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Mike, Mechanic
Category: Car
Satisfied Customers: 39198
Experience:  Hi, I have been a Car/vehicle mechanic 34 years. 29of -running my own repair/diagnostic business.
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Voltage regulator..the nature of the PCM signal to the L terminal

Customer Question

How do I test this Bosch voltage regulator F00M145873? More specificslly what is the nature of the PCM signal to the L terminal?
Submitted: 5 years ago.
Category: Car
Expert:  Gary replied 5 years ago.
can you tell me what year?make and moduel this alternator came out of ?
Customer: replied 5 years ago.
Bosch have several regulators that use the concept of regulating the voltage by a pwm signal to the L terminal. I need the details on the PWM signal. This is a smart regulator from Bosch.similat to GM RVC types. I dont have the car or alternator that it comes from but i could find out.
Expert:  Gary replied 5 years ago.
The voltage regulator controls the rotor field current in order to limit the system voltage. When the field current is on, the regulator switches the current on and off at a rate of 400 cycles per second in order to perform At high speeds, the on-time may be 10 percent with the off-time at 90 percent. At low speeds, the on-time may be 90 percent and the off-time 10 percent.
Customer: replied 5 years ago.
Just to clarify, Is the 400Hz signal applied to the L terminal with thye 10% to 90% duty cyles? and at what voltage 5vp-p or 12vp-p?
Expert:  Gary replied 5 years ago.
Voltage Set Point: 14.5 V Slipring OD : 14 mm Regulation: A-Circuit »» LRC 2.5 Seconds,
its 12 volts
Customer: replied 5 years ago.
Hi ,
I asked a follow up question , as the answer is only half complete.
If I had to scope the L terminal, what would I see:
square wave 5v or 12v. Did not get a response to this last bit?
Expert:  Gary replied 5 years ago.
Customer: replied 5 years ago.
I tried this.
I applied a 12v signal , 400Hz and varied the pulse width 10% to 90%. I am unable to control the regulation. Are you absolutly sure that the ECU signal via the L terminal is a PWM(10% to 90%) or a digital signal such as LIN. I can control the Lamp Output and the choke drive output on the L terminal successfully by applying a stator input >150Hz.
Justanswer sells you as a "Bosch Technical expert" hence this question to you.
Expert:  Mike replied 5 years ago.
Hello and Welcome to justanswer..

Can you please tell me what the overall problem is that you have / ie, is it non charging / over charging etc?

Rgds, MIKE.............................................
Customer: replied 5 years ago.
Hi Mike, I am a technical consultant to a company that makes a regulator tester.There is no car problem, no alternator problem , just a generic question on this type of regulator.
I am looking for the technical details on the L terminal signal that come from the ECU.
Expert:  Mike replied 5 years ago.
Hello again - thank you for your reply.... I see the situation -

I was going to say at the outset that you need a special tool / equipment to test them properly but thought I'd ask first ! For many many years I have personally used such equipment that was made by a company in England - can't just think of the name / make now but it was the company own name.. on the equipment as we do alternator (etc ) rebuilds - we used to do a lot more than we do of late - but you needed the equipment to test just the reg - that was equipment dedicated to the regs themselves -

As regards the L far as I recall that is the light terminal (on the dash ) and is wired through the ecu on smart charge systems...( I dont have any specific diagrams on that - they would be different for each model of vehicle anyway)

If I can find any more info I'll gladly let you have it ..

Best Rgds - MIKE..

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