We seem to have less electronics expertise than in the past, what
hppened to Andrew Gabriel?

I have one of the cheap 2T 650W gensets based on the Yamaha 50cc
capacitively excited generator handed me by a mate to fix, a NUTool .

It won't start because the HT is too weak to produce a spark and I
currently put that down to loss of magnetism in the flywheel magnets.

These things are cheap low quality copies and generally not worth
repairing but I also have my first machine saw from 1974 that exhibits
the same problem. They are both capacitor discharge ignition.

Any suggestions for a simple battery powered circuit which could sense
the trailing edge of the pulse to the coil circuit I and use that to cut
the current running through the coil and produce a decent spark?

AJH pretended :
It won't start because the HT is too weak to produce a spark and I currently
put that down to loss of magnetism in the flywheel magnets.

Magneto ignition. Could you not simply re-magnetise them?

In article ,
AJH wrote:
We seem to have less electronics expertise than in the past, what
hppened to Andrew Gabriel?

I have one of the cheap 2T 650W gensets based on the Yamaha 50cc
capacitively excited generator handed me by a mate to fix, a NUTool .

It won't start because the HT is too weak to produce a spark and I
currently put that down to loss of magnetism in the flywheel magnets.

These things are cheap low quality copies and generally not worth
repairing but I also have my first machine saw from 1974 that exhibits
the same problem. They are both capacitor discharge ignition.

Any suggestions for a simple battery powered circuit which could sense
the trailing edge of the pulse to the coil circuit I and use that to cut
the current running through the coil and produce a decent spark?

I'd guess you want a BIP 373. It's a Bosch IC in the shape of a TO220
which takes 5v in (usually from a microprocessor), and drives a coil
direct. You can usually find them sold singly on Ebay (under MegaSquirt)
or from an MS dealer online. May be tricky to source from the more common
electronics suppliers.

--
*ATHEISM IS A NON-PROPHET ORGANIZATION.

Dave Plowman London SW
To e-mail, change noise into sound.

On Thursday, 9 April 2020 13:24:35 UTC+1, AJH wrote:
Any suggestions for a simple battery powered circuit which could sense
the trailing edge of the pulse to the coil circuit I and use that to cut
the current running through the coil and produce a decent spark?

Anything like this?

https://www.rmcybernetics.com/scienc...on-coil-driver

But I'd be the first to admit I have no idea what you're talking about...

Owain

AJH wrote:
We seem to have less electronics expertise than in the past, what
hppened to Andrew Gabriel?

I have one of the cheap 2T 650W gensets based on the Yamaha 50cc
capacitively excited generator handed me by a mate to fix, a NUTool .

It won't start because the HT is too weak to produce a spark and I
currently put that down to loss of magnetism in the flywheel magnets.

These things are cheap low quality copies and generally not worth
repairing but I also have my first machine saw from 1974 that exhibits
the same problem. They are both capacitor discharge ignition.

Any suggestions for a simple battery powered circuit which could sense
the trailing edge of the pulse to the coil circuit I and use that to cut
the current running through the coil and produce a decent spark?

CDI Capacitor Discharge Ignition Circuit Demo

https://www.youtube.com/watch?v=0yK3Opq_i0M

Primary side V
| ___
| ___| |
| ___| |
| ___| | ___
| ___| \ ___|
| ___| | ___|
| __| \_|
+-------------------------------------------- Time
excitor charges C, ^
SCR dumps to coil |
spark on
falling edge

The excitor cannot raise the capacitor voltage too
high, or the output of the ignition coil could rise
to too-high a voltage and damage the insulation in
the ignition coil. As drawn in the Youtube video,
the circuit does not have any regulation and runs
open loop. And relies on the ratio of excitor pulses
to firing pulse, for correct operation. There are
ways to fix this (add some regulation), but those
ways would also add failure modes to the design.

Since the SCR drains the capacitor exactly (SCR
only stops conducting at a low voltage on that
falling edge), the capacitor starts from a
known state after a firing. It can't "drift off"
or anything. The charging stairstep starts
at close to zero.

So then the question would be, what needs fixing
in the circuit ? Which part has failed, and what
do we need to fix ? If a semiconductor fails short
(as diode-like devices tend to do), a failure to
function could just be a semiconductor problem.
It doesn't always have to be a magnetics failure.

It's the kind of circuit, you'd need to see an oscilloscope
picture of it working, to know how to deal with failures later,
as the picture would tell you what a "normal" peak voltage
on the primary is. The ignition coil has some turns ratio.
You know you need a certain voltage to make a sufficiently
hot spark, and so on. But seeing the waveform, and
comparing to the current waveform, hints at how big
a "fix" is needed, and what's going on. If the thing
remains "flat" as you try to start it, then something
has failed short.

I've been thrown across the basement floor by a
spark coil, so you don't have to tell me about
safety or anything :-) When I came to, my first
question was "how did I get over here?". That's
how far the shock made me jump. Stay safe...

Paul

On Thu, 09 Apr 2020 14:54:57 +0100, Harry Bloomfield, Esq.
wrote:

Magneto ignition. Could you not simply re-magnetise them?

A lot of youtube videos show how to do this (though often using some special
equipment). Also, some suggest demagnetising the coil yoke...


Thomas Prufer

On 09/04/2020 18:43, Paul wrote:

CDI Capacitor Discharge Ignition Circuit Demo

https://www.youtube.com/watch?v=0yK3Opq_i0M

Primary side V
|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* ___
|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* ___|Â*Â* |
|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* ___|Â*Â*Â*Â*Â*Â* |
|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* ___|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* |Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* ___
|Â*Â*Â*Â*Â*Â*Â* ___|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* \Â*Â*Â*Â*Â*Â* ___|
|Â*Â*Â* ___|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* |Â*Â* ___|
| __|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â * \_|
+-------------------------------------------- Time
Â* excitor charges C,Â*Â*Â*Â*Â*Â*Â*Â* ^
Â* SCR dumps to coilÂ*Â*Â*Â*Â*Â*Â*Â*Â* |
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* Â* spark on

Thanks Paul, this system is a bit later than that I think, I would have
to pull the flywheel to see, the magnets are on the inside of the
flywheel and it rotates round the excitor coil, Difference is the
exciter and sensor are all in one. I think the trailing edge current
from the discharge is what should cause the spark but because the
magnets are weak the current generated in the primary isn't high
enough to cause the voltage in the secondary to creat the spark.

Hence I was looking for something to switch the current in the coil
primary from a 12V battery off when it senses that trailing edge.

I was hoping someone would know of a simple circuit where the present
live feed from the CD was taken to ground by a suitable resistor and the
voltage across the resistor would cause a current to flow therough the
base of a transistor which would switch the current through the coil
off and reset.

On 09/04/2020 15:17, Dave Plowman (News) wrote:
In article ,
AJH wrote:


I'd guess you want a BIP 373. It's a Bosch IC in the shape of a TO220
which takes 5v in (usually from a microprocessor), and drives a coil
direct. You can usually find them sold singly on Ebay (under MegaSquirt)
or from an MS dealer online. May be tricky to source from the more common
electronics suppliers.


Looks interesting Dave and reasonably cheap but I would need a circuit
diagram to know how to get it to work in the situation

In article ,
AJH wrote:
On 09/04/2020 15:17, Dave Plowman (News) wrote:
In article ,
AJH wrote:


I'd guess you want a BIP 373. It's a Bosch IC in the shape of a TO220
which takes 5v in (usually from a microprocessor), and drives a coil
direct. You can usually find them sold singly on Ebay (under MegaSquirt)
or from an MS dealer online. May be tricky to source from the more common
electronics suppliers.


Looks interesting Dave and reasonably cheap but I would need a circuit
diagram to know how to get it to work in the situation

I'd guess it depends on how the original coil was triggered. The BIP is
designed for logic pulses. Anything much greater would need to be clipped.

It couldn't be simpler, circuit wise. Logic pulse straight in to Pin1. Pin
3 to ground, Pin2 to the coil. Other side of the coil to 12v. It's a
fairly bomb proof device with short circuit etc protection.

--
*What hair colour do they put on the driver's license of a bald man? *

Dave Plowman London SW
To e-mail, change noise into sound.

This is like coming in on episode 8 of a 20 episode serial!
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
Harry Bloomfield; "Esq." wrote in
message ...
AJH pretended :
It won't start because the HT is too weak to produce a spark and I
currently put that down to loss of magnetism in the flywheel magnets.

Magneto ignition. Could you not simply re-magnetise them?

Are we sure the coil is not just knackered?
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Dave Plowman (News)" wrote in message
...
In article ,
AJH wrote:
We seem to have less electronics expertise than in the past, what
hppened to Andrew Gabriel?

I have one of the cheap 2T 650W gensets based on the Yamaha 50cc
capacitively excited generator handed me by a mate to fix, a NUTool .

It won't start because the HT is too weak to produce a spark and I
currently put that down to loss of magnetism in the flywheel magnets.

These things are cheap low quality copies and generally not worth
repairing but I also have my first machine saw from 1974 that exhibits
the same problem. They are both capacitor discharge ignition.

Any suggestions for a simple battery powered circuit which could sense
the trailing edge of the pulse to the coil circuit I and use that to cut
the current running through the coil and produce a decent spark?

I'd guess you want a BIP 373. It's a Bosch IC in the shape of a TO220
which takes 5v in (usually from a microprocessor), and drives a coil
direct. You can usually find them sold singly on Ebay (under MegaSquirt)
or from an MS dealer online. May be tricky to source from the more common
electronics suppliers.

--
*ATHEISM IS A NON-PROPHET ORGANIZATION.

Dave Plowman London SW
To e-mail, change noise into sound.

AJH wrote:
On 09/04/2020 18:43, Paul wrote:

CDI Capacitor Discharge Ignition Circuit Demo

https://www.youtube.com/watch?v=0yK3Opq_i0M

Primary side V
| ___
| ___| |
| ___| |
| ___| | ___
| ___| \ ___|
| ___| | ___|
| __| \_|
+-------------------------------------------- Time
excitor charges C, ^
SCR dumps to coil |
spark on

Thanks Paul, this system is a bit later than that I think, I would have
to pull the flywheel to see, the magnets are on the inside of the
flywheel and it rotates round the excitor coil, Difference is the
exciter and sensor are all in one. I think the trailing edge current
from the discharge is what should cause the spark but because the
magnets are weak the current generated in the primary isn't high
enough to cause the voltage in the secondary to creat the spark.

Hence I was looking for something to switch the current in the coil
primary from a 12V battery off when it senses that trailing edge.

I was hoping someone would know of a simple circuit where the present
live feed from the CD was taken to ground by a suitable resistor and the
voltage across the resistor would cause a current to flow therough the
base of a transistor which would switch the current through the coil
off and reset.

To make a bipolar transistor work, you need to know
whether the pulse is negative going or positive going.
To use the pulse directly, would likely be ugly, and
involve a lot of "luck" regarding the incoming pulse shape.

The pulse shape probably does not make an ideal
"gate" for the job. The gating period might need
to be longer than the SCR firing period. The transistor
has to be held in the state we want, until the SCR is
finished.

For example, a monostable might produce a pulse of a
known length. And then the shape of the pulse
signal is rendered slightly less important. And
when using the monostable, we can set up the
circuit so that the monostable delivers the
right amplitude of signal to the transistor,
to make it saturate when on, and go open when off.

You can see examples here of the idea. The 555 isn't exactly
the friendliest chip, but the article shows how it
takes a short input pulse and makes it longer. There
are some other circuits that might have a bit fewer
pathologies. (I think I still have some 4538 chips here.)
You can see in one diagram, how they show the 555 used
with an NPN transistor, and in the other case, a PNP
transistor. The signal to the transistor base has
to be slightly different for those.

https://www.electronics-tutorials.ws...555_timer.html

It's possible the 555 runs between 5V and 15V. I'd have
to check the datasheet. This constrains how the
circuit could be kept simple. If the voltage the
excitor is working with, is well outside this range,
we might need to come up with another idea.

That's why I mentioned having an oscilloscope picture
of the thing when its running, to get some idea whether
the project is relatively easy, or absurdly hard.

If they kept the primary voltage low, they might be
able to use cheaper components to switch the primary.
But perhaps the turns ratio on the coil would have
to be extended, and it would take many many additional
feet of wire while making the transformer. If the
primary drive was say, 100V, then the turns ratio can be
a bit lower. If the primary was 100V to 1000V, maybe
I could use an IGBT to switch the exciter replacement source.

You probably have a much better feel for this circuit
than I do. I don't really know what to expect, and
I also don't expect the components in the thing
are well marked, so we can't get any hints from that.
If you found a 1000V SCR, we might assume one thing.
And if we found a 40V BJT, we might assume another.
If the capacitor only had a 25V WVDC, then the
555 circuit is looking more feasible. Maybe our
555 won't be destroyed by kickback from the
transformer :-)

When I made a 15kV supply once, using a couple 2N3055,
a flyback and a voltage doubler, the kickback from
the action on the primary, blew out the feedback
loop in a Hewlett Packard 10 amp bench supply.
They had used insulated gate MOSFETs (diff pair), with
only about 40V gate rating, and I guess the switching
transients got in there. The instrumentation guy
invited me into his little repair room, to show
me what I blew up, and how he was installing a new
one (the transistor he was installing is easily
damaged by ESD, and it has a shorting strap that
stays around the four legs of it, until it's soldered
into a circuit). I ran my high voltage supply off
two 6V lantern batteries from then on.

The best part of my 15kV supply ? Never getting
a shock from it.

Paul

Many many years ago my then boss bought his son a Benelli motorcycle with an electronic ignition module. It failed and even in those far off days a replacement cost over a hundred pounds. He brought it to me and we discovered it was cast in resin, making it impossible to investigate. Fortunately a trip to the local reference library provided a photocopied circuit diagram and I was able to etch a pcb and create a replacement for only a few pounds.
I've not spent a lot of time looking at specs but eBay search for electronic ignition could be a useful starting point for you.

On 10/04/2020 06:33, Brian Gaff (Sofa 2) wrote:
Are we sure the coil is not just knackered?
Brian

It may be, it shows a few ohms resistance and draws over 250mA with a
1.5 cell across it and doesn't spark the plug when the circuit is
broken.. I'll need to pull one off another to check but I don't have one
here atm.

In article ,
AJH wrote:
On 10/04/2020 06:33, Brian Gaff (Sofa 2) wrote:
Are we sure the coil is not just knackered?
Brian

It may be, it shows a few ohms resistance and draws over 250mA with a
1.5 cell across it and doesn't spark the plug when the circuit is
broken.. I'll need to pull one off another to check but I don't have one
here atm.

Ignition systems generally run at a few amps average. Try flicking a 12v
car battery etc across the coil while looking for a spark.

Coils ain't designed to have volts applied constantly for any length of
time.

--
*Why is the man who invests all your money called a broker?

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
AJH wrote:
On 10/04/2020 06:33, Brian Gaff (Sofa 2) wrote:
Are we sure the coil is not just knackered?
Brian

It may be, it shows a few ohms resistance and draws over 250mA with a
1.5 cell across it and doesn't spark the plug when the circuit is
broken.. I'll need to pull one off another to check but I don't have one
here atm.

Ignition systems generally run at a few amps average. Try flicking a 12v
car battery etc across the coil while looking for a spark.

Coils ain't designed to have volts applied constantly for any length of
time.


Transformers are designed to work with AC signals.

Applying DC to coils isn't always a safe thing to do.
Depends on numbers, resistance of coil, and so on.

If you measured the resistance of the primary on the
coil, and it was 2 ohms, you'd expect 12V/2ohms = 6 amps
to flow, and 6 amps * 12V = 72 watts. Which is likely
to be too much for the physical design of the coil,
if left there for any period of time.

It's hard to control the "intermittent" connection of
a battery well enough, to ensure safety or a lack of damage.
You might use or need an "interruptor" ("joy buzzer"),
as a means of exciting the coil.

Drivers for coils might involved the usage of capacitors,
if you knew what voltage to use. Like what voltage was normal.

Another option, would be to place a 1V amplitude AC signal
on the primary (small enough that the SCR might not interact),
then measure the voltage on the secondary (which is unloaded).
And from that, determine the functioning turns ratio. Since
ignition coils can develop wind-to-wind shorts, the
number of turns still functional in a coil, might not
be the original value.

Much of these tests rely on your knowledge of what would
be "normal" for the circuit, in response. I bet, given
my drothers, I could make that coil throw a spark, but
that's not going to make the device run properly
exactly. Such a test would prove there wasn't a dead short
or an open in the coil. Like if the secondary was shorted
out completely, you wouldn't expect to see a spark or any signal
come out.

And based on my experience of being thrown across the basement
floor by a car ignition coil, remember your elfen/safety.
In my case, I'd thrown a cloth over something (because the
workbench was dirty), and I happened to lean on the cloth, and
the damn red high tension wire just happened to be
underneath there. I swore an oath that day, that I would
never again subject myself to something like that, and
so far, it worked. The oath worked. No more HV accidents.
No more throwing shop rags where they don't belong. And I've worked
on HV stuff since then, with zero incidents to report. It's
funny how coming to on the basement floor and wondering how
you got there, clears the mind.

Paul

On 10/04/2020 19:39, Paul wrote:
Dave Plowman (News) wrote:
In article ,
Â*Â* AJH wrote:
On 10/04/2020 06:33, Brian Gaff (Sofa 2) wrote:
Are we sure the coil is not just knackered?
Â* Brian

It may be, it shows a few ohms resistance and draws over 250mA with a
1.5 cell across it and doesn't spark the plug when the circuit is
broken.. I'll need to pull one off another to check but I don't have
one here atm.

Ignition systems generally run at a few amps average. Try flicking a 12v
car battery etc across the coil while looking for a spark.
Coils ain't designed to have volts applied constantly for any length of
time.


Transformers are designed to work with AC signals.

Applying DC to coils isn't always a safe thing to do.
Depends on numbers, resistance of coil, and so on.

If you measured the resistance of the primary on the
coil, and it was 2 ohms, you'd expect 12V/2ohms = 6 amps
to flow, and 6 amps * 12V = 72 watts. Which is likely
to be too much for the physical design of the coil,
if left there for any period of time.

It's hard to control the "intermittent" connection of
a battery well enough, to ensure safety or a lack of damage.
You might use or need an "interruptor" ("joy buzzer"),
as a means of exciting the coil.

Drivers for coils might involved the usage of capacitors,
if you knew what voltage to use. Like what voltage was normal.

Another option, would be to place a 1V amplitude AC signal
on the primary (small enough that the SCR might not interact),
then measure the voltage on the secondary (which is unloaded).
And from that, determine the functioning turns ratio. Since
ignition coils can develop wind-to-wind shorts, the
number of turns still functional in a coil, might not
be the original value.

Much of these tests rely on your knowledge of what would
be "normal" for the circuit, in response. I bet, given
my drothers, I could make that coil throw a spark, but
that's not going to make the device run properly
exactly. Such a test would prove there wasn't a dead short
or an open in the coil. Like if the secondary was shorted
out completely, you wouldn't expect to see a spark or any signal
come out.

And based on my experience of being thrown across the basement
floor by a car ignition coil, remember your elfen/safety.
In my case, I'd thrown a cloth over something (because the
workbench was dirty), and I happened to lean on the cloth, and
the damn red high tension wire just happened to be
underneath there. I swore an oath that day, that I would
never again subject myself to something like that, and
so far, it worked. The oath worked. No more HV accidents.
No more throwing shop rags where they don't belong. And I've worked
on HV stuff since then, with zero incidents to report. It's
funny how coming to on the basement floor and wondering how
you got there, clears the mind.

Â*Â* Paul


I stuck a coil out of an MGB into it, it gave a v weak spark but the
thing didn't fire even when spun up with a drill.. Just for interest
I'll mark the fan at TDC and put a strobe on it. It's a strange beast
in that it isn't piston ported and the carb is directly mounted on the
crankcase, reed valve I expect.

In article ,
Paul wrote:
It's hard to control the "intermittent" connection of
a battery well enough, to ensure safety or a lack of damage.
You might use or need an "interruptor" ("joy buzzer"),
as a means of exciting the coil.

Think of Kettering ignition. Points, and the engine cranking. The points
will be closed for much the same time as 'flicking' a battery across one.

A car ignition coil will sustain the full battery volts across it for a
while. Certainly a lot more than a few seconds.

--
*You're never too old to learn something stupid.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
AJH wrote:
I stuck a coil out of an MGB into it, it gave a v weak spark but the
thing didn't fire even when spun up with a drill.. Just for interest
I'll mark the fan at TDC and put a strobe on it. It's a strange beast
in that it isn't piston ported and the carb is directly mounted on the
crankcase, reed valve I expect.

Dwell is important. This is the time volts are applied to the coil to
allow the flux to build up to the maximum, before they are interrupted and
the spark occurs.

--
*A backward poet writes inverse.*

Dave Plowman London SW
To e-mail, change noise into sound.

On 11/04/2020 12:19, Dave Plowman (News) wrote:
In article ,
AJH wrote:
I stuck a coil out of an MGB into it, it gave a v weak spark but the
thing didn't fire even when spun up with a drill.. Just for interest
I'll mark the fan at TDC and put a strobe on it. It's a strange beast
in that it isn't piston ported and the carb is directly mounted on the
crankcase, reed valve I expect.

Dwell is important. This is the time volts are applied to the coil to
allow the flux to build up to the maximum, before they are interrupted and
the spark occurs.



Yes I didn't expect the car coil to do anything so there was a bit of a
bonus it sparked at all.

In the meanwhile I'm sitting back and taking stock. The owner says he
barely used the genset at all so I'm thinking it's more likely a problem
from having been laid up. Else it's one of those early problems that
show up from a manufacturing fault, typically the failure rate over time
is bimodal, a large number of faults in machines early in life then a
fault free period then an increase as items fail at end of life.

I've plenty else to get on with.