Battery Charging Question

[wagwar]

I have six 8D AGM batteries in a 730 AH, 24 vdc bank. I've discharged them to 80% based on the Trimetric monitor. So by my thinking I need to put about 155 AH back in to 'top' them off to 100% (73 * 2 * 1.06 = 155 based on 94% efficiency). So, I set my Trace inverter to 15A AC Max charge amps and the absorption time to 3 hours. I estimate that 15A AC should be about 60A DC. So, 155 / 60 = 2.5.

After a full bulk/absorption charge cycle, the Trimetric reads only 93% full.

Obviously, there is something wrong with my math and understanding of battery charging. Can someone help me do the math right?  Also, if I vary the Max charge amps, that should raise or lower the required absorption time, but by what factor?

TIA

[bobofthenorth]

Someone smarter than me will no doubt fill in the details but there's 2 reasons why your calculations won't work:
- first your charge rate will drop off as the batteries "fill up"
- second the SOC monitor isn't perfect - the longer you have been away from full charge the worse job the Trimetric will do of indicating what your true SOC is.

One of the smart guys can fill in details but that's the bare bones of the answer.

[Sean]

We just had this whole discussion here, only a week ago.  Read this thread:
http://www.busconversions.com/bbs/index.php?topic=24290.0;all

Most likely, you need to adjust your Tri-Metric.

-Sean
http://OurOdyssey.BlogSpot.com