can i add a capacitor to starter?

Hello all,

I have a HIGH compression street bike (2006 Sportster) with NO option to add a larger battery (the battery box is flanked by frame or oil tank).

can I add a capacitor to the starting circuit to add more cranking power when I hit the starter button? If so please help with sizing and wiring diagram.

I now live with buying a new battery every other year and use a trickle charger at all times. when I hit the start button, the motor will spin to first compression and stall the starter, I then hit the start button a few times to bump the motor past TDC then it will usually spin over and start.

I have 0 timing till the motor reaches 100rpm then it goes to 10 degrees BTDC. this setting has helped me get a second season from a battery.

The battery is 200 cca 12 volts.
No option to change starter/clutch ring gear for more torque in starting.

Any thoughts for adding a capacitor like the high power car amps do?

-------------
100hp Sporty

Oops ... that would be a 1000 rpm not 100 for the timing spec.

-------------
100hp Sporty

Your only hope will be a second battery somewhere.  A cap is a waste of money in the audio world, and a bigger waste of money in your case.

Wow 100 HP out of a Sportster, that must be at least a 15:1 compression ratio to pull that off.   I am betting it does not like pump gas.

Ditto. And a cap is absolutely pointless.
(A cap is not a power source as many seem to think. It is an energy store - with no more voltage that the system it got it from (ie, the battery), and even a 100F cap will have under 1,000 LESS capacity than your battery. Think of a cap as being a (very) small battery at best.)


At first I was thinking get a reduction starter, but maybe they don't exist for yours. (They should if hi-comp is common - else how do they start?)

Then "the Big 3" - fatten your ground from battery to engine/chassis. Then try the same for battery +12V to (starter solenoid) to starter.


Then the battery - bigger or extra. Though I assume you have tried an AGM battery? And confirmed the idea using a bigger (car) battery in parallel etc?
An AGM should provide nearly double the cranking current (or rather, be able to supply double).
The AGM may last longer since it will crank for less time (assuming current supply is the problem, not a weak starter), but it may also not last as long (yes - AGMs can provide high currents, but they hate doing it - it is usually somewhat detrimental to their lifespan; that's another thing many fail to understand - hence one legit reason for using a cap in audio systems).


Not sure why you have to trickle-charge your battery - the bike would surely recharge ok.
But longest battery life is by keeping it on float - with an occasional conditioning if it's in common use (ie, occasional high current charge, or "equalisation" (over-voltage) charge.    

The bike comes stock with an AGM battery.

No option for a reduction starter.

I have cleaned and tightened the battery wires.
.... I will look into oversizing them.

My thoughts on a cap ... when I first hit the starter button, there would be a voltage drop and the cap would "discharge" so the starter would not see a drop in voltage.

Is this wrong thinking?


(Dyno proven with 93 octane pump. Not stock bore or cams)

-------------
100hp Sporty

It's really the cap that discharges so then the battery discharges.

But they are parallel connected so their voltages are the same.

And the capacity of a battery compared to a capacitor - over 1,000:1 based on volume.

hi,
maybe a compression release? allows the motor to spin over faster during starting.
mark

I would put compression releases in only IF I need to service the heads by removing them.

-------------
100hp Sporty