115923 Ametek motors (Fire Potential)

[Thomas Vaught]

I recently ran some distribution testing on a mass air meter style
metal flow bench using the Ametek 115923 flow bench motors,
(same as the SF ones).

The bench is divided up so that we can stage the capacity of the bench
in 4 stages (8 motors total). Each stage has a air inlet control valve
(mechanically adjustable), Two 115923 motors, a control relay, and a
cooling fan for that relay.

We originally did some low air flow distribution testing and the first
pair of motors functioned great.

We went up in air flow to the next level so we added a second pair of motors. There was a lot of sparking around the brushes so we closed off the air to that pair, killed that pairs power, and moved to the third pair of motors.

The third pair of motors functioned fine as did the fourth pair of motors.

Once testing was completed we decided to determine what was going on with the one pair of motors. When we inspected that pair of motors we saw that the insulation around that pair of motor brushes was melted badly and if you ran the motor there was a large "fireball" around the brushes. This had occured on that pair but not on any of the other pairs. no fireballs above their brushes at any time but some natural sparks from the brushes.

We decided to buy a couple of new motors from Ametek (Grainger) and install them. We installed the first motor right out of the box and with a brand new motor had the same fireball.

I had a slightly used motor from another project and we installed it and
no fireball so I know the wiring etc is good.

Same deal with the second new motor out of the box. Fireball.
Installing another older motor and no fireballs anywhere.

What is up with that deal?

Tom V.

[Tony]

Usual reason for the "fireball" would be shorts between commutator segments, or a faulty armature winding. It may have been a manufacturing defect, or subsequent damage caused by overheating or overloading etc....

I don't like vacuum motors, especially in wooden benches. Although I have never tried it, a smoke detector located downstream of the motors may give some useful warning that something is wrong.

By the time you smell something burning, it will probably be well alight, and may be pretty difficult to access to extinguish. Not a pleasant thought.

[Thomas Vaught]

Agree, we have some extra 4" Beckman port holes in the bench to allow adding extra air to the
bench on blow thru testing on the inlet side. Same deal on the exhaust side of the motors.
The exhaust side has the clear covers so the fireball is obvious through the covers. Covers can be quickly removed to blow co2 at thge motors if necessary BUT I really want to pin down the root cause. The other motors have no visible damage and are seeing exactly the same temps, load, etc as the failing ones. Defective motors?

Tom V.

[Tony]

Most likely a defective motor. I have no idea what sort of quality control goes on in third world countries where most of these motors are probably manufactured.

But I very much doubt that they are built to aerospace quality standards with full ISO traceability (giggle).

[Thomas Vaught]

I spoke with the head Ametek guy today and he feels that the motors may have bad comutators. I will probably sent him the bad units for inspection.

He says they should never fail like that.

Tom V.

[dragv6]

[Thomas Vaught]

Brand New out of the box. I did have a couple of the older but not second hand motors that worked fine.

Tom V.

[Griffin]

It must be something in the air - we had a motor go up in smoke tonight.

[dragv6]

[larrycavan]

FWIW - Quality control seems to be at a low in many industries these days. A variety of reasons can be attributed to that situation. The company I work for has purchased 40 brand new Western Star trucks over the past 2 years and you would not believe how many problems they've had with them. The problems are not only with Detroit powered trucks but also with Cat motors. Everything from air compressors falling off to radiator hoses blowing off have happened. Worst part is the trucks went through factory QC and then Dealer prep.....still, parts are falling off, motors are coming through with knocking noises, heads have been a problem....you name it...it's pretty much happened. :angry:

I'd be on the phone to Ametek to discover where the motors are made and demanding to know why the high dollar item doesnt' seem to hold up as well as the surplus center chepo variety of motors.....Someone knows the answer.

JMO

[jsa]

[Thomas Vaught]

[color=#000000]Quote by Larry C.:

[larrycavan]

[larrycavan]

[color=#000000][quote="Thomas Vaught"]Quote by Larry C.:

[gofaster]

The danger of fire in our wooden or composite material benches is a very real danger. I touched on it briefly a few years ago when I mentioned that my Blue 110 bench caught fire. Part of the problem was that while I was flow testing, the air moving through the bench exited upward, and it was carried away from me. Luckily, someone came into my shop and interrupted me. He said he could smell something burning. Sure enough, smoke was coming out of my bench.

The manufacturer had terminals bolted through the plywood joining the control circuit to the motor circuit on the other side of the bulkhead. The bolted connection came loose over the years, and that became the source of heat. Add air flowing past the heat source and you can guess the rest. If there had not been any interruption, I might have burned the shop down that day!

I have pictures posted somewhere on the forum that show how I wired my new bench. I used commercially available terminal strips for making connections, and I used cord grips to seal the wires when they went through a panel. They are pretty much the NEC way of moving power through walls in hazardous locations. Other forum members have said it, and I'll say it again. When it comes to powering the bench, it is very important to adhere to proper wiring practices. If it is beyond your ability to do it right, hire a qualified electrician to either oversee/help you, or to actually do it for you.

Tony suggested that smoke alarms mounted downstream of the airflow may be a good idea. I think he may have something there. The piercing noise they emit could be audible over the noise of flowtesting. I don't know about the rest of you, but I often end up running the flowbench after shop hours when I have no interruptions, i.e., I'm alone in the shop. A smoke detector could make the difference between having a little trouble, and burning the place down.