10 replies to this topic

[sparkymae]

Hello everyone. Would it be ok to wire in a rheostat switch on the original heater on a 1990 Mini. Not sure if it needs the full 12V to run. Thanks. Have a happy new year.

[Spider]

Happy New Year to you too mate !

You could use a Rheostat, it would need a fair rating though. Most multispeed fans use a switch of how ever many speeds you'd like a few resistors of fixed value placed in the air flow stream so they can get away with smaller wattages.

If you wanted something that was fully variable, you'd probably be best off using a PW type of controller.

[SKIDDERWOLF]

Happy new year!

I’ve used this cheap PWM controller from Ali Express for exactly this reason, mounted the rotary speed dial on the dash and I am able to fully regulate the motor speed.

https://www.aliexpre...0874821094.html

Seems to work ok.

[Steam]

Yep, a cheap PWM off ebay would probably be cheaper and certainly better than a rheostat. You can get ones with a seperate control pot so the main unit can be mounted out of sight. The quality os OK I have used a few for various tasks and they work well.

Edited by Steam, 02 January 2026 - 07:48 AM.

[SKIDDERWOLF]

I did just this Steam, managed to squeeze the main unit onto the void above the heater and then route the control pot up through the dash.

[shera12]

You can do it, but it’s not really recommended. The heater motor pulls a fair bit of power and a rheostat can get hot or fail. The motor is meant to run on full 12V, with speed controlled another way. Happy New Year and enjoy the Mini

[yeti21586]

I got the resistor from a golf or poplo, my dad then stripped the plastic from around the blade terminals and worked out which blade reduced the current by how much and then did a smiliar thing with the control switch by fiddling with the wires and connecting them to resistor and the motor.anyway he came up with this idea of were to mount it so it stays cool and is hidden etc. and then once its all wired you push all the wires up through the hole the 2 normal heater power cables come through and attach a plug for easy removalYetI

[yeti21586]

The one I bought was similar to this
https://www.autodoc....iAaApA-EALw_wcB

[alpder]

A rheostat (presumably mounted on the dash) will get pretty hot.

 

For example, on my Mk2 (old-style metal heater) I've replaced the on-off toggle switch with an on-off-on toggle. One "on" connects "+" direct to the fan, and the other "on" connects "+" via a wire-wound metal-cased resistor which is mounted inside the fan casing, riveted to the metal and mounted in the airflow, to keep it cool and also to keep it away from flammable bits of the car. I can't recall the exact amperage (nor the resistor I used) but let's guess 3A with a resistor of, say, 2ohms. To get the wattage do: current x current x resistance = 3x3x2 = 18W. I have soldering-irons - which reach ~300C - with less power than that. So 18W into a little resistor is plenty enough to burn people or melt plastic. Which is why it has to be mounted out of harms way, on a heat sink, and in a draught. Which all means that using a resistor (including a rheostat) to control fan speed is quite a faff to engineer and could be a bit of a fire risk if the heat isn't allowed-for.

 

So, as others have suggested, for continuous speed adjustment a PWM controller is the way to go. Likely to be less expensive than a rheostat, too.

[Shooter63]

I'm not sure if this helps but early MK1's with the " fug stirrer " type so called heater came with a rheostat,  the switches are still available.

 

Shooter

[sparkymae]

Big help, thanks everyone.