Inverter, how big do I really need? Solar??

[nothermark]

Originally Posted by OldJohnT

Had I arrived earlier I would have recommended at least a 1000 Watt PSW Inverter,,,,,,,,,,,,, At least 100 Watts of Solar (preferably two in series for 200 Watts) no way Id mess with a wimpy measely 50 watts, that will barely charge a rubber chicken lol,,,,,,,,,,,,, a "Smart" 3/4 Stage MPPT Solar Charge Controller,,,,,,,,,,,,,, At least two 6 volt true deep cycle golf cart batteries in series.


Now lets do the math. A 1000 Watt Inverter operating at 12.6 volts would draw 1000/12.6 = 80 full load amps. Therefore, I would size the conductors from batteries to Inverter to have a minimum ampacity of 100 amps and Id locate it as close as possible to the Inverter to reduce line voltage drop but NOT (its a potential spark producing electrical device) in the same compartment as the battery where explosive gasses may be present during a high charge. I would use an overcurrent protection device to protect the wires located right at the energy source, the batteries and if it were rated at 80 amps it will limit the Inverter to drawing near its capacity plus adequately protect the wire. NOTE if the Inverter company recommends larger then 100 amp rated wire, fine bigger is better and reduces voltage drop. I still wouldn't use les then 100 amp rated wire however. NOTE the battery box needs adequate ventilation to vent the explosive gasses to the outside plus prevent overheating.



John T Retired Electrical Engineer

You forgot to adjust for efficiency. It will be more than 80 amps. ;-)

OTOH he may never need the 1000 watts. ;-))

[OldJohnT]

Had I arrived earlier I would have recommended AT LEAST a 1000 Watt PSW Inverter,,,,,,,,,,AT LEAST 100 watts of solar, preferably 200 wired in series for 24 volt operation, no way Id use a wimpy 50 watts, that's not enough to charge up a rubber chicken lol,,,,,,,,,,,,,, A "Smart" 3/4 Stage MPPT Solar Charge Controller,,,,,,,,,,,,,,,, AT LEAST two 6 Volt true Deep Cycle Golf Cart Batteries in series which yields around 200+ Amp Hours of stored energy,,,,,,,,,,,,,,I assume you already have a "Smart" 3/4 Stage Charger????????????

Now to the Inverter, here's how I was NEC trained to approach it:

A) Compute the load. A 1000 Watt Inverter operating at lets use 12.6 volts would draw around 80 full load amps.
B) SIZE THE WIRE I would size the wire to have an ampacity of at least 125% of the max continuous current, meaning Id use at least 100 amp rated wire from batteries to Inverter, BUT IF THE VENDOR SAYS USE BIGGER WIRE THEN USE IT BY ALL MEANS bigger wire = less voltage drop.
C) Size the overcurrent protection device to protect the wiring meaning it would be 100 amp rated

HOWEVER that assumes the Inverter has its own built in thermal protection such that if it draws much over 80 amps very long it will open to protect the Inverter. If such were not the case I may consider use of an 80 amp breaker AT THE ENERGY SOURCE BATTERIES, NOT DOWNSTREAM.

NOTE Id place the Inverter as close as possible to the batteries to reduce voltage drop in the cable HOWEVER NOT in the same compartment as the batteries where explosive gasses may be present especially during high charge rates. The battery box needs adequate ventilation to exhaust the explosive gasses to the outside plus provide some cooling

John T Retired AC Distribution Electrical Engineer

[OldJohnT]

nothermark, you asked

You forgot to adjust for efficiency. It will be more than 80 amps. ;-)

I used the 1000 watts as max INPUT energy and since no device is 100% efficient due to heat losses, the output would be a tad less then 1000 watts. If the device can produce 1000 watts OUTPUT, then it would take MORE then 80 amps on its input I AGREE WITH YOU. I see so many devices with hyped up advertised ratings, I'm used to figuring on the conservative side to be safe, just how I'm wired lol

Thanks for the input, no pun intended lol I used 1000 watts INPUT instead of 1000 watts OUTPUT.

John T