Interesting 7x12 motor speed controller problem

[Nsomnia]

I lost the plastic sheeting for the speed controller a long time ago so I had just wrapped the controll box in plastic wrap. I finally decided "bleh thats ugly" and so cut out some plexiglass to protect the electronics.

When I put it all together I guess a wire shorted to one of the grounds and she wouldnt go.

Everytime i replaced the fuse it popped instantly.


I noticed I got a tingle when I touched the heatsinks so I ran a ground wire to the building ground and then when I put a fuse in, she sparked bad again (smoke, one LED turns green and the other is out. The motor runs at full speed (mosfets are blown/shorted)

If I take out the fuse the second LED momentarily turns green as well then both go out as the fuse is fully removed.

Im going to replace all the ground cables, the power cable, check the recepticle ground and order a handful of mosfets.

Is there more of an issue here than a bad ground? I dont wanna resolder 24 mosfets just to learn I should just replace the board and all wiring.

I have a spare board of same model number (courtsey of my mini mill with broken gears on order) however before I blow that one too what should i be cautious of (other than replacing all ground wires)

[john_100]

What controller is it

with more than one heatsink I expect it to be a XTM.... series

XTM1135

look here Gerling Laboratories has establi

if it is you will have 3 diodes and 2 thyristors on 5 heatsinks

forming a controled bridge rectifier

is the manual for your lathe available as a free PDF file

with the extra info i'll be able to suggest some tests
to do before using the other controller

John

[Nsomnia]

you are right the 1135 littlemachineshop says its a bad mosfet due to full speed all the time.

Im going to replace all the grounds and the board and fuse with my mills and buy a new one.

[john_100]

Don't add any earth / ground wires to the heatsinks

on the FC250J /230V board in my lathe the heatsink is isolated
being insulated from the FET's and not connected to the PCB

but looking at a photo of a XMT series controller it looked like the heatsinks
are connected to the device they cool no insulating washer being visible

on the XTM 1135 controller you have a diode on three of the heatsinks and
a thyristor on the other two

the thyristor being a type of diode that only conducts when triggered
to give you the control

John

[knudsen]

Don't add any earth / ground wires to the heatsinks

+1

The tab on FETs and other drivers is tied to the center pin of the semiconductor. You can isolate that from the heatsink or let the heatsink "float" as they have. Usually, they isolate the tab from the sink electrically, but not thermally. Little "rubber" mats and plastic washers. If the mats and washers are there, one has failed (usually from over-tightening, usually the washer fails). I probably have some if you need them, just post a pic of the FET and I'll pop a few in an envelop.

Damn, you're about out of machines, I'm guessing. If you didn't go to metal gears, you might want to order a spare gear or two, if you haven't already. I blew two out in ten minutes one fine day.

[Nsomnia]

Im saying when I touched the heatsinks after it shorterd/full speed all the time I got zapped.

I added a ground wire from the regular green grounds to the building grounds and the 'sinks didnt zap me any longer.

Edit: Wired up the mills power cord, board, and switches etc. to the lathe and it works fine. Im going to try soldering some new mosfets onto the lathes old board and then see if it works. Infact I have an old board that was toast for some reason, maybe Ill try the mosfets off that.

[john_100]

Hi Nsomnia ,

looks like I'l have to investigate how you wire things in Canada

in the UK the domestic single phase supply is one of the phases of a 440V 3 phase supply ( any phase is 240V to earth / neutral)
the star point of the transformer at the substation is earthed and also connected to the neutral cable

the incoming mains earth is bonded to any metalwork in the home like the gas mains , water mains and internal plumbing so every thing is at the same potential
we don't have a separate local earth

having a look at more photos of XMT... type control boards the heatsinks are not connected to and any of the printed circuit
while I can not see any insulating washers its possible they have used isolated tab diodes and thyristors ???


John

[Al_The_Man]

In N.A. domestic supply is a 240v 1 phase center tapped transformer, the center tap is grounded neutral, and is grounded where the service enters the building Only.
120v to neutral is used for low current circuits, 240v is used for higher current appliances such as Range or Dryer etc.
I recall In UK, a separate local Earth ground used to be supplied via a Earth leakage trip and ground rod if the ground path back to the grounded star point was not sufficiently low enough resistance, but that was in another life.
Al.

[john_100]

Hi Al

are yes , the the earth loop impedance test
I once borrowed the test meter from the sparks at work
to test the wiring at home
the worst result was still under 50% of that allowed Im glad to say

so your mains supply is like the 110V supply used on UK building sites
( 110 V centre tap earthed )

180 degree phase difference between phases that I can understand

the unbalanced 3 phase that Canada and the US use I have real problems with

unless I have misunderstood , one version of the 3 phase supply at least
has a delta wired secondary on the transformer
the earth and neutral connected to a centre tap on one winding


back to Nsomnia's wiring
if connecting the mains earth to the building ( local ?)earth
stopped the shocks , to me that suggests a wiring problem that needs to be look into

John

[Nsomnia]

Found out why its fried.

A trace to one of the mosfets is completly burned out. Im going to try resoldering the trace and replacing the mosfet and see where i get.

[john_100]

Hi Nsomnia ,
you can test the speed control on your work bench if you use
a 20 to 100W GLS bulb ( tungsten not energy saving fluoresent bulbs)
as a dummy load in place of the motor

with a low wattage bulb you can test a FC.... type of controller with just one FET fitted
once you've checked the bridge rectifier and diode across the DC output

any chance of a photo of the damaged board and FET ?
in order to see what other components need testing

John

ps do you know part numbers on the FET's on your board ??

[Al_The_Man]

The three phase supply here in N.A. is no different from UK, whether Star or delta.
Just that the domestic supply is single phase source only, consisting of a 240v centre tap secondary, the primary of which is fed from 2 phases of a 3 phase supply.
When 3 phase only is used the star point is usually grounded or very occasionally one junction of a delta supply is sometimes grounded to obtain a neutral.
This is usually done at the local level and not a policy of the service supply Co.
Al.