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Chris727

What kind of 12 volt coil?

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Chris727
Hi. I recently put a 16hp CI Briggs in my 17GTH-L. The engine had a newer magnetron which was a piece of junk, maybe whoever installed it should have repolarized the flywheel, anyways I temporarily converted it to battery ignition and it ran great, smoother than ever. I recently learned that not all the car coils are created equal. Some have resistors built in, apparently the kohlers are like this, but if they don't then you need some kind of external resistor or else the points will burn up? I have several briggs which were converted to battery ignition using automotive coils which have been marked to be used with external resistors only. Does this mean that if I don't add an in-line resistor I will burn uo the points? Had not had any problems with these machines yet but they sit a lot and often without batteries in them so there's no juice to do harm. If I need another kind of automotive coil altogether, does anyone have any suggestions as to where to get a "Kohler" type or one with the right internal resistor? Are these expensive. Thanks in advance. Chris

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ehertzfeld
I get mine at Napa. I just tell them that I need a 12volt coil with internal resistor, and they bring me a Kohler or a Napa brand replacment for Kholer. The last one I bought, was $26.99 and the condencer was $4.69. Just make sure you ask to get a coil wire, they don't come with the coil. 7-01338 12volt compatable condencer 7-01634 12vot coil "with internal resistor" I forgot to get the wire so I don't have a price or part number, but I don't think they cost too much. Elon

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HubbardRA
The reason for the internal resistor is to prolong the point lift. On the automobiles with points, there was a bypass of the external "ballast resistor" to give the coil a full 12 volts when starting. When the ignition key was released and starter was no longer activated, the current flowed thru the ballast resistor and the voltage being switched by the points was dropped from 12 volts down to 6-8 volts. This helped to prevent burning of the points. It just made them last longer. Even then, the points needed replacement at around 3000 miles. Automotive ignitions were usually set up for this bypass of the ballast resistor, this is why it was elsewhere and not part of the coil. Most Fords and Chevys just used a resistance wire. The older Chrysler products had a separate ballast resistor that mounted on the firewall. I have one of them hanging in my garage. These are usually just a large, high current, 1 ohm resistor. This traces back to when cars were converted from 6 to 12 volt electrical systems. The coils were designed for 6 volts. The cars were started on 12 volts, but then the resistor dropped it back to 6. The coil design stayed the same. In other words, with a resistor it is designed for 12 volts. Without an internal resistor, the coil is designed for 6 volts, since the external resistor drops the voltage. Tractors will run fine without the resistor, but if you either hook up an external resistor or use a coil with an internal resistor then the points will last at least twice as long. Bottom line is that without a resistor, you will have to clean and re-gap the points more often, that's all. They run fine either way.

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GWGAllisfan
I was reading this topic and wondered if there was a common automotive coil I can go buy for this purpose? Like mid-60 chevy, ford,,,etc? I was hoping to just go buy one at AAP or AZ.

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clyde
When I converted my 1st Landlord, I searched different vehicles on NAPA until I found the cheapest coil and resistor. I believe I used a coil and resistor from a 72 Dodge PU with a 318 and non electronic ignition. They were about $20.00 total (before tax). When I did my 712, I never wired the side that bypasses the resistor and didn't notice it for quite awhile - it doesn't fire 'till you let up on the key, but still starts fine.:o)

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