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As they came out of the factory the primary for a CB should be 3.1 to
3.5 ohms. For RB cars and points ignition they were 1.5 ohms, with the
45DE4 electronic distributor they were 1.4 ohms, both with a 1.5 ohms
(approx) ballast resistance contained with the harness, which meant the
overall resistance and hence current are about the same for both CB and
RB. With the 45DM4 distributor they were 0.8 ohms with no ballast,
which gave a very high coil current but the 45DM4 is a variable dwell
system which gives very short pulses of current to the coil, much
shorter than points.
An easier way to check the overall system is to remove the wiring from
the coil -ve or CB, turn on the ignition, and connect an ammeter between
the coil -ve or CB and earth. With points and 45DE4 you should see
about 4 amps. With 45DM4 you should see about 15 amps which may well be
above the capacity of your ammeter, disconnect immediately, only run
that coil with a variable dwell system.
Lower than 4 amps you may well have a 12v 3 ohm coil in series with a
ballast resistance which will give a reduced spark. Higher - up to
about 8 amps - you may have a 6v 1.5 ohm coil with no ballast
resistance, this will overheat on anything except a variable dwell
electronic system, and with points will burn them.
PaulH.
On 25/02/2024 21:20, William Killeffer wrote:
> Hello everyone,
>
> My car's a 1974 MGB with an 18GK engine and twin HS4 carbs. I've been
> running a Pertronix distributor with its matching coil for awhile, but
> just got the car's 25D back from Jeff at Advance, and it looks better
> than what it probably did when it was new. I'm going to go back to
> using points and condenser with the rebuilt distributor.
>
> I still have the factory Lucas coil that came with the car when I
> first obtained it. I checked the resistance to see if it was still
> useful, and here's what I found:
>
> With a small handheld analog meter, it registered around 6700ohm
> across the secondary, and the little meter's not capable of giving a
> reading for the primary.
>
> On the new-to-me Sears Engine Analyzer, the primary shows 5.6ohm and
> the secondary shows 5100ohm.
>
> Either way, that looks too high given some of the other numbers I've
> seen. I haven't checked the Pertronix coil, but will before trying to
> use it.
>
> Am I right in believing this original coil shouldn't be used?
>
> Thank you,
> -Bill
> Sent from my iPhone
>
> _______________________________________________
>
> Mgs@autox.team.net
> Donate:http://www.team.net/donate.html
> Suggested annual donation $12.75
>
> Archive:http://www.team.net/pipermail/mgs http://autox.team.net/archive
>
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<p>As they came out of the factory the primary for a CB should be
3.1 to 3.5 ohms. For RB cars and points ignition they were 1.5
ohms, with the 45DE4 electronic distributor they were 1.4 ohms,
both with a 1.5 ohms (approx) ballast resistance contained with
the harness, which meant the overall resistance and hence current
are about the same for both CB and RB. With the 45DM4 distributor
they were 0.8 ohms with no ballast, which gave a very high coil
current but the 45DM4 is a variable dwell system which gives very
short pulses of current to the coil, much shorter than points.</p>
<p>An easier way to check the overall system is to remove the wiring
from the coil -ve or CB, turn on the ignition, and connect an
ammeter between the coil -ve or CB and earth. With points and
45DE4 you should see about 4 amps. With 45DM4 you should see
about 15 amps which may well be above the capacity of your
ammeter, disconnect immediately, only run that coil with a
variable dwell system.</p>
<p>Lower than 4 amps you may well have a 12v 3 ohm coil in series
with a ballast resistance which will give a reduced spark. Higher
- up to about 8 amps - you may have a 6v 1.5 ohm coil with no
ballast resistance, this will overheat on anything except a
variable dwell electronic system, and with points will burn them.</p>
<p>PaulH.<br>
</p>
<div class="moz-cite-prefix">On 25/02/2024 21:20, William Killeffer
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:D7B079A5-C4CE-4D9F-BBD1-E3C009485358@epbfi.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<span
style="caret-color: rgb(20, 20, 20); color: rgb(20, 20, 20); font-family:
"Segoe UI", "Helvetica Neue", Helvetica, Roboto, Oxygen,
Ubuntu, Cantarell, "Fira Sans", "Droid Sans", sans-serif;
font-size: 15px; -webkit-text-size-adjust: 100%; background-color: rgb(254,
254, 254);">Hello
everyone,</span><br
style="box-sizing: border-box; margin-top: 0px; caret-color: rgb(20, 20, 20);
color: rgb(20, 20, 20); font-family: "Segoe UI", "Helvetica
Neue", Helvetica, Roboto, Oxygen, Ubuntu, Cantarell, "Fira
Sans", "Droid Sans", sans-serif; font-size: 15px;
-webkit-text-size-adjust: 100%;">
<br
style="box-sizing: border-box; caret-color: rgb(20, 20, 20); color: rgb(20, 20,
20); font-family: "Segoe UI", "Helvetica Neue", Helvetica,
Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid
Sans", sans-serif; font-size: 15px; -webkit-text-size-adjust: 100%;">
<span
style="caret-color: rgb(20, 20, 20); color: rgb(20, 20, 20); font-family:
"Segoe UI", "Helvetica Neue", Helvetica, Roboto, Oxygen,
Ubuntu, Cantarell, "Fira Sans", "Droid Sans", sans-serif;
font-size: 15px; -webkit-text-size-adjust: 100%; background-color: rgb(254,
254, 254);">My
car's a 1974 MGB with an 18GK engine and twin HS4 carbs. I've
been running a Pertronix distributor with its matching coil for
awhile, but just got the car's 25D back from Jeff at Advance,
and it looks better than what it probably did when it was new.
I'm going to go back to using points and condenser with the
rebuilt distributor. </span><br
style="box-sizing: border-box; caret-color: rgb(20, 20, 20); color: rgb(20, 20,
20); font-family: "Segoe UI", "Helvetica Neue", Helvetica,
Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid
Sans", sans-serif; font-size: 15px; -webkit-text-size-adjust: 100%;">
<br
style="box-sizing: border-box; caret-color: rgb(20, 20, 20); color: rgb(20, 20,
20); font-family: "Segoe UI", "Helvetica Neue", Helvetica,
Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid
Sans", sans-serif; font-size: 15px; -webkit-text-size-adjust: 100%;">
<span
style="caret-color: rgb(20, 20, 20); color: rgb(20, 20, 20); font-family:
"Segoe UI", "Helvetica Neue", Helvetica, Roboto, Oxygen,
Ubuntu, Cantarell, "Fira Sans", "Droid Sans", sans-serif;
font-size: 15px; -webkit-text-size-adjust: 100%; background-color: rgb(254,
254, 254);">I
still have the factory Lucas coil that came with the car when I
first obtained it. I checked the resistance to see if it was
still useful, and here's what I found:</span><br
style="box-sizing: border-box; caret-color: rgb(20, 20, 20); color: rgb(20, 20,
20); font-family: "Segoe UI", "Helvetica Neue", Helvetica,
Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid
Sans", sans-serif; font-size: 15px; -webkit-text-size-adjust: 100%;">
<br
style="box-sizing: border-box; caret-color: rgb(20, 20, 20); color: rgb(20, 20,
20); font-family: "Segoe UI", "Helvetica Neue", Helvetica,
Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid
Sans", sans-serif; font-size: 15px; -webkit-text-size-adjust: 100%;">
<span
style="caret-color: rgb(20, 20, 20); color: rgb(20, 20, 20); font-family:
"Segoe UI", "Helvetica Neue", Helvetica, Roboto, Oxygen,
Ubuntu, Cantarell, "Fira Sans", "Droid Sans", sans-serif;
font-size: 15px; -webkit-text-size-adjust: 100%; background-color: rgb(254,
254, 254);">With
a small handheld analog meter, it registered around 6700ohm
across the secondary, and the little meter's not capable of
giving a reading for the primary.</span><br
style="box-sizing: border-box; caret-color: rgb(20, 20, 20); color: rgb(20, 20,
20); font-family: "Segoe UI", "Helvetica Neue", Helvetica,
Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid
Sans", sans-serif; font-size: 15px; -webkit-text-size-adjust: 100%;">
<br
style="box-sizing: border-box; caret-color: rgb(20, 20, 20); color: rgb(20, 20,
20); font-family: "Segoe UI", "Helvetica Neue", Helvetica,
Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid
Sans", sans-serif; font-size: 15px; -webkit-text-size-adjust: 100%;">
<span
style="caret-color: rgb(20, 20, 20); color: rgb(20, 20, 20); font-family:
"Segoe UI", "Helvetica Neue", Helvetica, Roboto, Oxygen,
Ubuntu, Cantarell, "Fira Sans", "Droid Sans", sans-serif;
font-size: 15px; -webkit-text-size-adjust: 100%; background-color: rgb(254,
254, 254);">On
the new-to-me Sears Engine Analyzer, the primary shows 5.6ohm
and the secondary shows 5100ohm.</span><br
style="box-sizing: border-box; caret-color: rgb(20, 20, 20); color: rgb(20, 20,
20); font-family: "Segoe UI", "Helvetica Neue", Helvetica,
Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid
Sans", sans-serif; font-size: 15px; -webkit-text-size-adjust: 100%;">
<br
style="box-sizing: border-box; caret-color: rgb(20, 20, 20); color: rgb(20, 20,
20); font-family: "Segoe UI", "Helvetica Neue", Helvetica,
Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid
Sans", sans-serif; font-size: 15px; -webkit-text-size-adjust: 100%;">
<span
style="caret-color: rgb(20, 20, 20); color: rgb(20, 20, 20); font-family:
"Segoe UI", "Helvetica Neue", Helvetica, Roboto, Oxygen,
Ubuntu, Cantarell, "Fira Sans", "Droid Sans", sans-serif;
font-size: 15px; -webkit-text-size-adjust: 100%; background-color: rgb(254,
254, 254);">Either
way, that looks too high given some of the other numbers I've
seen. I haven't checked the Pertronix coil, but will before
trying to use it.</span><br
style="box-sizing: border-box; caret-color: rgb(20, 20, 20); color: rgb(20, 20,
20); font-family: "Segoe UI", "Helvetica Neue", Helvetica,
Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid
Sans", sans-serif; font-size: 15px; -webkit-text-size-adjust: 100%;">
<br
style="box-sizing: border-box; caret-color: rgb(20, 20, 20); color: rgb(20, 20,
20); font-family: "Segoe UI", "Helvetica Neue", Helvetica,
Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid
Sans", sans-serif; font-size: 15px; -webkit-text-size-adjust: 100%;">
<span
style="caret-color: rgb(20, 20, 20); color: rgb(20, 20, 20); font-family:
"Segoe UI", "Helvetica Neue", Helvetica, Roboto, Oxygen,
Ubuntu, Cantarell, "Fira Sans", "Droid Sans", sans-serif;
font-size: 15px; -webkit-text-size-adjust: 100%; background-color: rgb(254,
254, 254);">Am
I right in believing this original coil shouldn't be used?</span><br
style="box-sizing: border-box; caret-color: rgb(20, 20, 20); color: rgb(20, 20,
20); font-family: "Segoe UI", "Helvetica Neue", Helvetica,
Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid
Sans", sans-serif; font-size: 15px; -webkit-text-size-adjust: 100%;">
<br
style="box-sizing: border-box; caret-color: rgb(20, 20, 20); color: rgb(20, 20,
20); font-family: "Segoe UI", "Helvetica Neue", Helvetica,
Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid
Sans", sans-serif; font-size: 15px; -webkit-text-size-adjust: 100%;">
<span
style="caret-color: rgb(20, 20, 20); color: rgb(20, 20, 20); font-family:
"Segoe UI", "Helvetica Neue", Helvetica, Roboto, Oxygen,
Ubuntu, Cantarell, "Fira Sans", "Droid Sans", sans-serif;
font-size: 15px; -webkit-text-size-adjust: 100%; background-color: rgb(254,
254, 254);">Thank
you,</span><br
style="box-sizing: border-box; caret-color: rgb(20, 20, 20); color: rgb(20, 20,
20); font-family: "Segoe UI", "Helvetica Neue", Helvetica,
Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid
Sans", sans-serif; font-size: 15px; -webkit-text-size-adjust: 100%;">
<span
style="caret-color: rgb(20, 20, 20); color: rgb(20, 20, 20); font-family:
"Segoe UI", "Helvetica Neue", Helvetica, Roboto, Oxygen,
Ubuntu, Cantarell, "Fira Sans", "Droid Sans", sans-serif;
font-size: 15px; -webkit-text-size-adjust: 100%; background-color: rgb(254,
254, 254);">-Bill</span><br
id="lineBreakAtBeginningOfSignature">
<div dir="ltr">Sent from my iPhone</div>
<br>
<fieldset class="moz-mime-attachment-header"></fieldset>
<pre class="moz-quote-pre"
wrap="">_______________________________________________
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href="mailto:Mgs@autox.team.net";>Mgs@autox.team.net</a>
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</pre>
</blockquote>
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