sundance-communications.com Forums Telephone Services Security, Alarms and Paging Dukane MCS350 24V PS Problems

I'm working on a Dukane MCS350 rack and found the main 24V PS was at 32 volts. Seemed like a problem because 24V goes to relays, regulators, consoles and I didn't want components to be stressed and fail. True, board regulators get the volts down but it means there’s that much more overhead to dissipate.
I took the supply apart and it's just a transformer, bridge rectifier and big capacitor. No regulation. I opened up the transformer and there are no voltage adjust windings.
So now I'm considering replacing the stock supply with a Power One 24V 4A linear.
-
A second problem: I found the 120VAC neutral is hardwired to the safety ground inside the supply. This means part of the return current from the hot side flows back through the safety ground. I plan to separate the two and connect safety ground to the chassis.
Next I need to consider the other grounds: DGND, AGND. In my opinion these should be connected, but at one point such that digital current does not flow through AGND and muck it up. Also, I think DGND should be connected to safety ground so that the electronics don’t float and drift up to some tingly voltage. Seems like the analog card would be a decent place for both connections.
Thoughts Anyone?

The MCS350 has an unregulated power supply by design from the factory. Do not modify the power supply. Why are you considering changing the power supply?

If it's not broken why fix it?

When you folks measure the 24V TP on a Card are you expecting 32V?

That's 33% higher.
It would be like running a 120VAC blender on 160VAC. Doesn't make sense to me.

If I measure 4.8 - 5.8 on a 5V TP that's good enough to get the job done without stressing the ICs.

Thanks for your help figuring this out. BB

The MCS350 does not have a regulated power supply. The regulators are on the boards themselves. 32VDC is normal for that power supply output -- I just measured on my MCS350 here to double check. What exactly are you going for anyway? What trouble are you having with the MCS350 that you're disassembling the power supply??

Hi Dean, Good question.
Because, if I break it, I’ll have something to fix. Very logical ya' know.

Hello Tim,
I think you guys did great job answering my question. Although the PS is labeled 24V, it was designed by the manufacture to run at the higher voltage. Originally, I thought maybe that was the case, but didn’t want to assume that without being absolutely sure. The reason I took it apart was to see if there was a voltage adjustment to correct the problem or at least understand the situation better. Thanks for the confirmation and measuring your system. Now I know something new. Can’t beat that!

What problem are you trying to correct?

What problem are you trying to correct?

"to correct the problem"

A +24V test point measured +32V. That was the problem I was talking about.

It's not normal for me to pull out a voltmeter to test a power supply just on a whim....I've got more important things to do than chase down problems that don't exist!