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Thread: Fake relay's ?
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15th May 2022, 09:07 AM #16Member: Blue and white apron brigade
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15th May 2022, 07:14 PM #17
Hi John,
Hi voltage ceramic capacitors should be ten a penny ! The actual nf value isn't very critical, their purpose is simply arc suppression. On one of the Ebay pages I saw some 2.2 nf 2Kv ones at 100 for about $6 Au, a nice bright blue colour. But use what you can get that is in the price range that you are willing to pay.
Bob: I used to buy solid silver relay contact points in packets of ten some years ago, and apart from cleaning them used to replace the badly worn ones. You would be surprised at the hammer they got at 60 volts AC switching 12 ohm coils, often at two or three times a second. I used to fit 1 nf 1 Kv ceramic capacitors across them just to reduce the arcing and sticking. If one wasn't enough I would sometimes use two or even three in parallel or use a larger value.
Just a comment about ceramic capacitors, the actual capacitance value changes with applied voltage particularly in DC circuits and can fall to half the rated value depending on the voltage. The low voltage ones seem most prone to this effect, but they all do it.Best Regards:
Baron J.
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15th May 2022, 10:46 PM #18Most Valued Member
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No worries Bob, I have ordered these for 45 bucks cheaper than the ebay ones https://www.aliexpress.com/item/1005...31340335%21sea who knows when i will get them?
I recently had 2 separate orders from shahe and they each took about 2 weeks but an order from milton tools in china took about 6 weeks....now it looks like the are gunna lock down beijing also so who knows when they arrive....
Thank you John, i will add those caps that Joe linked to to the above contactors and hopefully that should sort out my problem??
or...ummm....I dont think that i have a voltage spike problem but do you think that it would be worthwhile fitting these do dars that nigel suggested while i am at it? https://www.jaycar.com.au/460vac-250...r-mov/p/RN3415 if so do i use both together or does this thing also work for ark suppression?
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16th May 2022, 01:55 AM #19
Hi John,
There will be voltage spikes, but its the current ones (as in amps) that causes the arcing and metal migration between the contact surfaces ! MOV's or varistor’s won't help unless the voltage exceeds the MOV's ratings, where as a capacitor will tend to absorb the sudden change in current when the relay contact breaks.
I'm sure that you have seen transient suppression, where a resistor is used in series with a capacitor ! The resistor used to reduce the sudden change in current through the capacitor. Often seen in highly inductive circuits where large currents can flow for relatively long periods. In your case the use of just a capacitor should be fine.Best Regards:
Baron J.
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16th May 2022, 08:42 AM #20Member: Blue and white apron brigade
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If you read the data spec sheets for these types of contactors you'll notice they give two current ratings, 7a for "resistive loads" and 7b for "inductive loads" like motors
The Nixon 25A contactor shows 7a current rating of 25A but does not give a 7b current rating but does give a 7b "power "rating of 1.5kw which translates to about 6A. It also gives a 7a power rating of 5kW or 20A.
The HOFWGE 25A contactor info says it has a 7a rating of 25A and a 7b rating of 9A. This means to be safe with a 3HP motor is better to go to the 32A contactor which has a 7b rating of 12A. At those prices I'm going to get a couple of 32A contactors and try them out.
The 25A Nixon contactor specifically says it can withstand an over current of 72A for about 10s which helps with things like motor start up currents
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16th May 2022, 08:25 PM #21Most Valued Member
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16th May 2022, 08:30 PM #22Most Valued Member
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3rd Jun 2022, 04:26 PM #23Most Valued Member
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The contactors arrived a few days ago and fitted them today, being a bit slack i ordered the capacitors yesterday so the contactors will have about a one week test run before fitting those.
I liked the LED's in the fake relays as you could tell at a glance whether they were on or off, the contactors have a little window in the front that has a brown colored sliding thing that fills the window when energized but it is not easy to see.
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