Testing, Testing & more Testing

CALLD · March 2015

Ok, so I had one of those days yesterday where I just had to test things to see what they could do. I'm very interested to see what other like-minded people have come up with in the past with their systems - so please post your results here, it will help for those who may want to refer to them to see if their own system is running optimally.

1) Inverter efficiency test

Goal: Compare watts in vs watts out of the inverter.
Meters used: Battery charging watt meter on my Victron 150/70 Charge controller, Kill-a-watt style meter on the inverter output.
Method: take a fully saturated battery and measure the watts consumed to hold it at the float voltage for an hour - mine measured 7watts constantly to hold the battery at 27.6v. This would enable me to calculate the power draw of the inverter by subtracting 7w from the amount in watts shown on the charge controller to keep the battery at the float voltage of 27.6v. The charge controller would need a stable power source that is big enough to exceed all the different loads tested. Fortunately I had clear blue skies at mid-day for this test and 1490watts at my disposal. My maximum test load would go up to 1200w. Readings were taken after 5 minutes to give everything enough chance to stabilize.

Results:

Load on Kill-a-watt meter: 122w; Load on charge controller: 158(-7)= 151w. Efficiency = 81%
Load on Kill-a-watt meter: 204w; Load on charge controller: 262(-7)= 255w. Efficiency = 78%
Load on Kill-a-watt meter: 348w; Load on charge controller: 452(-7)= 445w. Efficiency = 78%
Load on Kill-a-watt meter: 456w; Load on charge controller: 482(-7)= 475w. Efficiency = 96%
Load on Kill-a-watt meter: 702w; Load on charge controller: 742(-7)= 735w. Efficiency = 96%
Load on Kill-a-watt meter: 1178w; Load on charge controller: 1252(-7)= 1245w. Efficiency = 95%

On my inverter there is a step at around 400w where it becomes stable an efficient above it, and a little erratic and inefficient below it. Annoying, but tolerable considering it was a bargain-buy Chinese job.

2) Battery test
Goal: Determine how long batteries can hold a decent load before the voltage gets too low for comfort.
Meters used: Kill-a-watt meter on inverter output, current draw estimated from previous test results.
Method: Apply a constant 800w load and trace the discharge voltage curve.

Results:
A) 260AH 24V AGM battery (Fully charged at 26.5°C)
0 Min 26.4v
30 Min 25.6v
60 Min 25.4v
90 Min 25.3v
120 Min 25.2v
150 Min 25.1v
180 Min 24.8v

100AH 24V FLA battery (Fully charged at 26.5°C)
0 Min 24.1v
15 Min 23.9v
30 Min 23.6v
45 Min 23.1v
60 Min 22.6v
75 Min 21.5v

Shows the big influence of Peukert's law & the difference between AGM and FLA.

MarkC · March 2015

Did you check "settled" voltages after each of your battery tests to obtain an estimate of battery capacity used vrs the manufacturers curves? I'd like to compare your estimated SOC's at end of run - especially on the AGM's since I've collected quite a bit of data on small SLAs/AGMs (not gel). Probably not directly correlate-able, but of interest. Can you measure voltages of each cell? or just not practical with your AGM? Since I'm into the Priups designs, I'll always be dealing with small SLAs to test and cold start the DC/AC inverters for data logging.

I'm not familiar with your AGM, but the curves that I use indicate that you could have been another hour or two away from going into the "knee" of the discharge curve? Stopping the test at 24 volts would still be quite conservative on the battery SOC? Need to check you battery discharge curve to make sure.

Blackcherry04 · March 2015

CALLD wrote: »

Results:
A) 260AH 24V AGM battery (Fully charged at 26.5°C)

60 Min 25.4v

100AH 24V FLA battery (Fully charged at 26.5°C)

60 Min 22.6v

Shows the big influence of Peukert's law & the difference between AGM and FLA.

A) 260AH 24V AGM battery (Fully charged at 26.5°C)
0 Min 26.4v
60 Min 25.4v = 1 v drop

100AH 24V FLA battery (Fully charged at 26.5°C)
0 Min 24.1v
60 Min 22.6v = 1.5 v drop

Shows the big difference in a 100 amp hr batteries vs 260 amp hr batteries. Based on your numbers, the FLA did as well or better than could be expected with the same load.

CALLD · March 2015

MarkC wrote: »

Did you check "settled" voltages after each of your battery tests to obtain an estimate of battery capacity used vrs the manufacturers curves? I'd like to compare your estimated SOC's at end of run - especially on the AGM's since I've collected quite a bit of data on small SLAs/AGMs (not gel). Probably not directly correlate-able, but of interest. Can you measure voltages of each cell? or just not practical with your AGM? Since I'm into the Priups designs, I'll always be dealing with small SLAs to test and cold start the DC/AC inverters for data logging.

I'm not familiar with your AGM, but the curves that I use indicate that you could have been another hour or two away from going into the "knee" of the discharge curve? Stopping the test at 24 volts would still be quite conservative on the battery SOC? Need to check you battery discharge curve to make sure.

Hi MarcC,

I didn't take any SG readings on the FLA's after the test neither did I wait the required 24hrs before re-charging to get the resting voltage but the "bounce-back voltage" was 24.2v immediately after the load was removed which suggests the SOC was around 50%. From experience I would have expected the resting voltage after 12 hours to be between 24.5-24.8v depending on temperature. Granted the AGM test should have been been done at 2.6x the load (2080w) to compare like with like, so I will do that soon and post the results so we can hopefully see the knee in the curve. The AGM's are 12v batteries and are totally sealed so no individual cell testing can be done nor would I ever want to try and take SG readings for fear of damaging something in the process. The FLA's have an SG lag which also makes taking immediate readings after the testing hard.

The batteries tested are

FLA's: 4x12v50ah in 2 parallel strings. Type RR1, age 9 months & 100 cycles to approx. 50% DOD. http://www.battery.co.za/products/leisure/

AGM's 2x12v260ah in series. Age 5 months & 80 cycles to approx. 40% DOD. http://www.sustainable.co.za/media/pdf/SonX%2012V260Ah(D).pdf

Will take further testing and post soon.

CALLD · March 2015

Blackcherry04 wrote: »

A) 260AH 24V AGM battery (Fully charged at 26.5°C)
0 Min 26.4v
60 Min 25.4v = 1 v drop

100AH 24V FLA battery (Fully charged at 26.5°C)
0 Min 24.1v
60 Min 22.6v = 1.5 v drop

Shows the big difference in a 100 amp hr batteries vs 260 amp hr batteries. Based on your numbers, the FLA did as well or better than could be expected with the same load.

Hi Blackcherry, the tests were maybe not the best comparison as the load on the 260ah AGM's was not high enough to pull the voltage down from the resting voltage of 26.4v at 100% SOC immediately. I need to conduct the test on the AGM's at 2.6x the load of the test on the 100ah FLA's. The resting voltage of the FLA's at 100% SOC was 25.6v and dropped to 24.1v immediately with the load applied, the AGM's took about 5 mins for the load to pull the voltage down to the operating voltage.

MarkC · March 2015

CALLD wrote: »

Hi MarcC,

I didn't take any SG readings on the FLA's after the test neither did I wait the required 24hrs before re-charging to get the resting voltage but the "bounce-back voltage" was 24.2v immediately after the load was removed which suggests the SOC was around 50%. From experience I would have expected the resting voltage after 12 hours to be between 24.5-24.8v depending on temperature. Granted the AGM test should have been been done at 2.6x the load (2080w) to compare like with like, so I will do that soon and post the results so we can hopefully see the knee in the curve. The AGM's are 12v batteries and are totally sealed so no individual cell testing can be done nor would I ever want to try and take SG readings for fear of damaging something in the process. The FLA's have an SG lag which also makes taking immediate readings after the testing hard.

The batteries tested are

FLA's: 4x12v50ah in 2 parallel strings. Type RR1, age 9 months & 100 cycles to approx. 50% DOD. http://www.battery.co.za/products/leisure/

AGM's 2x12v260ah in series. Age 5 months & 80 cycles to approx. 40% DOD. http://www.sustainable.co.za/media/pdf/SonX%2012V260Ah(D).pdf

Will take further testing and post soon.

It appears you were real close to the discharge curve of your AGM's. It also appears your AGMs could have gone for almost 8 hours to full discharge (don't want to do that), but would indicate the SOC at the end of the test was likely above 50%. Letting the battery "settle" for a several hours and using the following chart based on the measured voltage at correct temperature, seems to verify the load tests that I have done on my UPS AGMs;
http://jgdarden.com/batteryfaq/carfaq4.htm#mf_soc

Good luck on your tests,
MarkC

Testing, Testing & more Testing

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Testing, Testing &amp; more Testing

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Testing, Testing & more Testing