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Exciting Alternator without Battery: Marelli 63377002, D+ & B+ Outputs, Connecting to Receiver

miketbg 53046 12
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  • #1 17291003
    miketbg
    Level 6  
    Hello!
    I have some fears to unravel.
    I have such an alternator, most likely Marelli 63377002
    Exciting Alternator without Battery: Marelli 63377002, D+ & B+ Outputs, Connecting to Receiveraltermagn..to.jpg (21.52 kB)You must be logged in to download this attachment.

    The back has two outputs, probably D + and B +

    Well, I have such a question for more experienced people, whether by directly connecting to a current receiver after accelerating this alternator will the current flow on the receiver?
    I know that there is a 5W bulb between D + and B +, but then people have an alternator connected to the battery.
    There are self-excited alternators of the 9 LEDs, but as it protrudes from this second screw to connect it probably will not be my alternator? (comes from cars ~ 2004). So far I have no way to check it out, I will be able to do it after the weekend. Possibly, I would ask for some ideas on how to get electricity from it to the receiver, what to raise it. Thank you in advance for your help!!
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  • #2 17291175
    jakubek56
    Level 32  
    The alternator has a built-in voltage regulator that controls the excitation.
    If it does not exist, it means that it is an ordinary generator.
    The battery should be to relieve the alternator slightly and stabilize the voltage.
  • Helpful post
    #3 17291206
    ladamaniac
    Level 40  
    Generally, all alternators installed in Volkswagen were self-excited, so that they "surprised" it was necessary to exceed about three thousand revolutions on the engine. However, working without a battery is not recommended. The regulator may have problems with voltage stabilization. In the toddler, with the B + wire broken, the voltage could exceed 50 volts.
    B + is a battery connection terminal, D + is awake.
    Excitation is enough to give for a moment, then he will manage himself.
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  • #4 17291271
    miketbg
    Level 6  
    Will giving an excitation for a while through a small 12v accumulator pass the exam?
    The direct receiver occurs in order to permanently load the alternator
    Exciting Alternator without Battery: Marelli 63377002, D+ & B+ Outputs, Connecting to Receiverschemat-wz...dzenie.jpg (68.41 kB)You must be logged in to download this attachment.
  • #5 17292091
    ladamaniac
    Level 40  
    In the case of a battery charge it will work, at least in what I checked, it always worked, in the situation of another receiver it is difficult for me to say. The voltage can be given by a 3 to 5 watts control, there will be a control of the operation.
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  • #6 17292107
    Strumien swiadomosci swia
    Level 43  
    First of all, you can burn diodes in this way, secondly there is no such thing as a self-excited alternator.

    Your reasoning is wrong in its entirety.
  • #7 17292194
    Anonymous
    Anonymous  
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  • #8 17292203
    Strumien swiadomosci swia
    Level 43  
    mn997 wrote:
    All alternators are self-excited

    Most of today's are not self-aware, certainly not on the F00M regulators, most of the valeo and magneton. They need voltage for good morning because the controller is a PROCESSOR.

    After the second topic, it is straight into the basket.
  • #9 17292210
    Anonymous
    Anonymous  
  • Helpful post
    #10 17292242
    Strumien swiadomosci swia
    Level 43  
    OK, I checked the alternator is 6 LEDs.
  • #11 17292638
    ladamaniac
    Level 40  
    mn997 wrote:
    All alternators are self-excited (residual magnetization) after exceeding a certain speed, but they are unpredictable in terms of voltage if they do not get the standard in the form of a battery. Pozdrawiam. [/ Quote]

    But only a part can start charging without external excitation in the range acceptable to them, the VW Group starts at around 3 thousand engine revolutions, that is probably with 4.5 thousand of the same alternator, and Fiat can be turned into sections of the engine and nothing. Speech of alternators from the plus or minus range 1995 to 2005.
  • #12 17292680
    Staszek49
    Level 35  
    I have heard that there are self-excited alternators in which vehicles operating in difficult conditions are equipped. Mainly they were assembled in various vehicles, including "civil" ones in the former Soviet Union. A part of such an alternator will be made in the form of a "dynamo" and rectifier, which is used to excite the second part, ie a traditional alternator.
  • #13 18253612
    jancio1973
    Level 13  
    I know that the subject is old but I have to write my opinion on this matter because I know Fiat alternators from a toddler to those used today; first of all, "if it's a Fiat Alternator M. Marelli, e.g. AA 125r-14V ... it's obviously that it will wake up itself and doesn't even need high revs ... it just starts charging normally from about 1000 revs. Secondly, nothing will not happen if the excitation terminal or current terminal with load is not connected, because all ELECTRONIC controllers have a built-in voltage limiter, someone wrote that in a toddler voltage in this way jumped to 50 V .....- it could have been but if it was the regulator was not original or the original electronic one was damaged, otherwise it could not be so.

Topic summary

✨ The discussion revolves around the Marelli 63377002 alternator, specifically its D+ and B+ outputs and the feasibility of connecting it directly to a current receiver without a battery. Participants highlight that while the alternator can self-excite at high RPMs, operating without a battery is not advisable due to potential voltage instability and risks of damaging components. The importance of a battery for voltage stabilization and the alternator's functionality is emphasized, with some users noting that certain models, like those from Fiat, can start charging at lower RPMs. Concerns about voltage spikes and the necessity of proper excitation methods are also discussed.
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FAQ

TL;DR: Many car alternators need about 3,000 rpm to self‑excite; "B+ is a battery connection terminal, D+ is awake." Running without a battery risks unstable voltage; use a 3–5 W lamp on D+ to excite and monitor. [Elektroda, ladamaniac, post #17291206]

Why it matters: This helps DIYers safely get usable power from a Marelli/VW/Fiat alternator without damaging diodes or electronics.

Quick Facts

What do the B+ and D+ terminals do on a Marelli 63377002 alternator?

B+ is the main output to the battery or load. D+ is the field excitation and charge‑indicator terminal. You can apply excitation briefly to start charging, then the alternator sustains itself. "B+ is a battery connection terminal, D+ is awake." Running without a battery is not advised due to regulation issues. [Elektroda, ladamaniac, post #17291206]

Can I run this alternator without a battery, straight into a receiver?

Avoid it. The regulator may fail to stabilize voltage without a battery as a reference and buffer. That risks unpredictable output and component stress. Use a battery to stabilize and to protect electronics. If you must test, use a small excitation lamp and monitor voltage carefully. [Elektroda, ladamaniac, post #17291206]

Will a small 12 V battery on D+ work as a momentary excitation source?

Yes for battery charging use. Briefly supplying excitation works in practice when charging a battery. For driving other receivers, results are uncertain. A 3–5 W control lamp on D+ is a safer, visible way to provide excitation and confirm operation. [Elektroda, ladamaniac, post #17292091]

What lamp wattage should I use on D+ for excitation and indication?

Use a 3–5 W bulb as the charge lamp between B+ and D+. It will feed the field and act as a visual indicator of charging. That small wattage is typical for automotive dash charge lamps and suits excitation needs. [Elektroda, ladamaniac, post #17292091]

How do I safely excite and test this alternator without a battery?

  1. Connect a 3–5 W bulb between B+ and D+, and ensure the alternator case is well grounded.
  2. Spin the alternator and watch the lamp; dimming or going out indicates charging.
  3. Measure B+ voltage and connect a load cautiously, keeping an eye on voltage. [Elektroda, ladamaniac, post #17292091]

What rpm is typically needed for self‑excitation if I dont pre‑excite D+?

Some VW‑group alternators begin charging around 3,000 engine rpm. That reflects late‑1990s to mid‑2000s designs and varies by pulley ratio. Other makes, like certain Fiat units, may not self‑start without excitation. Confirm behavior on your model. [Elektroda, ladamaniac, post #17292638]

Are modern alternators really self‑exciting?

Many modern regulators use processor‑based controls and need an initial supply on their terminals. They will not self‑excite from residual magnetism alone. "They need voltage for good morning because the controller is a PROCESSOR." Examples include some Bosch F00M, Valeo, and Magneton units. [Elektroda, Strumien swiadomosci swia, post #17292203]

Is the Marelli 63377002 in this thread a 6‑ or 9‑diode unit?

It was checked and identified as a 6‑diode rectifier design. This affects internal wiring and how the excitation path behaves. It also clarifies that it is not the 9‑diode style sometimes referenced for self‑exciting behavior. [Elektroda, Strumien swiadomosci swia, post #17292242]

What happens if the B+ wire opens while the alternator is running?

A reported case showed voltage exceeding 50 V when B+ broke. That can damage electronics and bulbs quickly. Never disconnect the battery or B+ under load. Treat open‑circuit operation as a failure condition and shut down immediately. [Elektroda, ladamaniac, post #17291206]

Can I use this alternator as a standalone generator into a resistive load?

Its not recommended. The battery both buffers current spikes and stabilizes voltage. Without it, voltage can wander and stress the regulator and diodes. Connect a healthy battery across B+ and ground, then attach your load in parallel. [Elektroda, jakubek56, post #17291175]

Do Fiat/Marelli alternators self‑start at low rpm?

Some Marelli units do. A contributor reports normal charging starting near 1,000 rpm on certain Marelli AA 125r‑14V types. They also note that electronic regulators limit voltage, assuming they are intact and original. "It starts charging normally from about 1000 revs." [Elektroda, jancio1973, post #18253612]

Are there alternators designed for harsh conditions that truly self‑excite?

Yes, some vehicles used alternators with an auxiliary dynamo plus rectifier to feed the main field. These were found in equipment built for difficult environments, including some former Soviet designs. They are not typical of 2000s passenger cars. [Elektroda, Staszek49, post #17292680]

Could brief excitation or miswiring damage the alternator?

Yes. Incorrect setups can burn rectifier diodes or stress the regulator. Avoid running with no battery and random loads. Use proper excitation, verify wiring, and monitor voltage. If unsure, bench‑test with a battery and a 3–5 W lamp first. [Elektroda, Strumien swiadomosci swia, post #17292107]

Will a lamp‑excited setup charge a battery reliably, but not other loads?

Testing showed lamp excitation works when charging a battery. Performance into other receivers is uncertain and depends on regulation behavior. Use the 3–5 W lamp as both the excitation source and charge indicator for safer testing. [Elektroda, ladamaniac, post #17292091]
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