Game Gear Internal Battery Charger

Wanted to share something. I can explain in more details if people are interested.

 

This is beautiful. Thank you for sharing!

 

I'm currently looking at doing this for a Game Boy, so would definitely be interested in seeing what method you used and whether it would fit.

 

The charging circuit is based around the MAX712CSE+ It supports 1-16 cells. However there might be a better solution for 2 cell. If you read through the datasheet it tells you what you need to know. You will need to compute one resistor, wattage and resistance based on the number of cells/mah/voltage etc. This chip also supports temp turn off which I'm not using. It just does a basic deltaV and once the batteries stop taking voltage or the time runs out (in my case 3 hours) the fastcharge shuts down.

Here is my main PCB:




It terms of wiring, at least on the game gear you need to separate the batteries, power in and load out. I had to cut a few traces on the GG power board.

The led works using an inverter and NOR gate. The normal power light is still controlled by the GG itself, so when voltage goes to low it will still flash. If you plug in the power to initiate the charge the MAX712CSE+ has an output pin that tells me if a fastcharge is in engaged. I pump this into the NOR gate which shuts down the red LED.

I will take more pictures of the inside, but I had to drop a few inline diodes last night for the LED circuit, so its no pretty. Once I get it cleaned up I will show it off some more.

The transistor I'm using does not require a heatsink, I see temps around 65c under max load (Thats with the case apart though). I will more than likely install one still just to try and help keep everything cool. With a 2 cell project you could use a smaller transistor, maybe even SMD.

 

Couldn't you just replace the power board all together and accomplish the same thing? I have taken about countless game gears to recap them. It would seem to me at least that it would be possible just to make a replacement power board. It contains the positive and negative side of the battery terminals, power jack, and power switch. Just a thought.

 

Nice!

 

This may seem a little stupid, but what do the calculations equate to in real terms? I have calculated PDPNP at 4.725W, RSENSE at 0.0003 and R1 at 0.5, but have no idea what components I should use to fit these parameters e.g. does 0.5 equate to 500 ohm?

 

That would make for a very clean install. But it would be quite a bit harder than this simple soultion. If you look at the schematic there is quite a bit going on. Yes we could replicate the IC's functions etc. But is it worth the added cost and time?

Are you doing this with a 2 cell design? R1 regulates pretty much is just acting like a voltage reducer to supply 5V to the IC based on the wallcube. I used a linear regulator instead, the LM3480. If you are only charging two cells you could use a 5v charger and not even need a regulator or R1 for that matter.

They explain Rsense kind of wrong. Since they don't tell you to convert units. When you calculate |FAST use ah not mah to make it easier.

My calculation was like like this .25v/(2.3ah/3hours) which was around .3 Ohm

Make sure you use appropriate wattage for the resistor as well, mine is 1/2 watt

 

Have you done any "real world" testing to see how long a full charge lasts on your current setup?

Also, what was the thought behind going with NiMH when lithium ion is so plentiful?

Great work, by the way! This plus McWill's LCD mod would make the GameGear actually usable in a modern sense.

 

I will have numbers soon. I've left it on to discharge the batteries but it seems to turn off when I'm not around. I was more testing the charge circuit. I feel like I should have equal or better play time. I considered Lithium Ion but I didn't want to the destroy the back area. I like the look/fitment of AA in the there stock form. I'm sure I could handle a balance charger etc. but this nimh was just "easy"

 

Very cool.

 

Trying to avoid making the Game Gear Note 7, eh?

 

I must express my deep dismay and shock at your utter disregard for human feelings and general insensitivity. You see, good sir, my kin has passed away in a similar manner. And despite the opposing parties chortles and giggles, it is most certainly not humorous.


But cool mod.

 

You could use 14500 lithium cells, exact same size as AA.

 

They are a higher voltage.

 

True but I'd also have to modify the internal cut off so it doesn't over discharge the batteries.

 

What in the hell are you talking about?

 

I had based it on using a 7.5V charger, as that's what I found on eBay with a 2.35mm connection. I could obviously adapt a 5V source easily enough, but in the long run it would be cheaper and quicker to base it on 7.5V.

I'll be using a 750mah 2-cell design, so I figured that a 1/4W 25ohm resistor would be OK, followed by a 1A transistor and a 1N4001?

As for RSense, I'm still not too sure. I'm basing it on a charge time of 90 minutes based on the 80% efficiency rating and 1C battery charge rate, so my calculation looks like this: .25v/(0.75ah/1.5hours) = 0.5ohm

 

http://i.imgur.com/wJ5fcq8.png
http://bgr.com/2016/09/08/note-7-explode-fire-recall-florida-samsung/

possible to maybe add wireless charging? I know how awesome to be to have the charge in display cases, until use.

 

Perfectly doable - a Qi charging pad could easily just be stuck on the back of the battery cover, although I'm not sure about the amperage.