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Hi,

12v shoreline and the light was blinking, just one blink (low voltage I think?).

Checked the batteries and they were at 12.64 anyone know what an acceptable voltage is at the fridge.

The really odd thing is I turned the inverter off (not on shoreline ) and the light stopped and the compressor fired up.

This is the first time out of the marina for 12 months and the batteries have been on charge via the inverter.  

I have not yet separated the batteries to test individually.

12.64 after a 7 hour run and then engine off for 6 hours.

Any thoughts/suggestions more than gratefully received.

Pete

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Where did you check the battery voltage ? (at the batteries or at the fridge ?)

 

I bet if you check the voltage going into the fridge you'll find it probably 1v less than at the battery.

 

You obviously have a volt drop problem which is shown by the fact that you are dragging the battery down with the inverter so that by the time the reduced voltage gets to the fridge it is below what the fridge will accept.

 

Start the engine and you'll be getting 14+ volts at the battery, and probably ~13v at the fridge, the fridge will run perfectly with or without the inverter on.

 

The fact you have been living in the marina with the batteries permanently on charge has masked the problem that your fridge is wired in with the wrong cable.

I had exactly the same problem - the answer is to re-wire the fridge supply using the correct sized cable - this will dpend on the distance of the fridge from the battery and should be measured taking into account out & return (so twice the distance)

 

Your manual will tell you what size cable to use, mine shows :

 

 

For example if the fridge is 7mts from the battery the distance out & return is 14mts, 

14 metres require cable size A MINIMUM of 10mm2

Screenshot (454).png

Edited by Alan de Enfield
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I agree it sounds like low voltage but I don't think ding Alan's test will give you a different  voltage. It is the motor starting surge that pulls the voltage down for a few microseconds, and that is over so quickly a typical voltmeter will not sample fast enough to read it reliably. Its over too fast.

 

First check the cable size. Most manufacturers recommend 1sq mm CCSA for each meter between fridge and battery, using the same size for both pos and neg. Never skimp on electric fridge cable size.

 

Also check for  bad connections and faulty switches and fuses/circuit breakers on the fridge circuit, including the domestic master switch. Especially if it has a removable plastic key. Try putting both master switch cables on one terminal as a temporary test.

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I agree that undersize cables or dodgy connections are the most likely causes.

 

Howe er, if you have eliminated all of these then try switching the fridge on and off a few times.

 

Lead acid batteries kept on long term float charge can often suffer from "coup de fouet", a phenonema where the voltage collapses when they are put on load. However, after a couple of attempts at supplying load they quickly recover and then behave normally.

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8 hours ago, Tony Brooks said:

I agree it sounds like low voltage but I don't think ding Alan's test will give you a different  voltage.

 

He says the fridge is running if he turns the inverter off. So he can test it running.

When mine was running continuously, (but not cooling), I tested the voltage at the fridge and found it was about 1.5v down on battery voltage.

The fridge would perform perfectly all day whilst running the engine. even the ice box would freeze up. Ovenight the ice box would melt, all the ice cream would end up in puddles in the bottom of the fridge and all the stuff in the fridge would be wet.

 

Running some 8.5mm2 wires from the bus-bar at the helm down thru the floor into the galley (about a 2-3 metre run) solved the problem instantly.

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Thank you all

With fridge  on but the compressor not running 12.71v when the compressor kicks in 12.42v (that is this afternoon after around a 6 hour run).

 

It is an old fridge, to my certain knowledge 12years, probably as old as the boat 16years. 

 

Really dumb question I am sure how do you correctly measure cable size. I have a hole gauge for drill bits, do I stick the copper core through there?

 

Pete

 

 

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1 minute ago, baldlimey said:

Thank you all

With fridge  on but the compressor not running 12.71v when the compressor kicks in 12.42v (that is this afternoon after around a 6 hour run).

 

It is an old fridge, to my certain knowledge 12years, probably as old as the boat 16years. 

 

Really dumb question I am sure how do you correctly measure cable size. I have a hole gauge for drill bits, do I stick the copper core through there?

 

Pete

 

 

If all is good with the engine running, but you get one flash when the engine is not running, it is low v9ltage at the fridge. If it has previously been working OK without the engine running then you would thing the wire is big enough, so focus on and bad connections.  I had a similar issue develop, and when I started investigation I opened up the isolators switch that is in a cupboard next to the fridge, and the wires just fell out of the back of it.  In addition there was a couple of meters of additional length of wire for both the pos and neg wires under the cupboard, which the builders had not trimmed.  I trimmed the wires and connected back securely and all has been good for years now.

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9 minutes ago, baldlimey said:

Really dumb question I am sure how do you correctly measure cable size. I have a hole gauge for drill bits, do I stick the copper core through there?

 

It is normall / usually / some times marked on the ouside of the cable and will be in the format of either Xmm2 (squared) or something like 32/0.20

 

The latter denotes that there are 32 strands of copper each being 0.2mm diameter, take the cross sectional area of one strand (Pie R2) and multiply it by the number of strands and you have the cable size.

 

16/0.2 = 0.5mm2

24/0.2 = 0.75mm2

32/0.2 = 1mm2

 

30/0.25mm = 1.5mms

28/0.3mm  = 2mm2

30.0.25mm = 2.5mm2

 

56/0.3 = 4mm2

 

And so on.

 

You need to know the total cross sectional area of the copper, NOT the overall diameter of the copper, or the insulation.

 

Edited by Alan de Enfield
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9 minutes ago, Machpoint005 said:

 

Measure its diameter and multiply by pi (3.14 is close enough). The cable size is actually in mm² but the square (²) is often omitted -- incorrectly, and a huge cause of confusion. 

 

 

Pi x D is the circumference of the cable not the CSA. (Cross Sectional Area)

A huge cause of confusion !

 

Pi x R² is CSA

 

By doing that (assuming you mean to measure ONLY the copper (which you didn't specify)  you are building in more than a 10% error due to the intertices between each strand.

 

 

Edited by Alan de Enfield
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7 minutes ago, Alan de Enfield said:

 

 

Assuming you mean to meaasure the copper only that will give figures at least 10% greater than the true figure due to all of the intertices between each strand.

If you mean measure over the insulation then it could be out by 200%-600% depending on insulation thickness

 

For clarity, no, I don't.

I was going to mention the "it's printed on the cable sleeve" myself, but apart from the fact that it might not be, it's not all that likely that the visible section of cable it the bit with the printing on it. 

 

If you want to take the spaces between the individual strands of copper into account for a multi-strand cable, simply use a value of 3.11 for pi (that's pi times the packing density).

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Just now, Machpoint005 said:

 

For clarity, no, I don't.

I was going to mention the "it's printed on the cable sleeve" myself, but apart from the fact that it might not be, it's not all that likely that the visible section of cable it the bit with the printing on it. 

 

If you want to take the spaces between the individual strands of copper into account for a multi-strand cable, simply use a value of 3.46 for pi (that's pi divided by the packing density).

 

And your nonsense suggestion to use Pi x D as the cross sectional area ?

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6 minutes ago, baldlimey said:

Thank you again all

At least I not feel totally stupid after seeing the answers on how to measure the cable.

 

I will get the fridge out again and open the isolator switch.

 

Pete

 

The answer is that unless you have an accurate metric micrometer or vernier caliper, it's almost impossible.  if you have one of those you can count the number of strands, measure the strand diameter and calculate that strands cross-sectional area Multiply that by the number of strands. There are/have been two standards for the insulation, with one being much thicker than the other, so measuring the cable OD is no help. I suspect the insulation thickness might vary by manufacturer as well. However, in the cable size you are likely to find for a fridge, I suspect the strand diameter will be 0.30mm. So count the strands and calculate the conductor cross-sectional area (CCSA)

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I think that the batteries are goosed.   12.64v after a 7 hour run suggests not fully charged by a long way or duff batteries. You will always get some volt drop to a fridge, the starting current is quite high and if the battery voltage is not optimal it won't kick in.

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I think it was the  isolator switch it was very manky on the contacts so I have cleaned it back to bright metal and hit it with electrical contact cleaner and so far so good, inverter on and no flashing this morning.

 

Tracy the 12.64 was after sitting for 6 hours after a 7 hour run, does that still imply shot batteries.

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25 minutes ago, baldlimey said:

I think it was the  isolator switch it was very manky on the contacts so I have cleaned it back to bright metal and hit it with electrical contact cleaner and so far so good, inverter on and no flashing this morning.

 

Tracy the 12.64 was after sitting for 6 hours after a 7 hour run, does that still imply shot batteries.

 

In my view no - it implies that your batteries still have sufficient capacity and you had them fully charged the previous evening.

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1 hour ago, baldlimey said:

I think it was the  isolator switch it was very manky on the contacts so I have cleaned it back to bright metal and hit it with electrical contact cleaner and so far so good, inverter on and no flashing this morning.

 

Tracy the 12.64 was after sitting for 6 hours after a 7 hour run, does that still imply shot batteries.

I missed the bit about them sitting off charge for 6 hours, they would seem to be in good order if that is so.

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