Is there any reason to NOT over rate an MPPT

garynappi

I'm running a 12 volt system and I've had some issues with the PWM CC I bought and I am now looking to replace it.

At this point in time I really only "need" a 20 amp CC but considering the possibility of future upgrades / expansion (not grid tie) is there any downside / reason to not get a 40 amp model up front?

I'm looking at Epever MPPT controllers and the difference between the 20, 30 and 40a versions is not so wide as to make not needing to upgrade the CC at a later date less expensive. 

BB.

Larger MPPT controllers tend to take a bit more power to operate... See if you can find an efficiency curve vs current... If you have a reasonably sized array (closer to 50% of controller capacity vs 10%), it should not be a big issue.

-Bill

jonr

A typical MPPT charge controller will be slightly more efficient at 30-50% of capacity than anything near 100%.

Estragon

... and may run cooler under lighter load, generally a Good Thing for all things electronic.

fratermus

Estragon said:

... and may run cooler under lighter load

Isn't heat under light load more a function of PWM switching? 

fratermus

garynappi said:

I'm looking at Epever MPPT controllers and the difference between the 20, 30 and 40a versions is not so wide

Depending on the type of epever controller (A, B, whatever) the physical size differential can be surprising.  Check your available space against the actual size of the larger one to make sure it will fit where you want it to go.

mountainman

The epever specs 12ma self consumption on all the an controllers.

mountainman

Agreed on most efficient at 50℅ vs 100℅. also the highest voltage array is less efficient.  this a 3210 an

boB

At least those Chinese MPPT controllers are cheap enough that you can buy an extra or two in case overloading one should harm it.

What it will do when over PV'd is to run warmer because when it current limits its output to the battery, the input voltage will rise higher than normal.  But on cloudy days, you should benefit from the nameplate over-rating of the PV input.

mountainman

I've been using a 3210 an for 2 years now. 
On heavy  over cast days a 380 watt array 
Mt 50 shows 7 watts 14 volts .5 amps. 
On my 400 watt pwm on the same day I'm seeing~ 75 watts.
In my opinion these controllers are not a good choice for over paneling for more out put on over cast days.
When in full sun or light clouds seems to work fine. Slightly more power from 380 watts than 400 on pwm.

mcgivor

mountainman said:

I've been using a 3210 an for 2 years now. 
On heavy  over cast days a 380 watt array 
Mt 50 shows 7 watts 14 volts .5 amps. 
On my 400 watt pwm on the same day I'm seeing~ 75 watts.
In my opinion these controllers are not a good choice for over paneling for more out put on over cast days.
When in full sun or light clouds seems to work fine. Slightly more power from 380 watts than 400 on pwm.

You're chasing your tail, depending on temperature PWM may in fact produce more than MPPT, don't get caught up in minor discrepancies, you'll drive yourself crazy, each has its own set of advantages and disadvantages it is what it is.