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Whats a microfarad?

  • Thread starter Thread starter Adler
  • Start date Start date
A

Adler

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I'm thinking of getting a battery eliminator for my 550. Mostly out of curiosity, I could never really wrap my head around the idea of an engine that generates a lot of power requiring this huge power source just to start it. Whats wrong with a kickstarter?!

I know I can buy a product labeled "Battery Eliminator" but its just a capacitor in a fancy package. The question is... which capacitor is it?

My understanding is that a higher capacitance and voltage rating is better.

I found this one on a cursory glance of ebay... Is this ideal?
http://cgi.ebay.ca/7000uF-60VDC-Com...713?pt=LH_DefaultDomain_0&hash=item3cacce0569

EDIT: It seems like 15000uF capacitors in varying voltages are dirt cheap on ebay. Are these ok also???
http://cgi.ebay.ca/1X-25V-15000UF-L...492?pt=LH_DefaultDomain_0&hash=item5adf72832c
 
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Find out the best size, I can pick up a few dirt cheap in Hong Kong next week.
 
What is the advantage to eliminating the battery?

Would the capacitor discharge all at once when you tapped into it?
 
The Farad is a measure of capacitance but this unit is so large that in practice one uses microfarads i.e. a millionth of a farad.
You are right a capacitor will store energy and the bigger the farad number the better.
The voltage rating is given to ensure that the capacitor will not short when exposed to this voltage.
On a motorbike the voltage can easily rise to 15volts with no load ( like when the capacitor is charged) so you need to choose a model with at least a 20 or better 30 volt rating.
Now the bad news: when you hit the starter button the current can easily raise to 100 amps and very few capacitors can deliver this amount of current unless designed for this purpose.
Next the capacitor would have to be huge to deliver this kind of current even for only 10 seconds...
Not so easy I'm afraid:o
 
John Kat said:
The Farad is a measure of capacitance but this unit is so large that in practice one uses microfarads i.e. a millionth of a farad.
You are right a capacitor will store energy and the bigger the farad number the better.
The voltage rating is given to ensure that the capacitor will not short when exposed to this voltage.
On a motorbike the voltage can easily rise to 15volts with no load ( like when the capacitor is charged) so you need to choose a model with at least a 20 or better 30 volt rating.
Now the bad news: when you hit the starter button the current can easily raise to 100 amps and very few capacitors can deliver this amount of current unless designed for this purpose.
Next the capacitor would have to be huge to deliver this kind of current even for only 10 seconds...
Not so easy I'm afraid:o
Click to expand...

The intention is not to use the starter, you would definitely need a battery for that. This "upgrade" is only for bikes with kickstarters.

I found this:
As an Electrical Engineer, I just have to add to this discussion.

I would suggest a large electrolytic capacitor, which has a polarity so it must be connected properly. The advantage to an electrolytic is more capacitance in the same volume for less money. Buy the highest capacitance you are willing to pay for, with an 18 volt or higher rating. I would suggest .1 farad or greater.

The higher the voltage, the larger physical size of the capacitor for the same amount of capacitance, but it will fail if the voltage exceeds the rating repeatedly. The more capacitance, the more charge the capacitor will hold.

The practical difference between a capacitor and a battery are in the amount of charge stored, the leakage current, and the internal resistance. A battery has more internal resistance and can store much more charge than a capacitor, and a capacitor has much more leakage, enough that there will be no charge remaining after being left overnight. Due to the above factors, a capacitor is a poor substitute for a battery, but will give the charging system some reserve as long as you aren't trying to use the electric start.

And as a couple other people wrote, do not connect the battery terminals together, that would fry your charging system.
Click to expand...
http://www.thumpertalk.com/forum/archive/index.php/t-31838.html

It seems to imply that the voltage should be higher than the maximum our charging systems can produce (25v?) and the capacitance should be as much as we are willing to pay for. It should be electrolytic and I would suggest screw in terminals for ease of installation.
 
cableguy said:
What is the advantage to eliminating the battery?

Would the capacitor discharge all at once when you tapped into it?
Click to expand...

The advantages are as follows:
- removes about 5lbs.
- isn't filled with acid that could potentially explode.
- should theoretically last forever.
- no maintenance required.
- more space on the bike.
- all your friends will talk about how cool you are.

The disadvantages are:
- lights will only work for about 5 seconds with the engine off.
- absolutely no starter, the bike must be kickstarted. (I guess you could remove the starter for more weight gains).
- I'm not positive that the turn signals and horn will work right without a battery. It depends on how much power our bikes generate.
- I'm not sure it will work at ALL, if the bike doesn't produce enough power at idle to stay running then it will not work.

tkent02 - It seems the best size is about 25v (the higher the voltage, the less chance of the cap dying and the larger the size and cost) and the capacitance should be as high as is reasonably priced. Just how cheap are things in Hong Kong?

EDIT: Here is a great explanation of exactly what is happening that I found on another forum.
The voltage that comes out stator varies from a positive to a negative voltage, like waves in a tank, both above and below the water level (zere voltage or "ground"). The frequency varies as the rpms change. The amplitude (height of the waves) also varies, but is considerably in excess of 12 volts of a battery.

Next this voltage is run into the regulator, which clips the tops and bottoms off the waves, so that the voltage never gets too far from ground in either + or - polarity, (probably less that 35V, if I remember right).

Next the regulated voltage goes into a rectifier, which is an araingement of diodes that only let the current flow one direction. What this does is flip the sign on the negative voltage, so it becomes positive, but not vise-versa. So anytime the voltage is -20V, it becomes +20 volts, and any time its +20V, it stays +20 V.

Now you have a voltage that varies from 0V to something less than 35V. If you run this into a battery or a cap, its like taking a garden hose that is pulsing and dumping it into a bucket. A hole in the bottom of a bucket will flow at a steady rate that is the average of the pulsing garden hose. And that is what you use to run your lights, you get a steady voltage so they won't flicker.

Be aware that a battery is a very large bucket, while this cap will be a small bucket. So if your garden hose pulsing changes, the small bucket (cap) drains quicker than a large one (battery).
Click to expand...
http://www.thumpertalk.com/forum/archive/index.php/t-97283.html
 
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Adler said:
That's awful expensive for a capacitor. Though I do like the idea of spring-mounting it...
Click to expand...

Yeah, they're a lot cheaper over here - it was just the first one I found on US Ebay.

I ran a 550 like this for a while a few years back. The indicators didn't work any sense (erratic) so I dumped them. Also dumped the starter motor to save weight (you have to plug the hole up though). Horn was ok as were the main lights.

And what is the kickstart for if you don't use it? :D
 
SqDancerLynn1 said:
I believe you would also need a points ign !!!
Click to expand...

I have heard that before... Any idea why?

According to this source it will work on "all kick start bikes with a permanent magnet alternator."and, "If you can stick a wrench to the side of the alternator and have it stay there with the engine off, odds are you can use one of these."

Either way, bikes with kickstarters came with points from the factory.
 
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