Triumphrat

Darryl

I have a question about capacitors. The one on my bike reads '4500 mfd', and I have seen them around that are similar to that. But if you read enough you'll find some one say to use 48000 mfd (uf) which is over ten times the size I have. I did not put mine on, it came that way, but what difference does this make? I want what will make it run best. Its only a few dollars difference. Anyone know?
Thanks

Diego

It will have little or no effect on how the bike runs. You might notice a difference in brightness of lights, especially at lower RPMs, though. And it used to seem to me that the motor fired up a little quicker with a larger capacitor.

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John

OzBloke

Guys,

The larger the capacitor value, the more current it will take to initially charge it, and it will take a longer time to bring it to full charge, but the better job it will do in filtering the pulsing DC coming out of the rectifier, and it will be better able to handle the surges required by large loads (eg headlights being turned on, Indicators, Horn).

If there are restrictions (poor quality wiring or connections, poor magnet strength in the alternator) then going to a larger value will provide little or no benefit, and may actual degrade performance, because the charging circuit can't charge the capacitor fast enough. This may result in engine being hard to start.

IMHO - if 4500 microfarads is working for you, don't bother changing to a higher value, you probably won't notice any difference in operation.

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Per Ardua Ad Astra
(Through difficulties to the stars)

666Bonneville

i run a capacitor i bought from british cycle supply. i might as well run nothing and bypass it. it doesn't help. instead i switched to a negative ground and run an LED in my tail light. still not going to rock a battery...

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Triumph.... Turns an ordinary man into a mechanic.
2006 Scrambler
2005 CRF 450
1977 Bonneville
1973 Bonneville Bobber

panda

Ozbloke has it right. regard it as a small simple battery there just to help smooth the rectified dc ripples.

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A wise man learns from his mistakes..
A genius learns from other peoples mistakes.

happyray

Hmmm,

I don`t wanna argue with your reason because it`s all true.
On my Shovelhead I run pointers and I`m happy with them.
Now, I always mix up the units when it comes to Farad. You must excuse.
But I have the figures!
OEM Harley sells capacitors with 18.000 and 22.000.
They kept blowing fairly quick.
Then I got one for an old Volkswagen Beetle which has 25.000.
It`s still in place after an unbelieveable ~40.000 mls.
I`m not kidding. I`ve adjusted the ignition maybe some 6,7 or 8 times since then.
I needed to swap the pointer already but not the capacitor.

my .02

Ray.

Darryl

Thanks for all the info. Another side question to all that. Would blowing one out be related to the size/capacity or the maximum voltage rating. Depending on the maximum voltage it can handle, wouldn't it be spikes that would fry one rather than the number of farads it is made at?

OzBloke

Here's the scoop on capacitors/condensors (same thing, just old vs new names).

Capacitors have two main characteritics you need to be aware of.

Capacity - how much charge they can hold for a given period - measured in microfarads (μF)

Maximum working voltage - the maximum safe working voltage that should be applied - measured in Volts.

The capacity value depends on what they are being used for. The small condensors used in the points/coil circuit are relatively low in capacity (eg 0.1 to 1 μF) but have a high working voltage of around 400-500 VWDC (Volts Working DC). They need this voltage rating because the back EMF generated by the coils when points open can be as high as 400V.

The capacitors used as battery eliminators use a much high capacity (4,000 - 45,000 μF) but have a lower working voltage, usually around 25 VWDC.

The main reasons capacitors "blow" are:
- connected with wrong polarity. Most capacitors used in automotive electrics are polarity sensitive.
- wrong voltage rating - VWDC rating too low for the applied voltage.
- age - depending on the electrolyte or internal insulation, they can "dry out" or go "leaky".


Hope this helps.

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Per Ardua Ad Astra
(Through difficulties to the stars)

wibiker

that right but the time is measured in cycles, i think, so the time to charge it is still fractions of a second....all in all it may have been a typo too. 48000mfd is bigger than i have seen.