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Meddings Driltrue blowing fuse?

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C J29/01/2018 23:08:05
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111 forum posts
85 photos

Hi,

My recently aquired single phase Meddings Driltrue blew the fitted 7amp fuse in it's plug on the second start with the belt set at it's slowest speed.

Is the fuse just not rated high enough at 7amps or do I need a slow blow fuse for this machine?

Colin

Edited By C J on 29/01/2018 23:09:04

not done it yet30/01/2018 06:44:31
4630 forum posts
16 photos

What does the motor rating plate read? Soft or hard start?

Paul Lousick30/01/2018 07:36:35
1406 forum posts
540 photos

This is a previous thread http://www.model-engineer.co.uk/forums/postings.asp?th=95235 , Talking about a 3hp motor drawing 10.8 amps.

(the old trick was to use a 2" nail as a fuse. but not recommended)

Paul

Samsaranda30/01/2018 09:06:41
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927 forum posts
5 photos

Surely a 2BA bolt is a better fuse substitute - only joking.

Dave W

Lambton30/01/2018 10:05:36
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694 forum posts
2 photos

Colin,

It is hard to be able to offer any help with so little information to go on.

A good picture of the motor data plate would be most helpful. Try these simple things first.

Try the motor alone with the belt taken off

With the belt off try turning the drill by hand to see if there is any great resistance .

I do not know where the 7amp plug top fuse came from as this is not a standard size. Try a 13 amp fuse rather than bizarre suggestions (even in jest) about using nails or bolts.

Eric

C J30/01/2018 10:20:01
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111 forum posts
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C J30/01/2018 10:29:35
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111 forum posts
85 photos

An image of my motor nameplate above, I have since read somewhere that an induction motor can pull 5 to 7 times it’s rated amps during startup, so 2.8 X 5 = 14 amps. I then think the 7 amp fuse was just too low.

SillyOldDuffer30/01/2018 10:38:48
5753 forum posts
1217 photos

Posted by Lambton on 30/01/2018 10:05:36:

...

I do not know where the 7amp plug top fuse came from as this is not a standard size. Try a 13 amp fuse rather than bizarre suggestions (even in jest) about using nails or bolts.

Eric

Unusual maybe but 7A is a standard size fuse. It could be right. A picture of the motor plate would help. The Keighley webpage suggests the drill has a ⅓ HP motor in which case 13A would be over the top.

I think the motor is faulty; could an expert comment on capacitor, start winding and centrifugal switch issues? In my ignorance I'd change the capacitor and hope that was it.

Dave

Lambton30/01/2018 10:41:19
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694 forum posts
2 photos

Colin,

I cannot see your picture. What horse power is the motor?

I have a Meddings MB4 drill fitted with a 1 hp single phase motor which has never blown a normal 13 amp fuse in 20 years of use.

Eric

Steve Pavey30/01/2018 10:45:25
280 forum posts
32 photos

The Meddings Drilltru model shown on the lathes.co.uk site (a 15” capacity with a ½” chuck) has a 1/3hp motor, so in theory draws very little current when running, probably around 1-2 amps. I would have thought a 7 amp fuse would cope with even the starting current of such a small motor.

Since the fuse is blowing, rather than tripping an RCCD, that indicates there isn’t a fault to earth. That leaves either some sort of mechanical fault (seized or sticky bearings for example) or an electrical fault that is not due to earth leakage- faulty windings or a faulty capacitor or maybe a centrifugal switch that isn’t working correctly. Eliminate the mechanical faults by disconnecting the drive belt or removing the motor completely and running it on the bench - if it runs ok then check that the rest of the drive train spins freely. A bench test will also help to check the centrifugal switch (if there is one) as you should be able to hear it click off as the motor spins down to a stop. You could check the resistance of the start and run windings (the last 1 hp motor I checked had resistances of around 100 ohms on both the start and run windings). If you have a multimeter that can measure capacitance that would also be worth checking - they sometimes start to deteriorate and give strange symptoms before finally giving up the ghost.

A 13a fuse may work but if the problem is windings or a capacitor that are starting to fail it may just mask the real problem for a while. At the moment the 7a fuse is the weak link in the chain which is better than the start windings being that weak link.

C J30/01/2018 10:57:51
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111 forum posts
85 photos

The drill had stood unused for some years and I was even running it without a quill when the fuse blew, as I had the drill in bits and was concerned over a slight noise in the driven pulley bearings, which, as it wasn’t constant I put down to a touch of rust on one of the ball bearings snagging now and then when the ball was orientated in its spin for it to do so.

So I soaked a little SAE 50 into the both races and ran the drill for a while and the noise has now gone, perhaps polished away ?

C J30/01/2018 12:03:52
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111 forum posts
85 photos

Thanks for the input Steve, I will run my multimeter over the motor to be certain.

Ian S C30/01/2018 12:26:37
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7468 forum posts
230 photos

Here our three pin plugs are rated 10Amp, no plug fuse, and I run my mill, and lathe from that, they are both 1.5hp, have never blown a fuse in over twenty years. Also run a 140 amp stick welder on the same supply. Until you cleared the bearings, you were trying to start against quite a heavy load.

Ian S C

Mike Poole30/01/2018 12:46:40
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2572 forum posts
60 photos

The plugtop fuse is never going to protect the motor, to survive the start up surge the fuse will need to be too large to stop the smoke leaving the motor if it is overloaded. Drills often do not have a starter and are wired direct on with a simple switch. I feel it is worth fitting a starter and having the protection of an NVR and overload set to protect the motor. A starter also makes possible fitting as many emergency stops as you would like and even fitting a remote start and stop button in a convenient place, as to fit the starter where you would like the buttons is not always possible.

Mike

It is possible that the motor does have a problem and others have mentioned the likely places to look.

Edited By Mike Poole on 30/01/2018 12:57:27

C J30/01/2018 18:10:14
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111 forum posts
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C J30/01/2018 18:37:05
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111 forum posts
85 photos

I have now found a way of adding an image of the motor plate above.

Re Mike, the motor does just start at full speed, but spins freely, as I added some grease to both bearings via the grease nipples, it 's quiet, doesn't get hot and also clicks when I turn it off.

I can't see any capacitor on the motor, which I guess would be a fairly big thing, so it mustn't have one, but I will check the windings, finally I don't know what a starter is indecision

Adrian L10/04/2020 10:56:05
10 forum posts

Hi all,

I'm reading this thread with interest. I received a boxford pd8 yesterday, single phase, and upon fitting a 3 pin plug and a 3 amp fuse, the fuse blew straight off the bat. I then fit a 5 amp fuse and that blew too. I then fitted a 13 amp fuse and this seems to have worked. The motor is 370w and 3.8amp on the motor plate. The bearings sound a tad noisy so will try and put some clingy oil on them.

Adrian.

Phil Whitley10/04/2020 11:33:35
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1193 forum posts
145 photos

This sounds about right Adrian, if the drill is set to one of the higher range of speeds, the inrush current will be quite high, but only for a few seconds, and dry bearings will not help at all. Check the motor and the spindle with the belts off, and lube as required.

Phil

Adrian L10/04/2020 11:47:33
10 forum posts

Hi Phil W.

Thanks for your reply.

I'm hoping the bearings will be easy to access for lubing purposes. Be nice if I can quieten them down a little.

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