Hi All, I am converting my 1950 chevy from a generator to an alternator. I have read through many threads and cannot come up with a conclusive answer to how to wire it. I am using a GM 10si 3 wire alternator. I understand how to connect the two DA wires but have questions about the main power cable exiting the alternator. If I follow the original schematics with generator, it would suggest that the alternator Batt post (10ga) wire should be connected to the — neg side of the ammeter. A 10ga wire from the starter should be connected to the +pos side of the ammeter. I also read that the alternator 10ga wire should be connected to the +pos side of the ammeter. In addition to this a 10ga wire from the alternator should be connected to the starter. This acts like a by pass in the case that the alternator is shorted, the path of least resistance would be to the battery and not the ammeter. I’ve read that it is not safe to run higher amp alternators connected to the old ammeters. I am using all new wires, none of the original wiring is being used. I believe the alternator is a 63amp model. What is the proper way to wire this alternator. Should I continue to run it to the ammeter? Should I convert the ammeter to a voltmeter? If I change to a voltmeter how do I connect the alternator the the voltmeter?
It pretty much depends on how much load you gonna put on it. If you keep everything stock, you should be fine, but if you have just one powerhungry deice like an electric radiator fan, than you need to go a different route.
You could use a shunt though, if you want to keep the original ammeter.
Whatever you do - make sure the power sensing terminal of the alternator has a wire all the way to your starter (where the positive cable from the battery connects).
And than there is also a more "fancy" hybrid shunt solution to this. Here is what a friend who is really into this electric stuff was sending me a few years ago:
Quote
The best method when using an alternator is to make a "Hybrid Shunt" wire that bypasses around the ammeter.[Direct from the Alt to the Batt] The Hybrid Shunt uses 2 "forward drop diodes" in opposing directions [parallel in this wire] This is needed to get flow in both directions [charge and discharge]
The diodes have a fixed value of voltage drop to open them, whereas the ammeter [acting like a resistor] has a progressive/non-linear voltage drop. Below 30a there is less voltage drop across the ammeter than what is required to open the diode, so the ammeter flows current. [The path of least resistance]
At about 30a there is a point of equilibrium where internal resistance in the ammeter starts exceeding the forward drop value of the diode so the diode will flow the excess current. This ^^^^ usually happens when the ammeter is "maxxed out" on its scale. [after cranking over an engine] Once the battery recovers [enough] and the charge starts dropping off the ammeter reads as normal
Use 2 x Vishay 150a rectifier diodes connected together parallel [back to back] mounted inside an old regulator box. These have a 1.13v forward drop The diodes behave like an electrical "pressure bypass valve".
Also if the ammeter totally fails this will not leave you stranded on the roadside because All Voltage will flow through the diodes.
To make the shunt Mount 2 x Vishay 150a rectifier diodes back to back on a piece of phenolic plastic [using common studs and spacers] Then mount a wire with eyes each side on the studs.
1 wire to the Alt and the other to the Batt. Hide the diode board insde an old "period correct" regulator box. [you should have one left over from the internal regulated Alt Conversion]
Summary 99% of the time your Alt is discharging/charging in the -30a to +30a range and the ammeter works perfectly as original. When there is a massive load or charge beyond the range of the ammeter, the shunt opens and flows the excess current.
Hi All, I am converting my 1950 chevy from a generator to an alternator. I have read through many threads and cannot come up with a conclusive answer to how to wire it. I am using a GM 10si 3 wire alternator. I understand how to connect the two DA wires but have questions about the main power cable exiting the alternator. If I follow the original schematics with generator, it would suggest that the alternator Batt post (10ga) wire should be connected to the — neg side of the ammeter. A 10ga wire from the starter should be connected to the +pos side of the ammeter. and Battery pos to starter. I also read that the alternator 10ga wire should be connected to the +pos side of the ammeter.In addition to this a 10ga wire from the alternator should be connected to the starter. This acts like a by pass in the case that the alternator is shorted, the path of least resistance would be to the battery and not the ammeter. I’ve read that it is not safe to run higher amp alternators connected to the old ammeters. I am using all new wires, none of the original wiring is being used. I believe the alternator is a 63amp model. What is the proper way to wire this alternator. Should I continue to run it to the ammeter? Should I convert the ammeter to a voltmeter? If I change to a voltmeter how do I connect the alternator the the voltmeter?
Thanks, Skipper
A voltmeter would be a good replacement for the ammeter. That way you won't have to worry about the ammeter. (which will probably be OK to use) The voltmeter instructions will just be: ignition switched hot and a ground. very simple. A fusible link should be installed in the wire between starter and ammeter. Are you going to have an idiot light? What is your understanding of alternator terminals 1 and 2 hookup?
I have a 63 amp 10si alternator. I run it through the stock ammeter without issue. A 50 amp generator was an option back in 1954. I doubt that they changed the ammeter if the optional generator was installed.
I do plan on installing an idiot light. My understanding is that the with wire from the alternator two pin connector should run to the idiot light and to the ignition switch. The red cable on the connector should be connected to the starter post, which is connected to the battery. I am planning on running an electric fan and may draw more power than a stock. If I add the volt meter, it will be the one that directly replaces the ammeter in the gauge cluster. I see them on several vendor sites. I would guess that the alternator 10ga wire would still connect to the + pos volt meter post or should it be connected to the starter/battery.
I am OK with continuing using the ammeter but am worried that I may be overloading it. Is there any advantage to running a 50amp fusible link vs a 50amp fuse?
Before we go any further..... you have converted to 12V and now an alternator/voltmeter/ammeter. Did you use a harness kit for all this or what?. Are you done with all the wiring except for the alternator and deciding on voltmeter or ammeter?
I would guess that the alternator 10ga wire would still connect to the + pos volt meter post NO or should it be connected to the starter/battery. YES
"I am OK with continuing using the ammeter but am worried that I may be overloading it. Is there any advantage to running a 50amp fusible link vs a 50amp fuse?" Fusible links are just a piece of wire with a high temp insulation. The wire inside is meant to be sacrificial and melt to a open circuit. You buy them by wire size. They are sized 4 wire gauges less than the circuit wire they are protecting. So a 10ga gets a 14ga fusible link.
The ammeter, as you know, measures charge and discharge. One terminal of the ammeter gets battery pos and the other ammeter terminal gets all the "load" wires. Which is basically everything.
the wiring is complete, built a harness for it following the schematic in manual. Just want to make sure the alternator should connect to the ammeter and if so, is the ammeter capable of handling an alternator. If not, I could replace the ammeter with a voltmeter and with the suggestions on this thread, connect the alternator cable to the starter/battery post.
This is not aimed at anyone or to start an argument. Commentary: Well, this question about when converting to 12V and alternator, "can I still use the old ammeter?" comes up a lot...So let's finally get this answered. YES
There are two different kinds of ammeters used by the manufacturers and also available from the aftermarket. Gauges with shunts and gauges that require an external shunt. The '50 Chevy used a gauge with a internal shunt. My '67 has a gauge that requires a external shunt.
The first picture is a External shunt. The 2nd picture is of gauges with internal shunts. The 3rd picture shows that the 60Amp gauges have the shunt mounted outside, because they would get too hot to be mounted inside. the 20 Amp gauge does have the shunt inside as it will have much less heat. The 4th picture shows with the fat red arrow that 99% of the current flows through the shunt and less that 1% flows through the meter movement.
The 60 Amp Stewart Warner gauge shown, is considered a Internal Shunt gauge. SW has a separate Marine catalog and the Ammeters in that group require a separate External Shunt. My '67 uses a external shunt gauge, but they saved money by using part of the wire harness to serve TWO functions. The wire between the alternator and the battery is a measured length, with a specific resistance, that the ammeter sees as a shunt. The charging circuit, sees it as a charge wire connecting the Alt to the Bat.
It should be noted that the modern suppliers of ammeters say they don't support much after 40A and to use a voltmeter then and when using a modern alternator.
External shunts are used especially on boats where you have great distances between the Bat/ Alternator and the gauge. With a internal shunt you have to run large current carrying wires all the way to the cockpit and back . The greater the distance, the larger the wire, the greater chance of failure and the greater potential chance of damage. External shunts provide very low current to the meter and require very small wire.
>>unmeasurable low resistance. It does not get hot.<<
The lower the resistance, the higher the current, the higher the heat.
This 1st drawing you have probably seen before. The bottom half of the drawing has a 10DN Alt plus Ex Regulator. The top half has the battery, Ign switch, idiot lamp and resistance wire. The 2nd drawing is basically the same drawing. They just stuffed the regulator inside the S! Alternator. The '60s 10DN Alt and the '70s 10SI/12SI both have 3 wires connecting the Alt/Reg to the Battery, Ign switch and idiot light. Both have a 10 Ohm resistor inside the dash harness. Both have a ACC terminal on the Ign switch.
The 3rd drawing shows a 10 Ohm 10 Watt resistor connected across the lamp because of the absence of the ACC terminal.
Some, don't add the resistor and the Alt begins to charge as it should. Some, use a bulb with lower resistance, no 10 Ohm resistor and the Alt begins to charge as it should. They also appreciate the brighter idiot light.
I have edited my posts to just answer the questions and stay away from a shunt discussion. I don't believe the posters ammeter has one. These are permanent magnet moving coil meters. I believe it is OK to use because of what I stated in my edited post. The only wire is the coil wire around the needle shaft. This is 24-30 gauge probably. Regarding burnout danger: Wire not affected by the increase to 12V but is affected by current. Current is now lower (1/2) due to 12V conversion. I believe the current is passed to the coil thru opposing springs at top and bottom of coil. So they carry current also. I will apply the same no-burn reason.
The YES still stands as well as the ammeter vendors not supporting 40A or modern alternator outputs. Recommending voltmeters.
