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The TTR250 FAQ web pages -> TTR250 -> Repairs and maintenance -> Whats this ? (Diode in wiring loom near CDi - explanation now included)
Post Info TOPIC: Whats this ? (Diode in wiring loom near CDi - explanation now included)
locky


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Whats this ? (Diode in wiring loom near CDi - explanation now included)
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20150125_164115.jpg



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Andy B


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RE: Whats this ?
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Pretty sure that's the diode(s) for the starter circuit - it's connected to starter circuit relay via the clutch and neutral switches.

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petenz


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It's the Diode...
is a one way link so AC current dosn't come in contact with DC current...
The AC current is taken from the rectifirer & used to go though the starter button as it's not
big enough to handle DC current & would burn it out very fast...

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ttboof


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ive seen this question and explanations before but stayed quiet its a bit hard to explain but here I go .

the diode in question enables the cdi unit to double up on the start button wire with the neutral light . the cdi wire when earthed by the start switch retards the ignition  timing while cranking protecting the starter from kick back (also a bit easier to crank ) .

if you look at the diagram the starter switch actually switches the negative side of the solenoid and its only a small current , there is also another diode in the diagram close to the solenoid its actually a zenner diode to quench the induced voltage from the switching the solenoid winding protecting the rest of the electrical .

this has been around since the mid 80s , but one of those things that goes un noticed .

 

(coming from my 14 years  an  auto electrician in a past life )   my tip when working with electrickery is to think of it as plumbing works much the same .both water and power flow through pipes /wires

 

 



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BM Steve


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RE: Whats this ? (Diode in wiring loom near CDi - explanation now included)
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ttboof wrote:
 

(coming from my 14 years  an  auto electrician in a past life )   my tip when working with electrickery is to think of it as plumbing works much the same .both water and power flow through pipes /wires

 

So keeping with the plumbing analogy water and electricity flows I think you meant to say in both directions unless you stop it with a diode
or in plumbing terms a "Back flow Prevention Valve" 

I thought it must have been for something like that when I looked at the wiring diagram

I can do basic wiring on the bike and round the house but too deep into electronics and my eye's kind of "glaze over"



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brindabella


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yeah, I guess it stops something like "electrical water hammer".

there are other different unrelated diodes in the TTR by the way (several in the rectifier/regulator).

this particular diode under discussion here, has no effect except when starting.
the problem is that the coil in the relay stores magnetic energy while current is flowing to hold in
the solenoid switch to the starter, but when you release the starter button this stored magnetic
energy wants to collapse by converting back to reverse polarity electrical energy ("back EMF").
the actual energy (and so max current) is minimal, but a momentary reverse voltage of over 100V
could last for a few milliseconds without the diode - enough to possibly damage some electrical items
or create a small spark in the starter switch which would eventually erode the contacts.
this diode unit is really two diodes back to back, one being a zener diode which has the effect
of thresholding the reverse flow through its normal diode series partner.
because the diode unit enables easy flow at any reverse potential exceeding the zener threshold, the electricity
takes that easy path through the diode unit, and dissipates, instead of wreaking havoc elsewhere.


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ttboof


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BM Steve wrote:
ttboof wrote:
 

(coming from my 14 years  an  auto electrician in a past life )   my tip when working with electrickery is to think of it as plumbing works much the same .both water and power flow through pipes /wires

 

So keeping with the plumbing analogy water and electricity flows I think you meant to say in both directions unless you stop it with a diode
or in plumbing terms a "Back flow Prevention Valve" 

I thought it must have been for something like that when I looked at the wiring diagram

I can do basic wiring on the bike and round the house but too deep into electronics and my eye's kind of "glaze over"

yeah a diode is a one way valve the one shown is the one I described enabling the cdi to share the neutral light circuit .

 

your spot on with your comparison  Back flow Prevention Valve

 

we are surrounded by them in day to day life and they do a great job hidden away in black boxes biggrin

 

 



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brindabella


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a minor correction to my previous comment where I said the diode(s) "has no effect except when starting" -
I believe that comment and explanation is correct, but ONLY for the US model which has much simpler wiring.

ttboof is surely correct about other models, where there is a need to enable a neutral light.

Speaking of non US models - the Australian models, as far as I know, have a required combination of clutch switch,
neutral switch (with light), and ALSO side-stand cut out switch which affect starting (plus main and kill switch of course).

Anybody know if that is the case for all the European models too?
- apart from US model, I haven't seen a TTR wiring schematic.




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ttboof


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Spot on brndabella . I'm liking the chat about the humble diode smilesmile

I didn't think about the US model differences I'm pretty sure the European bikes are the same as our ozzy ones 



-- Edited by ttboof on Monday 2nd of February 2015 06:25:43 AM

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petenz


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This is the wiring loom I built for my TTR a couple years ago..

it has ignition/charge/start cirruts only..

I seem to have put  2 diodes in the system can't remember why

was 2 years ago..

The starter button has AC current running though it one of the diodes is a

link between AC & DC current.. I you put DC current though the starter

button it WILL burn out... "I have a burnt out TTR one in the shed"

 

anyways there is a tread here somewhere... where Jarrah & me

spent a lot of time sorting the system out...

 

The loom before I wraped it...



-- Edited by petenz on Monday 2nd of February 2015 08:17:54 AM

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dj9ten


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wiring loom diode
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Ok so the main switch on my ttr went out .....and so I connected a 3 prong on off switch (power/load/earth) and I think I shorted something out (pretty positive it's the diode in the wiring loom a ktm dealer said the diode was in open relay).....I can't find a part number for it or i can't find it anywhere online  .......any ideas on where to start looking or a "at home remedy" can I just cut the cconnector on the harness and add another type of diode (different prong shape but same amp rating) To replace the stock yahama one??

I know the starter works and the starter relay .....I'm just not getting a load between the  and brown wires (run switch) ...the starter button is connected and loaded  correctly (blue and blue/whitestripe) the kills switch (other 2 red/white stripe & brown) are on a seperate switch ....only one of those get voltage .....when I unplug the diode from the harness nothing gets power 



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TTRfan


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See here for an explanation as to what the diode does wink

Are there any serial or other numbers on it that can be Googled?

My guess is that Mr Yamaha only sells them with a complete loom no



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dj9ten


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That's what I'm thinking as well it seems to be diode S3H-02 they are identical to the ones used on a a lot of Honda bikes.... The part number for Honda is #31700-124-008

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dj9ten


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And also if the diode has gone bad can I still bump start it or will that kill  starting circuit completely ???

 



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TTRfan


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It would appear that you can - see http://hondacb650.com/viewtopic.php?t=9706

But I take no responsibility if your TTR goes up in flames bleh



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fourelms


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excellent thread, I never knew these things existed in motorcycle looms, thanks

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TTRfan


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Totally TTRs has a second-hand 3-pin diode from a TTR250 loom (and a couple of the 2-pin ones as well) in stock. If you are interested, drop Steve an email at sales@totallyttrs.com wink



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dj9ten


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I sent and email to Steve thanks

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ttr steve


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Received and will send you an email soonsmile

2-pin diode.jpg



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