I'm not sure about the draft. If it was saved in a different thread by accident or maybe in a PM it might not show up in this thread for you to Load Draft and then edit and post. I don't use the Drafts feature because if it isnt' on my own computer (in notepad) I don't trust it to still be there later (and nto really even then...so I also use Clipboard Magic and save multiple clipboards depending on what I'm doing, and by date, etc....harder to lose work that way. )
fourbanger said:
I'm still really unclear as to why a generator of a given efficiency wouldn't make an equally efficient motor all else being equal (rotational speed desired for a given application, for example), but I see now that asking someone to explain that to me in terms I can understand is a pretty big request
If I understood it well enough to explain it, I'd try.
I just have seen people post various systems built out of the other kind of spinny wired thing
that doesnt' work as well as it did as the original kind of spinny wired thing. Sometimes they do, sometimes they don't. (sometimes they have no way of knowing, having never tested it the original way first).
The simplest answer I found in a quick google search is this, but I couldn't tell you how accurate it is, and there are other answers on the same page:
https://electronics.stackexchange.com/questions/402283/do-electric-motors-have-the-same-efficiency-when-operating-as-generators
The efficiency of a DC machine will be similar whether working as a motor or as a generator.
Why not identical?
Another way of expressing efficiency is the power loss of the machine. The main power losses are ...
a) \$I^2 R\$ losses in the copper windings
b) Wind resistance between rotor and stator, and friction in the bearings
c) There will be a bunch of other losses, eddy currents, noise, vibration
When running as a motor, the (a) losses will increase the input terminal voltage, and (b) will reduce the output torque. When running as a generator, (b) increases the torque needed, and (a) reduces the output voltage.
The machine is never running under exactly the same conditions, the mechanical power and electrical power are never equal (the input always exceeds the output). So if you want to define efficiency at a particular power point, or speed, or torque, they will always be slightly different for motoring or generating. But similar.
As for the altermotors.. I caught on to these about a year ago and thought they were brilliant. I brought up the concept here at some point only to have it met with a resounding "meh". The general consensus was that if it worked so well then everyone would be doing it, and that there would be some major efficiency losses involved. Looking back, I'm a little dissappointed in myself that I would have given up so easily. I will definitely be looking into this again.
If you were to start a thread for the specific project it is for, we might be able to help you find a motor and/or moutning systme that will do what you want with a known-working motor system and not having to deal with repurposing something not designed to do what you want.
Altermotors are an interesting repurposing (which I'm always a fan of), but arent' likely to work as well as a purpose-designed motor for the same thing. Remember that mostly alternators are designed to be cheap and to spin really fast, and to generate sufficient power within the typical running RPM range they'll be driven by the engine at.
If you really want to repurpose something to do your project with, I would recommend finding something that is designed to operate within the same RPM range, under the same kinds of mechanical loads, and the same kinds of conditions, and the same kinds of power levels, voltages, and currents. If you don't, you won't be operating it within it's designed range, and it won't make motive power at the same efficiency level that it did in it's life as whatever it was designed to be.
It's rare that a repurposing can make something work better than it did in it's designed usage. Can happen...but not usually.
I've done a lot of repurposing of many things over my life
and various kinds of motors (from powerchairs, radiator fans, weedeaters, etc to drive bikes) since I started doing ebike stuff (including a cieling fan AC induction motor rewound by Karma for me as a BLDC motor...which worked but less well by far than I had hoped--I still have the core (but not the magnet ring I built) and maybe the casing if you know anyone in my area that would like to experiment with it and find out what I might have done wrong, if anything). It has taught me that sometimes things just work better for what they are made for than for things I want to use them for.
