schtoo avatar image
schtoo asked

How to switch on a fan from a mppt or 712?

I've been reading for a while to see whether the above is possible, and if so how to accomplish it with what is already installed.

Currently I have a Smart MPPT100/30 and the BMV-712 (and a 12/30 charger, that won't talk to the other two...) installed in a case along with a set of 3 x 130Ah AGM batteries. There's a real chance the temperature may become higher than desirable so I need to be able to switch on a fan to get some air through the case.

Basically, can I switch on that small fan without adding anything more or do I need to add in something like a temp sensor to the 712 to accomplish this? I'm not looking for accurate temperature data, just turn the fan on when it's too warm and turn off when it's all cool enough without adding anything unnecessary.

I've got an idea that it might be possible, but I haven't figured out how to do it yet and hope someone out there already knows how it is done and save me some angst working it out for myself.

And if possible, can someone quickly tell me if the 'relay' on the 712 can switch something like a <1A load, or if I need to add in a proper relay. Maybe I've missed that on the read throughs of the manual...

Thanks in advance, I hope.

(And if no answers I'll find out for myself soon enough. Would very much like to get back to it with a plan rather than a hope/dream.)

MPPT ControllersBMV Battery MonitorRelaytemperature
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2 Answers
Mark avatar image
Mark answered ·

Yes it can be done with the BMV relay function.

You need to purchase the additional temperature sensor;

Then under 'settings' > 'misc' > Aux input select 'temperature'.

Then under 'settings' > 'relay' select 'High temperature relay' and configure it according to the temperature that you want the fan to switch on and off.

The BMV relay specifications are;

1A max @ 50VAC

1A max @ 30VDC or 0.2A max @ 70VDC

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schtoo avatar image
schtoo answered ·

I thought that might be the case, i.e; I'd need to add the temp sensor.

But at least I don't need to also add a relay, which is handy. I do wish there was a 'nicer' temp sensor than the cable lug style. I've seen a round plastic one, but can't seem to find it any more.

Less a case of monitoring the battery temperature than the 'inside the case' temperature, but so long as it works (which it will) I can't be too worried.

I'd already worked out how to make the relay do it's thing with the virtual product thing on the app, and I expect I'll be able to let the mppt function a little better with the temperature info as well.

Thanks for confirming what I suspected was correct. It's saved me a lot of looking and not finding. :)

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Mark avatar image Mark ♦♦ commented ·

Actually I just remembered that the BMV type temperature sensor 'doubles' as the positive power cable - so for it all to work you must bolt the temperature sensor lug to the positive battery terminal and alter the temperature trigger points accordingly.

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