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Faulty Mitsubishi S-N25 Electical Contactor


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I have the above contactor installed in my panel and when the power is irregular (up and down - say fluctuating down to 180v) it starts to hum. I have found that a soft tap with something non conductive will stop the hum. Sometimes it also requires a manual restart when it is tripped which is not how I understand it should work. Also not helpful if I am away and the fridges are then off.

I suspect its faulty and wish to swap it out but I see there are different variations. As well as an S-N25 there is also a S-N35 and in the pic below where you will see 17.5S there is also a S-N25 18.5S. I have no idea what the 17.5S and 18.5S is referencing or the difference?

My electrician doesn't speak any English and I while I will ask him to do the work he will simply buy the same spec again.

So my question is do I buy exactly the same part (part number S-N25 17.5S) and assume it was faulty or do I also take an opportunity to upgrade where there might be a better model that might work more efficiently and also solve the hum and manual restart issue. This is a 3 phase rural connection and I want to stay with Mitsubishi and avoid any rewiring. I can see on my meter that the voltage is often fluctuating and particularly when its raining and very hot.

Screenshot 2024-05-06 at 07.31.43.png

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If you believe your contactor is faulty you should replace it with exactly the same type (all the numbers and letters specify coil voltage, contact form etc.).

 

What does your contactor actually do in your system? If it's an under/over voltage protection there should be a controller too where you can set the trip voltage.

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Thanks Crossy. It does have a controller and yes it’s as protection for under and over voltage. See the pic below. 
 

I still wonder whether the spec is right for this controller but as they are cheap I will replace it with the same one and see what happens. 
 

 

IMG_8004.jpeg

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Thanks Carlyai. Yes I have adjusted the trip voltage but its a balance between having power and not having power when there is such volatility at peak times. This will also be the third time that I have replaced the contactor (but over 10+ years). This was why I was asking myself about the specs because as I understand the feed from outside comes into this contactor first. I know we have dirty power like a lot of villages but when the voltage is fluctuating the humming is my primary concern especially as I can tap the contactor and it stops. Time to swap it out again i guess and see what happens. I can buy the contactor on line for about Thb600 so fairly cheap. Appreciate your response - it was good.

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I think the humming is the contractor rapidly switching between on and off, so it appears to be humming.

Crossy will know more, but if you have under and over protection on your mains incoming, it can be a pain when the trip points you set are correct, but the incoming voltage falls outside these limits.

You could have the 3 phase mains come into 3 stabilisers (one for each phase). Then when an incoming phase voltage drops, the stabilisers corrects this so you still have 220V output.

You could then just install over/under voltage protection on say your swimming pool motor feed. 🙂

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@Bosscat Do you have any actual 3-phase appliances? 

 

You could consider using 3 x single-phase regulators like @carlyai suggests (not a single 3-phase one) to regulate your supply or maybe go for 3 x single-phase protectors and retain the 3-phase one for any 3-phase appliances.

 

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Thanks Carlyai and Crossy. I don't have any three phase appliances at this point. I will try to ask the electrician on the option of 3 single phase regulators. Communication is always a bit of a challenge though but your advice here has helped me understand more. Thank you both. 

 

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When I was working in India our place in Delhi had 3-phase.

By the TV were 3 outlets, one on each phase.

Plug the TV into the "best" phase.

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Posted (edited)
On 5/19/2024 at 12:15 PM, Bosscat said:

I have found that a soft tap with something non conductive will stop the hum.

At times all that is required is to clean the rust/debri off the lamination shoes where they contact.

 

Around 7:00 on the video below.

https://www.youtube.com/watch?v=fMpAlUc20yQ&t=2s

Edited by bluejets
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Good advice bluejets. I will pull the old one apart when its replaced and have a look. This property is not my normal residence so not easy to check (4 hours from me in Bangkok). Will need the electrician to come anyway to pull the existing one out so might as well replace it at the same time. Hopefully the old one can then be a spare. Thanks for the tip.

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