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diy solar

Battery cable length - from Lynx distributor

FilterGuy said:
My uncalibrated eye measures about 4' more cable in the total round trip. That would make the voltage drop difference about .05V. Not enough to worry about and probably far less than voltage drops on the fuses, connectors, etc. Even if you double the calculated drop and call it .1V, it is not enough to worry about.
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I generally don't argue with you, but I definitely disagree this time. Sig link #6, 4.9.
 
Do what you want.
I have had two units in parallel with the same size conductors at different lengths. The one with the shorter length had a higher voltage and carried more of the loads. At low loads, the other one would just idle, carrying none of the load.
The difference is length was 14". And it definitely made a difference.
I'm not sure why you would ask a question. If you really didn't want the answer.
Good luck.
 
sunshine_eggo said:
When the authority is known to understand this issue, is consistent with education and training materials, and has implemented their own major system, it's not a fallacy.



Simple or complex error doesn't matter. You aren't paying enough attention to know that 70mm is not a diameter but an area, and blind reliance on a tool because it gives you the answer you want is confirmation bias.



The consequences have been stated. It's an inherent system imbalance meaning the inverter connected via shorter wires will carry more of the load. Will it be a problem? Maybe. Maybe not. Is it consistent with best practices? Nope.

Funny how everybody understands how important it is at that each parallel battery have the same length of conductors, but for some reason the length of the cable to the devices sharing loads suddenly doesn't matter?

If you see your electricing using oversized and/or unequal length for the AC side, fire them on the spot. Same reason but notably more significant.
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LOL. "
It's an inherent system imbalance meaning the inverter connected via shorter wires will carry more of the load."
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How MUCH more of the load will the poor inverter have to carry? What difference will it make to the inverter if it's carrying 1% more of the load? Do you think two inverters even give out exactly the same current at all times, with same length cables?

The reason the length of THESE specific cables doesn't matter, in THIS case, is because they are 70mm2, i.e. massive, and have a very low resistance. Talk about spreading FUD - Fear, Uncertainty and Doubt.

Look at the difference in length between the left hand inverter's 70mm battery cables and the right hand ones in the screenshot below, from Voltacon's video... THAT is what I was basing my layout on. They don't seem to think there's a problem, and they are the sellers of the inverters, so presumably they don't want you to set them up in such a way that it causes a problem to an inverter with a warranty.

Voltage drop in 70mm cable 2.PNG
 
timselectric said:
Do what you want.
I have had two units in parallel with the same size conductors at different lengths. The one with the shorter length had a higher voltage and carried more of the loads. At low loads, the other one would just idle, carrying none of the load.
The difference is length was 14". And it definitely made a difference.
I'm not sure why you would ask a question. If you really didn't want the answer.
Good luck.
Click to expand...

Umm... what size was the cable? 70mm2, or 25mm2?
I wanted an answer, but with enough information to see whether it was correct or not. You keep leaving out important information...

Again - please explain the Voltacon video above. Look at the length of the right hand inverter's battery cables. Each one must be two or three feet longer than the left hand one's.
 
timselectric said:
Do what you want.
I have had two units in parallel with the same size conductors at different lengths. The one with the shorter length had a higher voltage and carried more of the loads. At low loads, the other one would just idle, carrying none of the load.
The difference is length was 14". And it definitely made a difference.
I'm not sure why you would ask a question. If you really didn't want the answer.
Good luck.
Click to expand...

I think this is the most insightful bit in this thread.

"To argue" is the reason.
 
So more answers with no facts or anything useful, sunshine_eggo. I don't agree with you or timselectric, because you haven't given any substantial reasons why I should, just "it will put more load on one inverter", without any AMOUNTS, which is what all of us here are very familiar with - how much does x, y or z affect something? It's like having a display on an inverter which, instead of giving an output figure in Watts, just says "Quite a lot" and "Really really lots of power".
 
FilterGuy said:
What does that mean?
Click to expand...
It means anything but actually argue with facts and actual figures. I used actual figures - I made a mistake when I first used that online form, which is apparently the end of the world. I corrected my error and posted a new screenshot of it, which shows that the voltage difference is still minute and isn't going to make any difference to the inverters, but that wasn't enough. Apparently the different lengths are just 'wrong', and the reason is 'because', and I'm supposed to worry about it. Really scientific! Oh, and because Timselectric had a problem with a different inverter with different cables, I'm supposed to think that it's applicable to my set up, even though Voltacon have theirs set up WORSE than mine!

What size were the cables you had a problem with, Timselectric? Are we not going to find out, because they were much thinner than 70mm2?
 
SenileOldGit said:
does it matter that the 70mm cables shown are different lengths?
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timselectric said:
It does matter.
How much it matters, depends on how much load you have running.
Click to expand...

SenileOldGit said:
Argue, argue, argue
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timselectric said:
If in parallel, the unit seeing the higher battery voltage will carry more of the load.
Click to expand...

SenileOldGit said:
Argue, argue, argue (look, the "high quality" Chinese manufacturer making these cheap-assed units did it this way too). I based my installation on a video rather than best practices.
Click to expand...

Your question as stated has been answered. Methinks you only care about arguing and feeling right.
 
https://voltaconsolar.com/DOWNLOAD-FILES/Parallel-installation-Conversol eV-4K-5K-20140403.pdf

WARNING: Be sure the length of all battery cables is the same. Otherwise, there will be voltage difference between inverter and battery to cause parallel inverters not working.
Follow below chart to connect batteries. All battery cables are connected from inverters to batteries via the same BUS bar.


From page 3. I doubt they mean that the battery cables to the bus bar have to be identical and after the bus bars, the battery cables, can be whatever length you feel like.
 
I love it: "Your question as stated has been answered." Which apparently means the answer is correct, and helpful. It isn't helpful, it doesn't give me any figures to go on. The drop in voltage is going to be tiny - do you disagree, sunshine_eggo? Do you think a 0.01V drop is going to cause a problem? Or a 0.02V drop?

If so, why? If not, why are you pretending that there IS a problem, without actually stating any figures for your reasoning? I'm using figures for my reasoning, that there won't be a problem. Which is why Voltacon set them up that way, because they haven't had any problems. (They aren't a manufacturer, they are a UK inverter reseller, and therefore they probably don't want people setting up their inverters incorrectly and then making warranty claims, so I presume they can't have had any problems.)
 
norcom said:
https://voltaconsolar.com/DOWNLOAD-FILES/Parallel-installation-Conversol eV-4K-5K-20140403.pdf

WARNING: Be sure the length of all battery cables is the same. Otherwise, there will be voltage difference between inverter and battery to cause parallel inverters not working.
Follow below chart to connect batteries. All battery cables are connected from inverters to batteries via the same BUS bar.


From page 3. I doubt they mean that the battery cables to the bus bar have to be identical and after the bus bars, the battery cables, can be whatever length you feel like.
Click to expand...

Then below it says the cables should be 22mm2. So they are referring to 22m2 cables.
It's different for 70mm2 cables - the losses are less.
 
Partimewages said:
I love how people come here ask what people think and then argue how their wrong.
Why do they come to begin with!
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Should I just blindly accept what somebody says, when I think it's incorrect? Where would the forum be if we all just blindly agreed with the first answer anybody gave about anything?

I see no figures coming back from Timselectric or sunshine_eggo to back up their reasoning. Just fearmongering statements like "If in parallel, the unit seeing the higher battery voltage will carry more of the load."

How MUCH more of the load? That is what matters. What if it's 0.01% of the load? What if it's 0.1% of the load, and it doesn't make any difference to the inverter if that happens, and never will?
 
SenileOldGit said:
I love it: "Your question as stated has been answered." Which apparently means the answer is correct, and helpful. It isn't helpful, it doesn't give me any figures to go on. The drop in voltage is going to be tiny - do you disagree, sunshine_eggo? Do you think a 0.01V drop is going to cause a problem? Or a 0.02V drop?

If so, why? If not, why are you pretending that there IS a problem, without actually stating any figures for your reasoning? I'm using figures for my reasoning, that there won't be a problem. Which is why Voltacon set them up that way, because they haven't had any problems. (They aren't a manufacturer, they are a UK inverter reseller, and therefore they probably don't want people setting up their inverters incorrectly and then making warranty claims, so I presume they can't have had any problems.)
Click to expand...

Mostly because you just made up numbers. In the real world voltages are going to drop based on the resistance of the entire path, and if your cables are not close in length the difference will cause uneven charging/discharging. Yes it's generally low, but 0.1v is significant when it comes to charging/discharging batteries, and there are other factors that cause variations in the overall resistance of the cable, thus the best plan is to make them as identical as possible so discrepancies do not compound into wider variations in the actual connections, that needlessly reduce performance. But your stuff is your stuff, treat it as you will, in the grand scheme the likely hood of an issue is low.
 
You asked a very generic question and got a generic answer. 6 posts later You argue that it doesn't matter. If you already know the answer why ask the question.
If you want the exact answer then ask an exact question. This is al pretty simple math.
Please refer to your systems manual as It will give you the answer and if it doesn't then you bought the wrong system and you should consult a professional!
 
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