Appraising an electric motor

[RainbowsParticipant @rainbows]

My general philosophy on electric motors is that if the price is good it should be had regardless to how much you need it because when you do need one you will be unable to find one.

I think I got this motor for £20 at auction having seen it but not quite realise how heavy it was. Its a 2HP, 1 PH, Brook Motor with double V pulley. Its just too damn big and too damn heavy. It has a hook to be lifted by crane and I don't have a crane.

Now I wired it to a plug and it works beatifully so I plan to recoup my £20. If I listed this on ebay could anyone recommend a price to sell it at? People are selling "Myford motor"s for £200 and some people are selling motors for £25. Is its value directly related to how many times I mention myford?

[RainbowsParticipant @rainbows]

[EmgeeParticipant @emgee]

Not the ideal physical size for a motor, most people these days go for 3 phase with VFD for speed control, your motor reminds me of 1 my father had on a circular saw, it was under the bench and nearly always partly covered with sawdust. I think you may just about get your money back.

Emgee

[HollowpointParticipant @hollowpoint]

Why not auction it for a week with a starting price of £20? It will find its own value.

[RainbowsParticipant @rainbows]

Posted by Emgee on 26/02/2016 21:58:02:

Not the ideal physical size for a motor, most people these days go for 3 phase with VFD for speed control, your motor reminds me of 1 my father had on a circular saw, it was under the bench and nearly always partly covered with sawdust. I think you may just about get your money back.

Emgee

There was another lot which was a table saw with a motor double the size of this one. Looking at it I was amazed it never caught fire for the sawdust covering it and its big air vents on the body.

£20 starting auction probably isn't the worst idea. I wonder if a collection only option means they have to be the ones to carry it downstairs.

[John RuddParticipant @johnrudd16576]

Posted by Rainbows on 26/02/2016 21:35:49:

so I plan to recoup my £20.

You will need to list it higher than £20 to recoup your initial outlay….£25 minimum and free collection…

[KWILParticipant @kwil]

I would not mention Myford, it is too large and so you could be accused of mis selling.

[AjohnwParticipant @ajohnw51620]

The Myford motors are so expensive because they are made to an old standard – that's my understanding anyway. Frame size and spindle size to power rating.

John

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[Ady1Participant @ady1]

Now I wired it to a plug and it works beautifully

I think the day will come when you will use it and be thankful you never sold it

A decent older motor is a workhorse which can last a lifetime, they can run all day, hour after hour

It will still be whirring along happily in 20 years when most VFDs have blown their last puff of smoke

Thats my appraisal

Edited By Ady1 on 27/02/2016 00:06:20

[MuzzerParticipant @muzzer]

Modern TEFC (totally enclosed fan cooled) motors are more compact. Better thermal design and a proper external fan rather than fins on the rotor drawing air and crap through the innards. Little chance of swarf and coolant getting in there.

As for the sawdust fire (= explosion!) risk, at least these older, open induction motors don't inherently generate sparks due to their lack of a commutator but likely have centrifugal starter switch (on single phase version) which may present a risk at startup.

[Phil WhitleyParticipant @philwhitley94135]

That looks to me like a Brook Empress motor with the external centrifugal switch. You will have to buy a very expensive motor indeed to buy better quality than that. The assertion that modern motors are better in any way is an absolute myth. These were designed and built to go into industrial situations powering machinery for at least eight hours a day, and last indefinitely, and I can assure you that many of them did!. One of the first jobs I worked on as an apprentice in 1968 was reconditioning Brook motors which had been removed from a factory built in 1932. All original, stripped cleaned re-lubed, and back into service. Modern Chinese motors are awful rubbish, and very inefficient and noisy to boot. Italian ones aren't much better and that covers the majority of motors made in Europe. The Industrial stuff made by Alstom and the like is very good, very efficient and very expensive. but will last the course. Brook still make motors in Huddersfield, but are now Chinese owned. I have no idea whatever why people pay £200 + for a "Myford" motor as there is no such animal. Motor fittings and bases have been standardised for donkeys years and getting a motor to fit should not be a problem. Whenever I need one, I go to the local rewind shop, and buy a recon one! If you need a 2hp single phase motor, you will not get a better one than that!

[Arthur SixsmithParticipant @arthursixsmith43623]

I put one of these motors on ebay last year bin £40.It sold in 40 min. Buyer picked it up next day said at this price if burnt out it was worth rewinding! But like you say very heavy motor.

[Ian S CParticipant @iansc]

At least with a rewind it would have modern high temperature insulation. People complain about modern motors running hot, yes they do, they are designed to run hotter than the motors of 50 years ago. Another thing with a modern motor, it's a lot lighter.

Ian S C

[Phil WhitleyParticipant @philwhitley94135]

I don't think they are designed to run hotter, and I cannot think of any advantage electrically speaking, of doing this. They run hotter because the cases are now usually thin lightweight aluminium, finned to reduce heat. If you come up with a higher temperature varnish, you can use less metal in the case, which saves money. Most modern TEFC motors have a pathetic plastic paddle of a fan hiding behind the cover, so the cooling is just adequate, but usually the first time they overheat, they burn out.Heat always damages insulation and varnishes, and if the insulation on this motor is good, there is no advantage in rewinding it. A simple megger test would prove it. The weight of cast iron, which is in intimate contact with the stator laminations acts as a huge heatsink, I can't actually tell from the pic, but this looks like a drip proof type, which has an internal fan and bottom inlets and outlets for air. Always worth making sure they are clean and blowing through with the air line, and a couple of pumps of grease for the bearings, which will also last a lifetime, as you CAN grease them! Ambient temperature in factories are a lot lower than they used to be thanks to COSH/HSE. The old Brooks worked everywhere from freezers to foundries. They did occasionally burn out, usually when something went drastically wrong with the machine. I remember being sent on the "shop bike" with a box of tools and a megger to look at the mixer motor in the local animal feed (provendor) mill. 140Hp star delta Brook, and it was red hot, and burned out. Had to take the roof off the motor room, and the roof off the factory, hire a crane and lift it out. Brooks sent a low loader to collect it on the day it happened (Friday), it was rewound over the weekend, and returned on the Monday and reinstalled. The cause of the burnout was the chap who was greasing the motor DAILY! It was half full of grease, and a drip proof which meant that dust drawn in to the motor was mixing with the grease, reducing the cooling, and being drawn back into the bearings which were gradually seizing up. The motor soldiered on against this extra load, but it was not enough to trip the overloads, just enough to slow cook the winding. Some "re education" was done at the factory and it never happened again. We also suspected that they had tweaked the overloads a bit, they weren't supposed to touch electrics, but you know what millers are!

Phil

[Steven VineParticipant @stevenvine79904]

Hi Phil, that's interesting, thanks. I had an over-greased motor on the Myford I picked up a few years ago. The motor ran hot and I could see the grease blocking the vents. I stripped it down and found the grease was packed into every nook and cranny. I cleaned it out and have had no problems since. It makes me wonder about the greasing affair on these motors. If you pump a little grease in every now and then, where does the grease go. Eventually the motor must fill up with grease, which will then be doing more harm than good, or am I missing something here? How often, or when, do you have to pump grease in do you know?

Steve

[Phil WhitleyParticipant @philwhitley94135]

Hi Steve, as usual the answer is, it depends! This is going to be complex! If you are putting a motor into a position where it will be in service for a long time. It would be best to strip it, wash out and repack the bearings. Here I will be controversial, and tell you to pack the bearing full of grease on both sides, and refit it. Others will insist that it is incorrect, and will say that it should only be one third full, or half full, one side only etc etc. Tell me then how a bearing stays one third full when it is fed by a grease nipple? Many will quote what they have read in bearing manuals, and that I also take with a huge pinch of salt. The bearings we buy today are not sealed, they are shielded, and dust can still get into them, you can also pop the shields off with a jewelers screwdriver, and if you do, you will be horrified how little grease is in them, they are, in fact "sealed for (a short) life". as I have said above, I have washed out and repacked thirty odd year old bearings and refitted them to many many motors because they were still in good condition. So, if the shields do not seal the bearing, why are they there? The only conclusion I can come to is to prevent any more grease being added and thus shorten the life of the bearing, and increase sales. I have changed hundreds of car wheel bearings, but the cause of failure is always that the external seals have broken down and allowed water and dirt into the bearing. If a bearing is kept clean, supplied with sufficient clean lubricant, and not overheated it should last indefinitely, but modern bearings do not. From this I can only assume that they are made from inferior materials, which I doubt, or that they are incorrectly lubricated, which can occasionally mean too much but mostly by far, too little.

When you rebuild a motor of the Brook Type with grease nipples, you will see that the grease nipple is at the top of the motor, and underneath the motor, somewhere on the lower portion of the end shell is a grease relief plug. To lubricate correctly, you remove the grease relief plug, (which is what our miller did not do!) check the relief hole is clear with a piece of wire, then put a grease gun on the nipple, and add grease to the bearing until it (just) starts to come out of the relief hole, then stop and refit the plug in the relief hole. The bearing is now completely full of grease (which gives the lie to those who say this should never happen!) If a motor is in use 8 hours per day this process was normally carried out weekly, with the motor stopped! If you grease a motor while it is running the grease will tend to ooze into the motor as there is usually no seal to stop this. By doing this you are effectively changing the lubricant constantly and flushing out any debris in the bearing.

Different motors used different methods, some had grease cups which were filled and given a certain number of turns for a set period of time, (1/2 turn per day, refill weekly) usually all the information needed being marked on the motor plate.

In today's modern world of course, we have advanced so far that we no longer need old fashioned things from yesteryear like grease nipples, so today's motors last till the tiny amount of grease polymerises or gets some dust in it, and then the extra load overheats the motor, the grease turns to tar and the motor burns out, and we throw it away and replace it, which is exactly what the manufacturers intended.

As you have spotted Steve, the grease has nowhere to go unless there is a relief plug, so it will force its way past the unsealed shaft and into the motor, and you will also see some exit at the shaft end around the shaft, as soon as you see this STOP PUMPING! If grease has been allowed to escape inside a motor which is not totally enclosed then it will pick up dust and some of that dusty grease will be dragged back into the bearing by the rotation of the shaft, and dust laden grease is like grinding paste. Incidentally, later motors sometimes had an unplugged relief hole, and the same rules apply. It is also sometimes possible to look through vents into the motor to check that grease is not coming out round the shaft. On your Myford, or similar, if there is sufficient grease in the bearing, and assuming you use it fairly often, a couple of pumps four times a year is sufficient. You have started from the right place, because you were in doubt, so you stripped, cleaned and repacked the bearings, now you only need to grease occasionally. I hope I haven't bored you to death!

Phil

[SandgrounderParticipant @sandgrounder]

Many years ago I attended a Tribolgy Course run by the Atomic Energy Authority and they said then that the main cause of bearing failure was over greasing, however that was 50 years ago and things do change.

John

[Ken TibbittParticipant @kentibbitt75143]

> I don't think they are designed to run hotter,

Even my ancient Machinery's handbook gives the designed temperature rises for different types of motor. Open frame general purpose motors have a rise of 40C over ambient while totally enclosed motors with type B insulation are designed to cope with a temperature RISE of 105 C above ambient.

The main differences are in the insulation, but it is quite acceptable to run a TEFC motor so hot you can't put your hand on it.

Neil

[Ian S CParticipant @iansc]

Just don't grease it if it has Oilite bearings, you can reload them with oil. Until we got a new blower for the church organ just before Christmas, we'v been using the original 1hp single phase motor built in 1917. The bearings on that motor are interesting. The motor shaft is 1" diameter, the bearings are ring oiled with each bearing 1" long, that's a total of 4" length of bearing, after a century of life, the shaft is 1.000", the bearings 1.002". The motor would be about the same size as Rainbows 2 hp one. Stator windings cotton covered wire, and it seems to be ok, checked out with a megger.

Ian S C

[Neil WyattModerator @neilwyatt]

Posted by John Caines on 01/03/2016 06:50:06:

Many years ago I attended a Tribolgy Course run by the Atomic Energy Authority and they said then that the main cause of bearing failure was over greasing, however that was 50 years ago and things do change.

From what I've heard from bearing folks, that hasn't!

This is good http://www.mobilindustrial.com/ind/english/files/tt-electric-motor-bearing-lubrication-guide.pdf

 

Neil

Edited By Neil Wyatt on 01/03/2016 13:32:22

[Phil WhitleyParticipant @philwhitley94135]

`As I have explained, over greasing causes bearing failure by entraining dust back into the bearing. The assertion that having too much grease in a bearing causes failure of itself is a myth, or at very least a misunderstanding. Lubricant is there to prevent metal to metal contact, if there is insufficient, the bearing will fail.

"Even my ancient Machinery's handbook gives the designed temperature rises for different types of motor. Open frame general purpose motors have a rise of 40C over ambient while totally enclosed motors with type B insulation are designed to cope with a temperature RISE of 105 C above ambient.

The main differences are in the insulation, but it is quite acceptable to run a TEFC motor so hot you can't put your hand on it."

This may be so, but rate of rise and operating temperature drastically affects service life, see http://ecmweb.com/content/hot-issue-motor-temperature-ratings, for an explanation of this.

It used to be common practice to size a motor 25% more powerful than was actually needed in order to give a good reliability factor. For reasons of economy, today, motors are generally just powerful enough to do the job and no more, hence higher running temperatures. There is no electrical or mechanical advantage whatever at running at these higher temperatures, it just means the motor can cope with more overload and thermal shock before the insulation breaks down, but it will shorten service life, as the margin between running temperature and failure of insulation temperature has been narrowed, and it will also cook the grease in the bearings and allow it to melt and run out to some extent, which again will cause bearing failure, and when the bearings start to stiffen up, the motor goes into overheat very quickly, and burns out.

Motors fitted with grease nipples and relief plugs run with their bearings absolutely full of grease, and when greased correctly, have indefinite bearing life (30+ years as in my post above). Modern motors run hot and with the sealed for life type bearing, motor and bearing failure is commonplace. They are literally, disposable motors. A bearing failure will take out the winding insulation in a very short time.

So it may be "acceptable" to run a motor so hot you can't bear your hand on it, just don't expect it to last very long!

Ian SC, used to see ring oiled motors on "original Heidelberg" printing presses we used to service, very quiet and very long lived as long as they get an oil change regularly!

Phil

[Phil WhitleyParticipant @philwhitley94135]

Thanks for the link Neil, it is very good, and needs to be read carefully!

Phil

http://www.mobilindustrial.com/ind/english/files/tt-electric-motor-bearing-lubrication-guide.pdf

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