resistor

can i use a 1 ohm 10 watt resistor between coil and ignition on a to30 tractor for 12 volt conversion?

Why reinvent something that you can buy at any auto parts store. If you have an O'Reilly's auto parts in your area you can use either a VR-1 Or VR-2 ballast resister

(quoted from post at 12:52:42 07/21/16) can i use a 1 ohm 10 watt resistor between coil and ignition on a to30 tractor for 12 volt conversion?

Click to expand...

If you do the resulting spark will be so weak the engine most likely will not run.

Ideally you need a resistor that is close to the resistance of the primary circuit in the coil you are using. Most likely somewhere around 1.5 - 2 ohms.

10 watts is its power rating, it needs to be 2 ohms or there abouts. It also needs to be able to handle 60 to 80 watts, not 10 it will just get bright orange, then fall apart in
a ball of fire. Jim

If you're asking about the situation where you want to use a 6 volt coil on a 12 volt tractor, here's the answer:

You "could" use just a 1 ohm 10 watt ballast resistor, and the spark would be good and strong for a "while" and she would run great for a "while", HOWEVER; a) The points will burn sooner,,,,,,,,, b) The coil run hot and may overheat,,,,,,,,, c) And the resistor, being only 10 watts, WILL EVENTUALL OVERHEAT AND BURN UP.

THATS THREE REASONS WHY NOTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTT

A typical old tractor ignition ballast resistor for using a 6 volt coil on a 12 volt tractor will be more like 1.2 to 2 ohms range, and power rated for at least 25 watts (6 volts x 4 amps = 24 watts).

If you already have the 6 volt coil a correct ballast resistor IS CHEAP and so easy to wire between ignition switch and coil. Or buy a full true 12 volt coil no ballast required BUT THAT COSTS MORE THEN A BALLAST IF YOU HAVE A GOOD 6 VOLT COIL

Got it????????????

John T

i understand what u r saying but everything is 12 volt including
the coil. the thing i am trying to understand is the coil is a new
one and it says on the side of it to use a external resistor.everything that i have read on the net keeps telling
me it has to be a 1 ohm resistor. the coil is 2.2 ohms but don't say the wattage. here in oregon where i live all we have is
car quest and napa auto parts.

i thank you very much for your help
ps. cant find a 3 ohm coil.

(quoted from post at 12:52:42 07/21/16) can i use a 1 ohm 10 watt resistor between coil and ignition on a to30 tractor for 12 volt conversion?

Click to expand...

ell, thereyiu have it, tractor12………….one no answer, 3 partially correct answers. John's is closest & is on the safe side. Unless you have an unusual coil, what you propose will work, unless you leave ignition on with engine not running.

TRACTOR 12

THANKS for that new added information, based on it I will now correct and modify my answer based on this latest information............What I posted before was based on the limited info then available, which is why I noted it was for using a typical 6 volt coil on a 12 volt tractor, BUT YOU DIDNT TELL US it was 2.2 ohms AND YOU DIDNT TELL US that it said USE BALLAST. MY FIRST ANSWER WAS BASED ON THE LIMITED INFO WE WERE GIVEN THEN, BUT NOW CIRCUMSTANCES HAVE CHANGED.

BASED ON THE NEW INFO HERES THE CORRECTED ANSWER


1) YOU NOW TELL US: "the thing I am trying to understand is the coil is a new one and it says on the side of it to use a external resistor."

ANSWER: If it says "use an external resistor" THAT MEANS JUST WHAT IT SAYS. But what ohms should the ballast be?????? Typically a stock old tractor 6 volt coil (what my first answer was all about as we didn't have this update) was around 1.2 to 2 ohms (many were 1.5) SO THE APPROPRIATE BALLAST FOR A 6 VOLT COIL ON A 12 VOLT TRACTOR WOULD BE AROUND THE SAME TO FORM A 50 50 VOLTAGE DIVIDER so the ballast dropped 6 volts leaving 6 across a 6 volt coil IE 1.2 TO 2 OHMS


HOWEVER 1) Now we are told it has 2.2 Ohms, and indeed on a 12 volt tractor, it requires ballast JUST AS IT SAYS

HOWEVER 2) Since it has 2.2 ohms (NOT same as typical old 6 volt 1.2 to 2 ohms coil) and you don't want to exceed 4 amps of current the points have to pass and switch, THE BALLAST SHOULD BE AT LEAST 0.8 OHMS (so total is 3) AND TO BE SAFE A 1 OHM SHOULD DO JUST FINE


NOW WE MUST CONSIDER ITS POWER HEAT DISSIPATION RATING

Power = I Squared x R..........If we had 4 amps (with a 2.2 ohm coil and 1 ohm ballast actual current may be be less then 4 amps subject to battery voltage) but lets use 4 to be safe, so I squared R (4 x 4) = 16 times 1 ohms = 16 watts

IF YOU USED A 10 WATT RESISTOR AND EXPOSED IT TO 16 WATTS IT WILL BURN UP

NEW CORRECT ANSWER BASED ON UPDATED INFO A 1 Ohm resistor rated "at least" 20 to 25 watts will suffice (Id prob use a 30 watt if available to be safe) but a 10 watt will burn up

It helps if we are given all the info so we can better answer your questions next time.

Hope this helps, best wishes and God Bless

John T

JMOR, my original answer was based on the info then available, and as I noted in the answer it was for a typical old 6 volt coil (1.5 ohms) on a 12 volt tractor and I think it was correct based on what we knew then HOWEVER look at my updated corrected answer based on the new info and again I think its correct. If not please help me because I'm never too old to learn lol

Hope this helps, if you have any question shoot me an e mail or post back, I enjoy our past sparky chats and e mails

Take car my friend, best wishes and God Bless

Why do the posters hide or withhold info from us anyway lol, if we were told it was 2.2 ohms and said use ballast we would have given the correct answer the first time lol

John T

In case you missed it below:


TRACTOR 12

THANKS for that new added information, based on it I will now correct and modify my answer based on this latest information............What I posted before was based on the limited info then available, which is why I noted it was for using a typical 6 volt coil on a 12 volt tractor, BUT YOU DIDNT TELL US it was 2.2 ohms AND YOU DIDNT TELL US that it said USE BALLAST. MY FIRST ANSWER WAS BASED ON THE LIMITED INFO WE WERE GIVEN THEN, BUT NOW CIRCUMSTANCES HAVE CHANGED.

BASED ON THE NEW INFO HERES THE CORRECTED ANSWER

1) YOU NOW TELL US: "the thing I am trying to understand is the coil is a new one and it says on the side of it to use a external resistor."

ANSWER: If it says "use an external resistor" THAT MEANS JUST WHAT IT SAYS. But what ohms should the ballast be?????? Typically a stock old tractor 6 volt coil (what my first answer was all about as we didn't have this update) was around 1.2 to 2 ohms (many were 1.5) SO THE APPROPRIATE BALLAST FOR A 6 VOLT COIL ON A 12 VOLT TRACTOR WOULD BE AROUND THE SAME TO FORM A 50 50 VOLTAGE DIVIDER so the ballast dropped 6 volts leaving 6 across a 6 volt coil IE 1.2 TO 2 OHMS

HOWEVER 1) Now we are told it has 2.2 Ohms, and indeed on a 12 volt tractor, it requires ballast JUST AS IT SAYS

HOWEVER 2) Since it has 2.2 ohms (NOT same as typical old 6 volt 1.2 to 2 ohms coil) and you don't want to exceed 4 amps of current the points have to pass and switch, THE BALLAST SHOULD BE AT LEAST 0.8 OHMS (so total is 3) AND TO BE SAFE A 1 OHM SHOULD DO JUST FINE

NOW WE MUST CONSIDER ITS POWER HEAT DISSIPATION RATING

Power = I Squared x R..........If we had 4 amps (with a 2.2 ohm coil and 1 ohm ballast actual current may be be less then 4 amps subject to battery voltage) but lets use 4 to be safe, so I squared R (4 x 4) = 16 times 1 ohms = 16 watts

IF YOU USED A 10 WATT RESISTOR AND EXPOSED IT TO 16 WATTS IT WILL BURN UP

NEW CORRECT ANSWER BASED ON UPDATED INFO A 1 Ohm resistor rated "at least" 20 to 25 watts will suffice (Id prob use a 30 watt if available to be safe) but a 10 watt will burn up

It helps if we are given all the info so we can better answer your questions next time.

Hope this helps, best wishes and God Bless

John T

To John T, ok now i see exactily what u r saying.

i do appoligze for not giving all the info,and sure do appreceate
it. sorry about the spelling. just not very good at it....

thanks again tractor12

I added one for an 85 dodge v8 to my SM. Even had a
handy dandy hole in it I could run a bolt through
for mounting it.

THANKS TO JMOR for discussing how dwell time affects the power rating since the resistor isn't always conducting current, only WHEN POINTS ARE CLOSED so the static actual operating power is more then the dynamic. I'm well aware of that, but believing in over kill and over engineering and safety and NOT liking to run near the edge I STILL RECOMMEND A HIGHER THEN 10 WATT POWER RATING as its only chump change price difference in a 10 versus 20 watt resistor.

Thanks again to JMOR

John T Kind of an over safe over cautious CONSERVATIVE designer

THANKS TO JMOR for discussing how dwell time affects the power rating since the resistor isn't always conducting current, only WHEN POINTS ARE CLOSED so the static actual operating power is more then the dynamic. I'm well aware of that, but believing in over kill and over engineering and safety and NOT liking to run near the edge I STILL RECOMMEND A HIGHER THEN 10 WATT POWER RATING as its only chump change price difference in a 10 versus 20 watt resistor.

Thanks again to JMOR

John T Kind of an over safe over cautious CONSERVATIVE designer

agree because...

If you leave the key on... and the points are closed... and the engine is not running....

you normally just run down the battery.. but if you under- engineer the resistor, you also have a burnt up resistor, and if you have a small gas drip, you have a burnt up tractor, and if your in the barn, you have a burnt up barn,, all the hay, all the other equipment, and if its summer time, you also burn down the house, farm, well, and most of the neighborhood

However napa and everyone else sells the correct ceramic block resistor that safely does the job and has been around for 80 years or more, for around 10 bucks or less.

why are we trying to re-design daylight??? Next week we will invent low calorie water.

Yes, I believe that is more or less what John & I told him yesterday. But it never hurts to "tell them what you are going to tell them", "tell them", then "tell them what you told them". :wink: