Newbie needs help charging U27-12XP

limycenter

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Nov 15, 2020
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4
Hey all,

I live in a motorhome and am replacing existing lead acid batteries. I have the following components and am confused on what is the best setting to charge them.

Charging Inverter
Magnum MS2812

Interface unit (Monitor)
ME-ARC Remote Control

I called Magnum and they said to use the CC/CV setting, i've read in other places to use AGM2 setting.

I am charging them one at a time using the AGM 2 setting and the monitor says they are fully charged but the voltage is a bit low at 13.02 and the software says the cells are on the low side. I dont think im doing any harm here but am curious what the implications are, my gut feeling is that im not letting the batteries reach their full potential.

Thanks
 

ericgrand

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Sep 18, 2020
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70
I would use CC/CV, with a limit at 13,8V at least. But first, you have to be sure that internal cells are balanced. So connect to the battery and check the cells individual voltage.
13.02V is on the low side, you can't be sure the battery is charged.
 

limycenter

New Member
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Nov 15, 2020
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4
The cells of all 4 batteries that I bought are within 5mv of each other across all 16 cells (they came from the same truck) and only have 25 discharges on them.

So if I do setup for CC/CV. I have a huge range of settings and am not sure the right ones. The manual for interface/monitor is linked above but I've copied the relevant sections here with my comments/questions in RED

This is in an RV motorhome, I do NOT have solar and I am mostly plugged into 110V. I will occasionally be off-grid while driving from A to B and some boondocking. I have a 10KW Generator for boondocking to charge the batteries and enable AC. I do have some concerns about the 12V DC load emptying my batteries to a harmful level so I am considering buying the MIUSA-BMSLV if that will allow for balancing and low voltage cutoff.

Set Battery Type (CC/CV) – The CC/CV selection provides a Constant Current/Constant Voltage (CC/CV) charging method with an adjustable charge voltage and a setting that limits output current—if needed. It consolidates all the battery charge settings that are required for a 2-stage charging cycle (i.e., Constant Current and Constant Voltage). Note: CC/CV settings only display if CC/CV has been selected from the 03 Battery Type menu. Info: If CC/CV has been selected from the 03C Battery Type menu, the following menus are no longer accessible and display “CC/CV Controlled” when selected: 01D Max Charge Amps, 03D Absorb Done, 03F Max Charge Time, 03G Final Charge Stage, 03H EQ Reminder Days. This is to prevent charging conflicts that could occur while in the CC/CV profile.
CAUTION: Whenever the CC/CV battery type is selected, some settings—within the menus that are no longer accessible—are internally linked to the CC/CV settings and can be automatically changed. Because settings can be automatically changed once CC/CV has been selected, if a different battery type is selected all charge settings must be reviewed to ensure they are correct for the new battery type selection.

Set Max Charge Amps – Sets the maximum charge amperage allowed to charge the batteries during the CC/CV charge cycles. The range of settings are provided to limit the charge current to the battery bank, which helps prevent battery overheating caused by charging at too high a charge rate.
Default: 200 ADC
Range: 20 - 990 ADC

Is this the total amps of the battery bank? Or is it the maximum amps applied during the CC phase? It looks from the chart below that it is the max amps during the CC phase.

Set CV Charge Volts – Sets the voltage level at which the charger will hold the batteries during the Constant Voltage cycle.
Default: 13.8 VDC (12v), 27.6 VDC (24v), 55.2 VDC (48v)
Range: OFF, 12.0-16.0 VDC (12v), 24.0-32.0 VDC (24v), 48.0-64.0 VDC (48v)

Info: If the BMK (Battery Monitor Kit) is connected, the DC amps value determined by the BMK (under METER: 05D DC Amps-BMK) will be used by the CC/CV’s Max Charge Amps setting instead of the inverter’s DC calculated current (shown under METER: 01B DC Amps)—as it is more accurate (+/- .1 ADC).
I could set this as high as 14.6V which is what the battery says its maximum input voltage is according to the battery front. Here is where I'm concerned about making a mistake. Suggestions are much appreciated. I did buy the BMK, but have not installed it yet. I think this will be an ideal solution, however I would like to understand and implement this system without the BMK.

Figure 3-10, CV Charge Done Time/Amps Stages (INV/CHG)

1605493029549.png

Set CV Charge Done – These selections determine when the second stage of charging (Constant Voltage) is finished. If using the CV Chg Done Time or CV Chg Done Amps selections, once the Constant Voltage charge cycle is finished, it transitions to a Silent charge stage. After entering the Silent charge mode, the charger automatically stops charging, but is still actively monitoring the battery voltage. The charger will remain “Silent” until the battery voltage drops to the Set Recharge Volts setting, at which time the charger will start another Constant Current/Constant Voltage charge cycle (see Figure 3-10).
Default: CV Charge Done Time
Range: Time, Amps, Hold CV Chg VDC
This setting is confusing, wouldn't there be a better trigger than time or amount? I don't understand how this works, but intuitively to me, it seems like during the CV phase that the voltage would drop to a point where you would know its full. There is also an option for HOLD CV CHG VDC where a constant voltage is held on the battery at all times that I have 110V (plugged in or running the generator). I dont have solar YET. This specific setting is not copied into here. If discharging the battery to a certain threshold is ideal rather than keeping it topped off then that is probably not an ideal setting.


Set CV Chg Done Time – The CV Chg Done Time selection is used when a specific time is selected to be the best solution for determining when the batteries are fully charged and the Constant Voltage stage needs to end. This setting determines how long the charger will hold the battery voltage at the CV Charge Volts setting—based on a set time period. When using time, the battery bank size will typically determine the length of the CV Chg Done Time setting. The larger the battery bank, the longer the time needed to ensure a full charge to the batteries. If the setting is from 0.1 to 25.5 hrs, the charger transitions to the Silent charge mode after the battery voltage has been at the charge voltage setting for the selected time. Refer to Table 3-2 to assist you in selecting the CV Chg Done Time setting based on the AHr capacity of your battery bank. Note: After choosing Set CV Chg Done Time, the Set Max CC/CV Time and Set Recharge Volts settings must be determined (see next page).
Default: 2.0 Hrs
Range: 0.1-25.5 Hrs


Set CV Chg Done Amps – The CV Chg Done Amps setting is used when the DC amperage supplied to the batteries (also known as “return amps”) determines when the batteries are fully charged and the Constant Voltage stage needs to end. This setting determines how long the charger will hold the battery voltage at the CV Charge Volts setting—based on a minimum current setting (i.e., return amps). During the Constant Voltage charge mode, as the battery charges, the current from the charger slowly decreases. When this current decreases below the CV Chg Done Amps setting, the charger transitions to the Silent charge stage. Most battery manufacturers use a specific formula to determine the return amps that indicate a full charge for their particular type of battery. The formula used by most manufacturers to absorb the batteries is C/20, where C=Battery Bank’s Total Amp Hours. Basically, they take approximately 5% of the total battery bank size and consider the battery totally charged when the charger’s return amps drops to this level.
Seems less than ideal, but maybe better than the TIME method? I have NO clue though, so help is greatly appreciated.
 

limycenter

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Nov 15, 2020
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Table 3-2, Battery Amp/Hrs Capacity to Suggested Absorb Time

1605499037461.png

Continuing to charge past this level may overcharge the batteries. Check with your battery manufacturer to find out what the correct return amp settings are for your batteries.
Note: After choosing Set CV Chg Done Amps, the Set Max CC/CV Time and Set Recharge Volts settings must be determined (see below).
Default: 20 ADC
Range: 0-250 ADC

Info: Install a battery monitor if the CV Chg Done Amps setting is used. If a battery monitor is not installed, the CV Chg Done Amps setting relies on the METER: 01B DC Amps value to determine when to transfer out of the Constant Voltage charge mode. When a battery monitor kit (ME-BMK/ME-BMK-NS) is installed, the CV Chg Done Amps setting relies on the METER: 05D DC Amps-BMK value to determine when to transfer out of the Constant Voltage charge mode. This is the most accurate DC amperage measurement. The DC amps reading from the battery monitor is accurate to +/- .1 ADC.
Info: Setting CV Chg Done Amps to zero keeps the charger in Constant Voltage charge mode until the Max CC/CV Time setting is reached.
Info: When using the CV Chg Done Amps setting, the charger will stay in the Constant Voltage charge mode for a minimum of two minutes—independent of the actual CV Chg Done Amps setting.
Info: If DC loads are connected directly to the batteries, it is not recommended that you use the CV Chg Done Amps setting. DC loads cause the charger to increase the amperage delivered to the battery bank in order to charge the batteries and to run the DC loads. This scenario could result in overcharging the batteries since the return amps reading will be skewed by the DC loads.
So this section leads me to believe that CV Chg Done Amps is the WRONG setting for my use case since I am in an RV with constant 12V DC loads (lights, radios, etc etc.). This leads me to question a couple other things. See below

Set Max CC/CV Time – This setting is a safety feature that ensures abnormal conditions do not cause the charger to hold batteries at a high voltage for a prolonged period of time. This menu sets a maximum time the charger is allowed to operate in either the Constant Current or Constant Voltage charge modes. If the charger reaches the Max CC/CV Time setting, it will transition to the Silent charge stage. The OFF selection can be used if there is an application where 25.5 hrs is not long enough.
Default: 12.0 Hrs
Range: OFF, 0.1-25.5 Hrs

CAUTION: If using “OFF”, the batteries can be held at a high voltage for an extended time. Monitor the batteries to ensure they are not overcharged.

Set Recharge Volts – This setting determines the DC voltage set-point to which the batteries are allowed to fall—while the charger is in the Silent charge cycle—before the charger restarts and recharges to the CV Charge Volts setting. This setting should be at the lowest DC volts level that you want the batteries to fall before starting a new charge.
Default: 12.0 VDC (12v), 24.0 VDC (24v), 48.0 VDC (48v)
Range: 12.0-16.0 VDC (12v), 24.0-32.0 VDC (24v), 48.0-64.0 VDC (48v)


Should I let the batteries empty and then fill or keep them topped off? I do NOT have solar yet, so my normal use case is plugged in to 110V most of the time. But I have constant 12V loads. It looks like the lowest I can let the voltage drop is 12V. However during inverting (when driving or otherwise off-grid), I can set the inverter cut-off to 10V.
 

ericgrand

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Sep 18, 2020
Messages
70
Ok, I will try to answer as far as I can, as I don't know your equipment, just trying to put some logics in my comments!

I assume you have all 4 batteries connected in parallel to achieve a 12V/552 Ah battery bank, right?
Also, are you able to get a device plugged in the RS 485 network of the 4 batteries, to get the internal BMS activated?

The purpose is to get all 16 cells charged up to a level they are almost balanced, even if not perfect... Having few mV difference does not mean the same at 3.35 than at 3.5V.
Above 3.4/3.5, all cells are close if not at 100% charge. At 3.35, it could be 30% for one and 60% for another.

So you want to charge up to a level were all cells are near 100%.

So you end voltage should be around 3.45 * 4= 13.8 V.
You have to check that this end voltage of 13,8 is reached with all cells balanced...You can reach it with 1 cell at 3.35 and 1 at 3.65... meaning you would reach low level on the lowest cell too early, with the risk of damaging it.

So first step is to charge each battery while monitoring cell individual voltage and be sure they are all balaced. it is some kind of top balancing.
If you can, you could charge each battery up to 14.6V, at low Amps, to perfectly balance the cell. THe intenal BMS will activate only if a device is connected to the battery (i.e the green led is flashing each 5 second).

Set CV Charge Volts:
As explained above, as you don't have BMS intra cells active, I would stick to a conservative value, once you are sure all cells are properly balanced. So inital charge at low AMP up to 14.6V to get all cells balance under BMS supervision, then, I would set it between 13.8 and 14V. This will leave you with more than 90% capacity of the battery
13.8V is float voltage as given in the datasheet.

Set Max Charge Amps
This the max Amp value during charge. Even 200 A is suitable for your battery bank...it is around C/2,5 and this battery accept C/2 charge. I would anyway stick to something between C/10 and C/5, to increase life span. But this parameter will depend of the time available for charging compare to time off grid...

Set CV Charge Done
Here I have no particular answer...
Keeping the battery at high voltage is not good, but we have already agreed to charge them up to a safe level...I foresee no reason why you would wnat to discharge them before charging again.
I would use the "Hold CV charge" mode, to keep your battery charged for when you need them...
You could also stop charging once Amp fall below a certain threshold and start charge again when battery reach 3.35V*4=13.4V. Restoring charge at a lower value may lead to having batteries discharged to a certain level with grid available and still discharged when you disconnect grid or generator. Not the best scenario...
I know the manufacturer give an AMP value at 3.65V/cell under which the battery is considered 100% SOC, but I don' know the value for Valence.
In any case, you need to setup a time limit to revert to silent mode to avoid maintaining charge on your battery.
Anyway, this setting is not the most appropriate if you have direct DC loads on the battery.
So stick with a time setting of 2 hours, as given in the notice.

TO summerize, I would use:
CC: 100A
CV 14V
CV charge done: 2 hours at 14V
Recharge volt: between 13.4 and 13.6

If your loads exceed 100A, you may need to increase CC to avoid discharging batteries while connected to the Generator or the Grid...

Please consider other members input as I'm not a specialist at all!
 

texskeet

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Nov 11, 2020
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I have your exact charger in my last 2 motor homes. I switched both to lithium . You don't want cc-cv. You want custom. Then set absorb at 14.6 float at 13.6. If you will pm me i will help further.
 

ericgrand

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Sep 18, 2020
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14.6 absorb, if cells are not perfectly balanced will get highest cells over 3.65V...
 

limycenter

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Nov 15, 2020
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4
Thanks for the help guys, I'm coming up the learning curve here and just being able to have this dialog really helps me learn.

Im gonna keep reading/learning and playing with these batteries.

I got lucky that I have 6 of them and they are really balanced and low discharge counts. I see 3mV spread WORST case so far.
 

ericgrand

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Sep 18, 2020
Messages
70
The 3 mV spread does not mean a lot depending of the SOC...You have to charge each battery up to 3,65V/cell to check if cells are really balanced.
 
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