Inverter draw

[19D20]

I know there are many variables in the use of inverters, but Is there a "ballpark" formula for determining how long say a 1000 watt inverter draw will last using a running 100 amp alternator with a Optima "blue top" #34M, 1000 cca, without running out of power or doing damage to the charging system of the vehicle?


Joe R.
Kelso, WA

[19D20]

Thanks again for the suggestions/information. I'll keep you posted on the outcome.




Joe R.

[wolfe10]

Run it on propane.

And, as others have said if you decide to run it on 120 VAC, it is not the inverter's rating (that is MAXIMUM it can put out), but the actual load that is important. And there will be a sizable loss in voltage in the very long run from tow vehicle battery to the trailer battery, even with large-gauge wire.

Again, propane is the way to go when not on shore power.

[time2roll]

Fridge is closer to 360 watts with 2/3 duty cycle.
You may have a 100 amp alternator but you will be lucky to get 10 amps back to the trailer.

so 36 amps out of the battery x 2/3 = 24 amp hours out minus 10 amps in for about 15 amp/hours out each hour. Battery is maybe 30 amp/hours usable so I give it about two hours.... maybe three but your battery will be low upon arrival. You will need to plug in or run the generator immediately on arrival.

Some just turn the thing off and let it coast for the drive.

Most run propane. I run with propane on even when refueling. No fear, no worries.
Your choice but I think you may find you need more battery.

[pianotuna]

Hi Joe,

The fridge runs about 300 watts on 120 volts. That means a draw of 30 amps via an inverter. A 400 watt inverter will "do the deed". Duty cycle on the fridge may be 2:3 (40 minutes on, 20 minutes off).

The charging path from the tow vehicle would need to be beefed up considerably. If you proceed, think about #4 wire and Anderson connectors.

Another possible route is to have the inverter some where cool and dry inside the truck and run a 120 volt circuit back to the trailer. Even standard #16 light cord would work.

19D20 wrote:
I was thinking of running my fridge on 110v while traveling. The 12v don't get it done and I'm concerned that the propane, while working great, might be an issue during refueling.

My rig is a 1999 Tacoma 4x4 extended cab 3.4 Liter V6/auto 140 amp alt, Optima blue top battery towing a 2013 Travel-Lite Idea 18 GVWR 3500 lb. 3 cubic ft 3 way fridge.

Joe R.
Kelso, WA

[19D20]

Thanks for the numerous responses! It is refreshing to be able to ask a dumb question and not get the yelling at like other forums I've been on. The reason for the question is that I was thinking of running my fridge on 110v while traveling. The 12v don't get it done and I'm concerned that the propane, while working great, might be an issue during refueling.

My rig is a 1999 Tacoma 4x4 extended cab 3.4 Liter V6/auto 140 amp alt, Optima blue top battery towing a 2013 Travel-Lite Idea 18 GVWR 3500 lb. 3 cubic ft 3 way fridge. It's my first R/V and we've only been out in it 3 times, so I am a newbie. I've been reading up on the reference books out there and there's a ton of things my feeble mind has got to learn!

The next trip is the last week of Feb at the Winchester Bay RV resort at the mouth of the Umpqua River on the Southern Oregon coast.
It should be warm, but wet!

Joe R.
Kelso, WA

[pianotuna]

Hi,

Alternators are often a 1/3 duty. So if the load is 100 amps a 130 amp alternator is NOT going to be happy.

I do use my water heater powered from the battery bank/inverter/alternator while going down the road--but I find that after 7 or 8 minutes voltage starts to drop on the chassis battery. At that point I turn OFF the water heater and wait 20 minutes before I turn the water heater back on.

I can support a 40 amp load on a continuous basis. That translates to about 400 watts out of the inverter. Given a 100 amp alternator and an Optima battery you might do 30 amps or 300 watts.

[RoyB]

The only test I did with running a 1500WATT PSW INVERTER from a rental car powering up some high dollar TET EQUIPMENT working on testing a DOD Antenna system.

Powered up all of the test equipment which was around 1400WATTS total draw.

Lasted about 11 minutes before loosing standard car battery and alternator from rental car.

Rental car had to be hauled away. We claimed to Hertz it just quit working...

RULE NUMBER ONE for me camping is to NEVER EVER use anything associated with the start battery or motor system of the truck electrical setup. This is the only way to get home.

I would Beef up the converter system on the RV to include HD wiring and additional batteries for the required 12VDC load. Then I will run down my battery setup to around 12.0VDC which is around 50% charge state and then quit using high current loading. Then I will connect the trailer shore power cable to my 2KW Generator when allowed to run it at the camp ground using an RV30A-15A Adapter. This will allow my on-board smart mode converter to re-charge my updated battery bank to its 90% charge state in around three hours run time.

This is what we have been doing since 2009 when camping off the power grid with our 255AH capacity Battery Bank. This supports the normal 1-2AMPS parasitic drain 24/7 and using around 20-22AMPS DC current between 6PM to 11PM running the home entertainment and Ham Radio items each evening from our battery bank. We have to re-charge our battery everyday doing this. This is almost the same routine when camping at electric sites for us with the exception of NO Air Conditioning or high wattage Microwave being used when camping off the power grid.

Roy Ken

[MrWizard]

until the alternator overheats
your looking at over 80amps
the avg 100amp automotive alternator will not deliver 80% on a continuous basis

IF you specify the alternator mfg and model and the ambient conditions

somebody with more experience .. might be able to give you duty cycle info

[BFL13]

I was able to run a 600w 35a battery charger from a 1000w inverter connected to the truck's battery with the engine at idle. The limit on how much wattage (VA actually) the inverter will handle is when the truck's own voltage starts to slide from about 14v and drops away to the left on its gauge. It helps to turn off the climate control!

The inverter was on short #1 gauge wires but has to sit out on the fender clear of the engine heat or it would quit from the heat. This with the hood up. I ran it for over an hour at idle with no issues.

Revving the engine made no difference from idle. Nor did turning on the headlights (a story was that leaving the headlights on would make the truck think it had to keep the voltage up more, but that might have been from the old days, don't know)

You have to experiment to find your actual limit, keeping an eye on the truck's dash voltage meter to see when it starts to fall away.

[2oldman]

You'd probably run out of gas first.

[time2roll]

With a 1000 watt draw it will not last long.
What is the actual load on the inverter?