As mentioned - a capacitor on one or more of the motor leads helps energize the motor windings. An induction motor should retain some residual magnetism in the stator and armature. When the armature is turned it produces small electrical pulses in the windings. The capacitors can store this energy and supply it back to the coils improving the magnetic field. It works until the load becomes too large and then the self excitation energy is lost and the output stops until the load is removed. This makes the generator self protecting against overload/over heating. As mentioned - the motor needs to be turned slightly above it’s normal synchronous motor rpm to function well as a generator.
Some semi truck auxiliary power units use a belt driven single phase induction generator with an excitation capacitor. Thermoking had units built that way. I think they were rated for 2500-3000 watt.
I feel bad that I’m scrapping so many motors that some folks could use for induction generators. The pile is over 2 tons and growing.
The part I wasn’t seeing is where the caps were connected to the AC lines (and they might be i am not following the wiring well with the shadows). And I really thought caps weren’t needed after it started producing.
I am happily corrected by forum members.
I just read the delta configuration for the caps wasn’t ideal for standalone generation and was used for connecting to say the grid which came from a textbook. Which makes it much harder to chase down the reference, and it isn’t like textbooks and research papers can’t have errors in them as well.
That’s very interesting Ron , i have a Thermo king unit at the yard with a small Kubota 3 cylinder diesel engine running pulleys and belts to pumps and motors i wonder if that’s how my one works must try firing it up one day.
Dave
The Thermoking units that were at the shop I worked at had a serpentine belt that transmitted power to the generator. The capacitor was nothing special. I had one that went bad. For some reason I think the replacement was around $60. The same serpentine belt also drove the A/C compressor for the sleeper cooling…
Carrier Transcold units used a 12v DC alternator to maintain the truck batteries and then had an inverter in the bunk tool boxes. If you wanted a lesson on inverter 12v supply cable sizing there was a good example with those. The cables were quite large - possibly larger than the truck engine starter cables. I think the inverters were 3000 - 3500 some watts continuous as the inverter also powered the sleeper A/C unit which was an electric air conditioner.
I would look up a “noodle pump” if it hasn’t been mentioned. I’ve done this exact setup. I had mine setup on solar, variable voltage. If it’s sunny it pumps strong if it’s partly cloudy- still pumps. I worked for a power company with all sorts of different penstocks and turbines. My favorite turbine is the Francis. I suggest you look into how Helms pump storage is ran piggy-backed from Diablo Nuclear Power Plant. Wish there was a way to utilize the “Tesla Turbine” with water cost effectively.
I tried but get only children plastic toys
Helms pumped power station is very similar to our Dlouhé Stráně, but ours is man made, not natural reservoirs. As a system illustration very god example, but hardly applicable for anyone on DOW. While hundred MW scale works quite fine, kW scale is prone to huge loses due to efficiency of all devices participating on the solution. At the end, one may easily get less than half of primary energy generated. All means to solve the problem add to complexity, cost and possible fail. Unless one have natural conditions already in place at its property, there is no justification for such a project.
This comment was the most relevant:
" ‘Motors as Generators in Micro-Hydro Power’ by Nigel Smith is probably available thru your local library, and gives a comprehensive guide to setting up an induction generator, selection of capacitors for induction generators, with a good description of the process to get the motor characteristics to calculate the capacitance, and a number of sample calculations to guide you in the (not overly difficult) process. The capacitor is used to cancel out the reactive (inductive) current that the motor draws, apparently. This reactive current is relatively constant over the range of power outputs from the motor. A fair approximation of the required value can be found by (a) measuring the current drawn by the motor at no load, preferably with the cooling ducts blocked, to reduce the actual work being done by the motor. That current is mainly magnetising (inductive) current, with only a small ‘true power’ current driving the reduced windage, bearing friction, and low iron and copper resistive losses. (Some of the measured current is still driving resistive losses in the motor, but at no load, and with the cooling duct blocked, these losses are minimised, and most of the current will be reactive.) Then, (b) determine the reactance of the motor to draw that current. XL = V / I. That gives the approximate reactance the capacitor needs to have to compensate for the motor reactance. (c) The capacitance can now be found from C(uF) = 10^6 / (2 x pi x f x Xc). Example: a 1kW single phase motor draws 2.3A from a 230V supply at no-load. The motor reactance is approximately (230 / 2.3) ohms = 100 ohms. The capacitor that will also have approximately 100 ohms reactance at 50 Hz is… (10^6 / (2 x pi x 50 x 100) = 31.8uF. That’s the starting point for setting up the capacitor; it /will/ require a slightly larger capacitance to hit the ‘sweet spot’ for best operation. For 3 phase machines, refer to Nigel Smith’s book. The principle is the same, but the capacitors may be connected in either star or delta, and the capacitances and voltage ratings are different for each of those cases. The capacitor is not a motor-starting type - these are rated for intermittent operation only, and often less than the motor voltage. (That’s another story, though.) A polyester or other ‘motor-run’ capacitor is required, and should be rated at a higher voltage that the output voltage of the machine in operation. (Switching off a large load can cause a 50% surge in output volts in some machines!)"