BMW K bikes (Bricks)

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1Back to top Go down   Ignition live cable rating Empty Ignition live cable rating Thu Jul 09, 2020 2:18 pm

BooG

BooG
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The live red cable running from the starter relay up to the ignition barrel...what is the amp rating of that cable please? 
Thanks.

    

2Back to top Go down   Ignition live cable rating Empty Cable rating Fri Jul 10, 2020 5:44 am

daveyson

daveyson
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What's the go, do you want a siren, police lights and cb, or something like that?

I measured 100 Amps on mine with a stall test. Dunno how relevant that is though.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

3Back to top Go down   Ignition live cable rating Empty Re: Ignition live cable rating Fri Jul 10, 2020 10:34 am

Dai

Dai
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Not likely to be more than 33amp @ 12 volt rating. The K loom is load-distributed i.e. not all of the power goes through the ignition switch - see the load shed relay, for example, which provides power to the lights, indicators and horn. When rewiring I've only ever used a 25amp cable on that run and never had any trouble.


__________________________________________________
1983 K100 upgraded to K100RS spec, 1987 K100RT
Others...
1978 Moto Guzzi 850-T3, 1979 Moto Guzzi 850-T3 California,1993 Moto Guzzi 1100ie California
2020 Royal Enfield Bullet 500
    

4Back to top Go down   Ignition live cable rating Empty Re: Ignition live cable rating Fri Jul 10, 2020 11:04 am

Suzi Q

Suzi Q
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The 1984 handbook wiring diagram shows a 2.5mm red wire from the starter relay COM terminal 30, which goes to a loom junction and there splits and goes to various loads. One of these loads is a 1.0mm red wire to the ignition switch. This might be the wire you're on about.

If you're after adding the 'police sirens' etc (  Smile ) i.e. extra loads on this red wire, then its load capacity/max current can be calculated in theory, but it depends on de-rating factors such as ambient temperature. I'd suggest that the aged condition of the end terminations/ignition switch contacts etc. is a factor too, especially if you're getting near the limit. It is therefore not usually practical to do anything better than a good guesstimate, as Dai has done, and then play safe - you want wires not heating elements!

Best thing is to describe what you've got in mind and you'll get good advice on here. Safest route for add-ons is usually spangly new wire from the battery, a fuse and a relay.


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Sometimes I'm not really Suzi Quatro.
    

5Back to top Go down   Ignition live cable rating Empty Re: Ignition live cable rating Fri Jul 10, 2020 11:59 am

92KK 84WW Olaf

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Best thing is to describe what you've got in mind and you'll get good advice on here. Safest route for add-ons is usually spangly new wire from the battery, a fuse and a relay.


Best advice there- means no interference to the factory electrics and easy trouble shooting.


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011171 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 37,190 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 39.885miles.

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

6Back to top Go down   Ignition live cable rating Empty Re: Ignition live cable rating Sat Jul 11, 2020 12:48 pm

Dai

Dai
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chris846 wrote:The 1984 handbook wiring diagram shows a 2.5mm red wire from the starter relay COM terminal 30, which goes to a loom junction and there splits and goes to various loads. One of these loads is a 1.0mm red wire to the ignition switch. This might be the wire you're on about.
So... it appears I really, really believe in overkill. 1.0mm.sq PVC (which is what the original is) has a current rating of 8.75amps @ 12 volts. Makes sense. Trace the green wire back down through the loom and essentially it's only providing power for the load distribution relay coils. And a little bit else.

Next one I do only gets a 16.0amp cable for that feed bounce Very Happy

In truth, there's also the mechanical strength aspect to consider. I could run an 11amp cable to the ignition switch which would be more than adequate power-wise, but I'd prefer the increased stength of a 16amp cable in an area that gets a lot of movement.


__________________________________________________
1983 K100 upgraded to K100RS spec, 1987 K100RT
Others...
1978 Moto Guzzi 850-T3, 1979 Moto Guzzi 850-T3 California,1993 Moto Guzzi 1100ie California
2020 Royal Enfield Bullet 500
    

7Back to top Go down   Ignition live cable rating Empty Re: Ignition live cable rating Sun Jul 12, 2020 9:03 am

BooG

BooG
Platinum member
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That’s great info from everyone...thanks!
I am repairing damage to the cable from when my K75S was recently stolen. I am not adding anything else to the load regarding electrics. I just want to run a new cable rather than repair the old one.

    

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