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Kees,
I fit diodes per the 'standard:' https://en.wikipedia.org/wiki/Flyback_diode
I don't remember how I fit the transil; I'm pretty sure I did it
correctly because they came with instructions. AFAIK, transils are a
pair of zener/avalanche diodes in both polarity, so they 'breakdown' and
allow current flow at the nominal rating (IIRC, they were 20V or
thereabouts).
I think one possible problem with points is when they aren't installed
so as to promote the 'wiping' action to clean them.
Bob
On 10/20/2020 9:16 AM, Kees Oudesluijs via Healeys wrote:
>
> Bob,
>
> Did you fit the transil in the same way the diode was fitted? If so
> this is not correct. It should be fitted as the capacitor is fitted,
> between the small screw that holds the points blade and one of the
> bigger screws that fix the Bakelite bridge to the coil body. You can
> fit the transil instead of the capacitor or parallel to the capacitor.
> A diode is fitted in series with the points, a transil or capacitor is
> fitted over the points.
>
> Kees Oudesluijs
>
> Op 20-10-2020 om 17:18 schreef Bob Spidell:
>> The late Dave DuBois, who designed the transistor-switch fix, quit
>> doing the conversions when he found the reduced voltage cross the
>> points allowed them to oxidize. I tried the transil fix, but didn't
>> get much more longevity than a stock points setup with a diode; I do
>> know some have had better luck with them.
>>
>> I have a points/diode pump in my BN2 that works well, but I only have
>> a few hundred miles in the car. I've lost track of what I've got in
>> my BJ8.
>>
>> Bob
>>
>> On 10/19/2020 11:31 PM, Kees Oudesluijs via Healeys wrote:
>>>
>>> When rebuilding SU electrical fuel pumps I ad a transil (e.g.. 1.5
>>> KE18CA) over the points, parallel or in stead of the capacitor if
>>> fitted. This reduces the max voltage across the points to 18V
>>> instead of several hundreds when the contact is broken and the
>>> points spark.
>>>
>>> It is also important to clean and polish the points using flower
>>> paper (2-3000 grid), also when new!!
>>>
>>> A transil is more or less a bi-directional Zener diode. They cost
>>> next to nothing. I buy them in bulk and pay about $0,15 but when
>>> buying only one expect to pay between $1 and $5. Ebay is an
>>> excellent way to source transils (mainly from China).
>>>
>>> A transistor circuit similar to those used in early transistorised
>>> ignition systems does a similar job by limiting the current through
>>> the points
>>>
>>> Kees Oudesluijs
>>>
>>>
>>>
>>> Op 20-10-2020 om 07:50 schreef Ray Juncal via Healeys:
>>>> I'm rebuilding a couple of early S. U. fuel pumps for my 100. In
>>>> checking my reference files I came across an article from the MG
>>>> club about adding a transistor circuit to reduce the amps across
>>>> the points. That would keep the points from burning and extend the
>>>> life of the points. Has anyone on the list tried this? The author
>>>> of the article claims he has 20,000 miles on the conversion and new
>>>> looking contact points. Thoughts, comments, suggestions.....
>>>> Regards
>>>> Ray
>>>>
>>>>
>>>
>>
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Kees,<br>
<br>
I fit diodes per the 'standard:'
<a class="moz-txt-link-freetext"
href="https://en.wikipedia.org/wiki/Flyback_diode";>https://en.wikipedia.org/wiki/Flyback_diode</a><br>
<br>
I don't remember how I fit the transil; I'm pretty sure I did it
correctly because they came with instructions. AFAIK, transils are a
pair of zener/avalanche diodes in both polarity, so they 'breakdown'
and allow current flow at the nominal rating (IIRC, they were 20V or
thereabouts).<br>
<br>
I think one possible problem with points is when they aren't
installed so as to promote the 'wiping' action to clean them.<br>
<br>
Bob<br>
<br>
<div class="moz-cite-prefix">On 10/20/2020 9:16 AM, Kees Oudesluijs
via Healeys wrote:<br>
</div>
<blockquote type="cite"
cite="mid:4fff6613-fd75-0f1a-8556-0b66fb5b72df@chello.nl">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<p>Bob, <br>
</p>
<p>Did you fit the transil in the same way the diode was fitted?
If so this is not correct. It should be fitted as the capacitor
is fitted, between the small screw that holds the points blade
and one of the bigger screws that fix the Bakelite bridge to the
coil body. You can fit the transil instead of the capacitor or
parallel to the capacitor. A diode is fitted in series with the
points, a transil or capacitor is fitted over the points.<br>
</p>
<p>Kees Oudesluijs<br>
</p>
<div class="moz-cite-prefix">Op 20-10-2020 om 17:18 schreef Bob
Spidell:<br>
</div>
<blockquote type="cite"
cite="mid:c8d0ee37-49cd-9bd5-a3c2-1ceb87ae51aa@comcast.net">
<meta http-equiv="Content-Type" content="text/html;
charset=UTF-8">
The late Dave DuBois, who designed the transistor-switch fix,
quit doing the conversions when he found the reduced voltage
cross the points allowed them to oxidize. I tried the transil
fix, but didn't get much more longevity than a stock points
setup with a diode; I do know some have had better luck with
them.<br>
<br>
I have a points/diode pump in my BN2 that works well, but I only
have a few hundred miles in the car. I've lost track of what
I've got in my BJ8.<br>
<br>
Bob<br>
<br>
<div class="moz-cite-prefix">On 10/19/2020 11:31 PM, Kees
Oudesluijs via Healeys wrote:<br>
</div>
<blockquote type="cite"
cite="mid:73d5d6ff-dfc0-b415-c04e-e18d66fab85d@chello.nl">
<meta http-equiv="Content-Type" content="text/html;
charset=UTF-8">
<p>When rebuilding SU electrical fuel pumps I ad a transil
(e.g.. 1.5 KE18CA) over the points, parallel or in stead of
the capacitor if fitted. This reduces the max voltage across
the points to 18V instead of several hundreds when the
contact is broken and the points spark. <br>
</p>
<p>It is also important to clean and polish the points using
flower paper (2-3000 grid), also when new!!</p>
<p>A transil is more or less a bi-directional Zener diode.
They cost next to nothing. I buy them in bulk and pay about
$0,15 but when buying only one expect to pay between $1 and
$5. Ebay is an excellent way to source transils (mainly from
China).</p>
<p>A transistor circuit similar to those used in early
transistorised ignition systems does a similar job by
limiting the current through the points<br>
</p>
<p>Kees Oudesluijs</p>
<p><br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">Op 20-10-2020 om 07:50 schreef
Ray Juncal via Healeys:<br>
</div>
<blockquote type="cite"
cite="mid:1394757800.1379256.1603173043489@mail.yahoo.com">
<meta http-equiv="content-type" content="text/html;
charset=UTF-8">
<div class="yahoo-style-wrap" style="font-family:Helvetica
Neue, Helvetica, Arial, sans-serif;font-size:16px;">
<div dir="ltr" data-setdir="false">I'm rebuilding a couple
of early S. U. fuel pumps for my 100. In checking my
reference files I came across an article from the MG
club about adding a transistor circuit to reduce the
amps across the points. That would keep the points from
burning and extend the life of the points. Has anyone on
the list tried this? The author of the article claims he
has 20,000 miles on the conversion and new looking
contact points. Thoughts, comments, suggestions.....<br>
</div>
<div dir="ltr" data-setdir="false">Regards</div>
<div dir="ltr" data-setdir="false">Ray<br>
</div>
</div>
<br>
<br>
</blockquote>
<br>
</blockquote>
<br>
</blockquote>
</blockquote>
<br>
</body>
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