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Mecer 3.5kwh lithium battery 48v


VictorD

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Good day, hope i find everyone Good. I'm having a set up of 8kw / 48v Mecer Inverter and 3.5kwh lithium  48v battery which is running offices supplying essential loads, actually all the plugs that connects printers, lights and some stuff by the offices. Now the problem is when i switch on all essentials, the battery cut off and beeps.. I'm assuming it my be drawing too much current as the battery only supplies 74Amps. I'm suggesting adding another battery then connect it in parallel to increase Amperage, just a suggestion. Would that be the Solution?? Thank you 

V. D

Edited by VictorD
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22 minutes ago, VictorD said:

Now the problem is when i switch on all essentials, the battery cut off and beeps.. I'm assuming it my be drawing too much current as the battery only supplies 74Amps.

Most likely the BMS discharge overcurrent protection is triggered.

What happens when you switch on essentials one at a time? Does the battery hold with minimum load?

22 minutes ago, VictorD said:

I'm suggesting adding another battery then connect it in parallel to increase Amperage, just a suggestion. Would that be the Solution?

I would suggest adding another 2 batteries to make it 3 in total. i.e. 74*3=222A to match the inverter's 8000/48=167A max discharge current.

Edited by Kilowatt Power
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16 hours ago, VictorD said:

@Kilowatt Power this is the specs of my inverter, I'm a newbie here, how did you come up with 167A

Another thing what would be the correct battery fuses to be used. If you may plz provide the formula 

Thank you 

Screenshot_20230623_192108_com.opera.mini.native.jpg

Continuous discharge is 37.5A. At 48V that's 1800W. 

First thing is your inverter is going to try to handle 8kw with a battery that can't even supply a 1/4 of that. If you keep your loads low you'll get away with it, but it's a mismatch. 

In my experience a tripped inverter, given PV or grid, will restart itself, but a tripped battery is more of a problem. So my inverter has a lower limit than my battery and will trip first, then reset. 

Your 1.8kW is less than 8A on the AC side. More like 7.5A given losses in converting from DC to AC. That's not a lot. 

You're constrained on the battery side. Two batteries in parallel will give you 15A on the output side and the ability to run longer of battery. 

But you're already exceeding or hitting the 37.5a limit on the battery. And those batteries seem to go for about 22k.

For 35K you could get a Hubble am5. For 29K you could get 5kwh of Greenrich. Either is going to give you the ability to service greater loads and a more easily lived with system. (sell your current battery for 10K and you will pay 20 to 25k to be in a better situation). 

But if you have the cash, get 10kWh of 1C battery. Now you don't have that mismatch of inverter and battery, and you will be even better off. 

One thing: try to get a battery that is compatible with your inverter IE you can run a comms cable between inverter and battery, which gives the inverter better control of the battery.

Edited by Bobster.
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On 2023/06/24 at 2:49 PM, Bobster. said:

@Kilowatt Power this is the specs of my inverter, I'm a newbie here, how did you come up with 167A

As @Superfly mentioned, that's your battery (Mecer Dyness B3) and not the inverter. Please post specs of your inverter as well.

167A is a rough estimate of the inverter's current draw at full load obtained by dividing the rating (8000W) by the battery nominal voltage (48Vdc). 

With regards to adding more batteries in parallel, I suggest you heed @Bobster.'s advice. The alternative would be to use a minimum of 5 {five} Dyness B3/SOL-B-L-M3 batteries in parallel. i.e. 8000W / 48Vdc / 37.5A = 4.4 pieces rounded up to 5 pieces.

On 2023/06/23 at 9:51 PM, VictorD said:

Another thing what would be the correct battery fuses to be used. If you may plz provide the formula

It's important to note that fuses protect cables from melting and starting fires in overcurrent events or short-circuits. You should therefore select an appropriately rated fuse (current, voltage, speed, type etc) for your battery cable and application. 

For example, if using a 50sq.mm battery cable with an ampacity rating of 200A @ 70 deg C in free air (not enclosed in conduit or trunking), then your maximum fuse rating should be 200A x 125% = 250A.

I would however advise that you go with what is recommended in the inverter manual. Read it.

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  • 2 weeks later...
On 2023/07/07 at 11:07 AM, VictorD said:

Screenshot_2023-07-07-10-03-52-60_e2d5b3f32b79de1d45acd1fad96fbb0f.jpg

Excerpt from the SOL-I-AX-8M manual

image.png.49a6a8364f233b7d31acb6c51011eeab.png

On 2023/06/23 at 9:51 PM, VictorD said:

Another thing what would be the correct battery fuses to be used. If you may plz provide the formula 

Going by the manufacturer's recommendations, you should use the following cable and fuse sizes:

  • Cable size: 70sq.mm rounded up from 67.4mm^2
  • Battery fuse rating: 250A rounded up from 183.2A typical amperage x 125% safety margin
Edited by Kilowatt Power
Added 125% safety margin for fuse rating
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@Kilowatt Power thank you for your input...but the battery capacity is quite different from my set Up..mine it's 3,5kwh /74 AH with the maximum Discharge of 2.4 Kwh/50 AH and Charging Current of 50 A...do i still need to go for 70sqm cable and 200Amp Fuses?

Edited by VictorD
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8 hours ago, VictorD said:

@Kilowatt Power thank you for your input...but the battery capacity is quite different from my set Up..mine it's 3,5kwh /74 AH with the maximum Discharge of 2.4 Kwh/50 AH and Charging Current of 50 A...do i still need to go for 70sqm cable and 200Amp Fuses?

It is very important to select the right size battery cable. A small cable carrying high current will introduce undesirable effects (e.g. DC ripple), cause a fire or serious injury. I strongly suggest you read Wiring Unlimited, a book by Victron Energy on electrical wiring systems.

Ideally your battery cable should be able to carry the inverter full load current without significant voltage drop. Similarly your batteries should be able to provide the inverter full load current. Lastly, your fuse is sized to protect the cable.

If your battery cables are relatively short and not enclosed in conduit on a wall or in trunking then as per BS 7671, you can make do with with 50sq.mm PVC insulated cables with an ampacity rating of 196A @ 70 deg C in free air and a 200A fuse. 

Edited by Kilowatt Power
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Slight hijack, but does anyone have the pinout for the comms cable between two of these Mecer 3.5kw batteries?  Ive landed a second one im connecting tomorrow, but didn't receive the cable to connect them to each other.  Running solar assistant on the inverter so that part of the comms between inverter and master1 is sorted.  Need master1 to talk to slave now.  Please assist :)

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On 2023/07/09 at 2:38 PM, Kilowatt Power said:

It is very important to select the right size battery cable. A small cable carrying high current will introduce undesirable effects (e.g. DC ripple), cause a fire or serious injury. I strongly suggest you read Wiring Unlimited, a book by Victron Energy on electrical wiring systems.

Ideally your battery cable should be able to carry the inverter full load current without significant voltage drop. Similarly your batteries should be able to provide the inverter full load current. Lastly, your fuse is sized to protect the cable.

If your battery cables are relatively short and not enclosed in conduit on a wall or in trunking then as per BS 7671, you can make do with with 50sq.mm PVC insulated cables with an ampacity rating of 196A @ 70 deg C in free air and a 200A fuse. 

The book is very informative...Really Appreciated

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