Had a burst pipe in the workshop a couple of weeks ago, annoying as I don’t use the sink because taps used to freeze and burst in winter, but this burst was t’other side of the stop tap and fountained onto my Fobco Star. Anyway slight pop from the Brooks Crompton motor when the Fobco was switched on, and next time it refused to self start, so I gave the chuck a turn and off it went. I took the motor to pieces, cleaned the contacts (centrifugal start) and put it back together, all worked when fired up on the bench, so back on the drill this morning, and it won’t self start with the belt on. Has my start winding died, and how do I test it? Non technical description please as I am no electrician. It is of course a 5/8” shaft motor, so new ones cost more than the drill is worth.
- Thread starter merryman
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WorkshopChris
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Can you pop the cover off and post up a picture? Do you have a multi meter?
slim_boy_fat
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I won't be up at the workshop until the weekend, will get details then. I do have a multimeter.
No caps, centrifugal starter.
I may go for that if re-winding is too expensive.
WorkshopChris
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The insulation in older motors can be very fragile it doesn't take much to short a few turns.
brightspark
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they were coated with shellac and it can break down
WorkshopChris
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I have a old slow speed motor to re work when i get a chance, windings are ok but the old internal cable has broken down its like a bitumen rubber under cloth.they were coated with shellac and it can break down
Hopefuldave
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I've had good results hooking up a battery charger to the windings with a bulb in series (to limit the current), it heats the stator gently from inside to dry it out...
Dave H. (the other one)
wristpin
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Give it a gentle drying out inthe airing cupboard - if you have one.
I’ve got a Brooks Gryphon motor with centrifugal start on a lawnmower blade grinder which gave me the run around a while back when it looked as though the contacts were making but the fag paper test showed otherwise and they needed some careful tweaking to make firm contact.
Do motors with centrifugal switches never have a capacitor? My other bigger grinder definitely has a centrifugal switch but has a “ capacitor sized lump” on the side of the motor.
I’ve got a Brooks Gryphon motor with centrifugal start on a lawnmower blade grinder which gave me the run around a while back when it looked as though the contacts were making but the fag paper test showed otherwise and they needed some careful tweaking to make firm contact.
Do motors with centrifugal switches never have a capacitor? My other bigger grinder definitely has a centrifugal switch but has a “ capacitor sized lump” on the side of the motor.
Pete.
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Many motors have both, more than those that don't I expect.
Anyway, don't scrap your drill, I'm sure I must have a motor here somewhere that you can have for postage. I'll have a look.
timgunn1962
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Are you sure there's no capacitor? There's usually either a big terminal box with it in or a camel-hump-like cover on the motor casing over it. If you are lucky, you can read the old cap and order a new equivalent. The centrifugal switch on every single-phase motor I've ever had apart disconnects the power from the start capacitor and start winding once the motor is up to speed.
As I sort-of-understand things, the start winding is fed through a Capacitor to cause a lag in the waveform and move the AC waveform being fed to the start winding out of phase with the waveform to the main winding.
A single-phase motor is a bit like a disabled cyclist with no knees: the field can push straight down, but that's all. When starting, once the "crank" is at the top/bottom position, that's it.
A cyclist with working knees can also flex the knees, kick the crank forward when it's at the top position and provide a bit of torque to get through the top/bottom position until it reaches the point where pushing straight down works again. After a couple of cycles of this, there is enough flywheel effect in the moving system that the momentum carries things through the top/bottom position and all the work is done by the big muscles pushing down.
Give the disabled cyclist a push start to give momentum and he/she can keep going indefinitely.
The start capacitor and start winding in a single-phase motor effectively provide the knees: a field at an angle to the main winding with not nearly as much power as in the main winding, but just enough to get going until the main winding can do it on its own.
If the start winding system doesn't work (usually, but not always, because the capacitor has failed), spinning the motor will simulate the cyclist's push-start and get the motor running.
Start caps don't like to be energized for long and are prone to failure.
There are some single-phase motors with more than one capacitor (cap start, cap run), but they are less common.
As I sort-of-understand things, the start winding is fed through a Capacitor to cause a lag in the waveform and move the AC waveform being fed to the start winding out of phase with the waveform to the main winding.
A single-phase motor is a bit like a disabled cyclist with no knees: the field can push straight down, but that's all. When starting, once the "crank" is at the top/bottom position, that's it.
A cyclist with working knees can also flex the knees, kick the crank forward when it's at the top position and provide a bit of torque to get through the top/bottom position until it reaches the point where pushing straight down works again. After a couple of cycles of this, there is enough flywheel effect in the moving system that the momentum carries things through the top/bottom position and all the work is done by the big muscles pushing down.
Give the disabled cyclist a push start to give momentum and he/she can keep going indefinitely.
The start capacitor and start winding in a single-phase motor effectively provide the knees: a field at an angle to the main winding with not nearly as much power as in the main winding, but just enough to get going until the main winding can do it on its own.
If the start winding system doesn't work (usually, but not always, because the capacitor has failed), spinning the motor will simulate the cyclist's push-start and get the motor running.
Start caps don't like to be energized for long and are prone to failure.
There are some single-phase motors with more than one capacitor (cap start, cap run), but they are less common.
Progress of a sort on the motor, I needed to drill some holes today so hand cranked the motor into life to do them, then took it off the drill and fetched it home to check it over. Found it was self starting when on its side, but wouldn’t when on its end, as it is on the drill. Surmised that Wristpin’s idea about points was the most likely as, if the winding had gone, motor position presumably wouldn’t make any difference. Anyway took it apart and found the plastic collar that slides up and down on the armature seemed a bit sticky, closer examination and the shaft has light rust on it. Very difficult to remove, so put a drop of oil on, slid the collar up and down a few times, and it did free off. Gave the points another clean and stuck it back together. Bench tested and all seems well, but it was getting late so haven’t put it on the drill yet. Thanks for the suggestions, and the offer of another motor Pete but looks like the windings are OK so the Fobco lives again.
