Direct charge, grid tie or battery bank?

What is the best use of your pedaling time on a pedal generator? There are 3 typical avenues you could direct your watts:

  1. Direct charge: Directly use the watts coming out of your pedal generator, once converted to useful 12 volt current, and charge your devices using car chargers.
  2. Grid Tie: Use a grid tie inverter to send all your pedaling effort into the nearest wall outlet.
  3. Battery bank: Charge a bank of lead acid batteries.

There are advantages and disadvantages to each of these.

Method Pros Cons
Direct charging Efficient – 90%+ charging efficiency. You will need to round up enough gadgets to create the appropriate resistance for a good workout.
Grid Tie Directly offsets your utility bill with watts generated. Grid tie inverters are about 80% efficient in practice.  Put in 100Wh from pedaling, only about 80Wh will be put back into the grid.
Battery bank For those living off grid, augmenting their battery bank may be a necessity. Lead acid battery charge efficiency is only about 85% – so if you put in 100Wh, you only get out 85Wh.  Couple this with the efficiency losses of a charge controller and an inverter to get it back out as AC, and you might get 50% of what you put in.

I advocate for direct charging, and I’ll explain why.  Going out on a limb here, but I’ll assume everyone uses a mobile device or two, and maybe a tablet. Assuming you charge these things regularly, let’s look at the scenario of charging these using the methods above.

Direct charging:

Pedal generator -> Charge controller (90%+ efficient) -> 12v car charger  -> device(s)

Grid Tie:

Pedal generator -> Grid tie inverter (80% efficient) -> 110VAC wall charger -> device(s)

Battery Bank:

Pedal generator -> Charge controller (90% efficient) -> Battery bank (85% efficient) -> DC to AC inverter (90% efficient) -> 110VAC wall charger -> Devices(s)

As I discovered in the previous blog post, wall chargers have losses up to 30%+, whereas 2 out of the 3 car chargers tested had losses of just over 1%. Using either grid tie or a battery bank may result in 50% or more of your efforts wasted on conversion losses.  I do want to point out that the charge controller used in my pedal charger design is 90%+ efficient, so you will lose up to 10% in that conversion, resulting in a max of about 12% loss if you include the car charger losses – but far better than the other two alternatives!

Comparing USB chargers for charging the iPhone 7 Plus

I use a stationary bike pedal generator to charge my cell phone and other devices.  Getting the most watts into my devices helps me make the most of my pedaling time. A typical 1 amp charger puts about 5 watts into most phones, but will take several hours to charge even the smallest device battery. In this post, I’ll compare the output of several chargers and how many watts they can put into my iPhone 7 Plus.

Chargers included in this test:
1. Original Apple 5 watt wall charger
2. Original Apple 12 watt wall charger
3. RAVPower 24W 4.8A (2.4A x 2) Dual USB Wall Charger
4. PowerGen 4.2Amps / 20W Dual USB Car charger
5. Anker 24 wattdual USB PowerDrive 2 Car charger
6. Anker Quick Charge 3.0 42W Dual USB Car Charger

While testing each device, the phone was plugged into each charger with a low state of charge (~15-25%) and left on the charger for a couple minutes to ensure the circuitry of the charger had time to identify the device and provide the maximum charge it was capable of delivering. We use a low battery as the rate of charging slows once you approach 80-90% charge on the battery. You may have noticed getting the last 10% charge into your phone seems to take an eternity. This slower rate of charge is to protect the battery from damage and is by design.  Let’s see how each of the devices fared in this test.

The results

Device Watts delivered  
Apple 5 watt 4.74
Apple 12 watt 9.94
RAVPower 9.49
PowerGen Non-Apple port: 2.36
Apple port: 9.13
Anker 24 watt 9.82
Anker 42 watt IQ Port: 10.18
QC 3.0 Port: 4.81

As expected, the 5w Apple charger delivered just under 5 watts.  The 12w Apple iPad charger kicked out over 10 watts initially but settled into just under 10 watts after half a minute or so.  The PowerGen 12v car charger non-Apple port was the worst of the bunch, pushing only 2.36 watts, however it’s Apple specific port cranked out a respectable 9.13 watts.  The 24 watt Anker managed about 9.82 watts out of each USB port.  The final USB car charger in the test, the Anker Quick Charge 3.0 and IQ charger managed less than 5 watts out of the QC3.0 USB port, but cranked out 10.18 watts out of the IQ only port.

Overall winner: Anker 42 watt!

I suspected based on my experience using these chargers with my stationary bike generator that this would be the outcome I would get, but it’s was good to have metrics on the actual watts going into my phone.  Pushing only 10 watts on the pedal generator requires almost zero effort, so I typically change my iPhone along with battery banks (I’ll review what works best among those later) and any other devices around the house that need a charge.  Adding more devices to the mix creates more resistance when pedaling.  Devices I typically include are iPads, other family members cell phones (if I can pry them away long enough), an iPad mini, an iPod Touch, my Microsoft Surface Pro 3 , Chromebook, bluetooth headset, FitBit, and cordless drills to name a few.  I try to get 60 watts or more in order to get enough resistance to make it feel like I’m doing something.  I’ve been able to generate over 180 watts with the pedal generator, but I can’t sustain that for too long.  I’ve found the best range of wattage resistance for me for any length of time has been between 60 and 130 watts.  In future posts, I’ll test the limits of the pedal generator (and myself!) to see what the upper end of wattage is that can be produced.