[Cloter]

As we know, a car alternator can be converted to a semi BLDC ('semi' because you still have the slip rings, that are equivalente to brushes, aren't they?). It's also known that you do need to supply a voltage to the rotor. I used an old Chevy 30A alternator (made by Delco-Remy in Brasil) and the rotor measured 4,5 ohms, so driving it with 9 volts pulls about 2 Amps. You can do this math to obtain a reasonable magnetic field and keep heating under control. I designed, built and programmed an 'ESC' controller based on an ESP32S micro controller and 100V/50A MOSFETs for the power stage. The whole thing works beautifully. It's the basis for an electric bike that I am building.
And here is the question: the picture shows my attempt at the e-bike 'drive train'. All works well, but the three bolts get very hot. First I thought I was mistaken, then I ran several tests, and the bolts do warm-up real quickly and before any other parts of the alternator. I replaced the original (regular) steel bolts with stainless steel, so they would not interact with the magnetic fields, but there was no significant change. I'm thinking 'Eddy currents', 'Foucault Currents'? Any of you have seen this effect? Any suggestions? Thanks!

 

[remy_martian]

There are two types of stainless. One is magnetic, the other is not. I'm guessing you verified it's the latter?

The problem may not be magnetic. Measure to see if you have a voltage drop across the two case halves. If so, braided copper strap between the two, or pull your vehicle ground off the other half.

 

[Cloter]

There are two types of stainless. One is magnetic, the other is not. I'm guessing you verified it's the latter?

The problem may not be magnetic. Measure to see if you have a voltage drop across the two case halves. If so, braided copper strap between the two, or pull your vehicle ground off the other half.

I'll do the checks you suggested and post here. Thanks

 

[GE11]

For a few years now I have questioned the efficiency of alternators. Im using an alternator to generate 56V for a possible hybrid system and my static get very hot!!! My thought is, it is magnetic related to Eddie currents. This has been an issue for me too

 

[brian_]

There are two types of stainless. One is magnetic, the other is not. I'm guessing you verified it's the latter?

There are many alloys of "stainless" steel, of three major metallurgical types, and magnetic characteristics only approximately align with the types (ferritic and martensitic are usually magnetic, austenitic mostly not). And the degree of magnetic properties varies, not just all-or-nothing. Just take out a bolt and try a magnet on it...

 

[cricketo]

Time for titanium bolts!

I have a few alternators sitting around, need to find time to play with them too.

 

[piotrsko]

For a few years now I have questioned the efficiency of alternators. Im using an alternator to generate 56V for a possible hybrid system and my static get very hot!!! My thought is, it is magnetic related to Eddie currents. This has been an issue for me too

For the longest time Ripperton was having issues with his homebrew motors on his racing cart. Don't recall how he solved the issue, but it's searchable