OK so then I thought the electrician would be more impressed if I was totally "off-grid" - so then I had the tv also plugged in. But the load was too much - as my charging rate on the bicycle was not keeping up. I am still waiting for the DC/DC buck converter to increase my charge.
So then I got out the multimeter to double check how much amps at what voltage, etc. I was getting 3 amps at 12 volts - with no load hooked up (no battery). But when I tried increasing the amps up to 5 based on increasing the voltage - then it was much harder to pedal the bicycle!
So I thought - that's strange. My first guess was - is the multimeter somehow got a load to it when I switch it to test for amps instead of volts? This was a "stupid" question of course - but I had no other explanation for what was happening. So since I do not believe in "stupid" questions - I asked the electrician when she showed up. Luckily she had never seen a bicycle generator before and also not that type of battery generator. So she was not too upset by my stupid question. She said: No the multimeter does not have a load.
So I repeated my insistence it was much difficult to pedal on the multimeter then on the battery! She then said hmm - "Unless you're thinking about it too much?!" My response was: I better watch Pinocchio. haha.
So I'm watching Pinocchio and pondering this paradox. I knew it wasn't in my head. I thought to myself - hey I do qigong so I know I don't think too much. haha. I try to balance my "too much thinking" with extreme body exercise (including the bicycle generator). OK I know that for qigong it's true that I think too much - even qigong master Chunyi Lin told me this. So yes I know in terms of qigong then I need to "empty my mind and fill my belly. So yes the electrician was correct. But in terms of solving this DC motor paradox - I rechecked the V-belt - and the gears - and there was nothing I could see that would cause the increase in tension. Strange....
So then I stopped the movie - rechecked the multimeter and sure enough - I got the same increase in tension while trying to increase the amps. So then I unplugged everything and showed the electrician the battery charger - inside - since she had not noticed that the battery is also an AC inverter. So then we talked about the fan motor - and I wondered if maybe that would be better than the DC motor I was using. She said how it has a speed control. I said - so a potentiometer? Oh the circuit board. Yes that all would have to be removed. Then I looked at the power - only .6 amps! She said - yes they don't have much power.
OK so this inspired me to research the treadmill motor some more. Anyway - at first I realized - oh with a DC motor - then as you increase the RPMs then you increase the current but you ALSO increase the OHMs as resistance. So I pointed this out to the electrician and she said - yeah but I wouldn't think it would make that much difference - it's not like it's a substation. I didn't really answer - because I was not sure. I went back to research more.
A DC motor can be approximated as a circuit with a resistor, and voltage back-emf source. The resistor models the intrinsic resistance of the motor windings. The back-emf models the voltage generated by the moving electric current in the magnetic field (basically a DC electric motor can function as a generator)
Counter-electromotive force, also known as back electromotive force, is the electromotive force or "voltage" that opposes the change in current which induced it. CEMF is the EMF caused by magnetic induction.
the direction of the induces emf is opposite to the applied voltage. Thereby the emf is known as the counter emf or back EMF. The back emf is developed in series with the applied voltage, but opposite in direction, i.e., the back emf opposes the current which causes it.
Where Eb is the induced emf of the motor known as Back EMFSo then I found the real answer.
Once the rotor starts to rotate it will induce a back emf so the voltage 'seen' across the rotor will be reduced. The net current through the motor will be reduced.So a battery being charged means the battery is a load or the battery is a "draw" - it's drawing load.
Increasing the applied voltage will increase the speed (how much depends on the motor). With increasing speed comes increasing loss (friction, windage etc.) so there will be a corresponding increase in current.
Applying a load (torque) to the output shaft slows the rotation speed and reduces the back emf. This in turn will increase the motor current.
If something else (like your solar panel) can apply a voltage higher than the battery, then the battery becomes "the load", and current will flow through it in the other direction, reversing the redox reaction inside it, storing electric energy from the solar panel as chemical energy in the battery.This seems a bit paradoxical since the battery-generator has a diode on it to prevent charge for back flowing out (unlike just a straight battery). But when charging the battery it then "draws" a load. A battery has a resistance - a multimeter does not.
A multimeter set on current is a very low resistance, almost a short circuit and will draw as much current as your battery will supply till something melts. Always plug the Multimeter leads back to volts when you have finished testing to avoid blowing the fuse next time you use your multimeter.OK let's go back to the Motor's Constant.
The motor's "motor constant". This defines how the motor reacts to applied voltage over it's coils. It's a factor which relates voltage with current and torque. You can get little brushless DC motors for quadcopters these days with ridiculously high "KV" values, which is sort of like their "motor constant". KV values in the many thousands, where 1000 KV means 1 volt will product 1000 rpm on the motor output.
Motor velocity constant, back EMF constant. The Kv rating of a brushless motor is the ratio of the motor's unloaded rotational speed (measured in RPM) to the peak (not RMS) voltage on the wires connected to the coils (the back EMF).And so for a Treadmill motor?
Torque ~= current (Kt being the constant of proportionality).
But the motor is just a simple brush-type dc motor that will start turning at a slow speed with just 10 to 12 volts dc.
The easiest way is to install some potentiometer (or resistor) between battery and motor. That should decrease the voltage on motor and so RPM. Torque may also a bit decrease.
a treadmill, which at its lowest speed (I read ~6V across the motor free-running) has enough torque to move a large amount of weight. I measured the motor's resistance to be 0.9 Ohm, so at its lowest speed free-running the current draw is around I=V/R = 6.7A?
I'm just surprised a motor can provide so much torque with such little voltage.
a traction motor, probably series wound because that type of motor offers very high torque at low speed.So because the treadmill motor has such high torque that also means that increasing the RPM voltage with no load then greatly increases the "back emf."
So I need to measure the Ohm using the multimeter....but...
the motor acts as a generator and the result (it's called back-EMF) messes up the multimeter ohms circuit.
At no load condition,( i.e when there is no mechanical load connected to armature end) small torque is required to overcome the friction and windage losses. Since torque is directly proportional to armature current Ia, therefore the armature current Ia is small so the back emf is nearly equal to the applied voltage.
This means that at some rpm, the back emf is sufficiently large that the difference between supply voltage and back emf is so small it cannot generate a current larger than the friction. This is the maximum no-load rpm for DC motors
So the answer I got is voltage/speed current 130/39= 3.3 as the no-load rpm
https://circuitglobe.com/what-is-back-emf-in-dc-motor.html
So I is amps and R is ohms. So with "no load" you have 0/resistance....or total
If the load on the motor is suddenly reduced, the driving torque on the motor is more than the load torque. The driving torque increases the speed of the motor which also increases their back emf. The high value of back emf decreases the armature current. The small magnitude of armature current develops less driving torque, which is equal to the load torque. And the motor will rotate uniformly at the new speed.
No-load current = 800 mA, Load current = up to 7.5 A(Max)
speed torque curve (as you know the speed from voltage (rpm=k*v)) where k is the speed constant of the motor).
Also, one can think of DC motor as engine with built-in load governor, that is the significance of back emf, it changes with speed so that drawn current meets need of load torque, dynamic changes in speed settles down to stable point on torque speed curve, so that motor torque equals load torque and then motor operates at corresponding speed. The operating speed point at this torque (for given voltage and other parameters) is fixed and can be changed by suitably modifying speed torque characteristics.So u r not putting in extra torque, instead u r driving extra load, hence less speed
to determine the resistance of a brushed DC motor for force control. In that case the resistance varied with current: low current gave high resistance, high current gave low resistance. This was caused by the ionization of the air gap between brush and commutator.
The Reason that Torque and Speed are said to be inversely proportional is the ability to generate torque diminishes with increase speed.
The reason for this is because the BackEMF opposes the supply that is attempting to force current into the stator, that will generate EM-Torque.
If you increase the torque you increase the speed UNLESS you increase the load. The important thing to remember is that with electric motors there is a back-EMF (a motor is a generator too) which increases with speed and that limits the effective voltage and thereby the current and thereby the torque.
this is DC motor, it always "regulates" it's shaft torque to be equal to load torque!So that means the treadmill motor is not a "DC Shunt motor" that has a constant back emf no matter what the load is. Let's review my motor specs
5075 RPM at 15 amps and the voltage rating is 130 volts ; 2041 watt motor! At first I could not believe this. But I guess so. One horsepower (1HP) is also equal to 746 watts of electrical power. so more like 2 hp = 1492 watt
So 5075/130=39 as the speed constant or motor constant aka torque......................................................................................................................
Two horsepower is equivalent to about 1.5 KW , or about 15 amps at 120 VAC
The "2.5 HP" makes me wonder. Are they from treadmills? Can you tell us some nameplate data? Volts? Amps? RPM? Whether the motor has permanent magnets, is shunt or series wound? Does the motor case fully enclose the motor? Are there air vents? Is the motor's case "skeletonized" that is so that much of the motor's internal parts are visible?
Cooling at slow speed will be rotten. Keep motor speed up.
Treadmill motors are rated for "intermittent duty" which unfortunately can mean whatever the mnfr wants it to mean. The main issue is cooling, so if you are running the motor a lot at low speed, or continuously, use an external fan to blow air on it / through it (w/ filter).
You can generally tell the price of the treadmill motor by its max speed rating. If it is 6000rpm, it is probably a $25 motor.
A "real" 2 Horsepower DC motor weighs around 45 lbs.
"2 1/2 HP" Treadmill motor that is very popular at ******* is 2 1/2 HP Peak, 1 1/2 actual, and weighs 10 lbs.OK so "actual" power? We can reverse the watts back into volts and RPM. But the resistance VARIES with the watts.
the torque "constant" of the motor will depend upon the armature current, which will in turn depend upon the voltage drop of the rotor, which will in turn depend upon the torque [non]constant.
the motor is only a fixed resistance depending on its load. A motor with no load has lower resistance than a motor with a load,
- using the motor as a generator and spun the shaft to the point of RPM's equivalent to that of if i was giving it 12v, it will generate 12v of off that back emf? so therefor it reach its maximum- – Frank Jul 3 '15 at 6:43
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Yes. Back emf increases as the motor is tried to stop (increased load) so that the motor can sustain the same speed. When stalled, the EMF will increase and the drop will be supply/DC off state resistance. While running with typical load, the emf will be [supply] minus [current * DC off state resistance]
OK so now we move onto the "power capability" of the Chafon 31 amphour, 500 watt battery generator.
The power inverter provides a peak power capability of twice the continuous power rating
Likewise, a 1Ah coin cell has no problem providing a 1mA for 1000 hours but if you try to draw 100mA from it, it'll last a lot less than 10 hours.
high internal resistance (which is what makes them fairly safe if there's only one or two in use) so they can't provide a lot of continuous current:So power capability is based on the resistance in the Chafon which in turn increases the load and decreases the Back emf on the bicycle generator DC motor.
So the Chafon is 97 volts and 31 amps - so the Ohms is ~ 3.2
That means at maximum solar input the panel can deliver its rated power into a 18 volt / 5.55 amps = 3.24 ohms.Ah - now it's starting to make sense! So again that's the "LOAD" of the Chafon battery.... as it charges up, the resistance goes up.
That means at maximum solar input the panel can deliver its rated power into a 18 / 5.55 = 3.24 ohms. If I were to connect say a 2 ohm load the panel output would drop to 11.1 volts @ 5.55 amps or 61 watts.
https://forum.solar-electric.com/discussion/351767/battery-pulling-down-panel-voltage
Example of the solar panel volts being "pulled down" due to the low amps of the battery.
This means I can bicycle at HIGHER voltage - and the volts will still get pulled down.
When a battery is well depleted it will take a long time for the amps to get high enough that the volts starts to rise. When there is enough internal resistance to the Amps available the volts will start to rise and you will enter Absorb phase.
The better way to check the state of charge is after the battery been sitting for a few hour without charging or discharging the battery. This way the surface charge on the plate is dissipated and you will see a truer state of charge.So I just need to connect up my multimeter to the wire connection from the DC Motor to the generator. So that way I can monitor the voltage "pull down" by the generator - and just keep pedaling so it stays below 18 volts.
Kv — motor speed constant,in RPM/Volt, or rad/s/Volt
