Hello I have a bridge from the 12V alternator from the Ford Fiesta MK4 (Magneti-Marelli) to check - it is a simple 3f bridge composed only of 6 main typical, push-in diodes, there are no small excitation LEDs in the bridge. I have the bridge pulled out, I check the power supply from a small...

At 99% yes, check with the meter on the diode test then you will know if 1 of the diodes is damaged or more.

Buddy, you made 2 mistakes, 1 is too much voltage, the other is alternating voltage. Test with a constant 12v and a bulb.

Ok, then I will modify the test circuit, put in series with each phase, it hits the diode in the forward direction. This will slightly lower the voltage and give a constant ripple, not alternating voltage ... can it be? Nevertheless, when I check such a typical cube - the 3f bridge does not flow, and these bridges are the same. regards!

As they say to you test with constant and light bulb you are up to it. These car diodes can conduct in the reverse direction from about 26V for 12V bridges. Take a 21-50W light bulb, a battery or a 12 V power supply, each diode is conductive on both sides and the matter is done.

Hmmm, I can check each diode separately, but this is about checking the entire complex 3f bridge (without desoldering the diodes). regards

If there is no stator, what's the problem? . You can check each of them separately, even though they are bridged 3.

Ok, so in the existing 3f bridge system I check each of the 6 diodes with 12V DC with a bulb load. The remaining bridge diodes, although physically connected to the diode under test, will not affect the measurement? It will be such a scheme, we change - we only reverse the current source?

You take 12 measurements and you already know a little about the bridge.

Ok. And why the above colleague qualifies the application of trafa = alternating voltage as an error? regards

Because you have to find out if a given diode is conducting '' I '' in the second measurement or if there is no short circuit.

Checking 12V Ford Fiesta MK4 Alternator Bridge: Magneti-Marelli, 3f Bridge, 6 Push-in Diodes

tida1 5337 12

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#1 16315245 01 Mar 2017 14:27

tida1 tida1

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Post #1
16315245 01 Mar 2017 14:27

Hello

I have a bridge from the 12V alternator from the Ford Fiesta MK4 (Magneti-Marelli) to check - it is a simple 3f bridge composed only of 6 main typical, push-in diodes, there are no small excitation LEDs in the bridge.

I have the bridge pulled out, I check the power supply from a small 3-phase transformer (phase-to-phase voltage approx. 35V), but after connecting any two phases
5.5A current flows, of course the bridge output is not connected. Is this definitely a fault, more specifically a short circuit in the bridge?

regards! Tida
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#2 16315257 01 Mar 2017 14:33

rafcio_21 rafcio_21

Level 29

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Post #2
16315257 01 Mar 2017 14:33

At 99% yes, check with the meter on the diode test then you will know if 1 of the diodes is damaged or more.
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#3 16315496 01 Mar 2017 16:42

Strumien swiadomosci swia Strumien swiadomosc...

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Post #3
16315496 01 Mar 2017 16:42

tida1 wrote:
phase-to-phase voltage approx. 35V

Buddy, you made 2 mistakes, 1 is too much voltage, the other is alternating voltage.

Test with a constant 12v and a bulb.
#4 16315639 01 Mar 2017 17:53

tida1 tida1

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Post #4
16315639 01 Mar 2017 17:53

Ok, then I will modify the test circuit, put in series with each phase, it hits the diode in the forward direction.
This will slightly lower the voltage and give a constant ripple, not alternating voltage ... can it be?

Nevertheless, when I check such a typical "cube" - the 3f bridge does not flow, and these bridges are the same.

regards!
#5 16315668 01 Mar 2017 18:07

abart64 abart64

Level 33

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Post #5
16315668 01 Mar 2017 18:07

As they say to you "test with constant and light bulb" you are up to it. These "car" diodes can conduct in the reverse direction from about 26V for 12V bridges. Take a 21-50W light bulb, a battery or a 12 V power supply, each diode is conductive on both sides and the matter is done.
#6 16315687 01 Mar 2017 18:16

tida1 tida1

Level 9

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Post #6
16315687 01 Mar 2017 18:16

Hmmm, I can check each diode separately, but this is about checking the entire complex 3f bridge (without desoldering the diodes).

regards
#7 16315697 01 Mar 2017 18:19

abart64 abart64

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Post #7
16315697 01 Mar 2017 18:19

If there is no stator, what's the problem? . You can check each of them separately, even though they are bridged 3.
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#8 16315896 01 Mar 2017 19:28

tida1 tida1

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Post #8
16315896 01 Mar 2017 19:28

Ok, so in the existing 3f bridge system I check each of the 6 diodes with 12V DC with a bulb load.

The remaining bridge diodes, although physically connected to the diode under test, will not affect the measurement?

It will be such a scheme, we change - we only reverse the current source?
#9 16315989 01 Mar 2017 19:56

Strumien swiadomosci swia Strumien swiadomosc...

Level 43

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Post #9
16315989 01 Mar 2017 19:56

You take 12 measurements and you already know a little about the bridge.
#10 16316004 01 Mar 2017 19:59

tida1 tida1

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Post #10
16316004 01 Mar 2017 19:59

Ok.

And why the above colleague qualifies the application of trafa = alternating voltage as an error?

regards
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#11 16316057 01 Mar 2017 20:10

Strumien swiadomosci swia Strumien swiadomosc...

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Post #11
16316057 01 Mar 2017 20:10

Because you have to find out if a given diode is conducting '' I '' in the second measurement or if there is no short circuit.
#12 16316406 01 Mar 2017 21:29

andrzej20001 andrzej20001

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Post #12
16316406 01 Mar 2017 21:29

Measure with battery and 55w bulb. Each one separately
#13 16319651 03 Mar 2017 09:23

tida1 tida1

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Post #13
16319651 03 Mar 2017 09:23

Ok then problem solved, thanks everyone!

regards !
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Topic summary

The discussion revolves around testing a 12V alternator bridge from a Ford Fiesta MK4, specifically a Magneti-Marelli model featuring a 3-phase bridge with 6 push-in diodes. The user initially connected the bridge to a 3-phase transformer, resulting in a 5.5A current flow, raising concerns about a potential short circuit. Responses suggest using a constant 12V supply with a light bulb for testing, as alternating voltage may not provide accurate results. Participants recommend checking each diode individually to diagnose any faults, emphasizing that the physical connection of diodes in the bridge will not interfere with individual measurements. The user ultimately confirms the problem is resolved after following the advice.
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