Two phases installed on the stator. (Credit: FarmCraft101, YouTube)
As part of his quest to find the best affordable generator for his DIY hydroelectric power system, [FarmCraft101] is trying out a range of off-the-shelf and DIY solutions, with in his most recent video trying his hands at the very relaxing activity of rewiring the stator of an alternator.
Normally car alternators output 12VDC after internal rectification, but due to the hundreds of meters from the turbine to the shed, he’d like a higher voltage to curb transmission losses. The easiest way to get a higher voltage out of a car alternator is to change up the wiring on the stator, which is definitely one of those highly educational tasks.
Disassembling an alternator is easy enough, but removing the copper windings from the stator is quite an ordeal, as they were not designed to ever move even a fraction of a millimeter after assembly.
With that arduous task finished, the rewinding was done using 22 AWG copper enamel wire, compared to the original 16 AWG wire, and increasing the loops per coil from 8 to 30. This rewinding isn’t too complicated if you know what you’re doing, with each coil on each of the three windings placed in an alternating fashion, matching the alternating South/North poles on the rotor.
Each phase’s winding is offset by two slots, leaving space for the other two phases, which then correspondingly are 90° out of phase when running, creating the three-phase AC output. This is further detailed in the video.
To make sure the windings do not short out on the stator, each slot has a bit of Nomex insulating paper placed into it, and a PETG 3D printed slot holder makes sure that none of the windings sneak out of their slot after installation.
The phases were connected in a Wye configuration, which gives it the maximum possible voltage rather than optimizing it for current as in a Delta configuration.
With the rewinding done, the alternator was reassembled, and the three-phase output of the new stator tested. After some trial and error it was able to do 200 VDC after passing it through an external rectifier, for a total of 700 Watt.
While not an unmitigated success, it seems quite possible to use this alternator as a higher-voltage generator with the hydro setup, especially after the upcoming replacement of the rotor’s electromagnet with neodymium magnets to further simplify it. As a bonus, if he ever needs to rebuild a broken alternator from scratch, rewinding a stator is now child’s play.
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