# Battery capacity testing

I've finally acquired enough equipment to measure the remaining Amp-Hour capacity of my Lead-Acid and Lithium battery collection. The
first result that jumped out is that older batteries suffer from rising internal resistance as they discharge, enough that the automatic low voltage cutoff trips short of rated capacity, and then the battery slowly recovers to well above the full discharge voltage given in the specs.
http://www.power-sonic.com/images/powersonic/technical/1277751263_20100627-TechManual-Lo.pdf
The 5-year-old 12v 4.5Ah UPS battery I tested this AM delivered 2.45Ah at 3A, which is the average current my laptop draws while browsing. Table 2 shows in the 1 Hour Rate column that it should be good for 2.75Ah at 2.75A current.
Does anyone know a good reason why I can't measure the true remaining capacity in two steps by first discharging to 10V at the fairly high current of my typical loads, then continuing at the 20 hour rate AGM batteries are specified for until the voltage drops to [the appropriate endpoint] again?
The run time for a typical load tells me how useful the battery still is, but it combines the effects of capacity and resistance. I'm wondering if also knowing the Amp-Hour capacity at the 20 hour rate, with less interference from the internal resistance, would indicate how well my long-term maintenance procedures work.
-jsw
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That wasn't a good example. I have a 12V 12Ah AGM battery that is down to 1 useful Amp-hour because its voltage droops to 10V so quickly. Afterwards it recovers above 12.2V. -jsw
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On Friday, May 19, 2017 at 12:33:52 PM UTC-4, Jim Wilkins wrote:

7-TechManual-Lo.pdf

I think that doing the 20 hour test my provide you with academic indication of the condition of the batteries, but only at the 20 hour rate. In my rec ollection (based on 25 years ago designing a 100 station lead acid charger) , there is surprisingly little correlation between capacity at different di scharge rates.
So, I would suggest you test at your normal load and perhaps with a "normal minimum load" assuming that those rates are pretty far from 20 hours. Anyt hing else is, as I said, purely academic.
BTW, while I was buying the voltage reference, I also bought a USB power me ter (Drok). The Amazon add and the user's manual keep referring to "capacit ance" measurement. What they really mean is capacity of USB battery packs. Pretty funny. Sort of. You can actually buy this meter bundled with a USB l oad bank.
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On Friday, May 19, 2017 at 12:33:52 PM UTC-4, Jim Wilkins wrote:

I think that doing the 20 hour test my provide you with academic indication of the condition of the batteries, but only at the 20 hour rate. In my recollection (based on 25 years ago designing a 100 station lead acid charger), there is surprisingly little correlation between capacity at different discharge rates.
So, I would suggest you test at your normal load and perhaps with a "normal minimum load" assuming that those rates are pretty far from 20 hours. Anything else is, as I said, purely academic.
BTW, while I was buying the voltage reference, I also bought a USB power meter (Drok). The Amazon add and the user's manual keep referring to "capacitance" measurement. What they really mean is capacity of USB battery packs. Pretty funny. Sort of. You can actually buy this meter bundled with a USB load bank.
=======================I want to separate the effects of capacity and internal resistance to see if equalizing etc improves either or both of them. The internal resistance of AGMs has some strangely behaved component reputedly related to an oxide film. Otherwise I discharge them at the current my laptop draws when browsing as I have them for power-outage backup and NWS radar is the best indication of storms approaching my house that I've found. It tells me when to repair roof damage and when to tarp it.
I bought this which has an easily set low voltage disconnect and handles up to +/-30A, (Amazon.com product link shortened)
and previously this which is 10x as accurate at low current (Amazon.com product link shortened)
The first one measures charge and discharge current separately and counts the Amp-hours up or down accordingly, though the Watt-hours total is the positive sum of both (???). It has a more accurate voltmeter and a better timer that counts seconds and stops when the relay opens, allowing a pause in the measurement and a record of battery run time. Unfortunately the current resolution is 0.1A despite the display, so it doesn't handle small AGMs well.
The second one matches other ammeters to 1 or 2 digits and I use both in series for discharge loads up to 10A. Together they each make up for the deficiencies of the other. The 12V,12Ah battery is discharging on them at 0.5A. -jsw
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I've read that repeated capacity tests on the same battery don't correlate well.
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On Fri, 19 May 2017 16:13:34 -0400, "Jim Wilkins"

Hmm, there are 3 different pictures of the back of those. One has a built-in shunt, another a pair of relays, and another is bare. Which is the real meter pic for the "30a w/ relay"?

IF I ever get the weeding done around here, I'll get those panels up and build the control panel to see how those li'l Bayites work. You showed another link for a milliamp/millivolt-resolution meter a few weeks ago, too. How's that working for you?

The former part is cool. Not having proper resolution for decent data is never fun, though.

Did I ever ask you why you didn't use a real battery for that? <g> (real being 12v 35-275Ah) I set one up for use with the 45w HF trio of panels and was able to power a 14" electric chainsaw with the 2kW modified sine wave inverter, also from HF. It would have taken days to recharge it (or more panels if needed for continued use.)
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wrote:

The 30A model I received has a shunt and blue NC relay on the base module. The display module has a small red+black pigtail for external power if you don't use a USB connection. At first the USB connection on mine was poor and it intermittently shut off, or switched to wireless without losing power. The correct accumulated totals reappeared when it reconnected.
It displays current to 2 decimal places but is accurate only to 1 place +/-, for example 0.478A on a Fluke 8600A reads as 0.48A on the 10A "Electrical Parameter Tester", and 0.65A on the 30A unit.
A layer of Gorilla tape tightened the USB plug in the base unit against the circuit board contacts and it has remained connected when moved.

The 33.00V/3.000A meter is my favorite for recharging and equalizing batteries slowly from my solar panels. It clearly shows when a small AGM's charging current has decreased to 1% of the C/20 capacity, like 45mA for a 4.5A-h AGM battery. Currents around 1% are recommended end points for trickle charging. http://www.trojanbattery.com/pdf/TrojanBattery_UsersGuide.pdf Diagram 4 gives 1-3% for flooded, Diagram 5 gives 0.5% for AGM.
As mentioned, the current rises in older batteries and is an indicator of declining condition.

I first learned how to make accurate measurements as a chemist whose results might have to stand up in court, then when building very precise automatic test equipment for the semiconductor industry. Analog Devices' op amps and voltage regulators were tested on machines whose performance I was responsible for. https://en.wikipedia.org/wiki/Automatic_test_equipment

I do have "real" batteries that will run the fridge for about 20 hours. Once I'm satisfied with my discharge testing setup I'll get to them. For now I'm testing and risking smaller, older, less valuable jumpstarter and UPS AGMs. These tests are too long to watch and if the low voltage disconnect fails the battery could be drained flat before I notice. -jsw
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wrote:

Previously I was using a rewired Battery Isolator I bought from Quicksilver Radio for \$5 at a hamfest to disconnect the load when the voltage dropped. This describes the idea: http://www.fridge-and-solar.net/The-Redarc-Smart-Start-VSR.htm
The rewiring changed it from switching the load to the second battery when the main one's voltage dropped to switching one battery from the load to a charger.
As a discharge controller it has the disadvantages of still drawing current from the main battery to operate the relay after it has discharged to the disconnect voltage, and needing an adjustable power supply to set or check it.
I haven't seen that remaining for an hour or so at full discharge would further harm a battery and want to record the voltage it recovers to without any load as an indication of true remaining capacity and a safety check that I haven't set the disconnect voltage too low and drained the battery too far.
If not for its poor current resolution the 30A Drok unit would be a fine discharge test controller when powered from an external 12V supply that separates its operating current from the test circuit. The circuit board was drilled but not properly connected for an SPDT version of the SPST NC relay it comes with. I'll set the Battery Isolator to a lower disconnect voltage as a backup on the load side of the Drok.
Based on Amazon comments, it seems the 3-wire / 2-wire jumper may select battery circuit or external power to operate the device.
A DC-AC inverter powering a safe resistive load like a crockpot can be used as a discharge test load though you can't set the dropout voltage and it may cycle back on when the battery recovers. -jsw
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On Mon, 22 May 2017 08:34:11 -0400, "Jim Wilkins"

Great price!

Discharge in series? Sounds like a plan.

Those I've seen only engage the relay to switch to the secondary battery. Are you talking about when the secondary battery is discharged/cutoff and the relay continuing to be engaged? I see that as a problem, too. Perhaps rig up a kickout relay to disengage when the cutoff hits on the secondary?

Yeah, that's a fly in the ointment of capacity measurement. Are you saying "full discharge to cutoff point" there?

There ya go!

It didn't look like that was fully populated in the pic I saw. IIRC, it had only one pin/solder joint out of the 3.

Hmm, yeah.
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wrote:

This one remains powered by the main battery when it switches the load to the second one, perhaps to avoid the glitch while the break-before-make relay contact is moving. It drives the relay with an SCR and won't release and revert to the main battery until the user pushes a disconnect button, regardless of how high the main battery may have recovered or been recharged. This means that connecting NO to a charger won't make the relay turn off when the battery voltage rises.
I cut and jumpered the traces to redefine COM as the battery instead of the load, which is now NC. Originally COM was the load, NC the main battery and NO the secondary one. As you said it would simply allow the secondary battery to die, but retain whatever capacity the trip point left in the main battery.
Maybe running the anchor light as long as possible is more important than preserving a battery that sinks when the boat is hit?

Here's the problem: http://batteryuniversity.com/learn/article/how_to_measure_state_of_charge "To get accurate readings, the battery needs to rest in the open circuit state for at least four hours..."
The AGM I discharged at a little less than the 20 hour rate (0.5A) tripped at 10.0V (twice) and then recovered to 12.15V, which is over 40% State-of-Charge on that chart.
The point of knowing the full capacity is to find out why I'm not getting it, and see if anything I can do makes an improvement. I can't fix bad interconnects but a discharge - charge - equalize cycle reforms the active material. Only measurements will show how well equalizing and desulfating work. I know I can make them last much longer than usual, but is it worth the effort?
-jsw
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http://batteryuniversity.com/learn/article/how_to_measure_internal_resistance The two-tier DC load method is how the engineer had me test electric vehicle Lithiums, using a programmable electronic load and a much better DC current probe than I'll probably ever own personally. -jsw
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On Mon, 22 May 2017 20:53:17 -0400, "Jim Wilkins"

Interesting. It looks like I'm going to have to take their "course" to get more up to speed. Until now, I had never heard how CCAs were measured.

Indeed. Some equipment cost is measured by X years of debt and probe valued at X months of wages. =:-0
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http://batteryuniversity.com/learn/article/how_to_measure_cca_cold_cranking_amp The HF carbon pile performs the test as they specify, with a 15 sec timer to warn you to turn the current down before it overheats. So far it seems to be a good and relatively inexpensive tool to measure the margin your battery has over the starting current your vehicle requires.

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Here is a good, simple overview of battery charging: http://www.iotaengineering.com/pplib/Charging_Stored_Batteries.pdf
I use simple dumb chargers for the high current bulk phase and smaller, more efficient and better controlled ones for the final ones. It costs nothing to leave a battery on a solar powered charger. The big chargers draw idle power, transformer magnetizing current, that may be more than goes into the battery. I've added an input tap after the rectifier to let a charger operate on solar if available or grid power if not.
"The charging parameters discussed here are applicable to ?ooded lead acid batteries. Be aware that some available smart chargers may not be suitable for other applications."
However the makers post their products' parameters, which aren't hard to meet with a voltage-adjustable power supply with meters. Some of my AGMs have the charging conditions printed on the cases. -jsw
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On Mon, 22 May 2017 18:39:59 -0400, "Jim Wilkins"

That would do it.

(Which you didn't answer.)

And you thought the tripping was from the internal resistances, didn't you? But the deeper the DOD, the shorter the battery life. (Loved the Hot Tip on the Fridge and Solar site. Batteries love to be charged but don't much like being discharged, etc.) Speaking of which, what's the difference (other that price) between the standard Ford style starter relay @ \$12.99 delivered and the \$80 Enerdrive VSR super-duper battery disconnect switch? As I look at it again, I see that it has voltage-sensitive engagement. (\$0.37 worth of old 7400 series chips?)

IIRC, I recently read that EQ can be good, but frequent EQ shortens battery life.

Good question. Perhaps with a more expensive battery, it would be, or in a top-down situ where the grid is and stays out. I rather doubt it with UPS batteries otherwise, though. Q: are the internal plates and connections in the larger glass mat batteries the same as the smaller AGM UPS batteries? I do know that the larger, PV-rated LA batteries are more up to the task, and they're really heavy (massive lead plates) and pricy.
It seems like this would have been done and written about by many a battery manufacturer by now, or by their ad people. "Our batteries and chargers are better because..." But I grok the "need to know" function, too. I believe I'll be getting a lot of experience and experimentation in the next decade, too, playing with solar.
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wrote: > ...

Thus taking the battery down to 10V cutoff at the 20 hour rate wasn't a full discharge, so I couldn't answer. There was still capacity left that was unavailable for some reason, perhaps one higher resistance cell that I might be able to bring back by slow equalizing. I've had some luck restoring a weak cell in a flooded battery and had popped open that 12V 12AH AGM to add water, but it didn't appear to help enough.

I had bought some LM324s and a relay to build one before I found the Battery Isolator for \$5. It's a hand-drawn circuit board in a Radio Shack grey aluminum box, like the stuff I built as a kid, though it seems to work well enough.

Since I don't cycle my batteries daily I can afford to experiment with slow charging from the solar panels at a few percent of the Amp-Hour rating current. Rather than adding a current limiter which would cut into the already minimal voltage overhead of solar panels, I've been charging with simple, rugged LM317 and LM350 regulators with meters and bumping the voltage up a little when I walk by and notice the current has dropped. Before long the battery charges high enough that an AGM draws only C/100 current at 15V and a flooded battery at around 14.0V, though they all are different. The current lost to electrolysis seems to decrease, as shown by the battery drawing little more current above 14V than at 13.6V.
I built a homebrew power supply whose current limiter adjusts from <1mA to 0.4A. I use it to restore old electrolytic capacitors at about 5mA and to desulfate free batteries that need to be hit with over 16V to accept any current. For them the current needs a limiter to avoid pegging the ammeter as they recover. I've been using one such free "dead" battery in my tractor for two years.
I'm equalizing as gently as appears effective. The goal is to determine if a variable voltage source with high resolution volt and amp meters is enough to prolong and restore batteries IF operated properly, which is the tricky part; the hardware is cheap except for the Variacs that I already had.
It may be the sort of gizmo that only the inventor can make work, too troublesome to be commercially valuable. I've come up with several ideas that work fine for me but no one else.

AFAIK flooded batteries can be nursed to live longer than maintenance-proof ones, so I lack the experience to answer that. I don't own batteries larger than I can carry down the stairs and outdoors to let them gas freely when I equalize them.
This isn't New Orleans; after a natural disaster the local governments quickly clean up and repair and only expect FEMA to arrive afterwards and write checks to cover the cost. My father was the CFO of one of the state's departments that participated.
The dump trucks and loaders the towns need to clear snow can repair flood washouts and push fallen trees off the roads, really everything except paving and building bridges. My one-week storm preparations could stretch to two weeks but I don't think any longer is likely with the high level of response I've seen here.

Neon John posted a good reference to actual experience maintaining backup batteries. I haven't found much else that gives hard technical details instead of wishful copywriter promises. I did some work once on 48V telco battery banks, otherwise my industrial experience is mainly with Lithiums which are still overly expensive.
-jsw
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On 5/24/2017 6:49 AM, Jim Wilkins wrote:

There are some nifty hall-effect sensors with almost zero drop. Used one in a solar/wind system with a shunt regulator. Wind generators don't like being unloaded by a series regulator.
I've been

I'd like to hear more about your desulfation successes. High voltage didn't help. Other crazy ideas I'd read about, like AC at various frequencies to 'ring' the plates and shake off sulfation, etc. Got absolutely nowhere.

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http://www.ebay.com/itm/Bayite-DC-5-120V-100A-Mini-Digital-Current-Voltage-Meter-With-Hall-Effect-/361553795712
How stable is the zero reading? This is the best DC Hall effect ammeter I've seen and its zero drifts by several mA per minute if held still. When moved the Earth's magnetic field throws it way off. https://www.eevblog.com/forum/testgear/a-look-at-the-uni-t-ut210e/

http://batteryuniversity.com/learn/article/sulfation_and_how_to_prevent_it I've fixed several "dead" U1R lawn tractor batteries and used them for several years. The symptom was not accepting more than a few milliAmps from a commercial charger, although the resting voltage seemed OK. The fix was using the variable power supply to force 16V to 17V which caused the current to very slowly increase and then the required charging voltage to drop, an unstable condition that requires current limiting, such as with a low end lab-type supply like these if you can't rig up your own. (Amazon.com product link shortened)
After the battery had accepted enough charge to raise the electrolyte level I checked specific gravity and found one or two low cells. Charging at a current that didn't make the others bubble excessively, around 0.5A, eventually brought up the low cells. The resurrected U1R in the tractor now can put 150A into my HF carbon pile load tester.
I've read that salvaging batteries this way can take up to a week. I saw progress with salvageable flooded batteries in a few hours but haven't had much luck with AGMs.
The neighbors who give me these batteries know I can fix them, and that they will need frequent attention afterwards. I have to top up the charge at least monthly or their internal resistance will rise again.
I don't know if the cause is literally lead sulfate recrystallization or not but it's a handy suspect to blame. There's a theory that it's a thin oxide barrier between the grid and the active material. Whatever the cause, the effect is a very high internal resistance. Automatic chargers see the voltage rise as though the battery was fully charged and shut off. Some people have reported success using a Harbor Freight manual charger on a Variac as the variable supply. -jsw
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On Wed, 24 May 2017 09:49:55 -0400, "Jim Wilkins"

Hmm.

You added water to an AGM? How did you do that? And how had the AGM lost water?

I've seen soldered IC, resistor, capacitor forever encased in clear RTV which, while not purty, was fully functional.

OK, I think I now have the full picture.

So "dead" batteries go into meltdown mode once they do finally start accepting a charge? I see why most people have no success at it. Even with the "save your battery" goo scam.

I wish I'd grabbed the cheap Variac which was offered to me long ago.

For most people, plug-n-play is the only way. For Makers like those of us on RCM, fiddlin' is the only way.

Interesting. Remember seeing the difference between OK after a tornado and elitists in NY after a hurricane? Everyone came out to help in OK, while elitists sat surrounded by mess and complained to the Press about their blocks, all while not one single person came out to work to clean it up. Absolute night & day differences, wot?
NO: Save the city in a hole! Don't fill in the ground and bring it above levee level so it never happens again, just put in bigger pumps. Crom, those folks are smart...not. I wonder what genetic strains will come from those folks now living where thousands of fracking ponds (full of 600 different hazardous chemicals) were strewn by Katrina. I tend to not buy anything from LA nowadays.

Were I there, I'd have months worth of supplies for everything.

New Atlas had an article recently on doubling the density of lithiums. I hope Tesla Gigafactory takes advantage of it. That should drop the price considerably.
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wrote:

I pried off the cover plate over the rubber caps, which pull off easily. I don't know why some of the cells were dry. It's a replacement from Batteries Plus I bought in 2009 to revive a dead UPS. When new it delivered 82 Watt-hours; 12V times 12 Amp-hours is 144 Watt-hours, though only at or below the C/20 rate.
I measured computer run times on it a few times and plugged it in occasionally to recharge. It wasn't on continuously because I had changed from desktops to laptops that consume about 1/4 as much power and serve as their own UPS, and after I found the free APC1400 and rigged two external 105A-h batteries to it the small UPSs weren't needed. In 2015 I noticed that its run time was very short and began testing suggestions on how to salvage the battery.

I suspect that pulse desulfators are a simple way to apply a high enough voltage to break through sulfation while reliably limiting current with capacitive and inductive impedance instead of active control. Personally I prefer DC because an ammeter that reads milliAmps shows how much the battery is improving, or not. My own results and advice I've read suggest that a battery which needs over 17-18V applied before it accepts current can't be saved.
Dumb transformer + rectifier battery chargers have a moderate output impedance that makes the current decrease as the voltage rises and conversely increase as it drops, but not as sharply as a regulated power supply.
The charger I was using then was an old manual 6 Amp Schauer with a small 3 Amp Powerstat added to adjust for the current I wanted. The current didn't change all that much as the voltage rose or fell, so the battery didn't actually run away.
A tightly regulated power supply could possibly let a battery run away unless its current was limited by circuitry, its transformer or the solar panel source such as the HF kit which is a good match to slow battery reconditioning.
The power supply I built from a Variac and an arc welding transformer has a relatively high output impedance to give the arc its constant current characteristic, enough that the rectifier/cap output ripple at 20A is roughly a 1V sine wave. It puts out over 50V no load and drops rapidly to around 35V as the current increases, with 120V AC in. The output voltage then holds steadier up to around 25A out, its experimentally determined 100% duty cycle limit. It will briefly exceed 50A which is useful for testing components.
As a 20A 24V battery charger it holds its output current quite steady during the bulk charge phase but then becomes dangerous because it won't automatically decrease the current enough when the battery voltage rises to the gassing level. The simple fix is to pass the output through a P20L or similar cheap solar controller set to reduce the current when the voltage per battery reaches 13.6V. Light fizzing that varies a little between cells becomes visible around 13.8V.
My two series-connected batteries, of different ages and sometimes topped off to different levels, automatically self-balance to 13.6V each on the APC1400's float charging current. Each has its own voltmeter to watch that, also if one discharges faster.

Cheap Variacs may need new brushes, which are far from cheap. I bought a brass bar and some larger carbon brushes and machined my own replacements because the right ones were out of stock. The original brush geometry was too tricky to mill and assemble so I made the brushes thicker and thus less fragile and will have to trim the end contact width as they wear. http://www.carbonbrush.com/brushes.htm They use silver epoxy to glue in replacement carbons instead of pressing tightly fitted ones in like the originals, and after pressing mine in I understand why. I had better luck tediously cutting them to size with a razor saw and files than milling them because they are so brittle.

I think two weeks is probably enough in an area where people and local governments have the tools to recover, though not in cities where there's no place to run a generator. Germany and Japan kept their societies functioning pretty normally until the very end.
I assume my biggest need will be roof repair to prevent further damage. When a fallen tree top punctured my roof in over a dozen places I quickly covered the holes with sheet metal shoved under the shingles at the upper end. I lost the shiny finish on my 6061 aluminum but saved the house from water. Plywood covered with a large tarp would also have worked, unless everyone else had the same idea and the stores were empty. I happen to have the machines to work sheetmetal and the need to make electronic enclosures.
When Jay Leno asked New Yorker actress Lea Michelle how she handled TS Sandy she told him she didn't even own a flashlight. In my Mensa experience that's fairly typical of the complete dependency they accept as natural, can't change and don't think about. Let the good times roll.
-jsw
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