Which battery for an inverter?

[Squik]

I'm going to hard-mount an inverter in the Jimny's top glove box (will be open when running) and run the cables through the firewall. They will be alligator clip ends that will be disconnected when I am not using it (will be secured in the engine bay ready to clip on when needed.

Question is... which battery is best to run it off? I'm getting conflicting stories on whether to use the main or auxilliary...
I've scored a bigass 1000/2000w one, but it's simply to big for what I need - just need a 600w to run a laptop and charge camera/phone batteries... so that's all I will be using.

[drivesafe]

I take it, this will only be used while you are parked, as its absolute lunacy to use an inverter while you are driving.

While your parked, you connect the inverter to the auxiliary battery and while camera and phone chargers draw very little power BUT, how much power does your laptop use?

If you run that 600w inverter at only 50% of it’s power you will still be pulling more than 20 amps and thats a battery busting amount of power. No matter what type of battery you use, none of them will last long when that sorts of current is being pulled from them on a regular basis.

You will only get about 3 hours from a 100 A/H battery and need about the same amount of driving time just to put the bulk of the charge back. You would need at least 5 hours driving to get the battery back to near fully charged.

[chimpboy]

600W is by no means small.

For laptops, phones, cameras and similar devices that are already DC and within spitting distance of 12V, a DC-DC approach is way better than an inverter imho.

eg:

http://jaycar.com.au/productView.asp?UR ... &ID=MB3656

http://jaycar.com.au/productView.asp?ID=MP3474

I would be very surprised if you need anything like 600W for your laptop.

I see a lot of people using inverters for laptops and I find it kind of strange.

[nicbeer]

Why lunacy to use it when driving?

[drivesafe]

Hi nicbeer, because there is no way to make them 100% safe in case of an accident and should an accident occur, the is no indication to any potential rescuers that the vehicle is live.

There is some talk amongst some of the emergency services in a number of states, about getting some for of legislation in place to ban this sort of operation.



Hi chimpboy, the maximum potential power capacity of the inverter is not so much of a problem as long as it is not run at near maximum output and it is actually advisable to use an inverter with about 1/3 greater output capacity than you need so as not to overload the inverter. Lots of problems start to occur as you take an inverter close to it’s maximum output.

[Squik]

Howdy... after reading through here and doing some more research, I ended up going with a 300w. I need to charge a lot of camera batteries etc, as well as running a laptop.

Good point on driving with an inverter on - it would be easy to forget that you are basically turning your harmless 12v into a potential killer. This is why I didn't want to hardwire one in... I'm a bit of a wussygirl when it comes to 240v

On that note... water-crossings could end up lethal

Thinking out loud, would 300w handle a soldering iron?

[-Scott-]

Howdy... after reading through here and doing some more research, I ended up going with a 300w. I need to charge a lot of camera batteries etc, as well as running a laptop.

Good point on driving with an inverter on - it would be easy to forget that you are basically turning your harmless 12v into a potential killer. This is why I didn't want to hardwire one in... I'm a bit of a wussygirl when it comes to 240v

On that note... water-crossings could end up lethal

On a purely technical level, there are ways to improve the safety of the system. For instance, an RCD on the inverter output, with an auxiliary contact feeding the inverter input. As soon as the 240V tries to go somewhere else the RCD would trip and the auxiliary would turn off the inverter.

But it's probably better to NOT run the inverter while driving.

As has been noted, DC-DC solutions are available for charging laptops and batteries.

Thinking out loud, would 300w handle a soldering iron?

More than enough - but why? I have a 12V soldering iron which is adequate, and have also managed to re-solder joints using a jeweller's screwdriver heated on the gas stove. Then there's portable butane soldering irons too...

240V bites. There is usually another solution.

[DamTriton]

Why lunacy to use it when driving?

What happens if you are in a serious head-on accident and the 240V output lead gets severed and touches the body of the vehicle? Real nice surprise for those that are trying to rescue you from your vehicle......if it potentially doesn't do you in first! Just a plain silly idea, no further comment needed.

As stated the BEST solution is the low voltage solution, a 70 watt dc-dc converter for the laptop and any of a myriad of solutions for charging various batteries from your (IDEALLY) auxiliary battery. This is also the most efficient way of using the AH capacity in your battery.

Do not use your staring battery for anything that may be used when the vehicle is not running.

[-Scott-]

Why lunacy to use it when driving?

What happens if you are in a serious head-on accident and the 240V output lead gets severed and touches the body of the vehicle?

Yes. What happens? One phase of a 240VAC system is connected to the body of the car - let's call it "active". Where's the "neutral" connected?

In a traditional MEN system neutral is at earth potential, so it is the active line which is "hot" - with respect to earth. What's the earth reference in the car? Voltage alone isn't a problem - it's the current which does the damage, for which we need a complete circuit.

So, "active" is connected to the body, I touch the body. How does current get back to the "neutral"?

Don't say "body" of the car - because that's active, so if it's also neutral we've shorted the voltage source.

I don't see a risk in that scenario. But I do see a risk in having 240V in a situation where it is unexpected - and (arguably) unnecessary.

Stick with low voltage solutions, when they're available and practical.

[DamTriton]

Why lunacy to use it when driving?

What happens if you are in a serious head-on accident and the 240V output lead gets severed and touches the body of the vehicle?

Yes. What happens? One phase of a 240VAC system is connected to the body of the car - let's call it "active". Where's the "neutral" connected?

Precisely the point. In an accident it could be in contact with anything or anyone. All you need is one person (rescuer, not necessarily with the correct PPE) to make contact inadvertently with both....

Basically better to avoid at al costs simple situations that may have devastating results when safer methods already exist. (risk matrix methodology)

[-Scott-]

Precisely the point. In an accident it could be in contact with anything or anyone. All you need is one person (rescuer, not necessarily with the correct PPE) to make contact inadvertently with both....

Yes - contact is required with both, which is why (in my opinion) a "loose or broken wire" scenario isn't the issue. To me, it's that rescue personnel won't be expecting 240V in an automobile accident - regardless of whether or not (after an accident) the system remains intact.

Basically better to avoid at al costs simple situations that may have devastating results when safer methods already exist. (risk matrix methodology)

Yes. Number one choice should always be to avoid the risk. Find an alternative.

[DamTriton]

Precisely the point. In an accident it could be in contact with anything or anyone. All you need is one person (rescuer, not necessarily with the correct PPE) to make contact inadvertently with both....

Yes - contact is required with both, which is why (in my opinion) a "loose or broken wire" scenario isn't the issue. To me, it's that rescue personnel won't be expecting 240V in an automobile accident - regardless of whether or not (after an accident) the system remains intact.

Not necessarily severed, but bruised/abraded down to the copper could be as dangerous, particularly if there is some seperation between the abrasion and a severed (other) wire.


Could you be ABSOLUTELY sure in this circumstance?

[festy]

You might find that a smallish soldering iron won't work too well with an inverter.
My little 300w inverter won't start with a 20w soldering iron plugged in, I need to plug something else in to draw a bit more current so the inverter's auto-start circuit can see the load.
I gave up and bought a $15 12v iron from DSE - I've been using it for a few years and often use it indoors with a 12v battery I'm so happy with it...

Can you charge your camera batteries from 12v? Some chargers can, others can't.
A typical camera charger draws only 100ma @ 240v. Apart from the inverter starting issue above, inverters are horribly inefficient when used for tiny loads - that 24w of power being used by the charger would probably draw at least 60w from your battery.
As drivesafe said, inverters are most efficient when used at around 70-85% of their rated constant output (not peak output).
If you were going to use one to charge your camera battery, charge everything at once (laptop, camera and anything else you have) as to try and run the inverter more efficiently.

And if your charger is a Modified sine wave type, it's best to disconnect your laptop from it before using it.
They're usually fine for charging batteries, but your laptop battery may stop holding charge properly over time if you run it while charging often.

[Squik]

After looking at options and reading what everyone has been saying here, I gone with a 300w inverter (not hardwired and only used for charging camera batteries and a few little bits and pieces) and one of those 150w dc/dc chargers from Jaycar for my laptop.

Question though...

My Compaq AC power pack states:
Input 100-240v 1.6amp Output: 18.5V 3.5amp

The charger has options of 15,16,17,18,19,20,22 - no half points.

Do I run it switched to 18 or 19

[festy]

Either, your laptop would probably run fine from 16-20v.

[Squik]

Cool... thanks.

Just out of curiousity though... is it better/safer/healthier for your laptop (or anything for that matter) to run slightly under the mark or slightly over?

[-Scott-]

Cool... thanks.

Just out of curiousity though... is it better/safer/healthier for your laptop (or anything for that matter) to run slightly under the mark or slightly over?

In the old days of linear regulators I would probably have said slightly under, as the regulator would probably be "throwing away" any extra voltage anyway.

In these days of switching regulators I don't think it really matters - I've bought power supplies which will work from 85V to 264V input, so I don't think +/- half a volt would be significant. Your "12V" system in your car can vary from barely 12V to over 14V anyway.