jrnymn7 wrote:
BFL wrote:
"On recharge you must allow some AH for heat when figuring your SOC. The Trimetric uses 4% but this might not be what your batteries do at the time at your charging rate. The Trimetric AH comes out fairly close on cross-checking when you do get the batts to 100% as measured by hydrometer."
this seems to confirm what i have been considering, concerning the excessive gassing of my 430 Ah bank. before i installed the pm, i was using the peak 40 amper for all my charging. it would run for about 4 hours, rising to 14.8 - 14.9 volts, and holding steady at 40 amps for about the first hour, and then begin to taper. it would then hold its voltage, and amps would taper over the next few hours. all normal, yes?
however, this was all taking place when the batts were already between 90 and 100%. for i was charging at ~12.6v batts (~90% soc)(~ -22Ah). and if in fact 90% soc is when the charge current drops to about 5a per 100Ah capacity; so ~21a on a 430Ah bank; at 14.8v, and a little higher at 14.9v, then where did all those extra amps go??? for you can't put 40++ Ah's back in where only 22Ah's were removed... this has bothered me for months now. AND this is why i originally thought i was going thru way more Ah usage than i should have been, according to simple pre-calculations and actual real time usage.
so it seems to me all those extra amps the peak was pounding into the batts were turning into heat and boiling the batts. and charging at 14.9v at 80+ degree temps would only exacerbate this. having said that, i still don't understand why the peak's amps didn't taper faster? is it because there was still a considerable voltage spread between charger and batts? and is this the issue with trying to top charge a large bank, and why it takes soooo long?
First, 10% of 430 is 43.
Check my ugly graph and see that the 35amper gets to 80% on 220AH before tapering starts. (that is with a Vector that "trips" at 14v so your charger would trip a little later than that into the 80s. But the basic thing is the same, so now look at what a 20amp charger would do on 220. You go out to the right and it hits the curve at a higher SOC about 85% so yours might be near 90% at 14.8v. (20 amps on 220 gets you the same curve as 40 amps on 440)
So throw in that you are using 14.8v and the ugly graph is for 14.5 ish so the batts will accept more amps per SOC than that 5amps per 110AH at 14.5 marker I use.
Now throw in that the Trimetric "full" is maybe 97% SOC so your zero AH count starts down from 97 instead of 100 when you are doing your 10% = 43AH.
So after you get all that straight, anything left over could be AH lost to gassing more than the Trimetric allows for. :)
