# wiring battery box vent fans



## chamilun (Jun 17, 2008)

hello,
I cannot figure out how to wire the battery box so that the 12V dc fans engage when either the vehicle is being charged or the car is running.I know it involves a simple relay but Im at a loss.

Ive searched and searched for a schematic and found zilch.

thanks in advance


----------



## jlsawell (Apr 4, 2008)

chamilun said:


> hello,
> I cannot figure out how to wire the battery box so that the 12V dc fans engage when either the vehicle is being charged or the car is running.I know it involves a simple relay but Im at a loss.
> 
> Ive searched and searched for a schematic and found zilch.
> ...


I was under the impression you only needed to vent the box when charging. So put a pressure switch under the fuel cap so when the fuel cap door is open, the switch is "ON" and turns on the fans. When you unplug and close the fuel door, the fan goes off.

Of course, that only works if you're using the fuel door as a recharge point, but you get the idea.

If you want to run the fan while driving, just wire up a second missile switch on the dash, that way you can control the fans from both ends of the car.


----------



## TelnetManta (Jun 5, 2008)

Chamilun, I used a small spst switch under my fuel door. When the door is closed my main contactor is allowed to close. When the door is open it operates a relay at the rear of my car that will, when I get my cover made, operate two dc fans.

HTH,
Ben


----------



## chamilun (Jun 17, 2008)

i like that idea.  ill get a simple switch that closes the circuit when the 'fuel' door is open. hopefully I can find an always on circuit somewhere in the rear of the vehicle.

i was hoping someone would have an idea to sense voltage at the plug itself. b/c this comes from the charger, this is DC voltage


----------



## Hondacrzy (Mar 15, 2008)

I just used a plug in power transformer that runs off of the same plug the charger works off of. The fans run when the car is plugged in.

Chris


----------



## TelnetManta (Jun 5, 2008)

Chris, I really like that idea as well. Might have to rethink my plan. 


Ben


----------



## chamilun (Jun 17, 2008)

yeah, thats sounds what im looking for.

can you give a part number or example of the power transformer you are using?

thanks


----------



## Dalardan (Jul 4, 2008)

I simply suggest to go to a random computer store and get the cheapest power supply unit you can get (I got 6 used ones for 2$, because they where going to junk, but you can get one for around 20$) and then, on the 20 or 24 pins connector, short the green wire with a black wire. THis way, you'll get 12v between the yellow wires and the black wires (and 5 volts between the red ones and the black ones).

Hope this can help, I've done a lot of electronic setups with that.

Dalardan


----------



## Hondacrzy (Mar 15, 2008)

Hi I have not finished cleaning up the wiring, But I ran a cable between the charging plug in the gas door to a plug box I installed on the same board as my charger and dc/dc converter in the back (front) of the trunk. The transformer is a 1000ma 12v output. The two 80mm brushless fans only pull about 500ma. Works great. The only thing I would like to add later is a timer to shut the fans off after the charging is done. I will post a picture it my garage if you would like to see it. I do not have a hosting sight for the pictures so I can put it in this post.

Chris


----------



## chamilun (Jun 17, 2008)

b/c my charge will be in the garage, and not mounted in the car (220V), the plug on the car is dc voltage, not ac.

therefore, Ill need to figure out something from the constant on 12V wiring in the car.


----------



## john818 (Aug 1, 2008)

Isn't running a fan as long as a vehicle is plugged in a waste of energy? I assume most chargers will shut themselves off when the batteries are fully charged, so shouldn't the fans shut off then too, or soon after? I remember someone once mentioning a plan to somehow use a turbo timer for this.


----------



## ZenDaddy (Jul 22, 2008)

A relay that utilizes whatever your charge input voltage is can switch on or off 12v or pack voltage to whatever you want to run or NOT to run during charge. I use a dpdt relay to lock out voltage to my contactor (12vdc) AND turn on the vent fan (12vdc). You can have the fan running off "grid" voltage if you don't like the battery draw. Frankly a small vent fan just doesn't draw that much juice so I don't feel too bad about having it on whenever I plug the truck in. It also turns on a light on my dash to remind me to unplug the darn thing. (not that the fact that the contactor won't energise isn't enough, I just thought it would be cool)

Heres a spec sheet on the relay I used

http://www.nteinc.com/relay_web/pdf/R55.pdf

I bough mine from kta services for 16$.
They also have relays rated for dc across the coi that do the same thing.

On mine The control or "coil" voltage is 120v ac and the load is rated for 30 amps dc or ac. You can turn the load voltage on or off depending on what you want to accomplish.

It was very easy to install.

good luck

ZD


----------



## ZenDaddy (Jul 22, 2008)

Wire it Parallel to the dc cord between the plug and charger. Polarity does't matter across the relay coil. then just put the pos to the fan in series on the relays normally open leads. That way when you plug the charger in, the coil energises, closes the normally open circuit, and viola, fan on!

Just make sure the relay you get is rated for your dc voltage in.

Wait, did you say the charger is in your house, not on board?

I think the same applies, just make sure the relays "pull" voltage and "dropout" voltage work with the innitial charging voltage AND with the gassing voltage of your charger.

Since your charger is in the house and the relay is in the car, it will only run the fan as long as there is voltage from the charger.

Good luck

ZD


----------

