Modding an Apple Mac Power Supply, Part 2

 Now that we've got the Apple power supply running, we need to hook it up to the charger.  It turns out that standard 110V blades fit perfectly into the GND and 12V slots, so we just harvest a couple from an old wall wart.

Solder onto 12 gauge wire.  My charger has 4mm bullets, so I soldered that onto the other end of the wire.

 Shrink wrapped.  I measured how far the blades would go into the connector, and measured the shrink wrap accordingly.

 The fit is nice and tight.  I don't think it will slip out, but if it does that's safe since it will lose connection to the hot wires.

 I used a piece of bigger heat shrink to hold everything together.  Go onto ebay and you can buy a lifetime supply of various sized shrink tube for a couple of bucks. I think this was 10mm shrink tube.

 I tried fitting a switch in place of the paper clip.  I learned that you can't solder onto a paper clip!  The Internet reveals that they are typically plated with some sort of alloy (tin/nickel?) that isn't attractive to solder.

A couple of old male servo leads worked nicely, but was wobbly.  I might run this with a length of wire, and then attach the switch onto the charger.  Till then, it's a paperclip jammed into the connector, which somehow pleases me very much!

Out with the old, in with the new.  Goodbye old Dell power supply, and thanks for the years of faithful yet kinda ugly and a bit underpowered service you provided.

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Modding an Apple Mac Pro Power Supply

 I got an old Mac Pro power supply to replace my puny old Dell.  The thing is massive!  79A of 12V power, that's over 900 watts!!

But, there's a catch.  Like all things Apple, it's a beautifully crafted, high quality unit.  And unlike the rats-nest wiring associated with PC power supplies, it's got a single clean wiring harness which is sadly undocumented on the Internet.

 I guessed the large connectors would be for 12V and ground.  Measuring the voltages would indicate the polarity.  BUT  How to turn the unit on?  I was looking for the equivalent of the PC's Green PWR Wire, the one that if shorted out turns on the power supply.

Going strictly by guess, I started shorting out pairs of connections.  I figured it couldn't do much harm, since none of the wires would be carrying current if the PWR wire were not engaged.

Using a paper clip, I quickly found the pair of PWR,GND connection.  I'm not sure which one is which, but for my purposes it doesn't really matter.  I made a note of the connections so that I'll be able to recreate them when I cons up a connector to the charger.

The outside big connectors are both GND, and the inside big connectors are both +12.2V.  The PWR/GND pair is the outside small connectors, second from the bottom.  The connector is oriented so the left side is smooth, and the right side has the edge.

A slight bit of fiddling showed that the small curve of a paper clip was the perfect size to connect PWR/GND.  I snapped a picture of it and will cover it with tape to ensure it stays put.

That's it for the experiment phase.  I'll use the flat blades from an old extension cord to bodge up a connector for 4mm bullets which is what my power supply uses.  I'll update when I do that!

Note: I think it's this model:  Apple 661-5011 980 WATTS POWER SUPPLY


Here's a video walkthrough:

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DIY DJI Inspire 1 Battery "Charger"

"DIY" is one of the watchwords here at EastBay RC, so you can imagine it's going to be an interesting experience to deal with a real store-bought system like the Inspire 1.

Our first project: a power supply for charging the Inspire batteries.  Here's the prototype, which is working well.

The DJI power supply has these features: rated output of 26.3V, 3.83A (100W), proprietary connectors for battery and radio.

In order to get the 26.3V, I'm using a boost converter.  It will take input from 4V to 25V and convert it to 26.3V. I got it on Amazon for $12.  You can get it for about $8 if you don't mind waiting for China shipping.  Specs on my unit are

• 9A max input, 6A max output.

Double check the ratings for the unit you get.

We'll go into more details in a followup post about how to configure the boost converter.  Here's my initial test connectors.  They are two prongs from an old extension cord, and fit perfectly into the battery.  Positive is on the left.  I'll do a video with some more construction details as well.

 Here's a second connector.  I glued the prongs onto a piece of scrap wood and insulted with liquid tape.  I double and tripled checked the polarity was correct.

Here's the final connector.  It works really well!

I can now charge the battery using any 12V-24V power supply, including my regular charger on Pb mode.  Charging from the car should be OK as well, but I'll double check the amperage requirements.

Anyways, hope this quick note helped, and if you're interested in seeing more DIY Inspire projects let me know!


Power Equivalence.  The table below shows the required amperage at several voltage levels in order to provide the equivalent power.  The first amps column is the straight calculated equivalent, and the second amps2 column take into account the approximate 10% power loss from the boost converter.

Watts Voltage  Amps Amps2
100      26.3  3.83
100      24    3.3    4.5
100      20    5.0    5.5
100      18    5.5    6.1
100      12    8.3    9.1

Note that the 12V amperage is just barely within the maximum amperage specified for my unit, mentioned above.

If you have a standard RC 4-button charger, you can set it to Pb (lead-acid), 20V, 5A and be just a little shy of the maximum equivalent charging capacity.

There's a rumor that the built-in charger of the smart battery won't current-limit. Sadly, too much of the DJI world runs on superstition, so until a battery dies and we get to do an autopsy, we won't be able to determine if this is true.  In the meantime, if you don't exceed the  Amps2 number for your power supply voltage that won't be an issue. (update: see below)

(Update) Some people have asked why "Charger" is in quotes in the title.

• The technically correct terms are "power supply" for the thing that plugs into the wall and "charger" for the circuitry that supplies electricity to the cells.  This is also the common industry usage.  A typical RC charger includes the circuitry to properly charge "dumb" LiPo batteries.
• DJI uses the arguably "technically incorrect but more commonly used" term "charger" for the power supply.
• Displaying EastBay RC's famously pedantic nature, we therefore put "charger" in quotes.

(Update) DJI has some good information on their wiki.  Specifically, this datum:

7. Over Current Protection: Battery stops charging when high amperage (more than 10A) is detected.

If this situation is detected, the document indicates that LED2 will blink twice per second.

So the total power provided to the voltage converter should be under 260 watts.

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