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Old 08-27-2017, 10:30 AM   #1 (permalink)
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cb125s alternator output decrease.

Hello so ive restored and riding a cb125 (also have another to restore and loads of spare parts). I finally got it running almost good (carb still needs a fine tuning) and was starting to look at increasing the headlight brightness and everything else with leds. Issue i noticed is all points cb125 do not use a voltage regulator. The 6v system uses the battery as a regulator instead. Issue is when i switch to leds they will be using less current so then the battery will be taking the beating which i am sure it cant handle for very long.
So i was thinking of reducing the rotor magnets (reducing the weight and amount of power wasted to move it against the magnets). I do have a degree in electrical engineering but havent used it in 4 years and didnt have a good motors teacher so not much help there. Ill be reading up on it but i was wondering if anyone has done something like this before.

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Old 08-27-2017, 04:49 PM   #2 (permalink)
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Wouldn't a smaller battery, or eventually just adding a voltage regulator, achieve the same goal when it comes to the lighting output? Anyway, even though a decrease in the rotating mass of the generator could lead to slight fuel-savings, keeping the flywheel correctly balanced might also be an issue.
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Old 08-27-2017, 05:12 PM   #3 (permalink)
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Smaller battery would be worse. A bigger battery could handle a higher charge or more charging amps. The 125 has a 6v 6amp battery. For my current 125, i just planned on trying to keep the current draw of everything the same by adding a fan type a fan set up on the back section of the cylinder that never sees air flow. That way it helps cool the engine down and keeps everything the same in the process. My next cb125 (which will be more modded but still original looking) i was planning on doing this to it.

Yes issue is i dont really want to remove alot of mass just magnetic resistance from the rotor. And yes it will need to rebalanced afterwards. Which i figured i would statically balance first to test it. And tjen pay someone to perfectly balance it for the finished product. My whole issue is how much to trim off the magnet (i guess its time to pull out the old textbooks and do a **** ton of reading). And how to shave it (top to bottom or side to side).
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Old 08-27-2017, 06:36 PM   #4 (permalink)
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I'm no Electrical Engineer, but I would think some kind of Mosfet regulator would be a simple effective solution.

Not sure if being 6V would be a big problem though.
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Old 08-28-2017, 02:27 AM   #5 (permalink)
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I'd think you could set up your own pulse-width modulator to decrease the load on the stator/alternator and to limit output so it doesn't cook your battery.

If you didn't care about stator drag, you could just slap a plain old regulator on it and be done with it.

Or you could use both...a simple PWM set to roughly set the output/decrease drag, and a regulator to dump any excess output. Be a lot easier than building a pwm that adjusts it's output.

Or you could try a 6v solar charger controller and see what happens. They combine PWM with voltage limiting. Dunno if they'd appreciate the kind of output a stator puts out, though.

Lots of options...depends on what you are willing to try.
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Old 08-28-2017, 02:34 AM   #6 (permalink)
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Seems like your best option yet is to just adapt a regulator. And then a smaller battery, or eventually no battery at all, for the sake of weight-saving.
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Old 08-28-2017, 09:30 AM   #7 (permalink)
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Removing the 3ish pound batter and having to deal with idle issues and such would be more a pain then anyting. even with leds the alernator at idle is putting out basically nothing so i would have to run a higher idle etc. Deleting the alternator and switching everythung to 12v and running a lifepo4 set up woukd be way better. But super costly and would have to have a solar set up to charge it without paying to charge it (already have free panels to do so). I havent really started to work on my 2nd cb125 (calling it cb125hf) but when i do ill have play around with leds and such. I currently just hate how when i turn the turn signals on everything kind of dims headlight too) but i also dont want to bake the battery. I like my fan idea though to burn some of the extra amperage at high speeds. I could also design it to act like a regulator. For my cb125hf i plan on trying to make it look stock (no cafe racer or noticeable aero fairing). But get killer mpg by other means (weight and engine mods).
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Old 08-31-2017, 01:12 AM   #8 (permalink)
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I would honestly not to consider an alternator delete, especially in a spark-ignited engine.
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Old 08-31-2017, 02:29 AM   #9 (permalink)
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The cost of a Life shouldn't be too high on a bike? My Fiat cost around $150 to do. If a single charge is enough for your daily needs, the alt-less is the way to go. Life should maintain voltage enough for all your systems to function correctly.

The main gain of an alt delete is you get a lot of low end torque and drivability.
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Old 08-31-2017, 08:57 AM   #10 (permalink)
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what batteries and such did you use oldtamiyaphile. I am more worried about overdraining the batteries and kdestroying them. So i would have to set up protection from that. Honestly most I driven it in a day is like 20 miles (work is like a 6-10 mile round trip and sometimes to just go for a ride). Though I would love it if I never had to worry about charging it and such. I figures Ill get 2 spares and trim one 1/16 magnet size off and the other 1/8 and keep playing with trimming 1/16 down to where i get to what i want. Ill be statically balancing them and then for the final product Ill get it professionally balanced. Now its more time to find a headlight lens to do led with (sealed beam conversion).

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