Hello. I work for a company developing high-voltage relays. Since there's not much information available on contact cleaning, I'd like to inquire. Currently, we're using DC to eliminate oxidation at the contacts and reduce contact resistance. However, this isn't enough to satisfy our clients. So, we're planning to measure AC. I'd also like to know what the default settings are for AC. (Our relays are sealed, containing only hydrogen and nitrogen inside the chamber.)
I have no idea what to do with AC. Please help me.

 

I suggest looking at the product application information of the PICKERING company. They have been masters if excellect reed devices for over 30 years.

 

High voltage means exactly how high?
600V?
2kV?
30kV?

 

I suggest looking at the product application information of the PICKERING company. They have been masters if excellect reed devices for over 30 years.

Thank you for the recommendation. I checked with the company and it doesn't seem to be a high-voltage relay.
I'm talking about the high voltage relay that goes into the PRA.

 

High voltage means exactly how high?
600V?
2kV?
30kV?

No, I'm talking about automotive. For example, 400V@80A / 800V@250A

 

No, I'm talking about automotive. For example, 400V@80A / 800V@250A

Back when I was a teenager, Ive heard of a "wetting current" used on low power relays, to "burn off" the tarnishing over time
this was in an Audio mixer, where the mV Audio had around 10 mA of DC added ,to ensure that the contacts of the reed kept clean,

But if your at the 800V /250 Amp range, then quenching the arc is going to be the fun part, else the contacts will burn out quickly.
On big big relays, as in on a tram , Ive seen a large magnet field across the gap used to stretch and divert the spark,

There seems to be an old post on here about this as well,

https://forum.allaboutcircuits.com/threads/cleaning-relay-contacts-by-electrical-current.121499/

 

I've already read all the documents. Thank you.
But there was nothing about stabilization under AC conditions

Back when I was a teenager, Ive heard of a "wetting current" used on low power relays, to "burn off" the tarnishing over time
this was in an Audio mixer, where the mV Audio had around 10 mA of DC added ,to ensure that the contacts of the reed kept clean,

But if your at the 800V /250 Amp range, then quenching the arc is going to be the fun part, else the contacts will burn out quickly.
On big big relays, as in on a tram , Ive seen a large magnet field across the gap used to stretch and divert the spark,

There seems to be an old post on here about this as well,

https://forum.allaboutcircuits.com/threads/cleaning-relay-contacts-by-electrical-current.121499/

 

Won't they be clean enough after 400V @ 80A?

 

exactly... contact cleaning is for loads that do not use much current (less than 10mA). if this does not please your clients, use SSR.

 

It seems to me that what is far more applicable to relays in the class of "over 300 volts and over 20 amps" will be developing a magnetic-blowout scheme for extinguishing the arc. "Tarnishing over time" has never been mentioned as an issue for any high powered control relays in my industrial controls experience. Those voltages will instantly break thru any oxide layer.

Somebody making that demand is lacking basic understanding.

Besides that, contact oxidation in an oxygen-free atmosphere is rather unlikely. Contact melting caused by arcing CAN be a serious issue. I have seen that. The solutions to that are well known and common.

 

I think the application is the series contactors (a relay that carries high current is called a contactor) for electrical vehicle.
At the stated currents (250A) even a small contact resistance will have a large power dissipation (ie 250 x 250 x 0.01 ohm = 625 watts.
I am surprised that there is no literature about this as its a common challenge both in EV and electrical power switching .
For the poster, you need to look at contact materials that do not degrade with switching currents, and intrinsically have a low contact resistance. That may mean using silver or a silver alloy.
Also for DC , if this is switching large currents, rather than just being used as an isolator, you will magnetic blow outs, either coils or magnets or both.

 

As panic mode mentioned, use an SSR or similar.

If they need less power loss, have the relay in parallel to the SSR and only turn it on/off when the SSR is active.
(sort of like a torque converter lock up on an automatic transmission)

 

Consider the history of switching "high currents", that it has been for over 100 years, at least in the US. And the answers seem to work very well. The motor and lighting switching devices with the best lifetimes use heavier contacts and a lot of material that is a good heat conductor. The "Secret Trick", which I have used, is the SERIES connection of the mechanical switching and the solid state control device. So the mechanical contacts switch on and off with low load currents while the solid state portion does the much faster delivered energy controls. AND the mechanical contacts mostly open under load in "Emergency Stop" incident, where contact life is only a minor consideration.

 

Hi dr,
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Hi @chageunwon

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