With the increasing popularity of LED lighting on bicycles, why don't we make DC dynamo's? Current dynamo's are based on AC motors while these are (if I remember correctly) not as efficient as DC motors and you need a rectifier circuit to attach LED lighting to it. With a DC dynamo you don't need a rectifier and the overall efficiency is higher. Or am I overlooking something?
DC dynamo?
- Thread starter Erasmus
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msxtr
Newly Enlightened
All dynamos work with AC current, if you need DC current, only have you that put a diodes bridge of (rectifier), some very simply and cheap.
Greetings - Saludos
msxtr
Greetings - Saludos
msxtr
znomit
Enlightened
For LED lighting dynamo efficiency is not a problem. You can get over 500lm out of a hub dynamo and hardly notice its drag.
Rectifiers are simple to build from a few dollars worth of parts.
See www.pilom.com
Rectifiers are simple to build from a few dollars worth of parts.
See www.pilom.com
Probedude
Enlightened
Or using brushes and a commutator.
For longevity, use an 'alternator' where the core is a spinning magnet, the stator are your windings going to a rectifier and a cap. No brushes or commuatator to wear out anymore.
I was thinking of buying the largest brushless RC airplane motor (lots of cheap ones here www.unitedhobbies.com) and make a windmill. Could use one of these for a bike instead.
deathshadow
Newly Enlightened
- Joined
- May 23, 2008
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Which is exactly why most DC systems use an alternator instead of a generator... and VERY important to include that capacitor since the voltage coming out of the rectifier is going to be pulsed DC, usually in a 'humpback' waveform. (since the output from an alternator is generally a sine wave)
Alternators (which the majority of bike "dynamo" are - it's actually incorrect to call them dynamo's since the coil is fixed) are lower mechanical friction, lower mechanical wear, and in general a simpler circuit to deal with than the headaches of brushes and commutators... Much less another 'good point':
They are less prone to 'field action' - using a DC motor as a generator builds up electricity in the coils that apply drag on the motor opposite the direction you are generating power. The use of alternating current and fixed coils prevents too strong an electromagnetic charge from building up in the coils since they pole-swap.
Probedude
Enlightened
Don't quite follow you here. The mechanical load on the shaft of an alternator or generator is higher the higher the electrical load on the output (back EMF) regardless of whether it's DC or AC. There's no free lunch here.
n4zou
Newly Enlightened
Bicycle dynamos are perfect just the way they are! The design is super simple or KISS (Keep It Simple Stupid) so there reliable for many years with no brushes to replace or commuters to clean as would be required with DC generators. AC current will travel thin wire long distances where as DC current will be absorbed and turned to heat by the copper wire requiring larger wire be used. Adding a bridge rectifier consisting of four 1N5818 diodes is a cheap and simple way to obtain DC from an AC source. Here is a photo of one.
Here is a drawing of one if your not a trained in electronics.
The capacitor is not on the rectifier in the photos above. It's located in the headlight housing.
If you need to recharge your cell phone, GPS, or other device that can be charged by using a USB port on a computer here is a circuit showing how to do that.
Ni-MH batteries will automatically regulate voltage output of the dynamo due to it's claw pole design. As the recharging voltage from the dynamo approaches the battery packs design output internal impedance in the batteries starts increasing. They load the dynamo to the point it's simply can't produce more voltage keeping the output voltage regulated. With four 1.2 or 1.25 Ni-MH batteries voltage is limited to a maximum of 5.2 volts. This is well within USB standards and safe for the batteries. Nearly all dynamos can't produce much more than 500mA, which happens to be the sugested rapid recharging current for Ni-MH batteries, how cool is that! The batteries also filter and protect your USB powered/recharged device allowing you to recharge and power it as you pedal along. A company recently copied my design. Here you go if you don't want to do it yourself.
http://www.copycatsolar.com/
BTY; the solar panel is a marketing ploy. It's only good for about 50mA IF you keep it aligned with the sun. Thats impractable at best while moving.:sigh:
Here is a drawing of one if your not a trained in electronics.
The capacitor is not on the rectifier in the photos above. It's located in the headlight housing.
If you need to recharge your cell phone, GPS, or other device that can be charged by using a USB port on a computer here is a circuit showing how to do that.
Ni-MH batteries will automatically regulate voltage output of the dynamo due to it's claw pole design. As the recharging voltage from the dynamo approaches the battery packs design output internal impedance in the batteries starts increasing. They load the dynamo to the point it's simply can't produce more voltage keeping the output voltage regulated. With four 1.2 or 1.25 Ni-MH batteries voltage is limited to a maximum of 5.2 volts. This is well within USB standards and safe for the batteries. Nearly all dynamos can't produce much more than 500mA, which happens to be the sugested rapid recharging current for Ni-MH batteries, how cool is that! The batteries also filter and protect your USB powered/recharged device allowing you to recharge and power it as you pedal along. A company recently copied my design. Here you go if you don't want to do it yourself.
http://www.copycatsolar.com/
BTY; the solar panel is a marketing ploy. It's only good for about 50mA IF you keep it aligned with the sun. Thats impractable at best while moving.:sigh:
Probedude
Enlightened
Can you provide any links to explain this?
. .. rest of note deleted since I misunderstood your explanation.
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Calina
Enlightened
deathshadow
Newly Enlightened
- Joined
- May 23, 2008
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Only if you're dumb enough to view it in Internet Exploder... Though being the layout is COMPLETELY broken in anything else rendering the page useless... Hey look, all the telltales of the crap HTML output by Office 9.
Calina
Enlightened
Thank you for your very nice and constructive comment.
What is a trojan?
This website works 100% fine using either Camino, Firefox or Safari on a Mac.
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n4zou
Newly Enlightened
n4zou
Newly Enlightened
I just checked it myself. The website has been attacked and corrupted. Hopefully they will fix it soon. I have nothing to do with them other than they stole my design but I never patented it so there welcome to it as is everyone else.
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Steve K
Flashlight Enthusiast
As a general rule, bike dynamos are indeed very simple and reliable. Nothing to wear out, such as brushes.
The reason why AC power generation and transmission is preferred over DC is a little more complicated that the explanation by n4zou, but power loss is the heart of it. With DC power, the voltage is limited by the risk of killing the customer. As the voltage is lowered, the current required to deliver a given amount of power increases. If you want to deliver 100 watts at 1000 volts, only 0.1A needs to be delivered. If you limit the voltage to 100 volts, then 1 A is required. Since losses in wire are equal to the square of the current times the resistance, the 10 x increase in current results in 100 x the power loss!
The advantage of AC power is that transformers can be used to increase the voltage to very high levels (around 14,000 volts, I think..) for transmission over large distances. When it gets closer to the customer, other transformers are used to drop the voltage down to relatively safe levels.
Wonderful stuff, but not really relevant to bikes. AC is used because the dynamo is simpler, and incandescent bulbs really don't care whether they are powered by AC or DC. LEDs do care, and as mentioned, the bridge rectifier is a simple and cheap way to convert to DC power. If efficiency is a high priority, schottky diodes can be used, or even a bridge made of mosfets (very, very low losses).
Steve K.
Probedude
Enlightened
Yep, knew this but wondered if there was anything more obscure since we were talking about a bicycle application. It would be ridiculous to try and transformer up/down the voltage for the distance from the rear tire to the handlebars.
No mention of the voltage changing at all. Higher DC voltage gives you the same benefit vs lower DC, which is why I asked.N4ZOU said:
FWIW I've seen utility poles around here marked 25KV and 30KV. Pretty darn high!
Regarding 500mA charging not being too high for charging NiMH's, it is if they're fully charged! (and applied for too long) NiMH manufacturer's vendors don't recommend trickle charging cells continuously and if you do trickle charge at all to use a C/20 rate. In a bike application one wouldn't need to worry much about it since you have to stop pedaling sometime!
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Steve K
Flashlight Enthusiast
My first bike light design used 5 AA nicads, which were then used to implement a standlight. I didn't use them very long before they died from overcharging. Then I designed a fairly simple charger based on battery voltage, and the batteries lasted much longer!
Of course, I was spending an hour or two a day on the bike charging the batteries. If you only ride 30 minutes, maybe it would work for you.
Battery charging is an interesting subject, and there are a lot of different ways to do it. The best methods involve monitoring temperature since this is the most direct way of detecting when the battery is fully charged and starting to produce gas.
The alternative to a good charge method is to use a battery that can tolerate the charging current indefinitely. So, if you need a 500mAhr battery, and your charger produces 0.5A, you'll need a battery that can tolerate being trickle charged at 0.5A. Trickle charge current is nominally C/20, which means that a 10Ahr battery is required! Call me a wimp, but I don't want to carry around a 10Ahr battery just to avoid using a decent charging scheme. On the plus side, it certainly would be able to power a heck of a big headlight!
Steve K.
