need a electronic expert,

[muddstopper]

I am having problems with my power supply for my cnc mil. The machine is 90 something model. Checking the transformer on the machine, I have 120v input, but zero out put. I called signal transformer comp, they made this particular transformer and it seems it is no longer available, obsolete, but they will make me one if I can wait the 20wk lead time. Finding a substitute is proving impossible because this transformer is a 26v-52v output. Best I can up with, and this was thru signal transformer company, is a 24v/48 volt transformer. I have searched ebay to no luck. In the mean time, I took the transformer out of the machine and while I had it on the bench, I decided to hook an extension cord to it, just to see if I could figure anything out. Well, bang, it fired up and started humming, something it wouldnt do while installed in machine. Voltage shows 28v and 56v output. My question is why does it work on the bench, but not in the machine. I have verified the power going to the transformer several times.

 

[JustJeff]

Check your motor, it could have a fault in it causing the transformer to overload. Be an easy thing to eliminate.

Sent from my CLT-L04 using Tapatalk

 

[muddstopper]

I have completely isolated the transformer from any motor. Even while still installed in the machine I unhooked everything from it but the input power. I also went back a little while ago and reran my extension cord test and now there is no power on the low voltage side. This I dont understand, why would it read low voltage one minute and then an hour later not read anything. It wasnt doing anything but setting on the bench, not connected to anything.

 

[2412]

My vote is for a loose internal connection. Flexing it while removing allowed the circuit to re-connect. How big is it?

Next time it fails check for an open circuit on the inputs and outputs. Or put an ohmmeter on it and slap it around a bit.

 

[Bobby Kirbos]

It sounds like it's a center tapped transformer, 26-0-26. Other than the slightly odd voltage, if you know the secondary current requirement, you can replace it with anything that matches.

As for the voltage difference --

It's math time
- 120v input
- 52v output required
- 48v is the closest "off the shelf" you can find

- turn ratio of the "almost" x-fmr, input / output = 120 / 48 = 2.5
- 52 * 2.5 = 130
So, if you put 130v at the input of that 48v (24-0-24) x-fmr, you will get the needed 52v (26-0-26).

How to get 130v on the primary --
You can use a 10v x-fmr on the primary side as an auto x-fmr, just size the secondary of this one to handle the primary current of the 52v x-fmr. When you hook it up, you should have 130v on the primary of the 52v x-fmr. If you end up with 110v on that primary, the phasing is wrong on the auto x-fmr. Simply flip the wires on the primary to the auto x-fmr.

I can draw a schematic if that would help.

 

[blakey]

One thing to check would be to check continuity from the output lines to the metal casing of the transformer. If you have continuity then maybe it is shorting to ground when you mount the transformer in the machine. You would check this with power disconnected of course.

 

[Blue Oaks]

Is it heat related? I used to run a Fadal CNC that needed a big fan running on the main cage/board to keep it cool enough to work.

 

[muddstopper]

Power is connected to the zero and the 115 terminals at the top of transformer, the 100 terminal is not used.. The wires connected to the zero and 115 at the bottom go directly to a computer fan.On the opposite side there are three wires that go directly into the driver board. One wire for each terminal. The dimensions of transformer are 2.25 in thick. 6.5 inches long and 5.5 inches tall. The info I got from the engineers at standard transformer comp is that the transformer was custom made and is now considered obsolete and no longer available. They said they could make me one, but there is a 20 wk lead time. I also talked to SouthWest Industries, the company that makes the CNC for the bridgeport and they dont have and cant get a new or used transformer to fit this machine. That leaves me with trying to cobble something together to make things work. I pretty much need a transformer that puts out 56vdc and one that puts out 26vdc to pair inside the machine cabinet. I still dont know the amp size, but I am thinking around 9 amps and no more than 20 amps. I do know I can make the servo motors run with a 12v battery charger set on 60 amp boost. The motors may run off 12vdc and 40amp, but I didnt notice any movement when I tried it. I didnt want to fool around to much as those servos are $1200 apiece.

 

[muddstopper]

It sounds like it's a center tapped transformer, 26-0-26. Other than the slightly odd voltage, if you know the secondary current requirement, you can replace it with anything that matches.

As for the voltage difference --

It's math time
- 120v input
- 52v output required
- 48v is the closest "off the shelf" you can find

- turn ratio of the "almost" x-fmr, input / output = 120 / 48 = 2.5
- 52 * 2.5 = 130
So, if you put 130v at the input of that 48v (24-0-24) x-fmr, you will get the needed 52v (26-0-26).

How to get 130v on the primary --
You can use a 10v x-fmr on the primary side as an auto x-fmr, just size the secondary of this one to handle the primary current of the 52v x-fmr. When you hook it up, you should have 130v on the primary of the 52v x-fmr. If you end up with 110v on that primary, the phasing is wrong on the auto x-fmr. Simply flip the wires on the primary to the auto x-fmr.

I can draw a schematic if that would help.

Look at the pictures I posted above to see what I have. I dont understand what you are suggesting and a schematic would certainly help. I dont know how sensitive the electric circuits are in the driver board and nobody seems to have the info I need. I am sure the servos will run off different voltage as they normally are set for different feed rates. Of course not supplying full voltage would screw up the actual feed rate setting of the motors. I think I can work around that if thats all it does. Just for info. The key pad is self contained and only connected to the driver boards thru supplying ac voltage to the transformer.

 

[frank_]

would,nt the servo,s be stepper motors ?
and i ran my brushless motors at one time with a 30A £20 dc-dc circuit board that was fully adjustable

 

[jetsam]

You really don't need a transformer at all. If you want one, you could either take the old one to an armature place for rebuilding, or determine your amperage requirements and replace it with a new 26 and 56 volt pair of single-tap ones.

If it was me, I'd be looking at a solid state power supply. You know your voltages, you just need to figure out maximum draw on the 26v and 56v side, and you can spec out a power supply (or two).

 

[muddstopper]

You really don't need a transformer at all. If you want one, you could either take the old one to an armature place for rebuilding, or determine your amperage requirements and replace it with a new 26 and 56 volt pair of single-tap ones.

If it was me, I'd be looking at a solid state power supply. You know your voltages, you just need to figure out maximum draw on the 26v and 56v side, and you can spec out a power supply (or two).

Tell me more. I am already thinking along the same lines, I just dont know what to look for.

 

[jetsam]

The easy way: call the manufacturer and ask them what maximum draw on both rails is, then add a bit for safety. If they say the 26v leg pulls 5 amps, shop for 6 amps and up. (Or ask them what the load rating for each tap on the original transformer was; this is almost the same question but it may be easier for them to answer phrased that way.)

The hard way: 1) Get a grossly oversized power supply, then run the machine hard with ammeters inline to see what it pulls in the real world. 2) Get part numbers off of every component and add up maximum draw for the lot (may not even be possible, lots of unlabeled stuff out there).

Once you know amperage requirements, you are shopping for a power supply that takes in 120vAC and puts out 56vDC at however many amps you need, and 26vDC at however many amps you need (assuming those are the only two voltages you need).

If it's not a large power requirement you might find both right off the shelf. If it's larger you may end up having to make something.

 

[muddstopper]

The easy way: call the manufacturer and ask them what maximum draw on both rails is, then add a bit for safety. If they say the 26v leg pulls 5 amps, shop for 6 amps and up. (Or ask them what the load rating for each tap on the original transformer was; this is almost the same question but it may be easier for them to answer phrased that way.)

The hard way: 1) Get a grossly oversized power supply, then run the machine hard with ammeters inline to see what it pulls in the real world. 2) Get part numbers off of every component and add up maximum draw for the lot (may not even be possible, lots of unlabeled stuff out there).

Once you know amperage requirements, you are shopping for a power supply that takes in 120vAC and puts out 56vDC at however many amps you need, and 26vDC at however many amps you need (assuming those are the only two voltages you need).

If it's not a large power requirement you might find both right off the shelf. If it's larger you may end up having to make something.

I have already been around and around with the equipment manufacturer as well as the component manufacturer. I did manage to get a wiring schematic from equipment manufacturer, but no where on schematic does it give any amp ratings or voltage outputs. The component maker was able to verify voltage, but couldnt or wouldnt say how many amps, claiming it would be up the equipment builders to determine how much power needed. I kind of thought that was odd, but what do I know. The main use of the transformer is to power the servo motors and encoders for x and y axis, I cant even get the manufacturer to give me the specs on those motors and the tags on my motors are unreadable.
Now this is what I am considering trying to do. I know the wire going from the transformer is 14ga stranded wire. This leads me to think amp draw would be limited by wire size to 20 amps or less, I suspect only 9 amps. If I use a bridge rectifier to convert the 115vac to 115vdc, I can use a couple of buck converters to step down the dc voltage to the 52 and 26 vdc I need. As long as I dont exceed the amp rating of the wire, the motors will only pull the power that they actually need. Once I find out the max amp draw, I can then install a fuse to prevent over loading and melting parts that are hard to find and replace. Not sure how to put this together and make it fit in the enclosure box, but I'll mount another box if I have to.

 

[jetsam]

Wire gauge is one way you could guesstimate requirements if you really have to. What gauge wire was connected to the 26v and 56v taps on the transformer? Many manufacturers will use the minimum size required.

Your old wire stripper should be all you need to accurately measure the gauge. Be sure to use the stranded marks, not the solid ones.

(This is not a scientific approach, but you do know that the wire didn't melt under load before, so the load is less than whatever that wire can carry.)

 

[muddstopper]

Made a little discovery that might suggest amp draw. While studying the schematics, I found the 56vdc of the transformer goes directly to a mda2502 rectifier rated for 25amps. Rectifiers are usually sized to at least double the amp requirement to take care of any surge that might occur at startup. This would mean under normal load the actual amp draw would be about 12amps.

edit. Tomorrow I plan on cleaning all the wire post and installing test wires to make sure I am getting a good connection. I will be using my extension cord to supply power. If this works, I plan on reinstalling the transformer along with new crimps on the exsisting wireing and see if the led,s on the driver board will light up. If it works, I will just play with the controls for a while. If it dont work, then I am going to start taking the transformer apart. My train of thought is transformers either work or they dont. If they dont its usually burnt or broken wires. Burnt wires give off a burnt smell even if they have been burnt for a while. I cant see or smell anything wrong with the transformer.

 

[Del_]

Just noting that 26 and 52 VDC could be had off of 4 automobile type batteries. You'd have to disconnect the failed power supply of course.

If you have good meters you could measure current draws. Motors that move quickly can be hard to get good readings on.

How's that for thinking outside of the box?

I like Jetsam's idea about going with two separate transformers.

 

[J D]

If the transformer runs directly into rectifiers you can definitely run it of DC. I would suspect the voltage isn't overly critical either & a suitably sized center tapped transformer will be fine... Infact, depending on the current rating & normal input voltage variations a 48V transformer could have a higher output than your 52V transformer.
First thing I would do however is solder a new power lead to it as the most likely point of intermittent failure is the power cable at the point it was fixed, followed by the wired connections of the transformer where they are soldered.
If you can upload that circuit diagram I can probably give you some pretty good direction.

 

[Bobby Kirbos]

If the transformer runs directly into rectifiers you can definitely run it of DC. I would suspect the voltage isn't overly critical either & a suitably sized center tapped transformer will be fine... Infact, depending on the current rating & normal input voltage variations a 48V transformer could have a higher output than your 52V transformer.
First thing I would do however is solder a new power lead to it as the most likely point of intermittent failure is the power cable at the point it was fixed, followed by the wired connections of the transformer where they are soldered.
If you can upload that circuit diagram I can probably give you some pretty good direction.

I would want to see some of the other components in the power supply, or if possible, the schematic for the supply. They may be using a negative voltage as well, which would negate the ability to run a pure DC supply.

 

[J D]

I would want to see some of the other components in the power supply, or if possible, the schematic for the supply. They may be using a negative voltage as well, which would negate the ability to run a pure DC supply.

That's why I'd like to see that circuit diagram. I do think that's unlikely though given the way the transformer is marked & the OP stating the 52V runs straight into a rectifier.
You can still get a negative supply voltage with DC power supplies wired appropriately