Battery charge/discharge testing

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Will flames erupt?

Testing of the charge / discharge performance begins.

Ammeter install complete. Time to monitor some discharge loads. Movie night it is.
Ammeter install complete. Time to monitor some discharge loads. Movie night it is. Note that the idle current of 11.9 w is a combined inverter and TV “off” load. The inverter is measuring at over 10 w idle.
  • Added: Victron 48-1200 inverter. Would have preferred a slightly larger/parallel design. But this will suit for a year or two.
  • Cheap chinese ammeter/voltmeter.
  • Hooked up the TV for a load. And watched a movie. Perfect testing conditions.

So first tests of a battery with the inverter. Used 518 watts watching a two hour and a bit movie. My Summer in Provence, if you’re interested. Not bad. Good family/chick flick. Good acting.

Ammeter comes in
Ammeter in the house1
Ammeter in the house1

I got the ammeter on Amazon. 18 bucks. Including 100 amp shunt. Sheesh that’s cheap.

And yes. Okay. Its a voltmeter/ammeter etc.

Now, getting to some test results

The single battery starts at 47.80. I then discharge to 45.55. This measurement is taken while under a load from the TV of 200 watts, give or take.

Cumulative discharge is 518 watts.

Beginning the recharge

According to the ammeter I start with a voltage of 45.72. According to my voltmeter I’m around 45.8. And the solar controller sees a slightly higher battery voltage of 45.83. Eh. Close enough for the funny papers.

Moments after starting the charge
Starting things off at 45.75.
Starting things off at 45.75.
And the charge finishes at
Finshed charge moments before going into float.
Finshed charge moments before going into float.

Note how the absorb phase, which I have set to 30 minutes, is now a using a mere 30 watts. This was really neat. As you can see above my pollen coated solar panels were making 565 watts under good sun. Once they hit the absorb phase the power going into the batteries quickly halved to 250 watts. Then dropped steadily over the 1/2 hr absorb phase I have set. By the end, seen here about 3 to 5 minutes before the absorb period was complete, you can see I’m at 30 watts to maintain the voltage.

Conclusion: 30 minutes is a pretty good absorb phase time. Topping up the tank, as it were.

So, how many watts to recharge?

So I started at 47.80. I discharged 518 watts. This reduced the voltage to 45.83 (45.72 on the ammeter a 1v discrepancy). And I use 650 watts to recharge.

The discrepancy between the intial charge of 710 volts and these results (518/650) is partially explained by the test procedures.

My initial charge voltage was lower. The absorb time was only 15 minutes. And the “overhead” time on the solar controller was lower as the monitor time was greatly reduced. (Monitored over 2 hrs vs 24 hrs).

So, given the slight variation in conditions. The test is successful. And perfectly acceptable. Huzzah.

Drum role please. 640 watts to recharge.
Drum role please. 650 watts to recharge.
Huzzah! Another successful test

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