self-made electricity for camping

[greenelephant]

hello everyone.

I am a resonable enthusiastic camper so I often do go camping. However it has been brought to my attention that power inverters are capable or creating 240V and up to 3000W of power from a 12V DC source such as car battery. One example is here

STACKABLE POWER INVERTER 2500/5000 W 12V DC TO 120V AC - eBay (item 330341209933 end time Jul-06-09 11:08:50 PDT)

If I can grasp the concept correctly this should be almost like a sound system for a car with speakers and Woofer from which power is sourced from the amp.

This look like an easy solution but I would like to ask you as experienced sparky's, are inverter's reliable? I know the fuses will blow eventually after time but can inverters fulfill their job without damage to itself or the appliances they are powering? Eg can these still work after a few years ownership has passed?

thanks in advance for any feedback

 

[Mac]

I used to use one in the back of my van for many years,just to charge battery drills and that.But you can get bigger rated ones to power other stuff.the one i used plugged into a 12Vdc supply in the back of the van,just like cigarette lighters

 

[Wotsit]

If you can afford it try to get one with a pure sine wave o/p, especially if you want to run any inductive loads from it. The cheep Chinese ones are normally only square wave or modified square wave at best.

 

[greenelephant]

Thanks for quick reply. Do inverters have a shelf life ie will they decrease and decay in perfomance after a while?
Or will they be able to provide a few years service to the user?

 

[desertbootz]

Prices are coming down and reliability going up. They're mostly solid state so life will depend on quality (=cost) and operating environment. If you drive them hard for a long time they won't last as long.

You mention a 3kW jobby. Don't forget that will draw around 13A on the AC side and 250A on the DC... that's big cables and batt's! In fact, strap it across a car battery and yr likely to end up wearing acid, plastic and lead.

 

[saveloy]

Prices are coming down and reliability going up. They're mostly solid state so life will depend on quality (=cost) and operating environment. If you drive them hard for a long time they won't last as long.

You mention a 3kW jobby. Don't forget that will draw around 13A on the AC side and 250A on the DC... that's big cables and batt's! In fact, strap it across a car battery and yr likely to end up wearing acid, plastic and lead.

Just out of interest Mrbootz. I've always wondered how long you can run one of these inverters off a battery (without the engine running to charge it) before the battery goes flat.

 

[greenelephant]

ok desertbootz. Im not a bit novice when it comes to batteries. Can you recommend me any batteries that will cope with the demands from the inverter?

 

[desertbootz]

Greenelephant: Something that can hack a sustained load of >250A across the terminals. Are you really going to need 3kW? Is that peak or sustained? How about using a 24V or 48V jobby?

Saveloy: Mr Bootz? No need to be so formal, I'm just an averagely gorgeous, intelligent and gifted chap like any other :O)

Simple answer is, depends. Type and capacity of battery, type and load of invertor, circuit being driven, etc.

So-o-o-o many variables!

1. Calculate yr total load, that is how much grunt you'll need at any given moment in time. Let's say you've got a telly (100W), a toaster (700W) and a laptop (50W) that you want to run. They might conceivably be running all at the same time but not very often, after all, how much toast can one camper eat? I would maybe go for a 600W invertor that can give 1200W at peak (but not continuously!). Pure sine wave if you can afford it and as Wotsit pointed out already, especially if yr driving electronics off it.

2. Think about how long I would be running those loads, eg, TV 2 hrs/day, laptop 4hrs/day, 60 slices of toast, etc., and calculate the total W/hr used. Above example gives 200W/hr (TV) + 200W/hr (PC) + 600W/hr (scrummy buttery toast) for a total of 1000W/hr.

Divide the W(atts) by yr battery V(oltage) (eg, 12V) and you get current or A(mps). In this case a 12V system will draw 1000/12=84A/hr, a 24V sytem 42A/hr. Now look at yr battery, divide yr battery capacity (already in A/hr) by yr calculated number and that will tell you how many days use you'll get.
NOTE: Then divide that by 2 or 4 to allow for any fudge factors and you'll have a very, very approximate idea of how long yr battery will last although I wouldn't count on it due to batt condition, construction etc. probably being unknown.

Also bear in mind that sone Inv use current all the time and performance data for anything is usally bullsh*t.

The more I type the more I think of that's going to effect things so I'd better stop now. All of above will give you an approximate idea but I wouldn't go relying on it for anything important. Put it this way, when I did this sort of thing for a living we didn't use invertors and spent the money on DC versions of everything... just in case :O)