Replacement capacitor

Can someone recommend a specific (hopefully more modern and reliable) replacement capacitor for the original part, that could start a Boyer equipped engine if the battery is weak? This is for my 73 850, which doesn’t have one in the rectifier/regulator. Thanks.

Any modern capacitor with 50V rating with 4,700 uF so say 10,000 uF 63V would be an upgrade.

As for guaranteeing a battery free start that is a lottery. I have a B44 and a 850 Commando both with the same capacitor and Boyer ignition. Only the B44 will start battery free, the Commando needs a bump start.

If the battery is weak its best to take it out of the circuit completely so all the alternator output goes to the Cap and not the battery.

I would like a specific recommendation for a particular capacitor and where to get it? I’m not electrically knowledgeable and don’t know where to go to get one. Please be specific, if it’s not too much trouble. Maybe best would be an internet link to a particular one. Thanks!

linker48x said:

I would like a specific recommendation for a particular capacitor and where to get it? I’m not electrically knowledgeable and don’t know where to go to get one. Please be specific, if it’s not too much trouble. Maybe best would be an internet link to a particular one. Thanks!

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Readily available from several Norton parts suppliers...heres one from TheBonnevilleShop in the USA:

Tornado said:

Readily available from several Norton parts suppliers...heres one from TheBonnevilleShop in the USA:

Triumph Norton BSA Lucas-type 2MC Ignition Capacitor Battery Eliminator PN# 54170009 G 54483156

The Lucas 2MC capacitor was fitted from 1968 through 1975 on various British motorcycles as an adjunct charging system component, providing an energy

www.thebonnevilleshop.com

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That's a good one. I worked for Kemet for 25 years. Top quality.
Jaydee

Tornado said:

Readily available from several Norton parts suppliers...heres one from TheBonnevilleShop in the USA:

Triumph Norton BSA Lucas-type 2MC Ignition Capacitor Battery Eliminator PN# 54170009 G 54483156

The Lucas 2MC capacitor was fitted from 1968 through 1975 on various British motorcycles as an adjunct charging system component, providing an energy

www.thebonnevilleshop.com

Click to expand...

and the capacitors are not 'motorcycle specific', so you can save by buying them at non-motorcycle suppliers, like this example of the same one:​

KEMET ALT22A103CD063​

$16.72
Price for: Each
https://www.newark.com/kemet/alt22a103cd063/electrolytic-capacitor-long-life/dp/96K6383

can get them with screw connectors instead of the spades ($19.30):
https://www.newark.com/kemet/als31a103de063/cap-10000-f-63v-alu-elec-screw/dp/11AC9893

​

Here is something I wonder about - can anyone explain the reason?

from several sites, including the Bonneville Shop from link above:

"It is important that the capacitor is mounted with the terminals pointing downward."

Maybe so moisture doesn’t collect and bridge across the terminals?

YukoNorton said:

Here is something I wonder about - can anyone explain the reason?

from several sites, including the Bonneville Shop from link above:

"It is important that the capacitor is mounted with the terminals pointing downward."

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I thought the thinking was to keep the fluid electrolyte within covering the internal plates fully.

Perhaps there is air space inside to allow for heat expansion etc and tipping/inverting the unit puts air around the plates.

linker48x said:

Can someone recommend a specific (hopefully more modern and reliable) replacement capacitor for the original part, that could start a Boyer equipped engine if the battery is weak? This is for my 73 850, which doesn’t have one in the rectifier/regulator. Thanks.

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Amazon product ASIN B011NATCBS
Fits the spring, is higher capacity, requires soldering.

Unlikey to kickstart with any capacitor and a Boyer. Bump start on a hill - yes.

marshg246 said:

Amazon product ASIN B011NATCBS
Fits the spring, is higher capacity, requires soldering.

Unlikey to kickstart with any capacitor and a Boyer. Bump start on a hill - yes.

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Is it just Boyer or all Norton EI's?

Ed

Have a Boyer and a capacitor from Paul Goff on a BSA B40. Starts without battery, no problem.

APRRSV said:

Is it just Boyer or all Norton EI's?

Ed

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Some later type EI's have lower minimum voltage limits than original Boyers. I think the Wassel unit I have states 8 VDC limit while boyer is 10 VDC?

APRRSV said:

Is it just Boyer or all Norton EI's?

Ed

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I once, after great effort, got an 850 started with Tri-Spark on the capacitor I showed. I doubt that I would have with the original capacitor.

Some EIs don't fire until the second pulse - having the engine spin fast enough to have enough voltage to wake up the EI and to have it fire is really unlikely with a kickstarter and an EI. When using points, on a well-tuned bike, starting on the capacitor is not a problem. A bump start on a hill should work with any of them and a bump start on level ground will too if you can get moving fast enough before you jump on.

Tornado said:

Some later type EI's have lower minimum voltage limits than original Boyers. I think the Wassel unit I have states 8 VDC limit while boyer is 10 VDC?

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I can add that I once had a hard to start bike after stopping for a fuel up. Lights seemed really dim and flasher signals acting strange. Had a poke under the seat to find my fairly new battery all bloated around the sides. Zener must have failed and the over volts cooked the battery. Was able to start bike with lights off....this was with original 2 MU capacitor and my Wassell EI. On the short ride home, I did notice idle/low rpms dipping whenever I used the turn signals (still incandescent). So unclear if the bloated battery still providing any power to the system to aid in the start...not a true "Battery-less" fire up if so.

Tornado said:

I can add that I once had a hard to start bike after stopping for a fuel up. Lights seemed really dim and flasher signals acting strange. Had a poke under the seat to find my fairly new battery all bloated around the sides. Zener must have failed and the over volts cooked the battery. Was able to start bike with lights off....this was with original 2 MU capacitor and my Wassell EI. On the short ride home, I did notice idle/low rpms dipping whenever I used the turn signals (still incandescent). So unclear if the bloated battery still providing any power to the system to aid in the start...not a true "Battery-less" fire up if so.

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If you left the battery connected you did not start on the capacitor at all. A discharged or partly discharged battery will ensure that the capacitor has no higher voltage than the battery when the battery remains connected.

To start on the capacitor, you disconnect the battery (remove the fuse), start, and connect the battery to charge it.

marshg246 said:

If you left the battery connected you did not start on the capacitor at all. A discharged or partly discharged battery will ensure that the capacitor has no higher voltage than the battery when the battery remains connected.

To start on the capacitor, you disconnect the battery (remove the fuse), start, and connect the battery to charge it.

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How is that meant to work with reg/recs that have the capacitor built in? Are there instructions with them that say to disconnect battery or fuse if flat in order to start on capacitor?

Tornado said:

How is that meant to work with reg/recs that have the capacitor built in? Are there instructions with them that say to disconnect battery or fuse if flat in order to start on capacitor?

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The capacitors in the rec/reg units are small; the MityMax units have two rated at 1,000 which are wired in parallel for a total of 2,000 microfarads. They can start a points equipped bike easily but not so easy with ei. The red wire is positive ground and the black wire can be connected directly to the battery, or to the battery through the igniton switch on the BAT terminal.
I never saw any instructions that state to disconnect the battery to start with just the built-in capacitors.

Wiring Solid state Single phase Regulators​

Tornado said:

How is that meant to work with reg/recs that have the capacitor built in? Are there instructions with them that say to disconnect battery or fuse if flat in order to start on capacitor?

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Actual capacitor ignitions have points and no battery. For instance, the BSA B50MX that my grandson used to race had a set of points, a standard rotor and stator, a coil and PODTronic with capacitor - no Zener, no battery, no ignition switch.

Think of the capacitor as a small battery that charges almost instantly and discharges in less than a second. Also, at kicking speed you'll be real lucky to have 7-8 volts to work with.

You can prove this to yourself easily. Connect the capacitor across the battery (be sure to get the + and - right) with a voltmeter across the capacitor. Almost instantly, the capacitor will have the battery voltage. Disconnect it and it will slowly start losing the charge. Now connect it across a coil that has nothing connected to it - notice how long it takes to discharge. Now think about bringing an EI to life which will charge both coils - the meter will go to zero almost instantly.

The capacitor is only there when the battery is disconnected to smooth out the full-wave DC. With a battery connected, the battery does that.

Some, like the Tri-Spark MOSFET have a small capacitor across the output, but that is NOT for starting, it's just for smoothing. There is a version of PODtronics that has a big enough capacitor for a capacitor ignition like I described above but it is meant for no battery.

From Rider's manual 064135: