TorqueJunkie

Diesel alternator in Petrol car

11 posts in this topic

Posted (edited) · Report post

Hi,

 

I want to install an electric heater in a petrol car and probably would need more current at idle RPM. At idle, alternator can only provide around 40% of rated current (75A is rated at around 2500RPM).

The questions are:

1. is alternator's pulley size different in diesel and petrol cars? From some pictures I found, diesel one seems to be bit smaller (= more RPM).

2. If different, are the alternators otherwise more or less compatible in terms of mounting to the engine?

3. Can I spin the alternator slightly faster than rated? In electrical theory there should be no problem.

Edited by TorqueJunkie

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So I have found out that:

Roadster alternator is rated at 75A, and has a 4-groove 58mm pulley.

450 0.8L CDI has a 85A alternator with 5-groove 54mm pulley. These look bit different, including connectors. Mount looks similar. Should fit?

 

Also found several ebay listings for "97A" alternator, but that must be an error, right? Look identical to 75A model.

£95 https://www.ebay.co.uk/itm/NEW-ALTERNATOR-FOR-SMART-0986049111-OEM-QUALITY/142941593131

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They are wired differently.  You cannot make a diesel alternator charge when fitted in a Roadster or petrol 450.  Different connectors also.

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I have no fear of no connector. If diesel one wants some extra signal, that's a different story.

So, petrol pinout is: B+ D+ W+. From what I saw, D+ is not used, W is likely "charging" Lamp?

Diesel pinout is: B1+ B2+ L DFM. B1 and B2 are likely connected internally? L is probably Lamp. DFM is new, called "DYNAMO FIELD MODULATION - Duty Cycle signal from the ECU". Not sure where this goes. Not a huge problem even if it's a PWM from ECU.

 

Info on pinout: https://jasoceania.co.nz/articles/alternator-terminals-explained

 

smart-fortwo-450-roadster-452-alternator451_Lima_CDI_A0131546902_03.jpg

 

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Why fit a larger amp alternator in your petrol Smart?  There is no need for it.  

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8 hours ago, tolsen said:

Why fit a larger amp alternator in your petrol Smart?  There is no need for it.  

I have found a need, the question is if it is possible to fit.

 

The answer to your question is in first sentence of my initial post.

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The 451 Cdi has a 90 amp alternator same frame size as 450 Cdi but different regulator. 

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Posted (edited) · Report post

Thanks for pointing out the 451 CDI alternator, looks compatible.

I wonder if the DFM pin is used and if B1/B2 are connected internally...

 

Anyone has an electric schematic? I always struggle finding service manuals for these cars...

Edited by TorqueJunkie

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Hi tolsen,

 

I saw you have shared schematics some time ago, but I had some life emergencies and could not follow up with this.

Would you mind sharing them again so I can download and get back to it once I am ready? Thanks.

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