Author Topic: The basics of inverter overloading  (Read 4216 times)

The basics of inverter overloading
« on: March 30, 2010, 11:44 PM »
Sent: 4/8/2003

You must use Breaker Board to distribute the AC power from the
Inverter, even low amp AC can cause fires.

So you must run power line from Inverter to CB board in back, or move CB
board to inside near your inverter.

Especially if you are going to be powering a Microwave oven or TV off the
Inverter, your talking a Large amount of current that has in the past been
more than responsible for many many house fires.

When Dealing with AC in an RV use every precaution you would use in your
own home.

UL Listed Wiring and Breakers.

Splitting AC before a breaker box is asking for a fire.

Sully

Offline Collyn down-under

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  • Posts: 23
  • I own: I don't own one but I'm a vintage RV enthusiast!
Re: The basics of inverter overloading
« Reply #1 on: March 30, 2010, 11:45 PM »
Sent: 4/9/2003

Re microwave ovens - be aware that the rating indicates only the heat generated ('cooking watts') not the energy consumed. A typical 800 watt microwave is 60% efficient and thus draws about 1350 watts. If run via an inverter this equates to 1550 - 1700 watts. Or about 130 - 140 amps at 12 volts. In other words these things draw about twice what many people believe.
Collyn down-under 
Visit Caravan & Motor Home Books books that comprehensively cover all technical aspects of RV usage including electrical, solar and on-road stability - author is ex (UK) General Motors Research Dept - who changed careers in midlife to become a writer and successful publisher. Collyn's books are accepted globally as technically correct - yet are written in down to earth English (albeit not always in US spelling!).

He is also Technical Editor of the Caravan Council of Australia. His website https://caravanandmotorhomebooks.com/ has many technical articles on all aspects of RVs and their usage.

Re: The basics of inverter overloading
« Reply #2 on: March 30, 2010, 11:47 PM »
Sent: 4/9/2003

He's right.

130amps is close to 1/3rd the rating of a standard auto battery just to let
you know...

Deep-cycle Golf-cart batts wired in serial are a little better...

Have I stressed how important it is to send this amount of power through a
breaker board?

Sully

Offline MSN Member

  • Posts: 297
Re: The basics of inverter overloading
« Reply #3 on: March 30, 2010, 11:50 PM »
Sent: 4/9/2003

No, I didn't know that! I was relying on the usage charts that list a microwave at it's listed watts. The 1750 w inverter I bought shows it can run the micro, the tv, the carriage lights, water pump and various smaller uses all at the same time..but if the micro usage is actually double it's listed wattage, it certainly can;t do that, can it? Wouldn't that be false advertising? They also show 1,000w inverters doing much the same thing, and i bought the larger unit to have spare wattage in case I needed it someday..
Since 600w is about as small as micros come, doubling it would mean that 1,000w inverter CAN'T run it... is that right? I'll try to find info about it here, but I would appreciate it if you could give me a bit more info on this...

Thanks!

Offline MSN Member

  • Posts: 297
Re: The basics of inverter overloading
« Reply #4 on: March 30, 2010, 11:51 PM »
Sent: 4/9/2003

Phred says: Continuous running wattage of all loads to be run at one time. List all items you'll run at one time. Add up Watts. (From labels as W or VA, or as measured with an ammeter, or calculated as Watts = Volts x Amps, so 120VAC x 5A = 600 Watts.) Examples: Computer 160W, Monitor 40W, Printer 110W could operate from a 300W inverter. But, if total is near the max rating of the inverter, look closely at inverter manufacturer's data sheet. Some will state, "200W for 25 minutes, 140W continuous" or similar. (Not bad if drilling a hole. Terrible if running a computer.) With microwaves, don't mistake cooking power for actual running power. Read the label. A 500W cooking-capacity microwave might use over 1,000 watts actual power.
.............
phred's stuff is my Bible, so obviously you're correct. Good thing I got the larger Inverter!

Offline Collyn down-under

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  • Posts: 23
  • I own: I don't own one but I'm a vintage RV enthusiast!
Re: The basics of inverter overloading
« Reply #5 on: March 30, 2010, 11:52 PM »
Sent: 4/9/2003

It's not generally always understood that a 'watt' is a unit of work done as well as a unit of energy consumed.

This can be confuse people. A motor, for example, may be capable of generating 1 horse power and 1 HP equals 746 watts everywhere except the USA (and France!) where it's 735.5 watts.

(The difference is something to with the French helping you guys throw the British out, way back. They called it 'force de cheval' and Americans adopted it!)].

But whilst a motor is rated at 1 HP (or about 750 watts) what that means is that's the amount of work it can do. It does not imply that it draws about 750 watts. It's draw depends on the work its doing and it efficiency. In practice a 1 HP power (750 watt) motor is like to draw 1200-1500 watts.

Microwave ovens are rated the same way. The '800 watt' is the heat they produce (and that can also measured and expressed in 'watts'. The energy they
actually use however is about 40% more. So thats about 1330 watts.

As good sine-wave inverters are anything from 85-94% efficient the oven will draw 1550 watts upward.

Ok. Now your inverter.

Inverters are a bit like camels. They will carry their comfortable load for ever. A heavier load a short distance. A very heavy load maybe for a few seconds.
They are designed to work like this and if overloaded beyond their capacity they just lie down and have a rest.

If you don't know this about inverters (or camels) you may buy one that's bigger than you need.

The guy who sold you yours clearly understands the above. A 1750 watt inverter should be able to put out at least 3000 watts for a few seconds, about 2250 for ten minutes, and maybe 2000 for half an hour. This will cope admirably.

While on this subject may I strongly advise readers to buy full sine-wave inverters. Increasingly, electronic equipment demands proper sine-wave power (just like out of your sockets at home). A modified sine wave inverter may run your gear - a full sine wave inverter will.

Trust this helps
Collyn down-under 
Visit Caravan & Motor Home Books books that comprehensively cover all technical aspects of RV usage including electrical, solar and on-road stability - author is ex (UK) General Motors Research Dept - who changed careers in midlife to become a writer and successful publisher. Collyn's books are accepted globally as technically correct - yet are written in down to earth English (albeit not always in US spelling!).

He is also Technical Editor of the Caravan Council of Australia. His website https://caravanandmotorhomebooks.com/ has many technical articles on all aspects of RVs and their usage.

 

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