Neil P
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| posted on 14/4/09 at 08:07 PM |
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Got it running, now it won't stop!!
And no, it's not still ticking over on the drive.
I'm splicing a toyota engine loom into the sierra column switches and gauges. The ignition warning light went out when I ran the engine but it
wouldn't stop when I switched off the ignition. I had to cut the wire to the charge light to stop it.
I'm presuming from that that the alternator is energising the ignition circuit and keeping it going.
The questions are:
1. is there a diode in the sierra loom that I could find and use?
2. if there is, where should it go? in the cable between ignition live and charge light?
3. if there isn't one I can use what type do I need to get and where from?
I have SVA on Friday morning, the panic is setting in!! I might post a photo later, then you'd understand why.
Neil
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matt_gsxr
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| posted on 14/4/09 at 08:21 PM |
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alternator output isn't normally switched is it? Shouldn't this go back to the battery (via a fuse).
Matt
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omega 24 v6
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| posted on 14/4/09 at 08:21 PM |
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Quite a few of us using megasquirt have had to fit a diode. I have a spare one but doubt it'd be with you before your SVA.
Get one from your local Maplins.
If it looks wrong it probably is wrong.
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RichardK
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| posted on 14/4/09 at 08:52 PM |
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Mine does this so I'm interested to hear the answer to Neils question 2  , I'm running a megajolt but don't suppose that makes any
difference, what diode is it and where do I stick it?
Cheers
R
Gallery updated 11/01/2011
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tomprescott
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| posted on 14/4/09 at 09:08 PM |
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Don't know what diode you would need but have you given maplin a try yet? Just a thought, the store near me always has loads of wiring bits and
bobs. HTH
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RichardK
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| posted on 14/4/09 at 09:24 PM |
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Google brings up these 1N5822
1N4001 that are mentioned in various threads about similar issues. Don't know what the difference is though!
Cheers
R
Gallery updated 11/01/2011
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02GF74
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| posted on 15/4/09 at 09:46 AM |
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quote:
Originally posted by RichardK
Google brings up these 1N5822
1N4001 that are mentioned in various threads about similar issues. Don't know what the difference is though!
1N5822 = low drop schottky power rectifier, 3 A.
1N4001 = general purpose diode 1 A
schottky diode has low Vf (voltage across them when conductiong) from memory 0.2 V compared to 0.7 to silicon diodes.
Either will do the job but I suspect the schottky will be 2 x the price.
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02GF74
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| posted on 15/4/09 at 09:52 AM |
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^^^^ can someone post the circuit that has the diode? I am thinking, but not too hard, but canot see how this can happen.
The power to the coil and the ecu should be switched so when igntion is truned off, there should be no spark.
confused ...... 
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omega 24 v6
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| posted on 15/4/09 at 11:49 AM |
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From ign to alt light to diode( wire end without silver band) then from diode end WITH silver band to alternator.
Well thats how mines is. I'd use a bigger diode as well
say a 6 amp jobbie.
If it looks wrong it probably is wrong.
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02GF74
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| posted on 15/4/09 at 01:36 PM |
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quote:
Originally posted by omega 24 v6
From ign to alt light to diode( wire end without silver band) then from diode end WITH silver band to alternator.
Well thats how mines is. I'd use a bigger diode as well
say a 6 amp jobbie.
^^^ nope, still don't see it. that doesn't make sense to me as the cricuit is o.c. when ignition is switched off - there must be some
other connection not mentioned.
the only way ^^^ would work is if the output from alternator was connected to the charge lamp and then the igntion switch to the battery - that is
incorrectly wired.
igntion lamp is 2 W max; that is less than 1 A.
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Neil P
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| posted on 15/4/09 at 07:57 PM |
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I've put a 6amp diode in the cable between the ignition live and the charge light blocking current coming from the alternator via the charge
light into the switched side of the loom.
This is how it is wired in the toyota manual (presumably with diodes in the instrument cluster). All of the engine loom including the alternator
wiring is original. I simply identified the ignition live and connected it to the ignition live on the sierra loom.
Anyway, however the techy bit happens is a bit of a mystery to me most of the time.
All I can say is that the diode has worked a treat and sorted the problem.
74p from Maplins!!
If only they sold something to sort out my indicators.
Neil
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omega 24 v6
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| posted on 15/4/09 at 10:25 PM |
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OK when the alternator is not turning and you put the ign on a voltage is applied through thewarning light to the alternator and the exciter wiring in
the alternator. This is required to make the alternator start charging. After the alternator starts charging the same exciter circuit becomes positive
so you have n ign warning lamp with a pos at each side so it goes out.
However when you turn the key off then that same voltage can return through the warning light and keep a relay or low consumption device ( ecu)
powered up enough to keep the engine running.
Just fit the diode it should work. Yes it's only 1 amp but I fitted a larger one so that I'd never need to look at/replace it.
If it looks wrong it probably is wrong.
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02GF74
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| posted on 16/4/09 at 08:43 AM |
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^^^ agree but this is how I have seen alternators wired - no diode required.
You must have it wired up as per orange dotted line; therfore not only you need additional diode as the circuit to the right of thge switch is self
exciting, plus your ignition switch must be of higher current capacity to handle charging current.
TBH I cannot see any advantage in doing that.
 
Rescued attachment alt3.JPG
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omega 24 v6
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| posted on 16/4/09 at 11:41 AM |
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Sorry 02GF74 but what your diagram lacks is all the other circuitry on the switched side of the ign switch ( ie pretty much everything apart from the
hazrds.) You'll still get a voltage coming back through the bulb ( albeit at a lower voltage due to volt drop across the filament) this will be
enought ot keep certain electronic items up and running.
I agree it's not a prob on production cars but many of us building our own have found it to be a problem and this diode cures it almost every
time.
If it looks wrong it probably is wrong.
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