Series 3 SNGB Ignition Conversion

[chris420sa]

Hi All
About 2 years ago, I replaced the previous SNG ignition conversion on my Series 3 E-type with a new SNG Ignition conversion (not HE).

i just wanted to check the following with other forum members who have this converted ignition system:

1. the original ballast resistor (i.e. pre SNGB, "OPUS days") was required to ensure 12 volts to the 9 volt coil when starting the engine. After starting when the ignition key was returned to position II the voltage to the coil was reduced to 9 volt
2. with the SNGB conversion is that still the case OR is the "ballast resistor" now just a connector between ignition, coil and amplifier?
I checked the voltage on the coil for ignition switch positions II and III and it remained at 12 volts which would indicate that 2 above is correct?

I guess it's a question I should have asked some time ago!

Look forward to the usual well-informed responses
Chris

[MarekH]

...with the SNGB conversion is that still the case OR is the "ballast resistor" now just a connector between ignition, coil and amplifier?

Perhaps we can phone SNGB for you and report back? Just call them, instead of asking a random group of strangers who may or may not know the answer.

I checked the voltage on the coil for ignition switch positions II and III and it remained at 12 volts which would indicate that 2 above is correct?

This doesn't always necessarily tell you what you want. If you connect something to 12v and it isn't connected at the other end, it'll just end up all being at 12v, much like a bird sitting on a telegraph (or HT power) wire.* By contrast, when current is flowing and if components are connected in series, the voltage drop seen across them will be proportional to the impedance presented (as the coil charges).

kind regards
Marek

*Another example:- with a negative earth car, the s1 windscreen wiper motor is sitting permanently at 12v until the wipers are in use, when the earth side of the circuit is connected.

[jagwit]

1. the original ballast resistor (i.e. pre SNGB, "OPUS days") was required to ensure 12 volts to the 9 volt coil when starting the engine. After starting when the ignition key was returned to position II the voltage to the coil was reduced to 9 volt

In many ignition systems, the ballast resistor is bypassed during cranking to ensure the maximum coil charging during cranking. Keep in mind that during cranking, the voltage is unlikely to be "12V" but something much lower, depending on battery, cabling and grounding conditions. This lower voltage (whatever it may be) is what is then directly applied to the coil (during cranking only).

I've never heard of a "9V coil. (Not saying it does not exist). I have heard of 6V coils.

2. with the SNGB conversion is that still the case OR is the "ballast resistor" now just a connector between ignition, coil and amplifier?

I do not speak for SNG but being a modern ignition system, it SHOULD have all kinds of modern ignition system functionality built in, I would expect. Such as, voltage compensation - which should increase dwell time (coil charge time ) specially during cranking, when voltage levels are low as per #1 above. These modern ignition systems SHOULD also obviate the need for a ballast resistor (with built-in current limiting and RPM detection) and should also work best with a low primary resistance 12V coil on the V12.

Having a ballast resistor in series with the SNG ignition system MIGHT be counter productive - specially at higher revs. Best is to follow the installation instructions - hoping they are sufficiently comprehensive.

The ballast resistor MIGHT still be needed for other purposes, eg, like a series resistor in line going to the tacho, (to prevent the tach from being fried by the coil- spikes).

[chris420sa]

Hi Marek and Phillip
Many thanks for your helpful responses.
I contacted SNG Barratt and early last week I sent them my ballast resistor (BR) for testing. Their technical guy, Brian, spoke with me and advised that:
a) the BR as supplied with their Ignition Conversion Kit is totally different to that which was used for the original OPUS system
b) the SNGB BR has a direct connection across it for the "12 volt" supply from the ignition switch, and a resistor on the tacho part of the circuit, and
c) the supply to the BR and coil from the starter relay when cranking (white wire with straight blue tracer) is not connected across the BR and is therefore redundant when the Conversion Kit is fitted.

When Brian tested my BR he found that the tacho circuit was not working. SNGB will send me the test results.

I purchased a replacement BR, fitted it and all works fine.

Andy and Brian at SNGB were very helpful and I must commend them on their high service level.

Best regards
Chris

[Danetype3]

Hi Chris

I have had the same questions and got this schematic for the SNG ballast resistor. The original system used the ballast resistors to get a stronger spark during cranking. I guess the spark is now always strong, so that is not needed anymore.

I am not fitting this new ballast resistor anymore. Just a simple 10k resistor to the tach will do. One could also replace the double starter relay with a standard SPST relay. It is all just preferences. I like to keep things simple, but I know it can be more confusing for future owners to deviate from standard.

Paul