Two Wheels Better

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Number of posts : 4712
ETK say they're 33Amps which x 12Volts equals about 400Watts (396W to be exact). My '87 RS has the same alternator and I can roll down the motorway at legal speeds or less powering two heated jacket liners (a Gerbing @ 77Watts & a Powerlet Atomic Skin a bit less) at full blast on a frigid day. I don't have heated grips on that OZ-based bike. My AGM battery has never even hinted that it struggles to start during a trip like that, and the alternator light isn't glowing.
Same deal on my '77 Airhead with a Motorad Elektrik 400 Watt upgraded alternator. Heated grips switched to high and a Gerbings full heated liner and we're off. It does have a 28Ah battery so perhaps a bit on reserve over the 19Ah K100RS, but never a problem. Caveat: the bike isn't fuel injected with its bigger draw than a set of carbies (zero draw) and basic wiring loom stuff, H4 headlamp, taillight, indicators, etc., but does now have electronic ignition...
Back in "the day" the original dodgy 280Watt alternator on my Airhead still managed to power my ancient (forget the brand name, now defunct) heated vest with nary a drama. I just couldn't idle it round town too long, but out on the road above 3,000RPM it was all warm and fuzzy.
I reckon you're good to go.
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1970 R60/5, '77 R75/7-R100, '85 K100, '87 K75C, '87 K100RS, '93 K11-K12 Big Block, '93 K1100RS, '95 R100-Mystic, '96 K1100RS, '98 K1200RS, '00 K1200RS, '02 K1200RS, '03 K1200GT, '04 R1150R, '04 R1150RT, '05 K1200S, '06 K1200R, '07 K1200R, '09 K1300GT, 2013 R1200RT-P & 2022 S1000XR
"We take our bearings, daily, from others. To be sane is, to a great extent, to be sociable."
~John Updike.