Capacitor

Tornado · Feb 1, 2020

Madnorton said:
I thought the blue original cap has a tiny hole in the plastic crimped in end that has the connectors on it. Would not make sense to mount it with terminals pointing down.

Terminals point down is direction in the s hop manual I posted previously. Mine was on the bike that way for 45 yrs (presumably) and still works fine.

crusadersports · Feb 1, 2020

comnoz said:
maylor is correct. It works fine [actually even better] with a 3 phase.

Thanks mylar and Jim. Both Paul Goff and Al Osborn over here told me a 3 phase won't work with a capacitor, though as it was several years ago I don't remember exactly why.

Jim, what is it about the 3 phase that makes it work better with a capacitor?

Are you saying a Mk 3 with LED warning lights and a 3 phase alternator should start on the kickstart with a flat battery courtesy of the capacitor more easily than with a single phase alternator?

Tornado · Feb 1, 2020

My guess is they were saying reg/rec would need tobe swapped to a three phase typeto match a three phase alt. Some single phase reg/rec's have built in capacitor to replace stock 2MC so that might be part of confusion.

crusadersports · Feb 1, 2020

Tornado said:
My guess is they were saying reg/rec would need tobe swapped to a three phase typeto match a three phase alt. Some single phase reg/rec's have built in capacitor to replace stock 2MC so that might be part of

No, it was said to be incompatible with the complete three phase set up, that is obviously including a compatible 3 phase rectifier and regulator. Yes, some single phase gadgets come with a built in capacitor. I have not seen a three phase combined regulator rectifier with a built in capacitor though...?

comnoz · Feb 1, 2020

A three phase alternator puts out much more power at low rpm than a single phase so kickstarting is easier.

The pulses from a three phase alternator overlap so there is less work for the capacitor to do filling in the dips -so you end up with less variation in the voltage.

Single phase before and after rectifier -has big dips between pulses -the voltage drops all the way to zero between pulses.

Three phase before and after rectifier -voltage does not drop to zero between pulses

Three phase with full wave rectifier is even smoother.

grandpaul · Feb 2, 2020

I don't think a Boyer-equipped bike will start on a 2MC alone...

maylar · Feb 2, 2020

Does anybody know what the nominal capacitance of the 2MC cap is? AN isn't showing a "blue can" any more.

marshg246 · Feb 2, 2020

maylar said:
Does anybody know what the nominal capacitance of the 2MC cap is? AN isn't showing a "blue can" any more.

Not authoritative, but I heard 6,500 uf. I don't buy the ones available today.

The one I use is exactly the same size and shape, fits the spring, is 10,000 uf, 63 volt. I buy them from Amazon: https://www.amazon.com/gp/product/B011NATCBS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

The only negative is that you must solder wires to the terminals.

I have started a Tri-Spark equipped 850 using one. It is a bike that starts on the first kick on battery and on the second or third kick on capacitor.

maylar · Feb 2, 2020

marshg246 said:
Not authoritative, but I heard 6,500 uf. I don't buy the ones available today.

The one I use is exactly the same size and shape, fits the spring, is 10,000 uf, 63 volt. I buy them from Amazon: https://www.amazon.com/gp/product/B011NATCBS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

The only negative is that you must solder wires to the terminals.

I have started a Tri-Spark equipped 850 using one. It is a bike that starts on the first kick on battery and on the second or third kick on capacitor.

Thank you. You saved me the task of finding my old one and breaking out the LCR bridge.

comnoz · Feb 2, 2020

marshg246 said:
Not authoritative, but I heard 6,500 uf. I don't buy the ones available today.

The one I use is exactly the same size and shape, fits the spring, is 10,000 uf, 63 volt. I buy them from Amazon: https://www.amazon.com/gp/product/B011NATCBS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

The only negative is that you must solder wires to the terminals.

I have started a Tri-Spark equipped 850 using one. It is a bike that starts on the first kick on battery and on the second or third kick on capacitor.

I have measured used 2mc's at around that 6500 uF area.
I have a 10,000 uF on my bike.
With the EFI on my bike you don't kickstart it with a dead battery. But a good hill will start it.

HRD · Feb 2, 2020

ELLIS said:
I don't know that as i have not tried it. Just bought a new capacitor, only £16. The old one i replaced was the original so 45 years old. Fitted it on the bike and went for a short ride to charge it up, unplugged the battery and it started first kick. (result)

ELLIS

You were ripped off,16 quid for a capacitor,should have gone to an electronics supply outlet .You would have had to use your old mounting spring .
Paul

crusadersports · Feb 3, 2020

comnoz said:
A three phase alternator puts out much more power at low rpm than a single phase so kickstarting is easier.

The pulses from a three phase alternator overlap so there is less work for the capacitor to do filling in the dips -so you end up with less variation in the voltage.

Single phase before and after rectifier -has big dips between pulses -the voltage drops all the way to zero between pulses.
View attachment 14208
Three phase before and after rectifier -voltage does not drop to zero between pulses
View attachment 14209

Three phase with full wave rectifier is even smoother.

Wow. Thanks Jim. That makes sense to me. If the whole point of 3 phase is more power at low rpm, then that should also apply at kick starting speeds, I'd have thought.

What effect does electronic ignition have on starting on the capacitor alone?

comnoz · Feb 3, 2020

crusadersports said:
Wow. Thanks Jim. That makes sense to me. If the whole point of 3 phase is more power at low rpm, then that should also apply at kick starting speeds, I'd have thought.

What effect does electronic ignition have on starting on the capacitor alone?

Yes a 3 phase makes more power at kickstarting speed.

The capacitor alone will not start the engine. Alternator output with a capacitor is needed.

Most electronic ignitions I have tried could be started without a battery although it generally was tougher. A stiff kick and good mixture was needed.

I have tried Boyer analogue, Trispark and Rita successfully.

All I could get with a Power-arc without a battery was a kickback.

I have not tried Pazon or Boyer digital ignitions.

I was using a 3 phase alternator with a stock capacitor on a 74-850 for the tests. The battery fuse was pulled.

crusadersports · Feb 4, 2020

comnoz said:
Yes a 3 phase makes more power at kickstarting speed.

The capacitor alone will not start the engine. Alternator output with a capacitor is needed.

Most electronic ignitions I have tried could be started without a battery although it generally was tougher. A stiff kick and good mixture was needed.

I have tried Boyer analogue, Trispark and Rita successfully.

All I could get with a Power-arc without a battery was a kickback.

I have not tried Pazon or Boyer digital ignitions.

I was using a 3 phase alternator with a stock capacitor on a 74-850 for the tests. The battery fuse was pulled.

Thanks again Jim for the benefit of your experience. And yes, I did mean starting on the capacitor via the alternator, as opposed to via a charged battery.

Why did you remove the fuse? And is there anyway of testing if the bike will start on the capacitor without deliberately flattening the battery to see if it will still go?

maylar · Feb 4, 2020

crusadersports said:
Why did you remove the fuse? And is there anyway of testing if the bike will start on the capacitor without deliberately flattening the battery to see if it will still go?

A flat battery would drag the charging system down, you'd never be able to start the motor. Remove the fuse to take the battery out of the circuit. Replace the fuse once it's running, to charge the battery.

comnoz · Feb 4, 2020

Maylar is correct.
The only time you are likely to be able to start the motor with a very low battery is to disconnect it. [by removing the fuse]

But if the battery is completely dead and has been dead for some time, or if the battery has failed open, it may not have the ability to accept a charge immediately. In that case it would not load the alternator, so the bike may start.

crusadersports · Feb 4, 2020

comnoz said:
Maylar is correct.
The only time you are likely to be able to start the motor with a very low battery is to disconnect it. [by removing the fuse]

But if the battery is completely dead and has been dead for some time, or if the battery has failed open, it may not have the ability to accept a charge immediately. In that case it would not load the alternator, so the bike may start.

Thanks Maylar and Jim. Removing the fuse isolates the dead or flat battery. In other words, I can test if the bike will start on the capacitor simply by removing the fuse?

Will you get a better spark from a more modern style of capacitor, or is one as good as good as another? I know they can fail with age and leak backwards, I mean when buying a new one.

comnoz · Feb 4, 2020

crusadersports said:
Thanks Maylar and Jim. Removing the fuse isolates the dead or flat battery. In other words, I can test if the bike will start on the capacitor simply by removing the fuse?

Will you get a better spark from a more modern style of capacitor, or is one as good as good as another? I know they can fail with age and leak backwards, I mean when buying a new one.

If you are running a 3 phase you can get a small added benefit from a little larger capacitor. I would not go over 10,000 uF

With a single phase I saw no benefit.

A larger capacitor can hold more power but it also takes longer to charge -so the pulse from a single phase alternator ends up with the same power stored.

comnoz · Feb 4, 2020

crusadersports said:
Thanks Maylar and Jim. Removing the fuse isolates the dead or flat battery. In other words, I can test if the bike will start on the capacitor simply by removing the fuse?

Yes.

crusadersports · Feb 6, 2020

comnoz said:
If you are running a 3 phase you can get a small added benefit from a little larger capacitor. I would not go over 10,000 uF

With a single phase I saw no benefit.

A larger capacitor can hold more power but it also takes longer to charge -so the pulse from a single phase alternator ends up with the same power stored.

That's great Jim, many thanks. To return to the OP, a Mk 3 may or may not start on the capacitor. But if you have a 3 phase charging system, LEDS in the warning lights and electronic ignition you stand half a chance!

Capacitor

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