Author Topic: MN3548DIY battery current  (Read 141 times)

ewilhelm

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MN3548DIY battery current
« on: January 13, 2022, 08:26:19 PM »
Hi,

I have a MN3548DIY with 2 kW of solar and 5.1 kWh of LiFePO4 storage. The MN3548DIY reports higher battery current than the battery's BMS reports or I measure with a clamp-on ammeter. Here are some example values:

MN3548DIY batt current (+ input to battery), BMS and ammeter current
19, 12
7, 2
5, 0
-2, -3

For input, it looks like there's about a 5 A offset. Is it possible I'm misunderstanding something?

This is relevant for my setup because I want to set the max charge current at 20 A (as specified by the battery), and I am not sure the MN3548DIY is actually reaching that current.

Thanks,

Eric




boB

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Re: MN3548DIY battery current
« Reply #1 on: January 13, 2022, 10:43:54 PM »

We will take a look at this !

Thanks for the report.

boB
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ewilhelm

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Re: MN3548DIY battery current
« Reply #2 on: January 15, 2022, 02:08:02 PM »
Thanks for your help.

On this topic, the PV current display doesn't match what I measure either. Here's an example:
PV input reported on MN3548DIY display
102 V, 9.5 A -- based on sun conditions and what another, nearby solar system is producing, this seems very high
measured with handheld meter
103 V, 2.3 A -- seems accurate based on conditions
PV power reported on MN3548DIY display
0.500 kW -- note sure how this matches either the voltage and current display nor the measured voltage and current

It probably doesn't help, but I've included a picture (I ran the PV wire to the left of the intended hole in the case so I could land some flexible conduit there to protect the PV wire).

Wizbandit

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Re: MN3548DIY battery current
« Reply #3 on: January 18, 2022, 11:21:19 AM »
I have a 3548 and 5048 here I will test.  One thing I know from the past experiences with Charge Controllers, our Classic for sure,  is the noise on the PV wires will mess with the Hall Sensor used in DC Clamp meters and the reading will not be correct.  I will setup a shunt & Wbjr and run the DIY Inverters through it and see what readings I get...

I have contacted the SRNE Engineers to see if we can calibrate the voltage and current readings.

ewilhelm

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Re: MN3548DIY battery current
« Reply #4 on: January 19, 2022, 12:17:49 AM »
I typically run my system on "only solar charging" and "inverter priority mode". Today I switched it to "hybrid charging" and "mains priority mode" to fully charge a new battery. I noticed the MN3548DIY showed 20 A of battery input current, which was confirmed by the BMS and my ammeter.

Perhaps the incorrect battery current and PV current are related and only happens in "only solar charging"?

Thanks for your help.

boB

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Re: MN3548DIY battery current
« Reply #5 on: January 19, 2022, 02:14:37 PM »

I thought of an idea for this wrong current reporting for both PV and battery current.   Maybe....

For the situations where the currents are measuring wrong, are you sharing a common negative wire for battery AND PV ?

If the inverter/charger measures current on the negative legs only, then it may be necessary to run separate PV and battery negative wires to the DIY3548DIY.

Does the documentation say anything about this ?

boB
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ewilhelm

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Re: MN3548DIY battery current
« Reply #6 on: January 19, 2022, 04:52:31 PM »
The negative battery and negative PV are only connected to the inverter/charger's terminal blocks. I have not connected them to each other.

boB

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Re: MN3548DIY battery current
« Reply #7 on: January 19, 2022, 08:07:08 PM »
The negative battery and negative PV are only connected to the inverter/charger's terminal blocks. I have not connected them to each other.

OK, great !   Just thought I would check.

We are talking to SRNE to get this corrected.   Maybe it is just a software update or an adjustment  ?

boB
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ewilhelm

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Re: MN3548DIY battery current
« Reply #8 on: January 19, 2022, 09:00:08 PM »
And, here's more, hopefully helpful:

Output source: UTI, Charge source: OSO
PV current 12.2 on MidNite, 8.8 on ammeter
Battery current 12 on MidNite, 9.4 on ammeter (different battery without a display on its BMS, so no third data point)

Output source: UTI, Charge source: SNU
PV same as above (consistent, sunny day)
Battery current 25 (hitting the combined max charge current) on MidNite, 22.2 on ammeter

Seems like the "lost" current is related to the PV as current from the Mains through the inverter didn't change the offset between the MidNite's current and the ammeter's current.

Wizbandit

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Re: MN3548DIY battery current
« Reply #9 on: January 20, 2022, 06:38:46 AM »
I wonder if it's doing what you are asking from your settings...
Look at this parameter readout from the DIY3548.  The BLUE are charging parmeters.

PARM[07] is total charge current into the battery, PARM[28] is how much allowed from the GRID (AC IN) and PARM[36] is how much to allow from the PV IN.

The difference you are seeing may be because your battery charge current from PV might be minus what is being used to power the inverter and/or loads.  I'm reorganizing my "test wall" so I don't have a DIY Inverter powered up working just yet but I will test as soon as I get everything setup.  We are used to seeing separate readings from the charge controllers and inverters but remember this unit is integrated and shares the same control computer.

ewilhelm

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Re: MN3548DIY battery current
« Reply #10 on: January 20, 2022, 01:11:05 PM »
Thanks for your continued help. Here are my settings:

Parameter: setting
7: 25 A
28: 20 A
36: 25 A

Under Output source: UTI, Charge source: OSO, the mains are powering everything on the AC output, and only solar is charging the battery. In this configuration, I still see different battery and PV currents between the MN3548DIY's display on what I measure with an ammeter or the battery's BMS reports. In UTI and OSO, parameter 7 and 36 are effectively the same because no charging is permitted from the grid, and the inverter AC output is off since the loads are bypassed.

As noted in an earlier note (perhaps not clearly), when the battery is charging only from the mains without solar charging, the display, BMS, and ammeter current all match. There's something wrong with the PV input and/or battery from PV current.