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New fridge on. Start up


Dave Bebb

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Hi all just fitted new 12 volt fridge to replace our 240 volt one which I had to run of the 3,000 watt inverter when I turn on the fridge on at the 12 volt. Control panel the volt meter on the panel  drops to 9.6 volts from 12.7 just for two seconds then goes back to12.7 again ,just shows you how much power It takes to start up a 12 volt fridge PS running off 4 110 battery's 

Edited by Dave Bebb
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I seem to remember several years ago Gibbo (remember him?) saying that a 12v fridge takes a lot more powere to start up than to run. It was on a thread about voltage spikes damaging 12v TV's which were connected without a surge controller.

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14 minutes ago, Dave Bebb said:

Not sure I don't on how to check it was like this from new ?

If its on the distribution board then you could be suffering from volt drop in the cables that cauld cause problems as your batteries get closer to requiring recharging. You have an inverter, what does the volt meter do if you put a large load on that?

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How did you wire up the 12v fridge? You need to use beefy wire (maybe 6 to 10mm^2) or it will drop too much voltage and the fridge will fail to start when the batteries get a little bit low.

The batteries will only drop 0.2v or so, the rest is in the wiring.

Edited by nicknorman
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On 29/10/2017 at 15:25, Mike Todd said:

The fridge power draw will be intermittent - it does not need to be continuous once the required temperature is achieved. This means that readings will vary considerably and you will need patience to get a figure that you can rely on!

 

I think you might be confusing the transient start up current the OP is talking about, with the steady state current when cooling. The start up current might typically be ten times the steady state running current, hence the massive volt drop for half a second or so when starting.

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17 minutes ago, Mike the Boilerman said:

 

I think you might be confusing the transient start up current the OP is talking about, with the steady state current when cooling. The start up current might typically be ten times the steady state running current, hence the massive volt drop for half a second or so when starting.

That's what I was trying to say but some people might have misunderstood me ,been to the boat again this afternoon to check on fridge all working fine only set the fridge on number 1 fridge been on for about 15 hours friezer working good , and inside fridge nice and cool ,check battery power and still reading 12.7 so not using much power to run it ,I have got a solar panel on the roof glad I made the switch from 240 to 12 love it 

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26 minutes ago, Dave Bebb said:

That's what I was trying to say but some people might have misunderstood me ,been to the boat again this afternoon to check on fridge all working fine only set the fridge on number 1 fridge been on for about 15 hours friezer working good , and inside fridge nice and cool ,check battery power and still reading 12.7 so not using much power to run it ,I have got a solar panel on the roof glad I made the switch from 240 to 12 love it 

I am still worried about volt drop in your system, the meter shouldnt drop that much

 

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5 hours ago, ditchcrawler said:

I am still worried about volt drop in your system, the meter shouldnt drop that much

You’re right to be worried. The cabling somewhere (everywhere?) is way too small. My guess is that the fridge has been wired from a distribution board which was never cabled for such a heavy load instead of being wired direct from the batteries (or updating the dis board feed & fuse). 

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17 minutes ago, WotEver said:

You’re right to be worried. The cabling somewhere (everywhere?) is way too small. My guess is that the fridge has been wired from a distribution board which was never cabled for such a heavy load instead of being wired direct from the batteries (or updating the dis board feed & fuse). 

Same here, but Dave seems to be ignoring that point and is happy with his battery voltage

Edited by ditchcrawler
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If your existing cable to the fridge was sized just for the current at 240 volts, and you swapped to a 12 volt fridge and used the same cable to supply 12 volts to the fridge, that could explain the volts drop you are getting - especially on start-up.

 

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3 minutes ago, WotEver said:

Too much guessing. Until OP tells us how it’s wired (which appears unlikely) the only thing we know is that it’s been done poorly. 

Just a possible explanation based on what we have been told  (or perhaps not told) in support of your earlier suggestion about cables too small etc,

The OP will know if the fridges were just swapped and the new 12 volt one put in the same place and connected to the existing wiring. No need for knowledge of electrical theory or wiring practice to answer the question. 

 

 

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18 minutes ago, Horace42 said:

Just a possible explanation based on what we have been told  (or perhaps not told) in support of your earlier suggestion about cables too small etc,

 

 

 

Not really because the meter would have been at the other end of that cable

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Unless the voltmeter has been connected to the fridge end of the fridge supply cables, and that is highly unlikely, we can ignore suggestions that the voltdrop seen on the meter is caused by undersized cables running to the fridge itself. Voltdrop on those would not register on the voltmeter but would affect the fridge. I am not saying they are not undersized and suspect they probably are.

The voltdrop has to be between the batteries and wherever the meter is connected to so the most likely candidates are:

The fridge being connected to the distribution/fuse board with undersized cables between batteries and board with the voltmeter also connected there (as said),

A faulty domestic master switch - especially if it has a red plastic key.

Loose terminals/poor or dirty crimps between batteries are wherever the fridge wires are connected.

I also suspect the voltmeter because the fridge start up surge is transitory and my analogue meter had too much inertia to register it in any meaningful way and I susepct a digital meter porbably has a too slow sampling rate to get a consistent reading.

 

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On ‎29‎/‎10‎/‎2017 at 15:49, Mike the Boilerman said:

 

I think you might be confusing the transient start up current the OP is talking about, with the steady state current when cooling. The start up current might typically be ten times the steady state running current, hence the massive volt drop for half a second or so when starting.

Absolutely,

In my early days of not knowing that I didn’t know very much I wired a 65 watt 12v fridge into the boat via a 10 amp cigarette lighter socket.

No problem – 65 watts is only about 5.5 amps.

Short time later and a strong smell of burning. The cigarette lighter socket had totally melted into a big blob of plastic and all of the cables leading to it were all black and crispy. Whatever fuse was on that circuit had not blown and the power was still ‘on’ with the charred insulation still insulating the wires, it was all just getting hotter and hotter.

Had to re-wire the lot, but learnt, don’t try the fridge on a lighter socket again.

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6 minutes ago, ditchcrawler said:

The worrying bit is as his  voltage reads is OK when the is running or off he doesn't seem bothered that he may have a hidden problem, see

 

Well, you can only lead a horse and all that. We can probably expect a question when he is off shorepower/solar and ha snot run his engine for a while about why has my fridge stopped working and is beeping/flashing at me? Or why do my lights dim when the fridge starts up?

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5 hours ago, Tony Brooks said:

The fridge being connected to the distribution/fuse board with undersized cables between batteries and board with the voltmeter also connected there (as said),

That’s the likeliest candidate in my opinion. 

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20 hours ago, WotEver said:

Too much guessing. Until OP tells us how it’s wired (which appears unlikely) the only thing we know is that it’s been done poorly. 

Had a Marine electrical engineer to have a look at the fridge and control panel and he said it's just fine safe as houses , and he checked all the electrics as well all ok 

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