1800E Voltage Regulator (?)

[sleek lemur]

Hi all, continuing on form my "won't start" thread, I have a running car, but no battery charging. Red light in speedo is fully on bright. Voltage at battery with engine running 12.5v. This problem has occurred after the winter lay-off.

I have followed the advice on the previous thread and believe the issue is the voltage regulator (but am not certain!). So...

1. Alternator on its own is putting out 21v
2. I tested the voltage drop at the DF terminal with a multimeter from that to earth: Nothing. Also tested green terminal at voltage regulator and again nothing.
3. Tested voltage at alternator terminal where yellow wire from voltage regulator joins. 1.5V Also get 1.5V testing yellow terminal at voltage regulator. Is this correct? I was expecting 12v

Any ideas, advice gratefully received as always.

The voltage reulator is less than a year old.

[Ron Kwas]

SL;

"Alternator on its own is putting out 21v" The Alt output should NEVER be disconnected from Battery, including temporarily or for test purposes!

For info on 1800E Charging system see: https://sw-em.com/123GT_Charging_Sys...g_System_Notes

Good Hunting!

[sleek lemur]

Thanks Ron!

Alternator was bench-tested 🙂

Thank you for the useful link. Will do the following tests suggested by member Pidgeon and report back. One thing of interest is that a low voltage at the exciter circuit is correct.

"Disconnect the wire to the DF terminal on the alternator, then, with the engine running, connect the DF terminal to battery positive via an indicator bulb (21W) while measuring the alternator output voltage at the B+ terminal. What happens? What you should see is that the output voltage rises. It might rise rather high, but that won't matter as long as you don't maintain the connection for longer than is needed to get a reading. You should also hear the engine speed drop slightly because the alternator will be taking mechanical power, and the AMP light should go out.

If that's OK, then put the wire to DF on the alternator back; then disconnect the wires to the DF and D+ terminals on the regulator, and connect them together. Again, you should see the voltage on B+ rise, hear the engine speed drop, and see the AMP light go out.

If the first test fails, almost certainly the alternator is knacked.

If the first test is OK but the second one fails, probably the alternator is knacked.

If both tests are OK, it's probably the regulator.

To hear the change in engine speed, it may be useful to do the tests with the headlights and/or the heater fan on, to make sure there is a decent load on the electrical system."

[142 Guy]

Originally Posted by sleek lemur

2. I tested the voltage drop at the DF terminal with a multimeter from that to earth: Nothing. Also tested green terminal at voltage regulator and again nothing.
3. Tested voltage at alternator terminal where yellow wire from voltage regulator joins. 1.5V Also get 1.5V testing yellow terminal at voltage regulator. Is this correct? I was expecting 12v

2. Df is the alternator field winding terminal. It is effectively the 'input' to the alternator from the voltage regulator. If the voltage regulator is dead then it is not providing any excitation current to the field winding and the voltage at this point will be 0.

3. The yellow wire is D+ on the alternator which is the supply to the regulator and is also connected to the dash charge light. If the alternator and voltage regulator are working you will have around 14 volts at this point (or whatever your running voltage is). The fact that you are measuring only 1.5 volts is an indication that the alternator or regulator are not working - which is why your charge light is illuminated.

If the 21 v measured in a bench test was done by your repair shop, that is likely a full field test which is the same test as described by Pidgeon, so I would not bother repeating it. Presumably when doing the bench test the shop confirmed the other regulator connections so we should probably rule out the alternator as the failed item leaving you with the regulator.

I know that the B20E in my 1971 142E came with two alternator options, a Motorola / SEV and a Bosch. I expect that the P1800E was the same. I think the Bosch was the more common type. You never said which one you have. The older mechanical regulators are not interchangeable between the two types of alternators so if you found a replacement mechanical regulator you need to make sure that it is the correct item for your alternator.

As far as I am aware, the replacement voltage regulators for the older Bosch 35 amp and 55 amp alternators are now all electronic units. I don't know whether they will work with the Motorola alternator. On some Volvo's the original plug connecting to the voltage regulator has just two pins. The ground connection for the voltage regulator is made through the mounting screws for the regulator. On the newer electronic regulators there are three electrical connections on the bottom and one of those pins is a ground connection. You cannot rely on the mounting screws for the ground connection. You need a dedicated wire from the ground terminal on the regulator to a metal ground on the chassis. Note that the Bosch 35 amp and 55 amp alternators have replacement electronic regulators that look identical; but, are different. If you have a 55 amp alternator and got a 35 amp regulator you may have toasted the regulator.

If your replacement regulator is mechanical (and correctly matched to the alternator) you can remove the cover and inspect for charred remains. If there are no charred remains then there are some 'tests' you can do to check its function. In the case of an original Bosch regulator, there are some adjustments you can make.

[sleek lemur]

Thanks 142 that's a great help. So, if I'm not getting reading from the DF terminal where the green wire from the regulator fits, it sounds like my regulator is toast.

As far as the 1.5v I'm getting on the yellow indicator light side of the circuit, youk that's an issue within re regulator itself? Connections seem to be sound.

I have the later three pin regulator and my excitement level raised when the spade connector for the earth lead disintegrated in my fingers, but alas a new connector didn't cure the problem.

Interesting what you say about getting the right regulator. My Bosch alternator is 55amp. Brookhouse only seem to supply one type of regulator. As I said, mine is quite new. The previous one was only giving 13 amp charge and looked pretty manky. Wish I'd kept it! I wonder if the new one is only designed to handle 35amp? I'll take a look inside tomorrow. Also have emailed Brookhouse.

The part is only £31 and Brookhouse will always refund unused parts. But let's see what they say about the power rating of their regulators first.

[blueosprey90]

With reference to Ron's wiring diagram, I would check continuity of the wire labeled "Alt Excitation" to "Amp Indicator", including verification that the wires are actually connected.

I don't know about any of those fancy tests, but 90% of the time when I have had a non-charging situation with other models of car, it has been this line.

[sleek lemur]

Many thanks, BlueOsprey. Will definitely check that tomorrow. I must admit, I assumed that the fact that the amp light was lighting must mean that the connection is good.

I must stop assuming stuff.....

[blueosprey90]

Just yesterday, I started my car (the MGA) for the first time after pulling engine to replace the transmission. Red light on while running. Wire from the light at the generator not properly attached. Took two seconds to fix and I would have gone to play the lottery, but I had other more serious issues requiring me to pull engine once again.

I'm no big expert, but I believe the light essentially measures voltage differential between the battery and the generator. If there is no light means that generator and battery are essentially at same voltage.

The broken wire red light can mimic, I think, the condition when you turn the ignition and the car is not running - i.e., measures only the battery.

[sleek lemur]

BO, after your previous message, I looked at the wiring diagram again and I totally get what you say. Despite reading elsewhere re the voltage difference, I just didn't get it. Am excited to check this, but can't do so until this PM!

[142 Guy]

Response to your questions in red.

So, if I'm not getting reading from the DF terminal where the green wire from the regulator fits, it sounds like my regulator is toast. - That is the most likely cause of the problem.

As far as the 1.5v I'm getting on the yellow indicator light side of the circuit, youk that's an issue within re regulator itself? Connections seem to be sound. - Again, the most likely cause of the problem. If the charging light is glowing brightly when the engine is running that suggests that the yellow wire from the charge light to D+ on the alternator and regulator is intact and you are getting your field flashing current. As a test, disconnect the yellow D+ wire from both the alternator and the voltage regulator. Switch the key to the run position. If the charge light does not illuminate then the wiring is OK. If the charge light still illuminates you have a short circuit to ground on the yellow wire which is preventing the alternator from starting up.

Blueosprey90's comments about the light measuring the voltage difference between the battery and the alternator are correct. Normally, the light comes on when you have 12v from the battery and 0 (or 1.5) volts at the alternator D+ terminal indicating a dead alternator/ regulator. However, if there is a short circuit to ground on the yellow wire that will cause 0 volts on the alternator 'side' causing the light to illuminate and the alternator to fail to start up. However, your next comment about the disintegrated ground wire makes me think that the yellow wire is not the problem.

I have the later three pin regulator and my excitement level raised when the spade connector for the earth lead disintegrated in my fingers, but alas a new connector didn't cure the problem. - Did it disintegrate because it looked like it had been overheated? Overheating can be caused because the spade connection was poor causing the connection to heat up. This overheating would have been accompanied by voltage drop which would cause the regulator to supply additional current which may have exceeded the current rating of the internal pass transistor.

Interesting what you say about getting the right regulator. My Bosch alternator is 55amp. Brookhouse only seem to supply one type of regulator. As I said, mine is quite new. The previous one was only giving 13 amp charge and looked pretty manky. Wish I'd kept it! I wonder if the new one is only designed to handle 35amp? I'll take a look inside tomorrow. Also have emailed Brookhouse. - I would follow up with Brookhouse. My comments were based upon the fact that Skandix show separate part numbers for the voltage regulator for the 35 amp and 55 amp Bosch alternators. It may be possible that the 55 amp regulator will work on the 35 amp alternator. I have the solid state regulator that Dave Barton sells on my 35 amp Bosch.

https://www.prancingmoose.com/AdjustableVoltage.html

The information on his webpage indicates that his one regulator works for all the Bosch external regulator alternators so the Skandix listing may smell of fish.