Battery cable length - from Lynx distributor

[SenileOldGit]

My electrician is installing my Voltacon 5kW inverters in a new shed I built for them - does it matter that the 70mm cables shown are different lengths? Or are they so thick that the resistance difference won't affect the voltage that each inverter sees from the three Pylontech US5000 batteries I have? (Which will be fitted to the Lynx Power In on the right, next week.)

EDIT: Six months later, everything is working fine, I have had ZERO problems with this installation. (To save people reading all the way through to the last page.)

 

[FilterGuy]

I don't think it matters. If it does matter, the difference will be so small it will be negligable.

 

[timselectric]

It does matter.
How much it matters, depends on how much load you have running.

 

[FilterGuy]

It does matter.
How much it matters, depends on how much load you have running.

Please explain why.

 

[timselectric]

Please explain why.

Voltage drop is affected by size of conductor, length of conductor, and amperage flowing through the conductor.
When the two inverters are connected together (acting as one system).
If in parallel, the unit seeing the higher battery voltage will carry more of the load.
If in series (split-phase), when the voltage difference is enough. The units will error and shutdown.

 

[SenileOldGit]

How much of a voltage drop will there be through a 70mm cable, that short distance? What will the difference between the two sets of cables be? I imagine it will be miniscule.

 

[SenileOldGit]

It does matter.
How much it matters, depends on how much load you have running.

Saying "It does matter" and then "How much, it depends" is ludicrous. It might matter a tiny, tiny amount, so little that it doesn't affect the inverters at all... And I even gave you a clear photo of the length difference of the cables, and the (massive, 70mm) size of them...

Do you think my inverters will be able to detect 0.00027245V difference on the rare occasions (probably never) that I'm taking 10kW from my three batteries? (I set my inverters to charge at a max of 80A, so even on a sunny day, the voltage drop will be even lower than what's shown in the screenshot below.)



EDIT - THE ABOVE SCREENSHOT IS INCORRECT, see screenshot in my post below.

 

[timselectric]

How much of a voltage drop will there be through a 70mm cable, that short distance? What will the difference between the two sets of cables be? I imagine it will be miniscule.

According to the picture. The longer conductors appear to be twice the length of the shorter ones.
So , quite a bit of voltage drop at full load.

 

[time2roll]

I would perform an actual test once all is running. Only replace the connectors if needed.
My bet is that it will not matter.

 

[Q-Dog]

My electrician is installing my Voltacon 5kW inverters in a new shed I built for them - does it matter that the 70mm cables shown are different lengths? Or are they so thick that the resistance difference won't affect the voltage that each inverter sees from the three Pylontech US5000 batteries I have? (Which will be fitted to the Lynx Power In on the right, next week.)

View attachment 188897

You should ask the manufacturer.

 

[SenileOldGit]

According to the picture. The longer conductors appear to be twice the length of the shorter ones.
So , quite a bit of voltage drop at full load.

What does "quite a bit" mean? It's there in my screenshot - one foot of cable has a voltage drop of 0.00027245V... The fact that the longer cables are twice the length of the already short shorter ones is not as important as how much longer they are, which is about a foot. So can any inverter notice a voltage difference of 0.00027245V between battery cables?

 

[jonas]

Saying "It does matter" and then "How much, it depends" is ludicrous. It might matter a tiny, tiny amount, so little that it doesn't affect the inverters at all... And I even gave you a clear photo of the length difference of the cables, and the (massive, 70mm) size of them...

Do you think my inverters will be able to detect 0.00027245V difference on the rare occasions (probably never) that I'm taking 10kW from my three batteries? (I set my inverters to charge at a max of 80A, so even on a sunny day, the voltage drop will be even lower than what's shown in the screenshot below.)

View attachment 188939

I’m sure the cable diameter size is not 70mm, that is 2.75 inches.

 

[FilterGuy]

If in series (split-phase), when the voltage difference is enough. The units will error and shutdown.

If the cables are properly sized, I would think that would be very unlikely. For the OPs set-up the difference due to the wire lengths will probably be millivolts. In fact, I would not be surprised if the variances in fuses, lugs, connectors, etc would be greater than the resistance difference of a couple feet of 70mm cable.

If in parallel, the unit seeing the higher battery voltage will carry more of the load.

Will it? There is a lot of dynamic circuitry between the battery cable and the AC lines. Each inverter will draw whatever current it needs to supply the load it sees. If one inverter is seeing a slightly lower voltage, it will draw slightly more current to compensate.

Everyone is different, but if I were the OP, I would not worry about it.

 

[FilterGuy]

I’m sure the cable diameter size is not 70mm, that is 2.75 inches.

It is 70mm^2 (70 square mm) but since it is not easy to show the superscript 2, many people abbreviate it to 70mm. A 70mm^2 cable is roughly equivalent to a 2/0AWG cable.

 

[SenileOldGit]

I’m sure the cable diameter size is not 70mm, that is 2.75 inches.

Sorry - my mistake.



The voltage drop is 0.0118339V - I don't think the inverters are going to notice that either.

 

[sunshine_eggo]

How much of a voltage drop will there be through a 70mm cable, that short distance? What will the difference between the two sets of cables be? I imagine it will be miniscule.

Given that the cables appear twice as long, twice as much as the other.

Saying "It does matter" and then "How much, it depends" is ludicrous. It might matter a tiny, tiny amount, so little that it doesn't affect the inverters at all... And I even gave you a clear photo of the length difference of the cables, and the (massive, 70mm) size of them...

Do you think my inverters will be able to detect 0.00027245V difference on the rare occasions (probably never) that I'm taking 10kW from my three batteries? (I set my inverters to charge at a max of 80A, so even on a sunny day, the voltage drop will be even lower than what's shown in the screenshot below.)

View attachment 188939

FIRST you argue with a career electrician...

THEN you demonstrate you have no clue how to use a tool and post a result nearly two orders of magnitude wrong.

 

[sunshine_eggo]

Sorry - my mistake.

The voltage drop is 0.0118339V - I don't think the inverters are going to notice that either.

Voltage drop is affected by size of conductor, length of conductor, and amperage flowing through the conductor.
When the two inverters are connected together (acting as one system).
If in parallel, the unit seeing the higher battery voltage will carry more of the load.
If in series (split-phase), when the voltage difference is enough. The units will error and shutdown.

This.

@SenileOldGit you need to get an electrician that knows what they're doing.

 

[SenileOldGit]

Appeal to authority fallacy.

I do have a clue 'how to use a tool', I just made a simple error because I always refer to the cable as '70mm' rather than '70mm squared', no big deal.

So are you saying there will be a problem with this setup? If so, why? Based on that hundredth of a volt difference? How much more of the load will the inverter seeing the higher voltage carry? We are dealing with a hundredth of a volt difference at voltages around 48V.

 

[FilterGuy]

Sorry - my mistake.

View attachment 188947

The voltage drop is 0.0118339V - I don't think the inverters are going to notice that either.

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.

 

[sunshine_eggo]

Appeal to authority fallacy.

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.

I do have a clue 'how to use a tool', I just made a simple error because I always refer to the cable as '70mm' rather than '70mm squared', no big deal.

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.

So are you saying there will be a problem with this setup? If so, why? Based on that hundredth of a volt difference?

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 electrician using oversized and/or unequal length for the AC side, fire them on the spot. Same reason but notably more significant.

 

[sunshine_eggo]

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.

I generally don't argue with you, but I definitely disagree this time. Sig link #6, 4.9.

 

[Kiwi2000]

A good installer would have put the wiring inside a cable tray so you couldn't see the unequal length.

 

[FilterGuy]

I generally don't argue with you, but I definitely disagree this time.

What do you disagree with? Do you think the voltage drop would be larger?

 

[timselectric]

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.

 

[SenileOldGit]

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.

LOL. "

It's an inherent system imbalance meaning the inverter connected via shorter wires will carry more of the load."

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.