Schneider MPPT60-150 Aux Function

Horsefly · July 2020

My MPPT60-150 charge controller goes into a sleep / stand-by mode after some time with no PV. I'm interested in using the Aux output to drive a relay, but many / most of the times I would want to trigger would be at night when there is no PV production and so the controller will be in standby.

Is it a safe bet that the Aux function does not work when the charge controller is sleeping due to no PV?

To make it even more complicated: What I want the relay to do is to disconnect the PV input to the charge controller. So even if the charge controller is up and running, the trigger will cause the PV to disconnect, so the charge controller will soon go back into slumber mode. Will the Aux output continue until whatever event I set to turn it off, even if the PV input goes away and the unit goes to sleep?

Vic · July 2020

What are you trying to accomplish with this. There IS an input relay in the CC, that opens when the PV input voltage is below Vbat, as we recall it.

But, to answer your question, it appears that the Aux relay will remain active at night, when there is NO PV input voltage, as noted on PG 3-15, second paragraph, under High Array Voltage ...

FWIW, Vic

Horsefly · July 2020

Thanks @Vic. I hadn't seen that in the manual (it's actually one page earlier in my version, so there have been updates). I'm not quite sure that is what I am looking for, but maybe.

To answer your question: I am contemplating putting in LiFePO4 batteries in my system. However, at 9000 ft elevation in Colorado in a cabin that is unoccupied during the coldest 5-6 months of the year and may get below freezing even during periods when people are visiting, I'd need to come up with methods to deal with cold temps. Most specifically, I need to make sure there is no attempt to charge the bank if below freezing. I know there is a "battery low temp" trigger for the Aux output, and I'm trying to figure out if I can use that to drive a relay (or maybe drive a relay via an optoisolator) to turn off the PV input to the CC if the battery temps are too low. I have other ways to do it, but using what was built into the CC seemed to be the simplest, if it worked even when the CC is sleeping. I know there is an input relay inside the CC, but I don't want to try and hack into that.

I've already come up with a design to heat the bank inside an insulated battery box, so this would be just a failsafe for when that effort to keep the batteries warm enough failed.

I may do some experiments with the aux to see if it holds while there is now PV in.

Vic · July 2020

OK Horsefly, thanks for the context of what you want to do.

But, in that manual, linked, it gives an example of how to do a Nightlight, based on PV input voltage. This strongly implies that, therefore, a NL Aux output simply MUST remain active all night for the NL to work.

Anyway, always good to test everything. Good luck, Vic

Horsefly · July 2020

Yep, you are right. It certainly implies that it should work. I'll give it a try next opportunity.

mcgivor · July 2020

The auxillary will work, I use mine to power a fan based on the heatsink temperature using the battery temperature sensor, without the fan the heatsink temperature will exceed 70°C thereby derating it's output, when the ambient temperature exceeds the 36°C setpoint at night the fan dose still run.

Dave Angelini · July 2020

Unattended heating/electronics in cold country, good luck, you will need it. Too many things to go wrong and completely against the less is more concept for offgrid.

A pessimist would say you do not have a large enough bank to do this. I have seen 3 failures of this in just the last year. It would be better in my opinion to just leave them cold and slowly warm them up when you are there before you put a charge on. Off the cuff it sounds like you failed with a more expensive than needed AGM and are now going to an even more expensive choice that has new wrinkles. The AGM again, done right, might be the easiest. It is the cost of admission.

However,

People have used flooded batteries in cold country for over 50 years in unattended mode. Nothing new here. If the charge is not on, they don't use water. There also is a big misconception that a liquid battery can't sit long. As long as someone runs the charge correctly and does an EQ (before they leave and when the return) they will be fine for upwards of 6 months sitting. Charge them, measure SG, and add EQ time, if needed. I know a 14 year old who does this. She has two pilot cells she measures and adds EQ time. The good thing is you can arrive at site, turn the power on with the genset, or sun if there is any and not be a slave to battery replacement. Should last 5+ years if the battery is a good make. Unattended is always a challenge. I know this because I have done this many times. If you find a new way, I am all ears

Schneider MPPT60-150 Aux Function

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