Electrical Question

[ClubMed]

I have an old wireless home phone with a rechargable battery that would no longer recharge fully.

The rechargable battery consists actually of two AAA Nickel-Metal Hydride batteries which together produce 2.4V (so 1.2V per battery).

Now it also says 600 mAh. I'm assuming it means 300 mAh per battery? (since the voltage was for both too?)

I'm asking this because I bought two new rechargable AAA Nickel-Metal Hydride batteries each is 1.2V.

But each is also 750 mAh, so together that's: 1500 mAh.

Is that dangerous to put into an appliance designed for 600 mAh?

I have already connected the two batteries together and the phone works again, now it's charging, but I am afraid that the difference in mAh could be a problem?

[Gomer]

Not dangerous at all.

mAh are milliamp-hours. That number is an indication of how long the batteries can supply a current. The voltage is what is important.

Say for every hour your phone uses 10 mA of current. Your old batteries would conk out after 60 hours (600 mAh/10mA). Your new batteries will last for 150 hours.

[ClubMed]

Great, thanks.

[shahani]

That is correct. Its like a bigger water tank for watering your lawn. The pressure (voltage) remains the same but the capacity (watts or Milliwatts or mHA) is increased.

[ShawnD1]

What Gomer said is on the right track but not 100% true.

Say for every hour your phone uses 10 mA of current. Your old batteries would conk out after 60 hours (600 mAh/10mA). Your new batteries will last for 150 hours.

The amp (A) is a measurement of charge over time (C/s). There is no such thing as 10 mA per hour, that would be a rate of a rate. The rate of change for current is 0 (until the batteries die).

He's right about it being the amount of energy the batteries have. 750mAh x 3600s/h (seconds per hour) = 2700As (amp second)
E = Pt
E = VIt
E = (1.2)(2700)
E = 3.24KJ


It won't damage it though.

Power consumed by the circuit is determined by volts and amps. The volts is constant and the amps is determined by the resistance of the circuit. The resistance in the circuit doesn't change either which means the power usage will be the same.

[Gomer]

I am 100% right shawnd1. Current is indeed a measurement of charge over time C/s, and mAh is indeed a rate of a rate.

Most electrical devices such as phones and the like have constant current draws. The mAh number is expressing the length of time that rate can be maintained.

My statement was very precise.

To end this matter I called upon my good friend google. He says http://www.batteryweb.com/faqbw.cfm#q21

Good day =)

[shahani]

If Gomer post is 100% so is mine.

[Bill in SD, CA]

Originally posted by Gomer
I am 100% right shawnd1. Current is indeed a measurement of charge over time C/s, and mAh is indeed a rate of a rate.

Most electrical devices such as phones and the like have constant current draws. The mAh number is expressing the length of time that rate can be maintained.

My statement was very precise.

To end this matter I called upon my good friend google. He says http://www.batteryweb.com/faqbw.cfm#q21

Good day =)

Plug that into your socket and charge it!

Bill

[mad1]

"Current is indeed a measurement of charge over time C/s, and mAh is indeed a rate of a rate." That is current discharge rate,
mAh= milliamp per hour.

Current is the voltage divided by the resistance.
I=V/R
I=current
V=voltage
R=resistance

The movement of electrons is known as electrical current flow, or current. Ampere is the unit of current flow and is the amount of current flow represented by a rate of charge flow of one coulomb per second.

Electrical resistance is the opposition shown to the flow of current. Resistance is measured in ohms, or the amount of electrical resistance limiting the current to one amphere with one volt applied.

Voltage is the potential to perform electrical work of moving electrons. Measured in volts and is the amount of potential difference causing one amphere of current to flow through one resistance of one ohm.

[Wizzard~Of~Ozz]

Please keep in mind that these batteries are in series, so if they are both 750mAh then it will have a total ouput of 750mAh...

Mathmatically shown by

1.2V x 750mAh = 900mW x 2(batteries) = 1800mW

1800mW / 2.4V = 750mAh

So this means it will hold a longer charge (last longer) and *should* have no ill effects to the charger, definately no ill effects to the phone.

Reason for the possibility of damage to the charger is, the batteries can take more power instintaneously then the old ones (1.8w instead of 1.3w) however the transformer should not have a problem with over 1.5w total for the charging circuit.

So Gomer, assuming 10mA/hour the old would last 60 hours, the new will last 75 hours.