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12-10-2012, 04:00 PM
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#1
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Member
Join Date: Aug 2012
Posts: 33
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testing electrical relays?
Does anyone know of a simple way of testing an electrical relay, and what exactly do they do?
regards,
Chris
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12-10-2012, 06:37 PM
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#2
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Member
Join Date: Oct 2007
Location: USA
Posts: 74
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CoachCrazy,
A relay is basically a small switch that operates a big one. Sort of a remote control and power assist for a big, high power switch. A small amount of power is applied to the small switch terminal, which operates an electro-magnet to "pull" down a big switch. The big switch can handle a lot of power, example: enough to operate a motor or compressor. The electro-magnet and the big switch are in a box together and that is called a relay. The little switch is somewhere else - its the one you turn on/off when you want the big switch to do something.
DB
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David & Maria Ball
1989 Newell Owner
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12-11-2012, 01:14 AM
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#3
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Member
Join Date: Aug 2012
Posts: 33
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Thanks David That helps. I now understand what the relay actually does, which helps in the big picture.
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12-11-2012, 01:18 AM
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#4
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Senior Member
Join Date: Dec 2005
Location: Southern California
Posts: 1,018
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A relay is a switch, nothing more, it is usually operated remotely by another switch or controlling device.
There are several "Tests" that can be done on a relay, all that is required is a multi-range volt meter (or auto ranging one)
And a pair of eyes
First measure the voltage across the coil.. It helps here if you know what it is supposed to be and if it is supposed to be AC or DC (This info is often stamped or printed on the relay) If there is no control voltage.. The relay is NOT the problem.
IF there is control voltage.. did the relay pull in (Did the contacts change state) or not? If not, the relay IS the problem
NOTE: High power relays may move a little, but not pull in all the way.. That is a "Welded contact" condition.
Next we measure voltage across the contacts.. If the contact is supposed to be open, then the voltage should be whatever the voltage is there (NOTE: on AC relays used in auto transfer switches this can be misleading)
If the contact is supposed to be closed the voltage should be near zero.. as in .0x or .00x (If you can measure it it may well be too high)
In many cases, if the contact is not closing properly you can "Burnish" the contact. DO THIS WITH POWER REMOVED.
Now, that said relays come in both "Sealed/Enclosed" and Open frame types.. Open frame you can see the action, you can easily see what contact goes to what terminal
Enclosed (included sealed) you have to rely on the diagram printed on the case.... IF there is one.. Else you have to find it's "Data Sheet"
Some relays.. That can be a whole LOT of tests.
And... IF it is a 120 volt relay there is enough power there to be fatal.. So be very careful when running those tests.. Even 12 volt can cause you some serious discomfort (Like 3rd degree burns).
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1976 Newell Classic (Sold)
Home Base: Riverside, CA
If anyone needs my contact info private message me and I will send it to you.
-Joseph-
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12-13-2012, 01:19 AM
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#5
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Senior Member
Join Date: Jun 2009
Location: Idyllwild, CA
Posts: 1,340
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yep, Magnetic Contactor. I had to rewire mine right after getting the coach.
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have Coach will Travel
Steve & Tricia
1982 Newell 38' (built before #1) 6V92 DD, 5 Speed Allison, 12.5 KW Kohler, Couch used to make into a Bed but I fixed it!
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2007 Yukon, 1981 CJ7 Laredo, 2002 Honda CRV, 1955 Thunderbird, 1952 Pontiac Sedan Delivery, 1952 Ford 8N, 1958 Airstream, 1959 Glasspar 16' Avalon, Cabin in the Woods........what will I work on next
[SIGPIC][/SIGPIC]
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