Got an MG 10ee - VFD questions
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  1. #1
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    Default Got an MG 10ee - VFD questions

    Hi Guys,

    Well I ended up buying my second EE locally. This one is a MG - 1948 Vintage, and I am hoping to get it wired up as soon as possible. I am in a bit of a pickle however. Here is/was my plan:

    I was planning on using a Rockwell PowerFlex 40 VFD (22B-A012N104) which is rated at 3hp (12 amps). These drives have a 24 VDC source as well as several Digital inputs at their disposal. I was planning to run the control circuit with the 24 VDC source, which would basically be just start and stop. I would set the VFD speed to 60 HZ to drive the AC motor and use the existing DC voltage generated by the Generator/Excitor to power the spindle motor. The problem I am having is that @ 240VAC the Reliance AC motor is rated at 13.2 FLA. VFD's in single phase go up to 3HP, no problem right?. Well looking closer at the drive specs. the drive is rated at 12 amps which seems to be standard. I am assuming the higher draw on the Reliance motor is due to the fact that it is older/less efficient and also because maybe the losses in the generator are included in this rating.

    I know that drives are pretty smart these days in terms of overload protection, however I am hesitant to run a under-sized drive (12 amps) with this motor (13.2 amps). I have considered de-rating a 3-phase input drive, however it would be considerably more expensive to go this route as I would need at least 7.5 hp drive. I am not sure if there is anyone that is running a similar setup, or if you have any input. Thanks in advance!

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    Quote Originally Posted by PLC View Post
    Hi Guys,

    Well I ended up buying my second EE locally. This one is a MG - 1948 Vintage, and I am hoping to get it wired up as soon as possible. I am in a bit of a pickle however. Here is/was my plan:

    I was planning on using a Rockwell PowerFlex 40 VFD (22B-A012N104) which is rated at 3hp (12 amps). These drives have a 24 VDC source as well as several Digital inputs at their disposal. I was planning to run the control circuit with the 24 VDC source, which would basically be just start and stop. I would set the VFD speed to 60 HZ to drive the AC motor and use the existing DC voltage generated by the Generator/Excitor to power the spindle motor. The problem I am having is that @ 240VAC the Reliance AC motor is rated at 13.2 FLA. VFD's in single phase go up to 3HP, no problem right?. Well looking closer at the drive specs. the drive is rated at 12 amps which seems to be standard. I am assuming the higher draw on the Reliance motor is due to the fact that it is older/less efficient and also because maybe the losses in the generator are included in this rating.

    I know that drives are pretty smart these days in terms of overload protection, however I am hesitant to run a under-sized drive (12 amps) with this motor (13.2 amps). I have considered de-rating a 3-phase input drive, however it would be considerably more expensive to go this route as I would need at least 7.5 hp drive. I am not sure if there is anyone that is running a similar setup, or if you have any input. Thanks in advance!
    Some of the 'smooth' in an MG does come from goods wound for a wider RPM band, but nominally less-efficient - at least when not at optimal RPM.

    General sweet spot for an RPC to drive the motor-gen side of a 10EE is not less than 5 HP, better-yet 7.5 HP.

    A VFD can ramp-start all that motating stuff better, but yes - you would be better-off with a 7.5 HP or at least a 5 HP VFD running at less than max than a 3 HP dog-paddling for dear life and perhaps tripping-out while in the cut.

    And last time I looked, there WERE single-phase-input VFD at 5, 7.5, and even up to 15 HP. Just not all equally CHEAP.

    On which score ... an MG 10EE is happy enough with a dirt-simple RPC anyway.

    Bill

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    My '41 vintage EE spins up nicely with a 3 HP 1140 RPM motor with a 1.15 service factor for the rotary part of the RPC.

    The rest is dirt simple control.

    Bill

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    if its operational I'd stick with the mg for a while. If the Gen is screwed those have been replaced by transformer/ recifier combos ( one of mine is like that ).

    for what its worth I have several operational 10ee's in the shop
    1. square dial toolroom 20" 7.5 hp vfd with back gear
    2. MG transformer converted
    3. mg original
    4. beel dc drive conversion

    in operation I don't see much difference.

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    Hi Guys,

    Thanks for the input. I guess I didn't look hard enough because there are single phase 5 hp drives available just as Bill said. One reason I am thinking about going with the VFD is because I can run the control circuit at 24VDC. It needs to be rewired regardless. Also, the shop is small and I would like to keep the noise down. The benefit would be that I could add a switching circuit and use the RPC on other machines. I am going to have to think about this one .

    Also, I am planning on keeping the MG section. I just needed three phase to power the motor section. I only have single phase in my shop.

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    Quote Originally Posted by PLC View Post
    Hi Guys,

    Thanks for the input. I guess I didn't look hard enough because there are single phase 5 hp drives available just as Bill said. One reason I am thinking about going with the VFD is because I can run the control circuit at 24VDC. It needs to be rewired regardless. Also, the shop is small and I would like to keep the noise down. The benefit would be that I could add a switching circuit and use the RPC on other machines. I am going to have to think about this one .

    Also, I am planning on keeping the MG section. I just needed three phase to power the motor section. I only have single phase in my shop.
    Suggest you DO keep the MG.. at least for now.

    They are far easier to repair than anything else 10EE'ish, given that - for one example - a VFD + 3-P motor conversion - done often enough to have plenty of examples, and mostly GOOD ones - still does require some careful measuring and planning.

    Not to mention significant work and skill just to source the goods, get them into place, gearboxed, and wired.

    Best to "run what you got" - and fix it up a tad - until you have genuine reason to do otherwise.

    On -edit.. not to forget an RPC dasn't even have to live indoors, let alone in the same space. MG theirselves are noisy. Yes. Not quite as bad as a vintage Waste-King commercial dishwasher as used in bars & such - more akin to my heavy-dooty 21+ yr old Kitchenaid.

    BFD. You'll be making chips faster 'stead of creating a long-running 'project'. Something else can come sometime else.


    Bill
    Last edited by Monarchist; 04-16-2016 at 02:00 PM.

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    Regarding your noise concern, did you run the "new" MG lathe under power, say prior to purchase during your evaluation of it? A good low RPM RFC idler is silent in comparison to a 10EE MG set, they are loud. All the time...

    Have used many RPCs of both self built and commercial construction over more than forty years with absolute reliability, low cost and the ability to power many machines singly or simultaneously. They excel at startup torque with the right idler and can power difficult loads such as air compressors. Don't throw the RPC option out due to noise considerations unless you envision something like a noisy high RPM TEFC motor as the RPC idler.

    VFD have their place, using their ability to vary speed and acceleration in three phase applications is wonderful. You don't need either to simply power 60 HZ three phase machine tools at rated RPM.

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    Junk all the MG stuff do a full conversion 5HP 3 phase vector motor 10HP VFD 1 phase in 3 phase out. mount the 2 speed gear box on the c-face motor with a spacer
    You can sell off the old stuff to someone to off set the cost
    John

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    Perhaps I have overestimated the nouse concern for the rotary phase converter. I did in fact hear the mg before I purchased the lathe, and it did not bother me much. It looks like I should probably get a 10 hp rpc just to be safe, and the pricing isnt much higher from the 7.5 hp rpc. Do you have an recommendations?

    Sequim, for now I am planning on just running with old drive. I know it could change, but I really enjoy the older drives and have learned a lot in bringing them back to life.

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    A 7.5 HP idler motor is more than enough to run a 10EE's MG. There are many, many 7.5 HP RPCs in use with 10EEs with zero problems.

    Virtually all of the noise from the idler motor has to do with the cheap fan that's usually mounted on one end of the shaft. I removed the fan from mine and it's very quiet. I use a squirrel cage blower to cool the idler motor instead.

    Cal

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    Lack of torque at low frequencies is the main problem with AC motors powered by VFD's isn't it?

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    Quote Originally Posted by RC99 View Post
    Lack of torque at low frequencies is the main problem with AC motors powered by VFD's isn't it?
    Yes but... not much of a factor when most folk are using carbides & cousins at 'base' RPM and well above rather than below.

    From around 1,000 RPM and up, a decent VFD + a good 3-P 5 HP to 7.5 HP motor overclocked regulates way better under load than a 3 HP DC motor does when as deeply field-weakened as the 690 RPM-base MG units need to be for upper-range RPM.

    Not that I care.

    The Cobalt HSS, Stellite & c. is all paid for, and there are sooo many varieties of carbides and holders, I am too old, and too retired by half to be bothered to learn 'em, let alone BUY them so as to make a transition I don't need anyway.


    Bill


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