resistor output voltage

[Ben Taylor]

I have a to30 Ferguson that i am doing a 12 volt conversion on. My question is what should my output voltage be on my resistor? i
am showing 11.6 volts. I have not installed the altenator yet, just running off o fbattery power.

 

[Bruce(OR)]

Too long since I dd mine and too early in the morning to remember much.
I believe I ran 3.0/3.5 ohm resistor and about 8.35V or such to the points.
Others should chime in shortly with better knowledge.

 

[TR3driver]

The resistor only reduces voltage when there is a load on it. If you check it with the coil connected and the points closed, you should find somewhere around 6-8 volts.

 

[TR3driver]

With the engine running, the voltage from the resistor bounces around all over the place with every cylinder firing. What you read in that case will depend greatly on the particular meter you use.

 

[Ben Taylor]

I was using a digital multimeter, the
engine was running. I am mostly concerned
about burning a set of points up. Can I
change my coil out to a 12 volt coil and
be done or is the condenser in my points
only good for 6 volts?

 

[Ron(Ont)]

(quoted from post at 06:00:19 04/10/20) I was using a digital multimeter, the engine was running. I am mostly concerned about burning a set of points up. Can I
change my coil out to a 12 volt coil and be done or is the condenser in my points only good for 6 volts?

The condensors are rated for a couple hundred volts ,so no issue there. You can go with a 12 volt coil. It eliminates 2 wire connections at the resistor, which can oxidize and cause problems. Take note though, that the resistor should be 1.5 ohms. A 6 volt coil will measure about 1.5 ohms and a 12 volt coil about 3 ohms. A resistor plus 6 volt coil in series needs to measure 3 ohms total.

You really cannot measure the voltage at the resistor because, as you noticed, the voltage comes and goes as the points open and close.

 

[Ben Taylor]

Do I need to coil a 12volt could with a
built in resistor or just a straight 12
volt coil

 

[rvirgil_KS]

There are 2 versions of a ?12 volt coil?

One is marked ?12 volts ? external resistor required?. The primary winding (+ to ? terminals), is one continuous coil of wire with about 1 ? ohms resistance. This can be used on 6 volt system without a resistor or 12 volt systems with a resistor.

The other is marked ?12 volts-- no external resistor required?. It does not have an added resistor inside the can. The primary (+ to -) is one continuous coil of wire with about 3 ohms resistance. (As indicated it is for use in 12 volt system with no added resistor) In a 12 volt tractor use of this coil with an external resistor will give hard starting and poor performance. It will not work in 6 volt system.

NAPA IC14SB or equivalent is a 12 volt, no resistor required coil.

Check voltage at the coil with engine not running.
With resistor and 1 ? ohm coil you should have these approximate voltages:
Points open: near battery voltage on both sides of the resistor and both + and ? terminals of coil.
Points closed: Near battery voltage at input to resistor, half battery voltage at resistor side of coil, and near zero volts at output of coil.

With 3 ohm coil (no resistor) you should have:
Points open: near battery voltage at both + and ? terminals of coil
Points closed: near battery voltage at input to coil and near 0 volts at output.

Positive ground + of coil to side of distributor, negative ground ? of coil to side of distributor.

With engine running, a common volt meter cannot respond to voltage changes as rapidly as points open close, thus giving erratic reading.

Other than keeping battery charged, the alternator or generator has no effect on ignition system.

Condenser doesn?t care if system is 6 or 12 volt.

So you can either run original 6 volt coil with resistor, or direct 12 volt ? no resistor required without an added resistor.