Step 3: Charging System / Solar Panels
The solar panels need to be as large as possible to maximize the available wattage, but they also must provide the right voltage. Solar panels produce a range of voltages, which peak and drop, but the nominal voltage of the panel is what matters for selecting the right charge controller. I purchased 3 Q-cell brand mono-crystalline solar panels that I found on Ebay for $110 each. They produce 21.8 Volts peak and 17 volts nominal, at about 1.2 amps nominal. With the 3 panels wired in series, this makes around 66 volts peak and 51 Volts nominal, which is plenty over the 42V needed to charge the batteries. a basket was added in the front to accommodate the third solar panel.
From Ohm's law Power (P) is equal to voltage (V) times current (I), (P=V*I), so the panels produce ((17Volts*3)*1.2 Amps)= 61.2 Watts nominal, and over 80 Watts peak. A Maximum power point tracking (MPPT) charge controller tricks the panels by hiding the battery load from them and allowing them to operate at their peak power when conditions allow.
A charge controller was purchased from www.solarsellers.com, where Mr John Drake was very helpful in assisting me and ordering a custom charge controller for my application. The controller basically takes the varying voltage / amperage input from the solar panel array and converts it into a constant voltage (42V) or current, to optimize charging the 36 volt source. Maximum input voltage to the controller is 100 Volts, so the peak of 66 Volts will not harm the controller. The controller is a Maximum power point tracking (MPPT) type, which charges faster as more sun is available, rather than at a set rate as most controllers do.
In order to charge the batteries in a practical amount of time, they need to charge about as fast or faster than the provided 110V wall socket to 36V charger/converter, which charges at a rate of 1.5 amps. At 1.2 amps the panels do not quite achieve this, but with the MPPT Controller it takes right around the same amount of time for a charge. The bike is stored in a location that gets a few hours of sun every day (where I live the sun is pretty reliable), which keeps the batteries topped off and ready to go whenever needed.
And for those of you wondering, the electric motor draws up to 20 Amps, and the 1.2+ Amps added by the solar panels do not make it go faster, since the 1.2 amps are routed through the controller and only serve to charge the batteries. The motor speed controller does not see this extra Amperage, and outputs just the same as without panels, except the batteries will stay charged slightly longer, (extending your range) with the net drain being (20-1.2)A= 18.8A rather than 20A without the panels. The motor only pulls 20 Amps when taking off though, so the draw is much less when at cruising speed. The motor speed controller cuts the voltage off at 32V to keep the batteries from going below 10.5V, but I monitor the voltage and try not to discharge the batteries below 36V.
From Ohm's law Power (P) is equal to voltage (V) times current (I), (P=V*I), so the panels produce ((17Volts*3)*1.2 Amps)= 61.2 Watts nominal, and over 80 Watts peak. A Maximum power point tracking (MPPT) charge controller tricks the panels by hiding the battery load from them and allowing them to operate at their peak power when conditions allow.
A charge controller was purchased from www.solarsellers.com, where Mr John Drake was very helpful in assisting me and ordering a custom charge controller for my application. The controller basically takes the varying voltage / amperage input from the solar panel array and converts it into a constant voltage (42V) or current, to optimize charging the 36 volt source. Maximum input voltage to the controller is 100 Volts, so the peak of 66 Volts will not harm the controller. The controller is a Maximum power point tracking (MPPT) type, which charges faster as more sun is available, rather than at a set rate as most controllers do.
In order to charge the batteries in a practical amount of time, they need to charge about as fast or faster than the provided 110V wall socket to 36V charger/converter, which charges at a rate of 1.5 amps. At 1.2 amps the panels do not quite achieve this, but with the MPPT Controller it takes right around the same amount of time for a charge. The bike is stored in a location that gets a few hours of sun every day (where I live the sun is pretty reliable), which keeps the batteries topped off and ready to go whenever needed.
And for those of you wondering, the electric motor draws up to 20 Amps, and the 1.2+ Amps added by the solar panels do not make it go faster, since the 1.2 amps are routed through the controller and only serve to charge the batteries. The motor speed controller does not see this extra Amperage, and outputs just the same as without panels, except the batteries will stay charged slightly longer, (extending your range) with the net drain being (20-1.2)A= 18.8A rather than 20A without the panels. The motor only pulls 20 Amps when taking off though, so the draw is much less when at cruising speed. The motor speed controller cuts the voltage off at 32V to keep the batteries from going below 10.5V, but I monitor the voltage and try not to discharge the batteries below 36V.
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The Panels are made by a brand called Q-cell, I got them off Ebay, but in general, you should not have to pay more than 3 or 4 dollars per watt.
As for panel / battery voltage / amperage, the requirement of your panels is determined by your battery voltage. If you have a 36v battery, (or 3 - 12v batteries in series), you need a solar panel (or panels) that will be able to charge these batteries using the nominal voltage rating of the panels. For example:
A 12 volt battery charges at around 13.8V, with 12v being the nominal voltage. Now with 3 of these in series, gives you 36 volts nominal and around
42.4 volts needed to charge the battery/batteries. This means you need a solar panel or solar panels that will give you at least 42.4v nominal. A little higher voltage output from the panels is desired since the nominal rating is given for high noon on a sunny day, and you don't want your batteries charging from only 12:00pm to 12:01pm. So a panel with a little higher voltage
will be fine, since it will give the needed output voltage to charge the batteries throughout the day rather than only during a short time when the solar output is greatest. It is the solar charge converters job to regulate this varying voltage coming from the panels, so even if your panels are making up to 100v it will still charge your batteries at the proper charging voltage.
Check out the forum, if you search around on there you can find answers to any questions you might have regarding the electric motor kit / battery setups.
Thanks- David
golden motor forum
Cheers,.
timothywooi@gmail.com
Ideally you could setup a solar charging station at camp, and have two sets of batteries. Make them easily come out and connect to the bike and the charging station. Then you'd have more range at night :) Don't forget to include enough power to light it up!
Now I want one.
You need to rectify the AC from the dynamo to DC using a bridge rectifer,a typical 3Amp 100V PIV will suffice.
A typical 0.7 Volt will be loss after rectification and that is why you need at least 20% higher AC voltage to compensate conversion loss.r
Harnessing & regenerative collection of Energy,
timothywooi@gmail.com