Does a peltier device draw more current as it ages/starts to fail?

[Russell]

We have an electric cool box that is is some years old.  Checking it out for a drive to France it worked for some minutes then stopped working.  Examination showed a blown 5A fuse on the 12V feed.  It is rated at 47w which by my calculations is 4A @12V but is actually drawing 5A @13.6V from my battery charger.  The power plug shows it should be fitted with a 5A fuse.

All I can do, not having a selection of 20mm fuses to hand, is drill out the blown fuse and solder a single strand of copper (approx 0.2mm diameter) from a stranded cable to the end caps.  I'm assuming the car has a fuse on the 12V power feed. It is working but the internal temp is down to 2-3degs.

[mrcharly-YHT]

yes, I think so.

I believe the failure mode is usually a breakdown of the bond between the two metals (or corrosion). That increases resistance.

[Russell]

yes, I think so.
That increases resistance.

That would reduce current and efficiency I would have thought.

[mrcharly-YHT]

yes, I think so.
That increases resistance.

That would reduce current and efficiency I would have thought.

Hmm yes you are correct.

[Kim]

Is there a fan in addition to the peltier?  I note that the one on our electric coolbox has a dying bearing, and that stalled motors tend to draw more current...

[aidan.f]

Please, please get a fuse .. there are good firey reasons why the bit of wire is contained.

[Kim]

Yes.  I guarantee that the car's fuse will be more annoying to replace than the 20mm one in the plug.  Bonus points for it sharing a circuit with something important, too.

To say nothing of the current rating of the dubious bell-wire that seems to be compulsory for 12V accessory leads.

[Mr Larrington]

Now I'm kind of wondering whether use of the 12-vole anbaric pump was responsible for the unexpected battening of the Fast-Appreciating Future Classic's flattery the other day.  Although it’s a big sturdy flattery, as befits a diseasel, and there was no sign of anything catching fire.

[Diver300]

Depending on the battery charger, the output may be unsmoothed. If so, all bets are off as to how representative the current measured will be compared to running in a car.
 

[Kim]

Depending on the battery charger, the output may be unsmoothed. If so, all bets are off as to how representative the current measured will be compared to running in a car.

Also, depending on how you're measuring that 13.6V, if 5A is the charger's current capacity (which sounds plausible) it could be a dead short...

[Russell]

It's a home made 'charger', basically just a chunky transformer, 25A bridge rectifier and capacitor capable of supplying 10A and more. The ammeter is a 10A moving coil type.

Noted re fan, it still sounds as loud as it always has done so I think is's OK.  It cooled the box down to -1 yesterday while I was testing it, that's 15 deg below ambient.

The wire is still contained in the glass fuse, but for sanity's sake I'll see how quickly a single strand melts in a short circuit situation.

[Russell]

and capacitor

I lie, I see that I've written on the box "unsmoothed".

Well a piece of the single strand pretty much blows instantly when connected across the 'charger' and the meter does hit the end stop before it goes but not as if it was well over current.  I'll guess upwards of 10A but not near 20A.

I coulndn't find a figure of rupture current for 0.2mm diameter copper wire on t'web.