Spark quality and coil questions

[narrow_monza]

Hello Bob,

I ran 3 experiments and observed the spark plug for sparks:

1) No bridge block used (wire-lead from the ign.power-coil driving ign.system directly) ==> consistent blue spark
2) Neg bridge block output used (wire-lead from the ign.power-coil driving AC input, negative output of bridge block drives ign.system) ==> inconsistent/weak spark
3) Pos bridge block output used (wire-lead from the ign.power-coil driving AC input, positive output of bridge block drives ign.system) ==> no spark

What do you think of these results? I thought that either setup 2 or 3 would yield the same quality spark as setup 1.

Thoughts?

Thanks

-Adrian

[DewCatTea-Bob]

[quote= narrow_monza ...
" Neg bridge block output used (wire-lead from the ign.power-coil driving AC input, "

____ Is your alt.stator wire-lead (from the ign.power-coil) connected to just one, or both AC.inputs of the tested bridge-block ?



" negative output of bridge block drives ign.system) ==> inconsistent/weak spark "

____ What are the specs of the particular bridge-block which you used in the test ?
Did you ever try also connecting the pos.output of the b.block to any circuit,, or did you just leave the pos.output ignored & unconnected, (while testing the neg.output connected with the ign.system) ?



" What do you think of these results? "

____ First thing I'd suspect are the connections into & out-of the b.block's terminals. _ So are you quite sure that those terminal-connections were as tight as they could be ?



" I thought that either setup 2 or 3 would yield the same quality spark as setup 1. "

____ I don't recall ever directly comparing spark-quality between directly-connected stator-coil output and that which has been rectified, however it's naturally expected for there to be some loss whenever anything is included in series within any such circuit. _ So-thus spark-quality may slightly suffer but it shouldn't be quite so noticeable.



" Thoughts? "

____ While I've instructed others to try using a (now common) bridge-block for this particular job, (only because it's quite rather easy to mount),, I-myself, have only ever used power-diodes for the suggested-circuits, (since such power-b.blocks weren't so commonly found back-then as they are THESE-days).
And just as I've always preferred superior silver-wire over copper, (for various projects),, (for this particular ign.circuit), I've likewise always chosen germanium-diodes over silicon-diodes, which have a mere voltage-drop of about .25-volts (instead of the near .7v of the silicon-type). _ But I really don't think that such minor value-differences actually add-up to any real significance.
__ When you shopped for bridge-blocks,, did you happen-to notice whether there was any choice of silicon AND germanium (or Schottky) types listed, to select from ?


Hopeful-Cheers,
-Bob

[narrow_monza]

[quote= narrow_monza ...
" Neg bridge block output used (wire-lead from the ign.power-coil driving AC input, "

____ Is your alt.stator wire-lead (from the ign.power-coil) connected to just one, or both AC.inputs of the tested bridge-block ?

I tried it both ways, single AC input and both AC inputs and got similar results.

" negative output of bridge block drives ign.system) ==> inconsistent/weak spark "

____ What are the specs of the particular bridge-block which you used in the test ?
Did you ever try also connecting the pos.output of the b.block to any circuit,, or did you just leave the pos.output ignored & unconnected, (while testing the neg.output connected with the ign.system) ?

I tried both blocks (200V/50A and 200V/25A) with similar results.
I left the positive output unconnected.

" What do you think of these results? "

____ First thing I'd suspect are the connections into & out-of the b.block's terminals. _ So are you quite sure that those terminal-connections were as tight as they could be ?

I used GXL 14 Gauge automotive copper wire (about a foot) with crimp-on bullet connectors to spice in the bridge block.

" I thought that either setup 2 or 3 would yield the same quality spark as setup 1. "

____ I don't recall ever directly comparing spark-quality between directly-connected stator-coil output and that which has been rectified, however it's naturally expected for there to be some loss whenever anything is included in series within any such circuit. _ So-thus spark-quality may slightly suffer but it shouldn't be quite so noticeable.

One thing worth mentioning is the high-tension coil. I'm using a Japanese 6V coil from an early Honda. It's not the oil-can type but the epoxy type.
Could it be that this coil is the wrong type to use with a "rectified" AC pulse?

" Thoughts? "

____ While I've instructed others to try using a (now common) bridge-block for this particular job, (only because it's quite rather easy to mount),, I-myself, have only ever used power-diodes for the suggested-circuits, (since such power-b.blocks weren't so commonly found back-then as they are THESE-days).
And just as I've always preferred superior silver-wire over copper, (for various projects),, (for this particular ign.circuit), I've likewise always chosen germanium-diodes over silicon-diodes, which have a mere voltage-drop of about .25-volts (instead of the near .7v of the silicon-type). _ But I really don't think that such minor value-differences actually add-up to any real significance.
__ When you shopped for bridge-blocks,, did you happen-to notice whether there was any choice of silicon AND germanium (or Schottky) types listed, to select from ?


Hopeful-Cheers,
-Bob

[DewCatTea-Bob]

[quote= narrow_monza ...
" I tried it both ways, single AC input and both AC inputs and got similar results. "

____ By allowing the pair of diodes to split-up & conduct the total current, (by connecting to & using both AC.inputs),, the ratio of amperage to voltage-drop (within the diodes) is thus-then improved accordingly. _ So that doubled connection setup should be the best to go with, (and why I wasn't concerned with the use of silicon-diodes).



" I tried both blocks (200V/50A and 200V/25A) with similar results.
I left the positive output unconnected. "

____ Please again try the same test (using the 50-amp b.block), but rather with it's pos.output directly grounded.



" I used GXL 14 Gauge automotive copper wire (about a foot) "

____ Of-course that shouldn't make any difference.



" with crimp-on bullet connectors to spice in the bridge block. "

____ Perhaps an ohm-meter (set at it's most sensitive setting), ought-to be used to check your wire/terminal connections for any notable resistance.



" One thing worth mentioning is the high-tension coil. I'm using a Japanese 6V coil from an early Honda. It's not the oil-can type but the epoxy type.
Could it be that this coil is the wrong type to use with a "rectified" AC pulse? "

____ The rectified AC leaves only pulses of DC (for the ign.coil).
__ I'm unsure of the relative details of your Jap.coil, but I suppose that it's particular make-up could likely be less than optimum (for being matched-up together with the ign.power-coil).
Do you have any other ign.spark-coils you could try-out ?
If not, then instead try a test with the condenser disconnected, and/or connected on the other-side of the b.diode-block.

____ Has all your testing so-far, only been done just at mere kick-starting rev.speeds ?
And how wide has been the gap-setting on your test spark-plug ?
__ A more significant test will be when you can actually start & run the engine, to staunchly determine whether your weak-appearing ign.spark is actually a real concern.


Hopeful-Cheers,
-Bob

[narrow_monza]

Hi Bob,

The sparks tests I'm running are purely visual at kick-start speed so they might be very subjective.
I think I'm better off trying to start the bike and compare how it runs with and without the bridge block (and different configurations).

I think I'll go install the carburetor now.

Thanks

-Adrian

[DewCatTea-Bob]

[quote= narrow_monza ...
" I think I'm better off trying to start the bike and compare how it runs with and without the bridge block "

____ Indeed, as the original suggested test was merely to determine just whether your mag.rotor's preset polarity was already correct for combining with a neg.ground battery circuit, (which you've found it indeed is, since you got spark using the neg.output of the b.block).
__ So the next step which ought-to be explored & confirmed, is to check that your engine/ign.system all works as expected whilst it's wiring setup is kept arranged merely in stock configuration.



" (and different configurations). "

____ Speaking of such,, while there are many numerous master-configurations possible with Ducati-alternators, your selection (with it's grounded power-coils), leaves you with relatively limited possibilities,, yet, still with more than that which we've first chosen !
__ Your non-stock ignition-coil may prefer a different connection/operation-method with another/different circuit/wiring-setup. ...
The stock-Ducati magneto-type ign.circuit/wiring-setup rather appears as-if it's little-more than a 'short-circuit' (to those who are mainly familiar with battery-powered ign.systems), cuz the power-feed (from the ign.power-coil) runs directly*to the ign.points which are closed & grounded most of the time. - (* Along-with another connection to the ign.coil, thus arranging it in parallel -[rather than 'series'] with the contact-points.)
That's the (rather unusual) ign.wiring-circuit which you were supposed to be testing with, (and assumed along-with a stock-type Green-label ign.coil) !
However with your non-stock/Jap.coil, you could also try-out circuit-wiring it in a (more common) SERIES-circuit with the ign.points. _ This circuit-arrangement will rather create it's ign.spark due-to a SUDDEN collapsing flux-field (instead of the mere rapidly-expanding field). _ However, (even-though the resulted ign.spark is sufficient to run the engine), it's been my experience that various ign.coils merely create a somewhat weaker spark THAT-way (with pulsed-DC). _ So rather than having-to depend-on the collapsing-field of merely-just a single pulse of DC,, instead, you could rather store-up the other three (otherwise ignored & wasted) neg.DC-pulses and retain the combined energy of ALL-four neg.power-pulses (per Otto-cycle) stored into a capacitor, so as to 'filter' all those (originally separate) DC.pulses combined-together into rather 'straight-DC' and thus-then build-up a stronger & better-established flux-field before collapsing, to create a considerably stronger ign.spark.
__ This alternative conception/plan (as well as other possibilities), could become considered later, after you've completed your intended testing and-then decide which methods you most prefer to finally go-forth with.


Hopeful-Cheers,
DCT-Bob

[narrow_monza]

[quote= narrow_monza ...
" I think I'm better off trying to start the bike and compare how it runs with and without the bridge block "

____ Indeed, as the original suggested test was merely to determine just whether your mag.rotor's preset polarity was already correct for combining with a neg.ground battery circuit, (which you've found it indeed is, since you got spark using the neg.output of the b.block).
__ So the next step which ought-to be explored & confirmed, is to check that your engine/ign.system all works as expected whilst it's wiring setup is kept arranged merely in stock configuration.

Hopeful-Cheers,
DCT-Bob

Hi Bob,

The engine seems to start with ease either way (with and without the bridge block).
So I will go ahead and wire the bike with your suggested scheme (neg output of block driving the high-tension coil and positive driving a 6V battery).

Thanks

-Adrian

[DewCatTea-Bob]

__ So the next step which ought-to be explored & confirmed, is to check that your engine/ign.system all works as expected whilst it's wiring setup is kept arranged merely in stock configuration.

____ It seems that that step was covered in your other thread about things to have checked before the first starting attempt. - viewtopic.php?f=3&t=1855



[quote= narrow_monza ...
" The engine seems to start with ease either way (with and without the bridge block). "

____ Okay, good !
I had become concerned that your set mag.rotor timing may not have been set fully optimized for static ign.timing.
__ So does the spark-intensity still appear weaker with the diode-bridge placed in circuit, or did that issue disappear with firmer connections to the b.block's terminals ?
I was thinking that it might be worth including a germanium-diode in parallel along-with the b.block,, but if the engine starts equally easy already, then that added advantage is-not a real concern. _ And if you have no spark-intensity related starting-issues, then perhaps it's best to leave well-enough alone,, as your current diode-circuit may possibly act as a governor of-sorts, to help prevent kick-backs when the engine is kicked-over too slowly.



" So I will go ahead and wire the bike with your suggested scheme (neg output of block driving the high-tension coil and positive driving a 6V battery). "

____ Correct. _ As the pos.output of the b.block will keep the battery well charged ! _ In-fact, the pos.power-output will even trickle-charge a 6v.battery at mere idle, (and at the same rate for a 12v.battery, about 400-RPM higher).
At the other extreme (without any load), the battery could possibly become OVERcharged if engine-RPMs are kept above 5000 (on average) for over two hours. _ So if that kind of (no load) riding is expected to-be done on a regular-basis, then a regulator-unit may be called-for.
However if a (relatively small) load (other than the battery itself) is included, then that would better balance the system and tend to eliminate any use for a regulator. _ So if you don't care about battery-charging occurring near idle, then the load of a std.type taillight-bulb/filament will tend to keep the battery-system rather 'balanced'. _ As the expected charging-power output will, (on average), power-up a std.taillight AND keep the battery charged,, (unless of-course the brake-light or horn happened to get stuck & left 'ON' too long).
With the taillight as a constant load,, decent battery-charging won't occur much below 3500-RPM, (although the battery then won't significantly discharge either, [except below 2k-RPM] ),, and concern of overcharging the battery will-not be an issue (except with engine-RPM kept above 7k for over 2-hours).
With such fairly 'balanced' electrical-systems, the battery itself will maintain it's system-voltage, (just as Ducati their-self tends to take advantage of) !

____ I have hopes that you will keep us informed as to exactly how you plan to wire-up your intended wiring-system, as I could then give you suggested options for your consideration.


Hopeful-Cheers,
-Bob

[narrow_monza]

Hi Bob,

So to summarize the simple wiring scheme I plan on implementing, here's a schematic I drew (attached). Please provide some feedback when you get a chance.
I don't have an ignition switch/key yet so I'm not showing it on the schematic at this point.
Also, the Japanese 6V HT coil I am using has no polarity markings on it. Can I determine the primary/secondary winding polarity by using an Ohmmeter?

Thanks

-Adrian

[DewCatTea-Bob]

[quote= narrow_monza ...
" here's a schematic I drew (attached). Please provide some feedback "

____ First I must say that you've drawn-up a quite nicely done schematic-diagram, (although it's 'scheme' isn't the best) !
__ Besides having labeled the mag & ignition coils as "6V", (of-which they actually have no particular operating 'voltage' !),, there's a couple concerns with your wiring-scheme rather needing to be addressed...
First,, is that your horn-button/switch, (assuming will be handlebar-mounted), needs to be repositioned on the ground-side of the horn.
Next,, was this scheme of yours conceived before I posted concerns about your weak-spark with your Jap.ignition-coil ? _ Cuz your scheme shows the ign.coil wired-up as if rather within a battery-powered ign.circuit-type ! _ Yet I had expected that you've understood my post concerning the particular way that Ducati's magneto-type ign.circuit is actually connected-up.
So is this aspect-point of your drawing an ERROR, or did you find that your ign.coil's resulted ign.spark started better with this indicated ign.coil-connection ?
Does this drawing of yours presently correctly-represent your chosen wiring-connection to the ign.coil, as you've had your engine running ??



" I don't have an ignition switch/key yet so I'm not showing it on the schematic at this point. "

____ Then when you finally do, it ought-to then be indicated between the battery's pos.post-terminal and it's pos.line-out (so that the battery won't get run-down by the otherwise un-switched taillight).
__ It's not too common to find key-switches* which include an Off-position ground-circuit to kill/defeat the magneto-type ign.circuit (* like is found in 160; 1966-67 Scrambler; & 1973 350-Road models). _ So instead, you could possibly rather employ a relay-unit to activate the ign.circuit, using just a rather common std.On/Off key-switch.



" the Japanese 6V HT coil I am using has no polarity markings on it. "

____ That's because it really doesn't much matter,, as the only real difference it makes, is which direction the spark jumps. _ Although it's preferred that the spark-electrons jump from the spark-plug's center-electrode to ground.


" Can I determine the primary/secondary winding polarity by using an Ohmmeter? "

____ No, not with an OHM-meter ! ...
Rather, you could use a DC.volt-meter (which has a HIGH-voltage setting !), by probing between ground & the coil's HT.outlet. _ If the HT.output is indicated as 'positive' by the meter-readout, then you may/ought reverse the wire-leads connected to the ign.coil's primary/input-terminals (so as to obtain the preferred spark-direction).



____ And by-the-way (concerning your battery-system's planned wiring-scheme), did you not intend to employ at-least one fuse ?


Hopeful-Cheers,
DCT-Bob