Introduction: Fast Charging Portable Power Station

About: Interested in green energy with a keen interest in human power.

There are many different "solar generator" or portable power station products out there in all kinds of sizes and capacities. These "generators" are really just batteries with USB, 12v and AC output that can be used to charge our portable devices or power a TV, fan, CPAP or even a disco ball - if that's your thing.

I've been on the lookout for one of these type of devices for a while. The lower priced ones have about the right capacity for my needs, but they don't accept much input wattage. I want to be able to use my pedal generator (see my generator plans: bike trainer, spin bike, exercise bike) to charge up the power station during my workout in the basement, then bring it up stairs and plug in my phone, laptop, iPad or whatever and charge those devices up with the watts I've generated. On my pedal generator, I'm usually producing 100-200 watts depending on how energetic I'm feeling. Most of these smaller (200-400Wh) solar generators only take 40-60 watts input.

What follows is my attempt to build a portable power station that meets my needs, and maybe it will work for you too. Here's my wish list:

  • Accepts 200+ charging watts
  • Can store 200Wh+
  • Has 2+ USB charging ports
  • Has 2+ 12v socket plugs
  • Is small and light enough to not be a burden to lug around the house or on a trip
  • Uses safe/stable battery chemistry (that rules out LiPo)

I did find one that takes up to 200 watts input and was the right size for my needs, but cost was over $300. This instructable version can be built for $100-200 if you have some of the parts already.

After trying Sealed Lead Acid batteries (SLA) in the past, the smaller ones that would work for something portable like this do not accept more than 20-40 watts charging, so I ruled those out. I had also charged LiPo batteries with my pedal generator, but the risk of fire with those scares the snot out of me. In doing some research, LiFePO4 batteries seemed to be just what I was looking for - high energy density, no fire risk, light weight, and will accept much higher charging wattage. The 8Ah batteries that I used (see the supply list below) will accept up to 10 amps each, so with 2 in parallel, I could potentially put 20 amps * 14.6 volts = 292 watts in! With these batteries, I'm only limited by my charge controller (and fitness level).

One other benefit of building your own portable power station - if something fails, you can easily fix/replace it - unlike many of these commercial products. If my batteries wear out after 500 cycles, it's easy to change them out. Maybe there will be even better battery technology in the near future, it'll be simple to drop new battery tech in.


Tools that I used for this build:

Step 1: Put Some Holes in the Tool Box!

I decided to put all the socket holes on the right end of the tool box, you could go either end or front or back, just plan your inside spacing accordingly.

The end measures about 7 inches across, so I drew a center line at 3.5 inches. I took all the socket components out of the 4 hole bracket and just used the bracket as a template. I lined up two of the holes on the center line I just drew, ensuring the bracket was up against the top edge to keep it square, then drew outline circles in the two holes, and holding in place, outlined the other two holes. Then I slide the template over and outlined two more circles giving me a total of 6 holes. Next I drew lines across the center of the circles to mark the center to line up the hole saw.

Hold the tool box between your knees or otherwise brace it, line up and drill out the holes with the hole saw.

Insert the meter, switch, USB charger and three12v cigarette/automotive sockets.

Step 2: Add Input Connectors

I chose to use Anderson Powerpoles for my input connection, and I'm wiring them directly to the battery bank.

I needed to cut a hole 5/8ths by 5/16ths to accommodate the two Powerpoles while they are in the bracket. I used a utility knife to cut the hole after marking it with a pencil. Of course I ended up slipping and cutting a little beyond the end on one cut as you can see. Go slow and keep going over the line with the knife and it'll soon be cut through. Check the fit and trim as needed. Once the fit is good, mark the two bracket holes and drill for the nylon nuts and bolts to secure the brackets in place.

For the wires in the Powerpoles, I soldered the connectors before putting them into the plastic housing for a more secure fit.

Step 3: Brace Your Batteries!

I used some cardboard to hold the batteries in the center of the toolbox to make it more balanced to carry and to keep the batteries from sliding around in transit.

First I measured from front to back of the toolbox, looks like about 6.5 inches at the bottom, but I want the cardboard to sit a little higher than that, so I made the cardboard with about 6.75 inches.

Next I drew and outline of where the batteries would go.

I drew then cut about 1 inch diagonal lines from each inside corner, then cut each line and cut out the center.

Step 4: Mount the Low Voltage Disconnect

The batteries that I chose for this project have a built in battery management system (BMS) but I don't want to stress them too much by running the voltage all the way down to 10v. Adding this LVD will hopefully help preserve the life of these batteries.

I mounted the LVD to the bottom of the toolbox by placing it where I wanted it, marking through the holes with a pencil, drilling out the holes and mounting with nylon standoff spacers, nuts and screws.

I set the LVD to cut off at 11.4 volts.

Step 5: Wire It Up!

I used 12 gauge wire for the most part, but had to use 14 gauge on the blue spade connectors as 12 gauge wouldn't fit.

To simplify the wiring, I used 6 Wago lever nuts, these things are awesome and seem to grip the wire pretty well.

See the wiring diagram to hook this all up.

Step 6: Charge It Up and Use It!

Now for the real test - can I put 200+ watts from my pedal generator into this battery bank?

Yes I can! The way I have it wired, and with the charge controller I am using on my pedal generator, the peak output at 14.6 volts is about 215 watts going into the batteries. I could have wired the batteries in series to get higher upper limit on watts, but wanted to keep things simple. The 215 watt upper limit is suitable for me.

I was a little concerned about heat build up in the tool box while charging, but after 30 minutes of putting about 140-150 watts into the batteries, there was no noticeable heat, the batteries were room temperature to the touch.

I really like this portable power station. It works for my use case. I will charge it with my pedal generator all winter long and use it to keep my electronics charged. I will probably use a 5 watt solar panel to keep it trickle charged in the summer since I'll be out on my mountain bike during the good weather. If you want to charge this with a solar panel - some low watt panels may be able to connect directly and the batteries will handle it, but best to use a solar charge controller to be safe. There is enough room in the toolbox to put a solar charge controller as I show in the picture, so if you plan to charge it by solar, just wire it in between the Anderson Powerpole input wires and the batteries. Note most solar charge controllers will take care of the low voltage disconnect, so that can be eliminated from the circuit. When I tried using a solar charge controller with my pedal generator, it didn't work for whatever reason so I left it out.

You'll also notice I don't have a DC to AC power inverter wired in. I try to avoid using a power inverter as most of them lose about 20% in the conversion from DC to AC. I picked up a DC to DC automotive charger for my Lenovo laptop, PWR+ makes a wide range of these adapters and will be much more efficient than using an inverter. If you need to power a device that doesn't have a DC adapter option, I'd recommend getting a Pure Sine Wave inverter, especially if you are running a TV or motorized devices like a CPAP. If I were to add one to this build, I'd get the BESTEK 300 Watt as it can be hard wired in and would fit nicely on the cover of the toolbox with some heavy duty Velcro to hold it in place.

Step 7: Update: Added a Power Meter

With just the volt meter, I felt a little blind to the watts/watt hours that were being pulled out of the portable power station, so I added a Drok power meter between the LVD and the output sockets, this way the meter isn’t on all the time and can give me a good reading on output.

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