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Dave Bebb

New fridge on. Start up

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12 hours ago, WotEver said:

Of course it is but as best we know that’s not what was being measured. 

On 10/31/2017 at 17:00, Dave Bebb said:

Fergot to mention on the boats control panel with all the boat electrical things and all have what they work like horn lights there is about 20 and on is for fridge so must be right or why is it there ?

WotEver #47 is quite right. The only figure I know with confidence is the voltmeter on the panel and 13.4 volts is good. Even then that is subject to question. Is it when everything is switched on, or off, or on-charge (from a shore line - or fast revving engine.) These details are very important.

The general view is there is some unwanted resistance if the line (somewhere) and some tests under controlled conditions would help identify the source of the problem.

And being 'old-school' my best guess, and so easy to check and remedy, is the 'resistance' is at the battery lugs/clamps due to looseness or corrosion. 

But it is not a case of wiping the corrosion off the outside of the lugs - the clamps have to be removed and all contact surfaces must be cleaned by something abrasive like  sandpaper, wirewool etc. In fact it would not do any harm to do this anyway as a matter of routine maintenance.

If that does not fix it, then something more elusive is causing the problem and needs fixing. As ditchcrawler #48 says.

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Presumably because it has to be below the voltage for a set (short) time. The proof of the pudding etc will be when you are off grid and the fridge either starts up, or not. But that will be at an incredibly inconvenient time (Sod’s law!), so we are suggesting tis better to tackle the problem now, whilst it’s not a crisis!

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1 minute ago, Dave Bebb said:

Yes I understand what your saying ,why did the fridge not cut out when the voltage dropped down below the cut out  point very strange never thought of that one 

That is what I am unclear about. It is also why it would be very wise to test the voltdrop between each battery post (not the terminal) and the fridge on both positive and negative. As I said in my first post on this subject I have been unable to actually measure the voltdrop/voltage when the fridge starts and only get a small kick on the needle. The starting surge is only a few microseconds long so I find the fact that your measurement it perplexing and do wonder about the meter.

However that is only a sideline. What concerns me and a number of others who know is to do with the reliability of the fridge in longer term use,  especially when off a shoreline or some form of external generator. The basic symptoms you posted plus an informed assumption about where the voltmeter is connected still suggests undersized wiring , loose/dirty connections or a resistive switch between batteries and switch panel.

I think it would be wise to take some voltage measurements as the fridge start at the battery posts, input to the switch panel, output of the fridge switch and at the fridge but it could be difficult to actually get a reliable measurement unless the meter will store maximum/minimum values. It woudl at least give an idea about the reeliability of the boat's meter.

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1 hour ago, Tony Brooks said:

That is what I am unclear about. It is also why it would be very wise to test the voltdrop between each battery post (not the terminal) and the fridge on both positive and negative. As I said in my first post on this subject I have been unable to actually measure the voltdrop/voltage when the fridge starts and only get a small kick on the needle. The starting surge is only a few microseconds long so I find the fact that your measurement it perplexing and do wonder about the meter.

However that is only a sideline. What concerns me and a number of others who know is to do with the reliability of the fridge in longer term use,  especially when off a shoreline or some form of external generator. The basic symptoms you posted plus an informed assumption about where the voltmeter is connected still suggests undersized wiring , loose/dirty connections or a resistive switch between batteries and switch panel.

I think it would be wise to take some voltage measurements as the fridge start at the battery posts, input to the switch panel, output of the fridge switch and at the fridge but it could be difficult to actually get a reliable measurement unless the meter will store maximum/minimum values. It woudl at least give an idea about the reeliability of the boat's meter.

 

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Just remember that the likely faults are unlikely to cause burned wires so all may look OK but still be undersized.

is the voltmeter still dropping to 9v on fridge start up? If not it might just have been a single odd reading for some reason.

Edited by Tony Brooks

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1 hour ago, Dave Bebb said:

I know a marine electrician that has been working on boats all his life as its a bit to complicated for me 

Is that the same one who earlier commented that there was nothing wrong with your installation ?

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16 minutes ago, Alan de Enfield said:

Is that the same one who earlier commented that there was nothing wrong with your installation ?

I was wondering the same thing. 

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52 minutes ago, Tony Brooks said:

Just remember that the likely faults are unlikely to cause burned wires so all may look OK but still be undersized.

is the voltmeter still dropping to 9v on fridge start up? If not it might just have been a single odd reading for some reason.

 

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What I am going to do is pull all the  domestic battery's out and check for distilled water while there out and clean all the terminals then back put  vasoline on them ,and work back through the wiring to the fridge and check all connections for loose or corrosion  

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12 minutes ago, Dave Bebb said:

What I am going to do is pull all the  domestic battery's out and check for distilled water while there out and clean all the terminals then back put  vasoline on them ,and work back through the wiring to the fridge and check all connections for loose or corrosion  

Whilst doing that, also check the wiring size (NOT diameter) at each part of the run (battery to fuse / trip, and from trip / fuse to fridge)

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Just had a look what i need to wire from battery's to the new 12 volt fridge 10 mm2 hell thats think stuff  ,might get away with  8 mm2 i will have to see how fare away the fridge is away from battery's 

Edited by Dave Bebb

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2 minutes ago, Dave Bebb said:

Just had a look what i need to wire from battery's to the new 12 volt fridge 10 mm2 hell thats think stuff 

This is what we’ve been telling you since post #2. :)

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1 minute ago, WotEver said:

This is what we’ve been telling you since post #2. :)

But the voltmeter in the panel wouldn't have been measuring that volt drop, if it was a genuine voltage it measured then its a fault between the panel and the batteries.

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29 minutes ago, Dave Bebb said:

Just had a look what i need to wire from battery's to the new 12 volt fridge 10 mm2 hell thats think stuff  ,might get away with  8 mm2 i will have to see how fare away the fridge is away from battery's 

Image result for hallelujah

"Let there be light" & there was, and you could see for bloody miles.

Edited by Alan de Enfield

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On ‎01‎/‎11‎/‎2017 at 19:18, Glynn said:

I replaced our 12 volt freezer with a new 240 volt freezer, its on less often and for shorter periods and much better on electric consumption. The fridge will be next.

Me too. I binned the 12 volt fridge and again have mains, much cheaper to buy, cheaper to run and a better made fridge.

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56 minutes ago, ditchcrawler said:

But the voltmeter in the panel wouldn't have been measuring that volt drop, if it was a genuine voltage it measured then its a fault between the panel and the batteries.

Yes... because the panel wasn’t (isn’t) wired with 20mm(or larger) cable from the batts, which it would need to be if it was going to feed everything including the fridge. So the panel meter was showing the volt drop to the panel. Goodness knows what the final voltage at the fridge was. 

Edited by WotEver

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Just now, WotEver said:

Yes... because the panel wasn’t (isn’t) wired with 20mm2 cable from the batts, which it would need to be if it was going to feed everything including the fridge. So the panel meter was showing the volt drop to the panel. Goodness knows what the final voltage at the fridge was. 

But the OP doesn't seemed to be worried about that bit

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Just now, ditchcrawler said:

But the OP doesn't seemed to be worried about that bit

Oh, I think it’s sinking in slowly ;)

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11 hours ago, Dave Bebb said:

Just had a look what i need to wire from battery's to the new 12 volt fridge 10 mm2 hell thats think stuff  ,might get away with  8 mm2 i will have to see how fare away the fridge is away from battery's 

As written there is still room for problems.

1. You measure the distance off ridge from batteries FIRST.

2. Once you have that distance you use a cable that has 1 sq mm conductor cross sectional area (NOT CABLE DIAMETER) per meter of run. Use the same size for both cables (that is 0.5 sq mm ccsa for each meter of total out and back run.

3. With 12V compressor fridges you NEVER try to skimp on cable size. Many years of experience tells most of those who replied trying to do so always ends in problems.

Edited by Tony Brooks

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1 hour ago, Tony Brooks said:

You measure the distance off ridge from batteries FIRST.

And, if you're still going to go via the panel (I wouldn't, as I'm not sure that switch will last) remember that the distance includes batteries to panel, plus panel to fridge. Whatever size you end up with should be ADDED to the existing size going from batteries to panel and replace those with that. So for instance, if your distance calculation comes out with 10mm2 for the fridge, and the panel is currently wired with 6mm2 from batteries to panel, you need to replaced those 6mm2 cables with something bigger than (10+6) 16mm2.

Edited by WotEver
formatting

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32 minutes ago, WotEver said:

And, if you're still going to go via the panel (I wouldn't, as I'm not sure that switch will last) remember that the distance includes batteries to panel, plus panel to fridge. Whatever size you end up with should be ADDED to the existing size going from batteries to panel and replace those with that. So for instance, if your distance calculation comes out with 10mm2 for the fridge, and the panel is currently wired with 6mm2 from batteries to panel, you need to replaced those 6mm2 cables with something bigger than (10+6) 16mm2.

The switch on the OP's panel is totally inadequate for a compressor fridge. It probably will have 1/4" push on connectors which are not suitable for 10mm cable and will be part of the problem with voltage drop at high currents.

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56 minutes ago, Flyboy said:

The switch on the OP's panel is totally inadequate for a compressor fridge. It probably will have 1/4" push on connectors which are not suitable for 10mm cable and will be part of the problem with voltage drop at high currents.

But that still doesnt account for the dip in voltage at the volt meter if it was a genuine reading.

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44 minutes ago, ditchcrawler said:

But that still doesnt account for the dip in voltage at the volt meter if it was a genuine reading.

I think Flyboy was more picking up on my suggestion to not use the switch. 

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