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Hi!
I have a 90Ah LiFePO4, almost fully charged (13.3V).
Then:
Discharging: 1000 watts for 30 min at the inverter, means taken more than 500 Wh.
Loading: with MPPT 75/15; Absorption voltage 14.4V, max. Time 6h, float voltage 13.5V
Result: Bulk with 8-9 amps, after <1 min already absorption, but continue with 8A.
After 1 hour, about 100 Wh were loaded, then came Float with only 1.4A, although still missing 400 Wh!
What am I doing wrong? VolkerVlker
Hi,
If you can use VictronConnect to change the charger to the "LiFeP04" setting, (found in "Select preset"), without changing any values.
I suspect the charger thinks the battery is a lead acid.
Fulli This is quite a common problem in my world on boats at 14A charge rate with 2.5mmsq with 4 metre cable run you have a voltdrop order of 0.85V or 6.3%. The controller is seeing a charged battery.
I have found that I have to aim for a voltdrop between charger and battery of less than 0.5% to get the batteries fully charged which in your case means using order of 16mmsq to get the volts to the batteries
Hi Fulli,
My best guess is that you have high resistance between the mppt and the battery ( poor connection, thin or long cables...?). I presume that you have set 14.4 abs, 6 hour max time etc. With high resistance the mppt is likely seeing 14.4v at its terminals when significant amps are flowing, so it is switching to absorb, while at the battery terminals there is only, say 13.5V. Also, absorbtion time is adaptive depending on battery start voltage. If battery is more than 12.5v, and this is almost always the case with lithium, it is scaled back by 1/6, giving a max absorb time of only 1 hour as you observed.
Hi Leslieanne,
Maybe you are right with the long cables! From the regulator to the battery, there are about 4 meters of cable, 2.5mm2, with alligator clips on the battery. I will try shorter cables, thanks!
What I have done is to set the time to 12 hours or more, then I have over 2 hours of absorption; or is not that good for the battery?
Volker
Hi Volker,
Try to use the recommendations of your battery's manufacturer. It really depends on whether the battery has inbuilt BMS with need for balancing, and other things. In general for lithium too much time at higher voltage is not good for longevity. For example I routinely use about, 14v absorb for about 30 mins for my 4 series LiFePO4 cells from solar, and only occasionally charge to 14.2 volt with 2 hour absorbtion to balance the cells.
Hi Leslieanne,
it's this Battery:
I have 2 chargers, especially for LiFePO4, and both charge 14.6V. (?)
Now I'll use 6mm2 cables tomorrow and see what happens.
Volker
@Fulli For that battery I would be aiming for less than 0.5% voltdrop at 50% of max charge current to allow the charger to do its measuring properly. My guess is that battery has no BMS no any way that one can be added,
Hi Fulli,
According to the specs that battery does have an inbuilt BMS that works at cell level and balances. With thicker shorter cables and your original settings (14.4 abs, 6 hours equals one hour mostly, and 13.5 float ) it should all work well. Don't stress. Happy camping!
Hi Graham!
This is a clear message that also confirms Leslieanne, thank you!
In the MPPT 75/15 fit only max. 6mm2 in; I'll try that and make the cable a bit shorter. And extend the absorption. LiFePO4 do not have to be fully charged, I think.
Volker
Fulli if you get a couple of 6mm or 8mm power posts and mount them about 150mm from the 75/15 terminal you can come out with even the 2.5mmsq to the power post and then to the batteries with something like 35mmsq that should heavily reduce the volt drop.
A power post in case you do not know what I mean https://www.electricalcarservices.com/power-post-6mm-small-base-red-or-black/p-289-331-4263
Hi Graham,
thanks for the tip; I have already ordered 6mm2 cable and try it once so.
That would have to do a lot.
Volker
First Test finished, it works much better with the 6mm2 Cable! A long Bulk-Phase, short Absorption and longer Float up to 14,4V.
Thanks to all who helped me!
Volker
