Member postings for John Beke

Hi Everyone

I was very fortunate and was given a Holbrook C10 lathe which is a beast compaired to my Myford Super 7, it came from a local aerospace company, lathe being 3phase 420v having 220v domestic supply was a bit of a challenge.

Have overcome the problems see write up below picture, the same write up is on the Holbrook web site.

I was in the same situation as some owners of Holbrook C10- I do not have a 3 phase supply or 415V available to power the motor as it is for my home workshop.

Prior to my retirement, I was a maintenance technician at a nuclear power station and asked a good friend who was the chief electrical engineer what to do- his reply was “do you want an honest answer? I don’t know!”

After a long discussion we decided against having the motor rewound as motor rewind companies tend to copy the original windings and do not usually have the expertise to reengineer the motors, without cost, so this was a non-starter.

Another option was to obtain a rotary phase converter. However, there are two reasons not to go down this route. Firstly the cost (again) of the converter and secondly they are not very efficient as the motor has three different windings when changing speed and so there will be imbalance in the system. This problem also applied to a static converter as they are also poorly balanced, which affects the full power of the motor.

We therefore decided the way forward was to replace the motor and use an electronic inverter drive.

I had full confidence in this solution as the power station used electronic inverter drives in many places, being fully programmable with excellent reliability. However, this then required me to buy an inverter drive, a new motor and also an adaptor to make it fit the later.

Motor

First on the list was to look for a replacement - the original motor was 2hp but by choosing a 3hp motor and dropping down to the lower speed there is still plenty of torque available. After a long time spent time on the internet sourcing a 3 phase 220v 3hp 4 pole motor, eBay came up with a brand new Marelli motor and paid £40 which was a good start.

Inverter Drive

The next stage was to look for a AC Inverter Drive –and again after many hours spent searching on the internet and eBay, I took a trip to The Inverter Drive Supermarket Limited, which is in Chipping Campden, Gloucestershire. Once I explained my requirement, they recommended an ‘Altivar 12’ which is made by Schneider for the reasonable sum of £138.

It took an entire evening to configure the drive as the manual was a translation and is not laid out in logical technical English. There were three main changes to the configuration:

• The motor was programmed for a soft start, to change the acceleration characteristics to 3 seconds so to reduce the stress on lathe and motor when starting.
• The drive was programmed for three different frequencies to equate to the three speeds on the lathe speed change.
• The speed change contacts were wired straight to the digital input on the drive, so that the speed change works the same as the original lathe intended. I also wired the stop start reverse lever switch to the drive stop start forward reverse position.

By using an inverter drive, the speed of the lathe goes from the lowest to max 3000 rpm. This meant that with the motor running at max torque, the current would not exceed 10 amps (and therefore not tripping the house electrics!). Another advantage is there is a big gap between 3000rpm and 1492 rpm, but as the drive has a control on the front, any speed can be set manually.

Contunied on next posting