What is considered acceptable voltage at coils during start?

[Steve]

Can't give you the details on your particular bike, but whenever I have done that, I have found it easiest to remove the headlight bucket for access to the switch assembly.

The electrical portion of the switch is at the bottom of the fork lock assembly. The fork lock assembly is held to the bike with some larger bolts. The electrical part is held to the bottom with some smaller bolts. There is a chance that you <might> be able to unbolt the electrical part with the lock assembly still on the bike, but it will be easier if it's all removed. There should be a 4-pin connector about 6 inches away from the switch that will allow you to remove it from the bike for easier servicing.

While you have the lock assembly off the bike, take a few minutes to clean and lubricate it, too. Maybe even flush some of the crud from the keyway. Who knows? You might be able to actually use the fork lock again.

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[Gorminrider]

Actually, current flows through the coils and the ignitor almost all the time.

almost? what is dwell on these anyways? same as "points" bikes? I would guess so...oh well-different subject.

 

[Steve]

almost? what is dwell on these anyways? same as "points" bikes? I would guess so...oh well-different subject.

I don't know the actual numbers, but, as I mentioned in post #8, the current is stopped a lot shorter time with electronic ignition.

With points, a cam has to turn and open the points. It has to open them far enough to ensure that they don't arc. And, the lift curve needs to be gradual enough to keep the points from floating at high RPM. All of that demands quite a bit of rotation of the crank. With electronic ignition, the transistors only need to open for a split second to stop the current, which causes the magnetic field to collapse, then immediately start the current flow again.

It has been many years since I played with a dwell meter, but I think I remember a dwell angle of about 40 degrees for the car I was working on. Assuming that is correct, the "dwell angle" of an electronic ignition system might be something like 3 or 4 degrees, giving that much more time for the current to flow and saturate the magnetic field.

I have been curious about using dwell angle to adjust the point gap, but I have never seen it specified, and nobody around me has points, so I can't do a comparison.

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[posplayr]

This is a set of scope traces from my GS1100ED. It has SSPB, Accell 3 ohm coils and stock ignitor with mechanical advance. The data is from 6K RPM.

The yellow trace is the primary voltage measured at the (-) coil.
The Cyan trace is the pickup signal from the crank.

There are actually three phases to the (-) coil signal.

• Zero voltage meaning a direct short through the ignitor
• Post ignition when the voltage oscillates about 14V (about 10%)
• Settle period where coil (-) is 2.5V above ground.

Based on measurements the average current through the coil is about 2.5 amps with these 3.0 coils.
at 14V the peak current would be 14/3=4.7 amps. So the effective on ratio is about 2.5/4.7=53%.

I took this data when investigating building an electronic ignition system.

Apparently dwell is defined as:

Dwell angle is the amount of time (measured in degrees of distributor cam rotation) that the contact points remain closed. Initial point gap determines dwell angle.

So dwell will be a function of the number of cylinders and how many times the distributor has to fire per cam revolution. Converting a typical V-8 dwell into an On Ratio: there are 45 degrees per firing (360 deg/8) and IIRC 28 degrees dwell was typical so 28/45=62%

 

[Steve]

Dwell angle is the amount of time (measured in degrees of distributor cam rotation) that the contact points remain closed. Initial point gap determines dwell angle.

This makes sense and apparently I had it backwards.

I was thinking the dwell was the time the points were open, not closed.
As I mentioned, it's been a LONG time since I have dealt with points.

Regardless of actual numbers, the purpose of electronic ignition, rather than points, is to maximize coil saturation time and eliminate wear of the points.

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[posplayr]

This makes sense and apparently I had it backwards.

I was thinking the dwell was the time the points were open, not closed.
As I mentioned, it's been a LONG time since I have dealt with points.

Regardless of actual numbers, the purpose of electronic ignition, rather than points, is to maximize coil saturation time and eliminate wear of the points.

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From what I have read the idea is to achieve maximum saturation in the minimum time, but not to persist longer than necessary as it just heats the coil.

Becuase of that intermediate value of voltage (partial short), there is another factor involved. The other surprising thing is that the ignitor is able to achieve essentially a perfect short.

That coil has current flowing through it for 90% of the time.

 

[Steve]

The other surprising thing is that the ignitor is able to achieve essentially a perfect short.

If I remember correctly, someone did some research and found that they were pretty heavy-duty FETs in there. Very efficient in either ON mode or OFF mode, they only created heat during the transition. Otherwise, the ignitor would probably have needed water cooling.

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[posplayr]

If I remember correctly, someone did some research and found that they were pretty heavy-duty FETs in there. Very efficient in either ON mode or OFF mode, they only created heat during the transition. Otherwise, the ignitor would probably have needed water cooling.

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They are obviously not running in saturation (i.e. either ON or OFF) when at 2.5V. That is the third mode. It is steady state and therefore not a transition.

 

[DimitriT]

Do you have any data on the relays?
Grip warmers are about 1-1.5 amps
Coils are about 4 amps (peak) or 2.5 on average.

Here's the relay I used:

https://www.amazon.com/gp/product/B000CJ05WW/ref=od_aui_detailpages00?ie=UTF8&psc=1

I have it wired to supply power to the grip warmers (along with a toggle switch), a small grain bulb to indicate the heaters are on and a small digital voltage display.

The relay is rated as 20A/10A which means I think 20A peak with 10A constant load.

The grip warmers are your basic Polly Heaters:

https://www.amazon.com/gp/product/B000GTV7ZC/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

They draw 3A and I have a 5A fuse on their supply. So I should be fine with powering the coils from this relay if they draw 4A total.

 

[Gorminrider]

the transistors only need to open for a split second to stop the current, which causes the magnetic field to collapse, then immediately start the current flow again

...yes...but field collapses through primary coil too and resists "recharging" so there's something to chew on there too....found some comprehensible stuff per bikes here
Ignition FAQ
Anyways, I only went here because I took Dmitri's post too literally, per "correct voltage at coils" and it got me thinking (too much!) thinking that using a plain-jane digital multimeter, two cylinder bike ( that is running!) would always exhibit an average voltage drop that is less than the battery's...and maybe might be a little misleading trying to chase every perceived voltage drop ....when actually- it's ok!

But Dmitri found simpler issues so all's well