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  #1  
Old 8 Sep 2008
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Inverter are they worth it.

Will be i Mauritania and Mali in Nov and Dec getting Landcruiser ready most things in place but do I put an inverter in so that I can run a fridge. Getting conflicting reports on there efficiency, I want to run it while on the move, in my experience my fridge is better on 240 v than 12v but will an inverter keep it going for 6 or 7 hours or will it over heat?

Experiences views welcome please.
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  #2  
Old 8 Sep 2008
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You need to buy an inverter thats adequate for the task, gather some info about your fridge, how many amps it draws on startup - that one figure allows you to buy the correct sized inverter. eg 15amps startup current for the fridge means that you need a minimum of 15amps from the inverter - ideally you need about 20amps. How to Convert Watts to Amps Simplified -- Converting Amps to Watts the easy way gives all the formulae you need to convert amps to watts - most inverters give output in watts.

The next thing is to make sure that the fridge can operate on the type of 240V produced by the inverter - not all volts are equal!! Inverters produce two types of alternating current - a square wave form and a smooth wave form. Sensitive electronic devices often hate square form and just wont work. Obviously you need to buy one that works for your fridge.

Do you know how your fridge operates? Is it a compressor fridge when running on 240V and a peltier type fridge when running on 12V? or just a 12V fridge that converts 240V to 12V?

Other issues with inverters - ordinary car batteries dont like them, you need a leisure battery isolated from the car battery by a Zig unit or similar - you're bound to flatten the car battery in the most out of the way place that is dead level and cant bump start the vehicle. Inverters consume more power than they produce, most are about 90% efficient at the very best, so if you can get the 12V working on the fridge you wont "waste" so much energy.

Safety; you've got an unearthed and potentially deadly supply of 240V power in the vehicle if something goes wrong.

Is it worth it? I'd be trying everything possible to get the fridge working well on the 12V before lashing out on an inverter.
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  #3  
Old 8 Sep 2008
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There are two main types of fridge, 3-way (gas/12v/240v) and compressor (12v/240v).
The 3 way is the traditional caravan type fridge. Designed mainly to run on 240v hookup or gas. The 12v option is only to be used when the vehicle is running as it consumes so much power. Basically a heater at the rear is used to keep the inside cold, no moving parts so totally silent but very inefficient. There is also no temp control in 12v mode it's just on all the time. This is because 12v mode is only meant to be used when moving between caravan sites. Other disadvantage is that a 3 way fridge will only work if it is dead level or within a couple of degrees of it.
A compressor fridge works just like your household fridge. A small compressor moves gas around the cooling loop to keep the inside of the unit cool. Makes a little noise when running but not loud enough to disturb sleep. Unlike a 3-way it will also work when not level (up to about 30 degrees). Big disadvantage is cost, they are not cheap (£500ish).
I have a weaco cf500 in my self build camper van and it is fantastic. Will go to -10deg so you can use it as a freezer if you need to. Top loading cool box type design so all the cold air doesn't fall out every time you open the door. It takes about 7amps when running. The amount it runs depends on the temperature you set it to and the temperature of the air around it.
Even though a compressor fridge is energy efficient it would be a brave man thet used one from a vehicles starter battery. You really need to fit a secondary battery in order to make sure your vehicle will start in the morning. I have a 110aH secondary battery in the van charged via a "split charge relay" circuit when the van is running.

hope this helps

cheers
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  #4  
Old 9 Sep 2008
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Quote:
Originally Posted by thestens View Post
but do I put an inverter in so that I can run a fridge. Getting conflicting reports on there efficiency, I want to run it while on the move, in my experience my fridge is better on 240 v than 12v but will an inverter keep it going for 6 or 7 hours or will it over heat?
There are at least 3 questions here ..

Efficency of an inverter?
Well it varies depending on the inverter and its load .. at a guess say 90% effecient...

Efficency of fridge on 240v compared to 12v ... hard to judge .. the 240v operation might get you more cooling power .. but draw more energy compared to the 12v operation ..

Will an inverter overheat? Yes .. if pushed beyond its limits .. operation something a 'home' where temperatures are under 35C is different to operations where temperatures exceed 45C ..

I'd steer away from the inverter .. less things to go wrong/carry/buy/loose ...
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  #5  
Old 9 Sep 2008
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Whilst inverters are useful for equipment that you can't run on 12 volts I generally advise that you try to minimise their use.

Most equipment you will be running like laptops, etc are designed to run on 9-20volts - it makes little sense to take your 12 volts supply from your battery, boost it up to 240volts with the inverter and then to plug in the equipments power supply that then drops it down to the required (low) voltage - it is very inefficient - it makes far more sense to get a 12volt based supply for your kit.

As for the fridge, you don't say what type it is. The chances are that if it is designed to run off 12volts, the main internals will be operating on 12volts or something close to it, so it follows the same rules as above.
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Julian Voelcker
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  #6  
Old 9 Sep 2008
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To my knowledge, the most energy efficient 'home' fridges (A+) run on 12V/24V ("solar fridges" sold for stand alone solar systems). They also have a compressor.

It would surprise me that there would be nobody making such items for cars, trailers, and other 12V/24V environments.


But if you go for the 220-240V system, your inverter should be powerfull enough to cope with the starting power need of the compressor: this load may be a multiple of what's indicated at the back of your fridge...
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  #7  
Old 9 Sep 2008
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12 V or 24 V

There is another thing to take into the equation. I do run my laptop of a 150Watt inverter on 230V (despite its very inefficient) because my Landcruiser is 24V (completely). My laptop power supply is not available in 24 Volts, only in 12 Volts. A 150 Watt 24/12 volt converter is much more expensive than a 24/230V inverter. And with the 230V I do not need to buy 12 Volt power supplies for the Cell phone, Satellite phone, Mp3 player etc. Just charge them on 230V when needed.

Cheers,

Noel
exploreafrica.web-log.nl
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  #8  
Old 9 Sep 2008
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any reason you cant connect to just one battery, giving 12volts?

how could you find out if the fridge or the seperate inverter converted 12volts to 240 more efficiently?

i have 24volt and 12volt sockets in my camper, and 240volt uk mains sockets for when i'm plugged into a campsite. the fridge is currently a caravan type thing with a normal door, but i'm thinking that a top loading engel type thing would be more efficient, durable although a little pricey!
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  #9  
Old 9 Sep 2008
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Quote:
Originally Posted by grizzly7 View Post
any reason you cant connect to just one battery, giving 12volts?
Its not good news for the batteries to do this, one gets drained more than the other and the alternator is unable to set it right again.
I'm sure someone will set me straight if i'm wrong, but my understanding is, it will actually charge the better battery more than the drained one, so compounding the problem.

Sam
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  #10  
Old 9 Sep 2008
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electrical efficiency

Quote:
Originally Posted by grizzly7 View Post
any reason you cant connect to just one battery, giving 12volts?

how could you find out if the fridge or the seperate inverter converted 12volts to 240 more efficiently?

i have 24volt and 12volt sockets in my camper, and 240volt uk mains sockets for when i'm plugged into a campsite. the fridge is currently a caravan type thing with a normal door, but i'm thinking that a top loading engel type thing would be more efficient, durable although a little pricey!
Uneven loads on 2 batteries in series is not good. It will shorten battery life or could even destroy it. A friend of mine ran his 12V car radio on 1 battery (24V LC) and the other battery exploded under the bonnet. Always use a 24/12 converter to power 12 appliances.

I do have a 12 Volt compressor but I run this evenly on both batteries. While using it, it runs half the time on the one and half the time on the other, just to keep the batteries equally loaded.

A fridge directly on 12 or 24V is always better than via an inverter. The electrical efficiency of an inverter is about 80 to 90%. That means on a 300 Watt inverter, 30 to 60 watt is lost in heat only. That is equivalent to a very bright light bulb!

cheers,
Noel
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