When I had first purchased my 1930 model A, I was having some charging, wiring and ammeter issues, and had to get a handle on actual current drains of my Model A Ford. I venture there is a place I could have gotten all this, and some I found on the web, and the rest is just capturing the current drains of original bulbs for the Model A. If anyone has better info or corrections please share.
Henry's Model A Ford Current drains
- Thread starter DHZIEMAN
- Start date
BRENT in 10-uh-C
Well-known member
With all due respect, aren't you over-complicating this? With everything shut-off, there should be no electrical drains. The amperage requirements for bulbs will be directly proportionate to the candlepower of the bulb also factoring in the voltage of the bulb, ….therefore 'it is what it is'. The same applies to the Ignition Coil. Now you can easily test many of the components by removing the Negative (-) battery cable clamp from the battery and temporarily install a test light between the post and the terminal. If the system has a draw anywhere, the bulb in the test light will illuminate. If for example the ignition has a voltage leakage inside, chances are the test light bulb will be illuminated. The intensity of the illuminated bulb will generally indicate how severe the draw is. Therefore in reality, it does not matter the current draw of each component since most of the wiring harness manufacturers have already sized the wire correctly for you. Any accessories added to the circuit can generally be sized on a one-on-one basis.
I am going to stick with using meters, unless I need to do continuity checking! Meters are calibrated, bulbs are not! By the way, to get into it a bit, my coil was drawing heavy, and I replaced it along with some wiring to the Rt headlight. Car now has the right coil.
Bulbs have their place but so do volt and amp meters. I should have clarified the reasons!
MikeK
Well-known member
After reading your initial post and your reply to Brent I'm clear as mud on exactly what you want.
If it is just specs on original lamps I'll give you some, but with one caveat: The replacement bulbs sold today vary wildly from the original specs, both in filament burn temperature, actual current draw, and light output. Chinese lamps marked 32cp may be as low as 25cp or as high as 45cp.
What I also don't understand is, if you have accurate meters as your reply suggests, why you didn't just take out the bulbs you now have and measure their current draw yourself with a few jumper wires and your meter.
per.SAE std. J573d Mar.1918, rev12/68
21cp(cir.) 6.4V, 2.63A, black-body radiation 2725K
32cp(cir.) 6.4V, 4.01A, black-body radiation 2725K
50cp(cir.) 6.4V, 6.27A, black-body radiation 2725K
FWIW, If you like measuring things you can see what those Chinese replacement lamps are actually doing by adjusting the voltage input to achieve 2725K and then calculate their true SAE cir.cp rating by measuring the actual current draw and extrapolating from the above standard specs. You will then also know the true operating voltage of the replacement lamps. You can then roughly calculate their actual cir.cp output at your system voltage by measuring amperage at that voltage and then plotting your position on a graph line between 2725K @ 6.4V and the second SAE filament temperature spec- 2875K @ 7.1V (1920's running generator voltage standard)
Personally, my first line of attack in any Model A electrical problem is as Brent says.
If it is just specs on original lamps I'll give you some, but with one caveat: The replacement bulbs sold today vary wildly from the original specs, both in filament burn temperature, actual current draw, and light output. Chinese lamps marked 32cp may be as low as 25cp or as high as 45cp.
What I also don't understand is, if you have accurate meters as your reply suggests, why you didn't just take out the bulbs you now have and measure their current draw yourself with a few jumper wires and your meter.
per.SAE std. J573d Mar.1918, rev12/68
21cp(cir.) 6.4V, 2.63A, black-body radiation 2725K
32cp(cir.) 6.4V, 4.01A, black-body radiation 2725K
50cp(cir.) 6.4V, 6.27A, black-body radiation 2725K
FWIW, If you like measuring things you can see what those Chinese replacement lamps are actually doing by adjusting the voltage input to achieve 2725K and then calculate their true SAE cir.cp rating by measuring the actual current draw and extrapolating from the above standard specs. You will then also know the true operating voltage of the replacement lamps. You can then roughly calculate their actual cir.cp output at your system voltage by measuring amperage at that voltage and then plotting your position on a graph line between 2725K @ 6.4V and the second SAE filament temperature spec- 2875K @ 7.1V (1920's running generator voltage standard)
Personally, my first line of attack in any Model A electrical problem is as Brent says.