I have the opportunity to get an automotive 12v lithium battery, but I would like to test it for remaining capacity/life.
Is there a Lithium battery discharge tester in Electronics committee that can test 12v lithium batteries ?
Jay Johnson
The best Lithium tester I’ve found is this one:
http://www.usastore.revolectrix.com/Products_2/Cellpro-PowerLab-8-EC5-version_2
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The E Lab does not have one. Might check w/ R/C group and see if someone has one you can borrow.
It is unlikely that RC will have any testers that can be used with automotive batteries. Such batteries will tend to have extremely large nominal capacities and need to be tested under load. Expect thousands of watts of current draw…
You don’t need a specific tester. Elab has the tools to perform the measurements; however, you would need to find a suitable load. Something like a heavy duty heater coil.
Tanners does have some low ohm, high watt wire wound resistors.
Depending upon battery capacity it almost certainly is a high enough wattage. I would expect to need at least a 2,000 watt load. Probably more.
The PowerLab 8 I linked to above can charge at 40W (with a good enough power supply) and sink about 35W into a 50% depleted Lead Acid car battery.
I’ve done both with it, and if DMS starts doing more with Lithium batteries, it might be a good idea to get one.
Stan, to test a battery for remaining battery life, you need to place a load that is a significant portion of its rated capacity (typically about 20%). For a car battery that will be a load capable of drawing 2000-4000W. Which works out to 150+ amps.
Any automotive battery tester will be fine like the $25 one at Walmart or Harbor Freight. If this battery is indeed intended for automotive use then it’s lithium iron phosphate (LiFePO4) and is a drop in replacement for lead acid batteries. If you want to know the capacity I have a charger that will show the mAh as it charges (currently being used by @Brandon_Green for the trebuchet).
I actually made a battery tester in former life out of gpib controllable power supply, load resistance with switch, and custom labview software. WITH this simple setup, I was able to set up and cycle charge then load, and track the voltages and currents over time at user definable t intervals. Company I did this for wound up making a whole bunch of tester setups by purchasing a bunch of these supplies, a bunch of switches (I used relay if memory serves me right), and a bunch of loads (selected R with rated power exceeding that supplied wrost case). The ultimate goal here was statistical data. I was even asked to overcharge for some testing, and thus the battery ‘popper’ was born. Since small battery used in this case, pop was explosion of battery as insides expanded beyond capacity of casing to contain. Made holes in drywall. It’s good to not hang out in that room for long…lol…
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If you are wanting serious info about a battery intended for auto applucations, I would think that you may want to look at ways to charge at rates similar to real life, and discharge at actual discharge rates. Trickle charging can yield some info and you can infer what happens at higher charge/discharge ratea. But to know how the cell’s chemistry reacts to use case current levels, you would be well advised to replicate those levels.
Oh, and I don’t recommend overcharging aka ‘popping’ a car lithium battery…lol…
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Do these have the same charge/discharge cycles as the lead acid or are they like AGM batteries where when they are drained too far you have to slow charge them overnight before you can put a faster charge on them?
I built the test system. Which means I got to see/work on the system for a few weeks. The long term results i don’t have, as I moved on to make another computerized instrumentation thingamajig…
The original design spec calls for slow and fast charge modes.I think there was a pulsed mode charge option, pulse width modulated/duty cycle speed option. In the small amount of actual testing I did (I develop test systems, whereas typically an expert in battery science, maybe chemist, maybe physicist, maybe doctor, or team of all the above, takes custom system and uses for their specific interests.) But that is interesting question, as I was curious as well, and for these batteries, I could see no advantage to alow charge. it just took longer. and i do believe slow charge was dropped from design ultimately.
These were small watch style batteries of rechargeable variety. in my few weeks of testing while debugging, I did not see any convincing degrading of potency no matter what I did, except overcharge/pop. The little guys seemed to track near identical charge/discharge voltage/current curves even after weeks of full charge/full discharge cycles. Of course we know degradation occurs, but I guess it took months to years to see the effect, as this would be appropriate for application. That info is proprietary, and by the time sufficient data was compiled, I was contracting on different assignment, no longer with a need to know.
This brings to light another great reason to go with programmable computerized instrumentation type solutions. Sometimes it’s difficult to prescribe exactly what you need done at the beginning of large project. The realities about device performance evidence themselves under evaluation in the lab and ultimately the field. The datasheet, pretty as it may be, is a sales document. So it’s hard to know which way your design and marketing strategy needs to flex and bend along the way until you have thousands of units in the field for years, along with customer feedback data binning various failure modes, complaints, and competitors offerings… likely it will change a lot during development, so it’s a good idea to work with tools and design building blocks that have ranges of analog specs, oversized gate counts, and flexible test setups as well to accommodate the unforseen shifts. The resulting product may be unrecognizable from original inception. In this case it was. The product that sells today, and it was startup success ultimately, the successful product is completely different from what was originally proposed, built, and sold to some early adopters. It probably even used a different battery from the one I originally created the battery test system for.
And since this is probably what Raymond meant:
Is there a datasheet for 12 V lithium car battery in question?
Deltran BatteryTender
P/N BTL24A360C
12v
21-24Ah
CCA 360
New and unused, but on the shelf for 1 year.
My initial reading on it was 13.05v today, it had not recently been charged.
Jay Johnson
Its late, my math is probably jacked, but I get:
Discharge:
Assuming that Cold Cranking Amps has meaning…
R = v/i = 12/360 = .03333333333 Ohms
p = iv = 4320 W
Charge:10 A, so any 10 A 12 V charger should do, but if I were to work on this, I would prefer a power supply with current measurement capability with GPIB, USB, or serial communication control (so the computer can do all the cycling). If you could find an inexpensive 10 A charger off the shelf with USB, serial connectivity and API that could be just as good.
Switches that can handle the power surge. May have additional effects of that power surge. There may be some interesting electromagnetic issues presented when switching this to power the load. Might be best to take the switch off an automobile? Load will generate a lot of heat. I think numerous sets of series resistors, with bunches of these serial sets in parallel, with fan(s)… this would make a good load. Three 120 A automotive relays, and you have a switchable load.
So there is a way to test that battery for starting use case. Maybe this is not what you are looking for, however? Supposing anything is possible, would you like to talk about what sort of load you would like to see how well that battery, or similar, can drive?
Sitting for a year? It’s fine. I wouldn’t bother testing it. Just start using it.
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Yup, will do.
I decided to purchase it after getting the initial reading of 13v.
After reading some info on the web, people are reporting this battery to measure 14v when fresh/new.
So, with the purported time on the shelf, I was okay with the 13v reading and look forward to the reading after I give it a charge.
Jay Johnson
A brand new, fully charged, lead acid car batter or LiFePo4 should read about 14.4V, 13.6 is consider fully charged when under load.