Home made dew heaters.

[decoyp]

Just read Astroblaggers thread about home made dew heaters.

I just thought I should mention from my own experience, the importance of incorporating a suitably rated fuse in the dew heater circuit. The one that Astroblagger has illustrated does not seem to have one.

I made one of these dew heaters using exactly the same method (got the idea from IceInSpace as someone also pointed out). It worked great until one night when I was packing away the gear the dew heater leads shorted out. I was powering it off a car battery. The leads (speaker cable 1mm2) just melted in a matter of seconds. I was very lucky not to end up with melted PVC all over the OTA. It could also start a fire in a wooden observatory quite easily which would be much more serious and expensive.

I still use the same design of dew heater but have incorporated an in line fuse in the lead. You can buy them from maplin or RS. The rating of the fuse will depend on what size heater you are using. Make sure your cable is big enough to take the current and that your fuse is rated properly to prevent disaster in case of a short circuit.

Don't get caught out like I did.

All the best

Richard

[Psychobilly]

I had shorting problems with two "commercial" dew heater bands on Fiday night..

Luckily they were on a decent dew heater controller which limited the melt down... The bands themselves were fine its the cable that was fitted to them that failed where it was connected to the dewband...

Peter...

[yesyes]

I totally agree if a car battery (or similar) is being used. These can be very nasty. They can melt a spanner if you accidentally short the battery with it. Look what happens when you get the polarity wrong when giving a jump start:

Carsplotion - Imgur

On the other hand, when operating it from mains and using a proper power supply with short circuit / over-current protection, then the power supply should take care of that. An extra fuse can't hurt of course.

[studdedsole]

I totally agree if a car battery (or similar) is being used. These can be very nasty. They can melt a spanner if you accidentally short the battery with it. Look what happens when you get the polarity wrong when giving a jump start:

Carsplotion - Imgur

Holy s...h...1...t

[Dude]

wow... thats very nasty!

[Astroblagger]

Hello Decoyp yes your right i didnt fit a fuse directly to the dew heater but the 20aH sealed battery lead i use to connect up via the 12v plug has a 5amp fuse fitted, i should have mentioned that saftey first!

[decoyp]

Sounds like just the job.

I didn't mean to come across as telling people how they should do stuff. It's just that when mine went into melt down, it was a bit of a shock and I wanted to share the experience so that it didn't happen to someone else.

Mind you, it was a probably a bit stupid using a car battery to power it - I should have known better. Seemed like a good idea at the time.

Never mind. As they say "what doesn't burn your house down makes you stronger" or something like that !!

Cheers Richard