Battery cable size to feed new inverter

[stuhaynes]

I'm about to connect our new 24v x 1500watt soft start inverter, peak output 3500watt. The largest ac current is likely to be 1 KW. To avoid cable overheating problems can anyone recommend the best battery to inverter cable size? Cable length less than 2 metres.
Thanks. Stu

 

[VicS]

The consideration for a short cable run like this is the maximum safe current carrying capacity rather than volts drop which is of concern over longer runs

According to my information
for 1500 watts at 24 volts 9 AWG would suffice provided the cables are not enclosed or bundled with others but otherwise may need to be up to 4 AWG

For 3500 watts 3 AWG would be the minimum rising to 0 AWG if the cables are not freely ventilated.

I would however recommend that you follow the advice of the inverter manufacturer.

 

[ianj99]

I'm about to connect our new 24v x 1500watt soft start inverter, peak output 3500watt. The largest ac current is likely to be 1 KW. To avoid cable overheating problems can anyone recommend the best battery to inverter cable size? Cable length less than 2 metres.
Thanks. Stu

In the UK, 16mm sq should be fine for short runs. Otherwise voltage drop rather than just current carrying capacity becomes a consideration.

 

[stuhaynes]

In the UK, 16mm sq should be fine for short runs. Otherwise voltage drop rather than just current carrying capacity becomes a consideration.

Thanks for that. What does 16mm square actually equate to and does my local auto elec supplies know exactly what I need. Are we looking at something like an individual cable diameter of about 1/4 inch. Sorry to be thick but I am (carefully thick!). 2metres length should be enough

Thanks again. Stu

 

[VicS]

16mm sq, or 16mm², means cable with a cross-sectional area of 16 square mm

The diameter of the conductor will be approx 4.5mm

The nearest AWG size is 5

Of the sizes I mentioned earlier

9 AWG is 6.63mm²

4 AWG is 21.14 mm²

3 AWG is 26.65mm²

0 AWG is 53.46 mm²

 

[pvb]

16 sq mm is nowhere near heavy enough! You need to size the cables for the potential peak load on the inverter, and to minimise voltage drop. For 3500 watts, 16 sq mm cable would give around a 0.75V drop - far too much, and potentially enough to cause the inverter to go into "low voltage shutdown". The correct choice of cable would be at least 60 sq mm (say 2/0 AWG), which will have an outside diameter of roughly 16mm.

 

[VicS]

The correct choice of cable would be at least 60 sq mm (say 2/0 AWG),

I'd have thought 2/0 necessarily heavy but agree that 16mm is too light

I suggested AWG 3 provided it it is not enclosed. That has a resistance of approx 0.63 ohms per 1000m which will give a volts drop of less than 0.4 at peak power. Will that really be too much for a 24 volt inverter.

 

[pvb]

In the overall scheme of things, Vic, the cost of the heavier cable is a very small consideration. Every inverter manual I've seen encourages the use of heavy-gauge cables.

 

[VicS]

In the overall scheme of things, Vic, the cost of the heavier cable is a very small consideration. Every inverter manual I've seen encourages the use of heavy-gauge cables.

Fair enough. I did say earlier that the recommendations of the inverter manufacturer should be followed. What is it they say ...RTFM!

 

[ianj99]

16 sq mm is nowhere near heavy enough! You need to size the cables for the potential peak load on the inverter, and to minimise voltage drop. For 3500 watts, 16 sq mm cable would give around a 0.75V drop - far too much, and potentially enough to cause the inverter to go into "low voltage shutdown". The correct choice of cable would be at least 60 sq mm (say 2/0 AWG), which will have an outside diameter of roughly 16mm.

He did say that the expected max load is 1Kw hence why I suggested 16mm cable. 16mm is okay upto about 2Kw.

If there is ever likley to be a need for more than this, then fine, up spec the cable.

There is no reason to match the cable to the maximum possible inverter output otherwise.

 

[pvb]

He did say that the expected max load is 1Kw hence why I suggested 16mm cable. 16mm is okay upto about 2Kw.

If there is ever likley to be a need for more than this, then fine, up spec the cable.

There is no reason to match the cable to the maximum possible inverter output otherwise.

I've always thought that it's best to install equipment properly - after all, the subsequent owner of the boat may have problems if installation is below par. You wouldn't install a winch with small-diameter bolts just because you only intended sailing in light airs!

 

[ianj99]

I've always thought that it's best to install equipment properly - after all, the subsequent owner of the boat may have problems if installation is below par. You wouldn't install a winch with small-diameter bolts just because you only intended sailing in light airs!

That's a fair point, but to prevent the next owner overloading the cable, you would put the appropriate fuse in circuit close to the battery. (75amps)

For 3.5kw, allowing for 90% inverter efficiency and 22volts terminal voltage equals about 180amps so you'd need a substantial battery bank to supply it as well!

I use self tappers to hold all my winches and windlasses on as well the engine mounts and keep my wallet closed...

 

[pvb]

I use self tappers to hold all my winches and windlasses on as well the engine mounts and keep my wallet closed...