Brooke Compton Motors

[IP]

Greetings all,

I have a three phase 415V 0.37 kW motor made by Brooke Compton, the frame number is D71BD4E P30S I want to replace this with a single phase 240 V motor.

Can anyone tell me / advise re a suitable direct fitting replacement motor or where I can find details of motor frame size / fitting etc.

Regards IP

[Phil Sutton]

Ian,MachineMart sell electric motors,sigle and 3 phase,but these maybe too expensive for you.(and not Tel's prefered way of obtaining things)

Phil

[IP]

Phil,

Its not that model engineers are skin flints it just that we all have short arms and deep pockets!

Regards,

IP

[Phil Sutton]

Know where you're coming from Ian.

Phil

[houstonceng]

IP

I got a lot of useful info direct from the Brooke Crompton web-site as I was - maybe still am - thinking of replacing a single phase 2hp (1.5kW) single phase motor with a 3-phase and speed control on my lathe.

If it's marked P30S it usually means it's a 30 Short frame size.

Brooke Crompton make so many ranges of fractional HP motors including low energy / high-efficiency ones; low-cost; foot mounted; flange mounted; etc; etc., it's best to "consult the oracle" for accurate info. You'll also be able to compare torque and current ratings which you'll need to do because a single-phase and three-phase motor of - notionally - the same rating don't have the same characteristics.

First thing that (temporarily ?) halted me converting to 3 phase is that the 1-phase motor is 100 frame size (ie 100mm from mounting foot to spindle) and current 3-phase motors of the same HP are 90 frame size. econdly, the shafts are smaller - ie new CI pulley required. Thirdly - and most obvious 'cos, "since I are an ingineer", I can get around the first two with a lttle bit of fabrication - is the cost !!! Nearly £600.00 for the motor, inverter, wiring, etc.

BTW. If you go to the Brooke Crompton web-site, you can also E-mail their "help-line". I received a very prompt and helpful reply to a specific query.

If you don't have any luck, let me know via this vehicle and I'll try hunting out the downloads I made from out of the "BGH filing system of useful information" I have. It's in there somewhere. If only I had an index system !

ATB
A. N. Other Andy

[IP]

Andy,

Thanks for the info, I too have halted the change over for the moment for the following reason.

The place where I got the miller from also has a Harrison 600 lathe which is also three phase and may also be coming up for sale.

I haven't really got room for the lathe but at the price I'd be getting it at I'd be really stupid not to buy it, at least it could be stored ready for the day when the new workshop gets built. [You know the time between the kids leaving home and the grandchildren arriving]

However I am in a quandry as to whether to buy a convertor / invertor big enough to handle both machines or to go down the convert to single phase route. I am tending to favour the convert to single phase but would welcome any thoughts on the matter.

Regards,
IP

[houstonceng]

IP

You asked for some thoughts about Inverters / Converters & 3-phase motors vs converting machines to single phase. So here are mine. Please excuse me if some of this info is already well known to you. I'll bring the eggs and you can bring your Grandmother - learning for the use of.

I'll try to keep it non-technical - and please remember that "motors is a complex subject" so don't (and that goes for anyone else on the list) take me to task because I haven't covered the subtleties of Capacitor Start and Run single phase vs Capacitor Start / Induction Run. If you want that sort of detail my one finger typing tends to lead to RSI and broken finger-nails.

Firstly, Invert vs Convert.

Positives of Inverters
They give you the option of Variable speed range from practically 50% to 200% speed (theoretically 0% to 200+% but not wise).
You get dynamic braking including reverse under power.
You get (usually) selectable "soft-start"
They can be semi-compensated to give constant torgue or constant power across the speed range.

Downsides of Inverters
They are only used one-on-one with each motor
The motor has to be re-wired / strapped for delta connexion as they don't give 440v from 240v single phase mains
They can sometimes trip RCBs / ELCBs / GFIs if fitted in your house / workshop supply (mine does about once every 50 - 100 power downs at the end of machining sessions)
They can - not the good ones like I bought - generate RFI which will affect your TV or Hi-Fi (and your neighbours as well)

Upsides of Converters
They can supply 440v so your Star connected motors don't need reconfiguring
They can (if specified correctly) supply multiple motors

Downsides of Converters
No speed control
Don't - usually - supply a fully balanced 3-phase (unless expensive so called "rotary converters" are used) which can lead to some starting effects on the lathe motor
Sometimes need a slave motor (unloaded mechanically) permanently connected and running to create the 3-phase so that multi motors on your M/C tools can be started "on line".
Depnding on the max power you require they have a minimum load which may require the "slave motor" set-up.

My practical experience of a lathe fitted with a single phase 2HP (1.5kW) single-phase motor vs my mill which is fitted with a 3-phase motor and Inverter - hence the thoughts of converting the lathe.

3-phase motors runs quieter. This is due to the fact that single phase induction motors actually go round in a series of "impulses" at 50Hz (60Hz in USA) rather than producing smooth rotation as in 3-phase types. This is essentially because 3-phase electricary produces a true rotating magnetic field in the induction motor whereas the sigle-phase motor has to "create" a psudo rotating field as it's only got a single phase supply and that produces - essentially - an on-off magnetic field acros the poles. These "impulses" can result in harmonics and vibration in the lathe leading to spiral patterning on the finished turned parts unless the motor is mechanically "insulated" from the lathe. My motor is temporarily (initially as a test) bolted to the brick wall of my WS. As supplied it was rigidly mounted on the lathe and I got "patterning" on turned work. Some other MEs that I know have had the same problem. The bigger the motor the worse you hear and feel these "impulses".

Single phase motors induction motors in "lathe sizes" need starting windings, usually (but not always) capacitors to start them and an internal switch (but not always) to cut-out the starting winding. More to go wrong ! Not so on the 3-phase type.

3-phase induction motors are usually smaller power for power than single-phase. And reversing them is just a matter of swapping over two of the three phases. BTW. Try reversing a single phase motor under power and it will usually just carry on in the same old direction. It has to stop rotating fully to let the starting winding be effective.

Finally, most single-phase motors have a low "number of starts per hour" limit because the start winding is usually "cooked" through overuse. Not come across the same limits - of course there are some - on the 3-phase.

I bought my lathe with single phase and, from experience, then bought the mill. Now wish I'd bought the lathe as 3-phase in the first instance.

My advise is, therefore, stick to 3-phase. If your workshop isn't wired 3-phase then Convert or Invert from single-phase depending on what advantage you want. It usually comes down to Multi-motor (Convert) vs Single motor speed control (Invert) requirement.

Hope this helps
A. N. Other Andy

[IP]

Andy,

Many thanks for the exhaustive reply, the three phase motor I have is wound for a single voltage of 425v, had this been a dual wound motor then I would have gone down the invertor route.

The reason I don't intend to, having sought advice is primarily cost. To replace the motor and have an invertor would cost in the region of £180 whereas to replace only the motor will cost £60.

I do take on board very much your comments and thank you for the time and trouble in your reply, there is however one other consideration.

I am a licenced radio ham and the least amount of tvi that gets produced the better, I wouldn't want the neighbours to make any complaints of tvi when a convertor was to blame they of course blaming the radio.

Hope that all makes sense to you, once again thanks for your reply it has at least made some things clearer for the future.

Regards, IP