Farm Equipment - 12v coil on 6 volt system

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12v coil on 6 volt system

Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=123263
Printed Date: 12 Aug 2025 at 2:02pm
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Topic: 12v coil on 6 volt system

Posted By: Scott B
Subject: 12v coil on 6 volt system
Date Posted: 12 May 2016 at 7:17pm

Can I put a 12 volt coil on a 6 volt system without any concerns?
THink my current 6v coil needs to go back to china, planning on doing a full conversion in a couple of months so wanting a to short term fix with a 12v coil.
Thoughts?

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D17 Series 1
Allis B- 1939
Allis B- 1945

Replies:

Posted By: DougS
Date Posted: 12 May 2016 at 8:28pm

It *might* work. You'll have a weaker spark. I wouldn't recommend it. If it doesn't work you'll still have to buy another coil. Extra $$$. I'd recommend that you buy a 6 volt coil now and add a ballast resistor when you convert to 12 volts.

Posted By: Gerald J.
Date Posted: 12 May 2016 at 9:06pm

A 12 volt coil designed to work with an external resistor should work good on 6 volts but a coil wound for 12 volts or with an internal resistor for 12 volts will give a weak spark on 6 volts. It will depend on the coil details that we have no way of knowing of how bad the spark is at 6 volts, especially when the battery is pulled down while the starter is cranking and may be less than 6 volts.

Gerald J.