ARE INVERTERS SAFE? 12V to 120V

[Vanagon-tom]

HI,
I see many inverters for sale for continues use, 100 watts up to 1200 watts, 12 volts changed to 120 volts, are inverters safe to use? Will an inverter hurt any part of the electrical system?

Thomas

[curtis73]

Inverters are totally safe. What do you want to run?

All of your vehicle's wiring is fused. For instance, the factory determined that your taillights required 4 amps, so they used 14 gauge wire and fused it with a 5 amp fuse. If the lights try to draw more than the wiring can handle, it blows the fuse before it overheats the wire which could cause a fire.

So, running an inverter is safe because your vehicle's wiring is prepared for it. If you have a small inverter, it can run off the cigarette lighter. If you need a bigger one, you can wire it directly to the battery using the supplied wiring. The protection for the circuit is built into the inverter. If the appliance you run from the inverter is too hefty for its output, it shuts down before melting itself causing a bad situation.

The only thing you'll hurt is if you use an inverter that is beyond the capacity of your charging system. Lets say your alternator supplies 60 amps at 12 v. Thats 720 watts. Assume that your vehicle needs 10 amps to keep itself going, that leaves 600 watts available that you could use without draining more than your alternator can supply. Prudence should be exercised, though. You don't want to constantly stress your alternator to its max Although a 600 watt inverter would be fine, don't use it to run 600 watts all the time and you'll be fine.

[Vanagon-tom]

A TV, blender, maybe an extra heater. SO If I start my vehicle, turn on all accessories, like lights, radio, heater, and windshield wipers then dissconnect the battery and run my multimeter in series, that would tell me what amps I have left? How do you determine watts?

From,
Thomas

[curtis73]

Nooo... Don't do that. you'll fry the alternator and maybe the computers in the vehicle. You'll also possibly fry the multimeter if you have more than 20 amps. Never run the vehicle without the battery connected. That worked in 1935 when cars had generators, but not today Plus it will only tell you how many amps you're using. The alternator would only produce what the vehicle demands up to its rated capacity. If you have nothing on including the engine, you'll show 0 amps. If you turn on the lights, it will show 10 amps.

W = V x A, so if you know the amperage or wattage of an appliance you can figure out the other. A 120w light bulb would use 10a at 12v. A 2a appliance uses 24w. Just add up every possible component. The engine takes about 10 amps to run at peak demand. Stop lamps and running lights take about 7w each. Add them all up and determine the amperage you would be using if every single electrical item were on. Lets say that's 65 amps for instance. Since you NEVER have everything on at once, multiply that by 75%, or about 49 amps. Now find out how many amps your alternator is and that's how much surplus you have. Lets say you have a 60 amp alternator. that leaves 11 amps unused, which is 132 watts.

Keep in mind that wattage is pretty constant regardless of voltage. If you have a blender that takes 120 watts, that means it draws 1 amp from a household 120v circuit. But the inverter to operate it will draw 10 amps from the 12v circuit in order to supply 120w to the blender.

I run a 400w inverter in my station wagon. I use an 80amp alternator and two batteries. I could pretty easily get away with much more, but I want it to last through the night when I'm camping in it.

[curtis73]

Let me suggest something. Buy yourself a 12v TV. TVs have converters in them that take the 120v from the wall and convert it back down to 12v. You'd waste so much energy as heat converting it up to 120, then back down to 12v. Just skip it and get a 12v tv. No use taxing a huge inverter for that one.

[MooseNelson]

I use an inverter regularly in my car to power a laptop for gps and run my mp3 player, i bought a 300watt one with two outlets, though 300 watts can only be pulled from the direct connection to the battery.

I've been hoping to setup a decent sound system initially with a large deep cycle marine battery for outdoor funk parties, though I haven't really made the step to buy speakers yet, but essentially you wouldn't want to run it from your cigarette lighter, even a decent size tv or a blender I would run from the batt itself.

the nice thing about the inverter I have is an LED readout of the volts my batt has, nice to see exactly where its charged, last night I was installing a new stereo and had the dome light on the whole time, v's dropped to 10.5 when they are usually after my commute around 14.1, kinda nice to know how much juice I have for the cold morning starts here in boston.

here's a question: Put an oversized marine battery as you starter, it would charge via the alternator, I have seen some cars using marine batts as starters.

[curtis73]

I suggest using a marine starting battery. They are a half-way mix between a regular starting battery and an RV deep cycle.

Or, you could do like I did; I put a deep cycle in the back and a good cranking battery up front. They are connected by an ignition-triggered solenoid and a three way switch. The rear battery can be drained completely and it doesn't touch the cranking battery. I can use the three way switch to connect them never, by the key when the car is on, or all the time. Its nice. I can also jump start myself

[Vanagon-tom]

OK, is there a way to test how many amps my altornator produces or just go off the technical manual?

From,
Thomas

[Vanagon-tom]

Is it ok to add a marine battery with more cranking amps?

Thomas

Originally Posted by curtis73

I suggest using a marine starting battery. They are a half-way mix between a regular starting battery and an RV deep cycle.

Or, you could do like I did; I put a deep cycle in the back and a good cranking battery up front. They are connected by an ignition-triggered solenoid and a three way switch. The rear battery can be drained completely and it doesn't touch the cranking battery. I can use the three way switch to connect them never, by the key when the car is on, or all the time. Its nice. I can also jump start myself

[curtis73]

Its always fine to add a battery that is bigger. The van only draws what it needs, so its kinda like adding a bigger water tank to an RV. It won't add any pressure or hurt the system, its just that there's more reserve.

The tech manual is a good source for your alternator, as are VW forums like here or thesamba.com and vwvortex.com. Sometimes (if you can see it) its stamped right on the case. Mine says 80A

[KiwiBacon]

Originally Posted by Vanagon-tom

OK, is there a way to test how many amps my altornator produces or just go off the technical manual?

From,
Thomas

Yes, buy a DC clamp meter. A very cool piece of test gear that will read the current through any cable, just clip it around.
Mine is accurate down to 0.1 amps, the highest I've had it reading was 512 amps of starting current when I had a starter full of crap.

[Vanagon-tom]

You guys have been a great help, thanks, you mind me asking where you got this knowledge?