Some clarity on SBMS balance-lead wiring

[Marinepower]

Forum,

I have installed a new bank of LFP batteries (4P, 4S) in my boat which required a re-wire of the SBMS 12 pin balance-wire leads.

I have extended these leads 1.2 meters with a "break out board," so the wiring is my own ( and not the original ribbon wire).

I am very space constrained in the new install.  Before i had  a 1 amp fuses on each of the positive balance lines.  I not longer have space for these. 

As an alternative, I have replaced  the wires # 3 - 10 with 25 guage tined copper wire.  I figure if there is a short, the wire itself will act as a fuse.  

However, i have left wires 1 and 2 (the negatives ) as 20 gauge wire.

I have also combined wires 11 and 12 and left them 20 as gauge and fused # 11 &12 with a blade fuse rated at 2 amps.

I am assume the above is OK for the SBMS to function and get accurate volt readings from the LFP bank.?  If not, please let me know how to adjust....

Thank you!

MP 

[Dacian Todea (electrodacus)]

What do you mean by extending 1.2m ?  You will also keep the original 1.8m cable ?

Normally if you need more than 1.8m cable you will shorten the included cable to maybe 30cm then use thicker cable as extension.

1A fuses will most likely have a fairly high resistance and will have been a problem due to voltage drop on them during cell balancing.

25AWG should be fine but not great if they are on top of the 1.8m of included AWG28 ribbon cable.

You can combine 11 * 12 in a single wire but 1 and 2 need's to be separated from the SBMS0 all the way to battery terminal.

Wire 1 and wire 11+12 power the SBMS0 and wire 2 is voltage sense wire same way wire 10 is a sense wire.

[Marinepower]

Thanks for the rely.  I should have been more specific about the lay out of the wires.  It is a bit complicated.

So every wire except 11&12 have their own dedicated wire all the way to the LFP battery.

I have a 30cm ribbon cable from the SBMS to the break -out board.  

From the break out board to the battery compartment is 20 gauge shielded wire, approximately 1.2 meters in length.  These wires go to a 12-post terminal strip.

From the terminal strip, wires #3 through #10 are 20 inches long and 25 gauge wire and each wire is separate wire run.  Ring terminals are soldered. 

Wires # 1 & 2 are 20 gauge from the 12-post terminal strip , each a separate wire  ( I assumed if the negative path had a slightly different resistance it would not matter as each positive  wire is sensing voltage against the same reference?)

Wires 11&12 are also 20 guage and are routed through a 2 amp blade fuse.   I figured these wires don't measure voltage so should not matter?

MP

[Dacian Todea (electrodacus)]

Thanks for the extra info. Now I understand.

Yes it will work with no problem an yes the 2A blade fuse is not important as 11&12 are just to power the SBMS0 not used for measurement.