Thread: Upright Compressor Fridge - Solar

I attempted to use my multimeter to measure the charge current whilst charging 2 N70 batteries in late afternoon sun. The current was 5.6A but the battery voltage was 17.8V, as was the panel voltage and the MPPT controller's charge LEDs were all off. Obviously the multimeter prevented the controller from seeing battery voltage. Note to self - don't do that again! Anyway that output amounted to 100W in late afternoon so in stronger light the panels might just produce their rated 120W. I would still like to know the o/p current to know how efficient the controller is.

I have two Watts Meters, one on the battery input side and one on the output so can get instantaneous readings from any point in the setup.

The best I have seen direct from the 120w panels in full sunlight is 17v at 6amps = 102 watts. The best after the controller was 13.5v also at 6 amps = 80watts.

I have never seen anything like the 9 amps at just over 13v to warrant the 120w claim - but then we all know that sellers claims are a bit exaggerated.

Garry

Mine was outputting 14.1V charging 2 batteries with the panel at 20V and 14.8V charging 1 with panel around 19V so obviously wasn't using all available power in either case. I might have to get a Watt meter to check further.

Edit: Just bought a Watt meter so will do another test in a few days. My MPPT controller sells for $10-$12 so a real cheapie.

Garry, we are using a Morningstar Pro 30, it shows incoming amps and battery volts. The best I've seen is 16A and thats with 420watts of panels feeding 360A's of batteries.
I am a firm believer in Terry O's 5-3 rule.

The Morningstar Pro 30 is a pwm controller so presumably only pulses its max o/p voltage (14.0V to 14.4V) for the selected battery type resulting in never extracting the panel wattage, only the panel's max current. For my 2 60W panels labelled as 3.36A at 17.83V that would mean a maximum of 6.7A (with no current losses) whereas a good MPPT controller should provide over 8A at 14.4V if 97% efficient, which some claim.

Edit: My MPPT controller outputs a constant voltage even when its charge LEDs are flashing, as detected with my pocket oscilloscope. It does not pulse but unknown whether it can o/p more current at charge voltages than the panel.

Edit: If my controller doesn't o/p more current than the panels then I'll probably spend $89 on a GSL MPPT 12-1.

Originally Posted by garrycol

As Graeme indicated - yes is an option but not practical as if there is not enough power from the panels the fridge stops.

It just seems to me that the MPPT is not doing what it is supposed to do which is maximise charge to the battery and I don't want to fork out for another one (a better one and more expensive one) only to find the same issue.

Garry

I got this wrong. My controller is supposed to supply power to the load terminals from the battery if the load exceeds what the controller is extracting from the panel(s). However the controller's battery low voltage cut-out could be higher than desirable.

Originally Posted by Pedro_The_Swift

I am a firm believer in Terry O's 5-3 rule.

Whats Terry O's Rule - in that gas guzzler he drives - use 5litres of fuel for 3km travelled

its his ratio of panel watts to storage capacity,
so, simply put, you need 500 panel watts to maintain 300Amp storage capacity.
This allows you to use everything all the time and not concern yourself with counting amps.
The only thing we dont have is a 12V coffee maker,,