Resistor size

[Shadow Knows]

I have a Sunbeam waterbed heater that the main power supply resistor to the pad has burned out. Most of the color bands are burned off. I know the first is red and the tolerance band is gold, but the rest are not readable. The waterbed pad is rated at 400 watts. Is there a way someone can tell me what size resistor I need?

Sunbeam does not make them anymore and I have not been able to find out anything. I don't want to replace it as it requires draining the waterbed which has a Morgan mattress and really not easily done. So, I would like to repair the control.

Thanks

 

[davenn]

Hi there
welcome to the forums

have you tried putting a multimeter across the resistor and seeing if there is any resistance measurement at all ?

unless some one on the forum had the same model controller it would be next to impossible to know what value it originally was

Dave

 

[Resqueline]

What Dave said. Sometimes a resistor can still work even if it looks like that. If you can post a picture of both PCB sides we might be able to figure something out though.

 

[Shadow Knows]

Thanks for your replies. I did check the resistor and it is open. I thought with the pad being 400 volts that an engineer that knows how could calculate what resistor is needed.

I gave the control to a friend this morning that builds a lot of electronics to see if he can reverse engineer it ( he is not an engineer ). I will post pictures when I get it back if he can't figure it out.

It is a rather simple circuit. It has a temperature control rheostat on the board and temperature sender wired to it. The rheostat controls when voltage is sent to the pad controlled by the temperature sender that turns it off and on. The resistor sends direct power to the pad as nothing is on the board past the resistor.

The reasons I think the resistor may have failed are two things. 1st is age, about 15 years old. 2nd, we were gone for 3 weeks prior to the resistor failing while we had left the heat off in the house and the temperature was down to 43 degrees when we got back!! The waterbed heater was left on and I suspect it was heating pretty much steady when it was that cold to try and keep the bed to the 75 degree setting which caused the resistor to overheat. Normally the house never gets below 60 to 65 degrees.

Hope this information helps someone to figure it out.

Thanks,
Dennis

 

[Resqueline]

Most often it's the heating pad itself wearing out and failing. There's no way a resistor is the regulating element for the pad, but so far we can only guess on its real function.

 

[Shadow Knows]

Thanks Resqueline, my friend who looked at the control said it's the pad too. That confirms it and saves me time fixing this one, though now I will have to drain the water bed, not fun!!!

I think the resistor may be acting like a fuse when the pad goes out so you don't burn the house down. The board around the resistor got very hot! I would think the engineer who designed it would have used a fuse instead. When I get the control back I will post a picture. My friend is 40 miles away, so I won't be going back until Tuesday to get it.

Thanks again, this is a good forum.

 

[Resqueline]

Yes, that's a possibility. There are so-called fusible resistors that gives up the ghost without a fight. They are usually put in series with the mains input.
They can often be identified by their placement and unique body color. You can Google the term and choose images to see if you recognize it.
Thanks for the kudos!

 

[Shadow Knows]

I have the control back. In looking again at the resistor I can't really say it gave up without a fight as the board got extremely hot around the resistor before it failed, so I'm not sure it's a fuseable resistor. I'll post pictures soon.