Balmar smart gauge and 10 hour AH testing

You will eventually realize that all of your measuring gizmos will not align, perfectly. When you get new batteries, I'd suggest to familarize yourself with gizmos, choose the one that is the easiest to read, and rely on that. With new batteries, you'll be able to determine a baseline SG with a full charge. You can use that EZ Red as a reference to SG but don't depend on it for accurate measurement.
FWIW, I have a fairly good glass tube temp compensated hydrometer but it's not a Freas. The Freas Glass Works makes probably the only lab grade glass tube hydrometer. Also, all of my individual voltage meters and my Fluke handheld meter are with .01 V of each other. I like to use the Simpson analog meter for voltage measurement at a glance. That needle is big and easily visible from many angles.
Good luck with gizmo alignment!

Mex, you can get into trouble with that method when the battery is not as good as new. By waiting the full time and then checking, you can way overshoot and be down to whatever SOC. Why do that to your battery? By spot-checking the SG you can stop at 50% of whatever 100% is, and not overshoot.

That 4.16 is not the 20 hr rate, 5 is for the 100AH. It will take 10 hours at the 5, but not sure about 12 for the 4.16, because Peukert comes in, and I don't have the graphs for that--also don't know what that battery's factor is for using Peukert. (1.3? or ?)

CAPACITY B.S. TESTER

WARNING! Instruments, tools and effort required

This is a 12.000 hour test not an 11 hour forty two minutes or 12 hour 16 minute test. Be ready to stop load at 12.000 hours

• Get a hydrometer. Get a voltmeter
• Go to NAPA buy a 50 watt 12 volt screw in light bulb. Buy a pair of replacement battery charger clips
• Go to hardware store buy a ceramic light bulb base, 10 feet of duplex 14 gauge wire
• Go home and wire up the lamp just like it was a trouble light -- one wire pos the other neg. Good enough to test a single group 24 or group 27 battery
• Got an inductive DC handheld meter?
• This will make measurement more accurate
• Charge the battery to be tested as full as reasonably possible
• Connect the test lamp
• Note the voltage AFTER 2 MINUTES
• Is the battery a 100 amp hour model? Good, were are shooting for discharging the battery 50%
• Let's say the lamp is drawing 4.16 amps. Divide that into 50 amps = 12 HOURS later the battery SHOULD BE at 50% state of charge
• WELL, IS IT? YES? or NO?
• Check the state of charge by taking a hydrometer dip of all sic cells
• Then refer to a voltage chart for your battery
• WELL, IS IT at 50%? YES OR NO?

Excuse: Too much trouble I don't wanna do it. I want to guess then use tea leaves and E=MC2 parallel universe qualifications.

BFL13 wrote:
Balmar gauge reads 71% soc

So 3 x 7.5 = 22.5AH and the gauge says that is 29% of full. So it thinks full is 77.6AH (out of rated 150)

Does the gauge know there are two batteries?

EDIT--LY you are right this is not lab standard, but it is "close enough for government work". We are trying to use the top 50% where things are fairly linear on discharge.

It was argued here some years ago that the bottom 50% would be different, but that is illogical. We never resolved that argument.

Doesn't matter, the idea is to get some idea of how things stand compared with the rating "as new".

I will try to find that V shaped graph that shows SG etc.

The smart gauge needs 3 charge discharge cycles to calibrate its self per the manual.

Balmar gauge reads 71% soc

So 3 x 7.5 = 22.5AH and the gauge says that is 29% of full. So it thinks full is 77.6AH (out of rated 150)

Does the gauge know there are two batteries?

EDIT--LY you are right this is not lab standard, but it is "close enough for government work". We are trying to use the top 50% where things are fairly linear on discharge.

It was argued here some years ago that the bottom 50% would be different, but that is illogical. We never resolved that argument.

Doesn't matter, the idea is to get some idea of how things stand compared with the rating "as new".

The blurb here shows that you can use SG per SOC on the discharge

https://www.engineersedge.com/battery/specific_gravity_battery.htm

My opinion on 10 hour tests using the 20 hour rate is that one can use such a test at cycle 100 and compare it to results at cycle number 400, and from that comparison gauge capacity loss/ remaining.

I do not feel that the 20 hour load placed for 10 hours and judging voltage rebound or SG, can say whether the battery is still at full capacity, or some percentage thereof by trying to gauge 50% SOC.

Mex has stated before that the voltage below the 50% mark is not linear with teh voltage dropping from 100% to 50%, and while some batteries say 10.5v is 100% discharged, some others will have this 100% discharged number in the 11's.

Granted this is for an AGM, but Crown in the following PDF says 100% discharged is 11.64v:

https://www.wholesalesolar.com/cms/four-star-solar-crown-48-vdc-10-560-wh-with-mnbe-d-enclosure-8-battery-bank-agm-battery-maintenance-2936570746.pdf




After a recent rezeroing/reset of my AH counting battery monitor when known full, I can take my 52 month old ~750 Deep cycle 90AH Northstar AGM to 45Ah from full at 2x the 20 hour rate, and voltage rebounds to over 12.2 within 5 minutes on a battery well below 77f.

Northstar's 50% SOC OCV is spec'd at about 12.11v.

So if I were to infer 50% from rebound voltage, I Would conclude this well used and aged battery even now, has significanlty more than its rated capacity.

But it cannot, it does not, and I do not feel one can actually figure out remaining capacity without doing an actual 20 hour load test with a precice load applied and kept as voltage drops, with the battery kept at 77F for the whole time.

Who has the equipment or time to actually achieve this, and is it even worth the effort on a pair of Marine flooded group 24's? Can we dismiss battery temperature, no. CAn we dismiss hydrometer inaccuracy? no, can we dismiss ammeter inaccuracy and the 20 hour rrate being 5% higher or lower? No.

Perhaps if one were setting sail somewhere where there is no place to acquire a new battery and their premature death might also cause hardship to human, would it be worth it to actually perform the 20 hour capacity test, but such a person who puts their faith in group 24s in such a situation might just succumb to Darwinian principles en route, well before the batteries failed to 'hold a charge'.

So my opinion is 10 hours tests at the 20 hour rate are useful only for comparison to later tests when all variables are kept the same, and not useful for determining actual remaining battery capacity.

With SG readings, well same thing, One does not know if their hydrometer is actually accurate, nor what the true 100% SG reading should be, and the SG reading will be different with the electrolyte level 2Mm above the plates compared to 12 mm above the plates.

Too many variables that cannot be accounted for outside a laboratory environment.

But it will be obvious if a 20 hour rate applied for 10 hours on a questionable battery, that is destined for the recyclers soon. I doubt it would take 10 hours to determine this, especially if this is the second time one has tried and can compare data from the same battery using the same equipment and accounting for variables like temperature and electrolyte levels.

I can get pics to load to flikr.. Some type of issue.

Ill try this..

Anyway 3.5 hours. 12.34v.



Batts 6.4c




SG 1.250



This was @ 3.5 hours

lawrosa wrote:
3 hours.

SG 1.250
12.41volts measured @ batts

Your voltage is a tad high wrt the SG compared with the test I did the other day on my "new" 27DCs, which came out to 100% of rated and took the whole ten hours.

Believe the SG, not the voltage so much. Let's see what the voltages do, but don't go by them much for now.

In my case (YMMV) at 5 hours, voltage was 12.1 and SG was 1.250
At 8 hours, voltage was 12.0, SG 1.225, at 10 hours voltage 11.9, SG 1.200. Voltage bounce back from 11.9 was to 12.07 and next morning it was at 12.17 so my 50% notion was pretty close.

Your figures will not line up the same way as mine, but it gives you an idea. When doing 6s, the voltages were lower wrt SG, as to be expected where 6s are known to have more voltage drop under load than 12s. Something is odd about your high voltage readings wrt SG, but worry about that later, doesn't matter for now.

OK so watch your SG, which is already at 1.250 at 3 hours where mine was at 5 hours. I suspect you will get to 1.200 in less than 10 hours. Might be in 6 or 7, we'll see. Don't be surprised. That would be expected with 5 year old batteries of course.

Yes, as battery voltage goes down, the DC lights dim and draw fewer amps, so you do need to add some bulbs to keep amps up during the test. (It is the opposite if you were using an inverter with a 120v lamp as the load. As battery voltage drops, the inverter pulls more amps trying to keep power constant, so you have to reduce the size of the lamp)

On a discharge like this test, the AH count should be accurate, unlike on a recharge where there is heat loss so you have to use a CEF percentage (which gets worse above 80% SOC) Another thing is that SG is fairly linear on a discharge so this test works out well, but on a recharge there is "SG lag" which screws up any attempt to line up voltage/SOC and SG during a recharge.

Ampere hour cumulative assumptions (error) is what to strive against.

3 hours.

SG 1.250
12.41volts measured @ batts

Amps out may have reduced to 7.4 amps. I added a small led to get it back up to 7.56 amp draw.

Balmar gauge reads 71% soc.