Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

........your telescope is on fire!

  • Please log in to reply
14 replies to this topic

#1 pyrasanth

pyrasanth

    Gemini

  • *****
  • topic starter
  • Posts: 3,105
  • Joined: 08 Jan 2016

Posted 08 December 2019 - 08:32 AM

I had the 11" Celestron RASA returned to me from collimation on Friday. So yesterday morning I set it back up on the mount.

 

I connected everything needed and went back into the house for a well earned cup of tea and left the dew strips connected to power.

 

I'm drinking my cup of tea when my wife screams "....your telescope is on fire......quick throw a bucket of water on it!"

 

Well....the bucket of water was out but I did see flames coming out of one of the dew heater strips & small puffs of smoke. I cut the power very quickly (the circuit to the telescope is on quick stop switch).

 

Investigating the problem- one of the connections where the power cable meets the dew band had gone open circuit and there must have been a clear short circuit. I inspected 2 of the other dew strips & saw potentially the same issue to be forth coming. I have now replaced the dew strips.

 

Some lessons to be seen here-

 

1. check all your cabling for signs of wear.

2. Teach wife about water, electricity & optics?- in the wrong sequence it can all go badly.

 

Clear skies to you all.

 

Best wishes

Mark


Edited by pyrasanth, 08 December 2019 - 08:33 AM.

  • Scott Beith, Jon Isaacs, PrestonE and 7 others like this

#2 kel123

kel123

    Viking 1

  • -----
  • Posts: 946
  • Joined: 11 May 2019

Posted 08 December 2019 - 08:51 AM

Thanks to your wife, it was spotted early enough or it could have easily caused a lot more damage.
  • Jon Isaacs, PrestonE, airbleeder and 2 others like this

#3 Asbytec

Asbytec

    Guy in a furry hat

  • *****
  • Posts: 17,335
  • Joined: 08 Aug 2007
  • Loc: Pampanga, PI

Posted 08 December 2019 - 09:17 AM

Close one, Mark, and thanks for your wife catching it in time. I hope your scope is OK.

#4 Astroman007

Astroman007

    Voyager 1

  • *****
  • Posts: 13,534
  • Joined: 27 Oct 2017
  • Loc: Northern Ontario, Canada

Posted 08 December 2019 - 09:42 AM

Thanks to your wife, it was spotted early enough or it could have easily caused a lot more damage.

Thank your wife also for not acting on her own advice or not being more proactive. You wouldn't have anything now if she had followed through.


  • pyrasanth likes this

#5 pyrasanth

pyrasanth

    Gemini

  • *****
  • topic starter
  • Posts: 3,105
  • Joined: 08 Jan 2016

Posted 08 December 2019 - 10:19 AM

Hi guys- Thanks for all your kind words.

 

The wife is great- I love her to bits. She was just frightened-as most of us are when we see fire.

 

I'm surprised that the RCD did not trip but I guess it was seen as a "normal" current draw even though the dew strip was clearly burning.

 

The telescope escaped with no damage.

 

When I examined the dew strips which had failed I could see that the design looked quite poor. The cable was quite thin & where the cable entered the band there were no strain guards- expensive dew bands as well!

 

The ones I'm using now have really thick silicon sleeved cable & look to be far more robust. 


  • Scott Beith, Terra Nova, havasman and 1 other like this

#6 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 8,238
  • Joined: 04 Jan 2004
  • Loc: ROR Obs. near Pettigrew, Arkansas

Posted 08 December 2019 - 10:46 AM

It's probably best to fuse the dew strip circuit with an appropriately sized automotive fuse.


  • Astroman007, bchandler and OldManSky like this

#7 carolinaskies

carolinaskies

    Vanguard

  • *****
  • Posts: 2,259
  • Joined: 12 Dec 2014
  • Loc: Greenville SC

Posted 09 December 2019 - 11:48 AM

One of the issues with dew bands is they run off the idea of creating heat by variable voltage through a static resistance typically nichrome wire.  Having made them out of resistors in the old days I can attest to the weak point typically being connection points which weaken over time due to assembly/disassembly.  This can happen even to the nichrome wire if it is bent. 

Also, even a fuse is useless if the point of failure falls within the overall parameters of the system to allow 'near failure' before burning out the fuse.  Plenty of house fires have occured because an amp has overheated before a circuit breaker trips.  Sadly I had that happen.  So I'm glad your wife noticed the problem before you had even worse problems on your hands!  



#8 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 8,238
  • Joined: 04 Jan 2004
  • Loc: ROR Obs. near Pettigrew, Arkansas

Posted 09 December 2019 - 12:05 PM

The protecting fuse should be just large enough to pass the rated current.  Any excess current will therefore blow the fuse.



#9 coopman

coopman

    Fly Me to the Moon

  • *****
  • Posts: 6,528
  • Joined: 23 Apr 2006
  • Loc: South Louisiana

Posted 10 December 2019 - 09:19 PM

You'll never live this one down, because they never forget.  Glad that the scope itself survived OK.


Edited by coopman, 10 December 2019 - 09:19 PM.

  • pyrasanth likes this

#10 FDR

FDR

    Lift Off

  • -----
  • Posts: 23
  • Joined: 24 Jan 2019

Posted 11 December 2019 - 11:33 AM

It's probably best to fuse the dew strip circuit with an appropriately sized automotive fuse.

 

 

The protecting fuse should be just large enough to pass the rated current.  Any excess current will therefore blow the fuse.

A fuse won't help this situation. Fuses don't protect the equipment.

 

Current draw is measured for equipment and accessories. The wires are sized to carry that defined amp load over the expected distance (with a margin of safety). The fuses are sized to protect the wiring (with a factor of safety) so that a short/overload doesn't cause the wire to heat up, melt the insulation, and cause a fire between the device and the power source. Let's say you have a 5 amp device, choose a wire size that can carry 10 amps over the distance needed, and use a 7 amp fuse to protect the circuit. If the device fails and pulls 8 amps, it doesn't matter whether it's a 5 amp, 7 amp, or 10 amp fuse. The device already failed and cutting power won't save it

 

It still wouldn't matter in this case. Heating failures that let the smoke out of passive devices, such as this one, frequently come from a high resistance point - frayed wiring, broken solder point, tarnished terminals, fatigue, etc. The total power draw usually drops, but the heat produced in the failure point dramatically increases

 

Ever had an extension cord plug heat up and partially melt because the plug came out a tiny bit? Or seen car jumper cables smoke at the terminals while cranking? Both issues are caused by focused heating in resistive points that are passively reducing total load

 

That's why houses can safely have circuit breakers at 15 or 20 amps (North American 120v). They don't know what you're plugging in at the outlet, but they know what the wiring in the walls can carry



#11 astroseyer

astroseyer

    Explorer 1

  • *****
  • Posts: 69
  • Joined: 05 Jun 2019
  • Loc: Seattle, WA

Posted 11 December 2019 - 04:13 PM

This is such good awareness. I can see this happening and my wife wouldn’t even ask she would just react and open a hose full throttle. Thanks for sharing. A small portable fire extinguisher is probably best.



#12 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 8,238
  • Joined: 04 Jan 2004
  • Loc: ROR Obs. near Pettigrew, Arkansas

Posted 11 December 2019 - 08:00 PM

 

It still wouldn't matter in this case. Heating failures that let the smoke out of passive devices, such as this one, frequently come from a high resistance point - frayed wiring, broken solder point, tarnished terminals, fatigue, etc. The total power draw usually drops, but the heat produced in the failure point dramatically increases

 

All electrical devices run on smoke.  We knew it all along.  When the smoke comes out, they are broken.  lol.gif


  • Stelios, archer1960 and greenstars3 like this

#13 decep

decep

    Mariner 2

  • *****
  • Posts: 255
  • Joined: 19 Aug 2018
  • Loc: Georgia, US

Posted 13 December 2019 - 10:11 PM

Some lessons to be seen here-

 

2. Teach wife about water, electricity & optics?- in the wrong sequence it can all go badly.

If you look at this from a point of view where you are not invested in the equipment, someone dumping a bucket of water on the equipment would have been a totally justified action.  Water is not so bad anyway.  It is worse for the electronics than the optics.

 

 

This is such good awareness. I can see this happening and my wife wouldn’t even ask she would just react and open a hose full throttle. Thanks for sharing. A small portable fire extinguisher is probably best.

I am surprised nobody commented on this.  I would take the water in almost all cases rather than the more common fire extinguisher, especially if you have any interest in saving equipment.  Most fire extinguishers are dry chemical based and probably not friendly to optics, electronics, or the mechanics in mounts.  You would specifically need an CO2 (food and electronics rated) extinguisher.  There might even be a risk of damaging optics with the CO2 due to the rapid cooling of the expanding CO2.
 

 



#14 archer1960

archer1960

    Viking 1

  • *****
  • Posts: 572
  • Joined: 26 Jul 2011
  • Loc: Southern New England

Posted 14 December 2019 - 10:46 AM

If you look at this from a point of view where you are not invested in the equipment, someone dumping a bucket of water on the equipment would have been a totally justified action.  Water is not so bad anyway.  It is worse for the electronics than the optics.

 

 

I am surprised nobody commented on this.  I would take the water in almost all cases rather than the more common fire extinguisher, especially if you have any interest in saving equipment.  Most fire extinguishers are dry chemical based and probably not friendly to optics, electronics, or the mechanics in mounts.  You would specifically need an CO2 (food and electronics rated) extinguisher.  There might even be a risk of damaging optics with the CO2 due to the rapid cooling of the expanding CO2.
 

Yup, dry chemicals will be a lot harder on the scope and electronics than fresh water. CO2 is best, and you don't need to worry about the rapid temperature changes harming anything, because there isn't nearly enough mass of cold gas to cool down an eyepiece significantly, unless you hold it aimed right at that spot for an extended time.



#15 greenstars3

greenstars3

    Messenger

  • *****
  • Posts: 402
  • Joined: 20 Dec 2017
  • Loc: Wind River valley

Posted 15 December 2019 - 07:35 PM

Sometimes after fire training in the summer we have cooled off a 6 pack of beer with a CO2 extinguisher and as a warning it is best to use gloves when using one (you can frost bite your hands). Best thing to do in an electrical fire is to kill the power first. After the power is off, water on scopes would be my first choice. But CO2 is for class C electric fires if you can not kill the power. Most dry chemical extinguishers are rated for class A & B fires some are also rated ABC. Class A fires are regular materials like wood and paper, class B fires are flammable liquids like gasoline and solvents.

Be careful out there and please have an extinguisher in your house and car and I had not thought to put one in my RoR even though it has line power to it but I will get a small ABC extinguisher for it now. All fire extinguishers will clearly state what type of fire they are rated for.   

 

Training Captain HVFD

Robert  


  • mrki233 likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics