Charging a cell phone via USB?

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benutne

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Apr 22, 2011
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So I want to know if anyone has any thoughts on using the 6V wire coming from the engine to charge a cell phone (or any device really) via a USB plug. I don't know enough about electricity and current gadgets available to make an informed decision if this is something I want to do.

I was thinking it would be cool to charge my cell phone while riding. This way it would stay on when clipped onto my handlebars too.
 
Pilotgeek

Pilotgeek

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This would certainly be doable, though I don't know how quickly it would charge.

Because the bike provides AC power, it needs to be switched to DC and cleaned up a bit. Basically, this could be done using a diode and a large capacitor. USB runs off 5v, and a diode has enough voltage-drop to bring the 6v down to about 5.2-5.3v, which the phone should be able to handle. I don't know how stable the power output on these engines is though, so It's kinda risky as this would not be a guaranteed regulated supply.
 
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benutne

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Pilotgeek said:
This would certainly be doable, though I don't know how quickly it would charge.

Because the bike provides AC power, it needs to be switched to DC and cleaned up a bit. Basically, this could be done using a diode and a large capacitor. USB runs off 5v, and a diode has enough voltage-drop to bring the 6v down to about 5.2-5.3v, which the phone should be able to handle. I don't know how stable the power output on these engines is though, so It's kinda risky as this would not be a guaranteed regulated supply.
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Didn't know about the engine providing AC. That would change things. For some reason I thought they'd put out DC like a cig lighter in a car.

Edit: Also charging speed doesn't concern me much. I just want it to be able to keep the screen on without completely killing the battery.
 
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2door

2door

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Keep in mind that the white wire output voltage varies with engine RPM. If you take a voltage reading you might see anything between 4 and 9 volts AC between idle and WOT.
Tom
 
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benutne

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2door said:
Keep in mind that the white wire output voltage varies with engine RPM. If you take a voltage reading you might see anything between 4 and 9 volts AC.
Tom
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Yikes. Any way to even that out? Maybe a capacitor for the undervoltage and something to dump off the overvoltage?
 
Pilotgeek

Pilotgeek

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AC doesn't change things too much. A simple half-wave rectifier would be enough, which essentially consists of a diode from the white wire.
 
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Pilotgeek

Pilotgeek

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Well... to dump off overvoltage, you'd want a regulator. A simple linear regulator essentially 'burns off' extra voltage as heat. It may not deal well with the voltage dips though.
 
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benutne

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Hm. This sounds like it could be a fun summer project. I'm wondering what the easiest way to handle the variable current would be. So basically, first, convert from AC to DC using a rectifier. Then go a regulator to drop it down to 5V. I'm thinking maybe since the lower end of the voltage supplied would be 4V it might not be so bad. Then where?
 
Pilotgeek

Pilotgeek

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Well, before plugging anything resembling a phone into it, I'd do extensive tests with a multimeter to make sure it's giving the right kinda voltage. But really, after you get it rectified and regulated, it's a matter of wiring up the right plug and using it.
 
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benutne

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Yeah, I figured I'd need to go out and buy a nicer multimeter. The one I have is pretty basic (like the $5 harbor freight one).
 
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benutne

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Anyone know how many amps the motor puts out? 2Door mentioned 4-9V AC. I'm looking for circuit parts now to start building.
 
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benutne

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Oh, and why a half wave rectifier vs. a full wave rectifier? Wouldn't a full wave rectifier be more efficient? I'm thinking of device longevity here too. I ride almost every day.
 
Pilotgeek

Pilotgeek

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A full-wave would be more efficient. I'm just looking for simplicity in explanation. I think these motors put out about 3 watts typically.
 
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Bmonette8385

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Go get a nice fluke. Your best bet is looking to make a solid state voltage regulator. so you dont have to tinker with vibrating type. im guessing it'd be too much work to get that working. So you'll have to get to know transistors . I have a schematic for one that we had to study for class. It's simple enough, but its for aircraft generators and alternators. And full wave rectified is more efficient. there is going to be a lot of experimenting for this project. Ide like to hear how it turns out. Good luck.
 
Pilotgeek

Pilotgeek

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Look at radioshack for a 7805 voltage regulator. It's a solid-state 5v regulator. I've used them in many projects.

Also, here's another vote towards getting a fluke multimeter.
 
DuctTapedGoat

DuctTapedGoat

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You don't NEED to use the full 5v.

Cool thing about USB is that it will still charge at 2.5V, or even 1.25V.

For example, when you have a non powered USB hub, it's got 4 ports coming off one port. The 5v is shared between all 4 ports, and that brings you roughly to 1.25V per hub port. You can still charge fine - the only time it really causes problems is when you're dealing with data transfer, and the device can't get enough power to transfer data - though when we're dealing with white wire, we're definitely NOT transferring data.
 
Pilotgeek

Pilotgeek

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DuctTapedGoat said:
You don't NEED to use the full 5v.

Cool thing about USB is that it will still charge at 2.5V, or even 1.25V.

For example, when you have a non powered USB hub, it's got 4 ports coming off one port. The 5v is shared between all 4 ports, and that brings you roughly to 1.25V per hub port. You can still charge fine - the only time it really causes problems is when you're dealing with data transfer, and the device can't get enough power to transfer data - though when we're dealing with white wire, we're definitely NOT transferring data.
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Are you sure it works that way? I thought it was only the current that dropped with multiple devices. With devices in parallel, voltage drop should be a non-issue.
 
2door

2door

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Hey, here's an idea. Leave the cell phone at home on the charger and go enjoy your bike. That way you'll have no distractions :)
Tom
 
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bmc_az

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I considered everything and I ended up with several small solar panels from HF to charge a small 12vdc batt then you can just use a regular 12v lighter socket to USB it also powers other accessory to.
BMC_az
 
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