Capacitor to help with staring?

Hemmek post=846311
​I must clarify one thing thou, I didn't intend to replace the battery  
Just helping out with the voltage drop during the starting event. 

I realize I didn't actually answer your question directly. I was really just curious myself to work out how a capacitor compared to a battery in terms of energy storage. 

You're not alone in thinking that super caps can be used to supplement lead-acid batteries.  This is one that I found that is advertised for exactly that purpose.

media.digikey.com/pdf/Data%20Sheets/Skel...elStart%2012V_Br.pdf

Of course this one is $1217, so maybe not really practical at this point.  But the idea is sound enough.

However, a normal AGM battery in good shape should start your bike without any help.  The other day I started a '74 Z1 with ~1250cc  and ~12:1 compression with a 1/2 size battery because that's all I happen to have handy.  I did maybe 6 starts before it noticed it start to slow down.

If you're having trouble with slow starting, you either need a new battery, to check your charging system, or do some work on your harness.  

I'm kind of a fan of the K.I.S.S. method (keep it simple stupid).

Inserting another device in the path is just another thing to go wrong.
I'm a fan but my electrics tend to be more rube goldberg.
I've had relays go bad when I could have just increased the wire size and not had the issue.

I would increase your wire size first. I think my starter pulls 80amps at 12V.
With that amperage...12V  4ft.  A 1% voltage drop requires 4awg.
The stock bike is not 4awg. It may be closer to 12awg which is a 6% drop.
Size your wires correctly then add the supercap if you need it.
Your ground wire to the frame should be 4awg as well.

photo: wirebarn wire size calculator
 

A super capacitor is already a sort of hybrid between capacitor and battery.  I would think it much easier to just put in a bigger battery, possibly lithium, if you are going to make room for a super capacitor.  Like F64 said, why complicate it.

Thank you all
Got some real good info here  

Well i guess i will put the idea to rest for now, will try it if i happend to find a cheap supercap just for shits and giggles. 

Will probably end up scrapping the entire wiring harness from the KZ750, since its been modified, burnt, bypassed, spliced and fucked over by PO. 
It works but you will have some anxiety about it  

(I actually found 5 diffrent splices on a 30cm cable once) 

Guess I'll have to see how she runs after that

Funny, I just had this same idea the other day, and now here’s the answers. Interesting stuff! 

Thank you for this topic! This forum can help a lot. I bought myself a motorcycle and am just starting to figure out how it works. However, I found a site with a lot of information about engineering and cars, as well as companies that are engaged in various types of engineering.

It's the HV circuid that dies rapidly.Here's a circuit that I have driving/floating my TCI/Ignitor on my '95 1100 Yami VIRAGO Their TCI shuts itself off below 10V !?!!  Pionts/Condensor would need higher capacitance(More Joules/Culombs), but the 'Stick Diagram' circuit should provide a stable 12V Float time during start...Again, new to Kawi but the physics is the same...

Choppers that run a Magneto, and no battery, sometimes use a small capacitor for kickstarting(hot spark for a couple kicks,even if you don't get your magneto spinning fast enough).They are smaller than a coke can but bigger than d cell battery. about $70-100.
But I got nothing on these electrical engineering folks.just saw what works for others.
Be Well