Heater control speeds

[Gaz22]

My Macwester has a car heater box piped directly from the engine, and is powered with 12v through a fused switch. This setup heats the boat very well during the winter time but now summer is coming again (hopefully) l would like to be able control the speed of the fan, firstly to reduce the air flow through out the boat as the boat overheats, secondly to reduce the powerdraw from the batterys.

As electrics are not my strong point can anyone suggest a variable speed/2 speed switch or similar that can be bought from Maplins or another electrical retailer, did have a look on Maplins but didnt find anything or understand some of the electrical jargon.

Thanks in advance for any advice.

 

[claudio]

The cooling water usually goes through a matrix and returns to the engine. Doesn't the fan have an on/off switch? Can't you just switch the fan off or do you need speed control ?

 

[Gaz22]

Yes would like a speed control of some kind, rather than just on off switch.

Thanks

 

[claudio]

Most car heaters have a three speed fan, speed is controlled by a switch. Can you identify the heater box ?

 

[oceanpilgrim]

most car heater systems have a resister to reduce the power to the motor,this will slow the motor but use the power to heat up the resister,slower motor but not saveing energy,why not place a water control valve in the water line,or visit a car scrap yard and find a late heater system with a digital controler and brushless motor fan

 

[Gaz22]

Re Mytutu we think the heater box is from an early escort.

Interesting point about the resistor, wasnt aware that power consumtion would not drop with lower fan speeds.

We did look to replaceing with a newer model but most modern car heaters are about 3 times bigger and woudnt fit, this could still be an option next winter if a smaller one could be found.
As l will be doing the 3 canals around scotland this summer being able to control the fan speed will be important with helping to keep the cabins comfy, also to dry the sailing gear when it rains, as it will do on the west coast.

Last summer l installed a bypass valve to regulate the water flow to the heater.

 

[GrahamP]

Gaz,

Assuming that a resistor is added in series with the heater motor to reduce the voltage across the motor the current will be less. As power = current squared x resistance I reckon the total power used will be less.

 

[NormanS]

Why not just switch it off when it's not needed? Speaking as a fellow Fifer, think of all the lovely money you'll save when it's off. /forums/images/graemlins/laugh.gif

 

[Eygthene]

Rather than varying the running speed, you could use a timer to switch it on and off at adjustable intervals (like some windscreen wipers). The on and off times could be set, so that it comes on for a few seconds, then off for a time (variable) how would that suit? If this appeals, a suitable unit may be available from a car dismantlers.

Alternatively, one can get a controller that switches on and off hundreds of times a second (variable) so as to deliver a reduced amount of power to the fan, which would give a variable speed control. A version of these is used to control a modern electric fork-lift truck.

Finally, perhaps a simple room-temperature thermostat would be suitable to switch the fan on and off to maintain a comfortable temperature?

 

[claudio]

Can you measure the current supplied to the fan. If it is less than 3A, Maplin do a PWM speed controller, very efficient on power see here. There will be other versions for more than 3A, a google search should come up with something.

 

[Gaz22]

Good one Normans you must belong to the other end of Fife, where the polar bears live /forums/images/graemlins/wink.gif

John_b, l do like the room thermostat idea, will look further into that one.

Mytutu, thats what l`v been looking for /forums/images/graemlins/grin.gif, will get someone to check the amps for me.

thanks for suggestions
G