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Float transition trigger point

PostPosted: Fri Nov 11, 2016 7:23 am
by Lever
We have our somewhat odd dual alternator 530 amp system, turned way down to 180 or 280 amps up and running well. I didn't put thermostats on it, but have a digital thermometer on the dash of the RV so we see the temps of the alternators all the time when the engine is running. They are staying well under 200 degrees F on a case bolt that goes to the heat sink.

The only question that came up was the transition to float point if we let it run automatically. It seems to do it very early, while the 440ah bank is still accepting about 90 amps. Finish amps for our Lifeline batteries would be 2.2 amps to get the Lifeline preferred .5%C. It is not a big deal to us, as we use the absorption lock, but would be if we didn't use it that way.

Is the transition determined by timers only, or are there other things involved also like field % or other parameter?

Re: Float transition trigger point

PostPosted: Fri Nov 11, 2016 1:13 pm
by Coulomb
Absorption period will be truncated if the battery voltage reaches absorption set point soon after the start of charge.

Have you asked Lifeline how long the absorption needs to be applied before reaching 0.5%?

Re: Float transition trigger point

PostPosted: Fri Nov 11, 2016 3:28 pm
by Lever
Yes, I have talked to them several times about it, and tested at home with the 100 amp shore charger. From a 50% discharge with the 100 amp output it will run about 6-7 hours at absorption setpoint, but the amperage starts to drop even before it gets to setpoint, which was a surprise to me. Lifeline said that time and amp drop is perfectly normal, but could be shortened a little by going to high end of the allowable charge voltage which is 14.6v, but didn't recommend it. I did try on cycle at 14.6v and the change in time was under 15 minutes, so not worth it. Total charge time with 100 amp charger is 9+ hours for 50% recovery. Using the big alternators while driving got the first part of the charge done in barely over 1/2 the time, and it got to absorption voltage much sooner because of the big output. The total time from 60% down (253ah) was 8.5 hours to get to .5%. The first 4 hours were on alternator and the final 4.5 hours on the Magnum shore charger. The amps were at only 13 when it was switched to shore power, so it was already at absorption voltage for quite some time, and took 4.5 hours to get from 13 amps to 2 amps. It is no wonder the boat folks don't have enough time to get their batteries full when they motor with no shore power option available. From what I have been seeing in RVs, almost all have batteries that are either regularly over or under charged, or both. Shore chargers nearly always leave the batteries considerably short, some as low a 80% or less full. When the batteries are charged off the stock regulated automotive alternator, they are often overcharged depending on how long the driving day is (over 8 hours is relatively common) and how full the batteries are when they started. Good solar chargers often use a shunt based amps transition to float, so they will do a perfect job if there is enough sun, long enough. I think your system with central controller is capable of doing the same for alternator charging by using the absorb lock on the regulator.