earthing of battery bank?

[mich22call]

hi, i am new to the group and am confused! some wiring diagrams i looked at run the negative side of the battery bank to earth others don't. so does it matter and what is the difference? any replies are appreciated, Michael

[Sunking]

What does earth do?

NOTHING. It is forbidden to use earth as a conductor. Anyway the choice to reference a system to something depends on the nominal system voltage, and how you intend to implement over current protection. Below 50 volts, there is no requirement to use a Grounded System.

A Grounded System is prone to unnecessary outages, and Dangerous in small systems. But if you are going to Float a system means you must use Over Current Protection Device on both polarities.

[mich22call]

hi Sunking, thank you very, very much for your reply!! as it is only a small set up (1kw) i will float the system. i am trying to install 1000w in mono panels (4x250w), a 100 amp controller going to 520amh (4x130amh, deep cycle) battery bank. now that is where i scratch my head., what size fuse would be required to go on both polarities + and - between the battery bank and inverter (8kw/32kw surge)? i would really appreciate it very much if you would find the time to answer me that question.thanks again, Michael

[Sunking]

It will take 4 fuses. The two facing the Charge Controller are sized to the max Current being supplied by the Controller. Not sure where you came up with a 100 Amp Controller, but no such thing exist nor needed. What Battery Voltage will you be using. 24 or 48 volts?. If you have not determined that yet make it 48 volts, and 12 volts is out of the question. If you use 48 volts with 1000 watts of panels only requires 20 amps, and 40 amps @ 24 volt battery. So either a 25 or 50 amp fuse depending on what battery voltage you end up with. Whatever rating your controller is add 25% more to determine fuse and make sure you have the right size wire.

The Two Fuses Facing the Inverter are sized on the Inverter Requirements. What voltage and wattage is the Inverter? Regardless IT SHALL NOT BE GREATER THAN 100 AMPS If you need anything more means your system is running at to low of a voltage. Real simple the limits are?

<= 1000 watts @ 12 Volts
<= 2000 Watts @ 24
<= 4000 watts @ 48 volts.
If you are in those limits, you will not need more than 100 amps. Even at 100 amps you are playing with FIRE.

Use Fuses that connect directly to the battery term post.Connect them like shown below.




A great source of battery Fuse Blocks is Blue Sea. Use the 2151 dual fuse block. You need 2 of them with 4 MRB Fuses.

[mich22call]

oh wow, thank you for taking the time to reply, very much appreciated! so far everybody recommended to opt for a 12 volt system. hence i worked out: 4x250 watt panels (1kw) on 12 volt gives me 83.33 amp, hence the 100 amp controller and sorry to say they do and i got one right in front of me. (~£57).. i also got a 12 volt inverter (8000watt/ 32000watt surge) i am thinking of getting 4/5 130 amh deep cycle calcium batteries for storage. i got the fuse size to go between the controller (max current of it, 100amp) and the batteries and i assume 100 amp fuses to go between the batteries and inverter would be amble? furthermore i was going to use 50mm2 cable (345 amp) to run between the controller.and inverter/batteries and across the batteries. sorry for being a complete idiot but i am trying to learn and the more i get into it, the more complicated it gets! wish i had half of your knowledge! thank you again ever so much again, Michael

[Mike90250]

You have 250W panels, which are likely in the 30-40V ballpark.
There is NO MPPT controller @ 100A, You may have a cheap PWM controller, which will work fine - - - - If you don't mind throwing away half your panel capacity.

But, I'll warn you, you have a completely out of balance plan, and I'd advise to return what you can and get a refund and then plan what you CAN safely
do, and conserve your $$

Rules of Thumb:

over 300w = MPPT controller

50-1,000w inverter = 12V system
1,000 - 2,000w inverter = 24V system
> 2,000w inverter = 48V system

1,000w of panels, @ 12V would need a 80A controller & 4 ga wire - 5.18922mm di, 21.2mm²
@ 48V would need only a 20A controller & 12ga wire - 2.05232mm di, 3.31mm²

48V system would use 8 golf cart batteries (6v, 200ah) 9600 watt hours
12V system would use 6 specialty batteries ( 2V, 800ah) also 9600 watt hours, but uses very expensive wires, and other components (crimp lugs)

[mich22call]

hi Sunking, thank you again very much. i will do as you advised and see what i can do. thank you again for your time. best wishes, Michael

[Sunking]

Micheal do everything you can to return your Inverter and Controller. A 8000 watt 12 volt Inverter is beyond ridiculous and is a BOMB waiting to explode. a 8000 watt 12 volt Inverter will require a minimum 800 Amp fuse and copper cables the size of your leg that you stand absolutely no chance in Terminating them as it takes a 20-ton press.

Here is something that has escaped you. You asked earlier about C/10 charge rate. Well batteries have maximum Discharge Rates, and Rolls is C/4. You have a 428 AH battery, and a C/4 current = 428/4 = 107 Amps @ 48 volt battery voltage. How much power is that? 48 volts x 107 amps = 5136 Watts. Now just because you can use up to 5000 watts does not mean you should. It just means you can get away with it. A good design rule is Inverter Wattage to be no greater than 1.5 x Panel Wattage. Again that does not mean you should push the limit to 1.5 X.

Having said that if you elect to go with 12 volts, I will not help you, nor should anyone else. That should raise a Red Flag that what you intended is dangerous and I want no part of it.

The bottom line here is at no point you exceed 100 amps of current. With a 100 Amp current limit means is the most power you can run is:

1000 watts @ 12 volts
2000 watts @ 24 volts
4000 watts @ 48 volts.
8000 watts @ 96 volts.

FWIW all the above require the exact same 80 amp MPPT Controller to be used.