DF Limaklemme: What is it used for?

Hello,

Can anyone tell me what the DF terminal is for? I have a 1998 AFN engine from a Passat.
And which pin on the 80-pin control unit does the DF signal come from, and what is the wire color? Maybe someone has a wiring diagram handy.

Thank you and best regards.

Thorsten.

dokatoto wrote:

Can someone tell me what the DF clamp is for?

Hi Thorsten,

It reports the alternator's load to the engine control unit. If the load approaches 100%, it deactivates the glow plug heating to prevent the vehicle's voltage from dropping (initially).
DF is therefore only important in winter - I don't know of any other meaning.

Quote:

And which pin of the 80-pin control unit does the DF signal come from, and what is the cable color? Perhaps someone has a wiring diagram handy right now.

Here's something about a Golf 4 / Bora: Pin 22 is brown-red.
Whether that also fits the Passat:

Tip: Measure the resistance to ground at the engine computer connector (hopefully something will be displayed), then disconnect the alternator connector. If the measured value changes, you have found the DF terminal .

Thank you and best regards.

Actually, all newer Bosch alternators have this type of terminal.
Normally, it's called the DFM.

It's not just needed in the winter. The EDC (Electronic Control Unit) monitors the alternator's load and, of course, also checks the vehicle's on-board voltage.

If the utilization reaches 100% and the voltage continues to drop, the idle speed will be increased to provide the alternator with more power.

The connector for the indicator light also has two functions:
On one hand, it turns on the lamp; on the other hand, it can also, for example, activate a relay (or a digital input) that the vehicle's onboard electronics then uses to switch on other consumers. The purpose here is to prevent the alternator from struggling to start due to unnecessary load. Anything that is not essential is only switched on after the alternator has reached a stable voltage. However, to my knowledge, this is not used by VAG (at least not in our vehicles). This connection is also no longer necessary for the pre-excitation of the alternator, as the alternator handles that internally.


CU Gremlin.

Okay, can anyone tell me if the DF connector is the same as the W connector used in the older Lima models?

I want to install a Lima 150A alternator from a VR6 engine, but my car requires a DF terminal.

Greetings.

DF (Dynamo Field) corresponds to the connection of the excitation winding.
In older controllers, the knobs were actually physically connected directly to the hardware. The controllers currently used provide the signal directly from the circuit to the drivers.

'W is a tap on the three-phase winding, so you'll find an alternating voltage there. Diesel engines, in particular, used this to connect a tachometer (since there are no other speed signals available in a mechanical diesel engine).'

CU Gremlin.

Okay, so...
I once looked at a diesel locomotive with a DF coupling.
It appears that the DF terminal is connected to the regulated excitation winding via a diode.
Can I simply tap into the excitation winding using a diode?
I want to install a different alternator, but it doesn't have the DF terminal that my engine control unit requires.

Greetings.