Author Topic: New 55A mp alternator (Read 6081 times)

harrycovert · « **on:** December 13, 2019, 08:23:23 »

Just fitted a new 55amp alternator
B+ wire connected D+ connected to ingnition light.
Switch on ignition light comes on
Start engine, ignition light goes out but battery voltage stays the same ie 12.5V
I would be grateful of any help.

Naj ✝︎ · « **Reply #1 on:** December 13, 2019, 12:03:12 »

Hi,

Faulty voltage regulator.

Is it inbuilt to the alternator or the original external one?

naj

harrycovert · « **Reply #2 on:** December 13, 2019, 13:32:58 »

Inbuilt to the alternator
I have just checked the voltage of the ignition light wire to earth and it`s 1.6v is this about right?

Naj ✝︎ · « **Reply #3 on:** December 13, 2019, 14:26:21 »

Hi,

Don't know about the ign light voltage.

The regulator is part of the brush plate screwed at the back of the alternator, and available separately.
I have experienced this issue with a new car before

naj

WRe · « **Reply #4 on:** December 13, 2019, 15:01:48 »

Hi,
in this thread you'll find some information and possible testings:
https://www.sl113.org/forums/index.php?topic=29492.msg213347#msg213347
Attached a wiring diagram with alternator connections.
Did you check your connections espec. to ground?
You need a ignition light with 4W to excite the generator, a LED lamp will not work.
...WRe

harrycovert · « **Reply #5 on:** December 13, 2019, 15:51:39 »

I assume the ignition light is correct wattage [not easy to check]would the 1.6 v be enough to excite the alternator
I have continuity between the alternator case and the negative battery post
I have connected a wire direct from the B+ to the positive battery post
Anything else I can try?

WRe · « **Reply #6 on:** December 13, 2019, 18:01:31 »

Hi,
the alternator/generator has 4 connections: cable colors can vary
- D+ red/blue: connection to D+ at voltage regulator, blue to ignition light (contact 61 charge indicator/charge control light)
- D- brown:. connection to D- at voltage regulator/ground
- DF black: connection to DF at voltage regulator
- B+ red: connections to starter and ignition starter switch (contact 30 from battery+ direct), black to battery
...WRe

harrycovert · « **Reply #7 on:** December 14, 2019, 07:11:44 »

The replacement 55 amp alternator I have used only has two terminals B+ and d+

WRe · « **Reply #8 on:** December 14, 2019, 10:21:14 »

Hi,
this is correct for your alternator with internal voltage regulator, means D- and DF is connected internally.
I assume that you have a problem with your charge control light or the wire to/from that light. 1.6V is not enough, that means only ~50mA. You need at least 300mA to excite the alternator.
You should take another/external lamp with 4W and connect this to the alternator and test it (+12V switched).
Some alternators (with internal voltage regulator) have an additional connector indicated with "L" (+12V switched) to excite the alternator.
Be careful, don't connect or disconnect your cables or battery with ignition turned on.
Can you tell us what type of alternator you have, maybe with a picture!?
...WRe

ja17 · « **Reply #9 on:** December 14, 2019, 15:06:28 »

The Mercedes 600 of the era used two Bosch 55 amp alternators with the standard single three prong plug and the pagoda type external voltage regulator. If you can find one, I think they are an exact fit with no modifications.

harrycovert · « **Reply #10 on:** December 15, 2019, 09:17:35 »

I connected a 5W bulb[ could not find a 4W one]from the positive terminal to the d+ .Still no charge from the alternator would the 1W make a differance?
The alternator is just a generic one that fitted

450sl · « **Reply #11 on:** December 15, 2019, 16:05:21 »

Seeing the green arrow makes me wonder if rotation cw or ccw has something to do with it.

WRe · « **Reply #12 on:** December 16, 2019, 07:26:50 »

Hi,
the rotating direction is not relevant for alternators only for an existing fan to cool the generator.
What about your battery, is it ok? If it's discharged deeply you should charge it first externally.
...WRe

harrycovert · « **Reply #13 on:** December 17, 2019, 11:28:50 »

The battery is showing 12.6v I think you have covered most options .Time to get another new alterator or get this one checked Professionally
Thanks all for your advice.

biffabeau · « **Reply #14 on:** January 02, 2020, 14:29:55 »

Hi
Can I ask where you got the alternator and what the rough cost was please?
Is it a Bosch AL72?

Thanks

harrycovert · « **Reply #15 on:** January 04, 2020, 10:29:04 »

Hi. I got it off Ebay . No identification apart from the number R489024 stamped on the case ,this is the link below.

https://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItemVersion&item=183747791996&view=all&tid=2046019448008

Floridaenglish · « **Reply #16 on:** January 21, 2020, 15:54:47 »

Just purchased a Bosch AL64X 55amp Alternator from Summit Racing for $122 including shipping and $20 Core. For $20, I'm keeping my old one to rebuild and save a spare.

Floridaenglish · « **Reply #17 on:** January 21, 2020, 22:31:43 »

Sorry, meant AL64X 35amp Alternator.

harrycovert · « **Reply #18 on:** January 28, 2020, 14:40:24 »

Follow up to this saga bought another new alternator fitted it all working Ok .Note to self just because it`s a new part don`t assume it`s Ok
Thanks once again everyone for the advice .Fantastic forum.

Pawel66 · « **Reply #19 on:** January 28, 2020, 19:02:17 »

sounds like once again, as someone wrote here: NEW = Never Ever Worked.

Tyler S · « **Reply #20 on:** January 28, 2020, 22:51:20 »

Just a note and warning to anyone upgrading to a 55 amp alternator. The large charging wire that is attached to the back of the alternator and goes to the starter is only a 10ga wire rated at 30 amps. I highly suggest you replace this wire with at least an 8ga wire rated at 50 amps. If your battery ever goes flat and the car is jump started, the alternator will be close to full fielding and try and send 50 amps through thst wire, possibly starting a fire. It is not fused.

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Author Topic: New 55A mp alternator (Read 6081 times)