Making a Battery Pack for a Bicycle Dynamo Hub (5v in AC Current)

Well the first thing I notice is that the dynamo hub needs to produce considerably more than the 3 watt capability that I have seen for these hubs...Ideally you need enough generation to cover the load and charging the battery pack at the same time...as you go up in generating capacity you create more and more drag, so harder and harder to peddle....are you sure this the (uphill)path you want to go down?

The hub is already installed in my bike, theres barely any drag at all, if thats what you mean
The light doesnt have to be on the same time its charging, most of the time I cycle with the lights off, only turn them on in night time / darkness

Or am i missing the point? haha

There's barely any drag because you are generating very little current...so if it is the case that you charge the batteries during the day and use the lights just at night, then you need to figure out how long it will take to charge the batteries, but the 3 watts if used to step up the voltage will be diminished, there is always some loss in transition.., so you need to flesh out the design to know how much voltage you will need and calculate the losses in converting 6 volts to whatever, bearing in mind that you will need a voltage higher than the pack total when charging...you might also need to add some safety features if they are not preexisting...so the first thing to do is draw a diagram of the components with voltages and wiring schematic....then post the drawing here for scrutiny...and make it large enough for old people to see haha...

there isnt any step up converts as the 4 cells in series can make the current i need

to charge there will be a connection of the cells in parallel, 5 volts from the dynamo to each 4.2v cell

i havent got a diagram yet as my first goal is to figure out what i need for the AC to DC conversion, do you have any advice regarding that?

thank you for your time

Yes I would use one of these....

https://www.sinewavecycles.com/pages/revolution-faq

..."If you want to use your battery like a buffer, and connect from Revolution to battery and battery to USB device, you need a battery that supports 'pass through charging'. This feature is not always clearly advertised and is implemented differently by different brands. We do have some particular recommendations if using a battery in this configuration:"...

Voltaic Systems V15

Cinq Smart Power Pack

..."Don't use a bridge rectifier. It's inefficient, because you need two diode drops in series, and it doesn't allow you to use the frame as ground for a DC lamp (like, a modern LED bike light). Instead, consider a voltage doubler

https://electronics.stackexchange.com/questions/57039/converting-and-stabilizing-output-voltage-of-a-dynamo-hub

i was afraid of that, inefficiency, so say i get 5vAC, and a full bridge rectifier connected to convert that to DC, how many volts would i get?
each of my cells are: 3.4-4.2v

..."Rectifier efficiency is defined as the ratio of the DC output power to the AC input power. The maximum rectifier efficiency of a bridge rectifier is 81.2% which is same as the center tapped full wave rectifier."...

https://www.physics-and-radio-electronics.com/electronic-devices-and-circuits/rectifier/bridgerectifier.html

http://www.learningaboutelectronics.com/Articles/Voltage-doubler-circuit.php

I would read this whole thing as well as the replies...

https://electronics.stackexchange.com/questions/57039/converting-and-stabilizing-output-voltage-of-a-dynamo-hub

after looking at that circuit you linked me and looking up what each symbol is (lol) its starting to make sense, but doesnt AC to DC convertion require 4 diodes? will 2 diodes work just fine in charging cells?

so from what im seeing is:

2 x Diodes 1n5819

2 x Capacitors 500uf

1 x regulator

1 x dynamo hub (which i already have)

1 x headlamp (which i already have)

i understand what diodes do and why we need them, to convert ac to dc, but i dont understand why we need capacitors or regulators, since I am charging cells and using the cells as a power source, im a little bit confused

Ohms calculations

The resistance R in ohms (Ω) is equal to the voltage V in volts (V) divided by the current I in amps (A):

The resistance R in ohms (Ω) is equal to the squared voltage V in volts (V) divided by the power P in watts (W):

The resistance R in ohms (Ω) is equal to the power P in watts (W) divided by the squared current I in amps (A):

Amps calculations

The current I in amps (A) is equal to the voltage V in volts (V) divided by the resistance R in ohms (Ω):

The current I in amps (A) is equal to the power P in watts (W) divided by the voltage V in volts (V):

The current I in amps (A) is equal to the square root of the power P in watts (W) divided by the resistance R in ohms (Ω):

Volts calculations

The voltage V in volts (V) is equal to the current I in amps (A) times the resistance R in ohms (Ω):

The voltage V in volts (V) is equal to the power P in watts (W) divided by the current I in amps (A):

The voltage V in volts (V) is equal to the square root of the power P in watts (W) times the resistance R in ohms (Ω):

Watts calculation

The power P in watts (W) is equal to the voltage V in volts (V) times the current I in amps (A):

The power P in watts (W) is equal to the squared voltage V in volts (V) divided by the resistance R in ohms (Ω):

The power P in watts (W) is equal to the squared current I in amps (A) times the resistance R in ohms (Ω):

Here's a calculator that should help....

https://www.rapidtables.com/calc/electric/watt-volt-amp-calculator.html

Don't forget that LEDs themselves are rectifiers. You have the entertaining possibility of using two headlights, one formed by the bridge rectifier you are using to convert dynamo AC to charging DC, the other being the lamp driven by battery power, both illuminated at the same time while you are pedalling.

Here's some setups that might appeal to you...

Light: https://exposurelights.com/revo-dynamo USB charger: https://www.sinewavecycles.com/collec... Dynamo hub: http://www.sp-dynamo.com

i have seen and looked at those products but the prices are complete rip offs

$120.00

for an AC to DC converter, voltage regulator, usb porb, some cabling,

thats an insane price

i want to build and learn this myself as it doesnt seem overly complicated, i appreciate your time in sourcing those clips but they are not for what i want help with

i wanted help with converting ac to dc, which i now found myself
my next goal is to attempt charging 1 of my cells (4.2v at 1600mAh) with my dynamo hub

but i think i need a protection board first which is what im trying to find now

This is very informative:

https://www.instructables.com/id/Voltage-Regulated-5-V-Bicycle-Dynamo-Light-USB/

afraid those links refer to ready made products, im after making it from scratch myself as stated before

found it myself

full bridge rectifier is what i needed, i wasnt sure at first because most of where i looked refered to house hold 220-240v, didnt know if they applied to low voltages, but apparently this does what i needed for my first step:

8A 1000V diode full bridge rectifier KBU810 KBU-810

https://www.ebay.co.uk/itm/8A-1000V-diode-full-bridge-rectifier-KBU810-KBU-810/173285027070?hash=item285897acfe:m:mquQe9AtvMIHHXj3VUnxFug

now to figure out how to charge 8 cells of 3-4.2v each with dynamo 5vDC

First, congratulations for wanting to build this yourself! You'll learn a lot in the process.

That KBU810 is a very poor choice! if you look up its spec. sheet, you can find :

Look at the row labelled Maximum Forward Voltage Drop... It shows 1.1V per element. In a full bridge, the current always passes through two elements (two diodes), so you lose 2.2V whenever you use the bridge at 4 Ams. Stef already recommended using Shottkey Diodes. They have significantly less voltage drop.

Secondly, you list the 810, which is a 1000V bridge (700V RMS). The 800 (the lowest in the series) has a 35VAC rating, which still way more than your requirements. Within a series like ths, the higher voltage devices always cost more, and you need no more than the 35V.

Keep working at it!

yeah it may be a poor choice but at least im figuring out whats needed to convert haha
yeah 2.2v is drastic considering how low the voltages i am working with are, so thats out of question

Shottkey Diodes, not sure how i missed that comment, do you have a specific part number that you would recommend?

googling it came up with "Schottky diode" instead

https://www.ebay.co.uk/itm/10x-SR5100-SB5100-SB5B0-SR5010-SR510-100V-5A-Schottky-Rectifier-Diode-TV-Solar/281884407018?hash=item41a19eb4ea:g:iNwAAOSwqNxd3Sj-

is it this?

i cannot seem to find the voltage drop information on this part, i see maximum dc blocking voltage, but not the voltage drop, where would i find this?

keep in mind the parts im linking are just the parts that im being recommended from other previous DIY projects for these dynamos

thanks so much for pointing me in the right direction

would you also agree that using a full bridge isnt efficient? using 2 diodes instead would be sufficient enough?

Sorry, my bad on the spelling of Schottky!

One possibility is https://www.digikey.com/product-detail/en/vishay-semiconductor-diodes-division/SB220-E3-54/SB220-E3-54GICT-ND/3711859

This is a 2Amp, 20Volt Schottky diode, with only 0.5V forward loss, with axial leads to make it easy for you to experiment. There do exist diodes with a forward voltage drop as low as 0.35V, but I didn't find any that could carry this much current or had axial leads.

In a diode bridge, the current must pass through 2 diodes at any given time, so you lose twice the voltage drop of a single diode. SE provided a voltage-doubler circuit, back around post #10. In that circuit, the current only passes through a single diode at any given instant, so you only have a single forward voltage drop, and you get voltage doubling as well.

If your dynamo produces 5VAC, that is presumably RMS voltage, an average value. The peak of the sine wave will be around 7V, so if the current requirements are low, you'll have about 6.5V after a diode, and the doubler will boost that to around 13V, which should be enough to run your charging circuit for one cell pair, or possibly two cell pairs in parallel. You won't know for sure 'till you try it.

<...then two of those in parallel to give more mAh,...>

Nope. The mAh storage capacity of the battery is not changed through either a series or a parallel connection.

Series gives greater voltage. Parallel gives greater current capability should it be needed.

Read the buck boost converter information on this ebay site;

https://www.ebay.com.au/itm/DC-DC-10A-Buck-Boost-Converter-Step-Up-Down-regulator-Module-for-LED-Driver-AU-/323741832248

I have used them to convert 12V to 24V for solenoid valves on a tractor.

5V DC appears to be the lower limit but you could try one with a bridge rectifier and capacitor to supply the DC. Use shotkee diodes which have a very low forward voltage drop so you may not lose too much of your 5V AC. Have you looked at the generated waveform with a CRO to see what the peak V is.

You need to drive the wheel with something simple like a rubber block on an AC motor to gather enough data to know if it is even possible. 5V @ 3W gives you 0.6A, not a lot to charge a battery with.

each cell is only 4.2v at 1600mAh / 1.6 amps

ideally i would rather charge all 4 cells in parallel, and use then in series to output 16.8v

i know its a slow charge but i cycle way more than i need the battery usage, its more of a backup thing

i read of buck convertors, step up convertors, etc, i dont think i would need them if i can use 4 cells in series

A 5 volt ac source will give you up to 7 volts dc to charge the batteries. A simple full wave bridge will work 100PIV and 1 ampere or more, filter capacitors will give you a higher output voltage, but likely not necessary. Most small battery float chargers have no filters, just transformer & rectifier.

Are you sure that the charge controllers take dc input? Don’t separate the charge controllers from the batteries, they are designed to work together, and you could start a fire if misapplied. You know about lithium ion batteries, I assume.

sorry but whats a 100PIV?

tried googling that but not sure what thats refering to (im an amateur)

the cells are currently connected to:

Over-Charge & Discharge protection board: HND-7V2-HY-V3

so they are currently charged with a 7.7-8.4v DC charger, i would like to change it to a different board once i figure out what i will need

preferably i would like to charge 4 cells in parallel, 3.4-4.2v each, and use them to power my lighting in series at 16.8v

yeah i havent disconnected the protection boards just yet, waiting until i figure out what i need before i make any changes, and prepare tests

PIV stands for Peak Inverse Voltage, The maximum reverse that the diodes can block.

It is NOT trivial to switch 4 batteries from all parallel for charging to all series for discharging, even if it were only the batteries. Add the (required) protection boards, and it may well be impossible.

You'll be much better off stepping up the input voltage, one way or another.

hmm, so at what point would you step up the voltage, because the battery packs that i was planning to disassemble currently output 8.4v (each cell 4.2v) so to charge that I would assume i would have to step up from the dynamo as you cannot charge a cell with a lower voltage

combing the two battery packs would be easy as i simply have to connect the two protection boards positive to negative, but i dont see how i could charge 8 cells at 16.8v with 6v 3 watt dynamo

hence the idea of charging in parallel at lower voltages

by the way thanks for being encouraging, seems like a lot of people these days dont encourage learning and look down upon it, sad times

Peak inverse volts for the bridge rectifiers, you could do with 50 volts.

if you look at a lithium battery charger, you may find that it already converts from ac to dc. I don’t know that you can find lithium charge controllers separate from the battery. They are normally built in, liability concerns and all that. If you cannot use the batteries as originally packaged, it’s unlikely you’ll be able to buy a controller designed for your particular desired battery combination.

You should verify that the protection boards you have are normally powered with dc, it could be they have an ac supply. There are threads on Cr4 from 2016 on this lithium ion equipment, but nothing of use that I could find.https://cr4.globalspec.com/thread/107232/PCM-for-Battery-Pack

yeah i found that exact post aswell here, which made me join this site actually haha
but surely protection boards can used universally as long as the minimum and maximum voltages are the same? or no?
https://www.ebay.co.uk/itm/1S-Cell-PCB-BMS-18650-Protection-Board-Li-ion-Lithium-Battery/173955620419?hash=item2880901e43:m:mC-ZqDQh1gs_hhsjL3PzLoQ
here for example, the minimum, and maximum volts match what im after

but what i dont understand, is way i want to charge all 4 cells at once in parallel, 3.2-4.2 volts, it would total 6400 mah, so would that be a problem? as the listing is mentioning the amps, so i guess it must matter?

Regulator for a Hub Dynamo

https://people.nscl.msu.edu/~daniel/sreg.htm

Very interesting links, but not for a beginner!

I'm confused by the battery pack being shown on the charger, but not on the main circuit. I have to assume that the V+ and V- points on the upper (controller) circuit connect to the V+ and V- points on the lower (charger) circuit. ...but assuming is always dangerous!

This allows for charging from a separate source in an emergency situation...optional I guess, but I would include it...If he wants to go simple he needs to simplify his system and make some compromises...doing what he wants to do with what he has, is not simple if done properly and safely....well, unless you just buy the components...that would be simple...

Thanks for that link and schematic, i actualy already seen that aswell, its actually excessive to what i need

if im to keep the protection boards as they are then that means im left with two battery packs of 4 cells each, 8.4v 6400mAh

if i could just figure out how to charge that from the dynamo then i would have progress
would a step up convertor work from the dynamo?

Why don't you just use a battery pack with a lower voltage? You could carry the other battery pack as a backup or something...

because its mainly there for my lighting system which requires 16.8v

Something is strange here. Bright LEDs normally run on a voltage between 3 and 5 volts, A driver for the LED should only require a couple Volts more. What lighting system are you using?

If your dynamo is currently running that lighting system without a battery, then the dynamo must produce enough voltage to run the light.

Did you acquire the dynamo separately from the lighting system?

Yes I agree, I don't understand why so much voltage is needed...USB is 5 volts...

https://www.amazon.com/Victagen-USB-Rechargeable-Bike-Light/dp/B07GJC17KF/ref=pd_vtp_468_1/144-8699111-5708226?_encoding=UTF8&pd_rd_i=B07GJC17KF&pd_rd_r=7b096045-d0ab-4679-8cf9-01432f0dc4f7&pd_rd_w=1DTY4&pd_rd_wg=H8LqS&pf_rd_p=5946f538-3793-4aed-94d1-6882674b98f9&pf_rd_r=Q5JB3F6140D9EENTHSH9&psc=1&refRID=Q5JB3F6140D9EENTHSH9

Well then I don't understand why you're using an LED array that requires such a high voltage, but if that's the case you can step up the voltage from the battery pack to the LED array easy enough....but all the batteries should be in parallel...that way charging is simple and a USB is also simple...

That's an excellent idea, except that I'm under the impression that he already has the ≈8V battery packs on hand, and also has some kind of lighting system that needs ≈16V on hand.

If that is the case, then one possible solution would be to connect the two 8V battery packs in parallel, use your voltage doubler circuit from Post#10 to charge them, and use an 8-16V DC-DC converter to power the light system. I haven't checked to see if such an up-converter is easily available...

In #23 he says he was planning to to separate the batteries already...I mean it's only 2 batteries in each pack,,,just rearrange them in parallel instead of series...

4 pack lithium battery holders

step up voltage

"In #23 he says he was planning to to separate the batteries already."

True, but I understood that the battery pack(s) on hand is(are) part of a module that includes a charge controller. He can't use a charge controller designed for two cells in series to charge the same two cells in parallel.

"I mean it's only 2 batteries in each pack,,,just rearrange them in parallel instead of series...". Yes, reconnecting the cells in parallel is almost trivial, but those parallel cells need an appropriate charge controller designed for that configuration. Then, once charged, it's NOT trivial to disconnect them and reconnect them in series to obtain the higher voltage. And the big problem is that the cells can't be charged and used simultaneously.

Especially after seeing how inexpensive that DC-DC converter is, the most logical solution is to obtain a cell/charger unit of appropriate voltage and capacity to be charged by the existing dynamo, and step up the voltage to whatever the lamp array requires.

Each protection board is made for a particular arrangement of cells, either in series or in some combination of series and parallel. The only way you could charge all cells in parallel would be to totally disconnect all cells from each other and from the protection board, then reconnect them in parallel to the charging circuit.

No simple switch can perform that function, because you MUST guarantee that ALL original connections are disconnected before beginning to reconnect them in parallel for charging. Then the same guarantee must apply for returning to the original configuration for powering the lamp.

That switching could conceivably be achieved using two or more multiple-contact relays, But then the parallel combination of cells must be connected to a totally different cell protection circuit made for single-cell voltage.

do you think a step up convertor would work from the dynamo itself to charge the battery packs as they are?, i could keep the 4 cells together but it would need to charge 8.4v

Assuming your dynamo produces AC, you could connect the output of the dynamo to the low voltage winding of a small transformer to step up the voltage. The transformer would have to have a turns ratio of at least 2:1, but not much above 4:1. The only readily available transformer I can think of at the moment would be a 24V doorbell or sprinkler transformer. They have a turns ratio of 5:1, which would step up your 5VAC to around 25VAC. That could work if you used a resistor and zener diode to limit the voltage, but it would waste energy.

yeah it does produce AC, which was why i need to convert to AC to DC in the first place

if i used what you recommended me then that would mean i would then need to use a step down converter to match my batteries, 8.4v or 16.8v
what would happen if I used a step up converter without a transformer, this way i could dial in the exact volts i need, or is transformer necessary?

really appreciate your time though in helping me out buddy

You need to start by finding out the actual output voltage of your dynamo, under load (which probably means connected to its normal lamp), and rotating at a speed corresponding to normal bicycle speed. Assuming that your dynamo currently connects directly to the lamp, the easiest way to do this would be to scrape the insulation off the wires leading to the lamp. Scrape one wire a short distance away from the scrape on the other, so there is no chance of shorting.

Then connect a multimeter to those two wires using alligator clips, set it to measure low AC Volts, put the meter in the basket of the bike, and start riding. Watch the meter.

If you don't already have a multimeter, get a cheap one now, then a good one as soon as you can afford it. It's never a bad idea to have two of them. Ditto for a set of alligator clip leads. Study the meter manual or have someone show you how to use the meter if you don't already know.

Once you know the AC output voltage under load, you can decide what transformer may be acceptable, and whether one is available.

Next, buy a few Schottky diodes (Buy extras; they're cheap, and sooner or later, you will destroy one or more) and a couple of capacitors, such as the 100µF ones shown in post #10. Those capacitors should have at least a 16V rating; higher is better. Construct a temporary diode bridge (pay very close attention to the polarity of the diodes) Connect the dynamo to the input and the capacitor to the output of the bridge (again, pay very close attention to the polarity of the capacitor). Set the meter to measure DC Volts, connect it across the capacitor, and go for a ride.

Then, construct the voltage doubler of Post #10, and again measure the voltage. You may well find that it is enough to run the charger. If not, we can proceed further...

In China,they have home-brewed bicycles that use battery powered drill motors and power packs,and carry a spare battery, fully charged for return.

Reported range of around 25 miles,but it depends on terrain.

Using regenerative braking,they will partially self recharge going down hills.

Easy to make using off the shelf components,but still requires you to use your own brain cells to implement it.

This is better that trying to re-invent the wheel from scratch.

You need to hone up your electrical/electronics knowledge if you really want to roll- your-own.

Learn the difference between: Power,energy,voltage,current,resistance,capacitance,impedance,inductance,Xc, Xl,ohms law,etc.

No one can step you through each obstacle you will encounter along the way.

Good luck in your quest for knowledge.

"Using regenerative braking,they will partially self recharge going down hills."

I assume (Yes, that can be bad) that they would use variable speed systems to avoid jerking. I know very little about them, but I would be surprised if drill speed controllers are set up so regenerative braking would occur.

The article I read did not go into details,but I presume they used a ReGen Brake board external to the drill motor.

Looks like a way to get a good mode of transportation on the cheap.

I remember many years ago,in the 70's a plant had a 3 wheel battery powered cart

that used a car battery and what looked like a wiper motor.

The front wheel was the drive wheel,and it was connected via a very small roller chain,maybe a number 25 to the motor.

Looked like maybe a one to ten ratio.

The battery was in front of the operator,who was standing.

When he reached his destination,he plugged the built in charger in to any nearby outlet

It would top off the battery while he was repairing or troubleshooting the machinery.

It had a triangular shaped frame,and a tricycle type steering.

They would run about 6 mph and could haul a 200 pound man and a 200 pound motor easily.

I have not seen any of them in many years,and don't remember who made them.They may have been made in house.

The maintenance guys loved them.

Hey all, ok Ive had major progress and I managed to get everything working the way I wanted, I also took your advise and made full readings, underload, at AC level, after diodes, DC level, after current regulator, im getting WAY more volts than i expected
charging works, current regulator works, now the weird thing is although the product is advertised at: 6V-3.0W (Shimano Alfine Hub Dynamo 3.0 DH-S501, 6V-3.0W)

Im getting up to 40 volts? this is really unexpected as the product is rated at 6v, so im a bit confused

I made a full video of my recordings here:

https://www.youtube.com/watch?v=T6reqyk7L_I

So im going to buy a current regulator at 16.5v and see how that performs because this dynamo is working 10 times better than i expected

Or do I have the readings mixed up somehow, feels like its too good to be true?

For the board i brought this product:

Laxzo Universal USB Power Bicycle Handlebar Dynamo Charger for Cellphones GPS

https://www.amazon.co.uk/Laxzo-Universal-Bicycle-Handlebar-Cellphones/dp/B082NXX7XQ

only cost me £8.99, so effectively it feels even cheaper than buying all the components from scratch

I also made a schematic of the board and put it in the video at the very end

So im wondering if i can replace the current regulator (which is currently a: 5v 78M05 LXM) with a buck convertor, they appear to be doing the same function, current regulator / buck convertor, or am i wrong?

I like the look of: LAOMAO DC to DC 4.5-30V to 1-30V 12A Buck Converter Step Down LED Car Power Supply

https://www.amazon.co.uk/4-5-30V-1-30V-Converter-Power-Supply/dp/B00HV4EPG8

Because this dynamo is working 10 times better than i expected

You need to test it under load to see how much current is actually being produced...volts times amps = watts(actual current) one has little meaning without the other....so you want to plug something into the USB port with a known load...I use one of these... 5 volts at 2 amps = 10 watts

https://www.amazon.com/DROK-Multimeter-Multifunctional-Electrical-Capacity/dp/B00J3JSEG6/ref=pd_lpo_60_t_2/144-8699111-5708226?_encoding=UTF8&pd_rd_i=B00J3JSEG6&pd_rd_r=07822457-c73e-419f-b1b1-1c3c4169c91a&pd_rd_w=TN3dE&pd_rd_wg=pZ3zL&pf_rd_p=7b36d496-f366-4631-94d3-61b87b52511b&pf_rd_r=PW7PD8W224V8K46T8JGX&psc=1&refRID=PW7PD8W224V8K46T8JGX

If your hub only produces 3 watts, when you put a load that requires more the voltage will drop to zero... if we start with the assumption that we only have 3 watts being produced, then we can determine the amperage capability by dividing the watts by the volts available, and we get 3 divided by 5 = 0.6 amps....if your phone or light needs 2 amps, this falls short...so we need to test this...

The 78M05 is not a current regulator; it's a voltage regulator, and it can only supply a relatively small current (0.5A max). It also has a maximum input voltage of 18 V; if I recall correctly, you recently said that you had measured an output of 40V from your dynamo. That voltage would almost certainly kill a 78M05. (I've killed several over the years.) It's quite possible that the 78M05 is controlling some higher current device, which would be the actual current regulator, but I don't have the circuit diagram of the device.

On the other hand, how fast was your wheel spinning when you measured that voltage? Most inexpensive (and many expensive) dynamos/alternators/generators produce an output voltage which is approximately proportional to the speed of rotation, so if you had the wheel spinning faster than the spin rate of a normal bike ride, then you should expect a higher voltage output.

I assume that the unit you are using was designed specifically for bicycle use, and more specifically for consumer bicycle use, not for racing bicycle use. If that is the case, then it should produce at least the specified voltage when running on a standard bicycle tire at level street speed.