How to add charging functionality to this homemade battery bank?

[scaryjam823]

So I recently bought a psp and one issue with it is battery life. 2-3 hours before it is completely dead. I looked around and bought same fake batteries for it off ebay, while they work, they aren't any better. So I got to looking around to see if anyone has ever made what I was looking for to solve this problem, alas nobody really has. So I put it on my shoulders to figure this out and hopefully write a tutorial later down the road if it works out, for anyone looking to do the same in the future. Because the battery life problem will only get worse and harder to find replacements as time goes on.

My goal is to make a battery pack that mounts on the back of the psp to boost the battery significantly. This is what I've come up with:

First is to use two 18650s (https://www.amazon.com/gp/product/B00WFXWUOE/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1) wired in parallel using this (https://www.amazon.com/gp/product/B01EJ9H79Y/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1) battery holder. This will add 6800mah to my 2200mah battery giving a big boost.

From the battery holder I will use this step up converter (http://www.prodctodc.com/ultra-mini-dc-256v-to-412v-step-up-converter-3v-to-5v-1a-phone-charging-module-mobile-power-supply-p-204.html#.WU1KIGjyuHs) to boost the 3.6v to 5v to allow the psp to charge. I will sacrifice a cheap charging cables end to go from the step up converter to the psp's charging port.

After ensuring everything fits and works correctly I will make a custom box from a larger hobby box to house all the components. After ordering everything and thinking about it, the only thing that is really missing is the ability to charge the batteries without taking them out of the pack. Which would be a great feature to add to this. So after some more digging I found this (http://www.ebay.com/itm/USB-5V-1A-1S-3-7V-Li-ion-Lithium-18650-Battery-Charging-Module-Charger-Board/172451426542?ssPageName=STRK%3AMEBIDX%3AIT&var=471295660016&_trksid=p2055119.m1438.l2649) Which I believe is what I need to charge the 18650s. What I am unsure of is how to connect this to the rest of the theorized battery bank.

My first thought is to just solder the battery case wires and the wires going to the stepup converter input to the output of the charging module. But I feel like if I did that and was charging while it was plugged into the psp it would send power through the stepup converter and cause some issue?

I'm not an expert at making custom things like this, I've done a good amount of repairs and feel confident in my ability to make this work. Just figuring out exactly what goes where is what throws me off, since I have little experience doing any kind of custom electronics. I'm trying to keep this as compact as possible. I have roughly 2 3/4"x 2 1/4" to make this work in. As far as thickness for the box that isn't limited, but obviously the thinner the better. So I don't have a lot of room to put stuff.

If anyone sees an issue with my design, can answer my question about where to put the charging module or has any other tips it would be greatly appreciated.

[bhorobec]

This seems like a good project that should work well. As for connecting the output of the charge circuit to the input of the step-up regulator, there's nothing wrong with doing this, it just means that the batteries will charge slower/not at all when the PSP is drawing a load, because the charging current will bypass the li-ion cells and be used to supply the PSP directly. Here are a few other issues you may or may not have already thought about:

You may not want to have the output of this battery bank always connected to the PSP. This is because the PSP is less likely to try to conserve power when it thinks it is plugged into a wall charger, so your 18650's might be slowly drained throughout the day while you're not using it. You could have a switch in-line with the output or just unplug the PSP from the battery bank when it's not needed.

Also, you might need to be careful with 2 18650's in parallel, because it is possible (quite easy) to accidently put one in backwards and cause the two cells to short out. Also, if the two cells aren't roughly at the same level of charge when you connect them, one will discharge to charge the other one, at an uncontrolled rate. So I would try to make the batteries non-removable so that you don't make either of these mistakes down the road.

Good luck with your project. You should post a link here to your tutorial/finished product when you're done.

[scaryjam823]

I thought that it might would just power the psp and not really charge the batteries if it was connected that way, just wanted to verify. As for that though, at default clock speeds on the psp a 5v power input can keep the device charged while in use. So basically it will trickle from the source through the 18650s, to the psp battery. Eventually keeping everything charged. However the intention is to only charge while NOT in use, as I have my psp overclocked it draws more power than a 5v source can produce. Which is a non-issue to me because at my rough calculations this will produce 12-16 hours of use before needing to recharge.

The battery draining could be an issue. But as I said 12-16 hours of battery life is a long time, that's based on heavy load testing with my 2200mah battery and using math to estimate time with the 18650s

Good to know about them being unbalanced. I will make sure they are at 100% charge before attempting anything. With every step I will be taking I will be checking voltage outputs before proceeding to the next step to ensure everything is working correctly BEFORE risking it on the psp. That was also part of my goal with adding a built in charger. To be able to secure the enclosure with some screws and never have to take the 18650s out, at least not for quite a long time. It is a lot easier for someone who doesn't know about electronics to plug in a micro usb cable, than it is to take two 18650s out with circuit boards crammed near them and charge them on an external charger.

I will go ahead and order the charge circuit since everything seems to be well. Some of these parts are estimated 2-6 weeks before delivery and I really need to have it all here before I can get started with anything. So it will be a while before I am able to start. I expect to be done in a couple days when I get all the parts however.

I am going to write the tutorial on gbatemp forum since that is where a lot of people will go looking for something like this. But I will gladly post a link to the thread when I get everything done.