Nothing is Too Impossible

This project discusses a DIY rechargeable battery system for the TASCAM HD-P2 digital audio recorder, using NiMH rechargeable batteries. The project could be easily adapted for just about any type of electronic equipment. Rather than focus on the battery packs themselves, this project explains a flexible approach to connectivity.

Essentially, we build 2 separate rechargeable units, connect one to the main battery compartment of the deck, and connect the second, when necessary, to the DC power jack. This way we can see the battery level of the original set, and if/when it gets dangerously low, we can plug the 2nd unit into the DC jack and the deck will then draw power from the second unit. If we can stop recording for a minute or two (long break between songs, set break, etc.) we can switch the two battery packs so the level of the 2nd unit can be monitored.

The way we do it is to run a line from the internal battery compartment to a female plug, and run a line from a battery sled to a male plug. Plug the two together and we have power. We also build cable with a barrel plug on one end and a male connector on the other, so a battery sled can also be plugged into the DC jack.

I chose specific components for this project, but you can use whatever you have handy or is available at your local store. Minus the cost of rechargeable batteries, the whole thing cost me less than $10.

I used the Switchcraft TA (sometimes called mini-XLR) connectors that I had lying around. I contemplated using Molex connectors (a couple of dollars at Radio Shack or wherever) but I like the mini-XLR’s and had some in my parts box.

I chose to use AA rechargeable batteries, mostly for their size. You could just as easily use C or D cells, and get mega-recording time from your deck.

I used to use a sealed lead acid battery, but they are heavy and these days NiMH batteries are cheap. You can find rechargeable NiMH batteries at WalMart, Costco, etc. as well as a gazillion places online. I found inexpensive ones at http://www.batteryspace.com/, and they seem to be working well (note: their batteries are not pre-conditioned and therefore must be charged/discharged 5 or so times before you use them).

Ingredients:

• 2-conductor connector, male (3-conductor Switchcraft mini-XLR used here)
• 2-conductor connector, female (3-conductor Switchcraft mini-XLR used here)
• 2-conductor wire (I used some from a broken wall-wart)
• 8 cell battery sled for each unit you plan to use, plus batteries
• 1/2″ diameter wooden dowel
• Small wood screws
• Heat-shrink tubing, Solder

On each battery sled, I connected some 2-conductor wire to the leads on the sled, taped everything up, then attached a male mini-XLR to the end of the wire.

 

I created another cable with a barrel adapter that fits the HDP2 (if anyone has specs on this, please let me know) on one end, and a female mini-XLR on the other. A battery sled can then be connected to the DC-in jack on the HDP2.

 

While we could dismantle the HDP2 and hardwire some leads to the internals of the deck, it’s easier just to make a couple of wooden battery stand-ins and connect our battery pack to them.

I cut two pieces of the dowel a little shorter than a AA battery, drilled a small hole in the center of one end, and sanded it so it was a little smaller than 1/2″ in diameter. These dowel pieces will act as “stand-ins” for actual batteries and will provide power via the battery sled to the battery compartment on the deck.

 

The screw will act as a conductor between our wire and the contact in the battery compartment. I also sanded one side of it a little flatter to accommodate running a wire down its length. I cut a piece of 1/2″ heat-shrink tubing a little longer than the dowel, and cut a small hole in the tubing about 3/4 of the way from the screw end. I fed one lead of a 2-conductor wire through the hole, wrapped the lead around the screw and tightened the screw down. Then I slid the tubing over the dowel and heated it with a hair dryer.

 

I repeated the whole process to create a second stand-in for the other lead. On the other end of this wire, I connected a female mini-XLR. The image below shows this wire prior to soldering, surrounded by some shrink tubing and the base of the mini-XLR jack.

 

NOTE: When using a 3-conductor plug, make sure you write down which lead is connected to which on the jack as it is very easy to get confused. Fortunately, on these Switchcraft jacks, each pin is numbered.

 

The finished battery compartment cable appears here:

 

I had to file a small notch in the battery compartment cover so the wire could pass through it from inside the compartment.

 

And here is the battery compartment with the stand-ins in place. Note that in the image, both screw-ends face right, and the positive one is closest to us in the picture.

 

And finally, here’s the closed battery compartment.

 

So here’s its intended usage: You load up batteries into your sleds. Connect one of the sleds to the battery compartment and start recording. Most of the time, that will be it. If your battery meter indicates low batteries, plug the second sled into the DC jack (or swap the two sleds at an opportune moment). This setup has an added convenience for those who use cases that completely contain the deck (e.g. PortaBrace) in that you’ll never have to deal with the flap/battery compartment again.

 

11/24/06 - Addendum: I have found a charger that will charge the whole battery sled; this way you never have to remove the batteries from the sled. The charger was recommended by a tech over at batteryspace.com- Wherever you purchase your rechargable batteries you should be able to find a charger like this:

http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2350

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This entry was posted on Wednesday, November 22nd, 2006 at 8:36 am and is filed under Live Recording, HD-P2. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.