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EFV-8 Club Forum / 1940 Ford Discussion / amp clamp for 40

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Discussion Topic: amp clamp for 40

dajo

09-26-2024 @ 6:21 PM

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My 40 just has a volt meter. I would like to get an amp reading just to see if generator is working. When I tried a digital vom it jumped all over so I went to my old analog and got a steady reading. My question is if I buy a digital amp clamp will I be able to get as steady accurate reading or will it jump all over also?
Thanks
Dave

JayChicago

09-27-2024 @ 4:52 AM

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Your dash voltmeter tells if it is charging.
The yellow part of the voltmeter dial indicates about 6 volt, battery voltage, not charging. When the needle moves into the green part of the dial, is measuring about 7 volt, indicates is charging.

40 Coupe

09-27-2024 @ 7:27 AM

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The voltmeter is a very good indication of charging. An ammeter is not needed.

ford38v8

09-27-2024 @ 11:28 PM

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Dajo, now you have three replies that agree on voltmeters being a valuable indicator of charger function. I really can’t understand why Ford switched over to amp meters.

Alan

This message was edited by ford38v8 on 9-27-24 @ 11:29 PM

dajo

09-28-2024 @ 1:39 PM

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I am not wanting to install one, just to be able to see output in amps for testing. That is why I asked about using a modern amp clamp testing device that would need to be purchased and not wanting to waste money buying if they don't work on these old systems.. Anyway thanks for the answers.

This message was edited by dajo on 9-28-24 @ 1:41 PM

TomO

10-06-2024 @ 5:12 PM

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Amps are current flowing in the circuit. a clamp om amp meter will measure it. The voltmeter lets you know how much voltage the generator is putting out to charge the battery. If you spend a lot of money for a top quality automotive amp digital amp meter, it will not jump around.

With a fully charged battery and a working voltage regulator and no lights on, an amp meter will show about 2-5 amps. This is the current used to run the engine and varies depending upon engine speed and ignition component condition. Turn on the radio and head lights and the current flow could go as high as 20 amps. If you have a discharged battery, the current flow will be greater and will decrease as the battery charges.

The voltage at 20mph should be around 7 volts and around 6 volts at idle. Any voltage greater than the battery voltage will try to charge the battery.

If you want to know if your generator is charging, connect your analog voltmeter a good ground and to the BAT post of the voltage regulator, start the engine, raise the engine rpm to about 2,000 rpm and read the voltmeter. It should show between 7.2 - 7.4 Volts.

This voltage will be there as long as the generator and voltage regulator are working and whether the battery is dead or fully charged. If the voltage is greater than 7.6 Volts, you could damage the battery and less than 7.0 volts, you will not fully charge the battery. Voltage is the pressure to push the current into the battery and the amps are the amount of charge the battery will accept. As the battery gets charged it will accept fewer amps at the charging voltage.

If you are testing to adjust the current regulator in the voltage regulator, you need a special resister with a 1% tolerance in the circuit.

Tom

This message was edited by TomO on 10-6-24 @ 5:40 PM

RAK402

10-07-2024 @ 4:43 PM

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My father was an electrical engineer and always thought the 40 should have an ammeter (he was surprised when I got my '40 sedan in 1975 that is had a voltmeter. He had a '37 and a '41, both of which had ammeters. The '39 Deluxe, '40 Standard, and '40 Deluxe were the only ones with volt meters, if memory serves.

An ammeter tells you whether the system is charging or discharging-real time.

The voltmeter tells you the result of whether it has been charging or discharging so there is a slight delay.

I added a Ford ammeter (because my father had always wanted me to), which is hidden in one of the ash trays.

Is it necessary? No, but it is very nice to have both.

This is one of the very few things I have done which is not stock (the others being seat belts and turn indicators).

https://youtu.be/0aV4c-E0ymw?si=E1AdVSekBp8SCMoL

dajo

10-08-2024 @ 4:29 AM

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Thank you for the replies both of you.

This message was edited by dajo on 10-8-24 @ 4:29 AM

TomO

10-08-2024 @ 9:48 AM

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Both an ammeter or a voltmeter will tell you if the charging circuit is working.

The ammeter tells you the current flow in the cars electrical circuit. If it is positive, the generator is supplying enough current to keep the battery charged.

The voltmeter shows to output voltage of the battery. If the output voltage is too low, the generator is not able to charge the battery. If it is too high the generator will be damaged. If it is the ideal range, it will supply the charging system with enough voltage to keep the battery charged. The voltmeter has the additional advantage of showing the state of charge of the battery. If the battery voltage is less than 6.3V at idle, the battery needs charging.

The ability to see if the voltage is too high can save a generator replacement. I had a voltage regulator go bad on 1950 Olds with an ammeter. There was no indication on the dash gauge and my generator was destroyed. I had a similar incident on my 40 Merc with a voltmeter. I was able to disconnect the generator and drive home on the battery. Then I replaced a much less expensive voltage regulator

Tom

This message was edited by TomO on 10-11-24 @ 8:52 AM

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