Power difference

[Canewrap]

Why is it some detectors take 4 AA's and some take 8 AA's? A lot of the old analog machines took 8 AA's and it seems that quite a number of the newer digital detectors take 4. Is it because it take less power to drive a digital machine? Could the digital machines have more depth or computing power if they were using 8 AA's? Is the battery power tied to in ground performance at all?

 

[go-rebels]

Can someone remind us about the "power rule" regarding coil transmission? I remember it was something like a 6th power law, meaning to double the effective signal power into the ground required 2^6 power or 64 times the input power into the coil.

 

[Canewrap]

My question isn't just about depth. I'm wondering why some of the machines are using 8AA and some are using only 4AA? There are some modern analogue (Tesoro) using 9v batteries and some using 8AA. My main question is why?

 

[UK Brian]

It doesn't really matter how many batteries the detector has, its the power it was designed to use. So you could have a machine with two PP3's giving 18 volts but its regulated to work at 7 volts so will have a very long run time before the voltage drops to below 7 when the batteries will need replacing. A similar machine might have only the one 9 volt battery allowing a smaller case design/slightly lighter machine and the voltage regulated to 7 volts and the performance would be the same as the first detector but would need the batteries replaced much sooner.

Its often suggested that modern detectors are far better as far as battery consumption is concerned but its a bit of a red herring as many older analog machines had both more depth and less power consumption. The Arado 120b could manage 14 inches in ground on sites with little mineralisation on a Victorian copper penny (1.25 inches wide). Two 9 volt Mallory 1604's would last for up to 100 hours.

There are tricks used nowdays to reduce power consumption. Pulse machines use to eat batteries but modern designs don't. Dave Johnson (T2, MXT and dozens of other designs) cut half the weight off his Fisher Impulse by running it off a few AA cells by reusing power scavanged back from the coil.