To achieve full rpm do I need a boost transformer for DC drive conversion on a 10ee?

cpd62 · Oct 21, 2013

Hi,
I'm researching a 10ee purchase. It's a 1944 MG. The owner took out the old defective generator and installed a modern Allen Bradley solid state DC drive system. I checked out the machine and it appears to be in good functional order except max rpm is 2100 in stead of 2500. The owner's explanation for this was not satisfactory. First he said the oil needed to warm up. So we ran it for 5 minutes and it didn't go further than 2100. Then he said it must have a bad tach (but the machine ran the full spectrum of speed just fine without issue).

Another member of this and another forum suggested I check out his DC conversion. He said the guy should have installed a boost transformer with the DC drive conversion (which was not done). My expertise of electronics is limited so I'm looking for advice.

Could the lack of a transformer be the problem with max rpm? If so, I'd like to diagnose the problem prior to purchase.

Thanks,
Christian

9100 · Oct 21, 2013

The 10EE supplies 240 VDC at 40% of the max RPM. Above that, the armature voltage is held at 240 VDC and the field voltage is reduced to produce the higher speeds. Search this forum for countless references. People either do not have the expertise or patience to get the original system working and paste in all sorts of other drives. Most of the time they just make a mess of a good system.

Bill

RC99 · Oct 21, 2013

So what did the Allen Bradley DC drive system replace?

The entire drive or just the MG unit?

cpd62 · Oct 21, 2013

The MG unit. It still has the original DC motor and all stock controls.

RC99 · Oct 21, 2013

So it could be brushes... It could be the rheostat, could be low voltage..

Mine only went to that speed when I got it, but then it had not been run for ten or more years....

It is still a complete unit though... New brushes, general clean up and minor repairs and it will do 3000rpm way over speeding the DC motor if I let it...

Also my tach under reads by 100rpm at full rpm...

Steve in SoCal · Oct 21, 2013

To obtain 240VDC with single phase power you need more than 240VAC input. The later tube systems used a large transformer to increase the AC bus voltage. If the AB drive is single phase it may need a boost transformer. Check the output voltage at the spindle motor, it is very likely below 240VDC.

Steve

cpd62 · Oct 21, 2013

Steve in SoCal said:
To obtain 240VDC with single phase power you need more than 240VAC input. The later tube systems used a large transformer to increase the AC bus voltage. If the AB drive is single phase it may need a boost transformer. Check the output voltage at the spindle motor, it is very likely below 240VDC.

Steve

I plan to ask the seller to check this. This seems fair wouldn't you agree? I think so because he says he's an electrical engineer and I assume he stated his credentials as a means of offering reassurance to me. If he checks and it reads below 240 is it fair to say we have a reasonable diagnosis?

C

RC99 · Oct 21, 2013

Provided you trust him...

cpd62 · Oct 21, 2013

RC99 said:
Provided you trust him...

Yeah that's a big factor. He could shoot a photo I suppose.

The biggest issue is does any of this fuss matter if the price is right? He'll deliver into my garage for $3000. It has an ELSR and taper attachment as well as coolant pump. I won't use the pump. It has a bad paint job and needs cleaning but seems fair if you factor in the convenience of delivery and the majority of th emachine in good working order. Also comes with a jacobs collet closer and full set of collets, steady rest, rocker tool post and holders and a 3 and 4 jaw chuck. It's ready to plug and go. If I never diagnosed the rpm issue and it always ran that way I'd still probably be OK. But I always like to know...

PaulM · Oct 21, 2013

I assume its the one in Franklin (Fred)? If so that seller seems to have a minor machine tool business, no idea where he gets the machines. From what I have seen (at least in the past) he does not do the rustolium restorations but I would not believe where the machine supposedly came from. Reason is my 1973 EE came from the same seller, bought by another member here who never used it then sold it to me (I missed it originaly as there was a snow storm which kept me from getting out). Anyway my EE supposedly came from a goverment lab in Saratoga and he was retiring and getting rid of most of the machines he ad accumulated over the years. Well per Monarch the EE was orignally shipped to a optics company in Southbridge MA - government labs generally do not buy used equipment.

All that said My EE was in reasonable shape and was fairly well tooled. So the listing is probably not a bad deal - I think he had a newer one listed about 6 months ago.

FYI should you need or want a back up drive motor I have 2 of them - you can have one for beer money - heavy suckers no one wants to ship these.
Paul

cpd62 · Oct 21, 2013

PaulM said:
I assume its the one in Franklin (Fred)? If so that seller seems to have a minor machine tool business, no idea where he gets the machines. From what I have seen (at least in the past) he does not do the rustolium restorations but I would not believe where the machine supposedly came from. Reason is my 1973 EE came from the same seller, bought by another member here who never used it then sold it to me (I missed it originaly as there was a snow storm which kept me from getting out). Anyway my EE supposedly came from a goverment lab in Saratoga and he was retiring and getting rid of most of the machines he ad accumulated over the years. Well per Monarch the EE was orignally shipped to a optics company in Southbridge MA - government labs generally do not buy used equipment.

All that said My EE was in reasonable shape and was fairly well tooled. So the listing is probably not a bad deal - I think he had a newer one listed about 6 months ago.

FYI should you need or want a back up drive motor I have 2 of them - you can have one for beer money - heavy suckers no one wants to ship these.
Paul

That's the guy.
C

donie · Oct 21, 2013

"government labs generally do not buy used equipment."

Perhaps not, but they have first shot at equipment before it is released to the public through the GSA, for free. Of course that is before they are drug out into the weather to rust.
My oldest EE was delivered new to Bendix Aircraft Division in New Jersey, it then ended up at Hanford High Energy Weapons Program, moved along to Battelle Pacific NW Labs Hanford. It would appear it was Gov owned when delivered to Bendix. That one wears many tags.
I have, and have seen other examples of machines that were shipped to private contractors when new, but yet have Gov tags.
Monarch will provide where a lathe was delivered, but not who paid for it.

9100 · Oct 21, 2013

Steve in SoCal said:
To obtain 240VDC with single phase power you need more than 240VAC input. The later tube systems used a large transformer to increase the AC bus voltage. If the AB drive is single phase it may need a boost transformer. Check the output voltage at the spindle motor, it is very likely below 240VDC.

Steve

Actually you can get close to 339 volts from 240 full wave rectified with large enough filter capacitors. Most systems don't go to that much trouble. The tube Monarchs needed the transformer to get full output with two tubes instead of the four they would need if they ran straight off the line. The transformer and two tubes running as a full wave center tapped rectifier would give effectively almost 240 VDC with 240 V each side of center. The inductance of the motor armature makes it look about like DC rather than the pulsating DC that it is. Naturally there will be some losses, so you need a little extra to make up for them.

Bill

PaulM · Oct 22, 2013

Thanks for the info on how a machine can change hands Donie.
I've been meaning to send the optics company a letter to try to find out some of the history (they are still in business) so maybe I'll finaly do that. Also the minute possibility that they may have any of the missing accessories sitting on a shelf somewhere.

And in case it was not clear I would buy a machine from that particular seller again, just not sure I'd believe its stated history.

Paul

toolnut · Oct 22, 2013

I have seen a couple 10EE conversions using Allen Bradley 1395 DC drives and they performed well without a boost transformer. Just ask what model the Allen Bradley drive is so we will know more.

Bruce

cpd62 · Oct 22, 2013

toolnut said:
I have seen a couple 10EE conversions using Allen Bradley 1395 DC drives and they performed well without a boost transformer. Just ask what model the Allen Bradley drive is so we will know more.

Bruce

He should be sending me a picture today and I'll get the model#. Seems like he was confident in the method and certainly respected the principles of design of the machine.
C

Peter. · Oct 22, 2013

If it hits 2100 I would ask myself what that 400rpm loss means to me in real terms. Just to receive it fully working puts you one step up on many people who visit here with their new acquisition - myself included. 400rpm off the top end would be the last thing I would fuss about.

PDW · Oct 22, 2013

Peter. said:
If it hits 2100 I would ask myself what that 400rpm loss means to me in real terms. Just to receive it fully working puts you one step up on many people who visit here with their new acquisition - myself included. 400rpm off the top end would be the last thing I would fuss about.

+1. If the price is right, it's well tooled and mechanically excellent WRT slides, screws, bearings etc the 400 rpm off the top I'd ignore. Deal with it when it becomes an issue.

FWIW my Colchester Chipmaster will go to 3000 rpm. Except for playing with it when I first got it, I've never taken it over 2000. I simply don't do the sort of work where I need those speeds.

PDW

cpd62 · Oct 23, 2013

Here's the DC drive. The owner said it's Allen Bradley but doesn't know the model. It was installed about

10 yrs. ago.

Any thoughts?
All I know is it works.
C

Steve in SoCal · Oct 23, 2013

If the drive is developing 240 VDC it may not have field weakening, at the base speed the motor is at full torque and horsepower. This is where the armature voltage is 240 and the field is the max voltage(there are a couple of different values here) let's say it is 115VDC. That is where the increase in RPM is controlled by reducing the field voltage, without a means to weaken or reduce the field voltage the motor will only run at base speed or below. The drive retrofits that have full RPM range generally have a field controller in addition to an armature controller.

Steve

To achieve full rpm do I need a boost transformer for DC drive conversion on a 10ee?

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