Battery Box vent fan controller question?

[[email protected]]

Where can I find a controller to start and start my battery box vent
fans? I have only found one so far at backwoodsolar. I thought I would
check and see what you guys are doing for battery box venting. I have
been using natural draft so far.
Offgridman

 

[Zathera]

Where can I find a controller to start and start my battery box vent
fans? I have only found one so far at backwoodsolar. I thought I would
check and see what you guys are doing for battery box venting. I have
been using natural draft so far.
Offgridman

What do you want to do? fans on by temperature? fans on by time?

 

[Scott Willing]

What do you want to do? fans on by temperature? fans on by time?

The usual approach is fans on by battery voltage, i.e. you only run
the fans when the batteries are gassing.

Would be a damn simple circuit - a handful of components from Electron
Hut would do it. Surely one of the DIY sites (redrok.com, or Steve
Spence's site) has published something? If not, they should.

-=s

 

[[email protected]]

Fans on at 13.8, Fans off at 13.8 that is what I would like to do.
Voltage seems the best way to control them.
Thanks
Offgridman

 

[[email protected]]

Oops on at 14 volts and off at 13.8 volts sorry.

 

[William P.N. Smith]

The usual approach is fans on by battery voltage, i.e. you only run
the fans when the batteries are gassing.

Would you want fans on while charging, or do they not make hydrogen
until they are charged and going into equalization mode?

 

[Steve Urbach]

Fans on at 13.8, Fans off at 13.8 that is what I would like to do.
Voltage seems the best way to control them.
Thanks
Offgridman

Zathera wrote:

Since the batteries should only charge when there is sun on the
panels, why not drive the fan from before the blocking diode on a 12 V
panel (fused the leads).. The batteries will continue to out gas some
after coming off charge, but the charge rate should diminish as the
panel output falls. 2@ 1N4004 (1A) feeding a computer case fan should
do very nice. No fancy circuits.

Steve U

 

[William P.N. Smith]

Unless, of course, you have a shunt-type controller...

That's interesting, seems like it should work, except sometimes a
generator is involved and it wouldn't work then obviously.
Also see Alternative Energy Engineering for voltage controlled switch.
I think solar converters makes them as well.

I'm still uncomfortable with voltage control (conceptually), wouldn't
it be much better to run the fans whenever current is flowing into (*)
the batteries and for some time afterwards?

(*) Do batteries evolve hydrogen when discharging? Something makes me
think they do... Maybe a small fan doing a continuous purge and a
larger one for power venting when charging?

 

[Steve Urbach]

Thats my understanding.

My main point is that batteries continue to Out Gas for some time
AFTER the charge potential is removed. My idea allowed that the panels
continue to output voltage (below that required to charge) for quite
some time after dropping below charging threshold (my fans will
continue to run on 10VDC) .
If you use a generator, just use a second fan that is relay(or wire to
the existing fan to transfer over) controlled ( this does have the
instant stop venting problem on generator stop, though) from the
generator.
Steve

 

[Scott Willing]

My main point is that batteries continue to Out Gas for some time
AFTER the charge potential is removed. My idea allowed that the panels
continue to output voltage (below that required to charge) for quite
some time after dropping below charging threshold (my fans will
continue to run on 10VDC) .
If you use a generator, just use a second fan that is relay(or wire to
the existing fan to transfer over) controlled ( this does have the
instant stop venting problem on generator stop, though) from the
generator.
Steve

While I like the idea of controlled venting (and I was drawn into this
thread on that basis) simplicity is good. The type of fans typically
used draw so little current that for all but the smallest systems you
could just let them run 24/7. That's what the fan on our Sunmar NE
toilet does.

The toilet is about to be fired into the sun on the end of a rocket,
but that's a different story.

-=s

 

[Bill Kaszeta / Photovoltaic Resources]

I use voltage. I have a 48V Zephyr Power Vent that is controlled by a
programmable relay in my SW5548. It turns on at 55.2V and off at 51.2V.
The 55.2V was derived from the voltage at which the battery mfg says the
battery will start to gas. (I think the gassing voltage is a bit higher,
but I put in a safety margin). The 4.0 volt hysteresis is to make sure the
box is completely emptied of hydrogen before the fan shuts off. It's
probably more than is necessary, but the fan doesn't draw much.


-- ron (off the grid in Downeast Maine)

You might consider a lower voltage. The main problem is that a
shorted cell will lead to overcharging of the other cells that are
in series with the shorted cell.

I sell telecommunication battery cabinets that use a hydrogen
detector to operate first a vent fan, then activate the alarm
system if the hydrogen is not cleared. Worth the cost on
$18,000 battery system.

Bill Kaszeta
Photovoltaic Resources Int'l
Tempe Arizona USA
[email protected]