Capacitor

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crusadersports said:
Thanks Jim. You have to wonder why they fitted a capacitor to the Mk 3, with its ignition and neutral warning lights?
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I wouldn't say it can't be started with the warning light on, but it does take a mightier kick with the lamp. Try it some time.

I rode an N15 for quite a while with points and no battery. With the two gauge lamps connected so they were on full time it was nearly impossible to start without a hill.

Connecting them back so they only came on with the headlight made it easy to start [-when it felt like it anyway.]
 
slimslowslider said:
True what marshg246 said on the dead battery.
Suffered once from a bad quality new one while on the road with a Mk2, disconnected it, and the bike started one kick on the capacitor only. Again and again.
Seems to me low / bad battery shows up when bike jitters / dies when you brake and/or put blinker on say at traffic lights, an extra 21 / 42 Watts kicks in.
Anyway, I am a Blue Can Fan!

Warning light bulbs on Mk3 are 1.2 Watt so perhaps a bit more than just milliamps?
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1.2 watts would be 100 milliamps. But then a cold filament would pull more than 100 milliamps.

And yes, a run down battery that is connected will make starting nearly impossible. So pull the fuse and start it -then put the fuse in. [or find a big hill]
 
slimslowslider said:
Warning light bulbs on Mk3 are 1.2 Watt so perhaps a bit more than just milliamps?
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Unless I'm having a senior moment, P=IE or I=P/E so I = 1.2/12 = .1 amp = 100 milliamps

In reality, about 13.8 volts, not 12 so 1.2/13.8 = 87 milliamps which is way less than the 2-4 amps drawn by the coils.
 
marshg246 said:
Unless I'm having a senior moment, P=IE or I=P/E so I = 1.2/12 = .1 amp = 100 milliamps

In reality, about 13.8 volts, not 12 so 1.2/13.8 = 87 milliamps which is way less than the 2-4 amps drawn by the coils.
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Yes, but now check the resistance of a cold filament. You will find it draws a lot more current during the short time it takes to warm up.

And you will not have 13.8 volts during cranking.
 
comnoz said:
Yes, but now check the resistance of a cold filament. You will find it draws a lot more current during the short time it takes to warm up.

And you will not have 13.8 volts during cranking.
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Even if triple the current, it's WAY less than the coils draw. There's no doubt that every load takes away from the available current available to charge the coils. Even the bridge rectifier or voltage regulator draws (wastes) some power. And, most old bikes probably have some connectors bleeding off power as well.

In the end, you either bring the coils up to voltage where when disconnected the collapse causes a high enough secondary voltage to create a spark across the coil(s), or not.
 
marshg246 said:
Even if triple the current, it's WAY less than the coils draw. There's no doubt that every load takes away from the available current available to charge the coils. Even the bridge rectifier or voltage regulator draws (wastes) some power. And, most old bikes probably have some connectors bleeding off power as well.

In the end, you either bring the coils up to voltage where when disconnected the collapse causes a high enough secondary voltage to create a spark across the coil(s), or not.
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Agreed,

But I just tested the starting draw of a single warning lamp. It is 2 amps. Cold resistance is ~6 ohms.

The currant tapers down as the lamp comes up to full brightness. That took about .2 seconds with 12 volts applied.

That is enough to take much of the power that would have went to the coil.
 
comnoz said:
Agreed,

But I just tested the starting draw of a single warning lamp. It is 2 amps. Cold resistance is ~6 ohms.

The currant tapers down as the lamp comes up to full brightness. That took about .2 seconds with 12 volts applied.

That is enough to take much of the power that would have went to the coil.
Click to expand...
Somewhere in our testing, there's apples and oranges!

I just bench tested a MKIII console neutral indicator using a battery that is charged to 13.5volts and a highly accurate analog meter.

Bulb 159 ohms
Current 85ma

As far as I know, it's OEM indicators - definitely not LEDs.

My meter is damped so I can't tell about the initial increased resistance and I'm too lazy to get out my o-scope.
 
marshg246 said:
Somewhere in our testing, there's apples and oranges!

I just bench tested a MKIII console neutral indicator using a battery that is charged to 13.5volts and a highly accurate analog meter.

Bulb 159 ohms
Current 85ma

As far as I know, it's OEM indicators - definitely not LEDs.

My meter is damped so I can't tell about the initial increased resistance and I'm too lazy to get out my o-scope.
Click to expand...

I tested it with a Tektronix 465 O-scope, a 1 ohm calibration resistor and a regulated supply set at 12 v.
I used a Tektronix multimeter for the resistance measurement.

The bulb was taken directly from a MK3 console that was in my shelves. It is a number 1445. It may or may not be original.

#1445 Miniature Bulb Ba9S Base - 14.4 Volt 0.135 Amp 1.872 Watt G3-1/2 Miniature Bayonet (BA9S) Base, C-2V Filament Design, 0.70 MSCP. 0.94" (23.88mm) Maximum Overall Length. 7/16" (11mm) Maximum Outer Diameter. 0.50" (12.70mm) Light Center Length (L.C.L.).
 
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My MKII 850 was able to start and get me home after the battery bloated due to overcharging from failed Zenor. This was with the Wassell EI and LED pilot light, headlamp off for the kickstart. I did find engine struggling to keep turning if and when I used the incandescent turn signals on my way home. Good to know the 45" yr old blue tin can still has what it takes.
 
L.A.B. said:
BA9S wouldn't be a standard Mk3 console bulb although I doubt it makes much difference.

https://andover-norton.co.uk/en/shop-drawing/153/console-and-headlamps
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Yeah, definitely not the same as my MK3. So I pulled a bulb from my stock MK3. [and of course broke the clip] It has 13.5 ohms resistance cold.

It pulled just under one amp initially and ramped down in about .3 seconds. [actually a little longer to ramp down]

Much better but still enough to make a difference on starting.
 
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Thanks Jim. Sorry to Ellis if I'm high jacking the thread, but I've also heard a capacitor won't work with a three phase alternator. Is that true?
 
crusadersports said:
Thanks Jim. Sorry to Ellis if I'm high jacking the thread, but I've also heard a capacitor won't work with a three phase alternator. Is that true?
Click to expand...

maylor is correct. It works fine [actually even better] with a 3 phase.
 
Forgot to add in my post that the bike in question had the points replaced by a black Boyer.
 
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.
Had two fail, but there are still loads out there still working. The failed ones were dry inside.
Now using the Tri Spark mosfet rectifier with the single phase stator and get 14.39V at tickover.
 
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