Need 12v, 500mA for 10-12hrs- lightweight

[Jim Elbrecht]

So my clock capacity tester has shown me that I've got a lot more bad
batteries than good ones. So I'm in the market for some new NiMH
cells.

I was going to use my wealth of AAs to run a wireless headset on my
metal detector.

The wireless system was designed for a car [12v - or should I call it
13.6?]. All I can find for specs on it is that it is rated at
500milli-Amps. It is a Luxma transmitter that I bought on ebay.
Looks like the transmitter that goes with this set-
http://www.luxmt.com/pages/lhp888ht.asp
[the headset came from Newegg, is also part of that set- and Newegg no
longer has them]

I want the battery pack to be able to run it 10-12 hours- though it
isn't likely I'll ever be away from a charger for that long.

Weight is a concern as it is on a metal detector- and I'll be swinging
it with one arm for extended periods.

My first thought was to run it on 8 AAs. [I've wired it up and it
works on 8 [alkaline] AA's- but I don't know for how long] Then I
wondered if 10 or 11 would be better. . . . or a combination of 9v &
AA's. . . . or a single 12v. . . .

My lack of knowledge makes me ask--
*If* the 500mA is a constant, and I'm using 10 [to keep the math
easy] 2700mAh AA batteries to produce 12v- do I then have 27000
mAh's- and in theory could run the thing for 54 hours?
[if true, then I might go with alkalines instead of rechargeables- 50
hours is probably more than a couple months of use]

Thanks again-
Jim

 

[Randy Day]

Jim Elbrecht wrote:

[snip]

My first thought was to run it on 8 AAs. [I've wired it up and it
works on 8 [alkaline] AA's- but I don't know for how long] Then I
wondered if 10 or 11 would be better. . . . or a combination of 9v &
AA's. . . . or a single 12v. . . .

Two of those square 6v lantern batteries
would work, but that's a bit weighty.

You might consider a motorcycle battery or
deep-cycle marine battery, if you have a
boat shop near you. You should be able to
find a battery of reasonable size and capacity.

Do you have a Battery Boys or similar battery
retailer in your area?

My lack of knowledge makes me ask--
*If* the 500mA is a constant, and I'm using 10 [to keep the math
easy] 2700mAh AA batteries to produce 12v- do I then have 27000
mAh's- and in theory could run the thing for 54 hours?

No. Stacking them in series to get 12 volts
means you still only get 2700mAh. Putting
them all in *parallel* would get you 1.5
volts at 27000mAh.

2 strings of 8, wired together at the ends,
would get you 12v at 5400mAh, 3 strings gets
you 8100mAh, and so on...

[if true, then I might go with alkalines instead of rechargeables- 50
hours is probably more than a couple months of use]

HTH

 

[ehsjr]

So my clock capacity tester has shown me that I've got a lot more bad
batteries than good ones. So I'm in the market for some new NiMH
cells.

I was going to use my wealth of AAs to run a wireless headset on my
metal detector.

The wireless system was designed for a car [12v - or should I call it
13.6?]. All I can find for specs on it is that it is rated at
500milli-Amps. It is a Luxma transmitter that I bought on ebay.
Looks like the transmitter that goes with this set-
http://www.luxmt.com/pages/lhp888ht.asp
[the headset came from Newegg, is also part of that set- and Newegg no
longer has them]

I want the battery pack to be able to run it 10-12 hours- though it
isn't likely I'll ever be away from a charger for that long.

Weight is a concern as it is on a metal detector- and I'll be swinging
it with one arm for extended periods.

My first thought was to run it on 8 AAs. [I've wired it up and it
works on 8 [alkaline] AA's- but I don't know for how long] Then I
wondered if 10 or 11 would be better. . . . or a combination of 9v &
AA's. . . . or a single 12v. . . .

My lack of knowledge makes me ask--
*If* the 500mA is a constant, and I'm using 10 [to keep the math
easy] 2700mAh AA batteries to produce 12v- do I then have 27000
mAh's- and in theory could run the thing for 54 hours?
[if true, then I might go with alkalines instead of rechargeables- 50
hours is probably more than a couple months of use]

Thanks again-
Jim

Your 500 mA figure is probably wrong. It is highly unlikely that
you need 6 watts to run that transmitter, in my opinion. Measure
the current draw to get the real, actual figure before trying to
figure the needed battery capacity.

Ed

 

[Eric R Snow]

So my clock capacity tester has shown me that I've got a lot more bad
batteries than good ones. So I'm in the market for some new NiMH
cells.

I was going to use my wealth of AAs to run a wireless headset on my
metal detector.

The wireless system was designed for a car [12v - or should I call it
13.6?]. All I can find for specs on it is that it is rated at
500milli-Amps. It is a Luxma transmitter that I bought on ebay.
Looks like the transmitter that goes with this set-
http://www.luxmt.com/pages/lhp888ht.asp
[the headset came from Newegg, is also part of that set- and Newegg no
longer has them]

I want the battery pack to be able to run it 10-12 hours- though it
isn't likely I'll ever be away from a charger for that long.

Weight is a concern as it is on a metal detector- and I'll be swinging
it with one arm for extended periods.

My first thought was to run it on 8 AAs. [I've wired it up and it
works on 8 [alkaline] AA's- but I don't know for how long] Then I
wondered if 10 or 11 would be better. . . . or a combination of 9v &
AA's. . . . or a single 12v. . . .

My lack of knowledge makes me ask--
*If* the 500mA is a constant, and I'm using 10 [to keep the math
easy] 2700mAh AA batteries to produce 12v- do I then have 27000
mAh's- and in theory could run the thing for 54 hours?
[if true, then I might go with alkalines instead of rechargeables- 50
hours is probably more than a couple months of use]

Thanks again-
Jim

Greetings Jim,
For light weight and long operating time consider using lithium ion
rechargeable batteries. Rechargeable lithium ion batteries have more
capacity by both weight and volume than other common rechargeable
batteries. The RCR 123A lithium ion battery has a nominal voltage of 3
volts but will actually put out about 3.15 to 3.25 volts fully charged
and can be as high as 3.6 volts just out of the charger. They have a
very low self discharge rate and can be recharged any time-they don't
need to be fully discharged like some batteries do. Below is a chart
comparing the capacity of different types of batteries. This chart is
only a comparison and of course individual batteries will vary some
from the numbers below.
Li-Ion= Lithium Ion
Ni-Cad= Nickel Cadmium
Ni-MH= Nickel Metal Hydride
SLA= Sealed Lead Acid

TYPE Watt Hr/Oz Watt Hr/Cu In
Li-Ion 3.827 5.980
Ni-Cad 1.304 3.277
Ni-MH 2.041 4.260
SLA 1.020 1.688
As you can see Li-ion batteries are compact and lightweight and could
be the best solution for your application. I'm personally sold on them
but the higher single cell voltage can be a problem for certain
applications such as flashlights using incandescent bulbs.
Cheers,
Eric R Snow

 

[Rich Grise]

So my clock capacity tester has shown me that I've got a lot more bad
batteries than good ones. So I'm in the market for some new NiMH cells.

I was going to use my wealth of AAs to run a wireless headset on my metal
detector.

I don't grasp this concept - what will wireless headphones accomplish, on
a thing that you're holding in your hand?

Thanks,
Rich

 

[neon]

I agree 500ma for this kind of ocillator is nonsense. If realy want more battery power then run wires to a battery pack on your back or shoulder. I carried a nine pound rifles for years and more then 10 hurs a day. get inventive. By the way DO NOT TIE BATTERY in parallel to get any more current it just doen't work that way. I believe your 500ma is the rating of the battery not whatt is actualy drawing out of it, check that out.

 

[Jim Elbrecht]

On Mon, 30 Jul 2007 09:26:07 -0400, Jim Elbrecht wrote:
-snip-

I don't grasp this concept - what will wireless headphones accomplish, on
a thing that you're holding in your hand?

In practice it will be laid down often so [hopefully] valuables can be
dug up.

Removing the wire makes one less obstruction while kneeling, digging,
grabbing a handheld probe- sifter, or whatever.

Jim

 

[Jim Elbrecht]

Thanks also to Randy and Eric- but I think I *should* start here.

-snip-

Your 500 mA figure is probably wrong. It is highly unlikely that
you need 6 watts to run that transmitter, in my opinion. Measure
the current draw to get the real, actual figure before trying to
figure the needed battery capacity.

Thanks Ed-

It will probably be a week or so- but I'll check this out and see what
the real numbers are.

Jim

 

[Rich Grise]

On Mon, 30 Jul 2007 09:26:07 -0400, Jim Elbrecht wrote:
-snip-

I don't grasp this concept - what will wireless headphones accomplish, on
a thing that you're holding in your hand?

In practice it will be laid down often so [hopefully] valuables can be
dug up.

Removing the wire makes one less obstruction while kneeling, digging,
grabbing a handheld probe- sifter, or whatever.

Oh, OK, I see.

Well, a transmitter/receiver pair for a 1M range should be almost
trivial.

Expecially[SIC] since you're only listening for the metal detector
tone. In fact, you could probably get wireless radio headphones...
just a sec, lemme go google a bit....
http://www.google.com/search?q=headphone+radio

And slap together a little AM transmitter, which there should be
hundreds of on the web...

http://www.google.com/search?hl=en&q=AM+transmitter+hobby+project

Good Luck!
Rich
BTW, if you find treasure using this method, do I get a percentage? ;-)

 

[Rich Grise]

Expecially[SIC] since you're only listening for the metal detector
tone. In fact, you could probably get wireless radio headphones...
http://www.google.com/search?q=headphone+radio

And the other benefit to these, of course, is that when you break
for lunch, you can listen to the radio. ;-)

Cheers!
Rich