Battery capacity testing

On Fri, 26 May 2017 10:21:39 -0400, "Jim Wilkins"


I don't recall seeing covers on AGM cells, just small perfs.

I got about 7 minutes from my desktop UPS (450VA IIRC). The rest have failed at the worst moments, NOT keeping my comp running when the power went off. I've bought maybe 3x the number of batteries than I have UPSes so far.

That's a lotta volts.

Ayup. That's safer.

I like the current limiting in the cheapie 0-30.0v 0-3.00A Chiwanese lab supply, and suppose I could get finer adjustment with a milliammeter inline and the fine tune pot.

Nice and beefy!

So, output from the PS to solar input terminals on the controller? Unusual, but I guess it'd work, wouldn't it? Cool.

Hooked up in series or parallel to charge? I don't know APC1400 specs or setup.

I nearly -ran- out of an electric shop once after getting a quote on brushes. I guess they hate competition.

They _are_, aren't they? Nasty stuff to work with.

Yeah, IF the local gov'ts do recover. What if the area is larger, like the whole east coast? Prepping is truly cheap, compared to the alternative.

That's why I took most of my trees down. I'd rather my house not be a target, thanks.

But the rich folks' armed bodyguards might take things from others if others aren't careful.
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wrote: >>>>I've had

They had to be assembled somehow.

Yep, works fine as long as I keep the voltage from spiking above the safe input limit when the current is interrupted. The welder transformer has that nasty habit and so do poorly regulated generators. Testing this stuff drove me to buy the (older) HF inverter generator, which holds a very steady 120V from no to full load. The Coleman I had been using need to be set close to 140V at no load to be able to supply barely 100V at full load. The APC rejected its output and stayed on battery until I found how to reduce the line quality sensitivity.

The APC1400 needs 24V, originally from two internal 12V 18Ah AGMs in series. Their heavy cables run to a rear panel Anderson plug, in a Y shape with the battery on one leg, the inverter on another and a safety disconnect shorting plug on the third, normally at the rear panel. Moving the short to the internal battery position makes the rear panel plug the input.
I ran fused twisted pairs from each battery to a voltmeter and switch panel under my Harbor Freight solar controller. They connect to a DPDT center off selector switch that can tie the HF controller to either battery. Both wires in the pairs are fused to protect against any switch failure, since the batteries may still be connected in series.

I lived in the center of the track of Hurricane Carol. The eye passed right over us and was quite spectacular, bright sun lighting an enormous dark ring wall. https://en.wikipedia.org/wiki/Hurricane_Carol Afterwards my father found gasoline at a station that had rigged a Jeep to run one pump and drove around to assess the damage, as far as we could since fallen trees blocked many roads. Back then few people had the chainsaws or generator so widely available now but we managed to recover without too much trouble.
Do you belong to a church or club with an experienced leadership structure, that knows members' abilities and how to organize events?
-jsw
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On Sun, 21 May 2017 19:49:32 -0400, "Jim Wilkins"

Duct tape to the rescue again.

I've downloaded both guides you've mentioned in the past several days and will have to compare them. Each one will have tidbits of info the other doesn't. That's the true benefit of research: gleaning tidbits.

That sounds like something I should pay attention to.

Cool! Nice legacy.

I forgot to ask what you meant by that. Are they drawing half an amp or showing that discharge rate?

Smart.

That wouldn't be fun. How often do the disconnect programs (or hardware/relays) fail?
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wrote:

I suspect it means that the self-discharge rate has increased and they may need more frequent topping off. I don't know how it relates to remaining capacity.

I kept the current from the battery close to 0.5A by tweaking the rheostat load. Surplus phone chargers power the meters and the relay independently from the battery, since I won't be wasting my backup by running these discharge tests into a dummy load during a power outage.
Some of my homebrew test equipment runs on AC power for better accuracy, some on DC from the battery being tested or the solar panels so it will still show demand or charging rate during a power outage. The load current varies too much for accurate measurement and battery remaining life prediction, but all I really need to know is if the batteries can run the fridge overnight.
The box whose components I tested this morning will have a switch for internal or external power. The meters have to be on external power to measure single 18650 Lithiums to their discharge endpoint which is below the minimum supply voltage..
The two of these I bought match the Fluke 8800A to 1mV. YMMV. (Amazon.com product link shortened)

How often do brakes fail?
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On 5/22/2017 9:34 AM, Jim Wilkins wrote:

One consideration for backup is the cost of failure. if the worst that can happen is a gallon of milk has shortened shelf life, that's a lot less serious than a mechanical fridge compressor that stalls when it tries to start under brownout conditions.
If you're serious about these kinds of measurements, wire up a LM317 (maybe with a booster transistor) as a current load.
If the voltage doesn't vary too much, an incandescent light bulb makes a current source that's more stable than a resistor.
A computer controlled dual-output power supply is a useful tool. Use one output to charge the battery and read back the voltage. Use the other output to drive a voltage to current converter for the load. Makes it very easy to control and log and graph and...
If I had a solar system, I'd have an arduino or some such monitoring it at all times.
I have a Palm Pilot monitoring the HVAC system. Had the installer come fix it before it quit completely.
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I'm more concerned with being able to replace the lost food after a hurricane or ice storm when the roads are blocked by fallen trees tangled in possibly live power lines (generator backfeed) and the stores don't have power either. The area I'm in typically stays dark for a week before the line crews get to us. https://en.wikipedia.org/wiki/December_2008_Northeastern_United_States_ice_storm

I had very nice, and expensive, equipment like that when I was the battery tech at Segway. While running the tests I found out what was important and what wasn't, and saw that I could obtain adequate results at home with much cheaper surplus equipment like old Ohmite rotary rheostats. Tubular variable resistors are difficult to adjust when hot, around 600F near their rated power.
The only time I programmed a load to change automatically was for two-level battery impedance measurements. Otherwise the voltages and currents remained constant until I changed them, which can be done as easily with a knob. We used our lab power supplies to recharge vendor sample Lithium cells to the appropriate voltage at a constant current.
The best representation of a real-life active load isn't constant resistance or current but constant power such as a DC-AC inverter draws, and I can just use one with a hotplate on a Variac for the adjustable load. Inverters usually have a functioning low voltage disconnect to protect the battery. However a fixed resistance load is fine for tracking battery ageing and easier than a switching load to measure accurately.
These connected to a laptop make a good data acquisition system for slowly changing parameters like battery voltage. (Amazon.com product link shortened) Since they are optically isolated they can be connected anywhere in the circuit without creating unwanted current paths through their cabling, a major concern with grounded instruments like scopes. You can combine their separate datalog files into a spreadsheet by aligning the timestamps.
A laptop makes it easy to set up in the best place to run the test. For me that's in the laundry room where I have running water to deal with battery acid spills. The laptop itself can be the representative load on the battery and its own internal battery will keep it running when the battery being tested drops out, so it doesn't lose the most important data point. The time that happens, saved in the system Event Log, may be all you need to know. Older, thicker laptops with CardBus or ExpressCard slots for port adapters to read multiple meters are cheap.
My pure sine inverter reports status over a hand-wired non-standard cable to a monitoring program I wrote but I haven't found much use for the results. This is more valuable: (Amazon.com product link shortened)95542138&sr=8-1&keywordsyite+100v+100a If that link doesn't work it's a Bayite PZEM-051.
This VAC-1030A could be great if they fixed a few minor bugs and wrote a decent manual. It's good enough already. http://www.ebay.com/itm/VAC1030A-The-New-Wireless-Bi-directional-Voltage-Meter-/262562495499 I haven't tried the 100A model, VAC-1100A, because I normally recharge at a current too low for it to measure accurately, though the VAC-1030A isn't much better.

Monitoring my solar system showed that clouds pass randomly and I still need a backup generator since I can't depend on a consistently adequate solar output, especially in the kind of weather when I'd need it most. I occasionally check the output and wiring drops on bright, clear days. A cheap HF DVM gives the short circuit current.and an RC wattmeter and variable resistor can find the maximum power point. (Amazon.com product link shortened) That's just an example, not the discontinued meter I own. It shows that the power doesn't fall off much on either side of the maximum, meaning there's little benefit from an MPPT controller on a small system.
-jsw
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What happens to the expensive power supply if the AC power fails while the battery is connected, or you accidentally connect the battery backwards??? http://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey 00003725:epsg:faq&nid=-35721.0.00&id00003725:epsg:faq "Active loads that create a sinking current should not be connected to a power supply."
I've been charging batteries through series diodes, using this meter to monitor the voltage beyond the diode drop: (Amazon.com product link shortened) "With reverse polarity protection to avoid burning out" A spare LM78xx from your junk collection can extend their supply voltage rating above the input limit, an LM7824 increases it the highest.
The one I tested the other night matched a 5-1/2 digit Fluke to 1 mV at 10V in. Notice where it was made.
The output protection I've been adding to my homebrew battery charging variable power supplies is a forward diode to block a meter-busting surge back into the 0.2 Farad output cap and a reverse-biased diode to ground that -should- pop the output fuse or breaker if a battery is connected backwards. The problem with testing breakers is that they have a maximum interrupting rating above which they may work only once, and of course with fuses is that you know they -did- work and hope the next one (from a different source?) is the same. -jsw
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On Mon, 22 May 2017 12:34:09 -0400, "Jim Wilkins"

Ahh, OK.

OK, so your -fridge- demands 0.5A? <titter> It's hard for me to conceptualize a half amp draw at 12v, as few things operate at that level.

I'm fairly fond of 18650s, having used them in the LED flashlights for awhile now. I love that Lithiums don't self-destruct, and don't suck their own juices from themselves while they sit on a shelf. Nicads and LAs have always bothered me with that nasty characteristic.

Amazing, but good news.

Notalotta, but it's a bummer when they do.
Are you trying to (or not to) tell me about a box full of 18650s you're putting together to run your fridge when the power's out? Testing those with a 6w drain just might be the connection my mind continues to search for with your bloody half amp thing.
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wrote:

Maybe I should have repeated that I was discussing a different battery closer to the mention of the fridge? I post all this to practice clear, concise technical writing and then try to determine why it's so often misinterpreted.
The fridge takes 120W initially, slowly dropping to 80W, as measured with a Kill-A-Watt on wall AC. When the power goes out it runs from an APC1400 SmartUPS pure sine inverter with two external 12V Group 31 batteries. Discharge tests on them could end in the middle of the night and let my fridge warm up, so I bought equipment to automate the capacity measurement with safe loads.
I'm checking out that equipment on less valuable batteries that don't take nearly as long to discharge. I've been posting a summary of significant observations, not a daily diary of my experiments, so I haven't always clearly indicated which battery or test load they came from. The 0.5A test was to measure the C/20 capacity of a smaller AGM battery from a 350W UPS.

I found a source of tabbed Li-ion 18650s for $2 each and hope to restore old laptop batteries etc with them. They appear to have been in storage long enough that some dropped below their low voltage safety disconnect, but still accept a charge applied directly to the tabs.
-jsw
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On Thu, 25 May 2017 07:53:31 -0400, "Jim Wilkins"

Data is far easier to get scattered on Usenet, where we potentially zip through hundreds of items with dozens of topics daily. But, yeah.

My 2002 Frigidaire 18cf fridge uses only 135w with the compressor running. I didn't track it while running, so mine may have tapered off once the system normalized. That figure really surprised me, it was so low. The '80s model before it took a lot more power to run. Progress is good.

Yes, I finally came to that realization yesterday after having some fun with you. So solly.

Z-tabbed for spotwelding, or other? I'm not sure if the cheapies I bought have the protection cell, so maybe you're talking about bypassing it on your genuine cells. Maybe I'll rip one apart and see if it's done properly. (Judging by Youtube vids, they don't have the protection cell.)
I found a source of (supposedly) new 18650s on eBay for a buck apiece with wild claims of up to 6000ma capacity. I figure 1,500 to be the norm, and they're worth a buck. AC and DC chargers go for a buck a pop now and then, too, so I stock up. Bright LED (XLM-T6 and Q5) flashlights and headlamps go for $2-5 each so I got sets for the whole family as stocking stuffers one Christmas.
The 18650/T6 combo lasts a couple hours on high, and my normal use is under 3 minutes (forgotten mail, raccoon in tree) so I'm happy. The zoomable waterproof lights are great, but I seldom use medium or low beam, or the flasher or SOS modes. http://tinyurl.com/l8xgsf7 The zoom function works well on the bike, but I'm not crazy enough to ride at night. It allows you to set your own beam width.
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wrote:

Don't be. I've intentionally chosen proofreaders who would take everything the wrong way when I was ambiguous. That's why I wrote the "press any key" routine that faked a crash on Alt or Shift.
-jsw
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On Fri, 26 May 2017 11:14:43 -0400, "Jim Wilkins"

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wrote:

Cute, but just a one-time sight gag unless you can write a routine that detects and responds to them.
I've used Dial-A-Prayer for that sort of prank. It's an ominous warning when -they- call -you-, right? (transfer the call)
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On Sun, 28 May 2017 07:33:45 -0400, "Jim Wilkins"

Yeah, it's only good for people walking by your keyboard and finding the infamous ANY key. I wonder how many they sell at $26 a pop!

Eek! (running away) I had a nice church lady spittin' nails a while back when she read the sign on my front window. I didn't have to answer the door, and I could hear her through the window and see her through the translucent white curtain. She wanted to spew religion at me and that sign made her show her true colors. I'll bet the man with her never went out with her again. He left with a smile on his face, following behind her. http://tinyurl.com/hyefhtu
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On 5/19/2017 9:33 AM, Jim Wilkins wrote:

I gave up. Never got any predictive information.
Most of my testing was done with Lithium batteries in laptops.
I consider a laptop battery bad when it won't run the laptop long enough. How vague is that? ;-)
Started with bad battery packs and tested cells. At low current, I almost always got something like specified capacity. The electrons are in there, but the laptop won't let you have them.
I don't know what the sampling interval is, but the laptop wants to shut down at some voltage so you don't lose data and call the vendor. Subtract the peak voltage across the ESR from the battery voltage. If it dips below the threshold, the laptop wants to shut down.
Turn off the power features that warn of impending low voltage shutdown.
The symptom is that the battery gauge decays slowly for a while then drops instantly to a much lower number. The laptop senses impending doom, but you've blocked that. I've had laptops run two hours past the point when the battery gauge hit zero. Problem is that when it dies, you lose whatever you were working on.
I've never had any success trying to fix the ESR. That's probably the same problem you have when your car fails to start. Never been able to do anything about that either.
The higher the peak current, the fewer electrons all those protection circuits will let you have. Even with a new battery, capacity is a strong function of load current.
Numbers from browsing the web won't help much when Microsoft decides to do an update and runs all your cores at 100%.
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    [ ... ]

    Well ... that is not a problem for me. The first thing I do when I pick up a new (to me) laptop is to remove the virus. The last virus was called "Windows 10". I replace it with either a linux or an OpenBSD system, so Microsoft doesn't have a say in when I update, and updates for the others are based on telling me that updates are available, and letting me decide whether and when to install them. :-)
    Enjoy,         DoN.
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The "fuel gauge" IC counts Coulombs in and out to determine actual Lithium battery capacity, on the assumption that they recharge at 100% efficiency. It resets its capacity estimate if the battery is nearly fully discharged and recharged, but if only partly discharged it can't detect the slow loss of capacity with age and retains the old, overly optimistic number from the last full cycle. That's why the sudden jump when it realizes it's wrong.
When you give the battery another full cycle it can measure and update the battery capacity to its new, lower value.
As an experiment I reduced the low voltage trip as far as possible and got almost as much run time from an old Dell battery below the 5% level as from 100% to 5%. It appears that Li-Ion cells can be discharged down to or even below 2.7V briefly without much damage. The normal settings are above 3.0V. http://batteryuniversity.com/learn/article/premature_voltage_cut_off
This gives you the battery voltage: https://www.hwinfo.com/
-jsw
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