single phase motor-calculating rpm

[Les Jones 1Participant @lesjones1]

Hi David,
Like Ted (john fletcher 1) I was wondering about the coil voltage. Also there is no nformation about which two of the three contacts provides the power to hold the coil in. From the lack of any mention of coil voltage in the information I am wondering if this is only a mechanical switch which trips out in the event of an overload. If this is the case it will not provide no volt protection. Close up pictures of the inside of the unit may help to identify if it uses a coil to hold the contacts closed.

Les.

[Keith LongParticipant @keithlong89920]

Well spotted Les & Ted – I've just checked the 4-6.3 amp version that I've got here – fortunately not wired up yet. It is purely a mechanical switch that gives overload protection NO NVR facility, in fact if you press the start button with no power applied, the contacts make and stay made until you press the stop button or trip the unit with the test facility.

As far as I can see Machine Mart make NO claims for it to be a NVR unit but then neither do they tell you that it isn't, just describe it as a DOL (direct on line) starter for motors – accidents waiting to happen come to mind!

Edited By Keith Long on 06/04/2015 17:56:40

[Les Jones 1Participant @lesjones1]

Hi Keith,
Thanks for confirming the function of this so called DOL starter. I would think resetable overload trip would be a better description of it.

Les.

[BazyleParticipant @bazyle]

Very shabby behaviour by MaCHINE MART selling an inappropriate item. See if you can get your money back. What you need is a something more like this It gives you the NVR and a nice emergency stop. The general search is 'no volt switch' but I knew Axminster did one and they are, in my op0inion, a generally far better supplier.

For a small domestic motor the normal plug fuse is far better than a thermal cut out. which is intended for a large multiHP motor on 3 phase where a fuse in one line would leave the other phases still connected.

Edit. Just read the reviewsof the axminster switch and it seems some customers didn't get the instruction sheet and you also need spade connectors but I still think it is a good bet. A deeper search might find one with screw connectors.

Edited By Bazyle on 06/04/2015 20:29:08

[David Brown 9Participant @davidbrown9]

Hi, Bazyle-the Axminster one you linked to has no overload protection-do I need this?

If I ever finish the mirror grinding machine I will write about it, thanks for all the advice. I have already made a very heavy duty grinding table from wood that I can barely move! The first thing I want to get working is a rotating turntable, then I will try adding the over arm to hold the grinding disc. Doing this by hand I have made this from concrete, poured in to a mold, with 2 pennies stuck to it. A lot of people use mosaic tiles.

Once I have made significant progress with the grinding I will write about it, about the techniques, I do not think these have changed that much in around 150 years! (At a guess). This will be in a few months, I am estimating somewhere between 6 months and a year to finish the mirror!

David

[Les Jones 1Participant @lesjones1]

Hi Bazyle,
I disagree with your comment on fuses being better than thermal overloads on small induction motors. A fuse that is large enough to not blow with the starting current is very unlikely to blow with an overload. Thermal trips are much slower to operate so one of a suitable rating to protect the motor from overload would not trip due to the short duration of the high starting current. Having said this the motor on my drill press and the original single phase motor on my lathe are not fitted with any thermal overload protection. The is probably just to save cost. As the mirror grinding machine will run for long periods unattended I think thermal overload protection would be a good idea. Both the original so called DOL starter could be used in conjunction wit the NVR switch you have suggested. One point about this NVR switch is it does not support the use of additional interlock switches or emergency stop button.

Les.

[LambtonParticipant @lambton]

When a machine is fitted with an electric motor there are three things that need to be considered for protection.

1. The wiring of the building. This is protected by the fuse which is there to prevent excess current flowing through the wiring which could damage it of cause a fire.

2. The motor itself. This is protected by a thermal overload which cut the motor off if too high a current is drawn by it e.g. in the event of overloading of stalling.

3. The person using the machine. This is provided in several ways first by earthing and earth bonding, the use of a Residual Current Device and by providing No Volt Release to ensure the motor cannot self-start following a power outage. Neither 1 nor 2 provide any direct

   protection to the person.

   An ideal set-up would incorporate all of these measures but often does not in the home workshop. Many small machines are only fitted with the 13 amp fuse in the plug top.

   Machine Mart obviously has a direct interest in 2 as this would probably be an issue when a motor is claimed to be faulty and a claim is made under warranty.

[BazyleParticipant @bazyle]

If the power goes off on a polisher when unattended the polishing plate will stick. When the power comes on again something will break. (idealy you should be thinking of an auto-lift on the plate). So you need an NVR.
A thermal cut out will only work on the stall current properly if it has been set up correctly. Fuses were invented to be a cheap and effective alternative until someone invented the electronic control boards for small lathes without back gear as an expensive alternative.

There must be a million drill presses made every year with neither, 100 thousand each of wood and metal lathes for amateurs, add in bandsaws, compressors, mills etc,

[David Brown 9Participant @davidbrown9]

So I could use the starter I have from Machine Mart and the NVR switch from Axminster and that would give me protection against overloadinng and posssible burning out of the motor and a no volt release so that the motor would not start up again after a power failure?

I need to know how to connect the motor to both the starter and NVR switch. There is no obvious way of connecting the motor to the electricity supply or anything else! I presume I need electric cable-any advice on what to buy whould be appreciated.

On taking the cover off the motor there are 6 terminals, to one side of these there is a motor starting capacitor on the other side there is something that looks similar to the motor starter capacitor but nothing is written on it. There are 9 wires going in to the terminals, one is red, 2 are blue, one is brown, one is yellow and there are 4 black ones. I will try to find some kind of manual/ wiring diagram on line.

Do I connect the starter/ NVR switch direct to the mains? Which should be connected first?

David

[David Brown 9Participant @davidbrown9]

Sometimes I am not very clever, there is a very small wiring diagram inside the cover of the motor!

It is headed connections, in two parts, CCW and CW. To CCW it shows two LINES,, one going to W2, U2 and V2. The other to U1, V1 and W1, I will have to double check all this when I find a magnifying glass as the numbers are very small, but I think I have got them right!

There are 2 LINES to CW, one to W2, U2 and V2, the other to U1, V1 and W1.

Any advice gratefully received! I will try to take a picture of the wiring diagram, increase the size and post it on here, once I fiigure out how to do this, probably at the weekend.

David

[LambtonParticipant @lambton]

David,

Respectfully I think it is time to get some competent on the spot help in wiring up the motor in a safe and workmanlike fashion as it is clearly a little beyond your present level of expertise to do it alone. Please accept this comment as I offer it in the kindest way possible.

Eric

[Neil WyattModerator @neilwyatt]

> Very shabby behaviour by MaCHINE MART selling an inappropriate item.

Not very fair, if a customer orders parts off a website you can't expect the supplier to vet every order, although I couldn't find a suitable switch on their website.

That said, I would have paid about £70 for a small pillar drill and stripped it:

• 350W single phase motor (0.46 hp)
• NVR switch
• Chuck
• Two multi-step pulleys
• Large diameter steel tube
• Some potentially useful castings…
• Various other bits!

Neil

Neil

[David Brown 9Participant @davidbrown9]

Oh well, on to plan B. I see no reason that I cannot use the motor from my existing drill press. In fact I should be able to use the main part, with the motor and drill, without dismantling anything. It anyway comes off the pillar easily. I can make the grinding machine so that it is easily removed. A number of d.i.y. grinding machines on line have a motor which is easily removed.

I can then use it again as a drill press when I need to, I am unlikey to need to for a few months.

The drill press has a NVR switch . It is a Titan 700 watt drill press, model number TTB541DBT, bought from screwfix. The lowest RPM is 210.

I will possibly try to figure a way to attach a pulley to the drill press chuck/taper. If this is not a good idea I could try using one of the pulleys that are used to change speeds on the drill press, without removing the pulley, I could posssibly use one of the existing belts or buy a new one if necessary, once I have calculated the length needed.

The only problem is that there is a safety mechanism which stops the motor starting when the cover where the pulleys are is open, I could figure out how to disable this or I could probably cut a hole in the cover for the belt to the second pulley to go through. The cover is rather flimsy, possibly tin?

I have bought a washing machine pulley which is 101/2 inches in diameter, I will work out the size needed for the second smaller pulley and length of belt.

I plan to use the machine to grind for no more than 2 hours at a time. I will not be leaving the machine unattended for more than very short periods as I will need to keep adding grit for grinding at frequent intervals. If I use the machine for only 4 hours in total a day at weekends I will double the amount of grinding I can do, as it is hard physcial work and I cannot see myself doing more than 2 hours a day maximum by hand, probably less.

I am not very fit and I am not as young as I was!

David

[David Brown 9Participant @davidbrown9]

By the way I bought the single phase motor from a Machine Mart store, I should probably have asked questions but the person who sold it to me did not give the impression of knowing anything about electric motors. When I said 'I think I need a starter as well?' he shrugged with complete disinterest!

I cannot imagine an electrician would charge less than £200, probably more, to connect up the motor, this makes the total cost too high for me, especaily as I have just bought a mini-mill!

I will spend the next few weeks reading about electric motors motors and electricity. For a start I will get Electric Motors by Jim Cox in the Workshop Practice Series.

When I think I have a reasonable understanding I will post again on how I think the motor should be wired. It may be in a few months not weeks! If I am confident I understand how to wire the motor, NVR switch and starter I will go ahead, after getting further advice on here, if not I won't. On the other hand, if the drill press motor works reallly well maybe I won't bother!

David

[Neil WyattModerator @neilwyatt]

> Once I have made significant progress with the grinding I will write about it, about the techniques, I do not think these have changed that much in around 150 years! (At a guess). This will be in a few months, I am estimating somewhere between 6 months and a year to finish the mirror!

If you have an hour or two to spare, read this thread on the Stargazer forum (warning its hasn't ended yet…)

stargazerslounge.com/topic/237343-the-22-mapstar-mirror/

This is a very different  and fascinating perspective:

sites.google.com/site/diy100atm/about-the-site

 

Neil

Edited By Neil Wyatt on 08/04/2015 20:43:20

[David Brown 9Participant @davidbrown9]

Hi Neil, I have read most of that thread and post quite often on Stargazers Lounge! (I am 'Dark Star'-after my favourite science fiction film).

That thread is the reason I am estimating 6 months to a year for the grinding, testing etc. of the mirror, and it could easily be a year and a half! Or even two years!That is the main reason I want to make a mirror grinding machine, to make the process faster. It has also taken me around a year to nearly finish my 14 inch mirror and telescope. The mirror is ready for aluminizing, which means it is basically finished, the telescope needs a bit more work but should be finished in 2-3 weeks.

David

[Jesse Hancock 1Participant @jessehancock1]

A case of don't shot the messenger I guess.

Sorry to say lads but due to cutting prices and costs, places like Machine Mart won't be employing professionals as they don't pay the wages. The guys at my local Machine Mart openly admit they don't have a clue since they haven't any expertise in engineering of any sort. Having said that I guess the way to go would be take an electrician or engineer with you if possible, or at the very least seek advice (catalogue in hand) from one.

As Britain sinks slowly into oblivion as far as a producer of goods is concerned I fear this situation will only get worse.

 

Edited By Jesse Hancock 1 on 09/04/2015 08:31:06

[Martin KyteParticipant @martinkyte99762]

Whilst I agree that the UK could and should do better regarding manufacturing a quick google shows the UK as 7th globally in 2012 at £233 billion and you might like to take a look at

**LINK**

to see that there is some pretty heavy engineering still going on. Selling 325 tonne castings to Germany of all places deserves some recognition.

regards Martin

[Author]

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