Why use a relay? - BMW Luxury Touring Community
 
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post #1 of 9 Old Aug 25th, 2006, 2:31 pm Thread Starter
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Question Why use a relay?

Hi guys, I want to fit an auxillary fuse box and am getting two different stories, some say it is essential to fit a relay between the ignition / battery and the fuse box. I want the easiest and safest option and would like the acessories to become live at the first position ie radio positiuon instead of turning the ignition all the way on. Looking to power GPS and Autocom for now, sure would appreciate your words of wisdom. Currently trying to choose either a blue sea or a centech unit. One of my suppliers in the UK is insisting I must use a relay. Thanks for your input guys.
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post #2 of 9 Old Aug 25th, 2006, 2:44 pm
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Amperage - conductors - weight - reliability - safety

All a relay is, is a 'remote switch'. You can use a much smaller switch (smaller wires, easier to mount or setup 'parasiticly' - such as an existing ignition switch) to operate a relay. The relay can handle MUCH more current than the smaller switch. As well as do it at a different location. Not so much wire to run, smaller voltage drops, lessens possability of chafing/shorting, etc.

A GPS receiver - not likley to pull enough draw on to be an issue. But lights, heated clothing, multiple low draw farkles? You betchya. Trying to use your ignition switch (small guy) to control a high draw item (like a fuse box with several accessories connected) is a sure fire recipe for arcing the points off your ignition switch. Things go badly wrong and stuff can get hot - get it hot enough you got a fire. Yea, few things have to go wrong to get that far, but why risk falling from top of the flag pole if all you want is to see the view? It's worth the effort and piece of mind to know you've put it all together right and avoided the problems that otherwise could have bit ya.

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post #3 of 9 Old Aug 25th, 2006, 4:20 pm
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Quote:
Originally Posted by Thor1340
Hi guys, I want to fit an auxillary fuse box and am getting two different stories, some say it is essential to fit a relay between the ignition / battery and the fuse box. I want the easiest and safest option and would like the acessories to become live at the first position ie radio positiuon instead of turning the ignition all the way on. Looking to power GPS and Autocom for now, sure would appreciate your words of wisdom. Currently trying to choose either a blue sea or a centech unit. One of my suppliers in the UK is insisting I must use a relay. Thanks for your input guys.
If you do not use a relay, you have little choice but to have the fuse block powered all the time, not a good idea. As you already stated you want it on only when you turn the ignition switch on, a relay is required. There is no switched line on the LT that can handle the current you will need for multiple auxillary devices.

A good place to pick up a switched line to control the relay is the front heated seat wiring. The plug is on the frame rail on the left side, under the drivers seat. Hook into the bike side plugs wires, not the seat side, so you can still remove the seat for service without messing with the added wire.

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post #4 of 9 Old Aug 25th, 2006, 4:52 pm
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Dave, I've heard some mention using the 'parking light' in the nose cone as well. The one in the headlight. Gives you an alternative 'aux' position as well as the 'run' position.

Just realized, maybe that's why guys're put'n their fuse boxes in the nose cone too, eh?

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post #5 of 9 Old Aug 25th, 2006, 6:09 pm
 
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more about relays

decent article
RELAYS

Overall relay

Last edited by ihbond; Aug 25th, 2006 at 6:25 pm. Reason: Update
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post #6 of 9 Old Aug 25th, 2006, 6:38 pm
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Quote:
Originally Posted by Zotter
Dave, I've heard some mention using the 'parking light' in the nose cone as well. The one in the headlight. Gives you an alternative 'aux' position as well as the 'run' position.

Just realized, maybe that's why guys're put'n their fuse boxes in the nose cone too, eh?
That will work just fine. My Blue Sea fuse block was on top of the battery, so the seat heater socket was just a few inches away. Very convenient for over battery fuse block mounting.

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

David Shealey
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EX: '01 Black LT, BAT BYKE (Totaled at 110,000 miles)
IBA SS, BB, BBG, 10/10ths.
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post #7 of 9 Old Aug 28th, 2006, 9:51 pm
 
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Stuart
You might consider using the BMW plug (powerlet) that is made for just this. The power is on when the key is in the ACC or On postion and then off when the key is turned off. I did not mind spending the $20 for the plug so I did not have to cut into any factory wires.

BMW 'powerlet' connector. Part Number: 61132316621.

I documented my install of the powerlet and Bluesea fuse box to power all my stuff at the the following URL:

http://kc6tew.com/mods/bluesea/bluesea.htm

Mark
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post #8 of 9 Old Aug 29th, 2006, 12:48 am
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Thanks for the install instructions. I need to do this so this is perfect timing!

05' LT Dark Grey, "Battle Star"
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post #9 of 9 Old Aug 29th, 2006, 3:15 am
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wiring the Autocom

I just relocated the power source for my Autocom on the weekend (still haven't gotten a fuse box yet, but will look at Mark's install instructions!!) from the heated seat to the rear power socket, because I was tired of switching off the ignition and not being able to still "talk" to my partner properly. After unbolting the topbox so I could get at the screw under the side plate, it was pretty easy to tap a wire into the back of the existing plug, without buying an adaptor socket, and I already had the earth on the frame for the autocom. I was Installing the Autocom rear-speaker switch kit, so it made sense to rewire the power at the same time.
Since the Autocom cuts power when you seperate your helmet connection, I figured this was a reasonably safe way to get constant power while in accessory mode.
My GPS is tapped into the map light, based on the wonderful instructions from this list.

Chris
Sydney, NSW
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