Another Battery Replacement Option for AN/PSS-11 Detectors
by Bob Fischer, WB8BEL, at Fischer Technical Services
Early in my working career, I had the good fortune to work for a prime defense electronics company. I was not only able to work on infrared imaging (night vision) and metalllic mine detectors, I was selected to work on R&D of a non-metallic mine detector and a radio-remote-control system for jeep-mounted mine detectors. That was high tech work for the late 1960s. Eventually, I was promoted to my first job as a supervisor. It was production supervisor for AN/PSS-11 mine detectors. I guess that is why I have a soft spot in my heart for mine detectors.
A collegue, David Ison, came across an AN/PSS-11 detector at a flea market and presented it to me. I was looking at one for the first time in well over thirty years. It was in the original carrying case and appeared to be in excellent condition except that the battery cap was missing. The cap provides the positive case contact for the original battery in addition to securing the battery in the electronics compartment. The battery itself, however, proved to be a bigger problem than the missing cap. The original 10.4 Volt, BA-1389/U mercury battery is non-rechargeable and no longer commercially available. Do not let that stop you from putting one of these fine metal detectors back in service.
There are a couple of Web articles describing construction of replacement batteries. Mark Blair's article (www.nf6x.net/greenradio/pss-11/pss-11.html) says the detector is designed to operate from 7.25 to 10.8 Volts. He uses two Eveready 523 cells and a spacer to supply 9 Volts. Brooke Clarke's article (www.prc68.com/I/PSS11.shtml) suggests using four CR123 Lithium Photo Batteries that will deliver 12 Volts.
A quick look around the garage found nearly everything I needed to build a 10.8 Volt replacement battery using rechargeable AA batteries. The following construction details will be easier to understand if you look at the pictures first.
I found that 1/2 inch PVC pipe was approximately the same diameter as the original battery. When cut to 5-1/16" it fits nicely in the battery compartment. A flat rubber faucet repair washer was cemented to the "negative" end of the PVC pipe. The black wire of a DC power cord runs through the washer and is soldered to an eyelet that I cut off a crimp-on wire terminal. I rounded the eyelet with a file and filled the center with solder. The eyelet was then cemented to the washer. The "positive" end of the replacement battery is a brass washer. I ran the red wire of my DC cord through the center hole, doubled it back and soldered it to the washer near the hole. I picked up a ten AA cell battery holder on ebay for a few bucks. Nine 1.2 Volt NiMH batteries will deliver 10.8 Volts. I drilled out the negative solder terminal of the holder, ran the black wire through it and connected it to the negative end of battery #9. I tried over a dozen hardware suppliers before I found something with male threads that would screw into the battery compartment. The threads on a Swagelok SS-810-C compression cap for 1/2" stainless steel tubing will work. The stainless steel fittings are $13 each at the hardware store. Their brass equivalent is a Swagelok B-810-C. They are listed at less than $2 on the Web (www.partsprospector.com/pages/bihc-lab.htm) but I could not find any of them when I needed them. Drill a hole for the DC cord in the center of the cap then give it a coat of olive drab paint. The voltage of this replacement battery is within the nominal design voltage of the mine detector and the nine NiMH cells should provide more than the 35 hours service rating of the original mercury battery. There is plenty of room for the new battery holder in the original canvas pouch for the electronics unit. See the pictures.