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Topic: Resistor decreases battery consumption? (Read 142 times) previous topic - next topic

gilperon

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?

CrossRoads

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 am Last Edit: Nov 15, 2014, 12:31 am by DVDdoug
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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.

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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

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

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

A 9V battery is about 0.55Ah so about 11 hours.

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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

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).

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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

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

OK you could tell by doing a chemical anailisis of the inside of the battery but that would destroy the battery.

cjdelphi

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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