12 volt change 420

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dr1zsk1
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12 volt change 420

Post by dr1zsk1 » Tue Apr 01, 2014 5:37 am

I have few questions.

When I bought my 420 it had a 12 volt "conversion".

I have 475 amp battery, a one wire alternator.

If I replace the coil what coil should I use and what resistor?

When I measure volts before and after the resistor on the rig it's the same about 12.07.
If man can break it man can fix it .. it just takes time and money.

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Post by Lavoy » Tue Apr 01, 2014 8:00 am

If you are putting on a new coil, just buy an internally resisted coil, that is what I do. If you put a regular coil on, use a Chrysler ballast resistor. Voltage will be high initially, then decrease as the resistor warms up.
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dr1zsk1
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Should it be a 12 volt or a 6 volt coil?

Post by dr1zsk1 » Tue Apr 01, 2014 8:31 am

Should it be a 12 volt or a 6 volt coil?
If man can break it man can fix it .. it just takes time and money.

johnwesley
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Post by johnwesley » Tue Apr 01, 2014 9:35 am

That will be an internally resisted 12 volt coil.
JWO

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Post by Lavoy » Tue Apr 01, 2014 3:26 pm

Good catch, yes 12 volt.
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johnwesley
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Post by johnwesley » Tue Apr 01, 2014 7:18 pm

I try to help when I can (not often) :D
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boler76
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12 volt change 420

Post by boler76 » Wed Apr 02, 2014 3:47 pm

if it is now 12volt, just buy a 12volt coil, no need for any resistors, now if you use a 6 volt coil on 12 volts , then you need a resistor

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Post by johnwesley » Wed Apr 02, 2014 9:16 pm

If you don't buy an internal resisted 12vcoil or put an external resistor on a 12vcoil you will burn up your points in short order
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Post by whiteclipse16 » Thu Apr 03, 2014 5:51 am

Correct, 12volt coil should only get 12volts during start. When running it should get 8 volts.
The 12 volts on start is not crucial, just makes them start a little better.
Ben

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Stan Disbrow
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Post by Stan Disbrow » Thu Apr 03, 2014 7:58 am

Hi,

12v to the coil on start is not needed with low compression. That was dreamed up for those big blocks with 14:1 running on Blue Sunoco 110 octane. The starter sucked so much more power, to turn over against the high compression, that the coil became starved by the massive system voltage drop. Hence, the coil resistor bypass.

My old M wheel tractor, with those custom pistons dad made up for it, is running 12:1 and needs 100 octane gas or it detonates and kills spark plugs. It puts out more power now than a end-of-life series 440. I have to watch that I don't overheat the poor thermocycle system ever since. Sounds great, though. Makes more of a 'crack-crack' than a 'pop-pop' sound now. I get this huge grin every time I fire it up. It is now a garden cultivator machine, so it has a steady job these days.

Anyway, my point is, it has way more compression than it ought to, yet it starts right up with the original 6v everything. We don't need to get all fancy with a new switch that bypasses the coil resistor on start for machines with 12v conversions.

Stan
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Useta Have: '58 JD 420c 5-roller w/62 inside blade
Useta Have: '78 JD350C w/6310 outside blade
Useta Have: '68 JD350, '51 Terratrac GT-25
Have: 1950 M, 2005 x495, 2008 5103 (now known as 5045D)

boler76
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12 volt coil

Post by boler76 » Fri Apr 04, 2014 1:51 pm

I am about to learn something. So if you need a resistor with a 12v coil used on 12v system, what is the voltage required on the 12v coil and what is the wattage of the resister that is needed?

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Stan Disbrow
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Post by Stan Disbrow » Fri Apr 04, 2014 2:24 pm

Hi,

Well, 6 volts is what you are after. The coil is around 1.5 ohms, so draws around 4 amps at 6 volts.

Stick 12v onto it and it will draw 8 amps. The coil is physically sized to dissipate 24 watts of heat, not 48 watts. So one can burn up the coil. I mean the wiring inside the coil case. It won't burst into flames. ;)

Also, the arcing at the breaker points will be double the energy as well. Burning up the points is likely to occur prior to burning out the coil. Sort of a safety for the coil, but either way the machine quits. Either in the worst spot, or at the point furthest from your tools. You pick! :P

Anyway, good old Ohm's Law comes to our aid. Using it, if we double the voltage, and leave the resistance unchanged, we double our current. And, current multiplied by voltage equals wattage, which is to say heat.

All we need to do is double the resistance when we double the voltage. So, add another 1.5 ohms in series with the original 1.5 ohms and we wind up right where we started from as far as coil and points current is concerned.

As for resistor wattage, it will be 24 watts. Resistors in the 20 watt range will be made from wire internally, cased in ceramic. They get pretty warm, so mount it somewhere away from the rest of the wiring harness.

The old school coils had a tin mounting bracket on the side of the case to hold the resistor. That was always a good spot to stick it. Use a radiator clamp around the coil. Bend it to go around the resistor. Don't tighten too much. The ceramic will crack....

Stan
There's No Such Thing As A Cheap Crawler!

Useta Have: '58 JD 420c 5-roller w/62 inside blade
Useta Have: '78 JD350C w/6310 outside blade
Useta Have: '68 JD350, '51 Terratrac GT-25
Have: 1950 M, 2005 x495, 2008 5103 (now known as 5045D)

boler76
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12v coil

Post by boler76 » Fri Apr 04, 2014 5:55 pm

I understand the problem with putting 12v on a 6 volt coil, but dont understand why a resister is needed if the coil is rated at 12v and the battery is 12v, How hot would an internally resisted coil get with a 24watt resister inside the can?

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Post by Lavoy » Fri Apr 04, 2014 6:13 pm

The points can not stand the continuous 12 volt load. Whether internally, or externally resisted, the load is reduced so point life is extended.
As far as what temp an internally resisted coil would get to, I have no idea, but it was designed to function with the resistor in place, so it is not an issue.
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boler76
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12v coil

Post by boler76 » Fri Apr 04, 2014 6:20 pm

OK thanks for the info

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