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Old 04-20-2018, 10:29 PM   #1
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Solar panel voltage through MPPT

Iím trying to wrap my head around all this information

Letís say I have 3 240 watt panels (24 volt) hooked to a MPPT charger to my 12 volt battery bank

Am I possibly getting the 720 Watts at 24 volts = 30 Amps to my 12 volt batteries

Or am I possibly getting the 720 Watts at 12 volts = 60 amps to my 12 volt batteries thanks to the MPPT?

Currently I just have 3 100 watt 12 volt panels so max around 25 amps

Just trying to determine if future upgrades to 24 volt higher wattage panels is worth it with a MPPT charge control capable of 60 amps charge rate
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Old 04-20-2018, 11:32 PM   #2
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Quote:
Originally Posted by Mgulley82 View Post
Iím trying to wrap my head around all this information

Letís say I have 3 240 watt panels (24 volt) hooked to a MPPT charger to my 12 volt battery bank

Am I possibly getting the 720 Watts at 24 volts = 30 Amps to my 12 volt batteries

Or am I possibly getting the 720 Watts at 12 volts = 60 amps to my 12 volt batteries thanks to the MPPT?

Currently I just have 3 100 watt 12 volt panels so max around 25 amps

Just trying to determine if future upgrades to 24 volt higher wattage panels is worth it with a MPPT charge control capable of 60 amps charge rate
The panel voltage is not relevant to anything once you are talking watts, the V vs A relationship is transparently handled by the MPPT, treat it as a black box, just look at the SC's charging output.

So 240W x3 =720W

Ignoring all the variables, in theory that's ~50A at 12V charging voltage of 14.5V for example,

vs well under 20A from your current setup

but in practice total output will usually be much lower.

The extra MPPT efficiencies means it will get closer to the 50A more often.
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Old 04-22-2018, 02:22 PM   #3
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Quote:
Originally Posted by Mgulley82 View Post
Iím trying to wrap my head around all this information

Letís say I have 3 240 watt panels (24 volt) hooked to a MPPT charger to my 12 volt battery bank

Am I possibly getting the 720 Watts at 24 volts = 30 Amps to my 12 volt batteries

Or am I possibly getting the 720 Watts at 12 volts = 60 amps to my 12 volt batteries thanks to the MPPT?

Currently I just have 3 100 watt 12 volt panels so max around 25 amps

Just trying to determine if future upgrades to 24 volt higher wattage panels is worth it with a MPPT charge control capable of 60 amps charge rate
From a video I've watched a few times the MPPT can take your panel voltage and drop it to a lower charging voltage your batteries can accept. It takes this ratio for the drop and applies it to the amperage so your wattage remains the same so it's much higher amp going to the battery than coming from the panel.

Basic math example (won't see these numbers in real world)

100W panel is 12v with 8.333 amps:
There would be no conversion needed as the voltage is already the same as the batteries so each panel would be providing 8.33amps to the battery bank.

100W panel is 24v with 4.167 amps:
A PWM would have to drop the 24v to 12v but that's all it would do so you would get 12v x 4.167amp = 50W from your 100W panel.
An MPPT would have to convert the 24v down to 12v to match the battery bank, this would be a ratio of 24v / 12v = 2. This ratio is multiplied by the incoming amps, so 2 x 4.167 = 8.333 amps. This with the voltage would yield 12v x 8.33amps = 100W from your 100W panel.

The Charge Controller rating is based on incoming amp (from what I understand, please correct me if I'm wrong). The first, running a PWM would need to be rated for at least the 8.33amp so to make it simple would be a 10A charge controller. A PWM for the second example would only have to be rated for the 4.167 but as shown you lose 50% of your power. Having a higher rated PWM doesn't help anything in this case. An MPPT in the second one would be to be rated for 4.167 but you would get the yield of the full 100W your panel is producing.

Hope this helps some for why MPPT is better if your battery bank and panels don't match with voltage rating.

Again, feel free to correct me if I'm wrong. This is what I've gathered from the video.

(source: )
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Old 04-22-2018, 02:34 PM   #4
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That advantage is from their DCDC conversion.

The MPP itself also gives greater efficiency even with 12V nominal panels, which by the way are usually rated 18-21V

And 12V lead batteries require 14+V for charging, sometimes even 14.8 or higher.
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