Topic: Idle speed increases when no battery attached

[1979CB650_Chris]

Hey everyone, i notice that when I do not have a battery attached to my motorcycle, the idle speed increases, does anyone know why this is?

Thanks Chris

[TwoTired]

Perhaps your battery isn't fully charged and the rotational energy to spin the alternator is taken from the crankshaft slowing the motor down.

Takes power from the engine to convert into electrical energy.  This is seen as a load.

[cb650]

Agree with Twotired.   Also check the cables.



             Terry

[jdpas29]

get a good, long trickle charge on your battery.  if you're using a car battery charger, stop now.  make sure it's a slooooow charge and do it for at least 12-16 hours.

also, don't take this as an insult because i did it myself  , but make sure your charger is set for 12V and not 6V if it has a switch.   

[dusterdude]

buy a battery tender

[cadler]

The reason the idle increases is because the alternator is not magnetised and allows it to spin freely, the engine has less resistance

[Bodi]

"The reason the idle increases is because the alternator is not magnetised and allows it to spin freely, the engine has less resistance"
If true there would be no ignition voltage, no spark, and no idle to increase.
Presumably the engine is running then the battery is disconnected; the only removed load would be the (charging?) battery. The regulator would be going nuts trying to keep the voltage steady without the battery too... overall lower load as it turns on and off?
Maybe the voltage is higher without the battery, giving a stronger spark that improves the ignition for the higher rpm...?

[eldar]

I would have to go with bodi on this one. A battery is not required to operate once you hit 2000 rpm or so. Which is not hard to do at all.

[TwoTired]

The Cb650, at least some models, has a permantent magnet type alternator (slip rings and brushes).  Therefore, it is self excited and will produce power as long as there is a load and spinning.
Varying the alternator load also varies the alternator's resistance to turning, taking power from the crankshaft.

Bodi is right that lots of electrical stuff in the bike see more stress with the battery disconnected.  If you want to find out where the weakest points are, then continue disconnecting the battery.

Finally, if the horse is still moving around, I can bring out a bigger club.  That should put it down once and for all.  And, we can proclaim it dead.

[DiscoEd]

Here's a good read...

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookEner1.html

and another...

http://www.the12volt.com/ohm/ohmslaw.asp

and my "in a nutshell (perhaps not scientifically correct) answer"...

If you remove the battery from the system, you are effectively stoping the flow of elecrtical current through that portion of the system. The battery and it's circuit present a load to the charging system. When this circuit is no longer complete the load is not presented to the alternator and in turn the load is not presented to the engine either. The demand for power from the engine decreases, engine breathes sigh of relief, RPMs increase slightly (if no control is in place to govern the RPM) with decrease in load.

When dealing with electricity the power(energy) created or consumed in a system is typically expressed in watts. In a mechanical system power(energy) created or consumed is typically expressed in terms of horsepower. Watts may be converted directly to energy units such as horsepower, Btu/hr, Calories/hr, Joules, and tons of refrigeration. Watts multiplied by 1.34E-03 will give the equivalent horsepower.

...what the heck was this thread about again?

Regards,
DiscoEd

[Bob Wessner]

I opened the first link and my eyes immediately glazed-over.  I like your synopsis better. 

[Dennis]

..... i notice that when I do not have a battery attached to my motorcycle, the idle speed increases, ......
Thanks Chris

Hey Chris,
 ..... have you "cooked" any diodes durng this experment?

I don't know what you are seeing but I would be concerned about the rectifier when disconnecting the battery.