Generators, KVAs and Run times, oh My!

[xmorpheus]

hi all,
We're looking into getting a generator. Now I have searched the forum and there are few threads that discuss the pros and cons, but I'm afraid I'm going to need a more basic explanation if anyone would be kind enough to help? (hopeful smile)

From what I've read, I'm aware that there is an anti-gen group here but we go to a lot of motorsport circuits and not all of them have electrical hook ups. Since we can be there for 3-4 days and I like to have some light and fresh food available, we have limited options available!

I've found a couple of generators that I like the look of and appear to offer what we need, and I'm seriously looking at one that comes converted to LPG.

However, I have absolutely no idea how to work out what time we'd get out of one. I've read about KVAs - I've seen the running time(s) on the various units we're looking at and I've found various online calculators - and I think I'm now more confused than I was before I started!

Basically, we want the fridge to run as much as possible for a 72 hour period on 12V. That's the most important one. It does run on gas but we've never tried it and I have no idea how reliable it might be. I know that it sucks the life out of the battery, but with nothing else running, how fast?

The LED lights, TV, mobile chargers and radio would be run at various points for a cumulative 2-3 hours of an evening, depending on level of tireness, weather, number of visitors to the caravan etc. etc.! All of these are 240V, not 12V so need to run from a mains supply, not the battery. But we'd like the battery to drip charge while the genny is on, which I presume would just be for the period of the evening when we want to use these services.

Can anyone help me get straight in my head exactly what we need to do here.

Apologies if I'm being dense, but all the sites I've read have left me more confused than when I started!
All help gratefully appreciated (unless it involves telling us off for getting a generator.... )

 

[WoodlandsCamper]

Basically, we want the fridge to run as much as possible for a 72 hour period on 12V. That's the most important one. It does run on gas but we've never tried it and I have no idea how reliable it might be. I know that it sucks the life out of the battery, but with nothing else running, how fast?

Fridges don't run on 12V unless being towed at the time, hence you've got to run it on gas. The rest of the 12v items (excluding a TV) will happily run on a good battery for 3 to 4 days. Water heating needs to be gas as well. Forget the noisy generator. :evil:

 

[Thingy]

Totally agree with WoodlandsCamper (jeez, can I call you Robin for short? )

Generators, apart from being noisy are heavy. Your fridge will run more efficiently on gas, did you know that? Gens are also very expensive to get a suitable one for caravanning, unstable supplies and spikes can do untold damage. If you are not going to be away for more than a few days, consider a two battery system with a good solar panel. If your van is fairly recent, you may already have the connections for a solar panel built in, but do check and see if it requires a regulator, most do.

 

[WoodlandsCamper]

Totally agree with WoodlandsCamper (jeez, can I call you Robin for short? )

Shorten it to WC, as per the avatar . Most people do. :lol:

 

[ProfJohnL]

hi all,
We're looking into getting a generator. Now I have searched the forum and there are few threads that discuss the pros and cons, but I'm afraid I'm going to need a more basic explanation if anyone would be kind enough to help? (hopeful smile)

From what I've read, I'm aware that there is an anti-gen group here but we go to a lot of motorsport circuits and not all of them have electrical hook ups. Since we can be there for 3-4 days and I like to have some light and fresh food available, we have limited options available!

I've found a couple of generators that I like the look of and appear to offer what we need, and I'm seriously looking at one that comes converted to LPG.

However, I have absolutely no idea how to work out what time we'd get out of one. I've read about KVAs - I've seen the running time(s) on the various units we're looking at and I've found various online calculators - and I think I'm now more confused than I was before I started!

Basically, we want the fridge to run as much as possible for a 72 hour period on 12V. That's the most important one. It does run on gas but we've never tried it and I have no idea how reliable it might be. I know that it sucks the life out of the battery, but with nothing else running, how fast?

The LED lights, TV, mobile chargers and radio would be run at various points for a cumulative 2-3 hours of an evening, depending on level of tireness, weather, number of visitors to the caravan etc. etc.! All of these are 240V, not 12V so need to run from a mains supply, not the battery. But we'd like the battery to drip charge while the genny is on, which I presume would just be for the period of the evening when we want to use these services.

Can anyone help me get straight in my head exactly what we need to do here.

Apologies if I'm being dense, but all the sites I've read have left me more confused than when I started!
All help gratefully appreciated (unless it involves telling us off
for getting a generator.... )

Hi,

Yes there are a lot of caravanners that would not thank you for operating a generator on a caravan site, Some sites may even ban the use of generators, but I fully understand you situation, and at motor sport meets engine noise is a constant given.

However even within that environment, there is a good case to look for alternatives. Just one generalised fact about small generators they are horrendously inefficient at converting expensive petrol or gas into useful power. Plus despite some manufacturers calling them silent, they are anything but.

Now I am not anti generator, I often have to use them at festivals
for powering sound equipment, but the genies we tend to use are 250kW or more and have broadcast quality silencing. - not something you can put in the back of a car.

Small IC engines struggle to achieve 10% efficiency of petrol to shaft output. Small alternators may hit 50% of shaft input to electrical power out, That give the generator as a whole at best about 5% fuel to electrical efficiency. so your wasting 95% of the fuel you put into the generator!

So what are the alternatives? the piece of equipment that need constant power is the fridge. all fridges designed for caravans can be powered from three sources. 12V when towing,(not on site) 230 when mains power is available or LPG if off grid. If no mains is available gas is the best choice - Provided the fridge has been installed correctly, and is periodically checked its perfectly safe, and pretty economic. and SILENT. Its gas efficiency will be a minimum of 70%!!!!

To put this into perspective for economy, The fridge will use about 270g of LPG in 24 hours. So if a 4.5Kg bottle of gas costs £23 the fridge will cost about £1.37 per day. The Honda EU10i (1kW generator) will consume a minimum of 6.9 Litres of petrol over 24 Hours, whether you are using the power or not. (current prices that £8.97 per 24 hours running minimum)

Then look at the cost of purchasing and maintaining a generator. You can buy a lot gas for what you'd pay.

Then there's the weight of the generator, which could be offset by the weight of carrying extra bottle of gas.

Most phones can be charged in the car.

So on balance, unless you need 230V for running power tools to repair a rally car etc, you should be able to survive 3 to 4 days quite happily without a generator on a fully charged battery and full gas bottle.