Bridgeport Series II Interact 2. Transformer/ DC power supply questions.

[danande]

Hi all!
I have a Bridgeport Series II Interact 2 milling machine that I wish to retrofit to a new servo control but still using the old dc motors.
But I need a dc psu for the motors, and was thinking to maybe use the transformer in the control cabinet to do this.
Will be using the DG4S-16035 servo drive which has a max operating voltage of 160v.

The motors are t SEM MT30R4-58.

Volts 145
Cont. Stall Torque 3.2Nm
Max RPM 2500

Power output motor: 3.2Nm*2500rpm/10 =800W / 145V = 5,5A.

The Bridgeport has a big 3KVA transformer that was used to power the servomotor drives with 180v.

Seeing the electrical schematics in the manual it looks like it is an autotransformer?


For information I live in Norway and we have IT net which is 3x230v power here. I also have 400v from a transformer in my shop.

Now, what my idea is.. The transformer can be hooked up to various voltages to give out 180v as seen in schematic. They probably made one model to make it work for all markets..
380v to 180v is a reduction of (380/180) = 2,11 times
So if I were to connect 230v to the 380v (230/2,11) I would get about 109V, and when this is rectified (109v*1,4) would give me about 153V.
Quoting Al_the_man here

For servo Power supply design the DC voltage should be at least 10% over the motor plate voltage, you can also go higher than this if needed.

So the 153VDC rectified is perfect for motors and within spec for drives.

Is it possible to simply do it like this? Obviously also have to put some decent caps and bleed resistor and maybe inrush limiter depending on size of caps..
I have looked at the wiring going to the terminals of 3KVA transformer and they appear to all be of the same gauge.
Still having read similar threads, I know there may be an issue with the efficiency, and derating of transformer when used like this..?

If the 800w per motor is true, then 2400w for all three motors is below transformer VA rating. I think I read an 80% requirement of total power req so about 2kw should be sufficient.

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[Al_The_Man]

I have those motors on a XLO about the same size as the B.P. by the looks of the transformer I think you can get away with it, the motors on mine rarely get to full load, if ever.
The transformer on mine is around 1.5Kva to 2Kva.
Al.

[danande]

Excellent, thanks for input!

Al, what are the specs on the capacitors on your dc psu for 3 of those motors?

Been thinking on how to correctly size the caps, wondering about the farads and the voltage rating.
I use a total current of 17A for 3 motors.
The DG4S servo driver manual specifies 2000uF per motor amp = 34000uF. That's some really big caps alright...
What about the voltage rating on them?
I will use cncdrive.com BRKC-180 braking circuit, so the drives or caps should not see over 180v once these kick in. See manual here.

[Al_The_Man]

I will have to check tomorrow.
Al.

[Al_The_Man]

The caps are 2x 8700µf (17400µf) 200vdc
Al.

[danande]

Thanks. Any ideas on why the DG4S servo driver require using 2000uF per motor amp?
I think I will also use 200vdc caps due to the braking circuit.

[Al_The_Man]

The 2000/motor amps is a general guide line that is usually stated, but remember it is VERY rare, if ever, that the motors all use the continuous torque amp rating at any one time.
Al.

[Tkamsker]

Hi i did similar convrrsion on an bridgeport 412 i which uses Bigger Sem servos i Even did the toolchanger ,.. Maybe you have a Look at Granite devices their vfd 160 do a Great Job Thomas


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[Jay Kyle]

I'm going through the same conversion but using AjaxCNC ALLIN1DC drive pack, single phase 240VAC, and a VFD on the spindle. On your transformer picture - it that a 3 phase transformer? - you'll have to check the windings if it is. Also the schematic you're using I also use as it's freely available on a few other sites from guy's who've also done the conversion. Notice it's a 460 VAC schematic - you can tell from the inputs on the other transformers and expected outputs, also notice the schematic shows a single phase autotransformer for T1 which threw me off for a while till I figured it out.

My servo's are also the original SEM's 145 vdc. My research suggests to keep the final DC voltage below the 145, this will be easier on the servo windings and the only consequence is slightly slower rapids. Given that, my 240VAC single phase line in will be using the 0-460 taps - output on the 0-180 (right) taps to yield: 240/460=.521 -> 180*.521=93VAC -> 93*1.42 = 133 VDC rectified which I'm comfortable with. I'm using the right 180 tap to keep line balanced (for no good reason).

The schematic is unclear what the servos are actually receiving as it shows 180VAC unbalanced pair and 380 VAC power going into the drives - but gut feel says Bridgeport wouldn't overload the servos when they're rated for 145VDC.

AjaxCNC sells cap/rectifiers on their web site for these conversions - they're using 12000uf 250v caps.

Anyway that's what my thinking is so far - and I'm no electrician either.

Jay

[danande]

The picture shown is a 1 phase transformer. Yeah I have noticed its almost the same for other Bridgeports too.
It's a very versatile transformer. You can connect it to 210,220,230, 240, 380, 400, 420, 440, 460, 480V to get 180v and 380v feeding the drives.. I have no idea how the drives work, how they get that 180vac rectified to 145vdc is beyond me.
Why keep final dc voltage below the 145 on motor plate?

I'm no electrician either

[Al_The_Man]

Lower voltage than the motor plate would mean you would not reach the motor rated rpm, but you probably cannot go that high with the mechanical configuration you have.
Al.

[Jay Kyle]

..Why keep final dc voltage below the 145 on motor plate?..

I've been doing a lot of reading on the AjaxCNC Tech Support Forum and Ajax Technical Bulletins to figure this out - specifically TB269 (Rev1) - Voltage ratings of DC drives and DC Power Supplies

I originally started this conversion planning on using LinuxCNC but gave that up as it took too long and too much effort to get the whole system figured out. Went to Ajax and never looked back - though my learnings at LinuxCNC helped provided a broader understanding.

Jay

[Larken]

The picture shown is a 1 phase transformer. Yeah I have noticed its almost the same for other Bridgeports too.
It's a very versatile transformer. You can connect it to 210,220,230, 240, 380, 400, 420, 440, 460, 480V to get 180v and 380v feeding the drives.. I have no idea how the drives work, how they get that 180vac rectified to 145vdc is beyond me.
Why keep final dc voltage below the 145 on motor plate?

I'm no electrician either

I've retrofitted a a BP like that. I think the old drives on your BP were SCR drives, so they ran right from the AC transformer.
An SCR drive running at 180 volts ac will produce average about 140 DC on the output. Just like a standard 90Vdc treadmill motor is designed to run from an SCR drive running on 120 Vac.

Larry K

[danande]

I've been doing a lot of reading on the AjaxCNC Tech Support Forum and Ajax Technical Bulletins to figure this out - specifically TB269 (Rev1) - Voltage ratings of DC drives and DC Power Supplies

That was an informative read. Thanks for link!

From TB269 (Rev1) - Voltage ratings of DC drives and DC Power Supplies.
When determining the operating voltage of a DC drive, it is extremely important to select a voltage that is
NOT
higher than the voltage
rating of the lowest voltage rated motor connected to the drive. Modern drives use switching output electronics that subject the motor to
the full DC supply voltage at various frequencies and duty cycles. Therefore, the DC supply voltage must not be greater than the
voltage rating of the motor to prevent insulation breakdown, a burnt commutator due to arcing, and exceeding the maximum motor
speed.

I will still use my existing transformer. Should get 154VDC. It's 9V above the baseplate reading on my motors... Should be okay

[Al_The_Man]

therefore, the DC supply voltage must not be greater than the
voltage rating of the motor to prevent insulation breakdown, a burnt commutator due to arcing, and exceeding the maximum motor
speed.

I refute this supposition totally, a motor has a drive between it and the P.S. see
Power-Supply Considerations For Servo Amplifiers | Electromechanical content from Electronic Design
A higher voltage does not harm it per se, motors are not built to that tight a voltage restriction, the thing to be aware of is that the higher voltage does not cause a higher than rated rpm, but as the link shows, this can be controlled by the controller and/or drive.
As the link shows a min of 10% and even higher than the motor rated is fine.
Al.

[danande]

So this retrofit got postponed long enough.

How do I correctly wire the autotransformer?

I noticed that the two 0 points are connected together, is it supposed to be like that?

I have illustrated how I intend to wire it in the picture. Please correct me if im wrong here.

EDIT: For information I have three phase 240v in my shop, so there is no neutral wire like you have in the US.

[Jay Kyle]

I had a jump on mine, I pulled it out, powered it up, and all worked as expected. Best I can say is see if there's continuity between the two zero posts without the jumper - that will tell you if the jumper is redundant.

[Al_The_Man]

It has been a while now!
Disconnect the o-o link and check you have the output needed, if so leave it isolated, and test output. If it is truly a auto transformer you may need it but it is best if you can also set up a earth grounded neutral.
Al

[danande]

Thanks for the reply!

I will disconnect the link and measure what I get

[danande]

There was continuity between the 0 posts, but I hooked it up with the link disconnected.
Turns out I have 240v instead of 230v.
I measured 103v between 180 and 0 when connecting to 420 and 0.
103*1.414 gets me 145v which is right on the money

Should I keep that link between the 0 posts?