using a DC to AC inverter

[perrynick17]

i want to know why this happens. so i used an inverter to power a shop vac from my car. the way i had set it up, was using an extension cord of 25 foot i cut the plug ends off and used 2 of the 3 inner wires for my positive and negative and had that set up between the car battery and the inverter in my trunk. i then flipped the inverter on and started up the shop vac and it ran like <Mod Edit> like it was not getting a good current, so i stopped and re-did the set up so the inverter was set up closer to the car battery and the wire used then was bigger in diameter but shorter in distance. i set the shop vac up from a second extension cord plugged into the inverter. this set up ran like a charm no problems. now this extension cord is obviously capable of running an appliance on 110volts and what ever amount amps and so is the inverter as its rated for 3,000 wats. so why would i have a hard time passing 12volts and X amps to the inverter with that same wire

 

[kanewolf]

i want to know why this happens. so i used an inverter to power a shop vac from my car. the way i had set it up, was using an extension cord of 25 foot i cut the plug ends off and used 2 of the 3 inner wires for my positive and negative and had that set up between the car battery and the inverter in my trunk. i then flipped the inverter on and started up the shop vac and it ran like <Mod Edit> like it was not getting a good current, so i stopped and re-did the set up so the inverter was set up closer to the car battery and the wire used then was bigger in diameter but shorter in distance. i set the shop vac up from a second extension cord plugged into the inverter. this set up ran like a charm no problems. now this extension cord is obviously capable of running an appliance on 110volts and what ever amount amps and so is the inverter as its rated for 3,000 wats. so why would i have a hard time passing 12volts and X amps to the inverter with that same wire

12V DC at 25 ft for 3000W requires VERY large cables.
This page shows -- https://www.altestore.com/howto/recommended-inverter-cables-sizing-and-breakers-or-fuses-a62/
That a 3000W inverter needs 400A and a 4/0 (also 0000 ) cable. You probably had a 14 or 12ga cable.
So you needed 4/0 which according to this chart -- https://diyaudioprojects.com/Technical/American-Wire-Gauge/ is almost 1/2 inch in diameter and you had say 12ga which is 1/10 inch in diameter. Your cable was too small.
You need cable like is used on arc welders to supply your 3000W inverter.

 

[perrynick17]

i think i am starting to understand this a bit more now thank you i have also looked into measuring ohms as well. do these inverters have a way of measuring resistance/ohms to allow so much current to be available

 

[kanewolf]

i think i am starting to understand this a bit more now thank you i have also looked into measuring ohms as well. do these inverters have a way of measuring resistance/ohms to allow so much current to be available

No. You use charts to figure that out. And a digial volt meter -- https://www.amazon.com/Multimeter-Auto-Ranging-Klein-Tools-MM400/dp/B018EXZO8M/ to measure the actual resistance in a wire.
There are website calculators that can help -- https://www.engineeringtoolbox.com/12-volt-wire-loss-chart-d_1689.html