to30 coil question

Jimmydog · Sep 28, 2018

Hi guys!
Some of you may already have seen my post up on the tractor talk board, but this is my first time down in this section. I'm looking foward to meeting some more fine folks with the same ethusiasm for fergies as I've been infected with. So I just got around to ordering some parts for it and a owners manual and it should be here next week. In the mean time I have a question about the ignition system. It came to me without spark and I found the coil is shot. It's still original 6vdc positive ground. While looking about for a coil I read somewhere were the coil is only 10amps max. current, and I read else where were the generator puts out 25amps max. now I know that 25amps is at high rpm but still what keeps the coil from frying? The one that's on there now doesn't have an internal resistor and there isn't any in wire harness. The wiring diagram I found on the internet is rather rudimentary and doesn't show any resistor either. So is this tractor supposed to have a resistor in the circuit? Any help would be appriciated, thanx. I'll check back in a couple hours as the mosquitoes haven't been feed yet today.

JD

Bob · Sep 28, 2018

Electrical system voltage and coil primary resistance determine coil primary current (and heating).

"6 Volt" electrical systems typically operate at about 7.4 Volts and the proper coils are designed with a primary resistance that limits current to around 4 Amps or less.

Dunno where you saw the "10 Amps" reference?

Even IF the generator is CAPABLE of 25 Amps, the coil isn't going to be affected much by what the generator is doing, unless it's SEVERELY overcharging/boiling the battery.

So if the charging system is operating properly and you purchase a good-quality 6 Volt coil, there should be no issues.

rvirgil_KS · Sep 28, 2018

" I read somewhere were the coil is only 10amps max. current," Coil max should be about 4 amps.

A generator with 25 amp max rating while capable of 25 amps will be limited by the regulator to the actual circuit load demand. If the current demand of a coil is 4 amps and the battery demands a charge of 10 amps the regulator will limit output to the required 14 amps. The coil and battery are in parallel so the demands of coil and battery are independent of each other. As the battery charges and its charge current demand goes down, the output of the generator will go down, but the coil will still maintain it's 4 amp demand. A generator will seldom output at it's max rating.

A 6 volt system does not require an external resistor for the coil

Ron(Ont) · Sep 28, 2018

A 6 volt coil will measure 1.5 ohms or so. A 12 volt coil will measure about 3 ohms. You can use a 6 volt coil on a 12 volt system by adding a 1.5 ohm resistor in series.

As said above, Current = voltage/resistance so 6 volts/1.5 ohms =4 amperes.

Jimmydog · Sep 29, 2018

Thanks for all the info people. I knew it was something simple I wasn't getting my head around. I was worried that the new coil might burn out as soon as I hooked it up. So now I'm wondering what caused the old coil to fail? It's definitely been replaced recently, it looks brand new. The voltage regulator looks like the worse part on the tractor so I ordered a new one of those from the fine folks at YT also. Anyway, stayed tuned as I'll have a lot more dumb questions to come as I putter around on this thing. I'll give a shout back after I get it to bark.

Thanks again.
JD

old · Sep 29, 2018

One thing come to mind as to how/why a coil may have burned out. If one used the stupid way of checking the charging system by pulling a battery cable off he battery when it is running that takes out the buffer of the battery so the coil can then see higher volts and amps causing all sorts of odd problems.

to30 coil question

Jimmydog

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Bob

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rvirgil_KS

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Ron(Ont)

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Jimmydog

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old

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