12 volt conversion
- Thread starter dsarge390
- Start date
Charlie Stephens
Well-known member
Bill,
I agree that an amp is an amp regardless of the voltage but that is not the problem. The Model A generator is probably good for slightly less than 20 amps but the proposed alternator puts out 90 amps. I realize that this amperage will not be reached except under unusual conditions. If the fan belt is tight enough to put out 90 amps the water pump bearing will probably soon fail. I do think however that the proposed alternator will be putting out far more than 20 amps on a regular basis. The shunt is an extra wire to carry some the current around the amp meter instead of running all of the current through it. I think that putting far more than the rated amperage through the amp meter on a regular basis would shorten its life but I don’t know this for certain. Original amp meters are hard to find and I haven’t heard good things about the reproductions. The 30-amp unit would be better but it is a current reproduction. I am not sure about its quality and if it is even large enough. I am attaching a picture of the back of the amp meter on my ’32. In this case I have a short coil of wire that approximates the resistance of the amp meter. The result of this additional wire is that the reading will be approximately half of the total current. There is a lot of room behind the dash in a ’32. If I was working with a Model A I think I would run two parallel wires from the alternator to the amp meter, each wire heavy enough to carry all of the load in case of an amp meter failure. I would then connect one wire to each side of the amp meter and and remember that the reading was low by a factor of 2. If the amp meter were still ******* on a regular basis I would fine-tune the system by changing the gauge of the wire that carries the current that goes through the amp meter.
Another concern I have is the original wire on a Model A heavy enough to carry the 90 amps? It might be a good question for the company manufacturing the unit. I would get an answer to this before I went too far. Other questions might be what do they recommend for an amp meter and can they throttle down the maximum output of their unit?
Final thought, why would someone need that many amps in a Model A? I wonder if dsarge390 planning to run electric heaters?
Charlie Stephens
Attachments
MAG
Well-known member
Agree with post 22.
Several Model A's in our tour group are equipped with AC. Consequently there is a large electrical load, approx. 30amp, constantly. That causes the alternator to charge at a corresponding rate. We noticed the ammeter (30 amp)gets very hot to the touch. (one actually failed) We created a shunt to parallel the ammeter which reduces the visible reading to approximately half the actual charge current. They are working well.
Several Model A's in our tour group are equipped with AC. Consequently there is a large electrical load, approx. 30amp, constantly. That causes the alternator to charge at a corresponding rate. We noticed the ammeter (30 amp)gets very hot to the touch. (one actually failed) We created a shunt to parallel the ammeter which reduces the visible reading to approximately half the actual charge current. They are working well.
MAG
Well-known member
"I tried putting a 22 gauge wire across the back of the 30 amp ammeter and it pretty much zeroed out any readings on the ammeter." Yes Carl, I tried the same thing with the same results.
So, I experimented with about 6 ' of 16gage (insulated) wire and wound it around a short (2 1/2") piece of 3/8" dowel. Wound tightly in two rows with two 6" pig tails and ring tongue terminators on each end. Taped it securely so the coils would stay in place. Connected it on the two terminals on the terminal box on the firewall, paralleling the ammeter. Coil is on the inside of the firewall not seen.
So, I experimented with about 6 ' of 16gage (insulated) wire and wound it around a short (2 1/2") piece of 3/8" dowel. Wound tightly in two rows with two 6" pig tails and ring tongue terminators on each end. Taped it securely so the coils would stay in place. Connected it on the two terminals on the terminal box on the firewall, paralleling the ammeter. Coil is on the inside of the firewall not seen.
BillLee/Chandler TX
Senior Member
Avoiding a pi$$ing contest.
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Penthode
Member
I do not understand either. At 12 volts, the current will be one half for the same power dissipation. The current will be less at 12 volts so the same ammeter will be fine.
Penthode
Member
This is crazy. The battery charge current should be limited to no more than 10 amperes. At 12 volts, the current usage is one half for the same power. If double wattage headlamps are used, then the headlamp current at 12 volts will be the same as 6 volts.
You will never see 90 amperes through any of the wiring apart from the starter circuit which is heavy gauge wire. 90 amperes will never go through the ammeter: if you attempted to do so, the wiring will likely burn up before the meter!
Charlie Stephens
Well-known member
You should go back and read the whole thread. The poster is upgrading to 12 volts and an alternator. If the battery is low (maybe he left the lights on when he went to dinner?) when he starts it the alternator will charge at a high rate. Will it be the 90 amps the alternator is rated for? No for several reasons but I m sure it will still be way above 20 amps and this is one scenario where the amp meter needs protection.
Charlie Stephens
Beater
Well-known member
my speedster has an delco alt update and 12v system. after start up I see the needle over to 30 plus amp for a bit untll the battery catches up ive never added a shunt, might not be a bad idea
Purdy Swoft
Well-known member
Mike V. Florida
Well-known member
What makes you say that?
For the same resistance, the higher the voltage the lower the current.
What would be used on the vehicle that would draw more than the car on 6 volts?
I just looked this up, the most common alternator used for the Model A, the 6 Volt Delco Remy type 10Si series positive ground alternator with self exciting (one-wire) internal voltage regulator can supply 53 amps. Does everyone who uses a 6 volt alternator change out or modify the ammeter?
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Charlie Stephens
Well-known member
What makes you say that? I say that because in the case when the battery is low (like someone left the lights on) the alternator (or a regulated generator) will put out more current to rapidly charge it.
For the same resistance, the higher the voltage the lower the current. This statement when taken by itself is wrong. I think what you were trying to say is that a system with higher voltage (12) will require less current than one with a lower voltage (6) to do the same amount of work (burn the lights/honk the horn). Please accept my apology if I am trying to put the wrong words in your mouth.
What would be used on the vehicle that would draw more than the car on 6 volts?
You are absolutely right but the draw is not the issue. The issue is that the output of an alternator (or newer generator) will exceed the output of the original generator.
Does everyone who uses a 6 volt alternator change out or modify the ammeter? I am sure that they don't. What I don't know is how long the amp meters will last when stressed by more current than they were designed to be used with. I admit I don't know but I also don't want to find out the hard way. If you have any data from amp meter life versus current tests I would sure like to see it. Otherwise I would rather err on the side of caution, good original amp meters are hard to find.
Charlie Stephens
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Charlie Stephens
Well-known member
Duplicate post in error - I sure miss that delete button
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30 Closed Cab PU
Well-known member
From a preceding Post - "For the same resistance, the higher the voltage the lower the current."
Correct me if I am wrong, do not think that is correct.
If using Ohms law - Voltage (V) = Current(I) x Resistance(R). Then Current = Voltage divided by Resistance.
So if Voltage is Doubled with the same Resistance, Current Doubles.
When Converting from 6V to 12 V, the 6V components have to be swapped out with higher resistance 12 V components, or limiting resistors are installed in series with the components to limit current/voltage to the 6V part
Correct me if I am wrong, do not think that is correct.
If using Ohms law - Voltage (V) = Current(I) x Resistance(R). Then Current = Voltage divided by Resistance.
So if Voltage is Doubled with the same Resistance, Current Doubles.
When Converting from 6V to 12 V, the 6V components have to be swapped out with higher resistance 12 V components, or limiting resistors are installed in series with the components to limit current/voltage to the 6V part
With a 12V conversion you should expect half the normal current reading as the 6V. If you add electrical accessories such as AC clutch and blower fans or - Lord save us - electric heaters, you should bypass the ammeter with properly sized wire.
An ammeter should not overheat within its dial range. If it does, the cause is faulty connections either internal or external. Wire terminals should be soldered for best connection. Those hardware store crimpers really don't do it.
An ammeter should not overheat within its dial range. If it does, the cause is faulty connections either internal or external. Wire terminals should be soldered for best connection. Those hardware store crimpers really don't do it.
I have already changed my 29 over too 12 volt system & I am still using the 6 volt starter, after changing the starter drive & getting along real good with the set up! the one thing you guys were talking about is a in line resistor for the horn! I have had no luck finding one that will work. I tried a voltage reduction device from speedway & it was too much of a drop in voltage, it would work fine on a constant load but not the horn. my question is where can I get the 3 ohm resistor that you have mentioned?
Purdy Swoft
Well-known member
The reason that I change over to 12 volts is not for high draw accessories . I change for the ease of finding 12 volt components such as readily available 12 volt batteries . I use the 12 volt can style voltage regulator from Fun Projects . I set the adjustable brush in the generator for a maximum charge rate of 10 amps . Ten amps is more than enough to run an original type system . I don't need to change over to negative ground so no wires need to be changed.. I use the 12 volt 35 watt halogen bulbs that fit the original sockets . These bulbs are brighter than the original bulbs but not as powerful as the 55-60 watt halogen bulbs that require an alternator and different sockets . This setup looks original unless the battery is seen . Lower amp draw will remove a lot of heat and strain on the electrical system components for longer life and service . For the model A experience , I don't need an air condition or radio . I don't use mine for regular transportation and they are only fun cars . I enjoy the music that my engine makes . If I want all of the modern accessories I will go in the modern car . That is just me and how and why I convert to twelve volts . Its an easy conversion and its still model A with upgrades that don't show .
Purdy Swoft
Well-known member
The Brattons horn resister would probably be a good choice , especially if you have an original horn . I have read here in the past that an old ignition coil could be used as a horn resister . The coil can be mounted inside the left frame rail so it would be out of site . Maybe someone that has done this will give some input . If the horn isn't original it may not even need a resister . I run the old repro ahooga horns that were sold by JC whitney and others . NAPA sold a version that they called a razz-ma-tazz Horn . I think that Hutchins made these repro ahooga horns . I have run these horns on six or twelve volts . They are nice and loud when used on 12 volts .