[bcarlson42]

I have a 1985 Acromax MX-16 with a Yasnac MX-1 controller and Yaskawa VS-626 MTII ( SEARCH: VS 626 MT 2 ) That blows 2 transistors if you decelerate the spindle from full RPM. This also blows the fuse, I think after the transistors short. I have replaced the 3 components, 2 transistors and fuse a couple times when the wrong S is commanded and care is not taken to slow the spindle before. This problem is 100% repeatable from 6000RPM. Never happens from 5000RPM. We have the acceleration/deceleration parameters set to the slowest possible, before doing this the same problem would occur from almost any RPM. The machine was run from a fairly poorly balanced phase converter for a few months but is now on 208V 3ph from the Grid. No change in behavior we discovered last night...

My only thought is that the large carbon pile resistors in the drive must be bad. They test good with a multimeter but this does not reflect the presumably high voltage one would see when shutting the spindle down. I'm thinking that under high voltage, the resistors don't offer very much... resistance. Can anyone confirm my thoughts here? I've seen other people who have this problem, mostly when using a phase converter but never anyone who found a solution other than to take it slow with the ramp down.

Not sure if this is the place to ask also so welcome to suggestions to go elsewhere. Thank you.

[mactec54]

I have a 1985 Acromax MX-16 with a Yasnac MX-1 controller and Yaskawa VS-626 MTII ( SEARCH: VS 626 MT 2 ) That blows 2 transistors if you decelerate the spindle from full RPM. This also blows the fuse, I think after the transistors short. I have replaced the 3 components, 2 transistors and fuse a couple times when the wrong S is commanded and care is not taken to slow the spindle before. This problem is 100% repeatable from 6000RPM. Never happens from 5000RPM. We have the acceleration/deceleration parameters set to the slowest possible, before doing this the same problem would occur from almost any RPM. The machine was run from a fairly poorly balanced phase converter for a few months but is now on 208V 3ph from the Grid. No change in behavior we discovered last night...

My only thought is that the large carbon pile resistors in the drive must be bad. They test good with a multimeter but this does not reflect the presumably high voltage one would see when shutting the spindle down. I'm thinking that under high voltage, the resistors don't offer very much... resistance. Can anyone confirm my thoughts here? I've seen other people who have this problem, mostly when using a phase converter but never anyone who found a solution other than to take it slow with the ramp down.

Not sure if this is the place to ask also so welcome to suggestions to go elsewhere. Thank you.

If it does not have a external Braking Resistor then you should add one, before the whole VFD is smoked

The Braking Resistor has to be the correct size for the VFD

Deceleration should be set to a higher number not a low number, that means it will slow the spindle down slower and will have time to reduce the back EMF voltage

[bcarlson42]

Mac,
They are in there, just not sure if they work right

I think they are right? I guess it's been 33 years so they may have been cobbed in but the manual suggests a part number I can't find anymore.

That's correct. It's set to the "slowest" setting, highest number. Slowest accel and decel.

Update:
Upon inspection, the unit has 2 wirewound resistors. Both 150W 800mOhm (0.8 ohm). They have the part number gr150w.

They can be found on ebay such as here: https://www.ebay.com/itm/RESISTOR-GR...UAAOSwG-1WyzBR (I'm sure that link will decay, sorry)

I've found replacements that I believe will work but are the wrong dimensions on Mouser and found that Ohmite will make to order one that is close enough although I don't know for what price yet.
Link: https://www.mouser.com/ds/2/303/res_280-1265358.pdf

Can anyone suggest a test to make sure these are the problem or help me to decide that they are likely the problem? My understanding is this is where the power goes when braking so it really makes sense as the problem. I'll likely order the ones that don't quite fit but have the correct specs and cobble them in to find out. I'll have some more transistors and fuses on hand of course. That or I just give up on this rusty pile and get something from this century.

[mactec54]

Mac,
They are in there, just not sure if they work right

I think they are right? I guess it's been 33 years so they may have been cobbed in but the manual suggests a part number I can't find anymore.

That's correct. It's set to the "slowest" setting, highest number. Slowest accel and decel.

Update:
Upon inspection, the unit has 2 wirewound resistors. Both 150W 800mOhm (0.8 ohm). They have the part number gr150w.

They can be found on ebay such as here: https://www.ebay.com/itm/RESISTOR-GR...UAAOSwG-1WyzBR (I'm sure that link will decay, sorry)

I've found replacements that I believe will work but are the wrong dimensions on Mouser and found that Ohmite will make to order one that is close enough although I don't know for what price yet.
Link: https://www.mouser.com/ds/2/303/res_280-1265358.pdf

Can anyone suggest a test to make sure these are the problem or help me to decide that they are likely the problem? My understanding is this is where the power goes when braking so it really makes sense as the problem. I'll likely order the ones that don't quite fit but have the correct specs and cobble them in to find out. I'll have some more transistors and fuses on hand of course. That or I just give up on this rusty pile and get something from this century.

Are these mounted External, do they get hot when you stop the spindle at speed, if not someone may have turned off the Parameter for external Braking, you can check them with a meter you will have no continuity if the are bad

[matiasjuarez1993]

How did this go?

- - - Updated - - -

Mac,
They are in there, just not sure if they work right

I think they are right? I guess it's been 33 years so they may have been cobbed in but the manual suggests a part number I can't find anymore.

That's correct. It's set to the "slowest" setting, highest number. Slowest accel and decel.

Update:
Upon inspection, the unit has 2 wirewound resistors. Both 150W 800mOhm (0.8 ohm). They have the part number gr150w.

They can be found on ebay such as here: https://www.ebay.com/itm/RESISTOR-GR...UAAOSwG-1WyzBR (I'm sure that link will decay, sorry)

I've found replacements that I believe will work but are the wrong dimensions on Mouser and found that Ohmite will make to order one that is close enough although I don't know for what price yet.
Link: https://www.mouser.com/ds/2/303/res_280-1265358.pdf

Can anyone suggest a test to make sure these are the problem or help me to decide that they are likely the problem? My understanding is this is where the power goes when braking so it really makes sense as the problem. I'll likely order the ones that don't quite fit but have the correct specs and cobble them in to find out. I'll have some more transistors and fuses on hand of course. That or I just give up on this rusty pile and get something from this century.

how did this go?

[bcarlson42]

This is really digging into the archives but it was something like this:

The resistors weren't a problem. I ended up finding a 5.5kW 626 MTIII ($300, some local guy had it) that I was able to retrofit in place. Everything plugged in except you needed to get a Yaskawa PRPT-01D2B ($30, eBay) which basically takes resolver output from the spindle and turns it into something this drive could read (IIRC, this was a long time ago).

I also needed to fabricate a new mount for the drive inside the cabinet. As far as I know this machine is still running with a guy in CT(?).

Other options was a retrofit from Yaskawa for $16,960.00 or a rebuild from simpler systems (which I would recommend, they have helped me with other Yaskawa stuff since then) for ~$1,200.00.

[joeavaerage]

Hi,
I think your braking resistors are faulty.....did you not say they are 800mOhm??? That sounds way to low to me.

If they are switched across the DC Link of 400VDC for example they'd draw 500A....that would blow the two transistors every time!
I would expect braking resistors to be something like 40Ohm

Craig