How do you read mAh?

[MarcSylex]

I know mAh stands for milliamps per hour but does that mean what the battery can deliver as the max for any time frame? In other words I'm powering a circiut that demands 500mA and the battey is rated for 500mAh guaranteed can I expect that battery still have enough life for reasonable application?

Or, does mAh represent the cumlumative current draw of the battery in an hour? In other words (using same example above) will the current only equal to about 1.4mA per sec?

Thanks in advanced for responding

 

[MikeHalloran]

500mAh means the battery can deliver 500mA for an hour, or 250mA for two hours, or 50mA for ten hours, or 25mA for 20 hours.

... theoretically.

Batteries are rated for capacity at just one current, usually a low one. The capacity is reported as the product of that current and that time. I.e., it's not mA per hour, it's mA times hours.

You probably won't get 500mA out of it for an hour.





Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

Add ing to Mikes good info;

Generally batteries are rated over 10 or 20 hours.
Call C/20 for 'capacity'(the Ahrs)

Typically your 500mAhr battery..
Will provide 500mAhr of energy if you DO NOT draw more than 500mAhr/20hr = 25mA.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[capuchi]

To MarcSylex,

I think MarkHalloran nailed it right on the nose. It s the same in car batteries. Only this time its not milliamps but amps. Does this help?

capuchi

 

[tomad]

Marksylex,

The designation mAh is read "milliamperes-hours", if multiplied by voltage would give energy.
In your case, 500 mAh would be the equivalent of 500*3600 => 1800000 mAs = 1800 As = 1.8 kAs.
For that particular battery, if it is a 12 V battery, the energy would be 500 mAh x 12 V = 6000 mAVh = 21600000 Ws = 21.6 MJ (Mega-Joule).

The representation for " milliamperes per hour" would be mA/h.

 

[MarcSylex]

Thank you all!

I interpretted the units wrong. Makes sense now. It should be like when the electric comapny reads your meter in KW*hours. Which is how much power hourly is being delivered to your home.

But because a rated for 500mA is not continous (by that I mean as the battery provides power to the circuit its voltage gradually decreases). So the battery has a battery life of 1-hour (much likey less) at 500mA.

But to extend the life you deliver less current as "itsmoked" mentioned.

Kinda a side question:
Why are power supplies rated in VA and not just Watts?

 

[itsmoked]

Depends on the type power supply.

Just about none of the supplies I have/use are rated in VA. VA generally is applied to AC type supplies.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[stevenal]

MarcSylex,

When batteries are tested, they vary the load resistance to keep the current steady. Most real world loads don't behave this way. Also, the rating is non-linear. You cannot extrapolate the 10 hr rating to find the 1 hr rating, for example. You will need the curves from the manufacturer for this.

 

[waross]

Why is any piece of equipment rated in VA? It is an indication of heating effects. The V in a VA rating is the supply voltage. The A in a VA rating is the current that is drawn. The supply system must supply this current. The watts may be much less than the VA depending on the power factor.
In the real world, distribution systems are based on VA, KVA or MVA. The current and losses in distribution systems are dependent on Volt-Amps, not Watts.
respectfully