Power source when engine running? - BMW Luxury Touring Community
 
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post #1 of 8 Old Jan 18th, 2008, 7:28 am Thread Starter
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Power source when engine running?

Hi all wire gurus!

A friend of mine would like to hook up pilot current for some relays from a wire that has power ONLY when engine is running. So not just the regular switched source like rear seat heater or map light. I could not advise him as I have never needed this myself.

Does anyone have any ideas where to look for such a cable? I know spark plug cables have power when engine is running but the voltage is probably too high...

Thanks in advance

PS. His bike is ´05 LT

Regards

Ari "the Farkle-Freak-Finn" Ignatius

Hyvinkää, Finland
2004 ('05) LT, Dark Graphite, "Sunset Cruiser II"

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post #2 of 8 Old Jan 18th, 2008, 8:40 am
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Here is one way that should work:

Use a standard automotive relay:

85 to oil pressure switch
86 switched power (15)
30 Battery power
87 to whatever you want to turn on.

Wolfgang

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post #3 of 8 Old Jan 18th, 2008, 8:50 am
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I remember reading, somewhere on this site, of using the 'ALT' dashboard light for that purpose.

...Bob
2001 K1200LT der LadungsTräger
1978 GL1000
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post #4 of 8 Old Jan 18th, 2008, 11:19 am
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Quote:
Originally Posted by sparky_k1200lt
I remember reading, somewhere on this site, of using the 'ALT' dashboard light for that purpose.
You have to be VERY careful attaching anything to the Alternator light. That circuit is the 'excitation' circuit for the alternator, and depends on the small current through the bulb to magnetically 'excite' the rotor so that the alternator will start charging, then the charge voltage takes over.

You can use a very small high coil resistance relay on that circuit to drive a larger relay though.

Best to use the oil pressure switch circuit to drive the relay though.

I don't want to achieve immortality through my work...I want to achieve it through not dying.

David Shealey
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post #5 of 8 Old Jan 18th, 2008, 11:53 am
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Has he got an intercom - if not, there's a switched power outlet under the stingray which he can get volts from - I was using mine for my Aux amp for an iPod.

  • 2005 LT - 17 countries, 2 CONTINENTS & counting !
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  • 1974 Triumph Bonneville 750

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post #6 of 8 Old Jan 18th, 2008, 1:11 pm
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Smile Use the Rear Power Socket

Which I did, via a 6 point distribution bus, to power relays as required directly from the battery. HTH

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post #7 of 8 Old Jan 18th, 2008, 3:31 pm
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But that is power with the key on as opposed to "engine running" only. I believe that was the request.

For that the oil pressure switch is the best way. Because the engine better not be running without oil pressure. And if it does, you have much bigger problems than the farkel that you are powering up.

Wolfgang

K1200LT 1999 Champaign SOLD
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post #8 of 8 Old Jan 18th, 2008, 3:43 pm
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Quote:
Originally Posted by Wolfgang
But that is power with the key on as opposed to "engine running" only. I believe that was the request.
Been a while since I added that bit Wolfgang, so you're probably right. My bad.
Rejoining "Jenna" the end of Jan so no way to check now.
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Last edited by Hilton; Jan 18th, 2008 at 3:49 pm.
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