Cheap China Solar Controller Failure

Posted By: MrWizard on 01/04/15 10:03am

I see miss conceptions and statements being repeated

"Heat screws with MPPT"....Wrong
Heat screws with panel voltage, if the voltage is low there is no excess voltage to use to create extra amps
You don't loose anything , you just don't get anything extra

EXAMPLE
Voc 22, working voltage 17.2 , isc 4.6 technically that's 78.2 watts
But with PWM you will be lucky to get 14.4v at 4.6a for 66 watts
And that's tilted tracking the sun, with batteries or load that will accept it, ( remember this is one panel in a bank, unless you have one panel and one battery )
You lose 12 watts, MPPT will recover some of that lost power

Now if the panels are hot and the voltage is down to 16v, max output is down to 73.6 watts,
PWM will still give 66 watts, MPPT will try to recover the other 7 watts, but there is less extra over head VOLTS aka lost watts, to recover

The hotter the panels the lower the voltage the less over head to recover

Heat "HITS" The panels Not the controller

I'll tell you from experience where MPPT really shines , is on days that start out over cast then clear up
Peak Sun on cool panels with low batteries
Panels are putting out peak power, Batteries absorb at a lower voltage and MPPT can take all the volts above absorption level and create extra amps, something PWM can not do

MPPT makes amps out of volts, not amps out of amps
Remember amps*volts is watts, because the panels operational voltage is higher than the voltage needed to charge batteries, the difference is lost excess over head when using PWM
Yes cost wise sometimes it just easier and cheaper to buy an extra panel for PWM, depends on the size of the array the operational voltage and roof real estate

* This post was edited 01/04/15 10:34am by MrWizard *