OK now I'll analyze the power specs on this thing. RPM - how many amps will I get via how fast I pedal? I don't know the ratio of the wheel to the motor. I'll see - one estimate I saw was 19 to 1 but I thing that person had some other kind of gear or pulley. Not sure.
So then figure out the amps per RPM on the motor - and so how fast I need to pedal.
What I figured out so far - based on the above hypothetical is this:
quoting one youtube channel:
but I think my normal exercise load was about 50 Watts (4 amps).So that is exactly what the 500 watt lithium battery charger/generator requires via car charging.
The best DC (Permanent Magnet)motor for use as a generator is the one that has the highest rated voltage at the lowest RPM figure (this applies to Ametek and treadmill motors).So that's what I have - a treadmill motor.
You should be able to calculate the number of RPM required to generate one volt. This figure is useful for comparing DC generators. Simply divide the stated RPM on the rating plate by the voltage on the rating plate. DC motors are linear devices, voltage and speed form a straight line graph. Lets assume that one volt is produced for every 20RPM. As the controller requires about 17v to fully charge a 12v battery (see Introduction above) then the DC motor will have to turn at (17 x 20) = 340RPM. This is frequently called the "cut in speed" which is the lowest speed at which the generator will charge the battery. At speeds above 340RPM the quantity of current generated and delivered to the battery will increase. DC generators require a "blocking diode" to prevent the controller/battery from powering the generator as a motor.OK so I will be charging a 12 volt lithium - so that is good news...
You stand a much better chance of charging a 12v battery than a 24v one as the "cut in speed" is half for 12v compared with 24v systems.
Now... I'll enlarge the photo of the motor to look at the specs....
So it says 5075 RPM at 15 amps and the voltage rating is 130 volts.
So divide the rpm by the voltage....
And the answer is:
39
Wow!!
39 is a lot better than the example above of 340. That's GREAT news!!
So 39 per minute is only one rotation or 2 rotations per second to create a charge - and that's the MOTOR - not the bicycle wheel.
Holy smokes. This thing might charge pretty fast. Maybe too fast? haha.
OH wait - that's for just ONE volt. oops.
Dang - so it is WORSE than the above example.
OK so 39 x 17=
663 rpm
So it's only half as good as the above motor example....
Now what's the bicycle wheel conversion ratio?
129.3 RPMs for 10-MPH
here
Really?
So I need to go - well I guess I'll be trickle charging the lithium AFTER all. That's o.k. -
So that's for a 23 inch wheel. Let me go check what size wheel it is....
Oh sweet - it's a 26 inch wheel!
OK so now...
26 x 3.14159 divided by a foot as inches.
6.8
(if X is 26-inches, Y = 6.81 feet)Yep! That's what I got.
OK....
Then we just calculate the number of revolutions needed to travel 880 feet:
(880 feet/min) / (Y feet/rev) = Z RPM (880 / 6.81 = 129.3 RPMs for 10-MPH)...which is equal to 12.9 for 1-MPH
DANG - that was for a 26 inch wheel!!
OK ... so trickle charge it is!
So let's say I do 13 volts - how many RPM or MPH and how much amps?
13 x 39=
507 rpm
Hold on now - I'm forgetting that I can change gears on my bicycle!!
So here is a calculation for a 27 inch tire with a 13 tooth rear cog...
For example say I pedal at 90 rev/min with a 42 front chainring and 13 tooth rear cog using that same 700C x 50mm tire;That's pedaling at 1.5 per second....
42/13 = 3.23
3.23 x 90 rev/min x 7.44 ft/rev x 1 mi/5280 ft x 60 min/hr = 24.6 MPH
https://www.4qd.co.uk/road-speed-calculator/
OK so based on the above ratio of 3 for a gear conversion...
I get a necessary speed for 17 volts as 663 rpm... equals:
17 miles per hour.
hey that's not bad!!
This might actually work!
I am not quite sure the calculation is correct but it seems to be....
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).Now I'm trying to convert RPMs to amps...
How much current a motor can tolerate when a voltage is applied depends on how much thick the coils wires are (thicker = higher current = higher torque), due to coils internal resistance (the higher the resistance, the higher the heat produced, till wires melt).So they use a 1000 watt motor as an example of not much power... So I get 130 volts x 15.7 amps = 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
But it makes sense - since the Treadmill motor has low torque while the above - at 10 volts gets an amazing 100 amps. .... so it would be 20 volts at 100 amps for a 2000 watt (not as much torque - at (100 volts is 10 amps), so 130 volts is 15 amps. I'm still confused....
The motor CANNOT tolerate its own stall current, which will soon melt wires.Hmmm....
That doesn't sound good.
OK I just need to divide the RPM I will be GOING or cycling divided by the volts - to get the amps. Duh!!
663/17 = 39 amps? Holy smokes!!
I only want 4 amps!!
Let's back this down to 14 volts.
I keep getting 39 amps
507/13 = 39 amps
hmm....
I only want 4 amps...
I need to figure out what's going wrong...
model C3365B2917
So I google it - and it's being used as a wind generator! that's a good sign...
So a vid on the voltage - but what's the AMPS?
http://pedalpowergenerator.com/dynamo/generator-output-voltage-vs-rpm-mph-kmh-pm-motor-treadmill-mcmillan-s3348b2716/
OH so that's MAXIMUM amps. Thank God.... but wait? 20 amps?
Peak Power Output (During 60 second sprint Adult 26″ wheel bike) | 300 | Watts |
Continuous Output Power Rating | 200 | Watts |
Peak Current Output (During 60 second sprint) | 25 | Amps |
Continuous Maximum Current Rating | 20 | Amps |
Absolute Peak DC Voltage Output using a bicycle with typical 26″ wheels. | 0 to 40 | V DC |
Typical DC Voltage Output Range Adult Rider 26″ Wheels | 10 to 17 | V DC |
Permanant Magnet Generator Style | 2-Wire DC Output (This has 4 brushes touching the armature) |
So I'm getting a 4 to 5 amp charge rate for the lithium batteries....
So those ratings are continuous maximum - and my DC motor is 15 amps continuous maximum...
In theory in the US you get 20 Amps from a wall socket.OK so I might need to convert the DC to AC - as was recommended for car chargers for this lithium battery at 4 amp charge....
hmm..
I'll be losing amps I guess in the conversion. Oh well.
https://electronics.stackexchange.com/questions/299665/is-lithium-battery-charging-speed-proportional-to-the-amps-provided-from-the-pow
So this might be the AC volts - 120 - at 15 amps....
A simple way to charge manually is pump in 10% of capacity till nominal voltage is reached. For a 200 Amp-Hour, 12 volt battery, pump in 20 amp till battery terminals read 12 volt.hmmm....
But that's for a 12 volt battery - 3 cell 'lead acid". A lithium might be way different....
At some point, the limits of the battery will apply, generally, it's around 10% of capacity, that you don't want to exceed, when charging. Otherwise, you overheat the battery and damage it. Even if it's only 0.5% each damage cycle, in a year (360 cycles) , that can add up. And that varys, when the battery is discharged , it's a little safer to charge it faster, but as it approaches 80%, you have to throttle back.
So based on my calculations - this bicycle generator is TOO powerful for a lithium battery. So I need a cheap golf cart 12 volt battery. Then use that to charge the lithium battery. Then use that AC source to charge the drill lithium battery. Or whatever other AC power I want....
The solar panels will only SLOW trickle charge the lithium battery - in like 12 hours. The AC current will charge it in 5 hours I think.
So it's a slow charge battery.
When charging an automotive battery, 10-amps or less is considered a slow charge. Fast charging is NOT recommended, 20-amps or above is generally considered a fast charge.Finally! Someone asks the SAME question as me! Took me forever to find this answer:
You stated 1080W of power using a 36V/30A controller, using W=V x A. If I do NOT use the controller what would my peak power be with 36V? Would it be 36V x 18A (motor rating), giving me 648?
This is because if electrical resistance in the motor is what limits your # of amps, then when you divide the voltage by 2, you have to divide the power you get by 2 squared (3, 3 squared, etc).
Yeah that means - if I divide the voltage by 10 - from 130 volts to 13 volts then the power is divided by 10 squared - so divide by 100 or multiply by .01 = 15.8 amps = .158 amps. or 15.8 MILLIamps.
So then if I get up to 17 volts at 17 mph then... so it should be just around 3 milliamps!!
Really? I went from TOO high to now TOO low? holy smokes.
OK so we are dealing with OHMs as Volts (130) divided by Amps (15.8) = 8.2 Ohms as resistance. Then take the volts (17) divided by Ohms (8) to get the amps again as 2 amps.
There that is more like it.
V is the voltage drop of the resistor, measured in Volts (V). In some cases Ohm's law uses the letter E to represent voltage. E denotes electromotive force.So above they used E as electromotive force. That's what confused me....
I is the electrical current flowing through the resistor, measured in Amperes (A)
R is the resistance of the resistor, measured in Ohms (Ω)
No comments:
Post a Comment