DMCH alternator

[dustybarn]

Actually if you just leave it disconnected it will internally regulate. Which is the "normal" installation. Just the output wiring bundle, and the one wire to the idiot light.

Yes, there does appear to be an internal resistor that makes connecting the "S" terminal optional. I elected to connect mine to the main passthrough stud below the bulkhead connections under the coil cover. A thin wire is sufficient because it's just a voltage-sensing wire.

[Bitsyncmaster]

$.02:

Don't hold me to it, but without looking at that type before, I'd bet it's odd behavior(s) is due to not utilizing a battery sensing circuit, as expected??

Looks like Ron the man.....

I first checked the voltage on the "S" terminal and it was zero volts. I was expecting it to be pulled up to the battery voltage. I then connected it to the battery through a 1 Kohm resistor so I could measure the current that "S" terminal would draw if always powered. Result is 187 ua.

Connected the "S" wire directly to the output terminal of the alternator. Started the car and put the loads on and waited and waited and waited for the dip (I'm just looking at the dash volt gauge). No dip seen so I disconnected the "S" lead (I'm just using an alligator clip lead for now), and did see the dip occur. Connected it back up again and no dip seen.

So it looks like I will permanently wire that "S" lead to the alternator output post.

I measured the voltage at my buss with it connected and it was 14.49 volts, without it connected it was 14.44 volts all when my loads were running.

I did discover a bug in my battery disconnect relay during this testing where when I switch the AC to off with the blower and headlights still on it glitches the disconnect relay and turns the engine off. I will need to fix that glitch.

[Bitsyncmaster]

Without connecting the "S" wire to battery voltage this alternator will flash the dash battery light. That flashing starts intense and then it looks like the duty cycle decreases so the flash gets less intense, then it repeats. This is all when you just turn the key to on (engine not running).

Connect that "S" wire to battery voltage and that flashing is no more. Light just comes on and stays on when engine is not running.

I guess we should have questioned why it was flashing long ago.

[Ron]

...
Connected the "S" wire directly to the output terminal of the alternator. Started the car and put the loads on and waited and waited and waited for the dip (I'm just looking at the dash volt gauge). No dip seen so I disconnected the "S" lead (I'm just using an alligator clip lead for now), and did see the dip occur. Connected it back up again and no dip seen.

So it looks like I will permanently wire that "S" lead to the alternator output post.

I measured the voltage at my buss with it connected and it was 14.49 volts, without it connected it was 14.44 volts all when my loads were running.

I'm not familiar with your buss, but it sounds like you are all set. ...A few notes for others:

First, I think it should be noted that the DMC "plug and play" wiring is probably ~OK as is.
But, for those with stock wiring, jumping the S terminal to the alternator's output terminal will give ~14.2V measured at the alternator terminal and ~13.2V measured at the battery -- Nothing to brag about....In fact, it can be worse than a true one wire setup (ie only has an output wire).

A much better setup is to connect the S terminal to the battery (+) [or main accessory feed/buss junction], which will give ~15.4 at the alternator terminal [...] and ~14.2V at the battery -- Ideal!
The longer the feed wire, the more this is needed.

Hope this helps....

P.S. What I would like to know about is the flashing.....

[Tillsy]

Great work Dave, my IT instincts had been telling me these reports of a flashing light with the new alternator meant "error".

[Bitsyncmaster]

Looks like this new alternator uses a microprocessor in the voltage regulator. Wish we could get more info on the error codes.

[DMC-81]

Very interesting!! Let me see if I follow....out of the box, the alternator self regulates after blinking on start up, but with the S terminal optionally connected to battery positive, you avoid the blinking light and the minor voltage dips?

A few questions if I may:

- are we saying the S connection provides more voltage performance?

- does this connected S terminal hurt anything on this unit, or on the other hand, help the unit last longer? i.e Are the voltage dips an intentional rest period?

- should the S connection be fused?

- if we want to connect the S, do you need a new plug, or can you add a wire to the 1 wire plug?

- and finally, would the solid brown ducy wire serve as a connection for the S terminal?

Thanks,

Dana

[dustybarn]

Very interesting!! Let me see if I follow....out of the box, the alternator self regulates after blinking on start up, but with the S terminal optionally connected to battery positive, you avoid the blinking light and the minor voltage dips?

A few questions if I may:

- are we saying the S connection provides more voltage performance?

- does this connected S terminal hurt anything on this unit, or on the other hand, help the unit last longer? i.e Are the voltage dips an intentional rest period?

- should the S connection be fused?

- if we want to connect the S, do you need a new plug, or can you add a wire to the 1 wire plug?

- and finally, would the solid brown ducy wire serve as a connection for the S terminal?

Thanks,

Dana

Connecting the S terminal to the vehicle power bus may provide a steadier voltage because any voltage drop in the alternator wiring is automatically compensated for (this has been my experience). There should be no effect on the longevity of the unit; it's designed to work that way. I see no compelling reason to put a fuse in the S lead because it carries almost no current.

[Bitsyncmaster]

Connecting the S terminal to the vehicle power bus may provide a steadier voltage because any voltage drop in the alternator wiring is automatically compensated for (this has been my experience). There should be no effect on the longevity of the unit; it's designed to work that way. I see no compelling reason to put a fuse in the S lead because it carries almost no current.

+1

Using the S terminal is a pretty common wiring option in a lot of cars. You would need to get a new connector with that pin connected to a wire or find the correct pin to install into the existing connector. I pulled the pin from my old connector which happened to have that larger pin (the other three are smaller). I don't think anyone ever uses a fuse for that wiring. It just draws micro amps of current. But if the wire insulation were to get cut and contact ground it would melt the wire (work like a fuse link). I used 16 AWG wire on mine.

Remote sensing is always used in large high amp power supplies for electronic units. The power supplies even have both ground sensing and + sensing. When producing 5 volt, 3.3 volt and now even lower voltage used for electronic circuit boards a voltage drop of even 0.1 volt over the wiring can cause problems.

[DMC-81]

Very cool. Thanks for all the information. Very helpful!

So, would the solid brown ducy wire serve as a connection for the S terminal, or not so much? It's just that it is really handy to the alternator, and not being used.

Also, this alternate 2 wire plug seems like a good new product for those running this unit.. Hint hint....

Although I wonder if it will void the warranty?

Thanks,

Dana