Infant Mortality battery tester

Use resistance wire and make up your own resistor, suitably shielded. You shouldn't have to mess with immersing it unless you want to. Pay attention to the resistance change of the wire as it heats up (immersion would help here), and design your mechanical arrangement accordingly.

If you need a precise current then switch in a number of individual segments in parallel, or use the wire to absorb the first 700-800 watts and a (well heatsunk!) transistor load to control the current.

attention

segments

Buy a commercial lead acid battery tester or two and nick the resistance element out of them.

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If this were up to me I would take a large plastic bucket, such as a 40 lb. laundry detergent bucket, and fill it with water. 12V is quite low and even with highly salty (like ocean water) water the current flow through water will be very small compared to the 110A or whatnot. It will also be quite safe to play with at 12V.

Once filled with water I would go here:

And find out what the resistance of some different wires are. I would probably use something like 18 AWG copper wire for this job. From the calculator we see the DC resistance is 20.9mOhm per meter. So you want

109mOhm, so about 109/20.9 = 5.2 meters. I would get this length of uninsulated or plain magnet wire and place this inside the plastic bucket of water. I would make sure to make good connections on the ends with something like 2 AWG wire leading to the battery terminals so that all the 18AWG wire is fully immersed in the water.

Voila. 0.109 Ohm resistor at 1.32kW. Cost may be nothing out of pocket if you have this stuff laying around. If I wanted to store it for any length of time I would make sure to include a lid for the bucket as well as putting something in the water like antifreeze to make sure algae and other biologics don't grow out of control in the water.

If you want something calibrated and engineered for you that is safe, buy a commercial high power battery tester. All the automotive places that do auto electrics will have these. They are not extremely expensive for what goes in to them. The ones that I have seen have a variable loading on them, and you can measure the point at which the battery starts to go down. You can then determine an exact measurement of the battery condition that would be repeatable, and accurate. The very high end ones use an actual variable type resistor assy that is properly rated. It works through a bridged loading with the amp and volt meters. This affair gives a very concise reading.

If you want to mess around, you can start by using nichrome heating element wire to make your resistors. Use many in parallel to take up the load, and to also be able to have low resistance with more mass, thus giving better stability. Remember, as this heats up, its resistance will also change, thus not making the readings linear. The commercial units are worked out to compensate for this.

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Greetings,

Jerry Greenberg GLG Technologies GLG ========================================= WebPage

Electronics =========================================

Here is another interesting project, I am to build a infant mortality battery tester.

the tester is to be designed to a 110amp load

for a 12 volt 16amp battery (the battery is actually capable of putting out 110amps for 16 seconds)

Hence after a 6 second with a load attached, the battery should recover and measure 9.6 volts.

running the numbers I came with

resistor= .109 at 1.32KW

Yes I know, why not lay a bare wire over the darn thing..? crude simple and effective which may cause personal injury burns, etc, blah,blah lawsuit. I think I will go with a test fixture. So far It has become difficult to locate a manufacturer for this type of resistor.

I've been throwing around other... a resistor in a can of mineral oil etc.. (the ole dummyload)

any ideas or suggestions?

I take it that what you mean by "a 12 volt 16amp battery" is that it has a 16 Amp-Hour rating. Therefore, a 110 amp load is *abusive*; look at the quote from Interstate Batteries! The spec from Interstate Batteries is: "If the battery can sustain a load equal to 2 times the Amp-Hour capacity, holding a voltage of at least 10.5 volts for 5 seconds, then the battery should be considered structurally sound." NOTE: the voltage mentioned is read *during* the load time.

Some testing procedures for heavy duty automotive and/or marine batteries (type not specified in the literature) mentions a 300 amp load for 15 seconds, but that clearly is not commensurate with your application or battery type/design. Looking at a lot of literature, i find that the 10.5V specification as being the most realistic; i suggest that you modify that 9.6V limit and also the reading method. A battery that cannot recover to full voltage is either not good or has been subjected to an abusive load, which can shorten its life expectancy at minimum, or create internal damage.

If the battery is useable, then the current will be constant for the purposes of the test, and if it is bad, then it does not matter that the voltage and current drops a lot. I have tested over a hundred reject batteries, some were useable for non-medical purposes (they were from motorized wheel chairs and scooters) as-found, and some were recoverable for non-medical purposes.

** There are automotive car battery load testers, and some of them are portable. They include a voltmeter, a resistive load in the region of interest, and heavy duty leads with heavy duty clips. That load resistor and its enclosure can be very useful for making of a suitable tester. Harbor Freight or other "discounter" (read: seller of Chinese made stuff) has such an item that is not too expensive for either casual or serious use.

...and pray tell, what the hell does guitars have to do with the subject at hand?

I saw a construction article in either Radio Electronics or Popular Electronics during the 1980s for a battery tester capable of loading a car battery. I received these magazines starting in 1982. They used a specific length of 1/2 inch steel strapping that was wound around dowels on a wooden base. The article can be found at the library if anyone is interested.

Ken

Resistors in the rating area you describe are used in the electric power industry.

I don't know if they still make them, but as of my last association with them the Square D Company made several lines of resistors for similar use, crane and hoist speed control and braking, etc. One model was known as the PX resistor and were of nichrome on ceramic construction. and quite low in cost. If that product line still exists I am sure they could provide something suitable. Post-Glover is another manufacturer of industrial power resistors.

wooden

We manufacture a unit which draws up to 450 amps out of 12V automotive batteries for around the time you require. Our load is about a stainless steel bar, roughly 1200 mm long, 20 mm x 5 mm cross section. Its easy to slide a contact (such as a heavy duty battery clip) along the bar to get the current you need.

Stainless steel has a pretty high temperature coefficient, but the exact current does not matter to us - and I suspect the current does not have to be precise for your application.

For high duty cycle use, we use a small computer type cooling fan to move some air over the bar. At only 110 amps, you shouldn't have nearly so much trouble with heat.

The battery voltage will drop under load, so you might want less resistance than you calculate using 12V and Ohms Law.

Your test spec looks unusual to me. Even a half dead battery will recover to above 9.6 volts when you remove the load, unless it has an internal open circuit. The standard Battery Council International load test for Starting Batteries is to draw 0.5 of rated Cold Cranking Amps for 15 seconds - the voltage should remain above 9.6 volts while the load is applied. Test temperature 18 degrees F.

Roger

wooden

We have one. However Hawker Genesis, belives that many of the reading from their lead battery might be erroneous. these batteries lead-accid are not in the sense lead acid batteries, they are more like Lead asorb by tin batteries.

the test I described, is recommended by them.

Thanks, the 110 amp load I got.. was from Hawker Genesis. they belive if I went over 15 seconds, it would be abusive to their batteries.

interesting however, they would want me to do a voltage read after the load test. If the battery recover to 9.6 volts, they consider it a good battery.

I Like your suggestion though, I consider it a bit more safe.

"Roger Lascelles" wrote in >

Your test spec looks unusual to me. Even a half dead battery will recover

that is the purpose of the test.. hence looking for infant mortality of the batteries in quextion. It seem that ther manufacturer does not confide mich in many battery testers. I am assuming that they have high turn over rate of failed batteries, that when is returned, by their standards is good. This creates a logistical problem, I intended to avoid on my end.

I suggest that you view my response and quote from Interstate. A load of 100 amps *is* abusive on those poor little batteries, and the spec is a higher voltage *during* load.

A 100 amp load can *create* "infant mortality" of the batteries due to excessive internal heating created by the massive current. Might as well put a #0000 silver busbar wire across the terminals and let the battery melt or explode. If a battery melts or explodes in those conditions, then it *WAS* good; if not, it was (and is) bad. Sort of like the joke about testing fuses.

Oh I know... hence my comment on the original post about laying a bare wire across.

however the manufacturer claims that it can hold 110amp load for 15 seconds.

16 seconds would be abusive. figure that one out. I think I might go a differnt route all together.

got a website? distributors in the states?

I would consider using several auto headlamps. The usual headlamp draws something like 20 amps or so, and they're relatively cheap. They don't need a big heatsink nor mineral oil, so you're way ahead in that respect.

That's some hummer 240W lamp. The H6054 is rated at 65/35W on 12V systems. mike

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