Power question

[jbailey19]

I have a 4 axis hobbycnc board running on a 36v transformer. In the middle of a cut today the driver board quit responding. I have been trying to trouble shoot it and have a question. My 36v power supply feeds ac to a bridge rectifier with a large cap and then feeds the resulting dc to the power input on the driver board. The board is marked as 36v max and even though I measure 36vac on the output of the transformer I am getting 50vdc after the bridge rectifier. Do anyone have any idea why I would be getting the 50vdc and I assume that this will cause the board to shut down.
Thanks.
Mike

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[jbailey19]

When it first stopped working my cooling fan was not running. I swapped the transformer out for a 24v one and now my fan is working but I still do not have motor control. I have requested a set of instructions from Brian so I can go through the board and see if I can find a bad component.
Mike

[KOC62]

Your transformer is said to be 36VAC. If so, the peak voltage will be 1.414 X 36V = 50.9Volts.
The bridge rectifier will give a small loss due to diode voltage drop and the capacitor will charge to the peak voltage after the bridge rectifier.
Your measurement confirms this.

Yes, over driving the board is a bad thing to do. It may have damaged your board.
What you need is a transformer that gives 36 / 1.414 = 25.45VAC.or use 24VAC as the next closest under 25.45 VAC.

EDIT:
Some transformers are designed to give the stated voltage under load, but could go higher by 10% under no load.
Then your local power line voltage could also be be high under certain conditions thus possibly driving your output another several % higher output. These variables are hard to predict, so accurate measurements can help here to make decisions.

[jbailey19]

I am not getting 5v on the 5v pad. I have replaced the LM317 but still am not getting 5v. I guess I need to pull the two resistors and check if they are good.
Mike

[KOC62]

Are you getting an input voltage to the LM317?

[jbailey19]

Turns out my board is fried. 2 of the drive chips are burnt up. I will be ordering a new board and if they are available I will get some replacement components and try to fix this one for a spare.
Thanks for the help.
Mike