mAh question....

Niku-Sama · Post by **Niku-Sama** » Wed Apr 13, 2005 6:31 pm

ok i just need to verify something real quick

i have learned that an item uses so man mAH and the power supply may have more mAH than the item that requires it but the excess mAH from the power supply wont fry the item...is this right?

like is a NES uese 7 mAH and a battery has 100mAH the NES will only use the 7mAh it needs with out getting fried by the other 93mAH....

is this right?

nos_slived · Post by **nos_slived** » Wed Apr 13, 2005 6:47 pm

Yea, that's right. As long as you don't have anything that can't handle the high current.

Niku-Sama · Post by **Niku-Sama** » Wed Apr 13, 2005 7:21 pm

ok, just want to make sure

nos_slived · Post by **nos_slived** » Wed Apr 13, 2005 7:55 pm

Reread that, I just edited it.

Niku-Sama · Post by **Niku-Sama** » Wed Apr 13, 2005 10:56 pm

so....wait now i am confused again

so the power supply with try forcing all the mAH onto the thing drawing power then

nos_slived · Post by **nos_slived** » Wed Apr 13, 2005 11:15 pm

Just place a couple of resistors in.

Niku-Sama · Post by **Niku-Sama** » Wed Apr 13, 2005 11:31 pm

can you explain at all?

SgtBowhack · Post by **SgtBowhack** » Thu Apr 14, 2005 2:39 am

mAh is a measure of current over time, and has little or no bearing on the amount of current output by the batteries. Certain types of batteries will always put out roughly the same current. A battery having a rating of 100mAh means that it can produce 100 milliamps for 1 hour. It can also produce 200mA for .5 hours, or 50mA for 2 hours. Therefore, assuming the NES needed 7mA to run (which is not true, sadly, but anyway), a battery supplying 100mAh will run for 100/7 = 14.3 hours. Batteries require electronic devices to pull current from them. If you're working with power supplies, it may be different.
Batteries cannot have power surges, but power supplies can, so fuses and other methods of minimizing surges in current that can blow electronics are used.

In short, do not confuse mAh ratings on batteries with mA (current). They are different. Batteries can output (theoretically) any number of mA you want, though realistically they are limited. They cannot blow up your stuff, unless they leak.

Niku-Sama · Post by **Niku-Sama** » Thu Apr 14, 2005 4:32 am

ok well....that just puts me back to thinking what i had origoanlly thought

SgtBowhack · Post by **SgtBowhack** » Thu Apr 14, 2005 3:38 pm

OK, but devices don't use mAh, they use mA. That was the big distinction I was trying to make.

e5frog · Post by **e5frog** » Thu Apr 14, 2005 4:55 pm

like is a NES uese 7 mAH and a battery has 100mAH the NES will only use the 7mAh it needs with out getting fried by the other 93mAH....

Nope, a unit (NES perhaps) draws 7 mA, if your powersupply is marked 1000mA it won't hur the unit - the unit can take as much as it needs. Powersupply can supply up to 1000mA, if you connect something that need 3000mA - that thing will simply not start (like my IBM laptop)

Batteries have a charge, you can basically pull 10 mA for 10 hours if it's a 100mAh battery, or 20 mA for 5 Hours etc. The more mA you pull however will warm up the batteries - if you'd short circuit the battery there will be a lot of mA (or A) and a lot of heat.

Any clearer?

If you want to charge a battery however, charging it with 10mA for 10 hours doesn't fully charge a 100mAh battery. There are losses. Usually there's a written recommendation of charge current one normal loading (for maximum amount of recharges) and one for fast charge (usually wears out the batteries faster) - In that case you cant just connect your powersupply (1000mAh) directly to the battery, then only the inner resistance of the battery limits the current (amount of mA) and you'll end up charging it with too much mA:s. The easiest way to prevent this is to put a resistor between powersupply and battery - but as the battery is charged the current will fall (as the voltage difference between the powersupply and battery decreases), perhaps too low to keep charging it.

That's why you need to get an expensive battery charger - there are circuits that keeps the charge current at the same level (at least a proper level) until the battery is fully charged (then it should stop charging)

Niku-Sama · Post by **Niku-Sama** » Thu Apr 14, 2005 11:57 pm

the reason i ask is because when ever i get my NES motehrboard i want to use the battery linked to below:

http://www.batteryspace.com/index.asp?P ... ProdID=432

the reason i want 12 volts is i want a slightly larger/higher quality screen....so i'll be sure and take the proper percautions to get it to the 7.5V for the NES

nos_slived · Post by **nos_slived** » Fri Apr 15, 2005 12:48 am

That isn't a bad battery, however, if you were to use 20 Energizer brand NiMH AAs (2 parallel series of 10), you will get 500mAh more capacity at almost half the weight, and nearly the same size.

Niku-Sama · Post by **Niku-Sama** » Fri Apr 15, 2005 11:44 pm

alright i got anoter question....

out of curiosity would a power supply out putting 12 volts and was stepped down using resistors to...lets say 7 volts....would it still use all 12 volts out of the battery?

or would it just use the 7 out of the 12?

nos_slived · Post by **nos_slived** » Sat Apr 16, 2005 12:59 am

If I understand correctly, the answer would be that it still uses the full 12V. All the resistors do is eat those 5 volts (and change them to heat). Pretty much the only time that a circuit doesn't use all voltage supplied, is when you short it (complete the circuit with minimal resistance). You can still get 12V from the battery if you run a second line before the resistors.

BTW: Are you still using that massive battery, or are you taking my advie and going with AAs.
PS: Some companies even make AAAs that are 2500mAh. Now that, would help your size

! Energizer used to, but I don't think they do now.