The diode is connected across the starter solenoid coil not the contacts for
the starter motor as per the extract from the build manual above. There is n
o diode across the starter motor shown in the build manual diagram, at least
not my version.
With 12v positive on the starter contacter coil the diode, with the cathode o
r marked end of the diode connected to positive terminal of the starter coil
, is reverse biased and so will not conduct. When the starter button release
the falling emf, magnetic field, produces an opposite voltage in the coil a
nd can spark across the starter switch contacts eventually damaging the cont
acts, the diode shorts out this so the spark does not happen.
If the diode is shorted out, or the wrong way round, then solenoid will not w
ork, assuming the solenoid will operate without diode connected as a test to
ensure it=99s the wiring of the diode that=99s the problem of c
ourse.
Isn=99t explaining electrical problems by email fun
.=F0=9F=A4=A9
Alan
Sent from my iPad
> On 7 Jun 2021, at 10:44, Kingsley Hurst <kingsnjan@westnet.com.au> wrote:
>
> =EF=BBHello Dave,
>
> I haven=99t got your previous posts in front of me but I assume you w
ant to put the diode across the starter solenoid.
>
> If my assumption is correct, you should connect the anode to the starter m
otor side of the starter solenoid and the cathode to the positive (starter s
witch) side of the solenoid.
>
> If you have had it connected the other way around and tried starting the e
ngine, the diode would have been forward biased trying to carry the full cur
rent of the starter motor and more than likely will be ruined.
>
> Either check the diode with a multi meter ( on ohms scale) to ensure it co
nducts in one direction but not the other or use a new diode.
>
> When connected correctly, on pressing the starter button (or key switch), t
he diode is reverse biased and has no effect..... all the current passes thr
ough the solenoid. On releasing the starter button (or key switch), the col
lapsing magnetic field in the starter solenoid tries to induce a high voltag
e spike but this is swamped by the diode because the diode short circuits th
e current induced by the collapsing magnetic field in the coil.
>
> Hope this hasn=99t made it more confusing for you. I could and prob
ably should have just said ..... connect it like the manual says.
>
> Best regards
> Kingsley in Oz.
>
> Sent from my iPhone
>
>>> On 7 Jun 2021, at 7:17 pm, david park <dpark748@me.com> wrote:
>>>
>> =EF=BBAllan have you put ANODE to switch contact?
>>
>> Dave Park
>>
>>
>>>> On 7 Jun 2021, at 09:35, Alan Burrill <alanb@dpy01.co.uk> wrote:
>>>>
>>> =EF=BBAre you sure the diode is not faulty?
>>>
>>> You can check it with an meter set to read resistance. Should be high re
sistance one way and low the other.
>>>
>>> Have you tried connecting it the other way round?
>>>
>>> Alan
>>>
>>> Sent from my iPad
>>>
>>>>> On 7 Jun 2021, at 09:02, david park <dpark748@me.com> wrote:
>>>>>
>>>> =EF=BBBud,
>>>> Still confused as Europa Manual wiring diagram shows Anode to Earth? No
t switch.
>>>> Regards
>>>> Dave Park
>>>>
>>>>
>>>>>> On 7 Jun 2021, at 01:06, Bud Yerly <budyerly@msn.com> wrote:
>>>>>>
>>>>> =EF=BB
>>>>> Dave,
>>>>> I didn't see anyone commented on your diode.
>>>>>
>>>>> Pretty much any diode will do. If you get it backwards, the saving gr
ace is the start solenoid is looking for 12 volts. Of course, the solenoid m
ust be grounded.
>>>>> Most mistakes are the ground is left off the solenoid when putting on t
he diode. Another problem is guys don=99t insulate the anode side of t
he diode and it shorts.
>>>>>
>>>>> The Rotax manual doesn't comment on the diode. But it is an accepted p
ractice to extend the life of the contacts in the starter solenoid. The Eur
opa Electrical Chapter 25 advises to use an IN5404 but any will do.
>>>>>
>>>>> IN5404
>>>>> <image001.png>
>>>>>
>>>>> silicone diode is shown above. Anode or plus side is on the starter s
witch tab and the cathode or negative goes to the ground bolt holding on the
starter solenoid. I use at least a #18 or 16 wire from the solenoid fasten
ing bolt to the main firewall ground.
>>>>>
>>>>> Best Regards,
>>>>> Bud Yerly
>>>>>
>>>>> -----Original Message-----
>>>>> From: owner-europa-list-server@matronics.com <owner-europa-list-server
@matronics.com> On Behalf Of david park
>>>>> Sent: Wednesday, June 02, 2021 2:44 PM
>>>>> To: europa-list@matronics.com
>>>>> Subject: Europa-List: Starter Diode
>>>>>
>>>>>
>>>>> I fitted a starter Diode and engine would not start. Orientation was a
s described with band end cathode on starter terminal and other end to earth
?
>>>>> Have I got wrong diode.
>>>>> Any advice appreciated
>>>>>
>>>>> Dave Park G-LDVO
>>>>>
>>>>>
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