How to power a fan only when solar is charging.

[TURNKEY]

I want to run an exhaust fan from my battery compartment to vent out hydrogen during charging cycles but I don't want it to run 24/7 as I do now. I tried powering a computer fan off my panels before the charge controller but the charge controller allows power back to the panels when they aren't charging, like at night.

The reasons I want to do this are:
-battery compartment is not that air tight and will be hard to make it so-I don't want the off gasses getting into the trailer.
-it is just a small draw..but watts are watts
-I like to do tiny tinker jobs like this one (I just installed thermostatically controlled fans in my fridge chimney)

One way would be a separate tiny panel just for the fan-expensive. Or some kind of voltage controlled switch (panels run at +17 volts when charging).

I'm running 200 watts on the roof and another 100 watts on an umbilical. Batteries are 2x225 amp golf cart bats. We almost exclusively dry camp. We do not have an inverter and run the genny once a month or less.

Any input or ideas would be welcome.

[red31]

trimetric shows no power to fan and it keeps spinning?

[TURNKEY]

MW that does look like a simple solution, I can get a 24v fan like that from Aliexpress delivered to my door for about$5.
So you are saying that because the fan is 24v vs 12v it will not run unless the panels are charging at around 19v? And the voltage off the battery that I get through my pwm Trimetric won't run the fan because it's too low?
That sounds like it makes sense but just to belabor the point (for the moderator's benefit), just because the fan isn't turning, is it not still using power? The magnets will still be charged just not enough to spin the fan?

[BFL13]

EDIT=--I tried to run a muffin fan from the array terminals- nothing on the two MPPTs, it would not spin on the PWM's but just sort of shook. So it tried to do something but no joy.
--------------

I have three controllers on my battery bank, but one has no panel at this time (so I am back to 555w) The other two arrays are covered with tarps, but some light might be getting through, not sure.

Measuring voltage at the controller battery terminals and array terminals I get:

MPPT Eco-Worthy (no panel)- 13.73/0.71 no amps
PWM Solar30 panels covered- 13.73/11.36 no amps
MPPT Tracer panel covered-- 13.74/24.0 no PV amps, no amps to Batt.

My panels all have their own diodes for night AFAIK the controllers don't have the blocking. ISTR my old ASC PWM controller did have one.

[MEXICOWANDERER]

Sometimes it is frustrating to offer an obvious answer and have it ignored. I am talking about my answer. I've only used it seventy times or so. 24 volt fan direct connect to + and - output of panels. Fan -- wires -- slam compartment door. There is no backflow through a controller. Write DIODES on a piece of paper. Shred it then set a match to it.

[TURNKEY]

MrWizard...for a moderator you sure aren't very friendly or hospitable. To say "Oh God!" and imply I am not competent is rude. Shame.

[MEXICOWANDERER]

if the fan I suggested is operated directly off the panels, there are no switches, diodes or kajinka dolls.

[MrWizard]

Oh God..!
Put a tiny diode between fan wires and panel wires that are connected to controller

You really need to have somebody else there doing this

[TURNKEY]

My set up is PANELS---*FUSE----CONTROLLER----BATTERY and I'm running the fan from the panel side of the fuse. To put a diode in place it'd have to be a big one because the panels to the controller will run through it. I have a Morningstar Trimetric 45 controller. The fan runs 24/7 in this configuration so unless the panels are supplying a small amount of power even after dark, the controller is allowing power back to the panels.

[BFL13]

red31 wrote:
I wonder how a small load would affect the controller scanning for mppt.

When the controller is off (scanning)/PWM/sleep the panels operate at a matched resistance as the load vs Voc, likely just a few volts for a small load.

https://www.youtube.com/watch?v=JZQEJ33xblE

I have been thinking the load on the input wires would be like added line loss.

[red31]

I wonder how a small load would affect the controller scanning for mppt.

When the controller is off (scanning)/PWM/sleep the panels operate at a matched resistance as the load vs Voc, likely just a few volts for a small load.

https://www.youtube.com/watch?v=JZQEJ33xblE

[wa8yxm]

Just figured out how to do it

Your solar set up looks a bit like this Note the location of the *

Panels------*-Controller--Battery

There may (should) also be a fuse in there somewhere

The way to insure fan only runs when charging is to hook it in at the * You may need a voltage regulator (simple device) but hook it in at the * That way it only gets power from the panels as there is a diode in the controller.

if you use a 12 volt fan (you can also get 5 volt)

Here is one list of 3 terminal regulators
Mouser Electroincs

[loggenrock]

Can't you just add a blocking diode in-line to prevent ANY back feed from the batteries? Isn't the sun up for a LONG time in Saskatchewan, anyway???
https://www.google.com/search?q=blocking+diode&oq=blocking+diode&aqs=chrome..69i57.12304j0j7&sourceid=chrome&ie=UTF-8

It would set you back about $0.40.... 😉

[MEXICOWANDERER]

EZ fix direct to panel output

https://www.ebay.com/itm/COOL-COX-CC8038H24D-2-wire-80mm-x-38mm-DOUBLE-BALL-BEARING-24-VOLT-FAN/1431...

[MrWizard]

if your tri-metric shows NO discharge at night
why do you think, there is a power back feed, when there is None

i'm guessing the ambient light is producing enough Milli-amps of power from the panel, to run the fan at night, but not enough to turn on the controller for charging the batteries, a tiny DC Fan will might run on ten volts and 50ma of current


connect your fan, cover the panels with a blanket or cardboard
and see what happens

if you can't hear it, and its running from the panels, not the battery
it would make no difference to me if it ran full time and never stopped
as long as the power did not come from the batteries

[TURNKEY]

Ed and Log.....As previously posted that's what I'm doing already. shastagary.....Oooooo that looks nice. Thanks