Max Discharge Current 2.0C5A ???

premelec

premelec

Senior Member
i can't be specific but this notation usually refers to different battery capacities at different drain currents - e.g. a 1 ah [1000 mah] capacity at c10 could mean that's what you get at a 10 hour discharge time - 100ma for 10 hours... and it would be less at higher currents....
 
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manuka

Senior Member
Although it's a tad crtptic their data sheet indicates 2 Amps max discharge current, although mention (at 7.3) of a 50 mOhm load test implies it'll deliver far more ! You may get away with occasional brief high current discharges hence- what is your application?
 
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JoeFromOzarks

Senior Member
hugoxp1 said:
Hi,

I "google" about C5A to mA conversion and haven't found anything.

Can anyone tell me what is this unit measure "C5A" and how can I convert to mA?

(I want to know what is the max discharge current (in mA) of this battery: http://www.sparkfun.com/datasheets/Batteries/UnionBattery-2000mAh.pdf)


Thank you
Click to expand...
“Ci -- The rated capacity, in ampere-hours, for a specific, constant discharge current (where i is the number of hours the cell can deliver this current). For example, the C5 capacity is the ampere-hours that can be delivered by a cell at constant current in 5 hours. As a cell's capacity is not the same at all rates, C5 is usually less than C20 for the same cell.” (source http://www.aaportablepower.com/BatteryKnowledge/BatteryKnowledge.asp)

Your battery is rated 2000mAh, but don't count on it.

Additionally: your document comes with warnings:

Cautions of batteries’ operation:
The batteries must be careful of proceed the operation for it’s soft package.
Short-circuit:
Short-circuit is strictly prohibited. It should damage batteries badly.
In case of electrolyte leakage contact with skin, eye, physicians shall flush the electrolyte immediately with fresh water and medical advise is to be sought.
The cell replacement should be done by professional people.

:) joe
 
B

BeanieBots

Moderator
The datasheet is very clear.
Standard discharge = 0.2C, and maximum discharge =2.0C
For THAT battery, C = 2000mA.
So, standard discharge is 0.2*2000 = 400mA
and maximum discharge = 2.0*2000 = 4000mA = 4A.

That C5A nomencalture is nothing more than a red herring (but correctly described by Joe above). There is no such thing as the conversion you are trying to find.
Battery discharge rates are specified as a multiple (or division) of it's capacity which is expressed as "C".

Standard discharge is the rate at which the battery will provide it's specified capacity. Maximum discharge is the maximum current you can draw before doing permanent damage to the battery.
 
J

JoeFromOzarks

Senior Member
BB is right on. 4000mA is what we affectionately called the “Gold” or “wrench” load. A gold bar or a wrench representing a 0 ohm load across the battery. (grin) The secret of a good battery design is to never tax the battery - especially with a wrench across the terminals – i.e. not having a significant (taxing) load.

Arguably, a battery is the least dependable, least reliable, least predictable device in an electrical circuit.

Using “Ci” or “CxA” in circuit design is analogous to specifying a transistor at its Maximum Ratings. Ouch.

I hope I’m not drifting off topic.
 
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geoff07

Senior Member
JoefromOzarks reminds me of the good old days of Strowger telephone exchanges, which I recall from being a student. My local exchange was powered by a 50v battery, made up of 2v cells each the size of a large domestic water tank, and providing 2000A. The feed to all the racks was via a busbar arrangement of probably ten 6in x 1/2 in cross-section aluminium plates bolted together. There was a 100kW genny and 14,000 gallons of diesel in the basement, which would kick in during power dips in thunderstorms. You had to take any rings off before working on the power, in case you vapourised your wedding ring and amputated a finger. Now the building is a hotel and the remnants of the gear are probably in a small cupboard. Though the wiring frame must still be there somewhere.
 
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manuka

Senior Member
I recall that gymnasium sized phone exchange era well- and of course the associated noise!

The wedding ring comment reinforces my reflection that many batteries can deliver brief high current spurts- tales abound of car batteries near vapourising dropped screwdrivers etc. I've personally witnessed mere 1.2V ~600mAh AA NiCads instantly melting miswired low voltage wiring, delivering perhaps 30+ Amps in the process.
 
J

John West

Senior Member
OT on battery power:
When I got my first electric car I was using a battery wrench that wasn't taped up. Of course butter-fingered me dropped it down in the battery pack. After a couple of big zapping sounds and flashes of light it bounced out of the battery box - literally tossed out by the arching.

Tape went on what was left of it (after it cooled down.) We live and learn. High voltages are not all we should worry about. High currents at low voltages pose their own dangers.
 
D

Dippy

Moderator
OT.
And that same principle should be remembered by newbie people powering simple little PICAXE circuits with honking great PC S/mode power supplies!!
 
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Piers

New Member
manuka said:
tales abound of car batteries near vapourising dropped screwdrivers etc.
Click to expand...
Can't they just... If they don't explode in the process, I've known that happen. Lad was taking a battery off a tractor, access wasn't good, positive first, grounded the spanner...

When I got my first electric car I was using a battery wrench that wasn't taped up. Of course butter-fingered me dropped it down in the battery pack. After a couple of big zapping sounds and flashes of light it bounced out of the battery box - literally tossed out by the arching.
Click to expand...
Saved you fishing it out though...:D

Piers
 
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