Zone valve microswitch arc suppression?

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Old 12-20-07, 08:00 AM
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Zone valve microswitch arc suppression?

Hello community,

A little background: There are 5 zone valves in our house and after a couple months of typical winter use, some of the zones stopped firing the furnace. I did some diagnosing and found that although the thermostat triggers the valve motor and opens the water path, the microswitch within the zone valve that is supposed to subsequently fire the furnace had poor contact. Upon disassembly of the switch, I found heavy carbon deposit on the switch contacts. I sanded the contacts clean and everything would work again for a few more months before the switch goes intermittent again.

This can't be normal and I was wondering if the wiring is missing an arc quelcher of some sort. I believe an inductive load is decaying the microswitches but someone should've noticed this in the design correct?

What can I do about this? Add my own arc suppression? Any suggestions or comments are welcome.

Thanks
 
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Old 12-20-07, 08:15 AM
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What type of zone valves are you using. How many transformers?
 
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Old 12-20-07, 08:25 AM
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I'd have to check when I get home , but they are similar to these "Normally Closed Two Way"

One transformer as far as I can tell.
 
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Old 12-20-07, 03:47 PM
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You mean like a resistor and a capacitor in series across the microswitch contacts ? How would you know what values to use ?
 
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Old 12-20-07, 03:58 PM
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Trial and error?

This would be last resort if I can't find out why it is doing this. Any ideas?
 
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Old 12-20-07, 04:47 PM
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I know there's a formula for figuring the values... lemmee see if I can find out from one of the EE's I know .

Maybe you have stumbled on a reason for early failures of the switches? (assuming there's nothing wrong with your installation...)

Sometimes sanding isn't the right approach though, if there is a thin layer of tungsten applied to the contacts (I doubt there is though, but some relays use it) sanding it will likely remove that coating. Normal wear probably eventually would wear through the coating too, one mode of failure. Tungsten resists the 'pitting' that occurs on circuit breaker, switch and other contacts.
 
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Old 12-20-07, 04:57 PM
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Try a .1 MFD (polypropylene probably best, but ceramic disk OK) with a 47 ohm 1/2 W resistor (preferably carbon composition)...

One manufacturer of...
 
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Old 12-20-07, 05:28 PM
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I'd like to know how much current is being switched, and what the end switches are controlling? Where is that much back EMF coming from? A relay coil?!
 
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Old 12-21-07, 03:31 AM
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I'm with Radio!

What is the voltage and current rating on the switches?

What voltage and current(amp draw) do you have on the end switch from the heater?

It sounds like either the heater side is wired wrong, or the switches aren't rated for that application.
 
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Old 12-21-07, 02:51 PM
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I'm thinkin' wiring problem too... but kinda hopin' that some experimenting will happen ... I like experiments

I doubt that the load on an endswitch is enough to cause that, but ????? who knows ???? maybe they all do it and we've just never looked inside the microswitch ?

Or maybe the switch is just plain worned out ...
 
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Old 12-21-07, 02:58 PM
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what zone valves?

Hey tra, you never told us what zone valves yer using?

How are they wired ?
 
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Old 12-21-07, 08:46 PM
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Thanks for the input guys.

The valves are Erie PopTop valves. 2 way spring close.

http://www.solidyne.com/products/pro...roductlist=130

https://shop.solardirect.com/pdf/wat...s/erie-emv.pdf

Not sure if there is a manufacturers page, but the 2nd link seems to be a decent datasheet.

As far as wiring, the end switches are wired to the thermostat or EMCS points on the boiler transformer.

 
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Old 12-22-07, 02:27 PM
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so what is the voltage reading at the end switch and what is the amp draw?

Does this system have two transformers, as in the one on the heater and another one installed for the zone valves?

Are they isolated from one another?
 
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