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Posted By Topic: Transformer Issue

May 21 2015 13:27

Hi, was hoping to find a bit of help with an issue I\'m having.

I was looking for issues on a machine that might cause random HMI display loss, and found the voltage at the HMI to be low, 81-85V ac (100-110v req). I checked power at the main transformer, and see the low voltage is occurring there. Power feeding the transformer is supposed to be 200v, but its 160-165v when hooked up to primary terminals. If I remove from primary, voltage is fine (200v). The secondary matches the primary voltage, I swapped transformer out but get the same result.

Transformer is a small 300VA 200-220v to 100-110v model.

What could be causing this?

Thanks in advance

Ben W

May 21 2015 15:34

Well, 200V isn\'t 230V so there must be yet another transformer. That\'s getting a convoluted. I\'m surprised the display unit doesn\'t just have full 230V on it, or at the very least have 230V on that step-down transformer you\'re looking at.

May 21 2015 15:45

\"Well, 200V isn\'t 230V so there must be yet another transformer.\"

Judging by his post, I\'d say he\'s in the USA.

May 21 2015 16:30

Japanese equipment, but yes, in the US..


May 21 2015 18:18

You need to figure out why the input voltage drops from 200v with no load to 160-165v when the transformer is connected.

Sounds like a problem upstream from the transformer.

May 21 2015 19:51

I agree Doug, but I\'m not certain what kind of issue it could be really. lines for Transformer are fed right from main breaker in cabinet from drop, when transformer lines are removed voltage is back to good.

Any ideas what could cause this? Weak contact on one leg of breaker in supply panel?

May 22 2015 00:42

Yep, with the transformer connected, just use a multimeter to measure the volts at each joint back from the transformer until you find a jump in voltage.