heating blanket blowup

[bernm]

Hi. Once again, I'm hoping I can get some advice please. This has to do with heating blankets.

Last year I posted a request for advice about bending (viewtopic.php?f=1&t=2361). Thanks again. I ended up buying the LMI international 220V heating blanket.

But ... I bought it last year and it sat there for a while until I could progress a little further with building. I was part way through building a side-bending unit and decided to test the blanket once I had the form shaped and the metal on it. This was just the other day. I plugged the blanket in, using a max-250V rated international plug adapter, and ... bang. Sparks. Smell of something burning. And no heat from the blanket. It wasn't as if it started up and I left it too long to fry, or anything like that.

Now I know this was a stupid move. I never did test the blanket. I should've done that when I bought it, even if I knew it would be a little while before I could build a bender. Thankfully, I emailed LMI and they were very quick and courteous and there's a new one on the way to me. They seem to agree that it looks like a faulty blanket.

But now here's my question. I am assuming it was a dud blanket because I can't think of what I might have done wrong. It was the international model, my plug adapter was properly rated (I since tested that on another international device to see if it was the adapter that blew, but that device worked fine - the adapter is okay). I used a power bar with individual on/off switches per plug and surge protector, and had my thermometer sitting there, so I could keep it from going too hot/long. But in case I've overlooked something, I thought I should run this scenario before the forum, so you can advise if I should have done something differently? Have I left out any steps in setting up and using an international blanket?

Comments? Advice?

As always, many thanks. Greatly appreciated. I'm learning so much by following the posts here.

Bern

[liam_fnq]

So you've eliminated the adapter. It must be the blanket. Is there any scorch marks or
Anyother unusual marks or cuts on the blanket or its cord? Is the burnt plastic smell isolated to a particular spot?

[bernm]

The blanket itself looks perfect. I just had a closer look though, in response to your question. There appears to be a dark spot just where the silicone comes out of the plug area. I can't smell the burnt smell now, but just after it happened the smell seemed to be coming from the blanket's plug area as well.

There is a screw on the plug itself, so maybe later when I get some time I'll open it up and have a look. Maybe the wiring was bad in the plug? Hmmm. I wonder if it'd be worth cutting the plug off and sticking an Australian plug end on it and trying to revive this one (if it was just a dud plug or the wiring into the plug)? Or maybe that'd be a recipe for disaster?

Would anyone know if anything electrical in my home wiring should be checked as well? I really just don't know much about electrical matters. I live in a pretty old house. The wiring to the shed is fairly recent though, much newer than most of the electrical work around the house itself.

Thanks.

[matthew]

if it had a US plug on it I reckon you probably got given a 115volt model.

[bernm]

It's the 220V model - not a North American plug. I opened it up and sure enough, it's fried where the cord meets the plug.

[liam_fnq]

Bern, I bought the same one a while ago. I changed the plug to an Australian plug. I haven't had any dramas with it.

In terms of electrical testing there's not a lot that needs to be tested on so simple a machine. Here's what you can do: use an ohmmeter to check what the resistance is across the two pins. If your blanket is rated at 1035W (like mine) theory says that it should read 50 odd ohms. I won't explain the theory unless someone wants me to. Just to check up on myself (I've been wrong before ) I just put a meter on my blanket and it read 50ohms. What this reading means is that the blanket is probably fine and I'd happily plug it in. If the reading was low (say 10 ohms or less) the blanket has a short circuit. If the reading is high or wont read at all the blanket is open circuited. Short circuit or open circuit means one of two things, either the blanket is buggered or the plug is buggered. It's not hard to trim the lead back and put a new plug on and then re-test.

Matthew, the 220v model comes with a European plug.

[liam_fnq]

You've answered my question before I asked them.

Congrats probably all it needs is a new plug and it'll be good as new.

[bernm]

Thanks. That sounds like a good way forward. I'll give it a test and see what happens.
Bern

[DarwinStrings]

Hmmm I am about to order one from LMI as my last one recently blew up, I hope that don't happen but as you said even after the length of time LMI is happy to replace it, I have never heard anything bad about LMI.

Jim

[liam_fnq]

Jim, silly question here but have you checked it's not something as easily fixed as Bern's?

[DarwinStrings]

Where the wires go into the blanket it is totally fried to the point that one of the wires dropped out, it is not a LMI blanket. Maybe it could be fixed but you would have to somehow solder the wire back into the (not sure what to call it) resistor or wire mat and then re-silicon over the burnt out silicon. I feel more comfy with a new one. Oh and mine never came with a plug to start with.

Jim

[liam_fnq]

Can't say I'd try to repair that either.