Quantcast

Here's something you shouldn't do...

The Rocketry Forum

Help Support The Rocketry Forum:

Winston

Lorenzo von Matterhorn
Joined
Jan 31, 2009
Messages
8,772
Reaction score
957
I had filled the spirals on a body tube with Elmers Carpenter's Wood Filler and was sanding it smooth. I'd been doing this for about 15 minutes and there really wasn't much dust visible in the air. Suddenly, I heard a high voltage arc, my PC died and my UPS alarmed. I was sanding about five feet from the (formerly) running tower PC.

The extremely fine dust apparently got inside the HV section of the not cheap CoolerMaster power supply (luckily, I got it on deep discount sale) and caused a short and arc. I'm posting this from my PC #2 (of three).

Lesson learned the hard way. Don't do that...
 

MarkII

Well-Known Member
Joined
Jan 18, 2009
Messages
8,255
Reaction score
9
Ouch! Sorry to hear that, and thanks for the warning.

My rocket workshop and my PC are at opposite ends of the house. I cannot ever see putting my sole unit (which I can't afford to replace) in the same room that I use to build rockets - I have enough trouble keeping the dust and dirt out of it as it is! If it ever goes kaput I will be offline for a LONG time.

MarkII
 

cjl

Well-Known Member
Joined
Jan 18, 2009
Messages
12,549
Reaction score
5
That's good to know. I'm kind of puzzled by the fact that the dust was apparently conductive.
 

Donaldsrockets

Well-Known Member
Joined
Jan 18, 2009
Messages
3,562
Reaction score
1
Location
Fort Myers, FL
Hopefully just the PSU was damaged and that it didn't take anything else with it - Motherboard, CPU, RAM, etc.

Sometimes that can happen if a PSU fails.;)

I'd check to see if the PSU is under warranty. If so, it'd be a lot cheaper to have the manufacturer replace it rather than have to buy a new one.

Thanks for the heads up though but I'm sorry you had to deal with this.
 

ben_ullman

Well-Known Member
Joined
Jan 18, 2009
Messages
1,523
Reaction score
0
The only electronics we have in the garage is a 27" LCD TV. Its mounted up on a wall so it doesn't get dirty to often. We go cover it if we need to paint/sand with the garage door closed.

Ben
 

Delta-IV

Well-Known Member
Joined
Jan 18, 2009
Messages
1,079
Reaction score
3
I had filled the spirals on a body tube with Elmers Carpenter's Wood Filler and was sanding it smooth. I'd been doing this for about 15 minutes and there really wasn't much dust visible in the air. Suddenly, I heard a high voltage arc, my PC died and my UPS alarmed. I was sanding about five feet from the (formerly) running tower PC.

The extremely fine dust apparently got inside the HV section of the not cheap CoolerMaster power supply (luckily, I got it on deep discount sale) and caused a short and arc. I'm posting this from my PC #2 (of three).

Lesson learned the hard way. Don't do that...
Humm...awhile back in my den (and rocket building workshop) I had a small fire in my PC Power Supply. I replaced the power supply and luckly my PC has continued to work. I was using that same material on filling some gaps in a scale launch pad deck for a display model of my Delta IV Heavy.

So I bet this could had been a reason????

Thanks for sharing that info!!
 

Winston

Lorenzo von Matterhorn
Joined
Jan 31, 2009
Messages
8,772
Reaction score
957
I used to use a homemade PC air intake filter that I cut from thin, fibrous window air conditioner filter material I got at Home Depot. It was very effective in keeping all dust out of the PC case. I took it out to clean over the summer and left it out to reduce temps inside the case (it restricted airflow, especially when I forgot to clean it regularly as I often did; it's easy to clean with just hot water). Removing that filter was another thing I wish I hadn't done.

The affected PC is a tower that's sitting only a few inches above the floor. My theory is that the dust dropped from the body tube as I sanded, rode along a cold air layer just above the floor and got sucked into the case through its air vents which are on the lower half of the case. There's a thin white layer of extremely fine dust on everything inside the case. Nothing extreme, but it's obvious.
 

Winston

Lorenzo von Matterhorn
Joined
Jan 31, 2009
Messages
8,772
Reaction score
957
Hopefully just the PSU was damaged and that it didn't take anything else with it - Motherboard, CPU, RAM, etc.

Sometimes that can happen if a PSU fails.;)

I'd check to see if the PSU is under warranty. If so, it'd be a lot cheaper to have the manufacturer replace it rather than have to buy a new one.

Thanks for the heads up though but I'm sorry you had to deal with this.
Yeah, I sure hope it didn't fry anything. It was quite a loud ZAP! sound when it failed. I'd planned to upgrade soon, but the new Intel 32nm CPU that I want to use isn't out yet although there is one USB 3.0 (a _HUGE_ speed increase) motherboard now available, something else that caused me to want to upgrade.

I'll check up on that warranty although I've already ordered a cheap power supply to tide me over until the upgrade.
 

Winston

Lorenzo von Matterhorn
Joined
Jan 31, 2009
Messages
8,772
Reaction score
957
Humm...awhile back in my den (and rocket building workshop) I had a small fire in my PC Power Supply. I replaced the power supply and luckly my PC has continued to work. I was using that same material on filling some gaps in a scale launch pad deck for a display model of my Delta IV Heavy.

So I bet this could had been a reason????

Thanks for sharing that info!!
Wow! I think that's more than just a coincidence.
 

MarkII

Well-Known Member
Joined
Jan 18, 2009
Messages
8,255
Reaction score
9
That's good to know. I'm kind of puzzled by the fact that the dust was apparently conductive.
As dust is drawn across a material, though a duct, etc. it picks up an electrostatic charge. This is probably what happened in Winston's computer. The large amount of dust that was being drawn across the floor and up into the vents of the CPU by the fan acquired a large amount of static electricity that eventually arced (discharged) to a conductor inside the unit. Electronic components such as cathode-ray tubes in televisions and motherboards in computers are great generators of electrostatic potentials which is why they are such dust magnets. Computer components are also very sensitive to ESD's (electrostatic discharges) and are easily damaged by them. In a typical tower-style CPU, there are other components besides the motherboard that do this, too, including the ventilation fans themselves. If luck was on his side, the ESD that occurred in Winston's computer didn't arc to any critical components on his CPU, or the system would be toast. There are ways to protect sensitive electronic components in such environments.

MarkII
 

stickershock23

Never Fly Naked
Joined
Jan 18, 2009
Messages
4,181
Reaction score
247
That is a lesson hard learned. I use my Laptop and my Vinyl cutter in the garage all the time, its where I do my decals and where I build rockets.

Every time I fire up my air compressor, I blow both units out. mostly because I know the dust does not help with heat, I never thought about a short or an ESD. from the stuff.

I wonder if the sandpaper has iron oxide in it, that is very conductive, the dust from that may have helped the arc too? just a though.

also know that most any kind of DUST if its fine enough will burn rapidly. so be careful with any flame in your shop after sanding. ask me why I know that! ok please don't LOL
 

Winston

Lorenzo von Matterhorn
Joined
Jan 31, 2009
Messages
8,772
Reaction score
957
Once I get the replacement power supply, I'll open up the old one and look for where it arced. I mirror everything that's important to a separate, networked PC via a gigabit LAN, so data loss won't be an issue for me if anything beyond the power supply fried. I never build with bleeding edge components anyway.
 

Winston

Lorenzo von Matterhorn
Joined
Jan 31, 2009
Messages
8,772
Reaction score
957
That is a lesson hard learned. I use my Laptop and my Vinyl cutter in the garage all the time, its where I do my decals and where I build rockets.

Every time I fire up my air compressor, I blow both units out. mostly because I know the dust does not help with heat, I never thought about a short or an ESD. from the stuff.

I wonder if the sandpaper has iron oxide in it, that is very conductive, the dust from that may have helped the arc too? just a though.

also know that most any kind of DUST if its fine enough will burn rapidly. so be careful with any flame in your shop after sanding. ask me why I know that! ok please don't LOL
With a laptop, the HV section of your switching-mode power supply is inside the sealed plastic power supply brick, so a power supply short like mine won't occur. However, even though the laptop operates at very low voltages internally, I suspect that iron oxide dust may be conductive enough to eventually cause problems if enough of it builds up. In my case, I was using a nifty, foam-backed, 150 grit sanding pad that I got from Walmart in a 2-pad blister pack. Works fantastic on body tubes and the white (not red iron oxide) abrasive doesn't wear off, at least when sanding body tubes which is the only thing I use them for. The clogged abrasive surface is easily cleaned by running the pad under a tap. The foam backing doesn't absorb significant amounts of water so it dries very quickly.

Fine dust suspended in air makes for catastrophic dust explosions, too:

http://www.youtube.com/watch?v=TAdElO1FCSM
 
Last edited:

mjennings

Well-Known Member
Joined
Jan 18, 2009
Messages
1,558
Reaction score
7
yup sounds like ESD to me. A very small amount of static charge can easily fry sensitive components < 3 volts, we hear static/see/feel static discharge of > 3000 Volts if I remember correctly, from the ESD courses I used to have every year at my old job. Static is caused by things being touched together and removed. Pulling Scotch tape off a role generates at least several hundred volts and since it is non conductive the charge can stay attached up to 2 weeks!!!!, that is why things jump to the tape at the last second when you try to precisely align things.

Mark II's analysts is likely right on.

Also a former coworker of mine hated saw/sanding dust because he clamed it could spontaneously combust in the right conditions. I don't know about that but it does make pretty good kindling.

More good reasons to keep the work area clean!
 

MarkII

Well-Known Member
Joined
Jan 18, 2009
Messages
8,255
Reaction score
9
Non-conducting materials (insulators) work well at generating and holding surface charges. In Winston's incident, the dust acquired and held an electrostatic charge precisely because it wasn't conductive. (Did you ever notice how an empty styrofoam cup attracts such things as hair or little bits of paper?) Friction generates electrostatic charges through a combination of the triboelectric effect (what mjennings was describing) and electrostatic induction. The movement of the dust across the floor as it was drawn toward and into the CPU by the vent fans, the friction of the individual dust grains against each other and the friction of the dust against the vents all generated a sizable electrostatic charge in the surface of the dust grains. Static electricity is characterized by high voltage and low continuous current. In other words, when a material containing a large static surface charge is brought in close proximity to an electrode, it will transfer (discharge) practically all of the potential in a very brief span of time. On human scales, this is perceived as a surprisingly powerful shock or spark. On larger scales, this is called lightning. Static electricity is a far more ubiquitous phenomenon than many people realize.

MarkII
 

Winston

Lorenzo von Matterhorn
Joined
Jan 31, 2009
Messages
8,772
Reaction score
957
The type of components within a switching power supply are not typically susceptible to direct, in-circuit ESD damage with the probable exception of the switching controller IC. These are mostly high power components with large junction/gate sizes. The only way I'd go with an ESD-based cause would be if a static discharge glitched the controller IC which then led to an major overvoltage condition in the output drivers of the supply causing their failure and the very loud HV arc I heard. Actually, I'd bet that this is the most likely cause of the failure.

I any case, no matter what the cause, I get back to my original warning: don't do this.
 
Last edited:

Luv2launch

Well-Known Member
Joined
Jan 18, 2009
Messages
463
Reaction score
2
I had a similiar incident with my pc a few months back from sanding balsa too close to it at least I am assuming thats what happened I was sanding near it at the time it went but I had been not long before.It went out with a loud crack then everything went black.Now I try to remember to clean out my pc every few months and I sand elsewhere.
 

Winston

Lorenzo von Matterhorn
Joined
Jan 31, 2009
Messages
8,772
Reaction score
957
Since dry balsa is not a good conductor at all, I think your incident pretty much confirms the ESD-based explanation, at least to my satisfaction. I'd further bet that it's caused by an ESD-induced controller IC malfunction. My runner-up cause would be a short in a very high peak voltage component, like an inductor, brought about by a high concentration of airborne dust reducing air gap resistance followed by the failure of one or more output power transistors.
 
Last edited:

luke strawwalker

Well-Known Member
Joined
Jan 18, 2009
Messages
9,147
Reaction score
16
Also a former coworker of mine hated saw/sanding dust because he clamed it could spontaneously combust in the right conditions. I don't know about that but it does make pretty good kindling.

More good reasons to keep the work area clean!
Yep... ever seen a grain elevator explosion?? TONS of grain dust can become airborne, and remain suspended, especially in grain silos where the air is contained and the falling grain of the filling silo keeps the air in a constant circulation flow inside the silo, keeping the dust suspended. If there is a spark, from say an electric motor brush or some other component in sufficiently thick dust, it can ignite a particle of dust, which ignites the one next to it, in an ever growing chain reaction that takes off explosively as the particles start igniting each other and form a wave-front. Inside a contained vessel like a grain silo, the forces are magnified by the compression shock wave and it can go off just like dynamite!

There was a grain elevator years ago near I-10 and the Beltway in Houston that had suffered a grain-dust explosion, and these solid concrete steel-reinforced silos were shattered and blown apart like some of the old A-bomb test footage from the force of the explosion...

Any dust from flammable source material can explode under the right conditions... much like a fuel-air bomb... when I was in high school, our science teacher did an experiment to show us... he took a Christmas cookie tin, cut a small hole in the bottom just large enough to allow a three foot piece of surgical tubing to pass through, then installed a small funnel inside the tin on the end of the surgical tubing. He poured a tablespoon or so of regular white baking flour into the funnel, set a lit tealight candle inside the tin, and popped the lid on, then quickly blew a puff of air through the tube to make the flour go into airborne dust inside the tin-- POW!! and the lid flew off and sailed straight up, trailing a ball of flame behind it, as it frisbeed across the room...

Mr. Petrash was COOL! :) OL JR :)
 

Winston

Lorenzo von Matterhorn
Joined
Jan 31, 2009
Messages
8,772
Reaction score
957
Don't get creamer dust near your PC power supply (that's a stretch to keep this barely on topic):

http://www.youtube.com/watch?v=yRw4ZRqmxOc

Calves milk substitute is often used for large pyrotechnics effects because it's far cheaper in bulk quantities and works as well or better than creamer.

BTW, the Mythbusters didn't use a large enough charge to disperse the creamer optimally. The high speed photography clearly shows that. Too bad, they could have produced an even more energetic effect.
 

roadkill

Well-Known Member
Joined
Jan 30, 2009
Messages
1,731
Reaction score
0
Sandpaper is mostly aluminum oxide,
so highly likely the dust is conductive....

At least here in FL you can do your
sanding outside the house just about year round...
 

Winston

Lorenzo von Matterhorn
Joined
Jan 31, 2009
Messages
8,772
Reaction score
957
Sandpaper is mostly aluminum oxide,
so highly likely the dust is conductive....
Yeah, but the sanding pad I use hasn't lost a noticeable amount of abrasive since I began using it some time ago. And I was sanding an LPR body tube, nothing huge.
 

Winston

Lorenzo von Matterhorn
Joined
Jan 31, 2009
Messages
8,772
Reaction score
957
http://www.accuratus.com/alumox.html

Maybe the Elmer's product is, though. Anybody have a pile of the dust that they can stick a DVM into?
Here's the MSDS:

http://www.hardwarestore.com/media/msds/260927.pdf

Don't see anything very conductive there. Just measured a wet pile of it and get 1.3 MegOhms with the probe tips as close as they can get without touching. Let me sand up a pile of dry dust to measure right next to my backup PC. ;)

I tend to think it's caused by static damage/glitching of the switching controller via static buildup on the PC board's top surface. Once that puppy does just one thing wrong, the supply will be toast.

Just opened up the bad supply and see no visible burned area(s) that I'd expected to see considering the huge HV arc ZAP I heard and the burned electronics that I smelled. There was the barest hint of extremely fine white dust on internal surfaces with that dust looking distinctly the same on my finger as the Elmer's filler dust. The PC board is single sided and, now that I think about it, all PC power supplies I've opened were only single sided, undoubtedly due to low component density. So, there is no solder mask on the board's component side. However, that doesn't change the surface static buildup theory since the board material is non-conductive and there is no ground plane on the upper surface of the board to ground a static charge buildup.
 
Last edited:
Top