Wattmeter failure

[Andre Majorel]

Left a 400 W dehumidifier running off a wattmeter. After a week
or two, the dehumidifier didn't work any more. The fan is on but
when the compressor tries to start, the display jumps to about
1200 W for a couple seconds, a click is heard (maybe a klixon)
and that's it.

The dehumidifier works fine without the wattmeter.

The wattmeter now reads 300+ W for three 36 W FT when it used
the read about 140 W.

Is this a well-known failure mode ? Bad shunt ?

Thanks in advance.

 

[tm]

RoHS strikes again.

 

[mike]

Left a 400 W dehumidifier running off a wattmeter. After a week
or two, the dehumidifier didn't work any more. The fan is on but
when the compressor tries to start, the display jumps to about
1200 W for a couple seconds, a click is heard (maybe a klixon)
and that's it.

The dehumidifier works fine without the wattmeter.

The wattmeter now reads 300+ W for three 36 W FT when it used
the read about 140 W.

Is this a well-known failure mode ? Bad shunt ?

Thanks in advance.

You've asked for help with the failure modes of a wattmeter while
giving no, zero, not any clues as to what kind of wattmeter.

It's like asking, "What's wrong with my car?" It doesn't work any more.

 

[Andre Majorel]

The only thing I can think of is to find out what inrush current is the
Wattmeter designed for. In other words is it rated for motors?

The manual only says 16 A / 3680 W (I'm not in 115 V-land).

Remember that a dehumdifier is a small regrigerator (with the door wide
open) and as such has a high initial current draw to get the compressor
motor started...

I'm sure someone here can answer the question of how much inrush
current/power to expect on a 400W dehumdifier, but at a guess I'd say 15
to 20A (1200 - 1500ish W).

So, yes, your shunt may well be compromised.

The shunt appears to be a cm-long piece of copper alloy wire, no
markings, CSA about 1 mm². When my free time becomes copious
again, I'll try to compare its resistance with a not-yet fried
unit.

Thanks everyone.