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05-16-2024, 08:36 AM | #1 |
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Automotive switch ratings?
I had a running and starting issue this week so I'm replacing my Petronix II with a Bob Drake rebuilt 1942 crab distributor on my 59AB. I'm planning to add a ceramic 1.5 ohm inline with the coil's primary resistance of 2.3 ohm. I have a 12v negative ground wiring system.
Running resistance = 2.3 + 1.5 = 3.8 ohm Ohm's Law I = V/R I = ~12v/3.8 = ~3.3 amps For starting I want to add a push button momentary switch so the coil will see about 5.5 amps when the ceramic 1.5a resistor is bypassed. My question is the rating marking on a switch I have with these rating values acceptable? 6a 125 VAC 3a 250 VAC 3/4a 125v What is the 12 volt rating. I need 5.5 to 6 amps? Please teach this ME with EE knowledge :-) Glenn
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Archives of historical but relevant older articles: ------------- Hover mouse over the links below and click! ~~~~~~~~~~~~~~~~~--------------- Rumble Seat's Notes Techno-Source for the 1932 thru 1953 Flathead Ford Last edited by glennpm; 05-16-2024 at 08:42 AM. Reason: added 12v system |
05-16-2024, 08:50 AM | #2 |
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Re: Automotive switch ratings?
Watts (VoltsXAmps) is a rating of total power, which would determine if the switch could handle the load.
So we have : 12X6=72 Watts required 6X125V=750 Watts 3X250V=750 Watts 3/4X125=93.75 Watts All three should be more than adequate; it all depends on the safety margin you want. You may want to recalculate using typical battery voltage of 13.6 Volts. |
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05-16-2024, 08:57 AM | #3 |
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Re: Automotive switch ratings?
Thanks Tubman
I used a lower voltage due to the drop when I'm starting up with the foot mounted starter switch, no solenoid. Even so 13.6v X 6a = 81.6 watts a question of the ratings, when the switch marking shows 3/4a 125v, is that the DC rating?
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Archives of historical but relevant older articles: ------------- Hover mouse over the links below and click! ~~~~~~~~~~~~~~~~~--------------- Rumble Seat's Notes Techno-Source for the 1932 thru 1953 Flathead Ford |
05-16-2024, 09:29 AM | #4 |
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Re: Automotive switch ratings?
I don't think current type matters, since it's not given in the rating. "Watts is watts", so it shouldn't be relevant. There may be some esoteric difference with the way the contacts handle the transfer of power, but that's above my paygrade. One more thing. These ratings are for continuous use. Since you will be using it momentarily, you are on solid ground no matter what you use.
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05-16-2024, 09:53 AM | #5 |
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Re: Automotive switch ratings?
Thank you!
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Archives of historical but relevant older articles: ------------- Hover mouse over the links below and click! ~~~~~~~~~~~~~~~~~--------------- Rumble Seat's Notes Techno-Source for the 1932 thru 1953 Flathead Ford |
05-16-2024, 10:03 AM | #6 |
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Re: Automotive switch ratings?
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