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Old 07-02-2014, 12:42 PM   #1
BorisM
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Question Friction Generator Dynamo on a golf cart

Did anyone try to use friction generator dynamos on a golf cart wheels to charge the battery pack while driving the golf cart? I know it sounds crazy, but theoretically it should work.



Supposedly output is about 12V 6W. Four of these should be able to produce some power.
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Old 07-02-2014, 01:05 PM   #2
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Default Re: Friction Generator Dynamo on a golf cart

Any dynamo will have friction and electrical loss so it would be a negative gain.
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Old 07-02-2014, 03:07 PM   #3
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Default Re: Friction Generator Dynamo on a golf cart

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Originally Posted by DOOmsman View Post
Any dynamo will have friction and electrical loss so it would be a negative gain.
Why would you say so?
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Old 07-02-2014, 03:15 PM   #4
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Default Re: Friction Generator Dynamo on a golf cart

Because it's true. You can't get something for nothing. The generator has an efficiency of less than 100%.

If you want to add friction to charge batteries while braking, get a regen cart.
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Old 07-02-2014, 03:33 PM   #5
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Default Re: Friction Generator Dynamo on a golf cart

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Because it's true. You can't get something for nothing. The generator has an efficiency of less than 100%.

If you want to add friction to charge batteries while braking, get a regen cart.
why is it assumed that a friction generator dynamo uses more energy than the electricity it produces?
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Old 07-02-2014, 03:34 PM   #6
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Default Re: Friction Generator Dynamo on a golf cart

Regen makes the most sense for golf courses, where you have a lot of stop and go, or if you typically brake while going downhill. The kinetic energy of the cart is converted into electrical energy, rather than heat. For my neighborhood driving, it really doesn't make as much sense. I usually coast downhill as fast a it will go, and can coast much of the way up the next hill. My hills aren't very steep. My buddies that have regen carts can't go downhill as fast, so even though they're recharging the batteries, the motor isn't 100% efficient when used as a generator downhill, then as a motor going up the next hill.
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Old 07-02-2014, 03:36 PM   #7
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Default Re: Friction Generator Dynamo on a golf cart

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Originally Posted by BorisM View Post
why is it assumed that a friction generator dynamo uses more energy than the electricity it produces?
Because if it weren't true, you could hook up a motor directly to a generator, which feeds the motor. Apply a voltage source to get it spinning and it should go forever. Perpetual motion. Perpetual motion by definition can do no useful work. You are talking about over 100% efficiency.
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Old 07-02-2014, 03:43 PM   #8
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Default Re: Friction Generator Dynamo on a golf cart

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Originally Posted by yurtle View Post
Because if it weren't true, you could hook up a motor directly to a generator, which feeds the motor. Apply a voltage source to get it spinning and it should go forever. Perpetual motion. Perpetual motion by definition can do no useful work. You are talking about over 100% efficiency.
I understand what you are talking about, but that would be true if wheels were spinning only to spin the dynamo, wouldn't it? In the case of a golf cart, the wheels spin anyway and the only energy loss is friction of the dynamo. In comparison to friction with the ground, friction with dynamo generator is minimal. What am I missing?
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Old 07-02-2014, 03:52 PM   #9
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Default Re: Friction Generator Dynamo on a golf cart

Energy can neither be created nor destroyed. In order to generate (really convert) electrical energy, you need to apply kinetic energy. If you only apply one watt of kinetic energy, you'll get less than 1 watt of electrical energy. Both your motor and your generator are less than 100% efficient. A better use of the battery/motor is to make it just go, and not try and use more energy and recoup a portion of that energy.

You can't get something for nothing. It's why cars don't come equipped with wind power generators mounted on the roof.

However, if the added friction is used for braking, it does work. It's called regen, but you aren't getting something for nothing. You add friction to the motor instead of adding friction to the brake pads or shoes.

EDIT: Watts are a measure of power - which is an instantaneous value. Watt-Hours are a measure of energy - which is a totalized value over a period of time, so above I misspoke when I said "If you only apply one watt of kinetic energy". However, the argument is still valid.
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Old 07-02-2014, 05:25 PM   #10
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Default Re: Friction Generator Dynamo on a golf cart

On the surface, your idea would seem to work. But look at the many varied issues involved. You would be adding resistance to those wheels with the generators attached. For a 36 volt cart, that means one wheel is being operated with less resistance.
How do you convert the three 12 volt feeds to one 36 volt feed to charge the battery Pack. Would there not be further electrical resistance in whatever you used to distribute the current? How could you be certain all three dynamo's were producing equal amounts of electricity? Even if you developed a feed for each two battery pack, from one dynamo, you would still run the risk of unequaled charging. Then there is the issue of the inside wheel speed versus the outside wheel speed. Every turn of the cart would cause different feeds to the pack.
One has to keep in mind, this is not a single unit being powered by a single source, (like powering a bicycle light with a tire driven dynamo). This is a complex piece of equipment with several interacting components that each need to be treated in their own particular way.
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