Siletzspey wrote:
BFL13 wrote:
noteven wrote:
... how long will the standard 7 way pin system take to recharge Li batteries?
Same time as "ordinary" batteries. ...
FLA batteries start to accept a charge and pull amps at 12.6V, but LFP batteries start that process at 13.6V, a whole volt higher. Depending on your alternator's voltage output and the voltage drop in your wiring, LFP could charge SLOWER than FLA, and FLP charging could fail to reach 100% SOC where-as FLA could.
With my 45A Progressive Dynamics Inc charger running in FLA mode, my old ~200Ah of FLA would pull 18A over 10ga wiring. Still running in FLA mode, my 200Ah of BB LFP at 30% SOC only pulls 4A over shorter and bigger 8ga wiring. Putting the charger into boost/LFP mode (boost the voltage) increases the pull to 39A. Point being, same charger, the LiFePO4 charge rate is 1/4th the flooded-acid rate.
Sterling (make of DC-to-DC alternator chargers) has some nice videos on YouTube where they wire LFP direct to an alternator with ~4ga wire, and the charging rate is pathetic. Then they insert a DC-to-DC charger in the line and the charge rate jumps substantially, because the charger can re-boost the voltage.
All in all, current is pulled based on volts being delivered. For 7-pin systems, the Achilles heel is voltage. Solve the voltage problem, and then you can start to worry about current problems.
--tg
Good info , thanks! Yes, the current amount depends on the "spread" between the charger's voltage and the battery's voltage. You see that when amps taper when the battery's voltage rises during a recharge, while the charger's voltage is constant.
Another thing working the other way for current is the lower resistance of an Li. makes comparisons more complex to test, an Li has a flatter voltage until nearly full and a low R too.
An alternator is not like a normal converter/charger with a current limit and a voltage set-point, so that's another thing. You don't dare try for the the alternator's current rating (very high) and its voltage is sort of variable as programmed or by what the engine battery is doing compared with the house batts and what the temperature is up by the alternator. Anyway--
On Sterling and DC-DC we had a thread (garbled on my part!) that could have used your input when it came up later in the thread. You can still add something useful to this thread--be very much appreciated by the tech issues crowd for sure!
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/30157504/srt/pa/pging/1/page/4.cfm
