1963 C10 with 10SI Alternator Question

[Cris]

OK. A bit confused right now. I have put in a 10SI alternator in my 1963 C10. It is wired per the many schematics on the web. I use the brown wire to the number 1 terminal to excite the alternator. The number 2 sense terminal goes to the horn relay junction, the output wire of the alternator also goes to this same junction.

Here’s where I get confused. With the key switch in the on position without the engine running, the voltage on the number 1 terminal (brown wire) is around 4 Volts.

My guess is that the brown wire connects to a brown white wire under the dash then to the ignition switch. The brown white wire is a resistance wire? I am also guessing that the alternator when not being spun is relatively low resistance at the number 1 excitation terminal. This low resistance would create current flow in the brown wire to illuminate a dash charging bulb. (My truck has a voltage gauge so no light). I’m also guessing that when the truck is started and spinning the alternator, the number 1 terminal goes up to 12V?

Any help would be appreciated, Cris

[VetteVet]

You will need to supply the no. 1 terminal with 12 volts with a 10 ohm resistance. I have a diagram of the 64 year with the charging light and one with the ammeter. In both cases there is a brown and yellow striped wire from the key switch to the forward connection on the firewall. It is the resistance wire for the regulator/alternator, on the stock truck or the SI 10/12 alternators.

If you are only getting 4 volts at the alternator then you may have a bad connection at the forward connection, or at the ignition switch. This wire is a 10 ohm resistance wire.

When I installed my engine in my truck I wired it so that I could control it from the engine compartment. Starting and charging and gauges etc. It's a 67 short stepside.

If you can't find the cause of the low voltage you can run a new wire from any key on, 12 volt power source with a 10 ohm or slightly greater resister, wired in series with the brown wire to the alternator. You can also use a CS newer style alternator but you need a larger resistor like 85 ohms. I cover all this in my Electrical FAQs. I looked at the schematic and the pink wire from the key switch to the fuse panel would be an excellent place to pick up the 12 volts. I used a light from another dash for my resistor, and it comes on with the key, and goes out when the engine starts running. The SI alternator shows 14.5 volts at 2000 RPMs.

I'll try to post the two diagrams for the 64 that I have and you can compare them to what you have.

[VetteVet]

here is the 64 with the light. It is called the gen/tell tale light.









here is a 65 diagram with the ammeter. It is very similar to the 64. I hope they are close to what you have.

[Cris]

VetteVet;

Thanks for the information. I should have written that I was running this set up for some time with no issues. I recently tapped into my engine harness to add electric fans and when I was doing some preliminary checks, I measured 4 Volts on the number one (excitation) terminal. I was confused because I was assuming that the number 1 terminal would be a high resistance. When I measured it with an ohmmeter I saw 40 ohms.

So it looks like (at start up) this will draw quite a bit of current. Of course this is being limited by the brown/white resistance wire going from the ignition switch. I haven't measured the brown/white resistance but by calculation it would be about 80 ohms to see the 4V at the number 1 terminal. This also means that the maximum excitation current applied is 12v divided by 120 (80+40) ohms, or 0.1 Amps.

Is this adequate current to energize the rotor? I can't find any spec on how much current is needed into the number 1 terminal to excite the alternator.

After digging up a really good reference on the 10SI alternators, it also looks like after the alternator is being spun (truck started), the number 1 terminal gets its voltage internally from the alternator. So I would guess my 4V will jump to 12V.

Here's the reference:

https://oljeep.com/gw/alt/edge_Alternator_Theory.html

[VetteVet]

I've read that site and many others. where did you tap in for your fans? I don't see how you are getting 40 ohms if the wire is 10 to 15 ohms. The alternator will generate 12 volts through the diode trio and turn off the charging light if you had one as per the link you posted.
There is some residual magnetism in the alternator windings which can start it charging even if there is no voltage on the no. 1 terminal but it will not maintain the 14 volts the alternator needs. You haven't said what your battery post voltage is with the engine running. The Bat terminal should also show 14.5 volts to equal the battery volts.

[Cris]

VetteVet:

I appreciate the help. I thought that the brown/white wire under the dash is supposed to be more like 75 ohms on a 1963 truck originally fitted with the stock alternator and separate voltage regulator?

The fans are disconnected at this point until I resolve this issue.

Thanks, Cris

[Cris]

OK. I measured the brown white resistance wire at about 14 ohms. I believe the 4 Volts at terminal 1 is correct with the key in the on position and motor not running. It essentially means terminal 1 is drawing 0.57 amps to excite the rotor.

Applying voltage to terminal 1 causes a transistor to turn on and ground one side of the rotor. The other side of the rotor is directly connected to terminal 1. So essentially terminal 1 sees the resistance of the rotor to ground. Inferring from the measured voltages, the rotor resistance is roughly 7 ohms.

Unfortunately, I have to infer a lot of this. My internet searches could not pull up rotor resistance for a 10SI alternator. I also could not find the values for the resistors internal to the alternator.

If anyone has a disassembled alternator, they could check this and add some valuable info.

Cris

[starterman99]

A Delco 63 amp 10SI should have a rotor field winding resistance of 2.4-3.0 ohms @80degrees. The current draw should be 4.0-5.0 amps @ 12 volts.

[Cris]

Starterman99

Thanks for weighing in. In my application, there is a resistance wire (from 12V at the ignition switch) in that goes to the number 1 terminal. Mine measured around 14 ohms, so current draw at 12V should be around 0.7 amps (12/17). So the number one terminal with the key in the on position and the engine not running should indeed be pulled down to a low voltage like I am seeing.

A simple calculation gives around 2.1V. I see a bit more than this. More like 3.2V.