In a prior thread, it was suggested that a 3-volt gel cell could be used to provide power to the Promark2 receiver for extended periods. I've been nosing around a bit on the web and have been unable to locate a 3-volt unit. I found one that's rated at 4 volts (technically not a gel cell, but a "sealed valve regulated lead acid" battery from BatteryStuff.com), and am wondering if that might be suitable. Any battery experts out there care to comment?


Modified By Jim Frame on 8/16/2001 at 11:59 AM

Jim,

There I go spouting off without looking. After reading this, I went and looked for a 3V cell. All I found was a theoretical lithium cell from Panasonic. I say theoretical cuz I can't find anybody that actually handles it !

If you can find/build a little circuit to drop/split the voltage to 3-volts the cell type shouldn't matter. Radio Shack used to have a soft-cover book with all these types of projects in them. If I can find mine I'll send you a copy of the circuit.

Jimbo

PS. Unless somebody from Ashtech knows that the input side of the PM2 has a voltage limiting circuit that will handle 4V input.

Jimbo,

ProMark 2 comes with a cable that will let you plug it into a 12v automotive accessory socket (once known as a cigarette lighter). If you don't want to leave a vehicle with the receiver, Radio Shack has a cord with such a socket on one end and battery clips on the other. 8-10 amp/hr gel cells generally run about $20 (often used for burglar alarm backup batteries).

Regards,
Brian

There's been a lot of discussion about this on the newsgroup sci.geo.satellite.nav, based upon information provided by owners of the Magellan 315, which appears to share a hardware platform with the ProMark2. For what it's worth (I can't vouch for any of it), what follows is the sense of the discussion so far:

It seems that the PM2 doesn't have an internal voltage limiting circuit. The speculation is that the 68000 processor needs 3.3v and cannot tolerate much more, so direct connection of unapproved batteries seems imprudent.

The 12v adapter reportedly has a switching voltage regulator that puts out 3.85v; when run through an internal blocking diode (intended to prevent reverse current flow), the result is about 3.25v, which satisfies the processor needs.

There is also reported to be an internal regulator that boosts the 3v provided by the two internal cells up to the 3.3v or so needed by the processor.

The safe approach would seem to be to follow Brian Ewing's advice and run any nonstandard input source through the provided 12v adapter. I haven't given up on the 4v idea yet, though, because the battery I'm looking at has a form factor that suits a setup I'm considering.

There is an external battery pack designed for the ProMark2 that delivers 18 to 32 hours of continuous data collection. It is from a small company in Grafton, MA. It uses the 12V converter designed for the Magellan 315.