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I set the system up with dip 3 on and dip 4 off which should result in max charge of 28.2v. Have temp compensation on and it is cold out like 15F. Batteries are brand new. Temp probe is in. Battery was charging at 29.71v from the Multiplus and I heard it boiling. Is the temp compensation creating this overcharge situation? Why doesn't it max out at 28.2v? Confused. I have only done dip switches; never setup any other way. About to hook up mppt tomorrow and a little worried..
The voltage settings are for 25C/77F. You don't say what temperature compensation value you're using, but your voltage doesn't sound too high. As the system is new, the batteries probably started at a pretty low state of charge. It will charge in bulk mode until it reaches the compensated voltage, then hold this for 8 hours to finish the charge. After that voltage will drop to float.
Mild bubbling is ok. The gasses given off will recombine.
I assume you did the dip switch cycle to enable the setting in the unit.
What is the current? What batteries are in the system?
I need to check the current. But it would be the default. The batteries are Roadrunner AGM group 27. Fleet Farm brand. Had a lot of success with them, but I fried one of them about 6 weeks ago.. assumed it was from the hot summer, now wondering if the charge current is just too high...I can run v e config. I need to order a longer cable; mine is like a foot short for perm setup to the plug in for pc. Based on my read of the temp compensation graph; the max voltage would be like 29.2 volts?
After I fried the one battery, I installed the temp probe and the system automatically adjusts unless I am mistaken. I did buy two new ones, so really nervous to hear bubbling. Charge current is likely too high. According to the bmv 712, the charge current went to about 11 amps; then dropped quickly to under 5, but still these super high voltages around 29.7v, the charge current after about 4 minutes was about 3.5amps only. About two more minutes and drops below 3 amps. But batteries are gurgling..and it is really cold, like 7F only, so seems odd the batteries are noisy.
Charge current should ideally be about 0.2C. As an example, if you have two 12V/100Ah batteries in series to get the 24V setup, you'd be looking at 20A. If the current is regularly higher, especially for long periods, battery life will be shorter.
At 32F you would normally be around 31V. So you're still under that and it will go higher.
Sounds as if you have to wait it out. If the current has dropped this low, then you're at least into absorption, might have hit float. How big are the batteries?
https://www.fleetfarm.com/detail/road-runner-agm-ace-marine-rv-battery-grp-27-36-mo-580-cca/0000000218721?bc=100%20-%20250&brandCrumb=2507182181&bn=road-runner
I am running two batteries in series to get 24v nominal. I'm gonna try to set up v e config and try to see if I can get the charge voltage lower somehow.
Look into the datasheet of the batteries or ask the manufacture.
Temperature compensation is not a bad thing and needed for the most lead batteries. So it is totally normal that you get a higher voltage at lower temperatures.
My Trojan flooded batteries have a 0.06V/°C @ 24V. At freezing, absorption voltage would be 1.5V higher than the programmed voltage. This is proper. If 28.2V is specified, 28.7V would be the absorption voltage.
At -15°F, it would be 3.07V higher or 31.27V.
The opposite occurs over 25°C/77°F. Absorption voltage is LOWERED accordingly to prevent damaging the batteries.
I am going to check each battery separately and make sure they are equal today. Will post findings.
One battery is 11.71v and the other battery is 13.05v. I'm guessing the gurgler is the low one. But the puzzling bit is this is the same battery I had go bad last time of the set. The battery with the ground node. ... hmmm wonder what that could be..any takers? Looks like I have some debug now. I have a few takeoffs that I ran from the middle node...bms and stuff. I wonder if that is causing them to be uneven. Anyone know if you can take off the positive from any node or if only from the opposing hot? The meter says it is 24v there...
I am taking power off incorrectly and the batteries are continually uneven. Thanks to all who posted; this issue is solved.
You are likely destroying your batteries. You may have destroyed both of them.
You immediately need to charge each battery fully with a 12V charger and reassemble as 24V. You need to monitor the individual 12V batteries moving forward.
The battery you have been pulling 12V from has likely deteriorated substantially due to being at a low state of charge. It may need to be replaced.
The battery that you haven't been pulling from has likely been damaged by running too high a voltage and over-charging. It is likely the battery that was bubbling. It may need to be replaced.
Before assuming they're trashed, bring both to the same voltage, the 11.7 isn't that low.
And the 13 isn't that high. As Matthais said, use a converter. Also fit a balancer. This will keep the batteries very close to the same state of charge.
Configure the mid point monitoring on the BMV and set an out of balance alarm.
11.7V resting is a very low SoC
13.0V resting is a full state of charge.
24.7V charging:
11.7V charging indicates the cell is at a horrifyingly low state of charge.
13.0V charging is a mid range state of charge
24.7V discharging
11.7V discharging indicates a low SoC
13.0V discharging indicates nearly fully charged
No matter how you look at it a deviation of that magnitude is a worst-case scenario. The low battery has been excessively discharged, and the high battery has been excessively charged.
Both conditions result in damage. The OP should be prepared to replace both batteries.
