inverter voltages

If you use a wire too thin, it gets hot if the current is too high.
That heat is a HUGE loss of POWER, maybe as much, or more that the load to and being delivered by the inverter itself.
And you risk a fire.
Thin wire = very short distance = lowest cost for manufacturer of inverter.
Your original plan was best.

Cheers,
Peter
OKA196 Motorhome

Hi kcandco,

A simple rule to remember is "use large diameter wires all the time".

Large diameter wires have less resistence to current flow and less voltage drop for a given length compared to a smaller sized wire.

Some people measure wires in "gauge". The only way to measure wire size is stating the Cross Sectional Area of the conductor eg
4mm² or 6mm² (pronounced 4 millimetre square or 6 millimetre square).

Not quite sure of your maths. When looking at wiring in motor vehicles/trailers the current drawn by the appliance is the main consideration when sizing your cable, not voltage.

A lot of appliances have electronics in them these days so i suggest some of them wouldn't work at 11v.

"But with the inverter being able to ....". Using thinner wire would only add to your problems, voltage drop, loss of efficiency. more current drawn, heat build up and fire.

SB

Hi kcandco.

To try and clear up the confusion:
(Using the formula volts X amps = watts)
1) A 300 watt inverter supplies 240 volts up to a maximum of 1.25 amps.
2) The same inverter needs to draw 21.7 amps at 13.8 volts to provide 300 watts (actually a bit more to allow for losses)
3) So the wiring from the battery needs to be able to carry 21.7 volts effectively so in practice 25 to 30 amp cable would be used.
4) The inverter cutting out if voltage of the supply battery drops below 11 volts is just a safety feature and this figure shouldnt be used in deciding wire size.
5) You said " if this is so we would only need to provide sufficient thickness wiring from the 12 v source so as to ensure delivery of 11v at this inverter with a 30 amp load applied" Although a 12 volt system most inverters etc work on a nominal voltage of 13.8 Volts. Now a direct 30 amp load at 13.8 volts = 414 watts which would trip the overload on your inverter. I know you may mean the load is on an auxillary battery which would be irrelevant to the maths pertaining to the inverter.
6) Finally on your point about being able to function at 11 volts, being able to function and running at the correct voltage is quite different. Once again 11 volt cut out is the llowest limit that equipment is deemed to be able to run at. Actually the lower the voltage applied the greater the current draw to achieve your 300 watts EG 300 W divided by 12 v =25 amps as compared to 300 div by 11 = 27.3 amps.

Hope this helps

Based on the above and most manufacturers allow 1.5M of cable before increasing size the inverter should have as follows.
12V at 28A at 1.5M will give 0.259V drop with 10GGE cable.
If you went to a 12GGE your value would be over 0.4V and above your own 0.3 that you indicate you like.

What a lot of people do not understand or are told that with switchmode or high frequency Inverters the surcharge factor is normally miniscule in time and the manufacturer knows that and they size the cable to suit knowing the unit will shut down before melting the cable.

They are refered to High Frequency units.

The Low frequency units that are heavy and use a transformer can sustain high surges such as 100% for 5 Seconds 75% for 15 Minutes,50% for 30Minutes 25% for 45 Minutes and the cable has to be capable of maintaining those load values.
Ian

Thanks everyone for your excellent answers. I knew there was something amiss but couldn't put my finger on it.

regards Kc