Need some assistance - Rechargeable battery cost per charge

[ShyStar]

Hi everyone,

I'm trying to get an office building to convert from buying disposable batteries to rechargeable batteries as a waste minimization strategy.

The battery charger I am using numbers for has the following specs

Input: ~100-240V 50/60Hz 7W
Output: 1.2V 360mA (AA) X4 140mA (AAA) X4

The batteries it came supplied with are Nickel-Metal Hydride AA's 'typ.' 2100mAh

Can someone please help me determine (formula would be nice as I also have some other Ni-MH rechargeable batteries which are 2000 mAh 1.2V)

a) How long (time) it would take to charge X4 AA batteries/ X4 AAA batteries
b) How much it would cost to charge

I am also fairly new to using rechargeable batteries and chargers - The light indicating that charging is in progress comes on with as little as 1 battery being loaded. Where say only 2 batteries are being charged in a 4 battery recharger, do they get charged faster? i.e. Twice as fast because it's half the work with the same input. Somehow I doubt this but figured I'd ask to make sure.

Thanks in advance.

[yawanur]

Originally Posted by ShyStar

I am also fairly new to using rechargeable batteries and chargers - The light indicating that charging is in progress comes on with as little as 1 battery being loaded. Where say only 2 batteries are being charged in a 4 battery recharger, do they get charged faster? i.e. Twice as fast because it's half the work with the same input. Somehow I doubt this but figured I'd ask to make sure.

I doubt it, but my energizer wall charger has indicators for half full and full, so you can time it and see. However, I know with the 4 batt chargers it's best to charge two or four at a time, and when it's only two place them both to slots on the left side because the circuit runs left->right

rechargable ni-mh are boss though, that's a great idea

[ShyStar]

I noticed I hadn't put the 1.2V information for the rechargeable batteries.

Someone please help - This isn't just for homework or something, I want to use the information to change some pretty shortsighted behavior.

Thanks again.

[ShyStar]

Also I have an approach to this but I want something simplified and confirmed.

0.36 (amp) X 4 AA batteries X 1.2V = 1.728W

1 2100mAh battery @ 1.2V equals to ~2.5W, right?

So X4 of these 2100mAh 1.2V batteries would need ~10W to theoretically fully charge?

If this is right I figured 10W / 1.728W (output) = Just under 6 hours, which actually seems about right.


Hoping for confirmation/correction and an easy to use formula.

[ShyStar]

In case anyone is interested I searched online and found a document that steered me in the right direction and I came up with the following.

Calculating charge time needed:
For a fully discharged NiMH battery, an approximate charge time can be calculated using the following formula:
Battery mAh capacity X 120% ÷ mA charge rate = hours of charge.
The battery capacity can be found on the battery label. The charge rate of the charger can be found on the products datasheet.
Example: A fully discharged 2450 mAh battery being charged at 200 mA would be fully charged in (2450 mAh X 120% ÷ 200 mA) ~15 hours.

Cost to Charge Batteries (electricity)
The typical cost to charge a set of batteries will be approximately one cent per charge. For example, using a charger which has an input rating of 7 Watts - In 6.5 hours of charge, it would require 46 Watt hours (6.5 hours X 7 Watts) or 0.046 kWh. If the cost of electricity is 20 cents per kWh, a charge would cost (.046 kWh X 20 cents) ~1 cent.

[Mantikore]

The math is a simple method of multiplication in theory.

But the voltage tends to deviate from a constant value at the start and end of a charge cycle.

[DiStOrTiOn]

Originally Posted by Mantikore

The math is a simple method of multiplication in theory.

But the voltage tends to deviate from a constant value at the start and end of a charge cycle.

and isn't a lot of the current lost as heat?


how does someone factor this in? Would they just measure the actual time it takes and subtract from the theoretical charge time?

[Nereth]

put an ammeter in line with a charging battery and a volt meter across it. Write down both values, every 5-30 minutes or whatever you think is appropriate based on how fast it is changing and how much effort it's worth to you, at the end of a charge you get a plot of power consumed throughout the charge. Converting to cost is trivial.

[-Fuck-]

The radioshack charge has AA, AAA and 9V. You press the "refresh" button, and it automatically drains the batteries, then charges them up to max. When they're charged, it automatically shuts that port off and the light goes off. Kicks ass, never had any problems with it.