Re: KR> master relay

[Jeff Scott via KRnet]

 

The master relay should be on a 5 amp circuit breaker, so you can't be pulling more than 5 amps. 

 

However, looking at the specs for the master relay in the Aircraft Spruce Catalog, the coil is rated at approximately 9 watts. Since P= IE. Or, 9=I (12). So for a 12 volt system, the current is 0.75 amps.  So put an ohm meter in line with the master switch and read the current on the relay coil when it is activated.  It should be 0.75 Amps, and should absolutely be less than 1 Amp.  If it is more than 1 amp, you likely have 6 Volt relay in a 12 V system.  9 watts shouldn't make the relay smoking hot.  It's exactly the same as if you had a 9 watt light bulb mounted inside the relay.  It's just not going to make that much heat.  So your likely scenario is that it is a 6 volt relay coil if you are using a 12 Volt system.

 

P = IE --- Power (in watts) = I (current) x E (Voltage).  You can deduce everything you need to know from this simple equation. 

Or,

E= IR --- E (Voltage) = I (current) x R (Resistance in ohms)  

 

Now you know E=IR, or 12 = 0.75 x (R)  Also stated as R = E/I, or R = 12/.75  so R =16 ohms.

That equation says the resistance of the coil should be approximately 16 ohms.  Measure it with your ohm meter.  If it is making a lot of heat, the resistance is likely substantially less than 16 ohms.

 

So knowing the expected Wattage of the device and that it is a 12 Volt system, you can easily solve for the desired values, then measure either the Resistance or the Amperage to know if you have the correct device.

 

-Jeff Scott

Cherokee Village, AR

 

Sent: Monday, August 06, 2018 at 9:35 AM
From: "Stef den Boer via KRnet" <krnet@list.krnet.org>
To: KRnet <krnet@list.krnet.org>
Cc: "Stef den Boer" <stefk...@ziggo.nl>
Subject: Re: KR> master relay

Thanks for the responce.
I checked the wiring again, no faults. Than I hooked up the master switch wiring directly from the bat, but stil after 15 min hot and smelly.
I will order a new one.
Stef

> Op 4 augustus 2018 om 8:31 schreef Stef den Boer via KRnet <krnet@list.krnet.org>:
>
>
> Hi all,
>
> The master relay I have installed getting very hot. That hot that hot that you can smel it a bit and you can not put your hand on it for 2 second. If you do it longer you will burn it.
>
> I have hoked it up directly from the battery but no better result.
>
> http://www.aircraftspruce.com/catalog/elpages/masterrelay.php?clickkey=3575
>
>
> Did I damaged the relay by wrong installation? I did the starter current via the relay.....
>
> Should I order a new one?
>
> Someone experience?
>
> Thanks Stef
>
> Steph and his dad are building the KR-2S see http://www.masttotaalconcept.nl/kr2 http://www.masttotaalconcept.nl/kr2
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