Salutary tale: Frying tonight.

[Tommohawk]

When I first started using a 12V splitter cable for the camera cooler, mount supply and dew heaters, I pondered long and hard whether to fuse the supply end at 8 amps, or each individual cable at 2 amps. I solved the problem by doing neither - what could possibly go wrong? And I've used it like this for the past 4 -5 years.

Last night I left the rig running (to capture IC5070 which is still work in progress but coming along nicely) but when I checked it at 5a.m. I noticed it had run to the mount limit nicely, and the imaging run had completed.... but I couldn't park the mount, and tons of error messages. Closer inspection showed one of the cables had pretty well fried. Oddly, it was a cable that wasn't being used and the plug was hanging downward.... so I'm pretty sure condensation must have dripped down the cable to the exposed live plug, and bridged the outer and inner conductors. In fact I can see the insulator in the plug has got heat damaged 

So what's all this about dew being pure water and therefore non-ionic and non-conducting??? Fortunately none of the kit seems to have suffered - apart from the cable of course!

Anyhow, the take home message is get some fuses in there, and cover any exposed connectors. I've become increasingly complacent about this and the warm weather lulls one into a false sense of security.

[wulfrun]

Hmm, I'd be very surprised indeed if a wet plug could draw enough current at 12V to do that. Is it possible it's partly shorted the centre terminal to something else on the mount? Is the plug showing physical damage? The "fault" appears to be at or close to the plug though, whatever its nature. I'd be looking elsewhere for a culprit than dew/condensation, although it's hard to say it's impossible.

EDIT: Just a thought, long-term corrosion of the plug due to repeated condensation? Is the plug normally unused?

Edited July 10, 2022 by wulfrun

[Tomatobro]

A wire (usually the centre one) has broken free and shorted to the negative. Take a Stanley knife and split the moulding to reveal the connections and you will see what I mean. I have seen this kind of failure before.

If the connections are ok then its whatever it was connected to is the problem.

[Tommohawk]

1 hour ago, wulfrun said:

Hmm, I'd be very surprised indeed if a wet plug could draw enough current at 12V to do that. Is it possible it's partly shorted the centre terminal to something else on the mount? Is the plug showing physical damage? The "fault" appears to be at or close to the plug though, whatever its nature. I'd be looking elsewhere for a culprit than dew/condensation, although it's hard to say it's impossible.

EDIT: Just a thought, long-term corrosion of the plug due to repeated condensation? Is the plug normally unused?

It's an 8 amp supply so there's about 100W frying power but I agree that conducting anything like that through condensation seems unlikely.

1 hour ago, Tomatobro said:

A wire (usually the centre one) has broken free and shorted to the negative. Take a Stanley knife and split the moulding to reveal the connections and you will see what I mean. I have seen this kind of failure before.

If the connections are ok then its whatever it was connected to is the problem.

I don't think the short was within the splitter - as wulfrun said it looks closer to the very tip. It wasn't plugged in to anything though...  it was exposed. I've just been looking again at the this and although the tip is basically concealed, its just possible for the plug tip to contact the metal work on the mount, so I think that's what must have happened.