How hot should a dew strap get?

[michaelmorris]

I've just been shortening the lead on a dew strap.  After shortening the lead from 2m down to 60cm I plugged it in to test it.

I noticed that it very quickly got very hot.  Thinking I had not wired it up correctly, I fitted a new plug. I tested it again and again it got very hot.

I then measured the temperature of the inside of the strap at 52oC.  For comparison I tested the temperature of the other 3 dew straps attached to the controller and found that the temperature of the other dew straps ranged from 45oC and 49oC.

Would I be correct in thinking that these are all much too hot? If yes, would I be correct to be thinking the problem is likely to be my ageing Kendrick digifire 7?

I have measured the voltage on the dew controller output at bang on 12 volts.

[Dr_Ju_ju]

What does the resistance of the straps read ??  & if your dew controller is putting out 12v then it is probably 'full-on', have you tried 'backing' it off. 

[StuartJPP]

A dew heater should be warm enough to just prevent the temperature of the air/glass of the objective from dropping below the dew point.

My dew heaters barely feel warm and it can be difficult to tell if they are on or not.

52C is a bit too high!

As above, check the resistance of the strap.

[Spikey]

Same here, mine barely feel warm to the touch and they certainly do the job.

[michaelmorris]

1 hour ago, Dr_Ju_ju said:

What does the resistance of the straps read ??  & if your dew controller is putting out 12v then it is probably 'full-on', have you tried 'backing' it off. 

Unfortunately I don't have access to a multimeter at present, just a voltmeter.  The high temperature is on all four dew straps, regardless of what I set the heating level at on the Kendrick Digifire 7.

 

[Dr_Ju_ju]

Michael, if what you are saying is true, I'd be Very suspect of the Kendrick (I don't know it as I make my own), but if trying to control it produces no change in output, & just runs full whack, it must have a fault....

[symmetal]

When you tested it was it just in free air and not attached to a scope. The ones I have get pretty hot running off full 12V just sitting on the bench. The scope acts as a good heatsink for the strap. The controller should allow you to run them at less than full power though.