AH capacity calculation ??? Please help !!

[europus2002]

Hi all ,
I have a unit that consumes 3A at 12V. It is delivering high voltage pulses with following numbers

4 channels
100mA max drain current into 4K load .
Max pulse width is 1mSec .
100 Pulses per second per channelx 4 = 400 Pulses
So i calculated as
(100mA)2 x 4k X 1mSec x 400 = 16W per second
makes it 57.6KWh and what next for Ah?
Doesn't this value look big??
With this i get the battery capacity of 12v / 30Ah for sustained operation for 8 hours .....
Am i doing something wrong??? somehow something is missing somewhere
Please help me with this Watt-hour to Ampere hour calculation.....thanks in advance

 

[sreid]

If I understand this correctly,

0.1 amp 1/10 duty cycle = .01 amp per channel

Times 4 channels = .04 amps

Times 8 hours = 0.32 amp hours

 

[IRstuff]

Am I missing something?

"I have a unit that consumes 3A at 12V"

Isn't that 8 Hr * 3 A = 24 AHr for 8 hrs operation?

TTFN

 

[itsmoked]

Or 3A x 8Hr = 24Ah

or

400ms of 100mA per second
100mA x 0.4s = 40mA average current.

40mA x 8 = 0.32Ah

Odd.


Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[VEBill]

You probably don't know the end-to-end efficiency of the unit, and you probably don't know how the current consumption of the unit varies during the entire duty cycle. Therefore, you might as well ignore the detailed characteristics of high voltage pulsing outputs. I suspect the information is incomplete on that end.

The input side seems fairly clear. The battery is (I assume) on the 12 volt input. If the box needs 3 amps (continuously), then for 8 hours you'd need 3 times 8 = 24 amp hours.

Since the frequency is relatively high (100 pulses per second - as compared to the normal meter) I assume that the 3 A is an average value (if not already filtered internally).

You should double check the low voltage definitions for both the battery and the box. If the box shuts down at 11.999 volts (an exaggeration for clarity), then you wouldn't get all of the spec'd Ah out of the battery.

 

[europus2002]

Hi all,
Thanks for the replies . sreid , i guess 0.32Ah will not work since circuit is consuming 3A approx continuously.
IRStuff, u;r right . i missed 20% addition for battery heat and losses. Also i forgot to mention the other parts of circuit which though fairly low power, but consume some power and 30Ah being standard in the market, i mentioned that number in my previous post....
IR : I got the same exact numbers as you do...but wanted to double check since i m going to be recommending a car battery for handheld / portable unit ...
Not me guys !!! Guys who developed specs !!

 

[itsmoked]

There is always Li-ion batteries if the weight is a problem. But they take some serious design work.. Not something you switch to at the end of the design process.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[europus2002]

u'r right VE1BLL: End to End efficiency was not mentioned but it works around 55% efficiency......i know that's very poor but what do you expect from off the shelve HV boost convertor ...Every project has to be finished in 3 months with circuit and PCB prototyping....And more to it, it should be something someone has never done before....and also with all latest features....I know all you guys will have stories....Back to point, i have 4 boost convertors and all work at 60% best at low voltage and around 50% loaded...12v/530mA input and output max @ 400V/ 7.5mA...This is what is killing my entire efficiency...

 

[europus2002]

Yes itsmoked, u'r very right...and am not in favor of using them since they have potential to explode on some extra charge....that;s scary from legal perspective as well....I am going with NiMH battery for time being....treadoff between NiCD and LiIon...what do u say?

 

[itsmoked]

Well before you trash can them entirely do consider that most laptops use them (>100 million) Generally they require you build a one or two cell at a time charging system with temperature monitoring. Not hard.. But required.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[IRstuff]

The only addition would be to add in some reserve capacity

TTFN

 

[itsmoked]

I would second IRstuff's comment and I mean 2X if the device will be used 8Hrs a day. You will get lousy battery life (sub year) if you drain the battery fully every day.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com