VFD on a salvaged HVAC motor?

You needn't, it isn't common knowledge.

I didn't know that until I worked with custom designed implementations of such motors and their controls at Segway; they drive the wheels. The explanation of how they work was similar to what I had learned about computer synthesized digital radio for NASA.

I was going to try to defend my wrongness with, "There are controllers for sale labeled as 3 phase DC controllers," but wrong is still wrong.

I was going to try to defend my wrongness with, "There are controllers for sale labeled as 3 phase DC controllers," but wrong is still wrong.

I've bought one of those and used it to convert a car alternator into a motor, not quite brushless as the armature needs DC power to generate a magnetic field. It works quite well.

I've bought one of those and used it to convert a car alternator into a motor, not quite brushless as the armature needs DC power to generate a magnetic field. It works quite well.

------------------------- How much current did the armature (rotor) take?

I ask because I did a quote for a production line machine that would measure full alternator outputs to sort them into current rating bins. All were made the same, the difference was in the size and uniformity of the magnetic gaps between the fairly rough edged iron core stampings.

I also built and set up a machine that tested voltage clamping when the battery connection opened during full charge, from corroded connections on a rough road, called a Load Dump. The energy stored in the armature dissipates as a voltage spike when the battery can't accept the full current. [The car company] couldn't test for the thermal load of rapidly repeating load dumps with their lab equipment, and their estimate of an adequately sized Zener was too low, it failed as I watched. That may have been a reason for side terminal batteries.

For some reason, perhaps union work rules, only Ford built their own production test equipment, the others had to order it from outside. The company I worked for was small and lean enough to accept 'oh-by-the-way' modifications and still deliver fast enough to win many of the bids. Mainly there was no delay from management overhead; meetings and waiting for multiple signatures on a purchase order. Once project manager I could build or buy what I wanted immediately. That's where I learned both mechanical and electrical fabrication, the full design and construction of a product.

Ahh, very good! Did you need to do anything special with the VFD apart from supplying field current separately?

How did the voltage specs for the VFD compare to those of the alternator? Did you vary the field excitation to aid speed range adjustment? Any further details would be of interest....

Thanks for writing!

bob prohaska

Ahh, very good! Did you need to do anything special with the VFD apart from supplying field current separately?

How did the voltage specs for the VFD compare to those of the alternator? Did you vary the field excitation to aid speed range adjustment? Any further details would be of interest....

Thanks for writing!

bob prohaska

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Google's AI states "A car alternator's stator and rotor winding insulation is typically designed to withstand a dielectric breakdown voltage between

Nevertheless I'd confirm especially a used alternator's safety at AC line voltage with a Megger before powering it.

The least expensive one I know of, and own, is the Amico ZC25-4. The hand cranked high voltage generator is a safety feature, it keeps your hands off the test subject and if shocked you stop cranking. The shaft needs light oil when difficult to turn. It's revealed bad insulation that a low voltage DVM test didn't in used equipment I've bought.

I just ran it up and the armature was taking 4A @ 12V. I had heard of the conversion having run across mention of it on the net and used a cheap brushless controller bought online and did the necessary to the alternator to connect it up and it works but I haven't a use for it, I just tried it as a bit of fun.

I just ran it up and the armature was taking 4A @ 12V. I had heard of the conversion having run across mention of it on the net and used a cheap brushless controller bought online and did the necessary to the alternator to connect it up and it works but I haven't a use for it, I just tried it as a bit of fun.

-------------------------------- Some have used spare alternators and small engines to make high current battery chargers. Theoretically 1 HP gives 746 Watts.

My high current DC charger is a 50A welding transformer controlled with a Variac. Being able to adjust the output voltage from zero to 50VDC is useful, low voltage for testing circuit breakers, 14V for car batteries and higher for UPS and golf cart batteries and this very nice power supply voltage and current regulator:

By itself the welder supply can charge a 24V battery pair at 30A, but since the transformer was for stick welding the voltage rises too far when the batteries near full charge and take less current. The DPS5020 is the better answer, checking voltage and reducing output the cheap one.

A mate mentioned they used a commercially made small portable welding set-up like that when he was doing his apprenticeship at an agricultural equipment makers. Apparently it was hard on the alternator as it was being used but worked well enough for the type of field repairs they had to do from time to time.