Calculation of the conductor cross-section - direct current DC, 12V

Question

Hi Please advise what cable to use for the following, thanks From a 12V 95Ah battery to a 1000W inverter at a distance of 2.8 - 3m

teskot · Answer

Apart from the fact that this battery is too weak for this inverter:

1000W/12V=~84A
The efficiency of the inverter is about 90%, it gives a current of nearly 100A.
3m inverter-battery distance equals 6m of cable. At 25mm² the voltage drop will be: U=100x0.018*6/25=0.432V. Power P=100x0.432=43.2W will be dissipated on such a wire.
I would use at least 25mm² or even better 35mm².

burczynski82 · Answer

Thank you. That's how I came out uncertainly from the calculations of 25mm2 The manufacturer of the inverter advises using a 100Ah battery. I'm 95 at the moment so I thought it would be ok Inverter it

teskot · Answer

The manufacturer of the inverter presumably recommends a battery "not less than 100Ah". Such a good quality battery will have a total capacity of no more than 50Ah at maximum load, ie at maximum load it will last less than half an hour, and its lifetime will be severely affected, especially if it is not recharged immediately after a deep discharge. A reasonable battery capacity with such a load is 500Ah.

Oh, I assumed that we were talking about a lead battery, and this is a lithium one. Yes, lithium can be charged more in the long term.

burczynski82 · Answer

The battery in the picture

teskot · Answer

We return to the starting point Li-Ion is not Lion Your battery is a regular lead only with the electrolyte trapped in a glass mat.

burczynski82 · Answer

I understand that if I add another one with the same or similar parameters, it will be a bit better

teskot · Answer

Sure, but it's good to combine batteries with the same parameters and condition to avoid problems related to the different internal resistance of the cells. As for the discharge current and the capacity dependent on it, I recommend that you read the first catalog note of the "deep discharge" battery. Example:
https://www.bto.pl/produkt/81850/zelowy-accumulator-12v110ah-dyno
In short, it can be said that for starter and buffer batteries, the capacity is usually given for a twenty-hour discharge current, for traction and other "deep cycle" batteries for a five-hour current.

burczynski82 · Answer

I will buy exactly the same, the current one is almost new.Now I'm confused - should I still leave the 25mm2 wires?

teskot · Answer

Yes, cables connecting the batteries as short as possible or individual cables from each battery to the inverter.

modziul · Answer

A more precise calculator with the ability to calculate short sections.

burczynski82 · Answer

Thank you for your help I just got an email from the manufacturer and he advises to use exactly 25mm²

Anonymous · Answer

For every 8 amperes, we give a minimum of 1 mm^2 cross-section.

teskot · Answer

I will not agree. While 8A for 1mm² may be acceptable in some circumstances for 230VAC installations, it means nothing. Following this lead, 10mm² would allow for a continuous load of 80A, and this has nothing to do with the permissible values. What counts above all is the allowable voltage drop on the cable, regardless of the power dissipated on it. 0.5V at 230V is nothing but at 12V it becomes significant.

Let's assume that we drop 0.5V on a given section of the cable, a 12V installation powered by batteries. The battery has 11.5V, 11V on the inverter and there is already a cut-off, so we do not have the full capacity of the battery available.

Graceee · Answer

>>20558185 Sure, but it is best to combine the battery pack with the same parameters and conditions to avoid problems due to the internal resistance inside the battery. As for the discharge current and depending on its capacity, I suggest you read the first directory description for deep discharge batteries.

Calculation of the conductor cross-section - direct current DC, 12V

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