Ballast resistor

D

DaveHerns

New Member
Does anyone know where the ballast resistor is on a 1973 3500S? There must be one as I get 10 volts on the + side of the coil when the engine is running and about 14 volts on any other live feed OR I have a voltage drop I need to find

I've just built a transistorised ignition kit from Maplins £9.99 which actually works. Not that dificult to build . It retains the points but they only switch a low current and in theory never wear out. Even the rev counter works

I had to take the live feed from the washer pump as my coil is only getting 10 volts at the moment. It works like this but I would like to be sure I'm getting full strength sparks
Dave
 
I think the ballast resistor is actually wrapped in the loom. They are normally a length of resistance wire.
I took a +ve feed from fuse box and ran it through the grommet near the wiper motor when I wanted a supply for a lumenition set up. I presume you must be running a 12v coil now?
 
No, I'm running the same coil as before which was the correct substitute for the original .This Maplin unit fits in the wire between the distributor and the coil (as well as a 12v feed and
an earth) so I figured the same coil would be OK
I have a 1970's Mobelec capacitative discharge unit - that worked ,but the rev counter didn't. I also have a Lumenition I took out of my Mk4 Cortina in 1983 and it's been on the shelf ever since.I suppose all that needs is the 8 cylinder "chopper" to go under the rotor arm ,Does the rev counter work with the Lumenition ?
Do you know why my distributor seems noisy- a rotating noise which gets less if you pull on the adjusting screw. Any cheap cure?
 
The original coil should be for a ballasted system in which case using with a 12v feed will overheat it as it will draw to much current. The idea of the ballast resistor is to allow it to be shorted out when starting to compensate for the battery voltage drop caused by the huge load from the starter motor.

One way to check is to measure the resistance of the coil ballasted =1.5 Ohm and unballasted =3 Ohm. If you want to get a bit more HT voltage from the system I'd get a sports coil like a LUCAS gold coil or ALDON flame thrower coil. These are available for ballasted and un ballasted systems so if you want to change to an unballasted system you can although there won't be any advantage either way apart from you might experience problems starting from cold with an unballasted system under tough conditions.

Note increasing the spark energy available doesn't neccassarily increase the HT spark voltage. If the plug gaps stay the same so does the HT spark voltage required to jump the gap. However a more powerful system will manage to fire a plug under more arduous condition i.e. higher compression ratio or poor mixture which is why they are normally used with an uprated engine. Saying that I don't think there is anything to be lost by uprating your ignition coil.


Noisy distributor is probably a loose base (the bit the point bolt to) it rotates to advance the spark as revs increase but is notorious for wearing (mines knackered to). I don't think there are spare parts available to recondition but you might be able to do something.

By the way I'm running standard coil and single points on an uprated 3.9 with weber at the moment and it works fine. I spent about 3 weeks messing around with lumention and mallory dual point distributors the best results came with the simplest set up. And that is measured using an ignition scope!
 
I also have a Lumenition I took out of my Mk4 Cortina in 1983 and it's been on the shelf ever since.I suppose all that needs is the 8 cylinder "chopper" to go under the rotor arm ,
Click to expand...

Lumenition kit uses same module but with different moutings for the optical sensor and chopper to fit different distributors. It is unlikely that the Mk4 cortinal distributor optical sensor mounting will be the same as you V8 ((?) distributor but you never know!! Look on Lumentiotion website applicaitons; lists the parts for a lot of vehicles.

Does the rev counter work with the Lumenition ?
Click to expand...
Very likely yes. The rev counter is connected to the LT part of the coil that is switched by the points or by Lumention module so it does not does not know as to how the coil is being swtiched.

Bear in mind that the Lumentiontion Chopper is cut out to set the dwell angle i.e. it is not adjustable and I have a feeling that that rpm counters average the voltage so the dwell will make a difference. (looking up ho analogue rev counters work so this may not be correct - after market rev counters have a switch for 4-6-8 cylinders so I have a feeling dwell makes a difference)
 
Thanks for that
My £9.99 Maplin electronic ignition kit is still working well
I'll spend any spare money on the forthcoming MOT....
Dave
 
Dave,

where did you get the 12V for the unbalasted ignition coil from?
Do you still feed the coil from the washer pump?

Bandito.
 
I used the original coil so I used the original feed
If it had been a 12v coil I see no reason not to use the washer pump live feed
This ignition unit is basically just a switching unit
 
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