Electric Throw Rug Basic Circuit

[TheClaw]

Hello. During winter I get very cold when sitting at my computer. I like to sit with an electric throw rug. Trouble is I have blown-up 3 or 4 of them over the last few years.

The most recent failed with an apparently dead controller. I got a new controller sent out under warranty, but that failed with a popping sound the instant I switched it on.

The rugs all seem to be similar. They have a 4-pin plug, lets call the terminals A,B,C,D
The resistance A-D is around 240ohms, and B-C is around 900ohms.

I have a brand new one which works, and I have the old rug which blew 2 controllers. The resistances are similar.

Can someone please explain the basics of the circuit to me? I'd like to understand what is going wrong, and perhaps how I can do a simple fix to continue using the "faulty" blanket. Perhaps in series with a light bulb??

 

[Martaine2005]

I'd guess that because they both have 4 terminals, they are internally wired differently.
Can you give us a link or links to the units you have now? It may be obvious why they are not interchangeable.
I am sure photos of the controller boards will be required as well.

Martin

 

[Martaine2005]

The most recent failed with an apparently dead controller. I got a new controller sent out under warranty, but that failed with a popping sound the instant I switched it on

More than likely a short in the old blanket.

Martin

 

[TheClaw]

If there was a short in the old rug, it has since gone away. Because the old rug and the new rug show similar resistance readings.
Does anyone understand the 4-pin circuit inside the rug?

 

[Martaine2005]

Does anyone understand the 4-pin circuit inside the rug?

They might do if you tell us what brand you have or link to your replacement controller as previously requested.

Martin

 

[Martaine2005]

Two terminals are most likely A-D the heating element/coil/wire. The other two terminals B-C are most likely the temperature sensor.
Checking A-D and B-C for resistance is fine. But did you check A-B, A-C, D-B and D-C?.
Controllers don't normally go 'pop' without a reason.
The fact that it did 'pop' instantly, suggests the blanket is faulty.

Martin

 

[TheClaw]

Oxford Square Heated Throw Blanket, model IA4144
https://www.aldi.com.au/en/special-...saturday-detail-wk18/ps/p/heated-throw-rug-2/

This is the new rug and it works fine.

I still have the old rug and it is extremely similar. I want to understand why the old rug failed, and if it can be got working in some crude fashion.
I want to understand the basic circuit.

A-B, A-C, D-B and D-C are all infinite on both rugs.

Do you think the controller applies 240v across A-D to heat the rug via a 240 ohm resistance wire, and monitors B-C which would be a chain of thermistors. If the reading is out of bounds, it switches off.

Any help would be appreciated.

 

[Pejayuk]

I'm now on my third one of those heated throws. Mine came from Lidl, so very similar to the Aldi one I'd guess. The first two failed within a few months, so I had them replaced under warranty. I'm sure they failed due to the blanket over heating because I used to have it switched to the maximum setting.

The manual says that if the LED on the controller doesn't light, it cannot be reset. I assumed there must be a non-resettable thermal fuse somewhere.

This last one is still going strong after several years because I never use it on more than the medium heat setting. I think if a higher setting is used, the blanket must be completely flat so as not to overheat the wires inside.

Sorry I can't help with the circuit, but if mine does fail again, I will be trying to fix it myself this time.