Large spark in CMS motor

Page 1 of 3  
When using my Kobalt CMS, I notice a large spark from the motor compartment when I turn off the saw. Sometimes it looks like it fills the whole compartment. Is this a sign the brushes need replaced?
Puckdropper
--
"The potential difference between the top and bottom of a tree is the
reason why all trees have to be grounded..." -- Bored Borg on
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Puckdropper" wrote:

Good place to start.
Might not be seated properly.
Lew
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I took the brushes out, blew out the sawdust in the brush chambers and put them back. The big spark is gone, and I think I picked up a little missing speed.
I'll have to add that to the occasional maintenance list. It only takes about 2 minutes.
Puckdropper
--
"The potential difference between the top and bottom of a tree is the
reason why all trees have to be grounded..." -- Bored Borg on
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Puckdropper" <puckdropper(at)yahoo(dot)com> wrote in message

I suspect that the fix will be short lived. I think you are trying to fix a normal condition.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Leon wrote:

Sometimes my old Skil looks like one of those 4th of July sparklers inside the case. I don't know if it's normal or healthy... I just know I won't use it around open cans lacquer or paint thinner. :-)
--

-MIKE-

"Playing is not something I do at night, it's my function in life"
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You would probably do well to not use any thing that sparks around flamable vapors. I am still in wonderment having retired from the automotive industry how GM prevented gas tank explosions. They used submerged electric fuel pumps and the gasoline literally went through the motor and brushes. No, gas tanks do not always have gasoline in them so being constantly submerged is not the answer.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Leon wrote:

I'm guessing the pump was low enough as to always be submerged, even when the tank was "empty?"
Reminds me of the Mythbusters episode in which they *could not* get a gasoline trail to ignite with a burning cigarette, like you see in the movies. Apparently, smoldering tobacco embers are not hot enough to ignite gasoline vapors.
Another interesting fact from my electrical engineer friend who works for a huge electric producer... Those giant electric turbine generators are cooled with direct water immersion. Turns out pure H2O doesn't conduct electricity. It's all the minerals and other stuff in water that does.
--

-MIKE-

"Playing is not something I do at night, it's my function in life"
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Even when the tank is "empty" it's not empty. It's full of gasoline fumes, which without air (oxygen) aren't dangerous at all. ...and there isn't any air in there either.
Liquid-fueled rocket and jet engines commonly use the fuel and oxidizer as a coolant.

The water going through turbines is hardly pure. I doubt water touches the generator windings themselves.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
krw wrote:

I'm not talking about the water running through the tubes from a dam, that spin the turbines. He was specifically referring to steam powered generators, btw.
And yes, he said they use pure H2O.
--

-MIKE-

"Playing is not something I do at night, it's my function in life"
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I was thinking more about hydro-electric turbines, which are also water cooled.

Nothing is pure. ;-) In this case it has to be as close as possible because of the process. If there were any impurities they would be deposited in the "boiler". Not a good thing in a nuke, either. ;-)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yeah, there is oxygen/air in there, every time you open the tank some gets in. Besides, the tank would collapse if it were totally sealed, Air has to displace the disappearing gasoline.

But gasolinr does on a Gm electric fuel pump. My fuel pump in on my 1975 Olds failed. I dropped the tank and replaced the pump, it is attached to the tank unit/gas gauge float assembly. I cut it open and the thing was spottless inside but the brushes were totally worn out. Gasoline went in one end of the motor and exited on the other. On one end of the motor was the plastic pump.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Nope. Not any more. The engine controls recycle fumes back to the tank. Tanks have been sealed for decades.

Sure. No one was arguing that point. It's hardly dangerous.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yes the engine compartment does recycle fumes back to the tank but there is a lot of AIR that goes with it. Additionally there are lots of peole driving around with lost gas caps, check engine lights and all. And again, the tank is not sealed when you open it up to fill it with gas. There is just way too much of a chance of the perfect combination for the electric motor to set off an explosion if there was not a fool proof way to arrest the spark. How that is accomplished even the Olds factory rep could not explain when I was the service sales manager back in the 80's.

Obviousely but the simple explanation has not yet been explained to me.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Nonsense. There is no air in there at all, even without a gas cap the vapor pressure of the gas will push any out.

Explanation for what?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Obviousely clueless.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Leon wrote:

...
Not quite, no...not _exactly_ "none" wrt to air but the high vapor pressure (very low flash point) of gasoline _is_ the key. To save having to dig up the flammability and explosive mixture data, the most cogent explanation I found on the web quickly was at a site discussing the Flight 800 explosion that went on to compare the situation w/ jet A and an airline tank and the fuel pump in automobile tank and gasoline. From that site--

In short, the answer is that the high vapor pressure of gasoline does create an atmosphere that is too rich for explosion even when the tank is uncapped if there is any liquid fuel at all in the tank at anything above very cold ambient temperature.
I will agree it _is_ something of a mental twist that the very volatility of gasoline is in fact the property that mitigates the fire hazard suppressant from the fuel pump when the tank is low (although I presume the pumps are mounted in a well or at least at the lowest point in the tanks in order to keep them submerged until absolutely all fuel that can be picked up has been. I suppose one could even raise the inlet pipe a little to ensure that; don't know if they do or not.)
hth....
-dpb
--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Snip

While the explanation is valid and works for 99.999% of the time my question is about the other .0001 percent of the time. When the lost gas cap is never replaced and the car is parked and sits for several months with little fuel. Eventually some one cranks it up and the tank has little fuel to submerge the pump. And if you think that is not common, repositions of abandoned cars filled the bill at the dealerships and many were often stripped.
Because the fuel pump is relatively tiny and totally enclosed, IIRC there was a check ball valve on the inlet side, perhaps in some instances of a low fuel condition there is an actual flash when the pump motor in energized, but the flash is contained with in the motor casing. I do recall the motor housing being rather substantial compared to most electric motors found on automobiles.
Thanks for the time spent gathering the information.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Leon wrote:

While perhaps it is relatively common, it's still highly unlikely to be a problem. If there's enough fuel to crank and start the engine, there's enough to suppress the spark and have high enough vapor pressure to prevent flammability at any temperature above about -10F. Remember the flashpoint of gasoline is -40C (which iirc is the magic point where -40C=-40F???).
About the only time above about 0F one could get a real problem would be an essentially dry tank w/ residual vapor and run the pump dry. I'd think that if vehicles were so poor condition as to be left w/ empty tanks and no lid there would be little likelihood of them being cranked in any near-term time frame. Hence the evaporation over a period of time would likely imo serve to remove even the vapors.
--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
dpb wrote: ...

And if your contention is that it is _possible_ under specific circumstances and there's no failsafe protection against that very dilute vapor case that is in the flammability region then yes, it is possible.
I hadn't actively thought about the Arctic conditions increasing risk, I don't know if there's anything done for the really cold areas out of the ordinary or not. I'd guess not; rely on folks in inclement weather areas having enough sense to keep adequate fuel on hand I'd guess.
--
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The problem is though people run out of gas, people run over things on the highway, Houston Freeways, that bounce up and puncture the bottoms of the tanks. Tanks commonly run dry with the pump running.

That is possible but GM has been using a fuel tank pump since the "early 70's I worked directly and exclusively with GM vehicles for 17 years and never ever heard of a problem. And I am not in doubt that what works, "works" effectively. I was and still am curious as to exactly what makes the set up "fool proof".
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.