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The question then becomes how do avoid overcharging the batteries?

During long summer days, you can get more than 10 hours a day of sun - especially in Alaska, but really anywhere here in the western US. Batteries do a lot better with controlled systems that do not over charge. Over charging can reduce the life of the battery.

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Having bought my first panels back in '83', I've gotten a fair amount of experience.

1. No matter where you go, if you need several days worth of battery power, you also need additional support; food, water, shelter, etc. Your vehicle can easily haul your power station to your camp site.

2. Because of #1 above, it is better to invest in a larger panel (50+ watts) for 12 volt usage along with a charge controller, SLA battery (20+AH) and a small inverter.

3. Use the standard charger made for your NiMH, Li-Po or NiCad batteries. The better chargers will take care of charge tapering and/or full-charge disconnect.

4. As geowizard pointed out, getting a system operating to support longer campaigns is not difficult or requiring a degree in electronic technology. A visit to any alternative energy store can get you set up. I would avoid RS as they're having financial difficulties and it has been my experience that generally speaking the owners and employees know as much about electronics as a short order cook.

5. There is one additional upside to my opinion. The larger panel will provide additional campsite power and if Murphy visits, you have the ability to recharge your vehicle battery. A 5 watt panel feeding a 12 volt battery only provides about 0.3-0.35 amps/hour. A 50 watt panel supplies about 10X as much.

If you are paying just short of $1000 to several thousand$ for a MD, even more for your vehicle and camp gear, it would seem wise to invest a few hundred$ in a battery charging system.

BTW, you can buy SLA batteries in 2V,4V,6V and 12V at almost any battery store. Quit using the AA's and carry a SLA battery pack in a hip pack. SLA:sealed lead acid

eric

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Right on guys,I don't have that sheepskin either but 44 years in the electrical business dictates,"Don't scrimp on batteries and chargers". They are expensive until you need one.

 

dick

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Steve's solar set up is similar to what you are talking about, but he goes from the solar panel into a 12V based computer controlled battery charger. These chargers are a bit more expensive than a battery holder, but only a few dollars more than the battery holder. The difference is about the same cost as one set of 4 NiMH rechargeables. The flexibility of the charger is that it can recharge AA, C, D and 9v size cells, where the battery holder is for one size only, plus it offers overcharge protection.

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The other thing about solar direct to battery holder, and perhaps even with solar to most chargers is that the reaction is reversible!

Yup, sunlight can energize the cells and voltage can go into the batteries, but the reverse is true if it gets shady or dark enough - the stored energy in the batteries can cause the solar cells to produce light! The light emitted is in the infra red range so you cannot see it, but the batteries can be depleted and it can be bad for the solar cells. The concept of a solar cell is the same as the concept of a light emitting diode or LED. In the solar cell light hits a P-N doped semi-conductor and electricity is generated, the reverse action is an LED where electricity energizes a P-N doped semi-conductor and light is emitted.

Many solar electric systems have special power diodes to prevent this sort of thing. On a large panel, if part of it is in shade and part in sun (such as the shade from a tree), the voltage from the sunlight part can cause the shaded part to produce light, and the net production of the panel is greatly decreased.

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I used to fabricate/sell 6 and 12volt powered Game Feeders. This of course required a solar panel to keep things hot and working via a trickle charger for weeks unattended. In this case  to prevent reverse current flow at night and other low light conditions I simply put a blocking diode in the circuit.

 

dick

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Guest yellowman

The panel forward biases the diode when the panel output voltage exceeds the battery voltage plus.

 

 

 

 

 

 

 

 

____________________

fifa coins

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PI is a separate issue, but even there the old days of more power equals more depth is near an end. More transmit power does not automatically equate to more depth. More transmit power definitely eats batteries quicker, but paradoxically can result in poorer depth in VLF detectors.

I appreciate you are trying to be informative Chuck. Lots of good stuff, much of it helpful. I just want to make sure that people do not get the idea that the batteries used in a VLF detector offer any idea of the performance of the detector. That simply is not the case with modern VLF metal detectors. In PI units you can make a loose connection there, but as I said, going forward that is going to change. These days it is more about the receiver end and signal processing than it is transmitter power.

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The OUTPUT power is equal to the INPUT power! Ref: The Law of conservation of energy.

Yah, its a bit more complex than that. Electrical energy is used to run amplifiers and any speakers or headphones. Some electrical energy is simply lost as heat. I would say the output of the coil cannot exceed the input power, but there are other directions the power goes besides the coil.

One of the factors that affect depth of detection is that all radiant energy goes outward as a cube of the distance, and then the returning signal has its own distance cubed, so to try to detect deeper, one has to deal with the fact that the signal decreases with the distance to the sixth power.  (ten cubed times ten cubed).

There are many factors that are important in sensitivity, power is one, but there are a number of others.

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