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Discussion Starter #1
G'day Guys

Just been doing a bit of tidy up work on the project bike and found as shown on the attached photos.

I've never had the bike running, but saw it started and running when I bought it. Looks like the original starter relay has been changed at some time and a pretty bodgey job done of reconnecting the new relay - it was a real mess. I've decided to put a new connector in to replace the dickey job and when I started I found what appears to be a diode (?) across the terminals of the original connector that connects to the coil of the starter relay (see first photo).

Can anyone please confirm if this is indeed a diode, if it is there as genuine and if so what is the function? If it is required, what size does it need to be as I think I'm gunna need a new one?

Thanks.

Regards

Muddy
 

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Short version
Leave it out.

Longer version.
When current flows through a relay coil (and an ignition coil btw) a magnetic field is developed.

When you disconnect power from the coil there is a high voltage spike induced by the collapsing magnetic field (which is why ignition coils fire spark plugs at high voltage). A diode across the coil contacts can be used to suppress the spike. However this is generally used if there is a transistor doing the coil on/off switching to protect the transistor from the spike.

On your bike the switch is mechanical (aka start button) it does not need protection. I understand that a diode may even slow the mechanical opening of the relay contacts and therefore increase the time an arc is sustained across the contacts thus reducing contact life and maybe increasing resistance and hence voltage drop across the contacts.

Richard
 

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It may have had an alarm system/immobiliser on it. I had one fitted on mine (Datatool) back when I bought my 900. I noticed that it had a diode in the wires to the solenoid when I stripped it out a year or so back, after it finally gave up the ghost (the alarm, that is). I think the diode is there to stop any current 'backfeeding' through the alarm/immobiliser.
 

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yep Diode to stop back EMF voltage. (looks like a 1N4004 power diode- common as mud)

Take it out if you dont have an alarm to go in but I dont see it hurting if its in either, the back EMF only lasts for a fraction of a second but on a 12volt circuit and a coil like a starter relay will give you lots of volts - prob 300-500vdc.

When i was at school i made a taser type device using a relay and zapped people when they stood on the old wire mat and went to open the door .... ah the fun we had :D
 

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Discussion Starter #5
G'day Guys

Thanks for the info. I have no plans for alarm or immobiliser, so will take the diode out.

I take it that this diode would not have been fitted as standard on the stock Ducatis?

Your help is really appreciated.

Regards

Muddy
 

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I take it that this diode would not have been fitted as standard on the stock Ducatis?
Definitely not needed as before and 99.99999999999999999999999999999999999% sure not stock.

My 2001 does not have one and will never have one.

BTW I have a Spyball alarm/immobiliser on mine from new and there was never a diode.

If it diodes were required because of the alarm then they would need to be on every relay.
 

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Definitely not needed as before and 99.99999999999999999999999999999999999% sure not stock.

My 2001 does not have one and will never have one.

BTW I have a Spyball alarm/immobiliser on mine from new and there was never a diode.

If it diodes were required because of the alarm then they would need to be on every relay.
I'm pretty sure the diode was to do with the immobiliser part of the alarm - which had the start button wire interrupted near the solenoid, and routed through the immobiliser, and back to the solenoid. Probably specific to that brand of alarm. If you had the key, you could turn on the ignition (and the alarm would scream at you), but no cranking would happen, until you deactivated the alarm. That was the only diode on anything (that I've found).
 

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Discussion Starter #8
Thanks Guys

No alarm/immobiliser fitted to the bike when I picked it up and no sign of one fitted, however the diode does look to be soldered in place, making me think it was professionally fitted.

Regardless, I've cut it out and will replace the connector with a mating unit to the starter relay.

Regards

Muddy
 

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Discussion Starter #9
G'day Guys

Just a question update due to a change in circumstances.

Bought myself a new Ignitech TCIP4 and plan to fit this during the rebuild. I've read about some the the peculiarities of these units with relation to resistivity of plugs, leads etc and made me think if I need to install the diode on the starter circuit to protect the TCIP4 at all? I'd prefer not to fit the starter diode if not needed, but if it is going to protect the TCIP4 in any way, I'd obviously prefer this.

By the way, I'm also adding a few headlight relays - do these really need to be diode fitted as well?

What do you guys think?

Thanks.

Regards

Muddy
 

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G'day Guys

Just a question update due to a change in circumstances.

Bought myself a new Ignitech TCIP4 and plan to fit this during the rebuild. I've read about some the the peculiarities of these units with relation to resistivity of plugs, leads etc and made me think if I need to install the diode on the starter circuit to protect the TCIP4 at all? I'd prefer not to fit the starter diode if not needed, but if it is going to protect the TCIP4 in any way, I'd obviously prefer this.

By the way, I'm also adding a few headlight relays - do these really need to be diode fitted as well?

What do you guys think?

Thanks.

Regards

Muddy
Re the headlight relays - No. Just the starter solenoid, as it's a LOT larger activating coil, so causes more of a voltage spike.

What I initially wrote:
Re the Ignitech system - maybe PM Liam (FastBikeGear) - he's pretty much the resident expert here on Ignitech systems. This thread may have some pertinent info - http://www.ducati.ms/forums/57-supersport/187881-new-unofficial-ignitech-manual.html
...but after reading the links posted below - I'd say put the diode back in! Seems like it's far better to have it in than not.

Here's some stuff about EMF protection (and why) on solenoid relays and 12v electronics... I did a search on "Diode across solenoid relay coil", the below are a small selection of the results:

This gives a good basic explanation - with pictures... Electronics - What is a Flyback Diode?

Protection diode for 12VDC solenoids - Electronics Forums

https://en.wikipedia.org/wiki/Flyback_diode

Protecting NI Switch Products when Switching Inductive Loads - NI Switches Help - National Instruments


Seems like having the diode in IS a good idea - if only to protect your starter switch contacts (from the spark caused by the back EMF) - but even better if you have any other electronics powered off the same supply.
 

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Discussion Starter #12
Thanks Guys - appreciate the advice. Might just buy a new one down at the electronics store and fit it to be sure (the old one got thrown away). :D
 

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Thanks Guys - appreciate the advice. Might just buy a new one down at the electronics store and fit it to be sure (the old one got thrown away). :D
As you are in Oz, just head to Jaycar or order the diode online from them.

1N4004 is the generic diode code for it.

It is a little black component about 1cm long and maybe 3mm diameter.

It has a silver band at one end. The end/leg with the silver band goes to the positive to the solenoid coil and the other end to the negative to the solenoid coil.
 
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