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Larry Miller 
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Joined: 21 Nov 2009
Location: NWIL
Points: 896
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 Topic: 6 to 12 volt conversion ?
Posted: 03 Aug 2020 at 9:32pm |
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Little confused on the 12 volt coil w internal resistor. Why do you need a resistor if you have 12 volt battery w 12 volt coil?
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I used to be young and stupid, now I am not young anymore.
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Dakota Dave
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Joined: 12 Sep 2009
Location: ND
Points: 3893
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Posted: 03 Aug 2020 at 9:41pm |
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12 volt coils were made with and without resistors. The early chevys had two wires going to the coil. One wire came from the terminal of the starter cap 12 volts hot to the coil boosted spark for starting the other wire came from the ignition switch had a resistor in the wire dropped to about 9 volts for continuous run if you ran that (12 volt coil) without a resistor the coil would burn your points to a crisp
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ac45dave
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Joined: 23 May 2015
Location: SE(IN)
Points: 1317
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Posted: 03 Aug 2020 at 9:49pm |
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As long as your coil is 3 ohms across the primary terminals no ballast resistor is needed on the 12v system for a 4 cylinder application.Some 12v coils were internally resisted and some were not.Check your primary resistance.
Edited by ac45dave - 03 Aug 2020 at 9:51pm
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54 wd-45gas ; 56 wd-45d N/F w/fact p/s ; 63 d-17 sIII N/F gas ; 60 D14 N/F ; 67 d-17 sIV N/F gas ; 63D15 sII W/F; 39rc#667 ; 2021 massey 4710 fwa ; gravely 2 wheel tractors
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Steve in NJ
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Joined: 12 Sep 2009
Location: Andover, NJ
Points: 11548
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Posted: 04 Aug 2020 at 7:20am |
Ballast resistors didn't work under the hoods of 60's Automobiles, never mind out in the elements on a Tractor. A 4 cylinder on 12V's needs 2.7-3.3 ohms of resistance in the ignition circuit in order to run correctly. Using an internal resisted 12V/3.0 Ohm Coil on your conversion keeps Mother Nature from messing with it. External Ballast reistors play havoc in high humidity area's as well as on rainy days. Engine missing, no starts, etc. are all part of the havoc Mother Nature plays with an external ballast resistor. HTH Steve@B&B
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39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife
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Larry Miller
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Joined: 21 Nov 2009
Location: NWIL
Points: 896
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Posted: 04 Aug 2020 at 7:39am |
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OK, so changing a WD 45 from 6 to 12, I want a 12 v coil w internal resistor - that right?
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I used to be young and stupid, now I am not young anymore.
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jaybmiller
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Joined: 12 Sep 2009
Location: Greensville,Ont
Points: 21460
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Posted: 04 Aug 2020 at 8:00am |
re: I want a 12 v coil w internal resistor - that right?
that'll work fine, just be sure to remove the exiting ballast resistor !
'old skool' ballast reistors did tend to fail, due to the ceramic casing. I've used Vishay Dale chassis mount resistors for decades with zero failures. These are neat ORANGE anaodized aluminum cases with the resistor inside. totally sealed, solder lugs on the ends, 2 offset small mounting holes. On the D14 I sold, I had a 50Watt version hangin between the coil and dist. They also have a 100W version. As long as you limit current to about 4 amps, you'll be fine.
Jay
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3 D-14s,A-C forklift, B-112
Kubota BX23S lil' TOOT( The Other Orange Tractor)
Never burn your bridges, unless you can walk on water
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Dave(inMA)
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Joined: 12 Sep 2009
Location: Grafton, MA
Points: 2395
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Posted: 04 Aug 2020 at 9:19am |
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As Steve said....check primary (the + and - terminals on the coil) winding of your 12v coil. Resistance between those terminals needs to measure about 3 ohms for the WD45 (4 cylinder engine). If it doesn't, go to your favorite auto parts store armed with your ohmmeter and find one that meets the 3 ohm spec. Discard any external resistor.
Edited by Dave(inMA) - 04 Aug 2020 at 12:48pm
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WC, CA, D14, WD45
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