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Old 09-04-12, 01:17 PM   #1
James123456
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Difficult question need Help!!!! please

So I just purchased this electric moped http://www.powersportsmax.com/produc...ducts_id/14516. i want to create a recharging system while riding utilizing a fan or "turbine" connected to a dc motor seeing as in how 25 mph will be generatiing quite a bit of wind. I need to know which motor would be sufficient to offset the power usage of the moped while riding? I know it's a high aimed goal but i think it would be possible? Any help would be much appreciated. Also, another Idea I had was running the dc generator by putting something like a wooden dowel on the tire causing it to spin or along the belt to the rear wheel, spiining the motor like the wheel would. Would an of these ideas work? Cn someone provide some knowledge on these ideas? Thank you.

Last edited by James123456; 09-04-12 at 01:23 PM. Reason: New idea added
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Old 09-04-12, 02:11 PM   #2
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It doesn't work that way -- the additional load you put on the existing motor would be more than any energy created.

What you're trying to create is basically a perpetual motion machine -- and it just doesn't work.

The only time what you're talking about makes sense is when you're intending to slow down already, and many electric bikes already have a feature that recovers some of that energy -- it's called regenerative braking. It's also found in hybrid cars (and really, it's the #1 reason for making them hybrid in the first place.)

In any event, if you're after regenerative braking, you don't want to use fans or turbines -- you want to use a generator coupled to a wheel. And since electric bikes already have one -- the main motor -- they just use that. (Motors and generators are basically the same thing.)
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Old 09-04-12, 02:24 PM   #3
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It doesn't work that way -- the additional load you put on the existing motor would be more than any energy created.

What you're trying to create is basically a perpetual motion machine -- and it just doesn't work.

The only time what you're talking about makes sense is when you're intending to slow down already, and many electric bikes already have a feature that recovers some of that energy -- it's called regenerative braking. It's also found in hybrid cars (and really, it's the #1 reason for making them hybrid in the first place.)

In any event, if you're after regenerative braking, you don't want to use fans or turbines -- you want to use a generator coupled to a wheel. And since electric bikes already have one -- the main motor -- they just use that. (Motors and generators are basically the same thing.)
So even if you used a large motor like http://coleco.freeservers.com/motors.htm#MOTOR750 , you wouldn't be able to offset the initial load? If you ran it off an already rotating source such as the belt or tire it still wouldn't help? There is no possible way to offset that initial load?
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Old 09-04-12, 02:35 PM   #4
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What I am essentially wondering is, if I supply the battery will more power that it takes to operate? Will it charge? If not, which seems to be the case, why?
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Old 09-04-12, 03:46 PM   #5
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What I am essentially wondering is, if I supply the battery will more power that it takes to operate? Will it charge?
Yes, if you're adding more current to the battery than you remove, it will charge.

But if this current is coming from a windmill that is being powered by the bike itself, which is powered by a motor powered by the battery ... your windmill will slow the bike, which will put more load on the battery than it will add to the battery. The laws of physics are not on your side here.

Now, if the windmill is charging the bike while it's parked due to it being a windy day, that's another matter -- but if the wind comes from the motor moving the bike, no, that's not going to work.

Look at it this way ... if this worked, why don't cars have air turbines on top? If we could make an electric car that charged itself while it was driving so it only needed a small battery to go hundreds of miles, we would, and everybody would be driving one because they'd never need gas or charging. But the laws of physics don't work that way.
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Old 09-04-12, 04:06 PM   #6
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Understandable. My previous part was meant in complete disregard top the windmill idea. If i were to just have the dc motor being spun off of thebelt or tire. Could i apply more power to the battery? Could multiple motors offset the initial load plus the additional load needed to spin the motors?
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Old 09-04-12, 04:23 PM   #7
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I get this all the time between the electric car and the electric bike. I
am surprised at some of the people that ask it, people who I would think would
really know better.
Repeat this until you understand.
There are losses in
ANY system, it may be friction, resistance in wiring, wind resistance or any
other number of things. You ALWAYS get less out than you put in.

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Old 09-04-12, 04:47 PM   #8
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I get this all the time between the electric car and the electric bike. I
am surprised at some of the people that ask it, people who I would think would
really know better.
Repeat this until you understand.
There are losses in
ANY system, it may be friction, resistance in wiring, wind resistance or any
other number of things. You ALWAYS get less out than you put in.

well how far could i extend my range? If i were to add motors sucj as the one s in my previous post?
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Old 09-04-12, 05:04 PM   #9
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well how far could i extend my range? If i were to add motors sucj as the one s in my previous post?
You would reduce your range.
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Old 09-04-12, 06:15 PM   #10
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You would reduce your range.
Absolutely. Dougmc has given you the correct answer in every respect. This is basic. You can't get any benefit from adding a lossy regeneration system. The losses you add are ALWAYS, ALWAYS, ALWAYS greater than the gains. Let's say you generate 10W with your turbine. You will require 10W divided by the efficiency of the turbine to obtain that power. Let's say the efficiency overall of your turbine (air screw + generator) is 50% (probably very optimistic). You will then require 10/.5=20W MORE power from your electric drive to overcome the additional drag for a net waste (loss) of 10W.
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Old 09-04-12, 06:38 PM   #11
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I am accepting the no turbine idea. But if a motor like the one i posted a link for was added along the drive belt and operated at the full 750 watts...still nothing? I would think that that amount of power would offset the drag or resistence and produce a usable amount of electricity. It would be direct belt to motor. No turbine at all. Can i get an equatios maybe to figure some of this out instead of asking generally the same question?
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Old 09-04-12, 06:43 PM   #12
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If you run your added motor as a generator it will require power from the first motor to generate electricity. If you run it as a motor you will be powering two motors.

Let me answer your question with a couple of questions to help you understand this.

How much power do you think it takes to run a generator?

Where does this power come from?
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Old 09-04-12, 07:05 PM   #13
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In other words, what everyone is trying to say, the ONLY way you will get any additional power is to run a second motor as a regenerative powering motor to slow you down.
If the scooter already has regenerative braking, then that's your best bet.
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Old 09-04-12, 08:06 PM   #14
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If the scooter already has regenerative braking, then that's your best bet.
Or think outside the box -- add solar panels!

They probably won't produce enough power while moving to power the thing by itself (unless they're huge) but they'll charge things a little -- even when parked.
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Old 09-04-12, 08:14 PM   #15
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Im not grasping the whole regenerative breaking adding another motpr concept.. as for the questions. I dont know. That is what i am tryong to figure out. I need to know how much power will be used to operate the 750 or larger watt motor i posted the link to at full power. If someone can give m e an answer, preferably numerical, to that i can see how it will draw the current in comparison the initial500 watt load. Sorry to,keep annoying those of you who see this as simple, i just dont without numerical proof...
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Old 09-05-12, 05:20 AM   #16
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How much power will a 750 watt motor take at full power? 750 watts would seem to be the answer, though in reality such a motor can probably handle a lot more than that for a short period. (The power ratings are usually largely about cooling.) Though I really don't understand what you're asking.

But as for recharging your battery to extend your range ... you want numbers?

Suppose your electric bike will use 250 watts to propel you at 20 mph on level ground.

You then add a generator that is powered by the wheels (or a turbine powered by the air, whatever) and this generates 40 watts of power that you add back to the battery.

However, you now find that your bike needs 350 watts to go at 20 mph on level ground. So you've spent 100 extra watts to generate 40 watts, reducing your range.

As for what regenerative braking (not breaking) is, consider that it's off most of the time. But if you want to slow down, rather than hit your usual brakes, you hit the regenerative brake, which slows the bike down -- by using a generator to charge the battery. So you recover some of the energy as you slow down, and that does extend your range. And since motors and generators are the same thing, in general you don't even have a separate generator at all -- it's done with the same motor you use to power the bike in the first place.
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Old 09-05-12, 08:52 AM   #17
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That was the original answer I was seeking. Sorry about the typo on breaking/braking, I was using my phone.
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Old 09-05-12, 09:06 AM   #18
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The reason I asked about the motor is becaused it wouldn't be using the scooters power source (directly), it would be creating power using the drive belt to spin the motor thus using it as a generator. The amount of resistance needed to spin the motor would be the only resistance (beside the slight bit of weight added). That's why this is not clicking. My question about how much power was more aimed toward how fast would that motor need to spin in order to create it's peak power? ( Spinning from the drive belt)

In referece to your recent example: If the electric bike will use the initial 250 watts to propel me at 20 mph I would need less than 250ohms of resistance ( to allow the motor to put out above 500 watts) to add more charge to the battery correct? And that is not possible...correct?
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Old 09-05-12, 09:47 AM   #19
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And if my scooter doesnt have regenerative braking, could I add a dc motor like my idea that would be engaged while wanting to slow down?
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Old 09-05-12, 10:14 AM   #20
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My question about how much power was more aimed toward how fast would that motor need to spin in order to create it's peak power? ( Spinning from the drive belt)
That's a complicated question, and there's not enough information available to answer it. It depends on the specific of the motor and the load on it (and even if you tell me all about the motor and such, I couldn't really answer it -- so I wouldn't suggest trying to figure everything out.)

Quote:
In referece to your recent example: If the electric bike will use the initial 250 watts to propel me at 20 mph I would need less than 250ohms of resistance ( to allow the motor to put out above 500 watts) to add more charge to the battery correct? And that is not possible...correct?
The 250 watt figure I gave was just an estimate, but it's not an "initial" figure -- the motor will need to produce something around that much power just to keep you going at 20 mph. You'll need even more initially to accelerate to that speed -- but it will only take a few seconds, so it's not really a big concern with regards to your range.

Quote:
And if my scooter doesnt have regenerative braking, could I add a dc motor like my idea that would be engaged while wanting to slow down
Yes, you could. But that motor would add considerable weight and complexity. I'd suggest instead just getting a speed controller that does regenerative braking with your existing motor -- no need for another motor or gears or whatever to engage it as desired.
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Old 09-05-12, 01:20 PM   #21
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a motor and a dynamo are both a few coils of wire rotating around a permanent magnet.

1 goes when the power is applied, the regeneration is having it make a little juice when
its off , and in coast down.. won't be 1:1 of course..
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Old 09-11-12, 01:54 PM   #22
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New question. How could I increase my top speed? And if I were to wire a battery in parrallel to extend my range what battery would work well?
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Old 09-11-12, 05:32 PM   #23
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New question. How could I increase my top speed?
Increase the voltage to the motor, probably with a new battery pack. Do be aware that this could possibly burn things out, and so I suggest not doing it unless you know what you're doing.

Quote:
And if I were to wire a battery in parrallel to extend my range what battery would work well?
If the new battery is of the same voltage as the first, yes. Ideally both batteries would be of the same type and both would be at the same state of charge when connected. Again, if you don't know what you're doing, you can cause some really serious problems (like make your battery pack explode!), and so I'd suggest not doing this.
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Old 09-12-12, 04:02 PM   #24
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Ok just brainstorming. Would jt have to be in series to keep the same voltage?
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Old 09-12-12, 04:19 PM   #25
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If you have to ask your last question, you should probably start googling battery technology first..
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