battery eliminator capacitor

[mitch]

been running my 1973 xs for several months. started stumbling, had to pull over. it will kick start but no power. it has a battery eliminator (capacitor), a PMA, centrifugal spark advance. otherwise, it's pretty normal. here's my question: DOES A BATTERY ELIMINATOR (capacitor) FAIL? what does a failure look like? i'm going through all the usual suspects. cleaned the carbs, checked for fuel blockage. changed the ignition unit. changed the coil. checked the cam timing... i'll find it, BUT... any suggestions? when idling, i notice a surge...

 

[X77S]

At idle check the voltage on the capacitor like you would a battery. It's very possible it went bad.

 

[mitch]

At idle check the voltage on the capacitor like you would a battery. It's very possible it went bad.

thanks, i will do that.

 

[X77S]

I have the same setup, just haven't used it yet.

 

[mitch]

I have the same setup, just haven't used it yet.

worked pretty good till now. if the capacitor turns out to be the culprit, i might put a battery in. but it was a pretty tidy set-up.

 

[X77S]

I found a pretty small 4 cell lithium battery I was considering kind of expensive but not too bad.
https://www.revzilla.com/motorcycle...-cell-120ca-lithium-ion-battery?sku_id=953325

 

[mitch]

a new 'battery eliminator' capacitor arrived the other day from tcbros. the bike started right up and ran with power. but why did it fail to begin with? how susceptible are those capacitors to heat, vibration, variations in charge...etc? i'm going to start cobbling up a small battery box in case the capacitor fails again for whatever reason...

 

[X77S]

Did you use the spring attachment it came with? I'm sure vibrations are a factor,

 

[RC4MAN]

Don't know about this set up for the Yam, but had lots of experience with Cap Discharge Ignitions on BSA's and Triumph's back in the day.
It consisted of a Capacitor, mounted by a spring to reduce vibration on the liquid filled capacitor.
It relied on a Zener Diode to bleed off excess voltage charge from the alternator. If either component failed the system failed and the caps failed frequently.
You could always tell though as the top of the cap had a hole covering a membrane that was designed to blow if over charged and the liquid would blow out.
Examine the cap and see if these are similar, but keep in mind if something in your charging system will cause an overcharge condition it will happen.

 

[mitch]

Did you use the spring attachment it came with? I'm sure vibrations are a factor,

the one from tcbros doesn't come with that spring. i remember that one from one of my old triumphs...

 

[mitch]

Don't know about this set up for the Yam, but had lots of experience with Cap Discharge Ignitions on BSA's and Triumph's back in the day.
It consisted of a Capacitor, mounted by a spring to reduce vibration on the liquid filled capacitor.
It relied on a Zener Diode to bleed off excess voltage charge from the alternator. If either component failed the system failed and the caps failed frequently.
You could always tell though as the top of the cap had a hole covering a membrane that was designed to blow if over charged and the liquid would blow out.
Examine the cap and see if these are similar, but keep in mind if something in your charging system will cause an overcharge condition it will happen.

Don't know about this set up for the Yam, but had lots of experience with Cap Discharge Ignitions on BSA's and Triumph's back in the day.
It consisted of a Capacitor, mounted by a spring to reduce vibration on the liquid filled capacitor.
It relied on a Zener Diode to bleed off excess voltage charge from the alternator. If either component failed the system failed and the caps failed frequently.
You could always tell though as the top of the cap had a hole covering a membrane that was designed to blow if over charged and the liquid would blow out.
Examine the cap and see if these are similar, but keep in mind if something in your charging system will cause an overcharge condition it will happen.

that was how my old triumphs were wired. my 'battery eliminator' doesn't have the spring; it's got a rubber lined bracket. the reg/rectifier is pretty modern looking. the capacitor has a 'blue dot' on the top... maybe that is something significant. if this acts up, i'm installing a battery.

 

[RC4MAN]

As an after thought, what I learned from the experience is always carry at least one spare. The rubber mount may be enough isolation.
I would examine the capacitor, write down any numbers on it, should have either a part number from the manufacturer or at least the voltage rating and capacitance.
Once you have that Google the info, you can probably find replacements cheaper than TC Bros.

 

[X77S]

I got my whole kit from Hugh's Handbuilt on sale for a few dollars cheaper than the xs charge system and I "upgraded" to the mosfet reg rec. The HH capacitor comes with a spring. $30 normal price if I remember correctly.

 

[mitch]

the capacitor from tcbros is JUST SHINY BLACK. there's a raised plus sign and a raised minus sign. and a mysterious blue dot. no numbers or anything informative.... hugh's handbuilt used to be down the street from me. but back then i had a harley..he's semi-retired, i guess...i might go ahead and fit one of those new small batteries... maybe i can find a source for a similar capacitor; probably from a brit site...

 

[X77S]

Always possible to find it at an electrical supply, itll probably cost an arm and a leg or a couple dollars.

 

[RC4MAN]

I looked at the TC Bros site and yes the cap pictured is as you say. The old bad cap you have, is the shiny black just a shrink fit plastic sleeve that could be cut and peeled off to expose a metal shell with information on it or did they paint it?

 

[mitch]

it was some sort of plastic sheathe which i gingerly removed to expose a shiny aluminum can devoid of info.

 

[X77S]

Does it seem to bulge? They do that on computer boards when they go bad.

 

[mitch]

no discernible bulge.

 

[RC4MAN]

Just checked ebay, there are lots of replacement units for the Lucas 2MC cap cheaper than the item from TCB. It might even work
Also found a part number for a Mallory capacitor rated for the same purpose, 4500 uF 30 VDC rating, CGS452U030RC