I made a cheap mobile power outlet so I can power many things on the go. It would be great for camping or whenever you need power on the go.

I used 18650 battery cells (9) from used laptop batteries and a 75 watt car inverter. The cells cost me about $2 and the inverter was $5. This could charge an i phone from zero battery to full about 12 times.

It would be easy to use a larger inverter and more batteries to power larger devices. With about 10 lb of batteries (100 cells which would cost me about $15 in used laptop batteries) and a 1000 watt inverter you could power a microwave for almost an hour. Many other things like small refrigerators, tv could be powered.

Step 1: Building It

First I built the battery pack.

I uses 9 cells, 3 sets in series of 3 cells in parallel. Voltage 12.6-9 from full to empty. Max amperage is about 13.2. I hot glued the cells together and then solder the ends with 22 gauge wire to form the 3p3s pack. I solder larger wires to the positive and negative pack ends.

I then connected the battery pack to my inverter and plugged my soldering iron to make sure it worked. It started melting solder quickly just as if it were plugged into the wall.

I soldered wires to the inverter. I flipped around the part in front of the fuse so that it pushed the spring back to connect the positive. I soldered the negative battery wire to a switch. I soldered the inverter to the wires. I pushed these solder joints through the box for charging and checking the battery voltage.

I hot glued to inverter and charge wires to the box.

Step 2: Charging and Battery Voltage

I just use a 12.3 voltage transformer that is rated for 3 amp to charge the battery. You can plug it in and leave it for hours and it will not overcharge. The battery pack can charge to 12.6V but when the voltage gets to 12.3v it will stop charging.

You can easily connect a multimeter to the wires to check the battery voltage.

You should cut pieces of cardboard out on both sides of the battery pack to check the voltage of each cell. You can the charge cells to balance them.

Step 3: Plugging Stuff In

I plugged a few things into this power box and they all worked great.

So far i have tried a 12W soldering iron, an I phone, I pad and laptop.

Just keep in mind the power limits of your battiers and inverter. My inverter can run at 60 watts continuously and the batteries are good for about an hour at this power.
Blkhawk yes this is just what I had lying around. I would suggest building a custom wood box out of 1/4 plywood for larger versions of this and mounting the large inverter on top of the battery so it doesn't overheat.
<p>Could you find or make a better enclosure for your project?</p>
<p>also it is better to use step down dc - dc circuits rather then ramping the voltage up then back down again it is more efficent to step down then step up then down using a dc to dc unit can give you a longer running time for iphone and ipad</p>
<p>yes you can over charge with this you have 3 banks in series any one of these cells could be low meaning the other could over charge</p>
I wanted to be able to run many different devices. You could add a USB plug and 12V plug. As it is now you can connect to the charging leads to get battery voltage 12.6-9 volts unregulated. I use this mobile power mostly to solder. I live in europe now and with an 110V soldering iron with a short cord it is much easier just to plug into this battery pack. My 12 watt solder iron can run for about 6 hours on this battery pack before I have to charge it.
<p>also charging the pack with out a balance charger is not safe and is very dangerous as you could over charge one of the banks in the unit </p>
<p>with out a protection circuit you could very easy run the voltage down of one of the banks to below the limit thus killing said cells</p>
<p>it would be better to have a car accsory socket and using adapters that are ment to run on 12 volt rather then stepping up then back down again</p>
<p>Stepping up and then down does waste a significant amount of power as heat.</p>
<p>if you over discharge the batteries, it will kill cells one by one in their paralel packs.</p>
<p>series packs are the problem not parallel</p>
<p>you will no doubt find the middle pack is the one that drops in voltage first</p>
<p>I know, But what i am saying is, once one of the cells in the parallel packs dies, it will kill the other cells in its pack.</p>
<p>this pack i am afriad is 11.1 and is 6.6 amp hours making it a 73.26 watt hour battery</p>
<p>fo the phone you would be better stepping the voltage down as stepping the voltage up uses the current of the load plus inveter normainal voltage been 11.1 and capacity of the pack been 6.6 ah and the inveter at full 75 watt would pull 6.25 amp your pack is not going to last long</p>

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