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By Y-oh-Y - 13 Years Ago
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I just installed a volt meter in place of an amp meter on my 60 292 and noticed I have a 2 1/2 volt drop when the starter is is used. Is this normal ? This may esplain why may attempts at installing a pertronix ignition failed. Any thoughts are appreciated. Thanks, Mark
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By jepito - 13 Years Ago
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Assuming 12.5 volts dropping to 10. You more than likely need a better battery.
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By Y-oh-Y - 13 Years Ago
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jepito (8/19/2012)
Assuming 12.5 volts dropping to 10. You more than likely need a better battery.I'm not sure what you mean by a " better battery". It has a 720cca in it now.
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By bergmanj - 13 Years Ago
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9-volts minimum at battery during cranking is one "accepted" standard that I know of; at 10 volts, you're probably doing just fine. Regards, JLB
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By The Master Cylinder - 13 Years Ago
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Mark, For what it's worth my '06 F-150 Screw drops to 9.8v when cranking.
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By jepito - 13 Years Ago
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10 volts is the minimum I use. I guess first I should have asked you if there was a problem or if it's just something you noticed.
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By Talkwrench - 13 Years Ago
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I thought a small drop was normal on start up. The only way to really check a batteries condition is to go by an Auto electrician and have the battery load tested.
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By Y-oh-Y - 13 Years Ago
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The engine starts as it should. I had just never thought about there being such a drop in voltage when the starter is engaged. I went through 3 Pertronix ignition installs and couldn't get any of them to fire. Could it be that with the voltage drop the Pertronix didn't get enough voltage to fire ? Pertronix says it needs a full 12v to work. Thanks, Mark
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By charliemccraney - 13 Years Ago
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Y-oh-Y (8/20/2012)
Could it be that with the voltage drop the Pertronix didn't get enough voltage to fire ? Pertronix says it needs a full 12v to work.
Probably not. No car will have a full 12v at startup. An easy way to test it, though, is to temporarily add a second battery to power only the ignition. This way starting the car will have no affect with the ignition voltage.
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By Y-oh-Y - 13 Years Ago
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It just dawned on me that if the voltage drop is normal then nobodys Pertronix would work, I'm a little slower than normal today  The things that come to you while your out feeding the chickens, LOL.
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By Granny'56 - 13 Years Ago
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Old Fords had a reputation of drawing a lot of current on initial cranking. One quick thing to check is how good the actual connection is between the cables and posts. A little discoloration there means increased resistance. When you're drawing a lot of current it can drop a bit of voltage there. It's the first thing I always check. I've been right more than once. If you have a hand held voltmeter you can actually measure the drop across that interface. One probe on the actual battery post, the other on the piece of lead attached to the cable. Crank the engine and see if any voltage shows. Do it for both sides of the battery.
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By rick55 - 13 Years Ago
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As others have said it is not uncommon for batteries to drop 2-3 volts while cranking. It is for this reason that on 12 volt cars you apply full battery voltage to the coil via the terminal on the starter solenoid and in so doing bypass the ballast resistor . This is to compensate for the drop in battery voltage whilst starting/cranking.
I seem to recall that at the instant the starter engages it draws something like 400 amps which drops to 70 or 80 once the starter is spinning.
This is why you need a decent battery. You battery should have plenty of capacity.
Regards
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By Granny'56 - 13 Years Ago
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It's also why you need a good set of jumper cables if you are going to jump an old Ford. I made up a set using #4 Welding cable. They never fail even cranking old six volt systems which draw about twice the amperage of a 12.
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By Granny'56 - 13 Years Ago
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You might borrow a different battery from a different vehicle and see how it performs. I suspect the drop during cranking is quite normal.
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