Can Pedal Power Light Bulbs Increase in Brightness with More Effort?

[colintonks]

Hi

Well I'm back again with as usual more questions that answers!

Ok I would like to build to following as an educational tool:

The generator is MY1016 DC PM motor that can produce upto 200watts connected to a child's bicycle. Kids around 10 or 11 should be able to do a 40watts burst.

The idea is this, a vertical row of low voltage incadencent or halogen bulbs, each around 10watts.

As the child starts pedalling and produces <10w the first bulb is lit, then between >10w and <20w the second and first bulb are lit and so on. I like to have around 7 or 8 increments.

Any ideas?

Thanks for reading!

 

[vk6kro]

Have a read of a data sheet for a LM3914 chip. Available on Google.

This converts a rising voltage to either a moving dot or a column of dots.

So, if you had a suitable load on the generator (like a lamp or some high powered resistors) and it had a rising voltage as more power was produced, you could scale this to suit the display.

For big lamps, you would need relays and relay drivers, but it could probably be done.

 

[colintonks]

Hi vk6kro

I'll take a look at the chip thanks.

Ah so what you are saying is that as the wattage increase and the resistance increase, hence the voltage will increase and this can be measured?

I might be able to get a hold of a relay driver like this one:

http://www.morningstarcorp.com/en/support/library/RELAYDRIVER_ENG_R1_7_05temp.pdf

Do you think that would also suffice?

Thanks you so much!

 

[colintonks]

One other question:

If the voltage is going to continue to rise is this going to blow a bunch of 12v bulbs?

 

[vk6kro]

If you wanted this to be strictly accurate, you would have to get into some serious maths.
If it is just for kids to have a bit of fun, you can be a lot more liberal (dishonest :) ) with the readout.

As a starting point, you could just hook up a meter and some light bulbs and see what sort of voltages you get. Try to relate it to RPM by counting the pedal axle rotations and multiplying by the gearing ratio.

There are a couple of complications.
1)The resistance of light bulbs changes with power. As the bulb gets hotter, the resistance increases.
2)The power dissipated in a resistor is proportional to the square of the voltage.
ie power = (voltage squared)/ Resistance.

So it would take some clever circuitry with discrete components to compensate for this, or the obvious way is to use a Micro to handle the Maths.
A Micro could also handle the display smart stuff, although you would still need relay drivers.

 

[Bob S]

You might look at dc-dc (SEPIC) converters to produce a constant voltage output (e.g, 12 volts), independent of pedal RPM. So the pedal force (torque) will be lower for higher RPM. There are a lot of SEPIC regulator ICs on the market.

Bob S

 

[vk6kro]

In this case, he wants to have a voltage out that varies with the effort of pedalling to drive the generator.

I'm wondering if he could have one lamp getting all the power and when the voltage across it rises to 12 volts, a relay pulls in (and latches itself on) and also switches in the next lamp in parallel with the first.
There would be a dulling of the first lamp when the second one came online and the two lamps would brighten with more effort.

Then do it again with a second relay and then a third etc.

So, if they were 15 watt lamps, you would have genuine 15 watt, 30 watt, 45 watt and 60 watt etc steps.
This would be more accurate than trying to do it with just the voltage and also easier to explain to kids and parents.