Sega Dreamcast VMU AAA Battery Pack

The Sega Dreamcast VMU has a battery life problem. It eats CR2032s for breakfast. Changing the batteries involves using a screw driver. It's a hassle to maintain.

Features

This project adds a battery pack to the VMU that allows you to power it with 4xAAA batteries. This will prolong the battery runtime to around 4 times of the CR2032s.

UPDATE: The first batch of 4xAAA batteries quit after around 280 days of standby time.

Should the batteries decide to leak (even CR2032s leak sometimes), it will be outside of the VMU and far away form it.

Instead of being separated from the VMU and getting lost, the original CR2032 cover will stay on the back of this battery pack and functions as an essential part of the assembly with the stock screw.

If you've lost the cover and/or screw, you can print a cover that's provided with the project.

It does not physically interfere with other common controller slot accessories.

The outline of the battery pack allows using it for cable management.

You can even attempt to stand the controller upside-down on the battery pack, but it's too unstable to be called a feature.

BOM

The BOM of this project is very simple. All you would need is a pack of AAA battery contacts, 4 sets of screws and nuts, and two pieces of thin wires. I hope a simple BOM and non-destructive design would encourage more people to try out this project.

• 3D printed shell
  • Front
  • Back
  • AAA Battery Door
  • (Optional) Separator Pieces Left & Right
• AAA Battery Contacts
  • Single contact size: 9x9mm (not including soldering tab)
  • Double contact size: 21x9mm
    
    • I bought mine from Amazon for dirt cheap).
      Note the sizes in the description are slightly bigger than the actual product I received. Please check the actual sizes below.

• M2 Screw & Nut
• Wire thinner than 1mm in diameter.

Printing

Print the two main pieces in the following orientation, with support.

Assembly

Clean up the support material from the main pieces. Run the wire channels and holes with a dental pick if some support material is stuck inside.

Place the M2 nuts into the back shell and tighten a screw from the touching interface screw to pull them into the slots.

Insert a negative single contact into the front shell like this, only half way. Run a negative wire throw the top and out from the side, then solder to the battery contact. Finally, push the battery contact all the way into the cavity.

<OPTIONAL> Insert the left separator piece into place.

Insert a double contact with the positive side on the left into the cavity under the negative contact.

On the right side of the front shell, insert a double contact with positive on the top.

<OPTIONAL> Insert the right separator piece.

Now let's work on the back shell.

First, solder the positive wire to a single positive contact. Run the wire through the hole on top  of the left side of the back shell, then slide the single positive contact into its space.

On the right side of the back shell, insert a double contact with negative on top.

Finally, before closing up, take a good at all the polarities: 

Now, line up the two shells, and close them against each other, while making sure the wires coming out of the shell from the VMU cavity are not pinched. 

Make sure wires are run like shown.

Tighten the front and back shell together with the M2 screws.

Slide two single contacts into the top of the back shell. Positive on the left, negative on the right.

Bend the soldering contacts inwards so they wouldn't interfere with the CR2032 cavity on the VMU. 

A pair of flat-head tweezers will greatly help you with the bending operation.

Please check the photo below for reference:

• I bent the positive soldering contact twice to form a vertical touching interface so it will work with the battery contact on the VMU, and then the 2nd face with the hole for soldering the wire to.
• I folded the negative soldering contact only once, slightly inwards, so it doesn't interfere with the VMU shell, nor does it with the spring on itself. When soldering to the negative contact, make sure the wire doesn't interfere with the movement of the spring either.

Thread the wires through the wire channel on the back shell so they are flush to the surrounding. Run the negative wire under the bridge structure. Solder wires to their respective contact. Don't use too much heat or keep the iron on the contacts for too long, as it will deform the plastic.

This concludes the assembly part. Test continuity between the single contacts to make sure, and test for short between the top contacts because you don't want that to happen.

Usage

Undo the screw on the VMU and remove the CR2032 door.

Insert the VMU at and angle into the battery pack. If the contacts on the back are interfering, bend it slightly backwards to make space.

Insert the stock CR2032 door into the cavity on the back of the shell and tighten the stock screw. Do NOT over tighten it as it will deform the original door and can damage it.

Insert 4xAAA batteries into the battery pack from the bottom, note the proper polarity. The VMU should beep once the last battery is placed in.

Then, slide the battery door in from the back.

Replacement CR2032 Battery Cover

Since the original battery cover and screw are required to use this battery pack, I've made a printed replacement. You need an M2x6mm screw from the same kit to go with it.

Note: This version is incompatible with the stock VMU. Don't attempt to use it in the original position on the VMU.

Troubleshooting

You can test if the voltage is going into the VMU from the test point holes on the back shell.