The problem

The Fiat Ducato 280 factory alternator is quite a shit, just 20 miserable amperes that my 300Ah LiFePo4 battery blows like your mum at saturday night.

So I decided to replace it with a bigger one, aware that it would be a pain in the ass.

Hey, but how did you choose the correct alternator?

Luckily, the Ducato has a lot of space around its (ridiculous) original alternator. I took down the original alternator and studied how it was attached to the motor, and I searched for an alternator with connections as similar as possible. I found the AS-PL A0437, a 200 ampere alternator made for agricultural machinery.

But the AS-PL A0437 is designed to be driven by multi-line belts on small pulleys, while mine uses a trapezoidal belt on a pretty large pulley, and this limit a lot the rotation speed of the pulley, so I just hoped it would run at least a quarter of its capacity.

Adaptation

The alternators had the same mounting scheme, but different hole spacing and a slightly different distance between the mounting point and the pulley. The hole spacing problem was resolved by welding an extension to the original belt tension adjustment arm. The mounting point-pulley distance problem was resolved with a custom spacer made with a lathe

The main problem

Was the belt. Driving a 200amp alternator is not an easy job. I broke at least 2 belts before understanding that it’s better to pull the belt VERY TIGHT rather than leave it loose for fear that it will break (because it will). If you start hearing the belt squealing from the engine compartment, that’s the sound of a belt that will last another 5 seconds

Final result

At the first start of the engine I got 100 amps of charge, beyond my expectations 🥳 But some time after the engine is started, the current drops to around 50-60 amps, and 4 years later, the drop is down to 40-50 amps. Anyway better than 20 miserable amps.

Suggestions for this project

• Don’t do it. Nah, I’m joking, but keep in mind that you need solid mechanical experience, tools, and machinery that not everybody has. If you don’t have any of these, you can still generate energy in many other ways.
• Search for a replacement with a technical diagram and measurements. You already need luck for this project, don’t force it.
• Some alternators have an rpm/ampere graph, very useful to calculate the gear ratio of the pulley.
• Don’t exaggerate, more amps = more power subtracted from the engine (and pulled by a belt designed for a specific force).