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  #1  
Old 8 Jan 2005
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Alternator output on '82 R100RS

I'm thinking of getting a heated vest for winter touring but have doubts as to their power consumption. The output on my bike is barely adequate as it is- at night when I have my 65Watt headlight plus two spotlamps, (50 Watts each), I have to keep to over 4,000rpm or else the alternator is unable to keep up and the battery starts to run down, so what I need to know is whether there is a worthwhile modification available? Also, can anybody confirm that heated vests are any good?
Cheers
John

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  #2  
Old 8 Jan 2005
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One of Horizons sponcers is -
http://www.motoelekt.com/
They have the Omega 400 watt kit.
I have had one for 3 years and they work great.
They have them in the UK but I am not sure who has them.
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  #3  
Old 8 Jan 2005
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Motorrad Elektrik (check the links page) makes a 400 watt "Omega" alternator/ rotor/ voltage regulator/ diode conversion that I have heard good reports of. I think it runs about $500-600 USD. The only other option I know of is to buy a newer bike with a 600+watt alternator! I guess 280 watts seemed like a lot back in the 70's.... BTW, it is not a bad idea to run above 4000rpm anyway, the airhead perfers a bit of RPM.

Good luck!

[This message has been edited by Timo (edited 08 January 2005).]
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  #4  
Old 8 Jan 2005
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Boy, You have to love the speed and efficiency of this site: 2 replies at the same time in less then 5 minutes! Where else do you get that kind of service and attention these days?!
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  #5  
Old 8 Jan 2005
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Thank you both for the lightning responses! I've just checked the handbook for the output and it's 280Watts, so obviously an increase to 400Watts is definitely worthwhile.

Mind, $575 is seious money to spend on an old banger that still needs a complete exhaust system, brake lines, two cast iron front discs, timing chain plus what else-I-dread-to-think.

Any technical bods out there that can tell me how to rewire / rewind my present alternator to increase its output? I did a degree in electrical engineering when I were a lad, I'd just love to give it a try.

Thanks

John

PS
I was browsing through some coffe-table books the other day in the book shop and in the section about the R100RS one said it was possibly still one of the world's best sports tourers. Must have been talking bollocks.... wasn't he....?

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  #6  
Old 8 Jan 2005
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No, He should have just qualified the remark: in the daylight, in a warm climate! Honestly, I 've never had the pleasure of riding an RS, but the legend is large indeed. The same people will tell you that the G/S is the best overlander ever made (which of course it is if you own one...). Love the one your with.

Boy, I'm glad you mentioned the bon-i-fide engineer bit, I might have gone and stuck my foot well down my throat. give Mottorad Elektrik a ring, maybe they can walk you through the procedure? Keep in mind the up-grade kit is more then just an alternator; the rotor (a weak point) and everything else in the charging system is improved as well.
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  #7  
Old 8 Jan 2005
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Timo, could you expand on what you said about keeping an airhead spinning at over 4000, please? Throttle response? Increased engine life??

Going back to your suggestion re getting another bike, well, the truth is I DO love the one I'm with, as you suggest! Decent fairing, ankle warmers (cylinders), quick enough (for me), panniers, luggage rack, and most times, roadside-fixable and roadside-puncture repairable (tubes). Decent lights with extra driving lamps. And by now we're used to each other.

Oh, as for electrically heated vests, are they really as good as they say they are; I'm planning on UK-Prague-Istanbul, possibly before April, failing that, some time after September; none too warm.

Many thanks

John


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  #8  
Old 8 Jan 2005
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The Omega kit has a larger stator and rotor.
The stator is a larger gauge wire.
I don't think that there is a way to increase the output without increasing the wire size.
If you get one you can find a stator cover cheap, wire that to the new stator. That way you can have a compleat stock alternator to put on your bike when you sell it.
There are voltage regulators that will increase the charging voltage for the battery for short distance riding but they don't increase the output, and they may cook a battery if used for a long time.
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  #9  
Old 9 Jan 2005
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What I have heard is that Airheads do not like to be lugged at low RPM in top gear. Most of the Airheads engines are tuned to run best at 3500 RPM and up, and are not as smooth at <3000. Apparently, BMW had a number of engine failures when they first started importing the twins to North America, which was traced to engines being run at low RPM's consistently in top gear (I guess the Americans were used to lower reving engines). On the electrical side, the Alternator is direct drive off the end of the crank shaft where as the newer oilheads have a the alternator turning at twice the speed of the engine, which helps to produce good current at lower RPM's.
The only negative I have heard about using the Omega 400 watt kit for overland adventure is that you are installing a collection of non-stock parts, so parts will have to come from Motorrad Elektrik only.
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  #10  
Old 9 Jan 2005
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RE

1. RPM for airheads - remember that the airhead was designed originally for use in Germany, where they have autobahns, and ride fast everywhere. Keep it spinning, not lugging - as Timo says, 3500-4000 is the bottom you want to run at for best performance and longevity. Lower revs are hard on it.

2. Rick Jones, the guy that runs Motorrad Elektrik, is probably the worlds foremost airhead electrics expert. He tried for YEARS to get increased output from an airhead alternator. The culmination is the Omega. You may be able to do better or nearly as good for less, but Rick's no dummy.

3. The only reasonable? alternative is an Australian made system that costs even more - but mounts a car alternator at the top front of the engine, and puts out huge power. There's more info on the site - somewhere - including a link to the manufacturer.

4. As for heated vests - no-brainer must-have. I bought mine in 1981 - and I'm still using it- well at least the wires, which have never failed, and it's been around the world. The fabric wore out and Susan installed the wires into a nice down vest. We wouldn't travel without one.

5. Note that EARLY airheads - /5 - were only 240 watts, and considered good. The increase to 280 was awesome... at the time...

6. re reliability of the Omega - most of the components have been sold by Rick for years, and are preferred long distance travel upgrades to start with. The only new parts are the rotor and stator, and thus far the reliability record has been excellent. Note that Rick does say not to overload it. Trying to run 500 watts of goodies off it is not good. If the rotor stator fails, used ones are readily available almost anywhere BMW parts are available, so it's no worse than if the originals failed - and the original rotor is notorious for failing on a regular basis. One of Ricks standard replacement rotors is a popular long distance travel upgrade, so the Omega should be very reliable.

hope that helps,

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[This message has been edited by Grant Johnson (edited 20 July 2005).]
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  #11  
Old 25 Jan 2005
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Thank you all for your, as always, well-informed replies.

Grant, I don't for a minute doubt that Rick Jones of Motorrad Elektrik has achieved the maximum output from the basic components and I'm quite sure that I couldn't improve on his results, it's just that I was wondering if by using a different gauge (thickness) of wire on the standard rotor and stator it would be possible to wring some more amps/watts out of it. Increasing the thickness would reduce the resistance allow the current to flow more easily, but would run hotter whereas reducing the thickness would make room for a greater number of turns in the space available but would result in a higher resistance, but again, might result in a higher number of ampere-turns, which is a good thing because the more amperes of current times the number of turns in a winding then the stronger the magnetic field it produces. The output depends on the strengths of the mag fields in both the stator and the rotor.

All clear then?

Funny, I don't remember writing all my notes at college in Greek and gibberish- sorry.

Many thanks, too, for the recommendation of the electric vest, I got one and tried it today: bliss! If there's anybody still out there unsure of whether to get one or not-GO FOR IT!

I also bought a new set of BMW heated grips at a bargain price (I repaired the old ones twice and they are by now beyond hope) and as the kit was for a different model of BMW I now need the little surround that fits around the panel-mounted off/half/full-power switch, Part No.03 8330 to allow me to mount it on the dash. ('82 R100RS) So can anyone tell me the part no of this bit, please? For possibly a greater audience I'm going to pose the question in a new thread- that ok by you, Grant?

Thanks again

J

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  #12  
Old 25 Jan 2005
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Hi,

Re starting anew thread - of course! Always the best thing to do keep the Topic Subject on track, makes finding things easier for others later. (So we don't have to answer the same question #$%# times!)

Glad you like the vest! Amazing how long we resist them isn't it? And when you get one, you wonder why you ever doubted it! Never met anyone yet who OWNS one who has ANY doubt!

Re rewiring the rotot - good luck - but Rick and I discussed this years ago, long before the Omega, and he had tried - and tried everything, and the improvement wasn't enough to be worth doing. Complicated interactions between the rotor and stator, with the BIGGEST problem overall is the alternator turns at HALF speed 'cause it's on the cam, where everyone else mounts it on the crank, or on a belt system, off the crank usually, and speeded UP not down.

Feel free to try and let us knw your results! There's a few thousand dead rotors out there to experiment on.

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  #13  
Old 26 Jan 2005
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Hello.
Re: electric vests, bought a used Gerbings from E-bay for $160...rode to Whistler and back last sunday durring heavy rain, and without a doubt they're the bomb!! Yes, your right...it's funny how long we wait before forking out the cash for this irreplaceable item!
Chris Walstow sent me a link a while back :http://www.motoren-israel.de/
They sell a high-output alt. cheaper than Moto-elec. Check it out.
Good luck!
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  #14  
Old 28 Feb 2005
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Have just seen a 400watt alternator available from Motor Works for £235. I'm going to go for that, I think, it should make life a lot easier i.e. warmer.

My grateful thanks to all concerned

John

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Old 26 Mar 2005
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Thought I'd let you folks know that I've fitted the new Motorworks 400watt alternator and that it works just great.

It now powers the 65watt headlamp and two 50watt driving lamps, BMW heated grips and also my heated waistcoat (plus all the rest like sidelamps, instruments and ignition etc)and it does so when the engine is doing 3250rpm. You may recall that with the original 280watt alternator I had to maintain 4,000rpm (70mph in top gear) and that was before I had the heated waistcoat (40watt, I think).

The kit consisted of a new rotor and a new stator and a new diode board, some new wiring plus heavier earthing straps.

Actually, there was a bit of work needed with these (the straps) The terminals were slightly larger due to the heavier conductors used to carry the increased current, and I didn't like to bend them like the original terminals were bent to fit under the socket head bolt where they go in the recess in the chaincase casting. What I did was to use longer bolts, 50mm instead of 45mm, and made two 5mm long brass collars, 10mm diameter and drilled 6mm. (As it happened the terminals were 5mm and had to be drilled out to 6mm at this end) The terminals were threaded on to the bolt followed by the brass collars and then they were screwed into the casing. The terminals were now level with the casing and so there is no need to bend them, with the collars taking up the space in the recess. The two bolts holding on the engine front cover were just the right length so I used those for the job and used the original 45mm bolts to hold the cover on instead, they only had four turns of grip, but with a touch of Loctite they did the job fine till the proper 50mm bolt arrived a couple of days later. Incidentally, having the head of the bolts protruding does not appear to be a problem; although the original loom carrying three-phase output from the stator to the diode board was routed past the bolt I would say there was still plenty of room for it, but the new loom carrying the three phases plus the Y conductor is now routed differently and is thus well clear of this bolt anyway. Another small thing was that the spade connector of the lead to the voltage regulator from the middle of the back of the new diode board had to be pushed over very carefully to provide clearance from the casing. I also changed the rubber mountings for the diode board even though, surprisingly, the originals semed to be in excellent condition. With these two longer bolts, remember to put them back in their correct places if you take the chain case off in the future, all the other bolts are 45mm

By the way, make sure that the lead from the trigger unit is tucked safely out of harm's way when you replace the front cover in case it gets pinched by the partitions forming the cooling channels at the side. I didn't do it myself, but my dealer managed it at my 600 mile service all those years ago.

Total cost was £200 plus VAT making £235. I've done about 600miles so far, with 200 miles with full (electrical) load, no problems so far, the max. voltage is still the same at 13.8 or so, and with no worries about the battery running down, and the battery acid level still ok. I know that this isn't much of a trial but if I get any problems I'll let you know. If any one is interested I've taken a dozen or so pictures which are still in the camera. (Digital cameras? Nah, never heard of them)

Thanks for everybody's advice,

John


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