Help with motor circuit design...

[wdSteve]

Hi all - newbie here...

My van has a 3 speed heater which works by passing the negative through various resistors to reduce the voltage. The original resistor pack has blown - new ones are £25+. Being unwilling to part with my hard-earned when I'm sure I can build something for much less I have tried to work out the resistances required to slow down the fan.
Did this and promptly blew my 1/4 watt resistor... hadn't taken into account the load of the fan motor??

How can I calculate the resistor load required? Could I put, say, 3 x 5W resistors in parellel to share the load and prevent them blowing or do I need to get a 50W resistor or whatever?

Thanks in advance

Steve

 

[GreenGiant]

What are the resistance values?

is this van a 12 or 24 volt vehicle?

 

[wdSteve]

What are the resistance values?

is this van a 12 or 24 volt vehicle?

The resistance across the fan appears to be 5ohm - may be wrong. 12v electrics. Original pack is blown beyond recognition...

Steve

 

[davelectronic]

Hi there wdSteve.
This might be of some use, yep 25 quid for a few resistors is a lot.


http://www.blackfiveservices.co.uk/fanspeed.shtml

PS. But yes take into account the fans power rating when you choose the resistors.

 

[donkey]

I am unsure if in the UK you guys have the same setup as here in Australia, but we can order a manual for cars to be lent through our library. you may get lucky enough to find information on this pack and how it works and what resistance values to look for.
if you don't want to spend the 25quid on the resistors I strongly recommend you don't buy the book as it costs more than that usually.
just a quick question though, do you have an idea as to what caused the fault? you may find other things further down to be a problem if there was too much current