Super Capacitors

maylar said:

1 time constant is just R*C, that brings it to 63%. Full charge is 5 time constants. The car audio guys say to put a tail light bulb in series with the cap and when it goes out, the cap is charged.

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My Capacitor welder is charged by a 2 amp 12 volt charger with an LED indicator that indicates the current flow into the 3.5 capacitor. It generally takes about 10 seconds to go from yellow (charging) to green (charged) It seems like at 12 volts, it would take longer to charge a more powerful capacitor from full discharge to fully charged...

I don't know if a capacitor on a motorcycle works like my spot welder does, (complete discharge for every weld, then completely recharged to be ready for the next weld) but perhaps it's similar in the sense that it only has to supply enough voltage for the first few sparks until the alternator raises the bike's system voltage...

If that's the case then there could be an optimum sized capacitor to make dead battery starting easier, rather than the 2MC (as Ludwig showed in his earlier post) I'd be interested in opinions of what that size would be, and what the pro's and con's of making that change to the bikes electrical system would be.

Different applications. Your welder is using the stored energy in the cap to deliver a short duration high current pulse. The same principle is used in camera flash devices and strobe lights.

With an ignition system the cap will charge to the peak voltage of the alternator and needs to hold that long enough for the ignition coil's inductance to charge up and then deliver enough energy to bridge the plug gap and ignite the mixture. The spark itself is only about a millisecond, the coil on time is a function of the ignition dwell and the charge time is a function of inductance. The cap is being constantly charged by the alternator at a frequency dependant on RPM.

What is the ideal cap size? I dunno how to calculate that. There is impedance in the charging system that will affect the charge time of the capacitor, so at some point the cap would draw too much current and not reach full charge. Some day I'm gonna put a scope on my electrics and see what effects different sized caps have.

I do know that my TriSpark ignition will run the motorccle down to 7.5 volts, so I suspect I'll be able to start and run with my 10,000 uF cap and no battery. I guess I should test that theory before it becomes necessary...

dero said:

Just looking into possibilities of a better system that might give enough extra oomph for the electronic ignition .
Maybe its not the answer .

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Here comes Mr Buzzkill

Too me a capacitor battery-less system is not the answer for a daily driver, or weekend warrior motorcycle with an electronic ignition on it.

A small battery, a battery eliminator, an electronic ignition box, and an alternator is a proven tested easy to install way to put together an easy to start kick start motorcycle, and power the entire electrical system when running. You can lighten it up and simplify it further with a small dual epoxy filled 12V coil. I run my Norton that way and it works even though I don't know a farad from a spade connector.

If I myself wanted to build a race only Norton, I'd put a Joe Hunt magneto on it, and get a roller starter. Best battery-less option I can think of. I'm living in the past though, so bare that in mind.

maylar said:

I do know that my TriSpark ignition will run the motorccle down to 7.5 volts, so I suspect I'll be able to start and run with my 10,000 uF cap and no battery. I guess I should test that theory before it becomes necessary...

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With: Tri-Spark ignition, Tri-Spark MOSFET Regulator, 10,000 uF cap, 2-wire stator, not wet sumped, normally easy starting 850, cold engine, hot day, and proper technique. Will kick start with the battery disconnected - I've done it. Tried the same conditions with a PODtronics POD-1-HP and after many attempts, it started. Suspect that a 3-phase stator would be better.

As far as I can gather , it is doable, just , but there seems to be nothing to be gained by improving the standard components .
For a battery less setup , it would not take much to upset the fine balance needed for reliable starting with electronic ignition .
So unless there is some advantage in the [ unknown to me ] characteristics of the super capacitors , then things are as they always were .
Thanks for every ones input , looking forward to any informed knowledge on the properties of the super caps.

On the bright side , Just put it to the test .
Trispark ig , std alt ,rec & zenner , std cap 1st start for the day , 10.30am ,warm 25c , pulled the fuse.....fired into life on the first kick .
I will try it under less ideal conditions in the future .
I suspect I may get a different result in a cold camp ground in winter , with a hangover , after a period of less attention to regular maintenance .