Inverters reports two different battery voltages

Phu

Hello All,
I am a new user here. I came here because ME support is so bad I can't seem to get any good answer from them for previous problems so I am not going to try to contact them this time around. I hope someone can shed light to my unusual problem. 
I have a parallel MS-PAE4400 system. I have two sets of 400AH AGM batteries, 16 batteries for a 48Volt system, with generator back up. It is monitored via a website run by Magnum Energy.
My problem is that the report says my batteries are at 100% but the system keeps shutting down saying the batteries are low and the screen on the Remote says 46V but the BMK says 56V. But my programming is set for low battery shut off at 40V. I have manually read the batteries and they all checked out as good and all together I read the same voltage as the BMK on my meter. I have look through all the programming and wiring and they all seem to be in good shape.

Has anyone come across this same problem or have an idea what would cause the different in the voltage readings?

Phu

littleharbor2

Wow, big difference.  Check all connections and maybe do a factory reset on both inverters and re enter all the setpoints?

Phu

I have done numerous reset, replaced the ME-RTR to a ME-ARTR, reprogrammed the router, My next item to replace is the BMK unit. But i am not sure that is the problem. I checked and rechecked all connections. There is nothing that I can find that is loose.

BB.

Have you used a DMM and measure each inverter"s dc input voltage?

Bill

Dave Angelini

Magnum is having huge issues with suppling product. Many of my cohorts are very upset with them.
That said,  Battery monitors are notorious for being programmed wrong, installed wrong, or just defective.
Don't use the Soc data for now and prove the system with just voltage readings.
Your LBCO sound very low for AGM's.  44vdc is typical, not 40vdc!

Phu

I have measured the voltages at each battery bank and they are exactly the same and are the same on the Router reading. All my monitoring reading all said the same and at 100%. When I turn the inverter on everything seems to work fine for a while and then something would trigger it, most of the time it is my 1hp 220V water pressure pump, when that kicks on the system would start to pulse badly and I would watch the router output and see that it quickly flash Slave Inverter Stack Error and low batteries. The only way to reset it is to turn on the generator, turn the inverters off and reset them. I know the LBCO setting is low because the router is new and that is the factory setting. I will reset that soon enough after I figure out what is dragging down one my slave inverter. The thing is less than a year old.

Photowhit

Phu said:
When I turn the inverter on everything seems to work fine for a while and then something would trigger it, most of the time it is my 1hp 220V water pressure pump, 

Sounds like the load reduces the voltage at the inverter.

This can indicate that the battery bank is undersized for the load, which doesn't seem to be the case, or that there is undersized wiring or a poor connection between the battery bank and the inverter. 

You can check the voltage drop using a DC voltage drop calculator, here's one;

Voltage Drop Calculator

Dave Angelini

I assume the 1HP pump is not a soft start VFD. If it was, you might not have this problem. Do what Bill and Photowit recommend.

Even a master and slave are going to have trouble with that pump even with good connections and Soc.

BB.

Did you measure the inverter's DC input voltage under heavy load/pump starting?

-Bill

Photowhit

Phu said:

I am a new user here. I came here because ME support is so bad I can't seem to get any good answer from them for previous problems so I am not going to try to contact them this time around. I hope someone can shed light to my unusual problem.

Hi and Welcome!

Perhaps we can add some education with our info. More info from you would be nice as well. I use a Magnum 4024 (120v only version) but not their web site.

You say;

Phu said:

My problem is that the report says my batteries are at 100% but the system keeps shutting down saying the batteries are low and the screen on the Remote says 46V but the BMK says 56V. 

I'm guessing the remote has seen the "system voltage" drop to 46 volts and trigger a shut down. I understand that Magnum inverters can be set for a very large voltage range, I would think around 44 is standard cut off for lead acid battery systems. But the more important part is that this is the "system voltage" and not the battery voltage. Many things effect the system voltage. a normal 48 volt AGM battery bank, fully charged, at rest should be around 51-52 volts. If the system is at 56 volts when this happened, it is likely charging. Here's a chart showing the rough voltages of a 48 volt AGM battery charging.



As you can see, the battery might be in 'bulk' and not much more than 60% charged, or adjusting down from Absorb to the float stage at which time it might be fully charged, assuming the correct parameters have been set from the battery manufacturer. It could be in a very high "float" voltage, doubt that would be recommended by many.

I would suggest the remote is recording and sending you a very specific point in time.

If the BMK is a shunt based battery monitor, it is important that BOTH inverters are hooked up so that energy drawn from the battery bank flows across the shunt!


Here are basics in the Charging cycles, knowing what you have set for absorb and float points would be helpful.

The voltage you are seeing is the system voltage and not the battery voltage. If you are connected to charging or a load it will effect the system voltage. Voltage will change and can be drastic, if a large load is applied to the system!!! A charging system may change from one in which the batteries are charging to one in which all the energy from the array and energy from the battery bank is drawn down at the same time!

During charging, there are basically 3 stages of charging, Bulk, Absorb, and Float.

BULK;

First thing when charging starts you will be in bulk, the voltage rises from what ever the system voltage was to a set point, around 14.5 volts. At that point the Charge controller stops the voltage from rising. Higher voltage can damage sealed batteries.

ABSORB;

Once the battery hits the preset point the charge controller keeps it at that point. Your batteries are roughly 80% full. Flooded batteries will start accepting less current at 80-85% full AGM/Sealed may go a little longer before accepting less current.

On many controllers you can set this point, Some will have different presets for Flooded, and sealed batteries, or flooded, AGM, and sealed batteries. 

The charge controller has a couple ways to know when to switch to float, Most inexpensive Charge controller are just timed for 1.5-2 hours. Some will also see less current flowing through the charge controller and shut it down when minimal current is flowing through the controller. On more expensive charge controller. You can set battery capacity to give the Controller a better idea of when to stop. you can also set a longer Absorb time. Or set 'end amps' a amount of amps flowing through the charge controller to stop Absorb and switch to the final stage.

FLOAT;

Once the Controller has determined the battery is fully charged it reduces the voltage to a point where very little current is flowing to the battery. This will prevent the battery from over charging and heating up.

While in 'Float' the charge controller watch for voltage drop, which would indicate a load. If the voltage begins to drop the charge controller will allow as much current to flow from the panels/array to compensate and maintain the voltage. If the voltage can be maintained, the load will in essence be running directly off the array/solar. If the voltage drops below the preset float voltage, the controller may start a whole new cycle if it stays there for a period of time.

The system voltage drop you see at night when the sun goes down is the charge controller moving into a resting mode with no energy to contribute to the system.

Phu

Thank you for all your suggestions. The VFD controller is a very good solution and possibly what I will need to stop the power surges related to my pressure pump. I will try that out. Both my inverters are connected together through a Magnum Energy box. All the batteries power go in through one shunt and the inverters pull from the same point of both battery banks.

Phu

Dave, 
Do you have a unit you would recommend for a 1hp, 220V jet drive motor?

Phu

It seems all the VFD controllers are set up for three phase motor.

BB.

Pretty much.... 3 phase motors have a "naturally" rotating internal field--They do not need starting capacitors and switches as larger single phase induction motors do. VFDs are usually the choice to drive 3 phase motors in soft start/variable RPM/Frequency applications.

There is a variant--Those are single phase motors with external starting capacitor (capacitor is at the wellhead/controller, not installed in the submersible pump motor)--I have seen from Franklin well pump company. With the external capacitor, that can be driven by a VFD (basically a 2 phase VFD output).

https://franklinwater.com/products/drives-protection/residentiallight-commercial/subdrive-utility/

I have no idea about the details of this unit. And don't know if other VFDs can drive "external capacitor" single phase pumps or not...

-Bill

Dave Angelini

Phu said:

Dave, 
Do you have a unit you would recommend for a 1hp, 220V jet drive motor?

Grundfos pumps are all I use for my clients. They internally use their proprietary electronics to soft start the variable drive.
There are other makes out there also that are not Jet drive!