Ever since I got my Z88, I’ve always been worried about running low on batteries. 20 hours on one set of batteries is nice, but good batteries are not cheap. Almost immediately I picked up an AC adapter for the Z88. This allowed me to work without the worry about going through batteries.
Since I always carried my AC adapter, I’ve never been too worried about finding a place to plug my Z88 into. That was until I went on one trip. I set up the Z88 on a desk with a lamp next to it. The only outlet close to the desk had the lamp plugged into it. Since I needed to use my modem (which takes up one plug), I was forced to run the Z88 on the internal batteries. Now, the most power hungry part of the Z88 is the serial port, which I was using to connect to the modem. This had me really worried about battery wear.
One neat feature of the Z88 is that the input at the AC adapter input is the same as the input from the internal batteries, 6 volts. I had heard about other Z88 users hooking in larger batteries through the AC adapter port and getting months of use.
I finally decided to build an external battery pack. I could have used a large rechargable 6 volt cell, but I wanted to keep to using standard batteries. To get the 6 volts for the Z88, all I needed was 4 1.5 volt batteries. Most standard batteries (A, AA, C, D) are 1.5 volts. I went with D cells because they were about the biggest I could get and did not cost that much more than C cells.
After looking at various electronic surplus places, I found that good old Radio Shack had exactly what I needed. Basically I needed a battery holder, a box to keep it in, and an adapter plug to fit the Z88. Below is the parts list for this project:
270-627 Experimenter Box (6.25"x3.75"x2")
270-396 D Battery Holder (6 Volt)
274-1569A Coaxial DC Power Plut (male) 5.5mm OD
2 Lead wire (same gauge as on an AC adapter)
3/8" thick Foam Rubber
4 Screws
4 Rubber Feet
The battery holder does not fit square in the box, it fits in at a slight angle. The box is plastic with a metal cover. I wanted to call the metal cover the bottom. Since I would be easier to mount the plastic battery holder on the plastic box than the metal plate, I mounted the battery holder upside down in the box with plastic model cement (use lots).
To let the lead wires out, I drilled a small hole near the top of one end of the box (since I put this all together upside down, it looked like I drilled near the bottom of the box.).
The two wires coming from the battery holder are not long enough to reach out of the box, I ran the other wire into the box and attached it to the battery wires. To make a good connection, I twisted the wires together, put some solder on the joint, and wrapped them with electrical tape. To keep the wire from being pulled out of the case, I wrapped some electrical tape on the 2 lead wire so it would not allow the wire to be pulled through the hole.
The length of the lead coming from the box to the plug can be as long as you want. I went with a fairly long lead about 20 inches. I connected the plug to the other end of the 2 lead wire. The Z88 requires that the inner part of the plug is positive ( be sure to get this right or you might blow your Z88 ). I would be usefull to use 2 lead wire with one lead marked ( usually with a painted stipe down it’s length ). The positive lead coming from the battery holder is the red one. I soldered the wires on and then ran some electrical tape around between the two connecting points. I wanted to make sure that I did not get a short in the system.
Once I had this all hooked up I put the batteries in the holder and, using a multimeter, checked to make sure that I was getting 6 volts on the plug. Since the batteries were fresh, I was actually getting about 6.5 volts.
I did not want the batteries to fall out, especially since there were going to be hanging upside down, so I put in some foam rubber to support the batteries and the battery holder. I did not glue the rubber to the metal cover, since some glue will eat foam rubber, plus I did not feel a need to have the rubber mounted.
I found it odd that the box had 4 mounting holes, but came with only two screws. The screws were too tight in the mouting holes, so I bought some smaller screws to make getting to the batteries easier. The screws stuck out beyond the cover and would scratch a table surface, so I got some stick-on rubber feet to prevent this. The metal cover is fairly tight and fits the box well. To make it easier to get the lid off, I created a small notch in the cover with a metal file. I did it just big enough to get my finger nail in and be able to pry the cover off.
Total cost for the project (not including batteries and wire) was under 7 dollars. Since I took my time to get everything right, it took me about 1 hour to build the battery box.
Exactly how many hours I will get out of the 4 D cells, I’m not too sure. I do know it will be far more economical than using lots of AA’s.