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Renogy DCDC/MPPT Battery health

PapaK

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Joined
Oct 23, 2020
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Hello everyone, I have a question and this is kind of a three in one. I didn't know exactly where to post so I hope I'l find all my answers here. After watching Will's video about squeezing more life out of Lithium Iron battery, I realized that the standard Li setting on my Renogy DCDC/MPPT charger is probably too high. If I am correct, I want my charger to limit the float charge to about ~13.4V to be in that 85%-90% range correct? After looking at the charts on my charger controller manual it looks like it is constantly in boost with no float in the Li setting? Am I better off switching to the "Gel" setting? Im hesitant to do this due to due to the charger having low temp protection on the Li setting. My battery has an internal BMS that the manufacture has assured me protects it from low temp charging but I wasn't able to find that in any documentation, just an email.

Screen Shot 2020-12-30 at 11.12.06 AM.pngScreen Shot 2020-12-30 at 11.01.40 AM.png
Or is advisable to figure out how to use the user defined settings and to program my own? The manual doesn't talk about how to do this. Im sure I can dig around to find out. I would appreciate if anyone had some parameters that they would recommend.


Also, with my two each 100Ah batteries and a 0.5C charge rate, I noticed when I took my van out at night with about 50% capacity, it charged to about 50% at 48A charge rate and then around 60% batt capacity that dropped down to about 25A. Does anyone else using this DCDC/MPPT charger know why that happens? It said it in the manual I should get 50A from the alternator alone when the sun is down. Even if my alternator was only putting out 13.7V or something, I would assume that it would get past 60% before dropping off.

My final question has to deal with my converter. From the manual it says:

"standard “Three Stage Charging”, run 14.6V almost 0.5 hour, 13.6V almost 12 hours and then to 13.2V. The voltage value of 3 stage charging will be changed with fixed voltage changed when the unit on “Three stage charging”."

To me that reads like it will be perfectly acceptable for me to use this unit as is to keep my battery "floating around" 70%. after an initial charge up to 90%. Am I thinking about this wrong? Does anyone have any comments or concerns?
 
Personally, I would create a USER battery identical to LFP but add a 13.5V float for your stated desires. If you're forced to enter an equalization voltage, just make it the same as boost. This should get you around 90%.

% charge readings based on voltage are garbage and give no meaningful information. The only things that give accurate % readings are Battery Monitors that are programmed with the battery capacity and actually COUNT the current in and out to determine the % SoC. Will has some recommendations on his site. If your concerns are about % readout on a voltage-based gauge, they are misplaced as your are reacting to something meaningless. You should adopt a practice of completely ignoring it or placing tape over it if you can't ignore it.

50A peak current is also limited by battery voltage. The charger lowers current to keep the voltage at boost or float as applicable. That's the lower half if the figure you omitted in your first image:

1609356977883.png

Typical RV converters with that 3 stage profile are fine. They'll get you to about 90-95% SoC during the 13.6V phase as the battery still pulls current at 13.6V if it's not fully charged.
 
% charge readings based on voltage are garbage and give no meaningful information. The only things that give accurate % readings are Battery Monitors that are programmed with the battery capacity and actually COUNT the current in and out to determine the % SoC. Will has some recommendations on his site. If your concerns are about % readout on a voltage-based gauge, they are misplaced as your are reacting to something meaningless. You should adopt a practice of completely ignoring it or placing tape over it if you can't ignore it.
Thanks for the reply.

I do have an actual battery monitor with a shunt to measure the actual in and out but all these chargers are just going off voltages so that's why I was using the percentages when I was talking about being surprised at the alternator charging etc.
 
Glad you have a battery monitor. It's not clear to me if you were referring to the % on the chargers or the % on the monitor.

If your monitor is properly programmed for your battery capacity and charge termination criteria, that's the only % number that matters.
 
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