wints Posted August 21, 2014 Share Posted August 21, 2014 I'm thinking of fitting an 'ordinary' 230v domestic 100 litre compressor fridge into my hymer, to replace an old AES fridge which is very unreliable on gas and 12v. According to the specifications the new fridge uses 117Kwh/year, this say approximates to 350 watts per day, which is 1.5 amps at 230v. Am I right in saying that this equates to 36 amps at 12v ? I've got 2 x 75 watt solar panels on the roof, feeding 2 x 110 amph leisure batteries. I would run the fridge via an inverter direct off the batteries. Is my thinking ok, or have I missed something, got the calcs wrong etc ? thanks in anticipation Allen Link to comment Share on other sites More sharing options...
sshortcircuit Posted August 21, 2014 Share Posted August 21, 2014 Somebody will follow with an explanation of the practicalities, however if its 350w a day then that will be about 14w per hour. which is still a high load on your batteries Link to comment Share on other sites More sharing options...
Brian Kirby Posted August 21, 2014 Share Posted August 21, 2014 No, because the figures are in Watt-hours, and not Watts. The 117kWh is the total consumption of the fridge over one year, under test conditions. Real life will differ. What you need to know is how many Amps the fridge draws @ 230V, which will be stated on its rating plate, or for how many hours the fridge is claimed to have been operating over the year to achieve the 117kWh consumption. Also, I would expect there to be a heavier start-up current each time the thermostat switches on the compressor, and this would have to be catered for by the inverter. However, I doubt that a domestic fridge would withstand the vibrations inside a van for long, or that you would withstend the noise from a domestic compressor fridge at night for very long! :-) Unless someone knows otherwise, I think I'd say don't do this! Sorry. Link to comment Share on other sites More sharing options...
wints Posted August 21, 2014 Author Share Posted August 21, 2014 sshortcircuit - 2014-08-21 4:29 PM Somebody will follow with an explanation of the practicalities, however if its 350w a day then that will be about 14w per hour. which is still a high load on your batteries Thanks for your input. 14w is just over 1 amp, my solar regulator / panel / leisure battery set up can 'do' 8 amps / hr for a few hours during bright conditions. I know with my present useage......led's, sat tv, water pump, blown heating....that I'm fully charged up most days by 11 am, and after that the solar regulator is hardly charging, so I feel Ithat I've gots lots of leccy to spare! regards Allen Link to comment Share on other sites More sharing options...
wints Posted August 21, 2014 Author Share Posted August 21, 2014 Brian Kirby - 2014-08-21 5:42 PM What you need to know is how many Amps the fridge draws @ 230V, which will be stated on its rating plate, or for how many hours the fridge is claimed to have been operating over the year to achieve the 117kWh consumption. Also, I would expect there to be a heavier start-up current each time the thermostat switches on the compressor, and this would have to be catered for by the inverter. However, I doubt that a domestic fridge would withstand the vibrations inside a van for long, or that you would withstend the noise from a domestic compressor fridge at night for very long! :-) Generalising, I think I've read that a compressor fridge may be on for 25% of the time, which possibly means that the fridge runs at less than 5 amps, what would be the start up current ? If it was double, at say 10 amps, then I'd need a 2.5 Kw inverter ! Sounds more like the kit for a large microwave ! regards Allen Link to comment Share on other sites More sharing options...
Keithl Posted August 21, 2014 Share Posted August 21, 2014 Allen, As Brian has said, the 14 Watts is a theoretical figure and you cannot base any calculations for running the fridge via an inverter on it. What you need to find is the ACTUAL running current at 230 volts and then convert this to a current at 12 volts before the inverter. And don't forget to add for the losses of the inverter, you may have to multiply the theoretical current by as much as 2 to make up for losses. I've just looked at our house fridge and it is rated at 80 Watts or 0.3 Amps. So 80 Watts at 12 volts is near 7 Amps, multiply by (say) 2 for inefficiency and you have a draw on your batteries of 14 Amps when running. If this is only 'on' for 25% of the time then this will be a drain of 3.5 Ah per hour or 84 Ah per day! Sorry but I don't think your batteries will survive this for long. Keith. Link to comment Share on other sites More sharing options...
Geoff Cole Posted August 23, 2014 Share Posted August 23, 2014 Hi Allen, I would not recommend putting a standard domestic fridge in a motor home. A normal domestic fridge is not suitable for motor homes, the compressor will not like being bounced around as it is mounted on springs within the compressor pot. You will find it will clonk about a lot when on the move and will fail also domestic fridges are meant to be stationary as bouncing about can cause the compressor oil to mix with the gas, this will cause the compressor to fail due to a hydraulic lock between the piston and cylinder head. The start up current is also high, which will give problems for you. I have a 12v compressor fridge in my camper but it is designed for the job, has more mounts within the pot and does not rattle about and will take the movement without the problems mentioned, it has built in electronics that control the current flow and cuts out if the battery voltage drops low, the downside is they are expensive. Mine draws about 6A when running, the amount of time it runs depends on the ambient temperature, I always have a couple of freezer packs in the ice box these help reduce the running time and keep it cool when off (i normally switch it of at night as it can be noisy in a small camper), however it works well, but is thirsty on the battery Regarding using an inverter to run your fridge, this will put a strain on your batteries, you will need an inverter that will produce a high start current at mains voltage because of the high current draw on start up. Rule of thumb is start current is roughly 5 times run current so in your case you will be drawing at least 35 Amps or more on start up. I have my compressor fridge on a separate battery so that if it does go flat when not on hook up at night the habitation electrics are not affected. Geoff C Link to comment Share on other sites More sharing options...
wints Posted August 31, 2014 Author Share Posted August 31, 2014 Thanks for all the advice, now looking at possibly installing a Waeco 12v compressor fridge. Anybody done it ? Any tips ? thanks Allen Link to comment Share on other sites More sharing options...
Retread24800 Posted August 31, 2014 Share Posted August 31, 2014 Not a built in but I have a mobile fridge/Freezer Which is surprisingly quiet. The first thing I learnt tho' was that the Electronic battery protection works...... but it senses Voltage and thus it is imperative to provide a 12V source as close to the battery as possible and with really thick wire. Its also great because I can use it in the boot of the car, on the terrace for cold drinks etc. Link to comment Share on other sites More sharing options...
Geoff Cole Posted August 31, 2014 Share Posted August 31, 2014 Hi Allen, Fitting a waeco fridge is the best way to go Mine is a waeco and works well. As for fitting make sure you have adequate ventilation at the rear of the fridge, i have fitted a 50 mm computer fan to aid ventilation as mine is under the sink. As for wiring, you can either take a cable direct to your leisure battery through a 10 amp fuse, the fridge draws about 6 Amps. Or you can take the wire from the fridge connection on your split charge relay, this will be the wire that powered your 3way fridge through a changeover relay, connecting as follows:The common connection on the relay will go to the fridge the N/C connection will go to the leisure battery the N/O connection will go to one side of the relay coil and to the wire from your split charge relay, the other side of the relay coil goes to a good earth point. This way the fridge will run directly from your cab battery when running allowing full charge to your leisure batteries, when stopped it will automatically connect to your leisure battery. I have mine connected like this,on a dedicated battery for the fridge, I also put a couple of freezer packs in the ice box to help the efficiency. hope this is helpful. Geoff C Link to comment Share on other sites More sharing options...
wints Posted September 1, 2014 Author Share Posted September 1, 2014 Thanks Retread & Geoff. Looking like I'll order & fit the Waeco 110 litre. I'll start another thread with Waeco more prominently displayed in the title as I'd like to know the best position to place the inline fuse. Next to the leisure battery will be the easiest, but will this introduce an immediate voltage drop in the rest of the 3 metre long cables to the fridge ? Allen Link to comment Share on other sites More sharing options...
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