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"Outback" MPPT solar power controller 60A - $525  on Craigs list.  I have 30Amps worth of Solar Panels is it okay to oversize the controller?

Rob at January 10, 2014 at 1:44 PM

"Outback" MPPT solar power controller 60A - $525  on Craigs list.  I have 30Amps worth of Solar Panels is it okay to oversize the controller?

Yes as long as the Voc of the array doesn't exceed the CC's max voltage limit. You can buy a new FM60 for $515.  http://www.solar-electric.com/oupofl60mpso.html     Is it new or used?

She said she never installed it. She has three 135w Panels she watns to sell too. She is asking like $325 for those, but I think that's a bit too much.

You'll get a 5 year warrantee with a new one.  I just sent back a 2 year old unit as it had a software glitch and they sent me a new replacement before I sent it back. They stand behind their warrantee 100%. I don't know if you'd get a warrantee with this unit you're looking at.

Good point....... 

Conext XW MPPT 60 Amp Solar Charge Controller is only $480 on that site.

I wonder how much shipping would be?  I better give them a call.

Maybe I'm nuts,but I can't see it.For $500 I can buy another 400 watts of panels.The test results I've read  are nowhere near the advertised output for MPPT controllers.Some as low as 7% gain.Maybe I'm just a crotchety old cynic.

The controllers can do more than just act as linear current boosters, they also can accept a wide range of voltage in and put out whatever you may specify...say 60 volts in, 12 volts out...

That said, I have a simple Solar Boost 50...I bought it when the company was RV Power Products for $149...

bulletbob at January 11, 2014 at 2:37 PM

Maybe I'm nuts,but I can't see it.For $500 I can buy another 400 watts of panels.The test results I've read  are nowhere near the advertised output for MPPT controllers.Some as low as 7% gain.Maybe I'm just a crotchety old cynic.

A valid point. I have a single 215 watt panel I use with my camper. It puts out 18.4 volts at maximum power and 11.5 amps. I use an el-cheapo PWM controller with it. I get 10 amps out of the controller into the battery with full sun. Not too bad. At best I could get another 10-15% with a MPPT controller. Now my leads are very short and the panel voltage is a good match for a 12 volt battery. Now if I took one of my 315 watt , 35 [email protected] amps, panels and used it with this controller I'd get maybe 2 amps at 12 volts. But if I used a MPPT controller with the one 315 watt panel I'd get +20 [email protected] volts out. The PWM needs to have the panel output voltage close to the battery voltage to work well. Very few panels made anymore that are designed for a 12 volt system. The higher the voltages one can output from an array the smaller the wire gets and the distances one can put the panels from the charge controller increase dramatically.

Rob at January 10, 2014 at 7:07 PM

Conext XW MPPT 60 Amp Solar Charge Controller is only $480 on that site.

I wonder how much shipping would be?  I better give them a call.

I'd pick the Outback FM60 for the extra $35.

snuffy at January 11, 2014 at 3:11 PM

bulletbob at January 11, 2014 at 2:37 PM

Maybe I'm nuts,but I can't see it.For $500 I can buy another 400 watts of panels.The test results I've read  are nowhere near the advertised output for MPPT controllers.Some as low as 7% gain.Maybe I'm just a crotchety old cynic.

A valid point. I have a single 215 watt panel I use with my camper. It puts out 18.4 volts at maximum power and 11.5 amps. I use an el-cheapo PWM controller with it. I get 10 amps out of the controller into the battery with full sun. Not too bad. At best I could get another 10-15% with a MPPT controller. Now my leads are very short and the panel voltage is a good match for a 12 volt battery. Now if I took one of my 315 watt , 35 [email protected] amps, panels and used it with this controller I'd get maybe 2 amps at 12 volts. But if I used a MPPT controller with the one 315 watt panel I'd get +20 [email protected] volts out. The PWM needs to have the panel output voltage close to the battery voltage to work well. Very few panels made anymore that are designed for a 12 volt system. The higher the voltages one can output from an array the smaller the wire gets and the distances one can put the panels from the charge controller increase dramatically.

Correction; I would get about 7 amps out of the 315 watt panel with the PWM  CC. However the PWM clips off only 14 volts from the 39 volt potential of the panel ( the current stays nearly the same).  7amps times 14 volts = 98 watts. Kind of a waste of a 315 watt panel. A MPPT CC would operate the panel at it's maximum power point  39 volts so I'd get over 20 amps output from the MPPT at 14 volts.  315/14=22.5 @ 90% efficiency= 20.25

I don't buy it.

bulletbob at January 11, 2014 at 7:36 PM

I don't buy it.

Buy what?

Your numbers.You show a 200% gain with an MPPT controller.Ain't gonna happen.I don't know where numbers like this come from(the tooth fairy?)All the independent and reliable tests I have seen show betwwen 7% and 15% gain in production.The 15% gain is under unusual and optimin conditions.I realize there is a lot of bogus info out there put out by people trying to sell something,and I think we should take these claims with a grain of salt.

It's actually a loss due to the mismatch between array voltage and battery voltage. The PWM can't convert the higher voltage of the array into an increase of current at a lower voltage. A MPPT can as it works sort of like a step down transformer (it actually has a high frequency oscillator circuit and transformer to do this, similar to a switching power supply) where a high voltage input at low current is transformed into a lower voltage and higher current. The power in watts is maintained  .minus heat losses.