With what you have said, as well as so many others in this forum, (thank you by the way) - what do you recommend I do.
I still recommend to do a 'proper' (series) voltage drop test to confirm the numbers/math adds up to the measured voltages on each end, they should all add up.
What system are you running? Do you have modern hardware? Do you have LFP, or Lead Acid?
Modern Victron SCC's with DIY LFP batteries, and copper bus bars and Victron BMV-712 shunt in between 2 negative bus bars.
What Charge Controller are you using? What is the reading at the posts of your charge controller terminals, and battery terminals during peak sun? Do you see any Vdroop?"
Thanks again.
Sure no prob...
So I did say what I kind of system have before to some extent, but I can list it again (all in the one place) real quick. I was able to go out and take a couple quick measurements, while my batteries were charging full-bore, both charge controllers were pegging at their maximum current of 100a output each. Victrons running very warm for sure.
My configuration:
-I have 2 Victron 250|100 charge controllers (each has their own 8-panel solar array, so 16 panels, 405w each, 4s2p wired).
-I am using 8 AWG cable on the PV solar circuit (from panel banks, each through a respective DC combiner box, then to each Victron SCC)
-I am using 2 AWG cable going from each of those Victron charge controllers to the main copper bus bars (one bus bar for + and two bus bars for - cable attachments on each side of shunt), and as such, the 2 AWG size is the largest gauge that can fit into the Victron SCC connection lugs, and what their manual says to use there (couldn't go bigger, unless I cut off some strands on a larger gauge cable).
-I am running from the copper bus bars to batteries, 3 SEPARATE sets of 2/0 cables, to each PAIR of 2x 12v battery packs
-Charging to a full bank of six, 280Ah 12v LFP DIY packs (1680Ah, 22KWh), with 6 Overkill 120a BMSs (JBD BMS)
My observations...
I do have a little bit of voltage drop in the circuit between charge controller and batteries.
-Sample voltage measured at Victron SCC terminal lugs is about
14.15v
-Sample voltage measured at the batteries connectors is about
13.79v
If I do a proper voltage drop test on the
positive cable (place the
+ lead of voltmeter to the Victron
+, and put the
- lead of voltmeter to the
+ of the battery connection), I measure
.2v drop in that run.
If I also do a proper voltage drop test on the
negative cable in the same way (place the
+ lead of voltmeter to the battery connection
-, and put the
- lead of voltmeter to the
- of the Victron), I measure
.17v drop in that run.
So the math all adds up. Add those two voltage drop numbers together from the positive and negative cable voltage drop tests, which is
.37v. For reference:
14.15v - 13.79v = .36v (.01v off but oh well, it basically adds up almost nuts-on).
I measure the temperature of the wires connecting the Victron SCC to bus bar (the 2 AWG cables) using an infrared temperature gun, I see
105° F (cable is rated for 221° F max).
I consider this to be about as good as I can get, since Victron doesn't make larger battery connection lugs on the 250|100. I could use bigger cables and trim out a few strands to make it fit the lugs if I wanted to try and lower the cable temperature, but I am willing to accept the minor loss, since the energy from the Sun is free anyways, it's just the cost of doing business at a most reasonable price vs expectation point.
A little bit different scale than your system, but kind of showing the workflow of checking out voltage drop is the same. In your case, the loss is not acceptable due to a full 1v drop being perceived here.
