MPPT Charge controller LOAD output stopped working

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raven asked Aug 4, '22

MPPT Charge controller LOAD output stopped working

Hello Everybody,

I have a problem with a bluesolar charge controller mppt 75/15 in a 24V system. I have a 24V solar array and two batteries. So far everything worked fine.

The charge controller has a 20A fuse that shows no damage. Batteries are fully charged and controller in Float.

So far I had an alarmclock and a water pump on the LOAD Output of the controller. The alarmclock has very little power requirement and the pump draws maximum 5 Amps (it is fused at 7,5A).

Since yesteday the charge controller refuses to power both devices. I also tried them separately.

With nothing connected to the load output I have the following voltage :

BATT : 27.4 V

PV : 44.3 V

LOAD : 21,7 V

It is already suspect to me that I don't read the same voltage on the BATT and LOAD outputs but maybe it is normal ?

If i connect any device to the LOAD output, the voltage drops to 2,5 V on the LOAD terminal and nothing is powered. The two other outputs keep their readings. The jumper is in the middle position.

Is my controller fried ?

Many thanks,

Rémi.

MPPT Controllers

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Answer 1 · 2022-08-04T16:27:34Z

sameo416 answered · Aug 04, 2022 at 04:27 PM

Won't claim particular expertise on the 75/15. It sounds like the output driver in the controller is damaged, as when it's loaded there is little voltage available and likely the same for current. A multimeter measuring voltage uses a very high resistance and doesn't really load the output.

I suspect the culprit is your pump. Start-up current or inrush current for electric motors can be several times the steady-state operating current, usually so quick that it won't cause a thermal fuse to operate. Even though it's a small motor, the repeated impact of inrush current on the output driver in the 75/15 would gradually damage the circuit (which I'm guessing is a digital switch of some kind). Usually only control motors with a motor-start rated start circuit/switch, so a better implementation would be to use the load output to switch a motor start relay that would start the pump.

This is sort of mentioned in the manual, "3.8 Some loads (especially inverters) have a higher current rating or start-up current rating. The current is higher than the load output can support. These loads should be connected directly to the battery. It is possible to control these loads by the solar charger so that a deep battery discharge is prevented. This can be done by connecting the load remote on/off terminals to the solar charger load output."

On an AC motor initial inrush can reach 20x steady state, followed by a transition period of 4-8x steady state as the motor comes up to speed. This is very fast (less than one full cycle of voltage) but can chew up relays and digital switches that are not rated for motor duty applications.

So the load output sounds fried to me.

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raven commented · Aug 06, 2022 at 12:06 PM

Thanks for the input. I think you are right about the pump and the startup current. I kind of hoped that the charge controller would be protected against that and you could just reset the thing to get it to work again but I suppose its fried. Cheers.

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