AC/DC circuit ????

[customcutter]

I am trying to figure out the power "board" on my old controller so that I can either keep it or start robbing parts to build the new controller.

On the board there is a 4 screw terminal block. The top wire is red #1, #2 is yellow, #3 is red, and #4 is red. The bottom 3 wires go to a remote start/stop switch that lites up when ON, and the top wire connects to the "breakout/control" board. When the switch is turned off I read 120v AC across 1 & 2, 1 & 4, and 2 & 3. I read no DC voltage across any combination.

When I turn the switch on, I read 120v AC across 2 & 3, and 2 & 4. I also read 150v AC across 1 & 3, and 1 & 4. With the red test lead on #1, I read 150v AC between 1 & 3, and 1 & 4, however when I place the black test lead on #1 I read -0 between 1 & 3, and 1 & 4.

When I switch my meter to DC volts, with the red lead on #! I read 68.5 volts between 1 & 2, and 1 & 4, with the switch ON. No DC reading when the switch is OFF.

It seems like one of the AC legs is reading as negative in DC??? I'm pretty sure that terminal #1 could be used for DC+, which one would I use for DC-???

If you need pics let me know. I've posted to linuxcnc forum, but haven't taken time to learn how here.

thanks,
Ken

[RancherBill]

If you need pics let me know.
thanks,
Ken

This is the vaguest question for a long time. What is the model number, what is the application etc. Pics would definitely help.

[Blackadder]

Ken

beware a volt meter when switched to AC can read a DC voltage at approx. 50 % due to the rectifier conducting one direction only

the only sure way is to stick a scope on it.

to muddy the waters still further it is possible to super impose a ac signal on dc ( we used to do it on the knock outs in the foundry )

Stuart

[Barrington]

customcutter - Judging by your picture posted on the linuxcnc forum, the chassis may well be being used as the 0V connection:-



The fixing I've circled in red - are there similar on all the boards?

The smaller board piggy-backed onto the power board appears to be a small switching power supply, with its output most likely to be on the two red wires on the overhanging end.

As for the yellow and two red wires going to the "start/stop" switch (on /off ???), I would have guessed the two red wires go to the switch with the yellow as the return for the indicator (i.e. to neutral) - BUT this doesn't correspond with all your readings so...?

As was said, a cheap meter can't be trusted to separate ac and dc components.

Cheers

.

[customcutter]

Ken

beware a volt meter when switched to AC can read a DC voltage at approx. 50 % due to the rectifier conducting one direction only

the only sure way is to stick a scope on it.

to muddy the waters still further it is possible to super impose a ac signal on dc ( we used to do it on the knock outs in the foundry )

Stuart

Stuart:

Thanks, between the cheap meter and imposing AC over DC that would explain most of what's happening. Sounds like I'll need t break it down into smaller pieces or just use the 50V transformer and scrap most of it.

Ken

[customcutter]

customcutter - Judging by your picture posted on the linuxcnc forum, the chassis may well be being used as the 0V connection:-



The fixing I've circled in red - are there similar on all the boards?

The smaller board piggy-backed onto the power board appears to be a small switching power supply, with its output most likely to be on the two red wires on the overhanging end.

As for the yellow and two red wires going to the "start/stop" switch (on /off ???), I would have guessed the two red wires go to the switch with the yellow as the return for the indicator (i.e. to neutral) - BUT this doesn't correspond with all your readings so...?

As was said, a cheap meter can't be trusted to separate ac and dc components.

Cheers

.

Barrington:

I hadn't noticed, but yes all of the boards are "grounded" to the frame.

As Stuart mentioned, I think the problem is the cheap meter, super imposing AC over DC, etc. I think I'll just scrap most of it, use the 50V transformer, pick up a bridge rectifier and 24 v transformer.

I've already ordered a 5i25-7i76 combo kit from Mesa, just need to figure out the power side.

thanks,
Ken