Powering monitor with light battery, what went wrong?

[Josh Bass]

Okay, so I'm trying to power my Sony PV14m2u with a juice box from my Bescor light. I was told to buy a power inverter to make this work. I did so. When I bought it, I asked the guy if it would power a monitor like mine. He plugged it into his computer monitor, and then into my battery, which I'd brought with me, and I watched it work.

Later, outside, I'm trying with my monitor, and it seems like it's going to work, but all I get is a horrible shrill, sustained beeeeeeeeeeeep, and the monitor never comes on. Later, I tried my battery with the light just to make sure it was charged, and it worked fine. What'd I do wrong?

The inverter is called a 140v power inverter. . .

[Jeff Donald]

Sounds like the invertor doesn't put out enough wattage for the Sony monitor. What wattage is the invertor rated at?

[Josh Bass]

It's rated for 140 Watts. . .115VAC. Is that the problem? The back of my monitor says it draws/uses/whatever 120V. Damn it. More useless crap.

[Rob Wilson]

Josh,

The voltage shouldn't be a problem, watt you're interested in is the total wattage drawn by your monitor. If' it's not specifcally listed, just multiply the current (amps) by the voltage (115/120). I'm guessing it could well be over the 140 watts your inverter will supply. If so, you might want to check your local Sams. Just got a 400 watt inverter for 29.99!

[Josh Bass]

It says "1.0 A" on the back. Is that the amperage? In that case, it draws 120 watts, as well. That means my little juice box will be next to useless with it.

[Jeff Donald]

The rating of the inverters for sustained usage is usually 1/2 it's rated power, or 70 watts.

[Josh Bass]

So like I said. . .more useless crap? I need like 350watt inverter. . .and a battery that'll last longer. Do they sell 'em cheap somewhere?

[Mike Rehmus]

Your problem is at 120 watts, you will be pulling some serious power out of the battery. Just divide 120 by 12 and, ignoring the efficiency of the inverter, which may be in the 70% class, you will be pulling 10 amps out of the battery.

A reasonably sized deep-discharge vehicular battery will not be able to sustain its output voltage for very long at those rates. The inverter will shut down when the voltage droops, stopping your viewing pleasure.

I use a automotive battery to run one or two 50 to 75 watt lamps when I shoot certain types of events. I started out also powering my (12 volt) camcorder from the battery as well. Within about 1.5 hours, maybe a bit less, the battery voltage would droop enough that the camera would quit.

I'd guess you will get from 1 to 1.5 hours before the inverter calls it quits. This isn't any formal calculation, just a reasonable guess.

The problem is significant enough that Sony makes a 12 VDC voltage stabilizer for their cameras that will deliver 12 volts when the input voltage drops to somewhere a bit more than 10 volts.

[Josh Bass]

I tried it though, and not no hours and no minutes.

Here's the thing: On the box, it says real bold "140 Watt Power Inverter" Somewhere else on the box it says "maximum 300 watts."

So I'm gonna try to buy another one through Ebay, and I'm not paying another $50 for one. . .so how do I know what it's REALLY rated for, as opposed to the false ratings?

[Mike Rehmus]

It is possible that the startup current of the monitor is higher than the inverter can supply. Hard to tell without 'monitoring' the power feed or finding more info on the monitor.

The inrush of the power as the capacitors charge up and the filaments in the jug heat up 'may' be much more than 300 watts for a brief time . . . more than the inverter can handle and therefore it won't start and the inrush current demands never get satisfied for the monitor. Catch 22. Depends on the internals of the monitor.

I assume the monitor will run when plugged directly into the wall?

Hmmm. After a little bit of a search I find that the specs on the monitor state that it requires 90 watts.

Have you tried the inverter with just a light bulb plugged into it? See if it will power a 100 watt lamp.

[Darrell Sullivan]

I saw a post in this thread where someone is using vehicular batteries with their inverters. While this will work fine, it is better to use a deep cycle marine type battery for this purpose. Vehicular batteries are not really designed to be constantly depleted and recharged while marine batteries are designed specifically for that purpose and will give you more recharges before the battery becomes unuseable. Hope this is useful.

[Mike Rehmus]

True if you are going to do it day-after-day.

However, I use a car battery maybe 6 times a year. When I drive to the shoot, I just pull the battery out of my truck. When I fly to the shoot, I go out and buy a cheap battery, use it and then give it away before I go. Sort of a door prize.

[Josh Bass]

How much are these marine batteries? Do I have to do any adapting to make the setup work?

[Darrell Sullivan]

You don't need to do anything special with the marine batteries.

As far as cost goes, that depends on where you get them and how big of one you get.

What is your planned purpose for the battery? I know you are wanting to power your monitor, but how often will you be using it and for how long at each use?

You can get marine batteries at Wal-Mart for about the same price as a similarly sized automotive battery and they are the same size and shape.

You can purchase batteries with higher capacity at places like "West Marine". But as the capacity goes up so does the size and weight which is why I was asking what your use will be. If you are planning to carry the thing around with you any automotive sized battery is going to be too large in my opinion and you may need to find a different monitor option.

As far as purchasing an inverter goes, I would try some place that will allow you to return it if it doesn't work for you like Wal-Mart so you don't end up with something you spend money on but doesn't work.

[Phil Reams]

Here's another consideration as well...

A lot of your cheapie power inverters do not generate a clean AC sine-wave. It's more of a jagged stepped square-wave when displayed on an oscilliscope.

A lot of monitors I have repaired in the past were quite sensitive to how clean the power was.

Personally, I have cannablized old computer UPS units that were tossed when the batteries finally fried, and direct-fed a deep-cycle battery into them with quite good results.

Just find one with a high-enough VA rating. They typically have a very clean output.

Just a thought... I have been known to be wrong. :-)

-Phil