The Ford Barn

coolcoupe · 06-08-2019, 01:00 PM

I wanted to know how to test condensers and resisters while their in the car?
Also which terminal on the coil you hook to when bypass everything and hook the one end to the battery ?
Also how to check how much the starter in drawing ? Moe

tubman · 06-08-2019, 04:56 PM

Both are pretty difficult to test while in the car. They are connected to other circuits that will change the readings. Out of the car, resistors can be checked with a regular "multi-meter set to the proper ohms scale. Condensers are another thing. A regular digital multi-meter cannot be used to check them. If you have an analog meter you can test them for functionality but not for the actual capacitance. To check for functionality; touch the leads from the meter to the leads on the condenser. Then remove them and touch the opposite leads. If the condenser is functional, the needle on the multi-meter will deflect a little bit on the second touch. You need a special meter to check the actual capacitance onf the condenser. They are not cheap. Luckily, my neighbor is an electrical engineer and has all kinds of trick stuff I can use.

To check starter draw, you need a BiG ammeter. I think most auto parts store have a tester that will give you some indication. Well, these days? Maybe not.

coolcoupe · 06-08-2019, 05:23 PM

Thanks for the reply.What are the reading if good on the condenser and resister
while off the car. Moe

tubman · 06-08-2019, 07:44 PM

I am not familiar with these early cars, (I'm an 8BA guy), but I'd like to see 220 to 400 nano-farads on the condenser. I am pretty deep into researching this stuff, but I have a very reliable 220 nano farad condenser that I supply to guys with early ignitions. If you want more information, PM me.

koates · 06-08-2019, 09:10 PM

Back in the day good quality Automotive condenser testers were available and most automotive electrical workshops and better garages or dealerships had them. Today they are few and far between. A quality tester tested for three different results. Capacity in microfarads (not nano-farads) which ranged from .22mfd (microfarads) to about .36 mfd. Early ford V8 condensers with the bakelite coils required about .36 mfd. Metal canister coils required about .24mfd. Another test was for series resistance. The last and maybe most important test was for leakage which required the tester to apply a voltage of 600 volts or more across the condenser to test its insulation. Most of these old time testers had a meter with separate scales for all these tests. Some just had a red flashing neon for the leakage test. Multi meters just don't cut it for a really good condenser test. Most new automotive condensers around today are to low in microfarads for the original early ford V8 coils though they will work. Don't ever bother to buy NOS (new old stock) 40 year old condensers because they are usually leaky and most people have no way to correctly test them. Another way of testing condensers is on an automotive tune scope or oscilloscope. Regards, Kevin.

tub1 · 06-09-2019, 03:33 AM

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hi koates please tell me were to get a 12v condenser to use with a crab distributor in Australia ,I went to repco got a universal 12 condenser uc11e as ive been using on things for years only to find now made in china and a different brand same number though of the 3 I bought from repco te best I got out of one was 50 miles another lasted less than that the 3rd didn't work at all so I put the old ford 6v one back on good as gold what are your thoughts

koates · 06-09-2019, 05:06 AM

Hi tub, condensers are not voltage graded for 6 or 12 volt systems, they are all rated the same at 400 to 600 volts approx. Please tell me exactly what coil you are using and does it have a ballast resistor inline and is the ballast correct for that coil. I would guess most condensers are made in china these days . Its very important to make sure the coils primary winding resistance weather it has a ballast resistor in line or not allows the current draw of the ignition coil not to exceed approx. four amps. Let me know what you have. Regards, Kevin.

tub1 · 06-09-2019, 06:01 AM

hi koates 12v coil no resistor or in built resistor ,I will have a good look at the coil tomorrow see what info is on the side of it , was driving the sloper today and its was going well ,I converted to 12v as was having generator /regulator probs and thought I was going in the wright direction as ive done same with my other old cars

tubman · 06-09-2019, 07:42 AM

220 nano-farads is the same as .22 micro-farads. There is some confusion with the symbol used for micro-farads, so I prefer to use nano-farads. As to capacitance required for a particular coil, you can only tell if it is correct by inspecting the points over a long period. From my experience, as long as it is close, there is little difference in point wear. Case in point : all of the Mallory brass condensers supplied in the past were 360 nano-farads (OK, .36 micro-farads), which would be considered high by most standards, but they worked just fine. I have some examples of condensers that look like the Mallory brass condensers only are larger with a steel case. These are over 400 nano-farads and are said to have been used in commercial applications (trucks and buses).

rotorwrench · 06-09-2019, 01:39 PM

There seems to be a range where they will effectively continue the spark after the points open. Too much and the points just close again anyway. There is only so much dwell time there. The early ones with the funky shaped coil cores could get a way with .33 micro farads due to the design. On the later can types .22 is good enough as is. You can really see this on an oscilloscope.

Resistors are generally read across the resistor whether they are in an operational circuit or isolated. Capacitors are a whole different ball game. They are primarily used in AC circuits but in an ignition system they work due to the pulsating half wave direct current caused by the points opening and closing. They will also absorb transient voltages so they use them for their radio frequency noise absorbing qualities.

Pete · 06-09-2019, 02:51 PM

There are several ways to find the optimum capacitor value for a given coil in an automotive ignition primary circuit.
The easiest and most accurate is a sweep generator and an oscilloscope.
However, you must understand, any given capacitor value is only ideal for a certain engine rpm. Changing capacitor values is like tuning a radio to different stations.
The best you can do is use a value that corresponds to the rpm range the engine is operated in most of the time.
The "Q" (quality factor) of an automotive ignition primary circuit is low due to the iron coil core. This is why a certain capacitor value will work over a wide rpm range.

To get technical, when the capacitive reactance of the capacitor is equal to the inductive reactance of the coil, the circuit will be in resonance, the impedance will be at the highest and the current flow will be at the lowest.

06-08-2019, 01:00 PM	#1
coolcoupe Senior Member Join Date: May 2010 Location: ontario,Canada Posts: 451	testing condensers and resisters I wanted to know how to test condensers and resisters while their in the car? Also which terminal on the coil you hook to when bypass everything and hook the one end to the battery ? Also how to check how much the starter in drawing ? Moe

06-08-2019, 04:56 PM	#2
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 10,304	Re: testing condensers and resisters Both are pretty difficult to test while in the car. They are connected to other circuits that will change the readings. Out of the car, resistors can be checked with a regular "multi-meter set to the proper ohms scale. Condensers are another thing. A regular digital multi-meter cannot be used to check them. If you have an analog meter you can test them for functionality but not for the actual capacitance. To check for functionality; touch the leads from the meter to the leads on the condenser. Then remove them and touch the opposite leads. If the condenser is functional, the needle on the multi-meter will deflect a little bit on the second touch. You need a special meter to check the actual capacitance onf the condenser. They are not cheap. Luckily, my neighbor is an electrical engineer and has all kinds of trick stuff I can use. To check starter draw, you need a BiG ammeter. I think most auto parts store have a tester that will give you some indication. Well, these days? Maybe not.

06-08-2019, 05:23 PM	#3
coolcoupe Senior Member Join Date: May 2010 Location: ontario,Canada Posts: 451	Re: testing condensers and resisters Thanks for the reply.What are the reading if good on the condenser and resister while off the car. Moe

06-08-2019, 07:44 PM	#4
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 10,304	Re: testing condensers and resisters I am not familiar with these early cars, (I'm an 8BA guy), but I'd like to see 220 to 400 nano-farads on the condenser. I am pretty deep into researching this stuff, but I have a very reliable 220 nano farad condenser that I supply to guys with early ignitions. If you want more information, PM me.

06-08-2019, 09:10 PM	#5
koates Senior Member Join Date: May 2010 Location: Melbourne Australia. Posts: 2,078	Re: testing condensers and resisters Back in the day good quality Automotive condenser testers were available and most automotive electrical workshops and better garages or dealerships had them. Today they are few and far between. A quality tester tested for three different results. Capacity in microfarads (not nano-farads) which ranged from .22mfd (microfarads) to about .36 mfd. Early ford V8 condensers with the bakelite coils required about .36 mfd. Metal canister coils required about .24mfd. Another test was for series resistance. The last and maybe most important test was for leakage which required the tester to apply a voltage of 600 volts or more across the condenser to test its insulation. Most of these old time testers had a meter with separate scales for all these tests. Some just had a red flashing neon for the leakage test. Multi meters just don't cut it for a really good condenser test. Most new automotive condensers around today are to low in microfarads for the original early ford V8 coils though they will work. Don't ever bother to buy NOS (new old stock) 40 year old condensers because they are usually leaky and most people have no way to correctly test them. Another way of testing condensers is on an automotive tune scope or oscilloscope. Regards, Kevin.

06-09-2019, 03:33 AM	#6
tub1 Senior Member Join Date: May 2010 Location: tasmania Posts: 221	Re: testing condensers and resisters Sponsored Links (Register now to hide all advertisements) hi koates please tell me were to get a 12v condenser to use with a crab distributor in Australia ,I went to repco got a universal 12 condenser uc11e as ive been using on things for years only to find now made in china and a different brand same number though of the 3 I bought from repco te best I got out of one was 50 miles another lasted less than that the 3rd didn't work at all so I put the old ford 6v one back on good as gold what are your thoughts

06-09-2019, 05:06 AM	#7
koates Senior Member Join Date: May 2010 Location: Melbourne Australia. Posts: 2,078	Re: testing condensers and resisters Hi tub, condensers are not voltage graded for 6 or 12 volt systems, they are all rated the same at 400 to 600 volts approx. Please tell me exactly what coil you are using and does it have a ballast resistor inline and is the ballast correct for that coil. I would guess most condensers are made in china these days . Its very important to make sure the coils primary winding resistance weather it has a ballast resistor in line or not allows the current draw of the ignition coil not to exceed approx. four amps. Let me know what you have. Regards, Kevin.

06-09-2019, 06:01 AM	#8
tub1 Senior Member Join Date: May 2010 Location: tasmania Posts: 221	Re: testing condensers and resisters hi koates 12v coil no resistor or in built resistor ,I will have a good look at the coil tomorrow see what info is on the side of it , was driving the sloper today and its was going well ,I converted to 12v as was having generator /regulator probs and thought I was going in the wright direction as ive done same with my other old cars

06-09-2019, 07:42 AM	#9
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 10,304	Re: testing condensers and resisters 220 nano-farads is the same as .22 micro-farads. There is some confusion with the symbol used for micro-farads, so I prefer to use nano-farads. As to capacitance required for a particular coil, you can only tell if it is correct by inspecting the points over a long period. From my experience, as long as it is close, there is little difference in point wear. Case in point : all of the Mallory brass condensers supplied in the past were 360 nano-farads (OK, .36 micro-farads), which would be considered high by most standards, but they worked just fine. I have some examples of condensers that look like the Mallory brass condensers only are larger with a steel case. These are over 400 nano-farads and are said to have been used in commercial applications (trucks and buses).

06-09-2019, 01:39 PM	#10
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,425	Re: testing condensers and resisters There seems to be a range where they will effectively continue the spark after the points open. Too much and the points just close again anyway. There is only so much dwell time there. The early ones with the funky shaped coil cores could get a way with .33 micro farads due to the design. On the later can types .22 is good enough as is. You can really see this on an oscilloscope. Resistors are generally read across the resistor whether they are in an operational circuit or isolated. Capacitors are a whole different ball game. They are primarily used in AC circuits but in an ignition system they work due to the pulsating half wave direct current caused by the points opening and closing. They will also absorb transient voltages so they use them for their radio frequency noise absorbing qualities.

06-09-2019, 02:51 PM	#11
Pete Senior Member Join Date: May 2010 Location: Wa. Posts: 5,407	Re: testing condensers and resisters There are several ways to find the optimum capacitor value for a given coil in an automotive ignition primary circuit. The easiest and most accurate is a sweep generator and an oscilloscope. However, you must understand, any given capacitor value is only ideal for a certain engine rpm. Changing capacitor values is like tuning a radio to different stations. The best you can do is use a value that corresponds to the rpm range the engine is operated in most of the time. The "Q" (quality factor) of an automotive ignition primary circuit is low due to the iron coil core. This is why a certain capacitor value will work over a wide rpm range. To get technical, when the capacitive reactance of the capacitor is equal to the inductive reactance of the coil, the circuit will be in resonance, the impedance will be at the highest and the current flow will be at the lowest.