Guidance requested (1 Viewer)

MarqG

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Jan 8, 2023
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Hi folks, I am a bit of an off-gridder, I have an upgrade to my system and while I have had a lot of help to get me where I am I wonder if anyone might be able to help with the last leg.

I have a Votronic triple charger VBCS 30/20/250 and a Pico Blue battery monitor - I can set these up separately as shown in the accompanying diagram however, I would like to combine both configurations onto the one battery - a Fogstar 460ah li-ion.

Secondly the VBCS charger is limited to 250 watt solar panel input and my goal is to add a further 800 watts - so will require a 2nd MPPT - how would I add this into the mix too?

Any help or guidance would surely be appreciated.
 

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MarqG

MarqG

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Jan 8, 2023
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cheers (y)

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Mar 30, 2019
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The battery monitor shunt should be connected to the battery negative terminal. All the other negative cables including the charger negative go to the other side of the shunt, usually via a busbar. This allows the shunt to measure all the power flowing in and out of the battery as it ALL has to pass through the shunt.
All the positive cables including the charger positive then go to the positive battery terminal via suitable fuses.
 
Last edited:
Mar 30, 2019
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You can add a second solar controller and connect them in the same way. They will work in tandem.
 
Apr 27, 2016
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For combining the two devices, the important thing is that one side of the shunt (and nothing else) connects to the battery terminal. Everything else connects to the other side of the shunt, including the chassis grounds. The idea is that all current flow into/out of the battery has to pass through the shunt, and there are no ways to bypass it. That negative connection for the loads looks like a busbar, which is a good idea.

Maybe you should rethink the inverter wiring. It looks like you have a 4000W inverter supply going through a 25A fuse on a distribution board and switch panel. I hope you appreciate that 4000W is 333A at 12V, so even a 250A fuse won't be enough. A 4000W inverter requires some serious hosepipe-sized cables and special fuses and switches.

On the other hand, the shunt will take 500A, so at least that will be fine. And the 460Ah lithium battery can probably take that kind of load, but obviously it will be draining rapidly.
 
Jul 6, 2009
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The cables on mine for 12/2000/80 inverter charger with 700 watts of solar.
 

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Lenny HB

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Oct 18, 2007
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For combining the two devices, the important thing is that one side of the shunt (and nothing else) connects to the battery terminal. Everything else connects to the other side of the shunt, including the chassis grounds. The idea is that all current flow into/out of the battery has to pass through the shunt, and there are no ways to bypass it. That negative connection for the loads looks like a busbar, which is a good idea.

Maybe you should rethink the inverter wiring. It looks like you have a 4000W inverter supply going through a 25A fuse on a distribution board and switch panel. I hope you appreciate that 4000W is 333A at 12V, so even a 250A fuse won't be enough. A 4000W inverter requires some serious hosepipe-sized cables and special fuses and switches.

On the other hand, the shunt will take 500A, so at least that will be fine. And the 460Ah lithium battery can probably take that kind of load, but obviously it will be draining rapidly.
The BMS on the Fogstar max discharge is limited 200 amps so max inverter size would be 2000 watts.
To run a 4000 watt inverter you would need 2 x 230ah batteries.
 
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MarqG

MarqG

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Jan 8, 2023
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The cables on mine for 12/2000/80 inverter charger with 700 watts of solar.
Hey Lenny, thanks - I currently have 16mm2 cables on the inverter - its difficult to tell from your pics but would this be adequate?
 

Lenny HB

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Oct 18, 2007
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On the coast in West Sussex
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Hey Lenny, thanks - I currently have 16mm2 cables on the inverter - its difficult to tell from your pics but would this be adequate?
For that size inverter for a 2m cable run you will need 95mm2 cables, 16mm is way undersize only good for about 700 watts.
 
Last edited:
Aug 6, 2013
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A few years ago there was an industry suggestion that a move to 50v would solve a lot of vehicle electrics problems (mainly the weight of 12v wiring). Wouldn't life be easier if it had happened 🙂?
 
Apr 27, 2016
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A few years ago there was an industry suggestion that a move to 50v would solve a lot of vehicle electrics problems (mainly the weight of 12v wiring). Wouldn't life be easier if it had happened 🙂?
Certainly would in this case. the 333A would reduce to 83A, a much more manageable current. Anything larger than a panel van has already moved to 24V.

The part of the habitation working off 12V only requires 200 to 300 watts total, so sticking to 12V with a high power inverter is debatable. Trucks use 24-12v converters where necessary to run bits of 12V kit. If it's 48V, one option is a small 12V battery, charged by a B2B from the big 48V battery. That way everything stays the same on the 12V side, and can be reverted if necessary. Alternatively a 48-12V converter can run all the 12V kit.

Then a 48V inverter/charger, a 12-48V B2B and a 48V MPPT will keep the 48V battery happy.

However I have the impression the OP has already bought a big 12V lithium battery and a 12V inverter, so the die is cast I think.
 
Apr 27, 2016
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its difficult to tell from your pics
In the first pic, the black cable has '95mm2' written on it. That's its cross-sectional area in square millimetres (CSA). Its diameter is about 18mm. As I said, serious hosepipe-sized cable.

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