Electrical expert advice please

[tysonn]

Not having any luck finding a rheostat switch to control a 12v fan(for my non mog project car).The same type as fitted to the early minors.They are available new but for almost £70!!!!!I wondered if I could use resistors to maybe just have a 2 or 3 way switch that would give me a choice of speeds?If so what sort of resistance/current rating do I need?Its for a new kit-car type 3.5kw heater that has a small modern type 12v fan that draws 3a at start up and 2a continuous running.
Any pointers much appreciated!
Mick

[meh]

Measure the resistance of a rheostat off your Morris, divide the total by the amount of switch positions you want then get resistors of about 20w of the value required. The other way is to make a transistor controlled circuit which could be found via Mr Google

[meh]

A link http://www.thebackshed.com/windmill/art ... orFan2.asp

Ignore the 240v conversion

[tysonn]

Thanks a lot for that.I dont have a resistor to measure though but I'll have a look around.

[meh]

Try a couple of ballast resistors and see how it performs.

[kennatt]

if you can find an oldish transit in a yard,they have three way switch for heater blower,the control/unit is under the front slam panel on the drivers side three wires which go to the switch in the cab,probably get it for nothing.

[Matt]

You are talking about pre '00 transits...

I wouldn't bother with a 2nd hand switch they are nearly all burnt out - as the resistors (by the drivers headlight up to '97, and in the heater box post 97) corrode/burn out then the switch is always left on position 3, melting the back of the switch and the loom. I have replaced many many switches and resistors on them (they are about £16 new, and resistors can be had for a fiver). They are fused at 30A on a transit, so your kitcar heater box wouldn't present a problem to it. A cheap bodge for a heater resistor is to use a H4 bulb ;)

[tysonn]

There looks to be plenty of rheostats on EBay from older cars that controlled the panel lights.Maybe they wouldn't be up to the current for a motor though?Mind you they also seem to fetch good money.I already have a suitable switch.I assume the transit must have had resistors on the heater motor itself.

[bmcecosse]

It would be better to control the voltage electronically - rather than 'waste' power in a series rheostat. Pretty sure Maplins will sell you something to do the job - just ask!

[tysonn]

Shame on you Roy!I aren't using this new fangled technology on my 60 yr old car.

[bmcecosse]

Two position switch then (ie lights switch) and use the first position via a headlamp bulb in series for low speed - and the second position direct feed for full speed.

[tysonn]

Just discovered an old resistor 3.3 ohm and put it in the circuit and its given me a second(lower obviously)speed.What should I be looking for to give me a third,even slower option? 6 ohm or something similar?

[bmcecosse]

Headlamp bulb is ~ 5 ohms - and the two filaments in series will be ~ 2.5 ohms. Should suit your speed requirements nicely. Only thing I don't understand why you want to make it run SLOWER ! I would want the heater fan to run FASTER!!

[irmscher]

Roy they are tough in Yorkshire

[tysonn]

LOL.When the PO stuck the big engine in the car he completely removed all parts of the heating/ventilation system to shoehorn the v8 in.My main concern has been the lack of screen demisting which hopefully now I have addressed.Thanks for all contributions.

[bmcecosse]

I would think with a V8 there should be enough heat to melt the screen - never mind 'de-misting' it.......

[irmscher]

Mick you can get plug in heaters off Ebay fan like things which turn and clear the screen fast and only cheap

[tysonn]

I bought a kit car type heater(not at all cheap but small and very efficient,4.5kw).Its all sorted now I used a 3 and a 6ohm high power resistor giving me 3 speeds.