Fan Wiring Question

[Samwise-100]

Hi All,

I have a little wiring issue i could with some help with...

I have a 12v extractor fan which i want to wire up to come on whenever my water pump is on. So that, when the water pump is activated by opening a tap, this in turn engages my propane water heater and so the fan would then come on to help ventilate the space.

I thought i might need a 4-prong relay, so have got one to try but can't seem to wire it up properly to get the desired effect. I wired it up to practice with a triple rocker switch on pin 86 and whenever the switch comes on, the fan on pin 87 comes on... But i'm not sure how to use it for the pump as it has no switch, it's just a positive and negative feed. I could be miles out here btw, just learning as i go.

I've attached a diagram of the fan working off a relay and switch. It's also tricky because i can't actually wire up the pump for trial and error - because i don't have my water system in place yet, and don't want to dry run the pump!

Could anyone please advise how i might wire up the fan to come on with the pump. ANy pointers would be much appreciated, cheers!

 

[Lenny HB]

Your wiring appears correct, blue on the pump is often positive but I question the wisdom of fitting a water heater that needs ventilation. You should only be fitting a water heater with a balanced flue in a Motorhome.

 

[Richard n Ann]

You won't need a relay. Just take the electrics cover off the pump motor and find the wire that goes positive when the pump runs, wire the fan in parallel

 

[Samwise-100]

Thanks for the responses guys.

Lenny HB, the heater i have is flueless but 'should be used in an open space' (although i've seen loads of instances where it's used in a similar van environment). It's fitted on the back door which would be open if used for any great length of time (ie. outdoor shower), but thinking the extractor fan is more of a measure for short blasts of the hot tap when the rear door is closed.

Richard, the pump has a positive wire coming out from one end, going into the other. Then a second positive and a negative wire come out with loose ends for wiring. Pic attached (note mine aren't terminated into a plug like the one shown). Could you please elaborate?

Cheers

 

[Richard n Ann]

That's same as our new one

a positive wire coming out from one end, going into the other.

Connect your fan to this cable. On ours I needed to connect onto it for the 'pump running' LED.. I managed to solder onto the spade where it grips the insulation and shrink wrapped it

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[mitzimad]

you are risking your life to save a couple of hundred pounds, get a proper water heater
adding a fan is just as likely to produce CARBON MONOXIDE AS DISPELL IT

 

[tonyidle]

Fan draws minimal current. Simply wire it directly to the pump - no relay needed. Include a 1A fuse in the fan +ve.

I have to assume you're using a balanced flue water heater? No other type is safe in a van.

 

[Lenny HB]

That is a pump with a pressure switch so you will have to take the pump apart and connect to the side of the microswitch on the side that connects to the pump motor.
The heater you are looking at using sounds like a suicide mission to me, fit a proper one and stay safe, stupid risking your life to save a few bob.

 

[DBK]

Leaving aside the safety issues you are only ever going to be opening the tap for short periods, probably 30 seconds max if that. This is nowhere near long enough to remove any fumes.

You will also want to use the extractor fan to remove cooking smells and for cooling in hot weather. I suggest just wire it to a conventional switch and turn it on when needed or when the carbon monoxide alarm goes off.

 

[Hoovie]

Thanks for the responses guys.

Lenny HB, the heater i have is flueless but 'should be used in an open space' (although i've seen loads of instances where it's used in a similar van environment). It's fitted on the back door which would be open if used for any great length of time (ie. outdoor shower), but thinking the extractor fan is more of a measure for short blasts of the hot tap when the rear door is closed.

Richard, the pump has a positive wire coming out from one end, going into the other. Then a second positive and a negative wire come out with loose ends for wiring. Pic attached (note mine aren't terminated into a plug like the one shown). Could you please elaborate?

Cheers

putting aside all the valid safety points, what you could do (depending on kit) is the following:

The Surflow pumps have the +ve on and the +ve out on the end - that end being the auto-on pressure switch. So splicing into the +ve out to go to the fan will turn it out whenever the pump is running.

But as has been said, it will be running for only a short while and you probably want it running longer whilst still automatically starting.
so ... get one of these - https://amzn.to/34opgHQ
Power the timer from the Pump +ve IN, start the timer count signal from the Pump +ve OUT, connect the fan to the timer relay out.
Then what you will have is a Fan that can only work when the Pump main switch is on, will start when the Pump actually starts and will continue to run for however long you set after the Pump goes off (settable from 1-99 minutes, or 1-99 seconds - maybe 10 minutes is about right for extraction?)

(I use that same Countdown timer to control an AC AutoTransfer Switch Timed Override and find it very good).

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[Lenny HB]

The Surflow pumps have the +ve on and the +ve out on the end - that end being the auto-on pressure switch. So splicing into the +ve out to go to the fan will turn it out whenever the pump is running.

I forgot that when I posted.