wiring transformer/votage to high

[scheek]

I would apprecaite if someone will guide me into figuring out why my voltage is too high.

I have 45VAC transformer http://www.partsexpress.com/pe/showd...number=122-705

Please look at the spec part at the lower part of the page. This will carry you to a PDF file showing the wiring schematic (also at the lower part of the page)

I beleive I have it wired in parallel but at the rectifier I hitting 79 plus volts.

On the DC side at my Geck Drive I hitting over 90 and rising.

Obviously this the reason my stepper cut off.

Here is the way I have it wired.

There are 4 large wires which I have wired accordingly.
Gray +
Brown +
Blue -
purple -

4 small wires
Red +
Yel +
Black -
Orange -

Thanks.

[Al_The_Man]

You appear to have it wired right, disconnect the secondaries from the bridge and measure the AC at the paralleled secondaries. You should get approx 45ac.
You may be getting higher than that due to off load current and high primary voltage, often Txfrs are wound for 110 but your outlet voltage could be 120v.
With a bridge connected and a capacitor on the output, with no load will be Min 63vdc.
This will depends solely on what actual reading is for the AC secondary.
One cure is if the secondaries are wound Bifilar, that is together, instead of one on top of the other, you can remove turns (in tandem) to get the voltage down, probabally approximately 2turns/volt.
Al.

[scheek]

If the drive are hooked up and motors hooked up, should the DC voltage increase.

I didn't want to say this before, but at one point I measured 98-100 VDC and climbing.

I would not be sure of how to unwind a tranformer.

[Al_The_Man]

If the motors are stationary normally it should not increase.
Are you sure of your meter, I know my fluke gives all kind of weird readings when the battery is low.
Al.

[scheek]

NO, I haven't check the batteries. I suppose I will. Good idea.

Just for the record, is the 45 VAC/45VAC, the way we have it wired capable of producing 100 and over VDC.

I would hope not for danger of blowing my drives.

Humm! if it's wired correctly, Still there is something killling my stepper. My motors are way to hot to hold on to. That may be normal. I don't know.

Too, at one point the VDC was about 65. But that was before I hooked all motors and such.

[Al_The_Man]

From the point of view of the DC supply, it should not be higher than ~63vdc, if the AC is 45vac, back EMF from motors can cause it to go higher, but not if they are not being driven.
Do you have large enough Electrolytic capacitance on the bridge output?
Al.

[kreutz]

Post a photo or more of your power supply so we can see how you wired it.

[scheek]

Originally Posted by Al_The_Man From the point of view of the DC supply, it should not be higher than ~63vdc, if the AC is 45vac, back EMF from motors can cause it to go higher, but not if they are not being driven. Do you have large enough Electrolytic capacitance on the bridge output? Al.

This is what I have as for capacitor.
Capacitor, Al; 37000muF; High Cap.

I hope that is enough. Will that tend to run up voltage?

[Al_The_Man]

The rectified peak should still be 1.414 x the AC, less a volt or so for the bridge.
Al.

[scheek]

Al,

Darn battery was bad in the okm meter. 64.5 VDC on the dot now.

Well, I'm glad that was not my problem for the failing motor. I see where I had the drives pressed against the heat sinks loosely with an elctrical tiedown. I resecured each with another tiedown. My grease is about or gone under them.

Is there anything else (household that will do)? Is the grease an absolute even if the drive is secured against the heat sink?

Maybe the drive overheats and lets the motor get too hot. Is that possible?

thanks

[scheek]

Ok.

This is so embarressing, but could it be that the motor failure is due to my license not being installed in MACH2. I just realized that it was still in DEMO mode and I had not dropped the file in the folder.

I have not put everything back together and tried the CNC to know.

I guess Art could tell me for sure. Just thinking, could the G-Code stop on the x-axis in the DEMO version after so many lines. If that is the answer, I'll kick myself.

Thanks

[Torchhead]

The MACH demo is good for 1000 lines of (give or take a few lines). It would just stop (all movement) but I don't see how that could cause a failure of any piece of hardware. No different than hitting the PAUSE or STOP Button. All movement would stop. The thermal "butter" you see is specially formulated to transfer heat. Don't try to use something else. The better the surfaces mate up the better the heat transfer. Two very flat and glass smooth surfaces clamped tightly will get good transfer if the materials are good heat conductors. Anodized metal is not perfectly smooth and few parts are REALLY flat. The thermal grease fills in the microscopically small cracks and uneven spots and improves the heat transfer. It has to have as good a heat coefficient as the two objects. The ability of an object to transfer it's heat to the air around it is a function of the total square inches of radiation area, the thermal mass of the object and the amount of air flow. With no air flow an insulating layer of hot air builds just above the surface preventing efficient transfer to the surrounding air mass. Even small amount of air movement helps breakdown that barrier. Larger amounts of air movement removes the heated air at the object surface even faster and really helps to keep componets form toasting themselves. For every deg C of heat above about 20 deg C the failure rate for components increase.

I suspect your hardware failure is due to other issues.