AA & 9V battery short circuit current

Hello everyone,

A battery powered product is headed for ?intrinsically safe? certification. The main test documented in prior certificates uses the open circuit voltage and short circuit current from the power source to see if an explosive mixture of gases can be ignited. The circuit capacitance is placed across the combination of a bench supply and a limiting resistor for the test.

I am looking for information on the short circuit current for 9V and AA batteries. This varies by manufacturer, model, and from battery to battery. I would also like to hear if anyone has ever tested small batteries for short circuit current.

Have a good day, Robert

Reply to
Robert
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Wouldn\'t the various manufacturers be the best sources for that data and
wouldn\'t it behoove you to make the short circuit current measurements
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Reply to
John Fields

certification.

for

Short circuit current depends on a lot of things such as, in no particular order: - state of charge, - temperature, - age of cell - Chemistry of cell - Brand of cell - Internal resistance - Length of time cell is sitting idle - Revision of cell - Terminal material and attachment method, internal and external - etc

For example, NiCd AA's could produce 100+A for a short duration. Cheap Zinc based AA cells might produce a short circuit current of a few amps. A 9V battery short circuit current would likely be around an order of magnitude less.

Reply to
Jeff L

"Robert"

** If you are after "worst case" values, then look up the figures for " internal resistance" for AA size NiMH cells and 9 volt NiMH batteries on their maker's sites.

A few rechargeable AA cells in series will have no trouble setting plastic coated wires and PCB component & tracks on fire. Then explode themselves.

Products using them are NOT safe unless there is no possible way the cells can be shorted and there is a fuse link or other current limiting device ( ie polyswitch) in series with the battery supply.

BTW: NiMH AA cells are sold all over the place now, so any product using "loose" cells can expect to wind up with them installed.

..... Phil

Reply to
Phil Allison

John Fields wrote in news: snipped-for-privacy@4ax.com:

Have not found anything on the manufacturers web sites.

The only measurements that will cound are the ones that CSA perform.

Hoping to work a bit smarter. My aplication is low current. If one brand or model tends to have a lower short circuit current, it would make acceptance testing less of a problem. As a department of one, there is more to do than will get done.

Have a good day, Robert

Reply to
Robert

innews: snipped-for-privacy@4ax.com:

It's there on the data sheet, it's called the internal resistance and cell voltage - add ohms law and you have the maximum short circuit current when the cell is fresh.

You are designing a product and didn't know this??

Dave.

Reply to
David L. Jones

"
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A pair is more than enough to source 10+A (initally closer to a

50-100A transient spark) for plenty long enough to reach red heat burning off wire insulation and PCB tracks. The chemistry starts to get out of hand pretty quickly when only the cells internal resistance is the limiting factor. Heat gases, boiling electrolyte, venting and then explosion releasing cell contents. Sanyo reckon 1.2v and 0.025 ohm at so around 50A 1000Hz. I have seen higher initial instantaneous short circuit currents than that.

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The old Kodak DC-120 camera managed to draw 2A continuously from 4x AA cells in worst case of macro mode with flash enabled. Modern digital cameras are a lot more frugal although their power packs still pack quite a wallop.

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Or better that a cell is used in a physically encapsulated way such that it cannot ever source a high current no matter what the external provovcation. The stuff I recall for flame proof areas also included armoured impact casing and devious mechanical interlocks to ensure that no-one could ever open one without the requisite servicing tool.

using

Yep. If it will fit then one day someone will do it. You also sometimes find AAA cells wrapped with cardboard to make up the diameter and extended with folded KitKat foil or even a mixture of different capacity cells which is another *really* bad practice. But the guy just wanted to get it working again and bodged around with what was in his toolbox. It is annoying that field engineers who should know better do these sort of things as a quick interim fix and then forget about them until something really bad happens (like the weakest cell dies horribly).

I find the prospect of the OP designing something that is intended to be intrinsically safe in an explosive atmospher particularly scary in the light of his question here. Hopefully the testing authorities will do their job adequately unlike USPTO.

Regards, Martin Brown

Reply to
Martin Brown

"Martin Brown" "Phil Allison"

A pair is more than enough to source 10+A (initally closer to a

50-100A transient spark) for plenty long enough to reach red heat burning off wire insulation and PCB tracks. The chemistry starts to get out of hand pretty quickly when only the cells internal resistance is the limiting factor. Heat gases, boiling electrolyte, venting and then explosion releasing cell contents. Sanyo reckon 1.2v and 0.025 ohm at so around 50A 1000Hz. I have seen higher initial instantaneous short circuit currents than that.

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The old Kodak DC-120 camera managed to draw 2A continuously from 4x AA cells in worst case of macro mode with flash enabled. Modern digital cameras are a lot more frugal although their power packs still pack quite a wallop.

Or better that a cell is used in a physically encapsulated way such that it cannot ever source a high current no matter what the external provovcation. The stuff I recall for flame proof areas also included armoured impact casing and devious mechanical interlocks to ensure that no-one could ever open one without the requisite servicing tool.

Yep. If it will fit then one day someone will do it. You also sometimes find AAA cells wrapped with cardboard to make up the diameter and extended with folded KitKat foil or even a mixture of different capacity cells which is another *really* bad practice. But the guy just wanted to get it working again and bodged around with what was in his toolbox. It is annoying that field engineers who should know better do these sort of things as a quick interim fix and then forget about them until something really bad happens (like the weakest cell dies horribly).

I find the prospect of the OP designing something that is intended to be intrinsically safe in an explosive atmospher particularly scary in the light of his question here.

** The OP is an utter ASS.

There is NO WAY a unit containing AA cells or a 9 volt battery will ever be allowed inside a potentially explosive environment. It will have to remain outside and be linked by an intrinsically safe interface to whatever sensor is involved.

My comments were only about the danger that now plagues all devices that allow the user to replace the cells or battery with whatever will fit.

Even a common old AA alkaline cell will explode if shorted ( ie by an ill designed battery compartment ) or if fitted in reverse in a series battery.

..... Phil

Reply to
Phil Allison

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So you\'re going to show up at the CSA labs with a bunch of widgets that
you\'ve not tested because a "department of one" couldn\'t get around to
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Reply to
John Fields

"Phil Allison" wrote in news: snipped-for-privacy@mid.individual.net:

Hello everyone,

The signal to noise ratio from google groups is quite low this morning. It may be time to reconsider some sort of filtering. Having received usefull information from unlikely places tells me to resist just blocking all google groups posts.

Is there a quick way of blocking all posts from google on XNews?

The public records will show many such devices have been approved. The last approval testing on this product showed over 10 amps from some 9 Volt batteries. That unit passes. Factors include how fast and how much energy is released.

'Anyone can speak Troll,' said Fred dismissively, 'all you have to do is point and grunt.' "Harry Potter and the Goblet of Fire" - J.K. Rowling (2000)

Reply to
Robert

"Robert the LIAR "

** Fuck off - d*****ad.

** But not for use *within* the hazardous area.

You LYING POS.

...... Phil

Reply to
Phil Allison

Google Groups,

Please accept by sincere apologies. You were falsely accused.

------------------ Phil,

*plonk*
Reply to
Robert

If you need an intrinsically safe level, please consider sealed apparatus. Otherwise the limits are like 50 uA and 5 V at all times. Moreover applications like explosimeters, are constrained to replacing batteries in clear atmospheres.

Reply to
JosephKK

ndividual.net:

will

It would be allowed inside a truly FlameProof certified casing. How do you think electric miners lamps work?

The point here is that an AA battery cell is not intrinsically safe. It can source way too much current and juicy sparks.

Anything that might spark internally is generally expected to be able to cope with the worst case explosive mixture inside it being detonated without showing any external signs of leaking flame or sparks. The kit might or might not work properly after this test, but it must not become a source of ignition.

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ull

I suggest you learn to read headers as well as about Ohms law V =3D IR. The manufacturuers specify V and R it is left as an excercise to the reader to compute I.

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energy

Lets see an example of one of these mythical devices that has been declared intrinsically safe with a 10A 9v spark source available internally. When you are in an explosive atmosphere you do not want any calorific sparks at all. Even inductors are carefully RC snubbed to keep the stored energy from causing trouble.

I think you are confusing FlameProof and Intrinsically safe designations. See

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for a brief introduction to the differences.

I think you need to heed that advice. Be sure to video the testing it should be amusing to watch on U-Tube as your kit explodes.

Regards, Martin Brown

Reply to
Martin Brown

Hmm. If you are certifying the device as intrinsically safe, you are going to want to do your testing/analysis with the worst case possible. That would be the battery with the highest s.c current/lowest internal resistance.

Someone is apt to ignore any vendor/part number specifications and replace the battery with the first one that fits found in the parts bin. This includes the possibility of replacing an alkaline battery with a NiCad or NiMH battery, both of which may have lower internal resistances if my memory serves me correctly.

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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Reply to
Paul Hovnanian P.E.

"Paul Hovnanian P.E." wrote in news: snipped-for-privacy@hovnanian.com:

I am sure that they will. Our customers return units (for repair or annual calibration) without the ground strap. Stating that we can't afford enough liability insurance to do otherwise, the ground strap is replaced and the customer charged for it. It is imposable to keep people from doing foolish things. The nameplate will have a list of approved batteries. The manual will probably have some words on why. We will remove batteries that are not on the list.

Back to the short circuit current. From scraps of information, lithium batteries seam offer the highest currents. They also have a reputation for spectacular failure. Fortunately I did not have to talk very long to get them off of the wish list.

Look for the test results towards the end.

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Robert

Reply to
Robert

JosephKK wrote in news: snipped-for-privacy@4ax.com:

This is a rework of an existing product that is already approved intrinsically safe. Unfortunately, like many businesses, documentation and history from the prior approval was not maintained.

The case is well sealed. Fortunately this redesign is just a new circuit board and replacing the 9V battery with two AAs.

Robert

Reply to
Robert

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