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leopard
leopard

Posted: Tue Sep 22, 2009 12:23pm

Post Subject: Mians fridges on boats

leopard
leopard

Posted: Tue Sep 22, 2009 12:30pm

Post Subject: Mians fridges on boats

Sorry, caught <CR> key accidentally - hence no post ! I'll try again - and by the way it should of course say mains ! One or two people have told me that mains fridges on boats are a no-no because they ruin batteries. I cannot understand why, especially if the inverter / battery / alternator / charger set up is matched OK as the fridge is surely just like any other ac load. The start up inrush will be of very small dyration and the 'peak' output of the invertor sould cope ? I'm at the point of fitting a fridge in my fit out plan and had thought to go mains but having been aleretd to this possible problem I can't find a reasonable explanation. In my case I have 4x110Ah 12v wet cell lesiure batteries, a 1800w (cont) 3600W (peak) pure sine inverter, dedicated 110Ah alternator and when connected to shoreline a 50A 3 stage mains charger. Any thoughts / advice / comments ? Thanks in advance, Andy

Tony-B
Tony-B

Posted: Tue Sep 22, 2009 12:32pm

Post Subject: Mians fridges on boats

Can't reply if there is no question - just add it as a reply to this post. The latest information I have is that it is likely to require more battery capacity to run a mains fridge via an inverter than a dedicated 12v fridge, However it is somewhat marginal so if you spend 85% of your time with a land line or generator running then the lower initial cost of a mains fridge make sit a worthwhile consideration PROVIDING you make sure your inverter, charging system and batteries are specified to cope while away from the mains supply. Tony Brooks

Tony-B
Tony-B

Posted: Tue Sep 22, 2009 12:43pm

Post Subject: Mians fridges on boats

That looks suspiciously like a modified sine wave inverter so be prepared for anything with electronics involved to play up in some way. Unless the fridge maker has fitted electronics to make it more efficient I suspect your inverter will cope, but as you give no information about the duration the inverter can supply the surge or the actual surge produced by the fridge one can never be sure. You also miss out one of the vital pieces of information, that is how long each of your charging will be in use each day. I suspect the mains charger will be on 24/7 when you have access to power, but when out cruising you must do a worst case power audit and then work out if you can put 30% to 40% more back into your batteries over 2 to 4 hours using half the alternator's maximum output. I can tell you that a 12v fridge rated at about 3.5 amps draws 10 times that on startup and there is a suspicion that this is a very conservative figure so you need to check the data for you chosen list of possible fridges. Tony Brooks

leopard
leopard

Posted: Tue Sep 22, 2009 1:00pm

Post Subject: Mians fridges on boats

Thanks Tony, Interested as to why you say tha the inverer lookslike a modified Sine Wave one ? The maunfacturer (Powermaster Systems) clearly state pure sine wave and it's very heavy so would appear to have a transformer of some kind. My original query was possibly more related to any thoguths on why others have experienced problems. My guess was that their elctrics simply werent upto the job, rather than any genreic trend ? Rgds, Andy

Tony-B
Tony-B

Posted: Tue Sep 22, 2009 2:07pm

Post Subject: Mians fridges on boats

The reason I said it looked like a modified sine wave one is that the surge current seems to be very high. Traditionally modified sine wave inverters were far better at providing for high current surges than pure sine ones but these things move on. I still have concerns about how long it can supply the surge power before tripping out. I suspect the fridge problems others have had are related to inverters with insufficient surge capacity or undersized battery cables. Tony Brooks

Tony-B
Tony-B

Posted: Tue Sep 22, 2009 4:37pm

Post Subject: Mians fridges on boats

Looking at your specification again it has just struck me that your reading of the specifications may not be correct. When looking at AC sources they should quote the output followed by RMS. RMS values are about 0.68 of Peak values. Peak values are useless when considering the work an AC source can do but its very useful for marketing departments to confuse the punters and make their equipment seem better than it is. Please get hold of the RMS output for your inverter and its SURGE capacity and time it can sustain this surge. I may be wrong but as 1800 is half of 3600 I suspect that 3600 is the peak value plus a tiny bit of surge capacity and the true surge capacity is much lower.

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