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minelab voltage regulator

A

Anonymous

Guest
i have a minelab sd 2100 and i want to increase the input voltage from 6 volt to 7.8...they are finding that these detectors run smoother and go deeper at this voltage...can anyone tell me how to build an adjustable voltage regulator for it...my input voltage will be around 8.4 volts...i need a reliable adjustable regulator that will keep it around 7.8 volts...also can anyone tell me how to build an audio amp for a detector...these minelab detectors dont sound off very loud...thank you
 
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Hi Dave,
I am sure there are several people who frequent this forum who are familiar with people using an increased voltage on the SD's. However, I am not sure that any want to recommend a design without knowing the exact specifics of the SD itself.
Also, I am not sure it would be possible to build a true regulator that has an input voltage of 8.4V and and output of 7.8V. At least, I wouldn't want to try to build one.
Voltage regulators require a certain "overhead voltage" . By this I mean there has to be a certain minimum voltage difference between the input voltage and the output voltage. This minimum level varies and is determined by the various regulators available.
Typical voltage difference required may vary between 1.2V and maybe 2 1/2V difference for a regulator to regulate properly. There are a few regulators that will operate with less than 1V but normally they are for low currentts.
Now, I have read where some people are simply installing a diode in series with the batteries to reduce the voltage, but this isn't regulation. A diode will typically drop about .6V so an 8.4V supply will drop to 7.8V. However, one should be sure the 8.4V is actually 8.4V. In most cases, a fully charged battery will be higher, so the voltage applied could be higher.
You might try posting your request on one of the nuggethunting forums. I now that several people who frequent them have built up battery systems. You might try posting on the main forum at: http://www.nuggetshooter.ipbhost.com/ or at: http://nuggethunting.com/ipw-web/bulletin/bb/viewforum.php?f=1
If either of the above links do not work, just go to the appropriate website and then to the forum. The two websites are: www.nuggetshooter.com and www.nuggethunting.com.
Now,as to your request for a schematic for a small amplifier, I personally would recommend you simply buy the Radio Shack mini amp. This amp sells for about $13 or so and can be used as an amplifier for your headphones or an amplified external speaker. It is commonly used by many of the SD owners now.
Hope this helps.
Reg
 
>regulator that has an input voltage of 8.4V and and >output of 7.8V. At least, I wouldn't want to try to >build one.
LM2941 positive and LM2991 negative, 0.5V dropout voltage.
OK this is teoretical and don't consider the battery voltage after a little discharge became 8.2V or lower.
The solution for a stabilized power plus a strong discharge can be realized with an High efficency Step-Up converter via MC34063 or a ICL7660 (better solution) followed by a low dropout linear regulator like the LM2941.
The first+second stage can have an efficency form 80-85% using tantalium capacitors but you can discharge at lower limit the battery-pack.
... and not last, you obtain a stabilized and adjustable power!
 
Hi Fernando,
Thanks for the info but the ML requires a fair amount of pulse current. Considering the transmit coil is about .4 ohm, even at the original 6V battery supply, the current could be quite high. A quick calculation would indicate it could be as high as 15 amps. I doubt it is that high, but I dont' kow for sure.
Since I don't know for sure just what they are doing, I made the statement I wouldn't want to design and build a regulator. I guess I should have been more specific. Also, somewhere I read where the average current is somewhere around 1 amp, which would indicate the pulse current is quite high. So, a proper regulator should be able to handle what is required.
Yes, one could step up the voltage and then regulate it back down. This is counterproductive when simply increasing the voltage some would be the logical choice. Then a heavier duty regulator could be used. I certainly wouldn't be as effecient as a step up switcing regulator, but then again, it would be simpler and less noisy.
I would expect a switching regulator operating at several amps to be a noise generator also, and as such would have to be properly shielded to minimize any radiated noise.
As you can tell, building something that actually meets the current requirements of the ML is a little more complex than most people realize.
Several people have indicated they used a simple LM 317 regulator. This regulator will generally current limit at something like 2.5 amps or so, which may be enough to match the ML original current draw during a pulse, but I doubt it. Then again, I doubt anyone would really notice the difference either if it didn't.
Reg
 
thanks for the info on the radio shack amp...do you know the part number for it?...i looked on their website and they have a few different amps...thanks
 
Hi Dave,
The Radio Shack mini audio amplifier is part number 277-1008, I think. Most ML owners use this as an external audio amp and don't use headphones. However, it can be used as a headphone amplifier also. I am not sure too many people have tried it that way, though.
I have and it works quite well.
Reg
 
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