC to the batteries.

If on an RV - I would use parallel ( more shading issues from trees, etc.) if on a shed (and no trees) - then probably serial connections. (If you can afford the SCC).
 
Here are my quick picks.
If you can change battery to 24v - that would be better - but I am assuming on an RV so 12v battery.

(I use Victron and really love it - but there are cheaper items out there).

Cheapest - panels parallel use a mppt 100/50. Anything over 700 watts (50 amps) will be clipped. However, flat panels on an RV - most of the time you will not get there. Only clear summer - noon-ish with lower batteries- if all these line up - the batteries will probably get filled anyway - even with the clipping of the watts. However having lots of panels will help produce more power when conditions are not ideal.

Most power parallel- use a mppt 150/60 this can handle 860watts. So in ideal conditions you get more power. (The couple of times you could get more than 860watts would not be worth the money to move up to a 150/70).

Most power serial - use a 200/60. (Probably the most expensive option). Don’t use serial on an RV. Some shade (trees) on one panel will hurt the entire array. If you are on a shed or ground mount and the distance from the panels to the SCC is longer - then this will probably be better.

On the Victron data sheet there is a line that gives nominal power @ 12v. Also - could you add a fourth panel - might you ever want to… that could also affect your decision.
 
What are these panels on - an RV, shed, etc. How long of a wire run (approx) from the panels to the SCC(solar charge controller) and from SCC to the batteries.

If on an RV - I would use parallel ( more shading issues from trees, etc.) if on a shed (and no trees) - then probably serial connections. (If you can afford the SCC).
Here are my quick picks.
If you can change battery to 24v - that would be better - but I am assuming on an RV so 12v battery.

(I use Victron and really love it - but there are cheaper items out there).

Cheapest - panels parallel use a mppt 100/50. Anything over 700 watts (50 amps) will be clipped. However, flat panels on an RV - most of the time you will not get there. Only clear summer - noon-ish with lower batteries- if all these line up - the batteries will probably get filled anyway - even with the clipping of the watts. However having lots of panels will help produce more power when conditions are not ideal.

Most power parallel- use a mppt 150/60 this can handle 860watts. So in ideal conditions you get more power. (The couple of times you could get more than 860watts would not be worth the money to move up to a 150/70).

Most power serial - use a 200/60. (Probably the most expensive option). Don’t use serial on an RV. Some shade (trees) on one panel will hurt the entire array. If you are on a shed or ground mount and the distance from the panels to the SCC is longer - then this will probably be better.

On the Victron data sheet there is a line that gives nominal power @ 12v. Also - could you add a fourth panel - might you ever want to… that could also affect your decision.
The panels are going on a remote camp already wired for 12 volt with no shading at all. So I'd rather not switch to 24 volt. The run to the SCC is roughly 35-40 feet. Cabling was overkill so I'm not concerned about that.

I was thinking about a parallel set up and using the 150/70 but wanted to make sure it would be worth it. Also, only 3 panels for now.
 
Yes the 150/70 would be just fine. With three panels in parallel you will need to fuse each panel (string).

Two more options - if it works (space wise and financially). If you had four panels in a 2s2p (2 in series and 2 in parallel), you could avoid fusing each string - you could even use the same 150/70 SCC (you would just have some clipping during peak - but more power during non-peak.

Second option - get a 24 to 12v converter (keep the cabin on 12v), change the batteries to 24v (put two 12v in series). Then you could use the cheaper 100/50 SCC (with 3p panels).

Have fun with your project!
 
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