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### Topic: Resistor decreases battery consumption? (Read 192 times)previous topic - next topic

#### gilperon

##### Nov 14, 2014, 11:43 pm
Hi, If I use a 1k resistor and 10k resistor in a simples cirtuir that goes from 5V -> resistor -> GDR will the 10k resistor make the battery (5v) last longer?

The battery has a "reservatory" of current or of voltage? What am I consuming when I connect a battery to a resistor?

#1
##### Nov 15, 2014, 12:15 am
Yes - current flow will drop from 5V/1000 ohm = 5mA to 5V/11000 ohm = 0.45mA

Battery has so many amp-Hours of capacity. For an AA, that might be 2500mA-Hour.

So 2.5AH/ (5V/11000) =  555 hrs.

The number obviously changes as the battery voltage starts to droop over time.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### DVDdoug

#2
##### Nov 15, 2014, 12:28 amLast Edit: Nov 15, 2014, 12:31 am by DVDdoug
Quote
Hi, If I use a 1k resistor and 10k resistor in a simples cirtuir that goes from 5V -> resistor -> GDR will the 10k resistor make the battery (5v) last longer?
More resistance = less current.  It's the "resistance" to current flow.  (Ohm's Law).

With less current, the battery will last longer.  Resistors in series add-up, so 1K in series with 10K is 11k.    No connection is infinite resistance = no current.

Quote
What am I consuming when I connect a battery to a resistor?
You are consuming electrical power  and converting electrical energy to heat.  With 1K or 1k and a small battery you can't feel or measure the small amount of heat.  If you connect a regular 1/4W, 1k resistor to the AC power line, it will burn up!

Power is calculated as, Watts =  Volts x Amps.

#### cjdelphi

#3
##### Nov 15, 2014, 01:42 am
Think of a battery as a bucket of water and resistors are the pipes that carry the water...

Bigger the pipe (smaller the resistor value) the more current can flow.

#### gilperon

#4
##### Nov 15, 2014, 02:24 am
Thank you so much! Now I can understand this concept. One final question: I have a 9V battery (like the one you can buy everywhere). If I use 50mA of it how many hours will it last? Is there someway I can check how long is it a battery last?

If I get a battery that I dont know if it was used, is it possible to check how many amps it still has available?

#### Grumpy_Mike

#5
##### Nov 15, 2014, 09:23 am

Quote
If I get a battery that I dont know if it was used, is it possible to check how many amps it still has available?
No

#### notapantsday

#6
##### Nov 15, 2014, 04:26 pm
If I use 50mA of it how many hours will it last? Is there someway I can check how long is it a battery last?
It's very important to understand the difference between A/mA (ampere/milliampere) and Ah/mAh (ampere-hours and milliampere-hours).

Ampere is the rate at which the electrons travel through the conductor. One Ampere means about 6 Quintillion electrons per second. If you keep that up for one hour, one ampere-hour of charge has travelled through the conductor.

So if a battery has 10 Ah (ampere-hours) of charge and you draw 1 A (ampere), you get 10 hours of usage. And if you draw 2A, you only get 5 hours of usage.

In your example, you're drawing 50mA of current. If your battery has 550mAh of charge, you just divide 550mAh by 50mA and you get 11h (hours).

Quote
If I get a battery that I dont know if it was used, is it possible to check how many amps it still has available?
No. For some battery types you can get a rough estimate by looking at the voltage (under load), this is what battery testers do. But there are some types like Ni-MH where the voltage really doesn't say very much about the state of charge.

#### gilperon

#7
##### Nov 17, 2014, 03:17 am
Thank you! I didnt know about maH! That is an amazing conecept and makes the understanding really easy. i would like to know how many maH is still left in an used battery that I may have used in the past. I cant believe tehre is not way to tell the maH left of a used battery..but if you say I believe!! Thank you so much guys, as always.

#### Grumpy_Mike

#8
##### Nov 17, 2014, 11:37 pm
OK you could tell by doing a chemical anailisis of the inside of the battery but that would destroy the battery.

#### cjdelphi

#9
##### Nov 17, 2014, 11:41 pm
You could create a device which measures current and voltage from the battery and have it determine capacity from total current drawn...

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