View Full Version : Air-cooled motor- enough juice to run a fan?

12-04-2007, 11:54 AM
I put this here instead of the 'cooling' forum because it's more to do with the alternator than anything..

Just bought this little rail (powedred by a 1980 GS 1100 air-cooled Suzuki engine), and it's got a few problems. *The previous owner has it set up to where it's got a large car battery that needs a full charge before the riding weekend.. the car has 2 fans, one comes on when the engine starts (it blows across the block and heads-sort of), and the other kicks in at 180 degrees and blows straight down over the heads.. *(the car also has an external oil cooler- no fan near it) *The story is that the stock alternator can't keep up with the demand the fans put on the system, so over a day or two of riding, the battery drains out and needs to be externally recharged. *I need to fix this so the car is fully self-sustaining. *Maybe the alternator/rectifier is bad.. I will be testing them soon.. I do know that the car won't run when the battery is disconnected- so obviously there's a wiring/charging problem somewhere..

I guess my question is this- and please know that electrical work is my weak point- when the stock system is working correctly, will this alternator put out enough to drive one fan- let alone two, or can it be modified to do so (rewired)? *This air cooled motor/system never had a fan, so I might just be asking too much of it.. *the seats totally block the wind, so it's little side scoops are the only air source.

I want to try and make this motor work, but not at a huge expense- if it's too much $$ to rework, I'll likely switch over to a liquid cooled motor..

Thanks for your thoughts- this is my first rail, and I'm learning at the speed of an almost idling sick motor *[smilie=mhihi.gif]

12-04-2007, 02:10 PM
It should be able to run one fan (10 amps) and maybe some lights, but not two fans. use the one fan, and maybe put a smaller one on the oil cooler, like one off a streetbike. I have one if you want it. It is about 6 inches in diameter.

12-04-2007, 02:42 PM
It does sound like the bike motor does have a issue in the charging system or not wired right like you said. Aside from buying a book on the bike so you can trace the motor wiring you need to seek out someone local who messes with ones like it. They can be of more help than you know. If they are in it for the hobby of it they will usually help for free or cheap some times too! Once you have the bike motor charging you can get info out of the book that tells you how much current draw you can put on it. The fans you have may be fine if they are small and have low current draw. Most decent amp meters will tell you what they are using. Same for the lights. You can consider a couple lights and a small fan off the bikes system. If you need more lights than the bikes system can handle I have seen an alternator connected to the rear axle with a belt pulley. It fed its own battery and a set of lights that were much higher than the motors charging system could deal with. Being it charged only when moving it was still fine as the driver simply did not use the lights when not moving (makes sense...) He said he set the alternator up so it spun proper rpms where he did most of his driving. Other than the extra battery weight and a lil alternator drag this to me was a dam good way to really see at night if you run then. * Bill

12-08-2007, 05:32 PM
The GS suzukis were notorious for regulator/rectifier problems which in turn would burn out the alternater coils. There are a couple of aftermarket companies making replacments...goggle up Rick's Rectifier for one good replacement. A word of caution do not replace the regulator without doing a full check on the charging system or you may burn out the new part. This website has a thorough explanation of what you need to test. *http://www.thegsresources.com/. Definately put a fan on the oil cooler.


12-10-2007, 11:29 AM
Wow! *Wayneh- thanks for the tip- that site literally spelled out what's likely wrong with my motor/wiring. *After digging around my buggy's wiring harness, I've found that someone cut all 4 wires at the rectifer and just ran this car directly off the battery.. my stator checks to be working fine (75 watts/ohms/amps- {I forgot what I was measuring- [smilie=ashamed.gif] doh!} at 5K RPM), if only it were wired into the system! *I guess the rectifier gave out (a design flaw- seems they ALL give out) and someone didn't take the time/$$ to fix it [smilie=banghead.gif] .. *I've got an aftermarket rectifer on the way, so after that, it's just a matter of can the fan(s) keep up with a properly working charging system..

12-18-2007, 03:54 PM
Ok- Put the new aftermarket rectifier in and it works great! *I haven't had a chance to truly run the car yet, but when I goose it up to 4/5k, it charges at 14.9 to 15.3 volts... *I've been unable to find out how much draw I can truly put on the system (can't find the info in my Clymer manual), so it might be a little trial and error- it does seem to handle running one fan quite easily.. *I'm just glad to have it run and be able to restart it! [smilie=non_banana1.gif]