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Post by Delta9 on May 12, 2017 22:31:31 GMT
I'm looking at this fridge or something similar from currys as 12v ones are stupid expensive. (getting too warm to keep my beverages on the well deck now) ao.com/product/r50052w-lec-fridge-white-25045-30.aspxI haven't been able to find any helpful figures about what the maximum power needs of a mini fridge are. Anyone have any idea what size inverter I would need to run it? Cheers.
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Post by Delta9 on May 12, 2017 22:48:58 GMT
Also, would a quasi sine wave be cool, or would it need to be pure sine wave?
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Post by Deleted on May 13, 2017 4:03:48 GMT
I'm looking at this fridge or something similar from currys as 12v ones are stupid expensive. (getting too warm to keep my beverages on the well deck now) ao.com/product/r50052w-lec-fridge-white-25045-30.aspxI haven't been able to find any helpful figures about what the maximum power needs of a mini fridge are. Anyone have any idea what size inverter I would need to run it? Cheers. Looking at the LEC web site it says it draws 0.45 amps (at 240v) . So that's about 110 watts. Add to that the inefficiency of the inverter then more like 120 watts. The thing is that when you get an inverter you will probably want to use it for other stufff, so it's probably worth getting something which will give you much more output. If you just want to run the fridge I wouldn't go for anything less than 300w. Other things to bear in mind. The inverter needs to take 12v as close to the battery as possible to avoid loses along the cable. The cables need to be rated to handle the max current demand. Some appliances with digital computer bits like timers can be affected unless it's pure sine wave. I doubt a fridge will have a problem with quasi but again, you may want to use it for something else, so get the best biggest inverter you can afford. To be honest, if someone can't work out what size inverter to get, it's probably best to leave it to a qualified electrician (which I'm not!). Boats and 240v don't go well together really so it's worth getting it right. Also, you'll need to put that energy back into the batteries. Unless you have regular access to a shore line, then you will be relying on your engine and alternator to charge them back up. That might be a lot of engine hours and fuel.
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Post by JohnV on May 13, 2017 6:24:18 GMT
If the unit you are thinking about uses a compressor then you really need a pure sine wave inverter, running anything with a motor off a modified sine wave inverter is a gamble. Motors do not like them and often will be noisy, overheat and draw excessive power if fed it.
Another thing to beware of is the fact that a compressor on start up will draw LOTS more power than it's run rating, it's very easy to underestimate this !!!
I run a full sized fridge/freezer on an inverter and allowed for a bigger drain and installed a 1Kw PSW inverter. I found that very occasionally the inverter would momentarily go into "fault" as the compressor kicked in ...... not every time just occasionally. (I have since upped the inverter to 2Kw) which allows me to use the supply for other devices drawing intermittent power.
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Post by phil70 on May 13, 2017 7:06:35 GMT
John has summed it up in a nutshell, I'm of the opinion that because of the way electronics are going, the days of quasi sine wave inverter is pretty much over.
Phil
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Post by Delta9 on May 13, 2017 7:20:27 GMT
I'm looking at this fridge or something similar from currys as 12v ones are stupid expensive. (getting too warm to keep my beverages on the well deck now) ao.com/product/r50052w-lec-fridge-white-25045-30.aspxI haven't been able to find any helpful figures about what the maximum power needs of a mini fridge are. Anyone have any idea what size inverter I would need to run it? Cheers. Looking at the LEC web site it says it draws 0.45 amps (at 240v) . So that's about 110 watts. Add to that the inefficiency of the inverter then more like 120 watts. The thing is that when you get an inverter you will probably want to use it for other stufff, so it's probably worth getting something which will give you much more output. If you just want to run the fridge I wouldn't go for anything less than 300w. Other things to bear in mind. The inverter needs to take 12v as close to the battery as possible to avoid loses along the cable. The cables need to be rated to handle the max current demand. Some appliances with digital computer bits like timers can be affected unless it's pure sine wave. I doubt a fridge will have a problem with quasi but again, you may want to use it for something else, so get the best biggest inverter you can afford. To be honest, if someone can't work out what size inverter to get, it's probably best to leave it to a qualified electrician (which I'm not!). Boats and 240v don't go well together really so it's worth getting it right. Also, you'll need to put that energy back into the batteries. Unless you have regular access to a shore line, then you will be relying on your engine and alternator to charge them back up. That might be a lot of engine hours and fuel. Cheers. I was hoping to put the inverter next to the fridge instead of close to the batteries, I know it's not ideal but it will make things a lot easier for me to fit. The cables running to the fridge are very thick so I was hoping voltage loss wouldn't be too much of an issue. I'm on shoreline most of the time, so recharging isn't an issue. I'm just trying to keep costs down as 12v fridges are so expensive.
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Post by bodger on May 13, 2017 7:43:48 GMT
err .... why are the cables running to the fridge very thick? They are 240v cables and could be much thinner than the 12v cables serving the inverter. There is minimal voltage drop in 240v cables (relative to the nominal voltage) and large voltage drop in the 12v cables (relative to the 12v nominal voltage). This is because the current in 240 v cable (on which the voltage drop depends) is about 1/20th of the current in the 12v cables for the same power vA being transmitted.
The reason why electricity is transmitted at, say, 220,000v is because the voltage drop (and therefore wasted energy) is minimal at higher voltages, even for relatively thin cables, when transmitting power over hundreds of miles.
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Post by Telemachus on May 13, 2017 8:10:53 GMT
err .... why are the cables running to the fridge very thick? They are 240v cables and could be much thinner than the 12v cables serving the inverter. There is minimal voltage drop in 240v cables (relative to the nominal voltage) and large voltage drop in the 12v cables (relative to the 12v nominal voltage). This is because the current in 240 v cable (on which the voltage drop depends) is about 1/20th of the current in the 12v cables for the same power vA being transmitted. The reason why electricity is transmitted at, say, 220,000v is because the voltage drop (and therefore wasted energy) is minimal at higher voltages, even for relatively thin cables, when transmitting power over hundreds of miles. I think he means that the cables running to the fridge for the previous 12v fridge are quite thick and he's proposing to use those to feed the inverter to run the new 230v fridge. I suppose if they were thick enough to prevent excessive voltage drop when the 12v fridge started up. They won't be too bad to use for the new proposal but it does of course represent a bit of a bodge, better to put the inverter near the batteries and run mains flex / cable to the fridge. D9, you can get fairly cheap PSW inverters from china these days, I've got one in my caravan and it's been fine so far, but you do need a lot of over-rating to cater for the startup load if it's a compressor fridge. What about the BSS requirement for a consumer unit?
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Post by Delta9 on May 13, 2017 8:42:16 GMT
Yes, the cables already in place are for the old 12v fridge and very thick. Would a consumer unit be needed even if it is just a small inverter for one appliance? I didn't consider that..
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Post by Mr Stabby on May 13, 2017 9:08:31 GMT
Is it not possible simply to replace the fridge's 240v motor with a 12v motor?
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Post by Delta9 on May 13, 2017 9:31:36 GMT
Is it not possible simply to replace the fridge's 240v motor with a 12v motor? Apparently converting a fridge to 12v is quite expensive so doing that wouldn't work out much cheaper than just buying a 12v one.
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Post by Mr Stabby on May 13, 2017 9:39:20 GMT
Is it not possible simply to replace the fridge's 240v motor with a 12v motor? Apparently converting a fridge to 12v is quite expensive so doing that wouldn't work out much cheaper than just buying a 12v one. How about then, if you mount the inverter inside the rear of the fridge if there is room? I'd presume (but am willing to stand corrected) that it would then still be a 12v appliance?
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Post by Telemachus on May 13, 2017 10:25:09 GMT
Yes, the cables already in place are for the old 12v fridge and very thick. Would a consumer unit be needed even if it is just a small inverter for one appliance? I didn't consider that.. BSS 3.9.2 says "check that all ac electrical circuits pass through a consumer unit". I'm sure there are plenty of boats around with a small portable inverter used to power phone chargers etc, that don't pass through a CU. But those might be considered portable / carry on equipment that could be hidden away prior to the BSS. Hard wiring an inverter to dedicated 12v cables and a fridge would seem to come under the need for a CU even though it might be considered overkill. Probably something that could be argued the toss over at BSS time but perhaps it would be best not to go there in the first place. Plus, these things have a habit of growing legs and you might at some time in the future decide you want to plug a few other bits and bobs into the inverter and before you know it, you have a significant ac system with no CU.
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Post by Delta9 on May 13, 2017 10:26:02 GMT
Apparently converting a fridge to 12v is quite expensive so doing that wouldn't work out much cheaper than just buying a 12v one. How about then, if you mount the inverter inside the rear of the fridge if there is room? I'd presume (but am willing to stand corrected) that it would then still be a 12v appliance? That is pretty much what I planned to do (put inverter on top of fridge) I'm getting my safety cert done soon so will ask Mr boatman his advice on that when he's here.
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Post by smileypete on May 13, 2017 10:45:37 GMT
I'm looking at this fridge or something similar from currys as 12v ones are stupid expensive. (getting too warm to keep my beverages on the well deck now) ao.com/product/r50052w-lec-fridge-white-25045-30.aspxI haven't been able to find any helpful figures about what the maximum power needs of a mini fridge are. Anyone have any idea what size inverter I would need to run it? Cheers. Would expect that 1kW should do normally but 1.5kW+ is better to be on the safe side. The compressor should run fine off MSW but electronic controls (very unlikely on cheap fridge) or some LED interior lights (possible) may go phut on MSW sooner or later. Maybe buy the fridge, check the bulb out and try a cheep 1kW MSW, if no worky go to a 1500W+ PSW, depends on your risk tolerance. The 12V fridge wiring will probably be inadequate for an inverter to run the fridge, but maybe worth a try. Typical cheep 1kW MSW: www.ebay.co.uk/itm/1000W-Car-Truck-Boat-DC-12V-to-AC-220V-Power-Inverter-Charger-Converter-Adapter-/232300880728If there's space, an undercounter fridge with two star icebox probably won't use much more kWh/year than a tabletop fridge, argos and currys used to do them, they're a bit thin on the ground these days but a good search might turn up one for £100ish, here's a typical one: www.debenhamsplus.com/p/1047676/amica-fm104.4-fk106.4-50cm-under-counter-freestanding-fridge-with-star-ice-box-white Last but not least check out the noise levels, 39 or 40 dB is fairly typical for a fridge but 42 - 45dB may be an issue if sleeping quarters are nearby. The little tabletop fridges can be a lot worse than some of the bigger ones...
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