Alternator External Voltage Regulator - Resistance Values

[David Yount]

I did a search on the Repair Questions forum back to 2009 and found nothing on this topic, but I did read many good threads! I don't know much about diagnosing and wrenching on autos but I enjoy details and thoroughness in everything I do.

I am referring to the Service Manual 1980, 1981, 1982, 1983, 1984 by Robert Bentley, 1984 (Bentley) and also to the Factory Service Manual for 1983 (FSM83). As an aside, Chilton's Tercel 1984-94 Repair Manual does not contain this level of detail for diagnostic testing for the External Voltage Regulator.

In Bentley chapter 3 page 25 and in FSM83 chapter Charging System pages 15 and 16 there are 9 resistance values to measure as part of diagnosing the External Voltage Regulator. The values between the two manuals are the same.

Six of my values are good and 3 of my values are suspect. I wanted to learn if my 3 suspect values may be what is causing my observed wildly fluctuating alternator output, and, if there might be any way to change those 3 resistance values?

I bought a simple Alternator / Battery Tester from Harbor Freight
http://www.harborfreight.com/12-volt-ba ... 66842.html
it simply plugs into your 12VDC accessory plug on the dash. I've used it in 3 other vehicles and the tester works correctly. With the engine on it shows alternator output and with the engine off it shows battery output. There are six LED lights on the tester, the lights are labeled as:
>14.8
13.4 - 14.75
<13.2 (presumably 12.7 - 13.1 ?)
12.4 - 12.6
11.8 - 12.35
<11.75
(basically it's a voltage meter with 6 quantized levels, it has 6 specific voltage ranges)

Since I bought this 1984 SR5 4WD I've had problems with alternator output. Sometimes it works well enough but never strong. Often the output is so low I'm running off the battery. I drive this car once a week, maybe twice. The OEM battery was rated something like 450 CCA? I upgraded to 795CCA / 1000MCA from Costco Item #12877 shortly after buying the car, about 2 years ago. I keep the battery on an automatic trickle charger at home, always. I test the battery with a 100-amp Battery Tester and the battery is strong.

When I plug in the Alternator / Battery Tester it shows my battery is 12.4 - 12.6 or 11.8 - 12.35, that's at home. My battery is fresh everytime I leave from home.

When I turn on the engine the tester usually does not change, it still shows the same value as it did when it was only measuring the battery. So I begin driving. Sometimes the tester shows the alternator output at <13.2 (which is a higher voltage than 12.4 - 12.6 )and on rare occasion I see the alternator output at 13.4 - 14.75 and I even see it at >14.8 as well. But in general the alternator output is something less than the battery's output. I run off my battery much of the time but my trips are less than 30 miles roundtrip and I measure the battery when I return home and it's usually from 12.1 to 12.3 and it immediately goes back on the automatic trickle charger.

I have removed the alternator and had three different auto parts stores put in on their test benches; the alternator has been tested 5 different times and everytime I'm told it's good. So the alternator works correctly and it is the correct alternator for the car, with no Voltage Regulator inside the alternator. I understand if the alternator had the IC Regulator then I would have strange problems because I do have the External Voltage Regulator that's encased in a small black box and lives on the inside wall of the left wheel fender, just behind and next to the battery location.

Alternator on a test bench is good. Battery topped off and strong. Alternator output measured in my car is usually below 12.4 but can also vary all over the place and even reach higher than 14.8


But I have not yet measured the cut in value and then adjusted the Voltage Relay, it is supposed to actuate between 4.0 and 5.8 but I no longer have a variable DC voltage power supply so I'll guess I'll just have to stack some used D-cell batteries in a row and see how many batteries it takes in series for the Voltage Relay to actuate.

And it's been many months since I took that alternator into an auto parts store to be checked on the bench.... maybe this time it would fail?

So I accept there are 2 things I could do before I get too interested in digging deep into those resistance values, but I am interested.

Resistance between terminals in the manuals (the terminals are labeled E, L, B, IG, N, F):

IG and F
0 ohms at rest
11 ohms voltage regulator relay pulled in

L and E
0 ohms at rest
100 ohms voltage relay pulled in

B and E
infinity ohms at rest
100 ohms voltage relay pulled in

B and L
infinity ohms at rest
0 ohms voltage relay pulled in

N and E
23 ohms

There are three values that are supposed to be zero ohms, but I measure 5.3 ohms for each of these three measurements. I looked at the contacts for both relays and didn't see any burn discoloration or physical damage.

.....and...... after reading many good threads while searching for deeper info on Resistance Values for External Voltage Regulators..... I realize I should probably perform due diligence and locate, detach, inspect, clean, re-attach all major grounding wires to the chassis as well as look carefully at the connection between the wire an the crimp terminal for looseness or corrosion....... could somebody save me the time of reading the entire electrical sections and tell me where to locate the major grounding wires? Believe it or not I've no idea, presently.

[dlb]

i'm at work so i'm going off of memory here but i believe the main grounds are

from the head to the firewall
from the negative battery terminal to the frame by the driver side headlight
from the block or the wire bundle (can't remember which) to the frame by the driver side CV joint

anyone please correct me if i'm wrong. there may be more that i'm unaware of, too.

[Petros]

Welcome to the list!

YOur charging system behavior looks to me more like a bad contact or bad ground. A fully charged battery at rest should show 13.2 volts (2.2 volts per cell x 6 cells), the battery does not charge unless the alternator puts out more than 13.2 volts, and up into the 14.5 volt range. The alternator should put out more than 13 volts at all rpms above idle. If the alternator is good, and it charges intermittently after you start it, than it must be either the voltage regulator or an intermittent contact.

Clean or replace the battery terminals (verify the actual cables are making good contact too). DBL identified the major ground straps, there is also one on transmission housing, one off the bell housing (next to the starter if I recall) and one at the back of the trans near the rear mount. Also remember to check the contacts on the alternator itself, for corrosion or wear that might result in a poor contact. I clean mine with tuner cleaner.

Good luck.

[David Yount]

Thanks to DLB and Petros for titling the 6 electrical ground wires. I just need a little description of some of these locations:

-from the head to the firewall
I don’t know what or where the “head” is? I do know that the firewall is the metal wall at the back of the engine compartment.

-from the negative battery terminal to the frame by the driver side headlight
Got that, it was all rusty and there was some green corrosion on the wire. I used a rotary tool to clean off the terminal and the bolt and the washers. I used Naval Jelly to soak the green corrosion and then used WD-40 to remove the Naval Jelly.

-from the block or the wire bundle (can't remember which) to the frame by the driver side CV joint
I don’t know what or where the “block” is?

-one off the bell housing (next to the starter if I recall)
I can find this, I know the starter is on the left side, and I know the bell housing is the large shroud of metal that is shaped liked a bell.

-one on transmission housing
Would this be located forward of the bell housing? And do you know left side or right side?

-one at the back of the trans near the rear mount.
I really have no idea where to look for this.

[David Yount]

Okay, took the same unregulated alternator that came with the car when I bought the car about 2 years ago, I took it in for the sixth time, to have the alternator checked. Yep, the unregulated alternator checked 100% fine. My wildly fluctuating, but generally too low, charging output was never the alternator.

So, I still had one diagnostic test to do to the External Voltage Regulator while it was out of the car. I needed to measure the cut in value (in volts), this is the volt value that activates the Voltage Relay. If this was out of the range of 4.0 to 5.8 volts, then bend the lower metal tab which supports the leaf spring. The leaf spring is connected to the armature, the switch’s arm. The lower metal tab can be bent down and this would decrease the force on the leaf spring so the electromagnetic Voltage Relay would activate at a lower voltage. Or, you can bend the lower metal tab upward and create more force on the leaf spring and the armature wouldn’t move toward the electromagnet until a higher voltage were applied to the Voltage Relay.

I don’t have a variable DC voltage power supply, so I got my container of used D-cell batteries. I lined up 3 batteries, in series they put out 4.1 volts, and the Voltage Relay armature did not move. I lined up 6 batteries, in series they put out 6.3 volts, and the armature did not move. The armature is supposed to be calibrated such that it moves with 5.8 volts at the most, but at 6.3 volts it wasn’t even making a slight buzzing, it wasn’t even trying to move.

Then I noticed that each time I touched the wire to the last battery, completing the circuit, I noticed a very small spark. Well, a spark means a significant amount of current. And from my 1980 highschool electric shop class I remember that

Volts = Amps (current) x Ohms (resistance)

V = I x R

R = V / I

And since I was only using 6.3 volts I should not see any sparking. The only way to see sparking when using low voltage is if there were a lot of current flowing. Since I had such a small voltage but I was noticing large amps (the sparking), that would mean that my electrical test circuit had very very low ohms.

( to be continued )

[dlb]

-from the head to the firewall
I don’t know what or where the “head” is? I do know that the firewall is the metal wall at the back of the engine compartment.

if you look at the engine, it's divided from top to bottom into four sections: the top is the valve cover, next is the head, next is the block, and the next is the oil pan. the valve cover just covers the rocker arm assembly and can be removed easily to adjust valve lash. the head is where the valves live. the block is where the cylinders are, and the cylinders are where the pistons live. the block also houses the connecting rods, crank shaft, oil pump, and other things. the oil pan is kind of like the oil's home base--it constantly leaves and runs around the whole engine but generally comes back to the oil pan. FYI, if you ever need to replace a head gasket it's between the head and the block.

-from the block or the wire bundle (can't remember which) to the frame by the driver side CV joint
I don’t know what or where the “block” is?

see above.

-one on transmission housing
Would this be located forward of the bell housing? And do you know left side or right side?

not sure, petros will have to answer that one.

-one at the back of the trans near the rear mount.
I really have no idea where to look for this.

the transmission extends towards the back of the car. near it's rear end, there is a mount made of stiff rubber that fastens it to the frame of the car. these mounts (engines have them as well) keep the trans secure but allow some give because engines and transmissions twist and move a certain amount due to the force of the moving parts inside of them. jack the car up, put some stands securely underneath it, roll under and take a look for the trans mount. it will be clear when you see it.

[Petros]

the ground straps on the transmission area there to prevent corrosion from the build up of static charge, not likely the ground straps on the transmission is giving you trouble. The battery terminals and where they attach to the body and engine are the most critical, and the alternator contacts, and perhaps the voltage regulator contacts.

Sounds like the voltage regulator is suspect, so if all of the contacts are good try replacing the regulator.

BTW, the head of the engine is where the spark plugs and distributor attach (aluminum), the block is below it (cast iron).

[David Yount]

( I'll add more to this, later )