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By bird292 - 11 Years Ago
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No more 6 volt. I am completing the change over and need a correct part number or auto parts store part number. I have read they can range from 0.50 ohm to 1.6 ohm. I have a new 12 volt coil mounted along with the 12 volt relay.
Thanks.....
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By miker - 11 Years Ago
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Boy, it's been a long time, so don't take this to the bank. I think the coil and ballast resistor are a combo, as you're looking for something like 6volts at the points to prevent pitting from arcing. If you used a '56 replacement coil, then go with that resistor. If not, the coil may have contained some literature, or perhaps the manufacturer can tell you. The old Mallory coils I used either came with the resistor, or gave you a part number. Hopefully, someone more knowledgeable will post further.
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By Pete 55Tbird - 11 Years Ago
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Find out what your coil resistance is first. Then do a Google search for the right ballast. You should end up with 9 volts + or_ at the coil in run if you are still using points. Pete
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By 2721955meteor - 11 Years Ago
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I used a after market resistor for chrysler product(lordco parts in bc. it gave the coiltouch over 8volts runing,cheap and avail.
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By junkyardjeff - 11 Years Ago
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There are coils made with internal resistors,I have one on my 37 Chevy p/u so it still looks like it is 6 volt.,I think its for a older VW
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By bayboy - 11 Years Ago
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didn,t ford produce a12 volt coil that didn,t reguire a ballist resistor because it was bilt into the coil ?
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By paul2748 - 11 Years Ago
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Yes - and I have one on my 12V, 312 powered 54
junkyardjeff (11/14/2014)
There are coils made with internal resistors,I have one on my 37 Chevy p/u so it still looks like it is 6 volt.,I think its for a older VW
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By ian57tbird - 11 Years Ago
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Unless there is an extra post on the coil an internal resistor is of no advantage, as the whole idea of the resistor is to be able to bypass it during start up to counter the voltage drop created by the large draw from the starter motor, and also to give a little extra boost to the ignition during starting.
The resistor is suppose to match the coil and balanced with the rest of the ignition to prolong points life. The 1957 resistor is specified at 1.3-1.4ohms and it appears to be the same part for 1956. Using the 56-57 version with the correct bracket and coil mount puts it in a good position on the manifold near the distributor. I cant see the sense in trying to hide it if you have a 12 volt battery sitting there.
Don't forget to have the bypass wire from the solenoid otherwise you might get hard starting.
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By bayboy - 11 Years Ago
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I think ford had used 12volts for starting and coil reduced voltage from the coil so they had 2 lines 1 from the ignition to coil and 1 direct from the start side of the ignition switch so that side was only12 volts used for starting only, which probably came from the starter side of the solenoid, what year they did that I,m not sure ?? so you don,t need a ballist resistor because its built into the newer coil they use 12 volts just for starting because the starter draws to much and it cuts back the voltage used at starting and that's why they have direct voltage to the plus side of the coil for easier starting
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By Campsite - 11 Years Ago
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Bird 292; When I changed my bird over to 12 Volt. The Ballast Resistor that I used was from NAPA. Brand name is ( Standard Part number is RU-10 ) works great. Also if you have a problem getting the part, you can Call Prestige Thunderbird and talk with Frank in parts, They will have that part in stock. 1-800-423-4751 or 562 944-6237
Hope this helps. Bob
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By Jimz Bird - 11 Years Ago
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Perhaps I can get some clarification on my thinking.
The Ballast resistor does provide a relatively stable voltage drop to the coil. It does that by heating up more and creating more resistance (expended as heat) as the engine idles. My understanding of the reason for that is due to the points being together for a longer time when the dizzy rotates slower at idle. As the engine spees up they contact more frequently but for less time per contact. It is similar to quickly touching a hot iron. You can tap it several times without getting burnt but holding your finger on it will burn your finger. It is evident that the resistance does change as the amps for a stopped engine is listed as 4.5 Amps and idling is 2.5 Amps. If applied voltage is consistent then the only other thing to change has to be the resistance of the ballast.
Coil resistance is given as 1.4 - 1.54 ohms @75 degrees and the ballast resistor should be 1.3 - 1.4 ohms @75 degrees. You want 2.7 to 2.94 ohms on the system when it is not running. While we can't take a resistance reading of it with the engine running we can measure volts and amps and use ohms law to figure resistance. That gets too complicated from there on for me as it gets into Joules and Watts of expended heat. It appears the ballast is a "variable" resistor to control voltage by expending heat. That would tend to explain it's design rather than just using a fixed resistor to drop the voltage after the engine is running.
I would stick with the recommended values for both the coil and the ballast if you are using stock points. I would not use a .7 ohm coil. A .7 ohm coil would put much more load on the ballast.
Of course, breakerless ignitions (PerTronix - DuraSpark) have other considerations.
At least that is my understanding. Am I missing something or over thinking it?
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By skygazer - 11 Years Ago
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I'm running 12v on my '55 bird. I'm using a pertronix which doesn't need a ballast... It can limit the primary current without it.
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By 2721955meteor - 11 Years Ago
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bayboy (11/16/2014)
I think ford had used 12volts for starting and coil reduced voltage from the coil so they had 2 lines 1 from the ignition to coil and 1 direct from the start side of the ignition switch so that side was only12 volts used for starting only, which probably came from the starter side of the solenoid, what year they did that I,m not sure ?? so you don,t need a ballist resistor because its built into the newer coil
the 12volt solenoiid has 2 small terminals, 1 actuates the starter from start switch ,the other is for full 12volts to coil,when started the ignit. wire goes threw the resistor . memery tells me you cant go wrong,use a jumper wire after starter wire and positive wire attached jump 1 if starter engages you know wher to attach starter wire from switch 6volt solenoids have only 1 terminal.
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By ian57tbird - 11 Years Ago
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Interesting hypothesis on the varying amperage Jim, but sorry to say it but it is not quite correct. The different readings from running and a not running engine are due to the points being open part of the time. Think of it this way. When the engine is not running and the points are closed it will read 4.5amps and if the points are open it will read 0amps. When the engine is at idle the points will be opening and closing about 40 times every second and it will get full amperage when they are closed and none when they are open. The needle on the amp meter can not physically move that fast and if it could it would just be a blur, so what happens is that it floats somewhere in between and gives a reading relative to the time that the points are closed.
Yes most conductors have an increased impedance as the temperature increases but it is not the reason for the two readings given.
I hope I explained it in a way that makes sense.
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By Jimz Bird - 11 Years Ago
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[quote]ian57tbird (11/22/2014)
Interesting hypothesis on the varying amperage Jim, but sorry to say it but it is not quite correct. The different readings from running and a not running engine are due to the points being open part of the time. Think of it this way. When the engine is not running and the points are closed it will read 4.5amps and if the points are open it will read 0amps. When the engine is at idle the points will be opening and closing about 40 times every second and it will get full amperage when they are closed and none when they are open. The needle on the amp meter can not physically move that fast and if it could it would just be a blur, so what happens is that it floats somewhere in between and gives a reading relative to the time that the points are closed.
Yes most conductors have an increased impedance as the temperature increases but it is not the reason for the two readings given.
I hope I explained it in a way that makes sense.
Thanks Ian, that makes sense.
I appreciate your input.
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