Bridge rectifier

Researching the topic. Diode Trio, rated at 3 amps.

Individual diodes are still available at auto parts stores. Auto Zone has them individually listed at $2.95, 50 amp, for Delco 10SI.

NAPA and Federated has diodes in a 3 pack. Four different packages listed by vehicle make and year. I did not research the amperage rating for any of these diodes.

Replacement bridges are available in many amperage ratings. Some as low as $29.95.

If in need of rectifier parts for a high amperage battery charger, research the truck section. Way back when I had a Dodge work truck with a 120 amp alternator.
 
JackF":2s0jgnk6 said:
Bus Driver, Landreo, Eugene and Jim

When you stated; diode trio is for the field current it seems as though the diode trio only operates low amperage part of the generator. This part confuses me because it’s attached to the rectifier and what I can see in the diagram is; the voltage regulator grounds the diode trio when current is required.

The diode trio is only for the field current through the regulator, standard "A" circuit like cub voltage regulators. THe diode trio is not connected to the bridge output. They share a common connection with the stator windings but the diode trio gets AC current from the stator not the DC coming out the other side of the bridge. The AC connection is all they have in common.

With the generator operating, AC voltages are generated in the stator windings, and the stator supplies DC field current through the diode trio, the field, TR1, and then through the grounded diodes in the rectifier bridge back to the stator. Also, the six diodes in the bridge rectifier change the stator AC voltages to a DC voltage which appears between ground and the generator "BAT" terminal which is connected to the storage cell. (Battery)

The field current starts at the stator windings to the common connection with the stator, diode trio, bridge. The bridge goes to the battery as high amp dc, AC from the stator goes to the trio to form the dc field current. No connection between the bridge and the trio outputs. The trio dc goes to the voltage regulator then to the field windings and then the ground. D2, zener diode, with a resistor voltage divider is the voltage sensor, t2 is the voltage on off that controls t3 then the power transistor t1 which controls the field current. D1 is a commutator diode for voltage spikes and does not affect directly the operation of the regulator nor does it carry any field current. The one 10 si regulator I unpotted and reversed actually had only t1 and t2. THe posted diagram may apply to a 12si

The end result is that the field and diode trio are independent of the bridge rectifier. The field current likely is only a few amps so no need for a large diode capacity for the diode trio.

Boring to many but I like "how does it work" discussions.
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Landreo stated:
Boring to many but I like "how does it work" discussions
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Sir, I can read what you have to write anytime you write it. How it works discussions are never boring just educational especially from you. Thank you again!
 
Lanreado wrote:
THe posted diagram may apply to a 12si
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I got my old book back out from which I copied the diagram and the caption stated 10SI-12SI. This is a GM training book and not a Delco book so it could be wrong. I know all the 10SI’s were replaced under warranty with the 12SI’s.

Trivia
The model 10SI Delco built alternator is the first generation, SI series alternator. It was introduced on the 1969 Corvette, and by 1973 most GM built cars and light trucks used this model alternator. It was an option with at least some 70, 71, and 72 GM cars, although it rarely showed up in those years, except for on the Corvette where it was standard equipment.

Assembled with all original GM components, the model 10SI alternator had a maximum output rating of 63amps. Output rating is determined by the windings in the alternator, and not all model 10SI alternators had the same windings.

There were 10SI alternators with 37amp, 42amp, 55amp, 61amp, and 63amp ratings. The smaller amp output rated alternators were installed on cars with no air conditioning, and few electrical accessories. The 61amp output rated 10SI was very commonly installed on 8cylinder cars, with factory air conditioning option.

For luxury cars loaded with electrical accessories, there were larger and more powerful models of alternators than the 10SI. A few of the full size Buick, Pontiac, Cadillac, or Oldsmobile could be had with model 12SI - 15SI, or possibly the model 27SI alternator. The 15SI and 27SI alternators looked the same, but were scaled up in size. They were physically larger and heavier, and output ratings were often 70amp, 80amp, and 100amp.
 
JachF,
I reread your post and believe I misunderstood your comments. I took the grounding diode to be in reference to D2 in the voltage regulator which is why I was discussing the regulator components, but now it is clear you were talking about the bottom 3 diodes in the bridge. The field current does get to the ground through those 3 diodes.
 
Sorry, I can’t write and chew gum at the same time. I was talking about the diode trio from the rergulator to the bridge. As you explained it does ground the voltage regulator on one side and the diode trio is not connected to the bridge output. They share a common connection with the stator windings but the diode trio gets AC current from the stator
(low amps) not the DC coming out the other side (output to battery) of the bridge.

The direct current from the rectifier bridge output terminal outside the generator supplies the battery via battery cable with potential high amperage.

Thank you again for your input and knowledge it was an honor and I learned a lot!
 
Bus Driver, Landreo, Eugene, Jim Becker, Jack F, and Beaconlight.

I had been following this thread since almost the beginning with interest, and sadly, got a refresher course on just how much I have forgotten over the last few decades about AC and conversion.

My go to manual for this subject is "Diesel Mechanics" Erich J. Schulz. c1977, of course primarily aimed at 12 volt automotive systems.

Mr. Schulz composed a very well laid out section devoted to generation and conversion to DC along with outstanding troubleshooting procedures which included a slew of GM technical photos and data in Unit 44, "Charging System (Generators)". The following unit, "Regulation" is also very good to reference back to for regulation problem solving.

I also have/had a very good Leece Neville 130 ampere hour technical manual which I seem to be having trouble locating at the moment.

If any of you gentlemen would ever find the need to consult my Schulz manual, I will kindly lend it to you for your reference. Just ask and I will drop it in the mail.

I had collected 2 battery chargers, one intermittently failing, the other completely NFG. Upon inspection I eventually found both of them to contain opens in the secondary circuitry, most likely at my hand from demanding too much from them. I spent way too much time isolating and testing each component with no factory data base to compare my results, but it was challenging and fun to get them fully functional again.
 
I think Beaconlight hit the nail on the head. Cracked wire. I parted out Dad's old charger, only to find it was the cables. Had a radio shop check the electronics, they said "dead". Saved the cables, and went to use them, no go:(
 
The two bridge rectifiers I ordered arrived. Supposedly rated 1000 volts, 50 amps. They look small for 50 amps and no way are the terminals suitable for 50 amps sustained current. Two different testers were used to verify the condition of one of the rectifiers--and that has created confusion for me. My BK Precision meter shows 1 when set for Ohms and the leads are not touching. It has no symbol for Infinity, which is what it really should read. Tested two adjacent terminals, one reading was the 1, for Infinity or open circuit, no continuity. Reversed the leads on the terminals and the readings are from 639 to 645-- all pretty close to each other and indicating conductance-- but not much. I have not applied AC power to the bridge, only the DC of the meter. A DC resistance of 640 Ohms suggests that at 6 volts, the current would be 0.009 amps, at 120 volts the current would be 0.178 amperes. I thought I understood these concepts well but something is just not right.
So what am I missing or not understanding?

The second part is that here in my desk, there is a Harbor Freight multimeter- the cheapest they sell-- and occasionally offer as a freebee. Occasionally useful in a hurry. It too shows the 1 when the leads are separated in the Ohms function. Same on the bridge in one position. But when I reverse them on the bridge, the display flashes some numbers for a split second, then goes back to the 1. Never displays a readable resistance value. How to explain that?
 
Maybe 600+ ohms is out of range for the cheap meter. If there is some capacitance in the rectifier, there may be an initial surge of current that it tries to read as a lower resistance.

As to why your rectifiers test out as such high resistance, I have no idea.
 
Bus Driver, I have a slew of the HF multimeters around here. I have found as they age, the 9 volt inside deteriortes slightly, the meter failing to produce the same reading twice in a row although a crisp LCD display is still maintained. Probably not the highest quality storage cell to begin with.

With so many of them you lose track of the newest one with the freshest battery. I started numbering them with Sharpies, I should just pitch them if they weren't so handy to have in every nook and cranny.
 
While I was focused here on battery chargers, one here with broken ammeter caught my attention. Really old, Allison brand, a minimal device in every way. 6/12 volt, 6/2 amps. Belonged to my Father. But it always has worked, even with the smashed ammeter. Found 10 amp ammeter that could be purchased from China, shipped to my mailbox, for the total of $4.22. That will not buy the gas for a round trip to the nearest Advance or O'Reilly's. And it was close to the desired size.
So the charger was modified to mount the ammeter. The original ammeter had no polarity markings. So the Positive battery clamp line was installed to the Positive on the new ammeter as the first hookup. To limit the amperage if the hookup was backward, a 33 Ohm resistor (used for alternator conversions for the exciter circuit) was used between the battery clamps and the charger was set on 6 volts. That would be about 0.18 amperes, enough to just make the needle wiggle. That worked perfectly-- the first guess was correct.
The original ammeter was truly the most minimal ( excuse my bad grammar) I have ever seen. The new one is high quality in contrast.
A new charger would be $40.00 and up and no doubt would be from China. And the time I spent on it would have been unpaid anyway.
 
Landreo":lxyy80xx said:
It takes 0.6 volts to activate a diode,
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This may seem like a piece of mindless trivia but is the key to your finding with the meter. The meter is trying to read a resistor that follows ohm's law. Diodes and all semiconductors are non-ohmic conductors, they do not follow ohm's law.

In the wrong direction the diode should not conduct and your meter will read infinity or a few hundred megs. In the correct direction the meter has to activate the diode and it may not have enough voltage or current or both to do that, the diode unactivated will be a few hungred megs or infinity. If the diode is activated then it will have a voltage drop of 0.6 volts no matter the voltage or current. Not completely true but close to completely true. The meter sees that 0.6 voltage drop and assumes it is due to a ohm's law following resistance and gives a resistance of around 600 ohms. The real resistance is likely less than one ohm. 0.1 volts into a diode gives zero out, 0.8 volts into a diode gives 0.2 out, 10 volts into a diode gives 9.4 volts out, 100 volts in gives 99.4 out. you always have that same voltage drop regardless of the voltage or current once over the 0.6 volt threshold. The meter does not know that and assumes the voltage drop is due to a resistor but it is not.

One meter may not have enough to activate the diodes and you will get infinity both ways, another meter may have enough to activate the diode and will read infinity in one direction and some other amount, commonly around 500-600 ohms, in the other. Your diodes seem to be OK. Some meters, my Harbor Freight cheapo, have a diode range which actually will read the forward voltage drop and will show something like .599, which is the actual voltage drop across the diode.

If you plotted the volts on the x axis and current on the y axis you would get a 45 degree line for a normal resistor, more voltage equals more current. For a diode, nothing would happen on the current axis until 0.6 volts then the line would jump almost straight up. At that point the resistance is near zero.

You can go to the company's website and download something called spice data which should have the actual resistance of the diode, the diode equation for that particular diode. In the old days I had to actually make a circuit, now I just put the spice data into a program, draw the circuit, and graph the results. Saves alot of smoke pouring out of the wires.


Bottom line, your bridge measurements seem normal. The 1000 volts may be the PIV rather than the working voltage
 
I sure am glad you folks know what you are talking about. I read the whole post, then had to go get a fresh cup of hot coffee :big smirk: :big smirk: :big smirk: :big smirk: :big smirk: :big smirk: :big smirk: :sick:
 
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