Poorly fuse in the blower mod circuit

red_dwarfers · Unread post by **red_dwarfers** » 19 Nov 2010, 17:22

In the words of the Chuckle Brothers "Oh dear oh dear".

This is the fusebox I put in for the blower module, I only happened to come across the condition of it while I had the dash clocks out to replace a few bulbs! I've checked all of the wiring I put in and everything else looks okay.
I'm guessing that this was caused by the warming of the fuse in an enclosed box. Looking at the colour of the blob, it was a 30 amp fuse I put in. Would this be on the very limit? Should I put in a slightly higher rated one? Could it be caused by having that lid over the top trapping in the small amount of heat, building it up?

kenhall1202 · Unread post by **kenhall1202** » 19 Nov 2010, 17:59

Sounds like a similar failure to that frequently experienced by XM owners.
The answer in my case was to fit a separate 30amp MAXI fuse and holder outside the underbonnet fuse box. The overheating of the smaller fuse at high current loads is caused by resistance where the the fuse spade terminals meet the metal spring blades and there is insufficient metal to dissipate the heat build up - result - melted plastic and burnt contacts. The physically larger MAXI fuse totally overcomes these problems. A higher rated small fuse will not help.

citronut · Unread post by **citronut** » 19 Nov 2010, 19:16

what was the rateing of the fuse holder,

i would susspect a bad conection maybe the fuse in its holder?????

if you put i bigger fuse it might not just stop at the fuse holder, and you might need to call the neeee nau's out with there big hose's

regards malcolm

Unread post by **Peter.N.** » 19 Nov 2010, 22:26

As Ken says, this is a common XM problem. When the blower packed up on mine I went straight to the fuse - it wasn't there, someone had wired an external one which was lying on the battery! that had gone too.

Peter

davetherave · Unread post by **davetherave** » 20 Nov 2010, 07:35

Even with my external fuse holder for the xm, it sometimes gets slightly warm and melts... Its still a standard sizd fuse though.

Unread post by **Old-Guy** » 20 Nov 2010, 09:10

citronut wrote:what was the rateing of the fuse holder,

I would suspect a bad connection, maybe the fuse in its holder?????

If you put in a bigger fuse it might not just stop at the fuse holder, and you might need to call the neeee nau's out with their big hoses

Malcolm's spot on. A standard (i.e. not quick-blow) fuse will take twice the rated current for many hours before it eventually blows due to progressive oxidation of the fuse element. I can't remember the typical figures, but at 4X rating current the blow time is still measured in minutes.

The second picture clearly shows that it isn't the fuse element (the thin U-shaped bit) that's got hot, but one of the spade connections. A poor quality or under-rated fuse holder is to blame.

Poor quality brass (soft and easily bent) is often used in cheap electrical kit in places where plated phosphor-bronze (nice and springy) is needed. You get the same problem with some cheap 13A plugs.

I doubt there is a short anywhere - just a failure of the fuse holder.

Unread post by **CitroJim** » 20 Nov 2010, 16:09

Absolutely spot-on Guy!

The blower takes about 20A on full chat and that can give rise to some serious heating if there's a modicum of resistance about...

I don't believe those fuse holders are rated much above 10A continuous even though you can fit a 40A fuse in them.

red_dwarfers · Unread post by **red_dwarfers** » 20 Nov 2010, 16:55

Thank you very much all

I shall look into getting a beefier fuse holder and keep an eye on it.
This 30 amp fuse. If you reckon the blower only takes 20A Jim should I be using a lower rated one?

Unread post by **Peter.N.** » 20 Nov 2010, 17:06

The standard fuse is 30a at least it is in the XM, I think the fuse itself might warm at 20a, if you have a short, the wiring is quite heavy to blow a 30a

Peter