Cc to battery wire size

[Takis]

Hello friends,

I have a renogy mppt 40amps max charge controller and my battery bank needs 30 to 35 amps to be charged.
I'm redesigning/rethinking my setup nowdays.
I've available 2 wire sizes, a 4awg and a 5awg.
The manufacturer suggests the 8awg as the maximum wire size.
4 awg needs some modifications so as to fit though, while 5awg fits like a charm.


So my questions:
1) using 5awg with full load (40amps) I calculate a significant voltage drop. Do the charger regulates that issue? Can I test it somehow?
2) is it better to go for the 4awg with less voltage drop and some gain?

Notes: 24v system
Distance from cc to batteries is less that a half meter (1.6 ft)
I can't contact manufacturer due to the lockdown. I guess they will answer in the future.

[SunEagle]

I am confused as to why a #5 needs modification while a #4 (which should be bigger) does not. A #8 should be able to handle up to 50amps but the wire may need to be bigger depending on the distance it is run which can affect the voltage drop.

Just a quick rule of thumb. Wire sizes get bigger when the number gets smaller. ie. A #12 is smaller in diameter then a #8 and carries less amps.

Based on the renogy CC being only 40amps a #8 wire should be enough. I think you need to recheck Vdrop calculations concerning that #4 wire. It should result in a lower VD% then a #5.

[Takis]

I am confused as to why a #5 needs modification while a #4 (which should be bigger) does not. A #8 should be able to handle up to 50amps but the wire may need to be bigger depending on the distance it is run which can affect the voltage drop.

You're right, I wrote them wrong due to the metric.

I've tried vdrop calculation with 5 awg and half meter for 24v. The result is 23.5. Which I think is not acceptable because charging manuals describe voltage settings using 2 decimal points.
Maybe my input data to the calculator is wrong.

What if I use 5 for a meter (3.2ft)?

[SunEagle]

You're right, I wrote them wrong due to the metric.

I've tried vdrop calculation with 5 awg and half meter for 24v. The result is 23.5. Which I think is not acceptable because charging manuals describe voltage settings using 2 decimal points.
Maybe my input data to the calculator is wrong.

What if I use 5 for a meter (3.2ft)?

I just ran a calculation using a #5 Awg copper wire running 24V and 40Amps for a wire run of 4 feet (more than 1 meter) in one direction. It resulted in a 0.1 volt drop which is less then .5% VD.

So if that #5 works then I would use it.

[Takis]

Thanks.

Two more questions.
If the charging parameters according to the battery manufacturer is 2.45 per cell, would that voltage drop affect the charging?

When we say "one direction" it means both positive and negative wires (one pair), right?

[SunEagle]

Thanks.

Two more questions.
If the charging parameters according to the battery manufacturer is 2.45 per cell, would that voltage drop affect the charging?

When we say "one direction" it means both positive and negative wires (one pair), right?

Well your charger should provide a higher output voltage to the batteries depending on what phase it is in. So for 2.45 per cell and you have (i assume12 cells) that comes to 29.4 volts which is about right for a 24V battery system.

The calculator just allowed me to input a length equal to "one direction" but for DC I presume it used both paths distances for the calculation. But even if you double that 0.1v VD you will get a 1% VD which is still under the 2% max.