To shunt or not to shunt? (shunt regulator)

[chris.poirier]

Hello out there,
Last time I was working on my project I cleaned up all my wiring and powered up to check the DC supply.
110VDC on the dot. I am ready for my install now and I decided to let everything run for 30 minutes.
I am running off a 10ph rotary phase converter and have a wild leg and just wanted to see if there was any risk of thermal overload.

Spindle overload contactor was fine, but the resistors on the shunt regulator started to smell, I did not check to see how hot they were.
I disconnected the shunt regulator and the DC voltage on the cap went up to 130VDC.
The DC supply has 2 bridge rectifiers and is using all 3 phases off the x-former.
Any input would help. I can post the system schematic if needed.

So I have some decisions to make.
1) leave as is and see if the regulator pops or just plain waste loads of electricity, is this shunt reg designed to run like this? (has 2 300W 6 Ohm resistors and a fan, fan was off at the time)
2) change the taps from 240VAC input to 250VAC and see if things calm down into an acceptable range. I am going to try this tonight.

I am running a DC3IOb with MPU11 and intend to buy the Centroid software.

Regards,
Chris

[diycncscott]

Chris,

You mentioned your spindle overload contactor - Are you referring to the braking resistors attached to your VFD? They should only be seeing power on accel/decel of spindle and shouldn't effect your DC Bus voltage to the DC3IOB at all.

Is your spindle motor AC or DC? What kind of VFD/Spindle drive do you have?

Yes the schematic would help. Please post it.

[chris.poirier]

Hi Scott,
On my 5hp lathe, I have an issue where the coolant pump overload contactor trips when not running the spindle at the same time. I believe this is because of the wild leg on the rotary phase converter.
I wanted to make sure the mill did not have this issue as it is only 3 hp. I am using a FWD/REV contactor. VFD some day.

From what I have researched, a shunt regulator is used on servo drives that can not deal with the back EMF from the servo when it has aggressive deceleration or unexpected stop. (crash)
The shunt regulator has a set point and when the DC bus voltage for the servos goes above that point it bleeds off the voltage. ( I may or may not be correct on this)
My old control was new in 1984.
This shunt reg board also made 5 and 12VDC for the old control boards I removed.

While I have your ear is there a gear bobbing add-on for the control?
I didn't make it into the shop last night, but am going to check the AC voltage at the bridge input to see if I can make 83VAC with some tap combination.


Any thoughts comments or pearls of wisdom?
Chris

[diycncscott]

Chris,

Are these "shunts" connected to the output of the axes on the DC3IOB? If so, please disconnect them, they are malfunctioning if they get hot just sitting there and there probably isn't any need for them on a knee mill. Actually, disconnect them regardless and pick a different tap to bring your DC voltage down to 120VDC or less (with the shunts).

There is no gear hobbing add-on

[chris.poirier]

"Not to Shunt"

I'll pull the shunt regulator and make adjustments.
The shunt regulator would have been connected to the cap before the DC3IOB.
Glad I asked before I installed. Fun starts tonight If I can make 110DC without it.


Thanks for the input.
Regards,
Chris

[chris.poirier]

I am still in a bind.

The X-former taps are set to 250VAC (highest setting) and I went out and bought an infrared thermometer at harbor freight.
Here are the things I tried with results.

Spindle on, no shunt regulator, I get 112 VDC
Spindle off, no shunt regulator, I get 128 VDC (is this too high?)
Spindle on, Shunt regulator installed I get 110.2 VDC, Shunt resistor temp 80F, after a 10 minute run.
Spindle off, shunt regulator installed I get 110.4 VDC, Shunt resistor temp shot up to 230F and I ended the test after 3 minutes.

I have a call into the company that sold me the phase converter, I have a low leg under load and the wild leg is higher than expected under no load.
Anybody have comment on Phoenix Phase Converters?

Regards,
Chris

[chris.poirier]

Hi Scott,
OK between changing the taps and removing a cap on my rotary phase converter I have the DC voltage down to 118VDC no load and 102 with the mill spindle on.
When I start my lathe with the mill running the voltage goes to 100 VDC.

Am I OK to run?
Hope you can get back to me I want to start installing tonight.


Chris

[diycncscott]

Chris,

Your DC voltage is fine and you should be ok to run without issue as far as the servo drive goes.

I'd be concerned that starting the spindle causes such as sag. I suspect either your phase converter
isn't rated for the load or the spindle motor itself. Does the spindle motor get hot?

[chris.poirier]

Great, thanks for the response.
I intend to let the motors fail if they are going bad and then replace them, is there a risk with doing this?

My long term goal is to convert the lathe to CNC, learn to make a POST for Pro-E then sell off everything and go shopping for better equipment (another couple of retrofits).
So I have bought them with the idea of not keeping them, just a learning tool. Maybe the lathe I'll keep, my DoAll/Romi is accurate as hell.
If I cause some big crashes better to do it on this equipment.
So far this is a success story I already have my the entire shop investment paid off with the 2 lathe jobs I have. (took 2 years, not exactly a day job but one hell of a hobby) I better never die, the wife would kill me if she had to get rid of this stuff.

I want some detailed info on adding scales at some point, once I am running.
I want to put them on x, y and the knee. (no quill handle, so better on the knee for summing in my book)

Caution below is a rant about the phase converter company I used.
Sorry in advance for the rant, but I just want to let other Ajax customers who are going to do what I have done know what they are in for.
If anyone out there is thinking of a phase converter I would recommend forget the phase converter and making everything 240 single phase with VFDs. I saved ~400.00 but not when you factor the issues worry, headaches and loss of adjustable RPM from the control. Phoenix Phase was the cheapest, but after calling them a few times they are very matter of fact/condescending and don't elaborate on any question as if being evasive. My converter was advertised as being 2% CNC grade. I would be lucky to have 2%, more like 6% after making my adjustment. (measured phase to phase with a true RMS volt meter) My gut reaction is they are not power engineers (neither am I) but are selling a product any way.
I called about my coolant pump overload tripping when the spindle was off, they told me to bypass it and put in slow blow fuses 2X the larger than required?????
This is all after I turned the overload all the way up, it still tripped.
240 single phase will help resale into the hobby market. 3ph has no advantage for resale. My mill will be sold with the converter at some point. Don't buy a Phase converter.
I have a 2.2KW Chinese converter I bought for 130.00 off ebay as an experiment. Let the fun begin.

Best regards,
Chris