Keep those battery contacts clean...

[Chris(SoCenWI)]

Snuck out for a little detecting after a day at the hardware store. I hadn't charged my batteries after the last outing but thought there was plenty of charge left. After walking a few blocks started detecting and within a couple of minutes got the low battery sound. Sometimes I can keep detecting for a half hour or more with this sound going off. Today the machine gave the flat battery warning and shut itself off. I restarted a couple of times and tried to keep going; couple of minutes later same thing happened. Finally took out the battery pack and scraped the contact area clean with my screwdriver. Put the pack in and the power meter read half charged and no more problems.

So... If this happens to you... clean them contacts.

For the electronic geeks: I'm guessing the low battery fault is caused by a low voltage reading;I must have had a considerable voltage drop across the contacts to go from empty pack to half full. Just curious what the math for this looks like. The internal resistance of the pack plus the load of the machine plus the resistance of the contacts. Wondering what contact resistance might be.

Chris

 

[Cody]

Chris, the algebraic sum of the voltage rises and drops around a closed loop must equal zero. Sounds complicated but not so. Let say we have a power supply of 12 volts so the power is a rise in power. A resistor or contacts with a resistance has to be considered. We can start from the negative terminal or positive terminal and follow a closed loop. If we start with the positive then it would be +12-X-Y-Z=0 where X, Y, and Z are the voltage drops across the resistances.

However, here is a problem in that you have a drop caused by the contacts, assuming both have a high resistance but we also have the electronics of the detector forming a complex circuit. The resistances of the contacts would be in series with the complex circuit. If both contacts dropped 3 volts then it gets us a little closer. My guess without going further would be we are in the very high K ohms of resistance per contact.

This is just an example and not intended to be the correct voltages.

 

[Captain Kirk]

Chris,

You might be interested in looking at my post on the battery problems. I found some very poor workmanship on the battery holder for the replaceable batteries.

HH,
Glenn