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Cable dimensions from MMPT controller to batteries


RickS
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I am going to be installing solar and wondered about the diameter of the cable needed from the MPPT controller to the batteries.

The controller is a Victron 100/50 and will have two 295W panels connected to it, wired in series.

The options seem to be 10mm squared or 16mm squared and I'm not sure which would be the most suitable.

Also, plan to have an inline fuse close to the positive terminal of the battery bank and wanted to know what size fuse to use. Would a fuse be better than an RCD switch? If so any dos and don'ts?

Thanks for you help

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46 minutes ago, Tracy D'arth said:

You mean MCB not RCD?

Do I? Good to know and just shows how little I know. Thanks Tracy

49 minutes ago, Jen-in-Wellies said:

How long will the cables be from MPPT to the batteries? That determines the size to get a certain voltage drop at max current. The maximum current would be 50A, so something like a 70A fuse to get some overhead. Use a Midi size fuse and holder.

Jen

Thanks Jen. I am hoping to get the controller as close as I can to the batteries. Between 1 and 2 metres maximum. Will that range be enough to make a difference in diameter needed?

47 minutes ago, matty40s said:

You will have to trim the end of a 16mm2 cable down to get it in the hole, so stick to 10mm2.

Hadn't thought about the size of the hole in the controller, good point. Thanks matty

39 minutes ago, Jen-in-Wellies said:

Are you planning to use the Victron voltage sensing bluetooth gadget? This will tell the controller what the actual batt voltage is and compensate for any voltage loss in the cables by increasing the voltage at the mppt end.

I am going to say yes as the Victron model is the Smart Solar with Bluetooth built in, but haven't got my head around the settings yet.

 

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51 minutes ago, Tracy D'arth said:

You mean MCB not RCD?

Just looked up the difference on the interweb and yes, I do mean MCB  (RCD was just a generic term I had floating around, but I should learn to be more exact in my terminology) Thanks again

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9 minutes ago, Rick Savery said:

Thanks Jen. I am hoping to get the controller as close as I can to the batteries. Between 1 and 2 metres maximum. Will that range be enough to make a difference in diameter needed?

Using the voltage drop calculator here, 10mm2 wire at 12V and 50A, with 2m between controller and batteries gives a voltage drop of 3%, which should be OK.

 

11 minutes ago, Rick Savery said:

I am going to say yes as the Victron model is the Smart Solar with Bluetooth built in, but haven't got my head around the settings yet.

The smart battery sensor is this. Communicates with the solar controller by Bluetooth, but it is a separate purchase from the smart solar controller.

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3 hours ago, Jen-in-Wellies said:

Using the voltage drop calculator here, 10mm2 wire at 12V and 50A, with 2m between controller and batteries gives a voltage drop of 3%, which should be OK.

 

The smart battery sensor is this. Communicates with the solar controller by Bluetooth, but it is a separate purchase from the smart solar controller.

Ah didn't realise it was a separate item, thought it was part of the controller setup. At the kind of price it's going for it seems crazy not to if it makes charging the batteries easier and more efficient. Thanks

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6 hours ago, Rick Savery said:

Ah didn't realise it was a separate item, thought it was part of the controller setup. At the kind of price it's going for it seems crazy not to if it makes charging the batteries easier and more efficient. Thanks

I've not used one. My Victron stuff predates them having Bluetooth, so can't recommend one way, or the other, but it looks like a good idea.

Jen

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