Pedal generator - advice please!

Andy Hunt · Post by **Andy Hunt** » 22 Jul 2008, 23:23

I bought a pedal generator for my bike off t'internet and I'm trying to set it up with a little off-grid system.

The actual generator is some kind of permanent magnet system which you can also use in a wind generator design apparently.

First off I tried connecting it directly to the battery, but all that happened was that it started acting as a motor and driving the back wheel of the bike.

Then I tried connecting it into the same input on my solar controller as the PV panel, but it seemed to short out the panel somehow and stop it charging the battery.

So I bought another, separate, small solar controller and I've wired the pedal generator into it. This still doesn't seem to work unfortunately, and the back wheel still seems to want to be driven by the battery. It turns out the positive connections in the solar controller are connected inside.

Any suggestions as to how I get the thing to work would be most welcome!!

Kentucky Fried Panda · Post by **Kentucky Fried Panda** » 23 Jul 2008, 00:31

needs a diode to stop the flow back to the motor/generator.

Andy Hunt · Post by **Andy Hunt** » 23 Jul 2008, 08:52

Thanks Haggis.

I'm going to try swapping the two charge controllers around, I tried the pedal generator briefly on the other one and it doesn't seem to have the same problem, it's a more expensive charge controller so I don't know if that has anything to do with it.

Otherwise I'll try the diode . . . how do I work out which diode I need?

Steve Houseman · Post by **Steve Houseman** » 23 Jul 2008, 21:58

I think haggis is right that a diode would be ok to do some testing .

for some reason I was interested in pedal power output and seem to
recall (and just googled) 300w for a fit cyclist and that the
man powered flight was maybe up to 1kw (dont quote me on that),
what Andy Hunt might achieve over the course of an afternoon ...
who knows ..

You can attach any old cheapo DVM and measure your max volts I guess
ie with nothing connected .... should be proportional to your speed.

The reason the voltage would be important would be the max input voltage
of the controller should be able to take that - it is probably easy to
exceed the max voltage .

A simple starter would be to put the diode in, and see how that went .
The key parameters of a diode are the reverse voltage , the forward current
and to a slight extent the forward voltage drop.

I guess that the max reverse volts would be the battery or the
max PV volts if using a PV controller ie ~20V , the current ?
300w into 12V -> 25A (is your battery up to that? or are you

).

Maplin do a range of schottky diodes of 30->50V and 25A (eg N20CC) .
Doesnt say what the max forward drop is at that current ,
but guess 0.3V (might be 0.4?) , -> 25 * 0.3 -> 7.5W in the diode so would need a heatsink.

even at say 50w op -> ~4A (@13V) -> 4 * 0.3 -> 1.2W so still need a heatsink.
Tis a long time since I did this sort of stuff, but if keep delta temp to
say 100C then at 7.5W -> max thermal R <= 13C/W .
or maybe just a sheet of ali and bolt it to with an insulating spacer?
Can feel it and see if it gets too hot

If you have info on the generators chrcs then please post them .

Cheers,

Steve

Steve Houseman · Post by **Steve Houseman** » 24 Jul 2008, 11:04

Hello Andy,

Just thinking about this again today , and had a look on ebay to see what was
available and what params are normally specced . One I found had :

NEW AMETEK 1150 RPM 38 VDC SERVO MOTOR WIND GENERATOR

speed : 1150rpm -> 19.1 rps
Voltage 38 VDC
Amperage 0.2 Amps
Max Current 12 Amps

max power -> 12A * 38V -> 456w ?

not sure what the no load current parameter is ?

For this example, the chrcs are
- expected speed
- voltage at that speed
- max current out (ppresumably at that speed) .

This one is 38V dc (at the given speed of 1150rpm) , and for that ,
a 'buck regulator' would be the obvious format for an efficient controller .

If you have the data for your generator and what power you think you might
push out then I would be interested to hear that .

Cheers,

Steve

Andy Hunt · Post by **Andy Hunt** » 24 Jul 2008, 12:50

Hi Steve,

It's this one:-

http://www.econvergence.net/electro.htm

The Assembled Pedal-A-Watt allows you to drop your own bicycle in the included stand, pedal and create 15 to 25 vdc at 5 to 10 amps.

I've tried it with my more expensive charge controller and at first testing it appears to work OK.

The current doesn't go back into the generator and try to drive the bike wheel, so maybe this more expensive charge controller has some kind of arrangement inside it to allow appliances such as this to charge the battery. I've connected my PV panel into the cheaper controller which seems to work fine with it.

I tried it for 30 minutes last night and it seemed to charge the battery a little bit. According to the 'blurb' it will probably only have produced about 100 watt-hours in that time though, which isn't much I suppose.

I think I am just going to have to experiment with it a bit more and make sure it is working OK. Otherwise, there is a voltage regulator available from the supplier which will deliver a level 14.2V and convert the excess voltage into current, which is an option I could choose if it turns out that the pedal generator is exceeding the maximum voltage of the charge controller.

Will have a bit more of a tinker - thanks for all the advice!

emordnilap · Post by **emordnilap** » 24 Jul 2008, 13:00

Andy Hunt wrote:Hi Steve,

It's this one:-

http://www.econvergence.net/electro.htm

The Assembled Pedal-A-Watt allows you to drop your own bicycle in the included stand, pedal and create 15 to 25 vdc at 5 to 10 amps.

Price in US: $40
Outside: $140.75

Steve Houseman · Post by **Steve Houseman** » 24 Jul 2008, 16:37

Hello Andy ,

Thanks for the info , it is clearer to me now (I had confused myself
about what you had bought

.)

Please excuse my curiosity , but it is all a learning experience for me ... I used to do
electronics for a living , 2 lives ago , and had decided there was no point now
and thrown piles of stuff out .
However with the (probable) boom in home PV and wind , it feels as
as tho there could be possibilities to earn some bread some how ,
some way , in the near future, once I have become more familiar with the
various bits , or maybe not

.

(Adam x's explanation of battery chargers the other day was of great interest for me from this pov.)

Their regulator should do the job but doesnt seem cheap .

And as emordnilap said , that's expensive shipping !

All the best and let us know how you get on with it .

Cheers,

Steve

Post by **adam2** » 25 Jul 2008, 08:53

I doubt that a charge controller is needed, the main purpose of a charge controller is to avoid overcharging from unattended wind or solar sources.

A cycle generatort can not be unattended, and unless the battery is very small, you will get tired of pedalling long before the battery is full and at risk of overcharging.

I doubt that an average person will be able to sustain more than 10 amps into the battery, a very fit person might be able to sustain 15 amps, for an hour or two.
10 to 30 A/H could be useful, but is unlikely to overcharge any but the smallest battery.

I would simply use a blocking diode, with a rating of at least 20 amps, to allow a good safety margin, and voltage rating of at least 50 volts. An ammeter would be useful, and would assist in choseing the optimum gear ratio and pedalling speed to obtain the most amps for the least effort.
Anything connected to a battery should of course be fuse protected.

Andy Hunt · Post by **Andy Hunt** » 31 Jul 2008, 10:53

Thanks all, I appear to have got it working with my second charge controller.