inverters, power cuts, generators, CH, etc.

[Bruce]

I wonder how much fuel they would need to boil, say, a litre of water?

[Dave Liquorice]

Petrol has about 35MJ/l. Water has a heat capacity of 4.184 J/gK.

1l water weighs 1kg. Say a delta T of 85K Energy required = 4.184 * 1000 * 85 = 356kJ 50% efficient energy from fuel = 712kJ. Fuel required = 712/35,000 = 20ml = 4 teaspoons.

[Appelation Controlee]

If I'm understanding that correctly, petrol as a portable medium for stored energy is hard to beat. (?)

[Stephen]

But if I plug it in for a boost, I still need to know the rating to make sure it's within the capabilities of my inverter.

I was thinking of buying a 300W continuous, 1kW peak inverter to try out. I thought this would be enough to power just the CH and I could unplug the CH and plug in the freezer as required. I will probably get a gas lantern and a small gas stove to boil water for hot drinks.

However, in your earlier post you said that 250W for the CH was too close to comfort to the 300W limit of the inverter. If it is rated at

300W continuously, shouldn't it be able to supply 300W continuously?

Does it make any difference whether I buy a 300W inverter and run it at high load or if I buy a 2kW inverter and run it at low load? I was just wondering whether they have to be run hard to run efficient?

I see some web sites list efficiencies of 90-94%. Are they really this good or is that marketing taking over?

Finally, I see that Black and Decker sell a 400W model with "ground fault interrupter circuit". Is that RCD to you and me? The B&D web site is pretty useless and does not say what the peak rating of the model is. Nor does it show an RCD on the photo.

If I buy a different make, is it advisable to fit a plug-in RCD to the output and earth the inverter to a spike? Is the neutral already connecting to the ground or do I have to do that too? Sorry if these questions are answered in the instruction booklet, but since I haven't bought one yet, I wouldn't know that.

Thanks.

[Rod]

Hence petrol camping stoves. But the great advantage is that a petrol burning stove (e.g. Coleman) is small and light enough to put in a backpack and carry. I wouldn't want to carry a generator...

[Bruce]

Wonderful! Thank you very much.

[Dave Liquorice]

It's pretty good but diesel is better around 38MJ/l. In fact 35MJ/l for petrol might be a bit optomistic, seen 32MJ/l just now.

[meow2222]

I cant see a battery big enough to power a 100w bulb fitting in there, and theres no reason they would make it several times as expensive. Its almost certainly LEDs. The dubious light output spec pretty much confirms that.

NT

[meow2222]

The thinner the fuse, the more often they die of natural causes. The last thing you want with a freezer is for the fuse to die, so you go as high as poss, ie 13A, regardless of load. 2A fuses are especially issueful in this respect, which is probably why theyre not common.

NT

[meow2222]

invertor losses are made up of a) pass losses, which depend on load current b) standing losses, which depend only on invertor design, and which occur regardless of load.

To answer your q fully you'd need to compare the quiescent consumption of each invertor.

one particular load yes, the rest of the time no. Under no load efficiency drops to 0%.

gfci is the US term for rcd, so yes, same deal. The rcd circuitry might be on the main invertor pcb, I dont know the model.

Small invertors and portable gens usually have close to nothing in the way of safety features. Typically no earth at all and no rcd. Many gens have a breaker (MCB), some dont even have that. Its up to you how much safety you want to add. Earthing plus rcd would be a nice idea.

NT

[Bruce]

Why do you think it is used in billions of cars around the world?

[Appelation Controlee]

No idea - if we still had a coal industry ...

[Dave Liquorice]

That's sensible but be aware that the "camping gaz" high pressure stoves can be a little unstable when they have a kettle or pan of water on top. They are also surprisingly tall.

A 300W cont should be able deliver 300W cont. I'm just a little sceptical about the ratings of cheap kit. It may well be able to deliver 300W cont but gets red hot in the process, excessive heat is a good way to kill electronic components. Hot is OK up to 50 or 60C package temp on a decent heat sink but IMHO much hotter is asking for a short life.

Probably better loaded up, they take some current even without a load.

Should be about that, they'd get seriously hot if they weren't.

Yep, left pondisium for RCD. It could be built into the unit so not obvious from the picture.

It gets complicated... if the live and neutral of the invertor are both truely floating with respect to real ground, then an RCD won't gain you much protection as there is no other return circuit to the invertor.

If one of the outputs ("live" or "neutral") does have a path to ground at the invertor then an RCD would be a good idea.

[Stephen]

I have had a read of the B&D manual for their 400W inverter. It says that it takes 0.7A when do nothing. That seems a lot to me. What is it doing? Surely it only needs to light the "on" LED?

The manual mentions nothing about an RCD or GFI. That's strange because it is used in the advertising literature as one of its plus points. If there is an RCD wouldn't there be test and reset switches? There are no mention of these.

The manual says not to connect N&E. Whether that's because they are already connected or whether it's because they will trip the RCD, I don't know. I'm waiting for clarification from B&D.

[Dave Liquorice]

0.7A @ 12v is only 8W, the circuitry is still active, oscilator running etc.

Yes.