Electrical – DC motor won’t spin without a push

You are in a way, going the shortest, easiest path to achieve what you what, i see nothing wrong with using that, since a DC motor's speed is controlled by voltage, you are technically reducing the voltage to feed the motor, the current limitation though, you could achieve something better if you would design a buck converter from scratch, but because im currently designing a switched boost converter, that basically does the opposite of what you want, i can tell you, to design one for an implemented system is kind of hard because there are lots of values that you need to know and would change how the system reacts if you change the load (i actually registered in this exchange to know if there's a way of doing a converter without being affected by the load, but that's my problem, not yours :p)

EDIT:Like @Anindo Ghosh Pointed out accurately, what i said before doesnt really apply since i misread the product info on the ebay link you sent, like he commented on your question you would need a filter, basically that controller will generate pulses, and a motor doesnt see this(im divinding a cycle in 4 for better explaining): (0)(0)(0)(48)<--for a 25% duty cycle, which is what is happening, but what the motor sees is actually (12)(12)(12)(12), so it will work half the speed, but when you introduce peak sensible components like LED's or capacitors that can malfunction or even blow up with higher peak voltages then what they are designed for, they see the: (0)(0)(0)(48), so for every cycle, half of the cycle they are exposed to 4 times what they are designed for, they will most likely blow up, to alter this you can:

Use a large capacitor to support the current you need and slowly discharge while the system is in it's OFF cycle, hence if it is well designed and chosen, you can have little ripple current, making it not oscillate a lot, but still, it's hard since the capacitor only filters voltage.

You can have a large inductor, so it charges in the ON cycle and discharges in the OFF cycle, making about the same thing as the capacitor but only with current, meaning you would still have those voltage peaks...

OR, ideally, you have a combination of both, with an inductor in series with the load, and a capacitor in parallel, this will ideally, make the load see those (12)(12)(12)(12) like the motor sees them, if this is well designed, you can even have little enough ripple for sensitive loads.

So, to answer the question: Can you use those? Yes Is it as easy as it seemed? No, you'll have to do a bunch of calculations and designing and go through all that sort of trouble until you can find what suits you and your needs...

You can opt on buying something like this, but for your power needs, you would need a lot, at least 5 to make those 15A that one of the others could get you, making it, in my opinion, not very cost effective, but if it is the only way...

I wonder if it isnt cheaper and would actually turn out safer in case one system fails, to have a separate 12V battery system for those needs...

Another product that might suit you

Regards and good luck :)

I haven't even bothered watching after "only DC motors can be used as a generator".

As far as I am aware, a motor can be of the following families:

1. Permanent magnet DC brushed. DC back emf.
2. Coiled stator DC brushed (as a separate winding, or internally wound as series or parallel). DC back emf IF the stator is powered. Single phase universal motors are a subset of series connection types for which, regardless of the polarity of the voltage, torque is always generated (needs moveable brushes or a different wiring to change direction though).
3. Permanent magnet AC synchronous (three phases). Three phase AC back emf.
4. Coiled rotor AC synchronous. I think those generally are not brushed but rather rectify the current induced by the stator. If brushed, no back emf unless the rotor is powered.
5. DC brushless. This one is basically a permanent magnet AC synchronous with hall sensors built in, to be able to electronically switch the phases. The back emf is however square or trapezoidal to maximise flux linkage.
6. Stepper motor (2, 3, 5 phases). Close to the PM AC synchronous in its construction, except that the motor is made to maximise the number of stable equilibrium positions of the rotor (many alternating magnetic poles at the rotor or variable reluctance). Back emf depends on how it's driven.
7. AC asynchronous (3 phases). The rotor is a closed loop (a coil, or a squirrel cage made of bars) which creates its field from currents induced by the stator. Can only be used as a generator beyond the synchronous rpm (+voltage at stator). AC back emf (TBC).
8. AC asynchronous (single phase). The motor cannot be self-started unless an out-of-phase auxiliary supply is created via a reacting capacitor, and fed to windings 90° from the main windings. Can only be used as a generator beyond the synchronous rpm (+voltage at stator). AC back emf (TBC).

There are many more (e.g. hybrids), but I think those represent 95% of the production. I'm sure I've missed a few important ones, please feel free to comment and I'll update the list.

The biggest clue to the type of a motor is the number of wires, but as you can see this is not enough. Some motors cannot generate power without an excitation, some not at all, and even if they do, the back emf is funny sometimes (trapezoidal for example) depending on its construction.

You could plan to try the various types of supplies on the motor, ramping up the voltage, and see if it does anything, but what's your "OK that's not it, better cut the power before I smoke it" point? If you don't know what type of motor it is, I assume you don't know anything about it. Including the voltage and current ratings, Max rpm. You could get that from eyeballing it, but there is no guarantee then.

For your specific problem though, if you are certain your motor is a DC bruhless but you don't know if the inverter+control circuit are integrated, look at the number of wires. Generally the motor does not have a circuit built in, and an ESC must be connected to it. You will have to identify which wires are the hall sensors.

ESC might or might not be used for current generation, it depends on how they are made. I don't think there can be any harm in hooking up a resistive load compatible with its current range at the input and test it.