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Sterilizer water pump 115 VAC with one probe

bargaincrusader

Sep 19, 2019
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Hi
I am trying to repair a sterilizer. It has 3 basic components that run on 115 vac. I do not have a schematic, and cannot get one. There is a water pump thatI looked up is run by 110 vac, a solenoid that runs from 24 vac, and a small heater 110 vac. And a compressor 110 VAC.

110VAC goes into the one main circuit board, then appears to be switched on and off by signals when required. Measuring the heater, compressor, solenoid lines with probes across I get no voltage, when the component turns on I get the 115 VAC, which seems normal. The water pump when off has 115 VAC, when it turns on to run it goes to 154 VAC. Also to note if I read across the lines of the pump I get 154 volt D.C., and it drops when the pump is triggered on. Lastly when I put a DMM lead on one side of the lines at the pump it reads 115 VAC without attaching the second lead?
The heater, compressor, solenoid all seem to measure correctly in my opinion, the water pump seems to have an issue. I also used an Oscope on the water pump lines to see if could see a D.C. wave but the sine wave appears normal and 60HZ. Also to note the oscope says 330VAC, and when the pump switches on, the reading changes to 115VAC with probes across the lines.
Any ideas of which components may make these type of readings? Thank you
 

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Tha fios agaibh

Aug 11, 2014
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I put a DMM lead on one side of the lines at the pump it reads 115 VAC without attaching the second lead?

You are reading leakage current of an open circuit via capacitive coupling. Some call it a ghost voltage. This happens using a sensitive (high impedance) meter that reads voltages at very low currents.

Line voltages measured with a loaded meter (low impedance) such as a solenoid tester (wiggy) or putting a slight load on a dvm meter leads will not mesure these ghost voltages that don't have much current potential.

If you don't have a low impedance meter you could get away with making a line voltage tester using an incandescent light bulb to see if the circuit is passing enough current to drive the pump/compressor.

Sounds like possible pitted relay contacts that shows a voltage, but isn't capable of passing enough current to drive the compressor.
 
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bargaincrusader

Sep 19, 2019
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Can you tell me if any of these components look like it may have relays in it. Originally I thought the big black module had relays but when I looked it up it said it has 2 voltage regulators inside the black box. Could it have relays?.
 

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Tha fios agaibh

Aug 11, 2014
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Can you tell me if any of these components look like it may have relays in it. Originally I thought the big black module had relays but when I looked it up it said it has 2 voltage regulators inside the black box. Could it have relays?.
I thought that too at first glance. Yes, It looks like a 12v power supply.
If you verified that the components aren't getting power, you need to trace it back to see what and where its supplied.
Perhaps a triac?
 

bargaincrusader

Sep 19, 2019
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Hi
Thanks for input.
The water pump gets power, and turns on, get inaccurate readings such as the VAC rises to 154 VAC, also measures 154 volt DC which decreases when the pump turns on. The problem is it intermittently does not turn on the water pump causing an error code that water is not present in the chamber. So it is an intermittent error along with the weird voltages
 

bargaincrusader

Sep 19, 2019
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that large black component is BV UI 303 0003 Hahn encapsulater transformer. It apparently may have 2 thermistors inside also as the number B59975-c120-Ato is also typed on the casing which made me think it only had the thermistors.
 

Tha fios agaibh

Aug 11, 2014
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As for weird voltages, I would make sure you trust the readings you have before delving in too deep. Try another true rms meter for comparison.

As to power supply, idk if it has thermistors or not.
If you suspect it's a problem, why not just test it?
Test its output voltage open circuit, and then shunt it with a 30Ω resistor to see if you still get about 12v under load.
 
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