Detecting points opening on a magneto question

[eatmorepies]

Hello

I've been asked to help set the ignition points on a 1950 Triumph
motorcycle - it has a magneto. I want to detect when the points open. My
first two circuits have attempted to detect the small (around 2.4R)
resistance change. Both circuits were based on potential dividers, one with
a NAND gate and the second with a bridge circuit and an op-amp. To keep the
current drawn from the PP3 low I had to use reistors in the order of low k
values - the tiny resistance change is thus hard to detect.

Now for my question. The magneto is basically a low inductance coil that is
or is not shorted by the contact breaker - so how do I set about detecting
the change from shorted to small inductance?

There's a capacitor across the points, I did think of detecting a current
spike as the PP3 charged C when the points open. I'd like to try detecting
the coil first. Any help would be appreciated.

John

 

[Jamie]

eatmorepies wrote:

Hello

I've been asked to help set the ignition points on a 1950 Triumph
motorcycle - it has a magneto. I want to detect when the points open. My
first two circuits have attempted to detect the small (around 2.4R)
resistance change. Both circuits were based on potential dividers, one
with a NAND gate and the second with a bridge circuit and an op-amp. To
keep the current drawn from the PP3 low I had to use reistors in the
order of low k values - the tiny resistance change is thus hard to detect.

Now for my question. The magneto is basically a low inductance coil that
is or is not shorted by the contact breaker - so how do I set about
detecting the change from shorted to small inductance?

There's a capacitor across the points, I did think of detecting a
current spike as the PP3 charged C when the points open. I'd like to try
detecting the coil first. Any help would be appreciated.

John


The coil is very inductive. Inject a high freq signal into the coil side

of the points and use a AC to DC detect circuit from that signal at the
point where it is connected.

With the induction there, you'll see the signal until the points close.

you'll need to factor in the cap that is on the points too, so don't get
to high in freq..

Most likely something in the range of 1khz from a 555 timer will do it.

Make sure you put a back to back Zener for protection so not to damage
your input sensing circuit.



Jamie

 

[John Larkin]

On Sun, 4 Dec 2011 10:31:34 -0000, "eatmorepies"
<jcpieman@lineone.net> wrote:

Hello

I've been asked to help set the ignition points on a 1950 Triumph
motorcycle - it has a magneto. I want to detect when the points open. My
first two circuits have attempted to detect the small (around 2.4R)
resistance change. Both circuits were based on potential dividers, one with
a NAND gate and the second with a bridge circuit and an op-amp. To keep the
current drawn from the PP3 low I had to use reistors in the order of low k
values - the tiny resistance change is thus hard to detect.

Now for my question. The magneto is basically a low inductance coil that is
or is not shorted by the contact breaker - so how do I set about detecting
the change from shorted to small inductance?

There's a capacitor across the points, I did think of detecting a current
spike as the PP3 charged C when the points open. I'd like to try detecting
the coil first. Any help would be appreciated.

John

Are you doing static timing? Why not run the beast and use a strobe?

For static timing, a good ohmmeter should resolve the closure. If not,
use an inductance meter.

Or run a little current through the points, 50 mA maybe, and measure
the voltage drop directly across the points, essentially a 4-wire
ohmmeter.

John

 

[Tim]

On Sun, 04 Dec 2011 10:31:34 +0000, eatmorepies wrote:

Hello

I've been asked to help set the ignition points on a 1950 Triumph
motorcycle - it has a magneto. I want to detect when the points open. My
first two circuits have attempted to detect the small (around 2.4R)
resistance change. Both circuits were based on potential dividers, one
with a NAND gate and the second with a bridge circuit and an op-amp. To
keep the current drawn from the PP3 low I had to use reistors in the
order of low k values - the tiny resistance change is thus hard to
detect.

Now for my question. The magneto is basically a low inductance coil that
is or is not shorted by the contact breaker - so how do I set about
detecting the change from shorted to small inductance?

There's a capacitor across the points, I did think of detecting a
current spike as the PP3 charged C when the points open. I'd like to try
detecting the coil first. Any help would be appreciated.

1: Why in heck can't you get it running and use a timing light?

2: Look for contact closure visually, or if there's a pigtail that can be
disconnected do so, and use an ohmmeter or just a light and a battery.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

 

[Tim]

On Sun, 04 Dec 2011 14:05:50 -0600, Tim wrote:

On Sun, 04 Dec 2011 10:31:34 +0000, eatmorepies wrote:

Hello

I've been asked to help set the ignition points on a 1950 Triumph
motorcycle - it has a magneto. I want to detect when the points open.
My first two circuits have attempted to detect the small (around 2.4R)
resistance change. Both circuits were based on potential dividers, one
with a NAND gate and the second with a bridge circuit and an op-amp. To
keep the current drawn from the PP3 low I had to use reistors in the
order of low k values - the tiny resistance change is thus hard to
detect.

Now for my question. The magneto is basically a low inductance coil
that is or is not shorted by the contact breaker - so how do I set
about detecting the change from shorted to small inductance?

There's a capacitor across the points, I did think of detecting a
current spike as the PP3 charged C when the points open. I'd like to
try detecting the coil first. Any help would be appreciated.

1: Why in heck can't you get it running and use a timing light?

2: Look for contact closure visually, or if there's a pigtail that can
be disconnected do so, and use an ohmmeter or just a light and a
battery.

3: RTFM: find a service manual and do what it says. It's amazing what
following directions can do for the reliability of equipment that you're
operating.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

 

[eatmorepies]

"Tim" <tim@seemywebsite.please> wrote in message
news:Cp-dnQH7rOmtTkbTnZ2dnUVZ_qmdnZ2d@web-ster.com...

On Sun, 04 Dec 2011 14:05:50 -0600, Tim wrote:

On Sun, 04 Dec 2011 10:31:34 +0000, eatmorepies wrote:

Hello

I've been asked to help set the ignition points on a 1950 Triumph
motorcycle - it has a magneto. I want to detect when the points open.
My first two circuits have attempted to detect the small (around 2.4R)
resistance change. Both circuits were based on potential dividers, one
with a NAND gate and the second with a bridge circuit and an op-amp. To
keep the current drawn from the PP3 low I had to use reistors in the
order of low k values - the tiny resistance change is thus hard to
detect.

Now for my question. The magneto is basically a low inductance coil
that is or is not shorted by the contact breaker - so how do I set
about detecting the change from shorted to small inductance?

There's a capacitor across the points, I did think of detecting a
current spike as the PP3 charged C when the points open. I'd like to
try detecting the coil first. Any help would be appreciated.

1: Why in heck can't you get it running and use a timing light?

2: Look for contact closure visually, or if there's a pigtail that can
be disconnected do so, and use an ohmmeter or just a light and a
battery.

3: RTFM: find a service manual and do what it says. It's amazing what
following directions can do for the reliability of equipment that you're
operating.

--
Tim Wescott
Control system and signal processing consulting

www.wescottdesign.com

This is a 1950 motorcycle using a magneto.

1. The manual suggests testing for the opening of the points using a small
piece of cigarette paper. This method gives +/- 10 degrees of uncertainty in
the timing. A visual method would be even worse.

2. It's a magneto - no pigtail. These things are fully enclosed with just
the high tension lead(s) emerging. You get at the points by removing a small
cover. You can't even see the capacitor, coils or any wiring without
disassembling it - which requires special tools.

Try Googling magneto and have a read.

John

 

[eatmorepies]

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message
newsxLCq.8421$c27.3557@newsfe22.iad...

eatmorepies wrote:
Hello

I've been asked to help set the ignition points on a 1950 Triumph
motorcycle - it has a magneto. I want to detect when the points open. My
first two circuits have attempted to detect the small (around 2.4R)
resistance change. Both circuits were based on potential dividers, one
with a NAND gate and the second with a bridge circuit and an op-amp. To
keep the current drawn from the PP3 low I had to use reistors in the
order of low k values - the tiny resistance change is thus hard to
detect.

Now for my question. The magneto is basically a low inductance coil that
is or is not shorted by the contact breaker - so how do I set about
detecting the change from shorted to small inductance?

There's a capacitor across the points, I did think of detecting a current
spike as the PP3 charged C when the points open. I'd like to try
detecting the coil first. Any help would be appreciated.

John


The coil is very inductive. Inject a high freq signal into the coil side
of the points and use a AC to DC detect circuit from that signal at the
point where it is connected.

With the induction there, you'll see the signal until the points close.

you'll need to factor in the cap that is on the points too, so don't get
to high in freq..

Most likely something in the range of 1khz from a 555 timer will do it.

Make sure you put a back to back Zener for protection so not to damage
your input sensing circuit.



Jamie

This seems to be the way to go. Thanks.

John

 

[Rich Grise]

eatmorepies wrote:

I've been asked to help set the ignition points on a 1950 Triumph
motorcycle - it has a magneto. I want to detect when the points open. My
first two circuits have attempted to detect the small (around 2.4R)
resistance change. Both circuits were based on potential dividers, one
with a NAND gate and the second with a bridge circuit and an op-amp. To
keep the current drawn from the PP3 low I had to use reistors in the order
of low k values - the tiny resistance change is thus hard to detect.

Now for my question. The magneto is basically a low inductance coil that
is or is not shorted by the contact breaker - so how do I set about
detecting the change from shorted to small inductance?

There's a capacitor across the points, I did think of detecting a current
spike as the PP3 charged C when the points open. I'd like to try detecting
the coil first. Any help would be appreciated.

In the olden days, we used to set the points by just setting the gap using

a feeler gauge.

Can a dwell meter handle a magneto?

Good Luck!
Rich

 

[John Larkin]

On Sun, 4 Dec 2011 20:45:49 -0000, "eatmorepies"
<jckipper@lineone.net> wrote:

"Tim" <tim@seemywebsite.please> wrote in message
news:Cp-dnQH7rOmtTkbTnZ2dnUVZ_qmdnZ2d@web-ster.com...
On Sun, 04 Dec 2011 14:05:50 -0600, Tim wrote:

On Sun, 04 Dec 2011 10:31:34 +0000, eatmorepies wrote:

Hello

I've been asked to help set the ignition points on a 1950 Triumph
motorcycle - it has a magneto. I want to detect when the points open.
My first two circuits have attempted to detect the small (around 2.4R)
resistance change. Both circuits were based on potential dividers, one
with a NAND gate and the second with a bridge circuit and an op-amp. To
keep the current drawn from the PP3 low I had to use reistors in the
order of low k values - the tiny resistance change is thus hard to
detect.

Now for my question. The magneto is basically a low inductance coil
that is or is not shorted by the contact breaker - so how do I set
about detecting the change from shorted to small inductance?

There's a capacitor across the points, I did think of detecting a
current spike as the PP3 charged C when the points open. I'd like to
try detecting the coil first. Any help would be appreciated.

1: Why in heck can't you get it running and use a timing light?

2: Look for contact closure visually, or if there's a pigtail that can
be disconnected do so, and use an ohmmeter or just a light and a
battery.

3: RTFM: find a service manual and do what it says. It's amazing what
following directions can do for the reliability of equipment that you're
operating.

--
Tim Wescott
Control system and signal processing consulting


www.wescottdesign.com

This is a 1950 motorcycle using a magneto.

1. The manual suggests testing for the opening of the points using a small
piece of cigarette paper. This method gives +/- 10 degrees of uncertainty in
the timing. A visual method would be even worse.

2. It's a magneto - no pigtail. These things are fully enclosed with just
the high tension lead(s) emerging. You get at the points by removing a small
cover. You can't even see the capacitor, coils or any wiring without
disassembling it - which requires special tools.

Try Googling magneto and have a read.

John

An audio oscillator of some sort and an earbud would be cool. You
could hear it open and close.

It might be possible to measure the points opening and closing by
measuring something on the HT wire. The audio thing might do that.

Hey: get anything that plays music or a radio station into an earbud,
like one of those FM radios you can buy at Walgreens for $3. Arrange
for the points to short the bud. I bet you can hear the open/closed
difference.

John

 

[Jamie]

Rich Grise wrote:

eatmorepies wrote:

I've been asked to help set the ignition points on a 1950 Triumph
motorcycle - it has a magneto. I want to detect when the points open. My
first two circuits have attempted to detect the small (around 2.4R)
resistance change. Both circuits were based on potential dividers, one
with a NAND gate and the second with a bridge circuit and an op-amp. To
keep the current drawn from the PP3 low I had to use reistors in the order
of low k values - the tiny resistance change is thus hard to detect.

Now for my question. The magneto is basically a low inductance coil that
is or is not shorted by the contact breaker - so how do I set about
detecting the change from shorted to small inductance?

There's a capacitor across the points, I did think of detecting a current
spike as the PP3 charged C when the points open. I'd like to try detecting
the coil first. Any help would be appreciated.


In the olden days, we used to set the points by just setting the gap using
a feeler gauge.

Can a dwell meter handle a magneto?

Good Luck!
Rich

Looking back over the years, I find it amazing that the point system

worked as well as it did.

Taking into account for worn cam shafts, loose cam bearings, cam
pads, spring tension etc.. And let us not forget the crappiest
condensers ever made along with the normally stripped out screws holding
it all in.

Jamie

 

[Jasen Betts]

On 2011-12-04, eatmorepies <jcpieman@lineone.net> wrote:

Hello

I've been asked to help set the ignition points on a 1950 Triumph
motorcycle - it has a magneto. I want to detect when the points open. My
first two circuits have attempted to detect the small (around 2.4R)
resistance change. Both circuits were based on potential dividers, one with
a NAND gate and the second with a bridge circuit and an op-amp. To keep the
current drawn from the PP3 low I had to use reistors in the order of low k
values - the tiny resistance change is thus hard to detect.

battery life is less of a problem is you use a low voltage op-amp (LM324)
or comparitor (LM319) and a 3V supply

Now for my question. The magneto is basically a low inductance coil that is
or is not shorted by the contact breaker - so how do I set about detecting
the change from shorted to small inductance?

You could use a higher frequency than DC, say 10KHZ, the magneto will
have a higher impedance at that frequency.

.-->probe
10Khz | |\ /|
--------[100R]---+------------| >========| | speaker
------------------------------|/ \|
|
--- audio amp
///

There's a capacitor across the points, I did think of detecting a current
spike as the PP3 charged C when the points open.

if the flywheel magnet is in place there will be other effects tat
depend on the speed of rotation etc.

I'd like to try detecting
the coil first. Any help would be appreciated.

Disconnect the magneto from the points and just measure resistance?



put a coil (old degausing coil? 100 turns of telephone wire? a spool
of hook-up wire?) near the magnetto supplied with stepped-down AC or an audio signal and connect an amplifier
and loudspeaker (pc speakers) to the plug terminal and chassis?

when the points oen the sound should get louder.

--
⚂⚃ 100% natural

--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---

 

[Tim Wescott]

On Sun, 04 Dec 2011 15:17:15 -0800, Rich Grise wrote:

eatmorepies wrote:

I've been asked to help set the ignition points on a 1950 Triumph
motorcycle - it has a magneto. I want to detect when the points open.
My first two circuits have attempted to detect the small (around 2.4R)
resistance change. Both circuits were based on potential dividers, one
with a NAND gate and the second with a bridge circuit and an op-amp. To
keep the current drawn from the PP3 low I had to use reistors in the
order of low k values - the tiny resistance change is thus hard to
detect.

Now for my question. The magneto is basically a low inductance coil
that is or is not shorted by the contact breaker - so how do I set
about detecting the change from shorted to small inductance?

There's a capacitor across the points, I did think of detecting a
current spike as the PP3 charged C when the points open. I'd like to
try detecting the coil first. Any help would be appreciated.

In the olden days, we used to set the points by just setting the gap
using a feeler gauge.

Can a dwell meter handle a magneto?

That sets dwell, but not the main timing. Changing the dwell does change
the opening time of the points, but you're generally less concerned about
getting dwell dead nuts on than you are about getting the spark timing
right.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

 

[Rich Grise]

Tim Wescott wrote:

On Sun, 04 Dec 2011 15:17:15 -0800, Rich Grise wrote:

In the olden days, we used to set the points by just setting the gap
using a feeler gauge.

Can a dwell meter handle a magneto?

That sets dwell, but not the main timing. Changing the dwell does change
the opening time of the points, but you're generally less concerned about
getting dwell dead nuts on than you are about getting the spark timing
right.

(slapping forehead) Of course! Duh! We'd set the timing by turning

the distributor itself!

Sorry for the brain fart.
Rich