Capacitor

[UTAH INFANTRY]

Has anyone tried or thought about putting a capacitor on there bike? I had a couple in my car when i was running a 2500W AMP. I would think that it would be the same concept. Would this replace me upgrading to a larger alternator?

One like this...

http://www.rockfordfosgate.com/products/product_details.asp?cat_id=5&series_id=40&family_id=87&item_id=108310&locale=en_US&p_status=

[Bobbo]

What in the world do you have on your bike that would require 200+ amps for a few milliseconds?!!      ???

[tank_post142]

one kick butt stereo or a rear vibrating seat. (for riders used to HD's)

[Bobbo]

one kick butt stereo or a rear vibrating seat. (for riders used to HD's)

I was in a local electronics boneyard/supplier years ago when a couple Harley bikers came in.  After looking around, I heard one ask the clerk for pager vibrator motors.  Apparently they put them under the passenger seat cover to give their lady friends a surprise!    I guess the V-Twin wasn't enough!   

[GOOSE]

i think they wanted to get paged.

[csj]

Ive been out at night, hit the horn button, relay pulls in
the compressor for my airhorn.
For a half-second the headlight dims,
and then the horn wails.
If I'd had a capacitor at the horn, the capacitor would
deliver the initial load of the horn, and most likely
the headlight would not dim.
The longer the voltage dip, the larger the capacitance.
The speakers on the bike act something like the horn compressor,
they suck down the voltage for short periods.
A capacitor would help, but it would be somewhat large
(tens to hundreds of uF). Those caps are not cheap.

[RP#62]

I thought about it, but not for the radio or horn.  I was thinking about putting a diode on the power feed to the ICM then putting a capacitor between the diode and the ICM.  That way, the ICM would always see 11-12 volts (battery voltage minus the drop across the diode) even when the starter pulls the voltage down.  Of course, the diode would have to be big enough to handle the in-rush current of the capacitor and it would delay the safety feature of the tilt switch, but it should make starting more reliable even when the battery is not at its best.  It would be a tradeoff though, just like anything else - possible improved performance, but more stuff than can fail.

Although there are reasonably sized 1 farad capacitors now, when I was in college, I remember the physics prof describing a 1 farad capacitor as the earth and the moon with a good dielectric between them.
-RP

[MarkT]

I have capacitors in my speakers to block low frequency sounds so as not to blow the speakers.  I don't know their rating - their product name was "Bass Blockers", supposed to block below 80 Hz.  I also have the lo-pass on the amp set to block below 100Hz.  Blew out the Blaupunkts eventually anyway.  Replaced them with Alpines.

[Jeff K]

I thought about it, but not for the radio or horn.  I was thinking about putting a diode on the power feed to the ICM then putting a capacitor between the diode and the ICM.  That way, the ICM would always see 11-12 volts (battery voltage minus the drop across the diode) even when the starter pulls the voltage down.  Of course, the diode would have to be big enough to handle the in-rush current of the capacitor and it would delay the safety feature of the tilt switch, but it should make starting more reliable even when the battery is not at its best.  It would be a tradeoff though, just like anything else - possible improved performance, but more stuff than can fail.

Although there are reasonably sized 1 farad capacitors now, when I was in college, I remember the physics prof describing a 1 farad capacitor as the earth and the moon with a good dielectric between them.
-RP

Ok, now we are talking about something I could use. During cranking the voltage drop can cause my EFI to turn off and then come back on. I never noticed it unless I have my laptop hooked up. It drops the communication for a second while cranking.

Lets talk about specifics.   

[csj]

Some of this talk may help the original thread owner,
so we're not hijacking the thread.

What RP62 said was put a diode 'in-series' with the
positive line feed to your ICM. Then put a good sized capacitor
on the 'cathode' side of the diode. The diode ought to be at least
2 amp rated, the capacitor ought to be at least 22 - 100uF 25V.
Of course the +ve of the cap goes to the cathode of the diode,
the -ve goes to the bike ground. Both new components should
be within an inch of the ICM, not far away.

The diode/cap prevent the ICM voltage from dipping during
starting/ voltage dips.

RP, the last 1 farad cap I saw was about the size of the bike's
battery. Don't gotta be that large, and the lag in charge/discharge
of that thing would be huge.

[Bobbo]

Ok, now we are talking about something I could use. During cranking the voltage drop can cause my EFI to turn off and then come back on. I never noticed it unless I have my laptop hooked up. It drops the communication for a second while cranking.

Lets talk about specifics.   

What is the current draw of the ICM during cranking?  That and the expected cranking time would determine the minimum capacitance.  Another thing to consider would be a low leakage capacitor.  A few milliamps would be OK for a week, but it may drain the battery if it sits longer.  In addition to the 25 volt rating, you would also want an industrial or automotive temperature rating of at least 105C.

[csj]

I threw out some industry standard current and voltage ratings
for parts. If 'really specific' were required, I could give
Manufacturer and exact Part Number.

A low leakage cap?, well, I have only seen leaky when the cap
is well beyond its MTBF (mean time between failure)
rating, generally 2-3000 hours.

The most compact 22-100uF cap is an Electrolytic cap,
it can be axial or radial. I suggested these values because they
are easiest to find at your local geek store.
The diode could be a few years old, the cap should be brand new.

[Jeff K]

Ok, now we are talking about something I could use. During cranking the voltage drop can cause my EFI to turn off and then come back on. I never noticed it unless I have my laptop hooked up. It drops the communication for a second while cranking.

Lets talk about specifics.   

What is the current draw of the ICM during cranking?  That and the expected cranking time would determine the minimum capacitance.  Another thing to consider would be a low leakage capacitor.  A few milliamps would be OK for a week, but it may drain the battery if it sits longer.  In addition to the 25 volt rating, you would also want an industrial or automotive temperature rating of at least 105C.

I'm not sure what the actual draw is but it called for a 30 amp fuse on the 12v supply.

I don't know much about electronics so I'd need someone with that knowledge to point it out. Capacitors come in so many forms... it's all Greek to me.

[Bobbo]

A low leakage cap?, well, I have only seen leaky when the cap
is well beyond its MTBF (mean time between failure)
rating, generally 2-3000 hours.

Yes, all capacitors leak, that is allow current to flow between the leads when in use, not that the electrolyte leaks out!  If the power to the ICM is cut off by the ignition switch, then leakage becomes a non-issue.

[Jeff K]

The EMU is on a relay

[Bobbo]

I'm not sure what the actual draw is but it called for a 30 amp fuse on the 12v supply.

I don't know much about electronics so I'd need someone with that knowledge to point it out. Capacitors come in so many forms... it's all Greek to me.

In this type of application, the capacitor is simply a short term storage unit for electrical power.  The diode is a one-way valve that allows the capacitor to charge, but stops it from discharging when the input voltage drops during cranking.  The capacitance determines how long the capacitor will supply power to the ICM at a minimum voltage.  If the ICM draws 1 amp during cranking, you will need a very large capacitor to maintain a minimum of 11 volts for one second!  A quick calculation shows that a 1 farad capacitor would discharge from 12.7 volts to about 11 volts in 1.2 seconds at 1 amp current draw.

[9Ball]

I have been using these for my car stereos for quite a few years (at least 5 different cars).

http://www.crutchfield.com/shopsearch/capacitors.html

When you're pushing the amps I use, these capacitors allow the subs to hit those extremely low notes (usually below 60 hz) and minimizes the strain on the car's electrical system.

My current amps use 4 gauge wire and I had to upgrade the alternator and battery...

Good luck....these are available in most higher end auto sound stores or Crutchfield (can't recommend highly enough...been a good customer for >20 years now)

[BlueValk]

Ok, now we are talking about something I could use. During cranking the voltage drop can cause my EFI to turn off and then come back on. I never noticed it unless I have my laptop hooked up. It drops the communication for a second while cranking.

Lets talk about specifics.   

What is the current draw of the ICM during cranking?  That and the expected cranking time would determine the minimum capacitance.  Another thing to consider would be a low leakage capacitor.  A few milliamps would be OK for a week, but it may drain the battery if it sits longer.  In addition to the 25 volt rating, you would also want an industrial or automotive temperature rating of at least 105C.

I'm not sure what the actual draw is but it called for a 30 amp fuse on the 12v supply.

I don't know much about electronics so I'd need someone with that knowledge to point it out. Capacitors come in so many forms... it's all Greek to me.

One could connect 10 AAA rechargeable batteries in series.  Then use a relay rather than a diode to connect the AAA's to the bike battery.  Connect the coil to the starter button like the headlight is now.  When you push the button, the relay opens and the ICM is running on the AAA's.
 
If you want to use a diode instead of a relay, Radio Shack has some 3A diodes for $1.50.  That should be enough.  But, if the bike's battery is a bit low, the AAA's will be even lower due to the diode drop.  Using a relay will give the AAA's just a bit more voltage.