Capacity Testing and 20 HR Rating
I'm thinking about doing a capacity test on my four GC2's. They have a 20hr rating of 215Ah. One thing I'm curious about is how the 20hr rating would have been determined. Being 6v, would they h...
Forum Discussion
Mex,
Regarding the 'ev battery monitoring' link;
I've read a similar article in the past, and I remember discussing this idea of what they call the "amp hour law" in another thread. And if I'm not mistaken, this is essentially what you have been recommending, when you talk about achieving instant absorption voltage. This means, a 430Ah bank, at 50%, could accept 215 charging amps without any issues. Boy, that sure flies in the face of the usual C/10 rates we often read about. And the guys at powerstream dot com would agree.
But putting using a 215a charger aside, as I perused the article, it dawned on me that the ideal Vabs setting would be one that brings the bank to an SOC at which amps would begin to taper just as the amount of Ah's missing is equal to the chargers current limit. As it is, at a little under 14.8v, my pm4b-45 begins to taper amps at about 91%... which happens to be about 39Ah's missing. At 14.8v (t.c.), my bank gasses a little more than I would like to see, (or hear, or smell), so it seems if I was to lower the Vabs somewhat, it would cause amps to taper a little sooner, like around 89% (45Ah's missing), and it would reduce gassing somewhat.
In one sense, this is nothing new, but it may be a practical answer to the common question of what constitutes an appropriate charging voltage. So, if you're using a 30a charger, find a Vabs setting that causes amps to taper at about 30Ah's from full. With a 75a charger... about 75Ah's from full. So, using my pm3-75 on my 430Ah bank, the proper Vabs setpoint would cause tapering to begin at about 82% soc (-75Ah's).
Regarding the 'ev battery monitoring' link;
I've read a similar article in the past, and I remember discussing this idea of what they call the "amp hour law" in another thread. And if I'm not mistaken, this is essentially what you have been recommending, when you talk about achieving instant absorption voltage. This means, a 430Ah bank, at 50%, could accept 215 charging amps without any issues. Boy, that sure flies in the face of the usual C/10 rates we often read about. And the guys at powerstream dot com would agree.
But putting using a 215a charger aside, as I perused the article, it dawned on me that the ideal Vabs setting would be one that brings the bank to an SOC at which amps would begin to taper just as the amount of Ah's missing is equal to the chargers current limit. As it is, at a little under 14.8v, my pm4b-45 begins to taper amps at about 91%... which happens to be about 39Ah's missing. At 14.8v (t.c.), my bank gasses a little more than I would like to see, (or hear, or smell), so it seems if I was to lower the Vabs somewhat, it would cause amps to taper a little sooner, like around 89% (45Ah's missing), and it would reduce gassing somewhat.
In one sense, this is nothing new, but it may be a practical answer to the common question of what constitutes an appropriate charging voltage. So, if you're using a 30a charger, find a Vabs setting that causes amps to taper at about 30Ah's from full. With a 75a charger... about 75Ah's from full. So, using my pm3-75 on my 430Ah bank, the proper Vabs setpoint would cause tapering to begin at about 82% soc (-75Ah's).
