[SCzEngrgGroup]

Taking AC readings on a DC supply gives you an indication of the AC component of the DC. If a diode in the rectifier section of your power supply is shorted or open, it will show up in your AC reading. Taking AC or DC readings cost nothing and if the readings don't match the expected readings, then it can indicate a problem. Taking a DC reading on an AC signal can indicate grounding or isolation problems.

Motor power supplies are generally unregulated, so it should be expected to have a significant amount of AC on the DC output. If you get a lot of AC or none, then there is a problem somewhere. In this case the AC reading is unstable, which isn't much help. It may help to turn the auto-ranging off and try again, otherwise skip it.

No, with a DVM, if you have anything but a stable ~60Hz AC component, you're reading garbage, which will even be significantly different using different DVMs, as the circuitry in the meter is incapable of giving a meaningful reading when the input is not stable for the entire sampling period of it's A/D converter, which is typically no more than a few hundred Hz, if that. An analog meter will give you something of limited value, if you know how to read it, because the analog movement will essentially filter the reading, giving you a good average. A digital meter will just give you garbage, with no correlation to what's really happening.

Regards,
Ray L.

[underthetire]

Err, its called ac ripple when checking for ac on a DC circuit. Its a very good indication on how the filtering capacitors are working. Very common practice.

[SCzEngrgGroup]

Err, its called ac ripple when checking for ac on a DC circuit. Its a very good indication on how the filtering capacitors are working. Very common practice.

Yes, but it is almost certainly not simply pure AC ripple, it is far more likely high-frequency noise, which will cause the DVM to read garbage, but will not affect operation of the motors in the slightest. If you haven't looked at the waveform with a scope, you have no way of knowing what it is. If you're going assume it's AC ripple, then you should be advising him to scrap his power supply, as 23V of ripple would indicate a serious failure - it should NEVER be that high, even under max load. Surely you don't believe his power supply has failed to that extent?

Regards,
Ray L.

[Don Clement]

The AC component is best measured using an O'scope under load. As to frequency the PS may not be just filtered/regulated 60HZ as nowadays the mains are rectified and then chopped at a higher frequency for conversion to another voltage i.e. switching power supply. Using a multimeter, analog or digital, is not going to give much info about the true nature of the power supply AC component or regulation. It could be that for the purpose of driving steppers that a well filtered regulated supply is not needed. One must look at the specs of the PS to see if AC component and regulation is within spec for the application.

Don C.

[underthetire]

I can't suggest anything, since I know nothing about that particular power supply, nor would I trust a radio shack meter. I'm just saying you can analyze a power supply this way to determine if it may be failing.

[BAMCNC.COM]

Does your meter have a HZ setting?

As for the reply to my earlier comment, I can't remember, but when I hit the reset button in Mach, does that turn off the drivers? If so that is all you need to do before unplugging the 4th to prevent any issues if there were any. I have a series 3, not sure if they built in any protection or not. I just simply unplugged it without thinking about it, no issues here.

[DLawrence]

The AC component is best measured using an O'scope under load.

Don C.

OK and that makes sense . . . . I got Tenma 25 mHz "digital storage" scope a while back so looks like this will be a chance to use it. There is now one axis drive board left working so I will hook things up

I am thinking a purely resistance load might give a clearer picture on an often hard to deal with o-scope screen ..... as a first test.
Think i will first try a 100 watt filament type light bulb as load and then progress to a stepper ;load

Dave

[DLawrence]

Before hooking up scope to check power supply voltage , I tried two different analog meters ,then my autorange only digital, all meters now report nothing , that is ZERO on AC and 70 on DC,
Didnt go ahead with the scope.

Called Tormach they informed me the "upgrade path" to 3 of the new 3 Phase steppers and appropriate new leadshine drivers , for my machine , seriel # 1287 is through first installing the spindle drive upgrade kit.

About $1400 And I will be able to do It in a few months.

In the meanwhile there is the possibility ,I suppose of repairing the two blown origional serIes 1 axis driver cards, and the two blown "new style " series 1 replacement cards,

or see about using the Geco 201 bought befoer buying the 1100 , and never used.

The X axis is running, If i can get the Y going I can use it to torch cut some gears out. . . . .