R2 Charging Jack/Socket

I feel like I’m on the home stretch getting R2 back together. Tonight I worked on the electronics a bit more.

I plan on re-install the same three 12V 7Ah batteries. However, when the skins go on it’s going to be hard to charge them. So I’ve devised a simple circuit using some automotive relays to allow me to isolate them from the main electronics with a single switch, and charge from an external plug that will run to my Vector Charger.

I wanted to mimic something similar to how Luke charges R2 on Dagobah. The original plug used is some sort of stereo audio jack, but in real life it would almost certainly short when inserted, so I needed to find an alternative.

ESB R2 - Charging Port

After a lot of browsing various electronic and automotive stores I’ve decided to use a 12V car accessory plug and socket for bunch of reasons –

  • They can easily handle the 10-15A the batteries will pull when charging,
  • It’s hard to short the system when inserting it, even if everything is live,
  • If someone was to accidentally plug him into something unexpected – I’d rather it be a 12V device which is almost guaranteed with this type of plug. I couldn’t say the same if I’d gone with some other type of high-voltage plug,
  • Replacement parts are easy to find if I ever need to make up a new charging cable,
  • Theoretically I could plug-in and charge or run other 12V devices off of R2.

I’m going to install the charging port in the same spot as seen in ESB, and I need to make a shelf to hold everything as there’s no frame behind the hole. I cut a curved piece of aluminum that would become the shelf.

I then bent an angle in it to secure it to the new speaker bracket I made a few days ago.

Everything is held in place with just two 8-32 screws

Originally I was going to use a heavy duty DPDT toggle switch to isolate the batteries

But I had problems finding a suitable switch that would work. The one shown above was to really clunky, hard to toggle and not quite heavy duty enough to handle the potential load the drive motors would pull from the battery. So I opted to use a much smaller switch that would toggle the high load through a few standard 30/40A automotive relays. I’ll probably end up replacing these with 60A relays when I get a chance.

To mount the smaller switch I cut a small piece of acrylic and drilled a few holes that would attach it to the 12V socket plug.

I then heated it up for a few seconds to bend it into shape

I also added a status LED so that I’d know for sure when R2 is switch on

Here’s a shot of the back of the automotive relays that will do the switching. I could have probably just used one and just isolated the positive line, but I decided to play it safe and use a second to switch/isolate the ground line as well.

I’ve just bolted them below the support bracket using the same screws that holds the 12V car socket in place.

This is the setup with all the wiring in place.

When the light is green R2 is on, and the charging port is disabled/isolated from the batteries

When the light is off the charging port is live and connected to the batteries. All electronics in R2 are off and I can safely plug in the charging cable which will glow red to show it’s connected to the batteries.

At some point I may also add some red LEDs inside R2 to mimic what’s seen in the movie.

All that remains is the wiring diagram. This is the hand-draw one I worked from, but I’ll try and come back later and clean it up and verify that it matches my final configuration.

Again note – I’m not an electrical engineer so please double check everything if you’re going to try and implement what I’ve done.

Posted by Chris on December 27th, 2007 in Electronics | 2 Comments

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2 Responses

  1. Bob Ross remarks on

    Hi Chris,

    Nicely made and great choice for the charging plug !!

    Although I can’t exactly tell from your schematic, it looks like you have to provide power to the relay (& LED) to have the R2 in operate mode. Would assume the batteries go to the NO, the charger to the NC, and the electronics to the COM. This is going to waste some battery power since the pair of relays draw a bit since they are large. Would be better to swap the NO and NC connections so the R2 operates through the normally closed contacts. Also, you really don’t need to have a relay in the ground (negative) circuit. Switching the plus side is all that’s required.

    Hope this helps,

    Bob

  2. Chris Simonds remarks on

    Hey Chris, looks nice. I cant make heads or tail of what Bob said, but this guy knows what he;s talking about. I cant wait to get mine up and running like this. Congrats!!

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