Alternator as CC source

[Plamen]

That generator stopped working years ago. Was made with aluminum coils and low quality. But since the engine was still running, i've removed the damaged 220v. alternator and connected an Truck alternator 24v./80a. Idea was to have it for emergency if left on the road with no battery. Anyway i've never used it. Once connected it with my previous lead batteries and even with about 10 meters of 16mm2 cable when connected it literally stops that engine.  I removed the voltage regulator with brushes. One is connected to (-). Managed to connect a cable to the other and to a laboratory power supply. Started the engine and began to rise the voltage from 0. Till 50 amps it was ok and about 53 the RPM started to fall quickly. Guess that engine label 13Hp is not even 3. I left it at 40 amps for some time and all was ok. Did not measure the alternator temp.

-   What is the safe temperature for a coil of adding some over temp. protection?

-   Is it possible to trick say a dc-dc converter to act as a current regulator using a shunt connected to it?

[Plamen]

[Dacian Todea]

Alternators are constant voltage sources only so they just assume the small starter Lead Acid battery will quickly get to 14.4V or so and thus not exceed the current rating of the alternator even if the battery is fully discharged. That is not the case with a very large Lead Acid or with a LiFePO4 battery that will take as much current as the alternator can provide even well above the spec.

Alternators are also very inefficient best case around 50% so say a 50A at 26V  = 1300W and so if is 50% efficient then 2600W is needed at the input of the alternator and yes that is less than 4HP at that specific RPM. Maybe it was designed for a higher RPM generator as engines have the peak HP output at a relatively high specific RPM and is also possible the rating as it is from other things is doubled to look better on the label :)   

[Plamen]

I forgot to add the loads i had at that moment, about 13a so a little better. Anyway it will be used only for 5-6 days in year or none with some luck.