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Old 03-28-2011, 02:44 PM   #57
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Location: Palm Springs, CA.
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Originally Posted by JeffinTD View Post
From what I've learned so far, there isn't much doubt that MPPT generates more amps of charge, especially when battery voltage is low, and the panel voltage is high (Lots of sun, low temp).

The point HandyBob made for me is to question whether spending the $ for MPPT is where you get the most bang for the buck in improving system performance.

The difference between a Tristar 45 amp PWM controller VS the same controller with MPPT is $270.

I'd like to see a comparison between systems with the PWM and the MPPT charge controllers, but not with the same solar panels. Test them with the PWM running panels worth $270 more than the panels hooked to the MPPT.

That would be the comparison I think might be most telling.

Direct comparisons are pretty tough, though. I was looking at a pair of 220 watt panels, and found 36 v panels at about $200 cheaper than 17 v-max power panels in that power range. Of course the 36v's would require a MPPT controller, and would offset all but $70 in the difference in the price of the MPPT controller. Still, that is a comparison of brand panels vs house branded...
Hey Jeffin TD or anyone else,

Why would an MPPT controler be required for (2) 220w 36v panels? I'm studying to put solar (2) 230 or 240w 30 to 36v panels on our coach and don't understand the MPPT over a PWM like the Tristar 45 or 60. The PWM have a max. solar VOC of 125volts. Why wouldn't they work??

Regards, Hamshog

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Old 03-28-2011, 03:44 PM   #58
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Location: The Dalles, Oregon
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From my understanding the PWM will basically reduce the voltage to what is required for battery charging, but doesn't change the current (amps).

For example, if you had 440 watts at 30 volts from your panels, you would have about 14 amps current coming in from the solar panels. The charger, though, would cut volts down to say 14.8 volts at the same 14 amps, or about 207 watts at the battery.

An MPPT charger, though, can reduce the voltage and increase charging current. In other words, with 440 watts of 30 volt panels, you might see 29+ amps at 14.8 volts at the battery.

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