Venting

54d18

Just fishing for some educated thoughts,
I have used a 12v computer fan connected
to my incoming 24v solar wires with a 500 ohm
resistor in series with the fan, this keeps the fan's
voltage at about 9v when the panels are at VPM.
It works well, but is there an easy way to regulate
the voltage so the fan runs at a constant speed,
it is somewhat annoying with the constant changing
of the sound.

mike95490

Re: Venting

You would need to step up the complexity some, and build a real power supply to regulate the voltage.

BB.

Re: Venting

Adding a charge controller and battery bank is the only way to get stable voltage. And usually that is too costly and complex for simple abdications.

-Bill

54d18

Re: Venting

I think I better clarify, I do have a battery bank, and controller,
the fan is connected to the incoming wires so that no switch
is required to turn it on, when there is sun on the panels, the
fan runs, the problem is that it does not run at a constant speed,
it varies according to the panel voltage which fluctuates.

Hope this clarifies my question...

BB.

Re: Venting

What is the current requirement for the fan?

Do you care about efficiency?

I assume you only want the fan to operate when there is sun shine... And you don't want the fan to vary in speed (too much) during the middle of the day...

The easiest way I can see to do this (without placing the fan on the battery side of the system) would be to use a current mode power supply of some sort in the fan circuit... You could use a positive voltage 3-T regulator configured as a current source--But it will not be very efficient--It would dissipate the unused power across the 3-T regulator (heat sink--Vreg-max-drop*Ifan).

You could also do the same thing with a switching regulator--I have not played with those in that configuration--but there should be some building blocks out there to do that.

Lastly, simply put the fan on the DC side of the PV system (battery side) and use a transistor (or relay, or FET, etc.) as a driver and sense the Array Voltage (or current). When it drops below a set value, turn off the power to the fan. It will probably be more efficient than the 3-T regulator setup.

Some people use a fan to vent hydrogen gas from the battery bank... So they turn on the fan only when the battery voltage is above ~13.6 volts or so--Again using a voltage controlled switch.

Depending on the application, controller, etc.... You may have to be careful about how you sense the voltage on the array and control the Fan On/Off -- Some controllers do not ground the PV Array negative lead directly--And you would need to isolate the array side from the fan side.

Lastly, look at using a larger / slower turning fan... Hopefully it will be quieter and you would not notice the change in sound (look at a 24 volt fan and you would not need the ballast resistor either--or can get a smaller one and waste less power).

-Bill