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Thread: Honey I shrunk the alternator

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    Question Honey I shrunk the alternator

    Why do alternators keep getting smaller? A few years back a 2007 K1200GT had 945 watts. From 2013 to 2014, the 1200RT lost 30% of the alternator output.

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    Small road corner junkie pffog's Avatar
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    945 is overkill, unless you are going to do it up Harley style with incandescent bulbs.

    cars up to about 1980 only had 65 amp units, and they ran alot more stuff, ac/heat/more lights, big radios etc.
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    When they change from a variable field alternator to a Permanent magnet type, there are advantages to making no larger than necessary. The electronics to control a 0 to 6 amp field at 12 volts are simpler, smaller, lighter. Depending on regulator type, shunt or series, you have horsepower losses or high voltages to deal with. And PM types seem to be more prone to overheating.

    Rod

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    . AntonLargiader's Avatar
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    I think your premise, that they keep getting smaller, is wrong from the start. The fuel injected bikes went from about 35A to 50A to 60A; only the most recent models had a decrease and that is probably because they need less power with more efficient fuel pumps and lights.

    Is there an actual output capacity problem that you are concerned about?
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    Registered User dieselyoda's Avatar
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    An odd note to add, not really relavant, but is, sort of.

    I cooked a 1/4 hp motor last week. The thing was a heavy, capacitor start and big. Connections were a bear to get off, screws.

    Direct cross from my motor to the replacement, new motor was half the weight, 2/3rd's dimensionally, no capacitor, instant reverse and spade connections.

    The biggest change for me was I got rid of the old rubber, non-reinforced FHP belt and used a polymer belt the same designation. Belts are better too.

    I've been running it steady for a week, less current draw gauged by how my lights would flicker with the old one, less heat and quieter.

    I'm going to take a wild guess that some of this electrical stuff is getting made more efficient than before.
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    not so retired henzilla's Avatar
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    < further hijack

    Power converters to convert single -phase to three-phase power have definitely decreased in size. Used to power three-phase motors on lathes,milling machines and such in a rural area without utility supplied three-phase power. Also used in oilfield applications.
    I saw some 50's era rotary units that were almost the size of a refrigerator. Now they are 1/3 the size with the same/better performance.

    phase converter 2013.jpg
    a 2013 rotary unit

    I wired a static unit ( no motor,good for light three-phase loads in a small shop, maybe 2/3 of nameplate output I believe,he can only run one CNC or lathe at a time) to my brothers one man machine shop located on his rural property. I was expecting the refrigerator, ended up with a box the size of a 5lg bag of sugar around 10 years ago. Still made him turn the breaker feeding it on as the cost at the time was pretty high!
    phase converters.jpg
    a mix of static and rotary units
    These things have definitely gotten smaller/yet more efficient.



    hijack off>

    Only bikes I worry about wattage -wise are the stock /5 and /6..Most of our other newer bikes have not been an issue to us...lights and heated gear on high have never been a big concern.
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    Quote Originally Posted by henzilla View Post
    [B] hijack off>

    Only bikes I worry about wattage -wise are the stock /5 and /6..Most of our other newer bikes have not been an issue to us...lights and heated gear on high have never been a big concern.
    My buddy rides a 2012 F800ST like mine and he has run the battery down on his daily commute with full heated gear running. Turns out he was short-shifting (he prefers "smooth" riding--his words, not mine--to my higher rev shifts which he calls "whinning" the engine. Once he learned to ride in a lower gear at slightly higher rpm his problem went away. I am not sure what the magic rpm level is (somewhere around 3,000-3,500 rpm, I think) but you apparently CAN drain the battery on a new BMW with electrical doo-dads.
    Royce
    On the coast of Kansas
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    not so retired henzilla's Avatar
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    Quote Originally Posted by royce View Post
    but you apparently CAN drain the battery on a new BMW with electrical doo-dads.
    Our Thumper 650 didn't care for short runs , PIAA's and full on heated gear & grips. learned it's habits and with a new battery all seems well.
    Steve Henson
    SABMWRA MOA Club#62's Flat Fixer/ current forum moderator
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    Still plays with trains. tinytrains's Avatar
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    I think ragtoplvr nailed it. Since a PM alternator produces more voltage the faster it spins, (unlike variable field automotive type alternators BWM used to use) the excess power and voltage has to dissipated. I don't know how BMW regulates them, but most Japanese bikes use shunt regulation. A load resistor is switched in to drain off the excess power. This gets hot and would regularly die on my 1980 GS550E. It is very inefficient. I hope BMW has a better way, but however they do it, the less excess power to get rid of, the easier it is for them to deal with.

    For those not familiar with variable field alternators, the voltage regulator reduces the field current in the alternator to keep the available output power in line with the power needs at the moment. A PM, or permanent magnet alternator, is a magnet spinning inside a stator of coils, that produces electricity based on the speed of the magnet, with no way to scale back the output. As a result, regulation must be done outside of the alternator.
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    Re: Is there an actual output capacity problem that you are concerned about

    Some riders have an audio system and lower power consuming GPS devices. The 540 watt rating will not be present at lower RPMs.

    The ABS system might be adversely affected by power sags. Just two years ago 700+ watts were common.

    Riding 2-up with full Gerbings costumes will consume 360 watts. Using a pair of 5100K 'keep you out of the hospital' conspicuity lights will use another 130 watts. That's a tad under 500 watts. 540 watt waterhead alternators are going to sell a great many batteries.





    Quote Originally Posted by AntonLargiader View Post
    I think your premise, that they keep getting smaller, is wrong from the start. The fuel injected bikes went from about 35A to 50A to 60A; only the most recent models had a decrease and that is probably because they need less power with more efficient fuel pumps and lights.

    Is there an actual output capacity problem that you are concerned about?

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    Quote Originally Posted by royce View Post
    My buddy rides a 2012 F800ST like mine and he has run the battery down on his daily commute with full heated gear running. Turns out he was short-shifting (he prefers "smooth" riding--his words, not mine--to my higher rev shifts which he calls "whinning" the engine. Once he learned to ride in a lower gear at slightly higher rpm his problem went away. I am not sure what the magic rpm level is (somewhere around 3,000-3,500 rpm, I think) but you apparently CAN drain the battery on a new BMW with electrical doo-dads.
    besides the revs, it might also be dependent upon how long he's riding for on his commute. 5-10 miles with heavy draw at lower speeds might not do much to recharge the battery, while 15+ could see a different outcome.
    Ride Safe, Ride Lots

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    rabid reader dbrick's Avatar
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    Quote Originally Posted by royce View Post
    I am not sure what the magic rpm level is (somewhere around 3,000-3,500 rpm, I think) but you apparently CAN drain the battery on a new BMW with electrical doo-dads.
    One can run a deficit by drawing more current than the alternator can deliver. If one does that, the battery will eventually flatten. At low rpm, less than full alternator output is being produced. How much current (ignition and FI system and lights and the rider's heated jacket liner and heated gloves and GPS) was being used? If the average consumption exceeds the average production...
    David Brick
    Santa Cruz CA
    2007 R1200R

  13. #13
    . AntonLargiader's Avatar
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    Quote Originally Posted by 1200rt@drywhitetoast.org View Post
    ...Riding 2-up with full Gerbings costumes will consume 360 watts. Using a pair of 5100K 'keep you out of the hospital' conspicuity lights will use another 130 watts....
    Sure, riders that pack 500W of accessories (a tiny number of riders) can have problems. They could have problems with the 700W systems also. I bet BMW's attitude is, "see you later." Those riders won't be missed if they go for Gold Wings or the like.

    180W heat per rider? Holy force field, Batman. I run about half that in the coldest weather and I'm pretty skinny.
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    Cam Killer marchyman's Avatar
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    Quote Originally Posted by AntonLargiader View Post
    180W heat per rider? Holy force field, Batman. I run about half that in the coldest weather and I'm pretty skinny.
    Yeah, but you probably don't wear your heated gear under a mesh jacket (and nothing else) in mid winter.

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    Registered User wbrownell9's Avatar
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    From another thread I noted that BMW is instituting some power-saving measures. Voltage to the high beams goes from 0 to 12V then back to zero, so there's about 10 milliseconds of full power then 10 milliseconds of nothing, etc. The filament doesn't have cool down enough to decrease its brightness, and it's too fast to flicker. But the result is that the average power consumption of the 2 55W high beam bulbs is decreased from 110W to 55W. Dash has low power needs, either LED or something like a cellphone display. LED corona, tail and fog lights require maybe 20% of the power of equivalent incandescent bulbs. Brake and turn signals aren't generally on all the time so they're not a constant drain, only intermittent, and they're LED too. ABS only needs power when it's actually working. OTOH all the computing power on the CANBUS probably likes juice. ISTR that I heard to allow 300W for the onboard electronics.

    Even with all-incandescent bulbs I could never figure why my Goldwing needed a 1200W alternator. Maybe so I could do some roadside arc welding?

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