Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Replicating 2 dcell batteries with a power adapter

  1. Nov 28, 2010 #1
    im new to finding this site and sorry for the lame question.. im just a tinkerer and in need of some info..im working on a project that uses 2 d-cell batteries in series as a power source. so i thought id get a power adapter to save on buying batteries sounds easy ? hardley for me, 2x d-cell batteries = 3.0 volts no problem, but amps is my question.. i found on another site that d batteries have 13000 m/a (i think i typed that right) so if u have 2 in series does that give u 26000 m/a ? if so i would need a power supply with 3v and 26.0amps. any of the above is subject to be wrong.. if anyone could help me make it right it would be much appreciated..ty bill
     
  2. jcsd
  3. Nov 28, 2010 #2

    vk6kro

    User Avatar
    Science Advisor

    You might have read 13000 mA-hours or 13 Amp-hours.

    A 13 Amp-hour rating says that the product of current and time the current is flowing for this battery is 13 amp-hours.
    It may not be able to actually supply 13 amps at all, but it might produce 1.3 amps for 10 hours, for example. The product is 13 amp-hours.
    It doesn't tell you anything about the current that can be supplied.

    13 amp-hours for a D cell sounds very high. Maybe 4 would be more like it, but that's just a guess. Assume it is 4 amp-hours.

    If you put two in series, the combination would still be 4 amp-hours, but at 3 volts.

    All of this is useless if you are going to put a power supply in instead of the batteries. A power supply has infinite (or indefinite) amp-hours because it works as long as you plug it in.

    A D cell might be able to supply 3 amps reliably and maybe 8 amps for a short burst.

    But you need to check on the load, not the battery. What current does it draw at 3 volts? That is the current you need to supply.
     
  4. Nov 28, 2010 #3

    uart

    User Avatar
    Science Advisor

    That would be 13000 mA-hrs. Possible for a good heavy duty D cell but actually irrelevant to the issue of the power adapter.

    Wrong, but as above irrelevant anyway.

    Nope. As pointed out above you're on completely the wrong track with the Amp-hr thing.

    You just need to determine how much current the device draws and spec the adapter accordingly (Amps ok, not Amp-hrs they're two different things). If it can be run on plain Carbon-Zinc D cells then it's probably not more than about one Amp, but you should check on the actual current requirements. The other thing you need to know is the allowable voltage variation. It runs on 3 volts nominal, but what is the actual max and min allowable voltages for correct operation. This will also help determine what type of pack is appropriate.
     
  5. Nov 29, 2010 #4
    well answers were kinda helpfull, let me tell u what im doing it might help. im copper plating my cast lead bullets with a solution of copper sulfate, it workes really well so far but i cant afford to keep buying d batteries.. so i guess i need to figure out how many amps its taking to do the work then buy an adapter thats rated at least that high or higher ? thanks for responses and sorry for the electrical ignorance on my part.
     
  6. Nov 29, 2010 #5

    berkeman

    User Avatar

    Staff: Mentor

    No worries. How long (in hours) do the D cell batteries last when plating?

    As stated, batteries are rated in their energy storage capability, which is Amp*hrs (* voltage). To keep it "simple", the units used are Amp*hrs (even though the units of energy are Joules in the main metric system used).

    Anyway, to figure out what current the batteries are running at, you would take the Amp*hr rating, and divide by the number of hours the setup can run before discharging. That gives you a ballpark estimate of the current that it is running at for that time.

    The voltages of the two batteries add in series, which is why you get about 3.3 to 3.0V with fresh alkaline D cells. The current is the same in both batteries since they are in series -- you are just getting twice the energy by virtue of twice the voltage (Power=V*I, Energy = Power * time).

    It looks like 12,000mA*hr (or 12 Amp*hours) is a typical D-cell alkaline capacity:

    http://en.wikipedia.org/wiki/List_of_battery_sizes

    So if your plating works for 2 hours on the D cells, then your setup is probably running at about half of 12 Amps, or 6 Amps. If it runs for 12 hours of plating, then your current is likely around 1 Amp.

    Makes sense?
     
  7. Nov 29, 2010 #6

    vk6kro

    User Avatar
    Science Advisor

    I have tried a bit of electro-plating and always got better results with a small current for a longer time.

    For something like a bullet, probably only 50 mA would be enough current. Otherwise you can get a mess of black Copper gunk which does not stick properly.

    You could get 50 mA from almost any small power supply. From 12 volts DC you could put a 220 ohm resistor in series with the electroplating cell. It would still only take 15 minutes or so to get a coating.

    I hope these are not live bullets you are passing electric current through? Are they?

    Why are you copper plating bullets?
     
  8. Nov 29, 2010 #7

    berkeman

    User Avatar

    Staff: Mentor

    I'm guess it's to keep the rifling cleaner. Maybe he casts his own lead bullets?
     
  9. Nov 30, 2010 #8
    lol no not live, i cast bullets for my own use and have to run them thru a star lubrasizer to size and lubricate them for use. its kinda messy and lubed bullets have to be stored carefully else the lube melts from the grooves. so if i can get the plating thick/tough enough i can delete the lube step, id still have to size but thats easy part lol...i just have to get the plating thicker i think for now .. its working but its a very thin coating VERY thin...thanks for everyones help, ill keep experimenting with it....bill
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook