68 Ducati 250 SSS minus an S

Black wire Ac voltage 4.35
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DesmoDog said:
To me that looks like a typical replacement for the original wires that were likely trashed years ago. I doubt it had anything to do with trying to match colors, that's just what was available in that type of wire.

I don't know what a derivation terminal block is, but that's not a diode it's a fuse.
Thank you the derivation terminal was listed on the wiring diagram. Now I know what an Italian fuse looks like!


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Wow DewCatTea Bob’s posts on Motoscrubs are amazing! Sorry to hear about his passing but thank goodness for Forums like DTT and Motoscrubs to capture and preserve Bob’s genius and legacy!


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Stage Right enter DewCatTEA Bob as Jay Leno says, "there is always a guy who is an expert in it"

So we found a Ducati Scrambler String with a similar wiring set up as ours and both are not stock as the diagram shows above.

http://www.motoscrubs.com/forum/viewtopic.php?f=3&t=2091&p=15738&hilit=28+watt+system#p15738

So here is the background info on our bike. We know it is above engine number 92172 and were are using the correct diagram in the Ducati Workshop Book.

We know that Mick Walker's Ducati Singles Restoration does not take in account the Ducati Scramblers for the use of a Diode and said it was "only fitted to the 160 Monza Junior"

We have been very curious why Ducati chose to go to a 28 Watt system from a 40 watt system but we think we know the answer to that now. It was to balance the system so Ducati didn't need to use a Reg/rec.

So here are our findings all three wires from the case have continuity with each other.

If you ground the ohm meter to the case

White wire has 1 ohm
Green wire has .5 ohm
Black wire has .2 ohm

at idle doing the same procedure

White wire 21vac
Green wire 8 vac
Black wire 4 vac

According to DewCatTea Bob the wire with the 1 ohm should be the ignition circuit.

He also said that the Green label
Ducati coil which is an AC coil should have a resistance of 1 amp however we have two of those coils and they are both reading what they guy in the post got on his 3.8-4 ohms. Now the new 6 volt coil we started the 250 Ducati Scrambler Wide Case Scrambler with has 1.8 ohms closer to what Bob said. Once our neighbors wake up will will fire the Duc up and test the white wire to see if it will start it without a battery. We wired it with the white and point going to the positive on the coil and we wired the negative to ground on the frame. We know the bike runs great and starts great because we first started it on total loss the only difference is the coil need to be wired differently with the positive of the battery going to the batter and the negative going to the points and condenser. Don't ground the negative to the frame it won't start!

DewCATtea Bob is the dude. I am pretty sure he is giving Ducati rides in heaven. RIP
 
DewCatTea bob was correct! https://youtu.be/KNFjhhzRPBg


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In regards to AC vs DC coils,
Coils are coils and they are both transformers.

A coil from a cdi ignition will be getting a substantially higher voltage from the cdi box than it would from a battery on a points system.

In order to have the same voltage at the spark plug, the inductance of the primary circuit must be different. This is achieved with either different cores, different size windings, different number of windings etc.

Long story short, running coils from a points system with a CDI might cook it, and vice versa might not spark as well.

It’s easy enough to compare if you have a known AC voltage source, you can hook it up to the primary side and see what voltage comes out the other. The ratio of resistances would also be a good indicator before hand as the relationship between resistance and the number of loops in the windings is linear (given the same gauge wire is used in both).
 
https://youtu.be/_JS4v1jhnV8 we test the other two circuits coming off the Ducati 28 watt magneto alternator.


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farmer92 said:
In regards to AC vs DC coils,
Coils are coils and they are both transformers.

A coil from a cdi ignition will be getting a substantially higher voltage from the cdi box than it would from a battery on a points system.

In order to have the same voltage at the spark plug, the inductance of the primary circuit must be different. This is achieved with either different cores, different size windings, different number of windings etc.

Long story short, running coils from a points system with a CDI might cook it, and vice versa might not spark as well.

It’s easy enough to compare if you have a known AC voltage source, you can hook it up to the primary side and see what voltage comes out the other. The ratio of resistances would also be a good indicator before hand as the relationship between resistance and the number of loops in the windings is linear (given the same gauge wire is used in both).
That is good stuff! We use 5ohm coils on our Dyna S electronic ignitions on our other bikes.

Ducati used two different coils one that worked with the Ac Mag and the other with the Dc system.


You would have to reference the other link DewCatTea Bob said that the Ac coils had a lower resistance of around 1 ohm.





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Another tinkering option is DewCatTEA Bob's brilliance! Check out his diagram at the bottom of the post! In this post http://www.motoscrubs.com/forum/viewtopic.php?f=3&t=394&hilit=12+volt+conversion+scrambler&start=20 Bob explains how to modify an existing Ducati 6v system to harness the wasted power using bridge blocks and convert to 12v

"As far as the difference between 6 & 12 volt charging goes, there would only be a slight difference in the RPM needed to actually begin any actual charging of the battery...
As a 6-volt battery's std.volatage-level would be able to feel charging-pokes from the alternator's voltage-peaks, at a slightly lower RPM than a 12-volt battery would,, as the RPMs climb, from a non-charging to a charging amount of alt.power-output.
So while that may seem like a worthwhile-bit of an advantage for prefering to go-with the 6-volt choice, it's not really very critical for normal (non-constant low-RPM) riding. _ Because a 12-volt battery won't begin to act as a load (and begin consuming alt.power-juice) at the same lower RPM, thus allowing the alt.power to fairly quickly build-up from the 6v to the 12v level and therefore tends to reduce the otherwise seemingly quite noteworthy advantage, (which is actually only a slight one). _ (Keep in mind that a battery that's able to receive any CHARGING-juice is also a 'load' that's partially wasting the charging-system's power-juice, since unlike a capacitor, the battery can't give back everything it has taken !)
__ And from the other point of view, a 12-volt battery system will not as likely make any use of a voltage-regulator."
The AC-output (of that lighting power-coil's two wire-leads) would then need to be full-wave rectified by a 10 or (25-amp) bridge-block, of which it's DC-output should then be switched so that it's only turned-on when the lights are running off the battery.
____ The other alt.stator power-coil -(meant for ignition & brake-light), would also have to have it's Yellow & White wire-leads connected to another separate bride-block, so that it's full-wave DC-output could then keep the battery charged and run a 12-volt battery-powered ignition-system. ____ The full-wave diode-bridge for the lighting alt.coil should have at least a 6-amp rating, and the battery charging circuit's diode-bridge should be at least 4-amp, and both ought to have greater than a 50PIV rating.
__ But those bridge-rectifier units which you may find, (while quite cheap), may be difficult to mount & wire-up.
So I'd recommend buying a pair of bridge-blocks with 25-amp & 200PIV, as that is such a commonly produced diode-bridge size, that it's quite cheap for it's specs and also easy to mount & wire-up !"
 
Tinkering https://youtu.be/BWXitFxhGQk
 

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First ride...a few little issues https://youtu.be/sHIbKW-b8j0


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