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New fridge on. Start up


Dave Bebb

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On 29/10/2017 at 22:26, 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). 

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 ?

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1 minute ago, 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 ?

You are very trusting! If such things “must be right” life on here would be very boring! But seriously, do check the voltage at the moment the fridge compressor starts up again. If it show 9.something again, then something is wrong and you will get problems down  the line when the batteries are less than well charged.

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1 hour ago, Dave Bebb said:

Had a Marine electrical engineer to have a look...

I don’t know what one of those is. 

1 hour ago, Dave Bebb said:

he said it's just fine safe as houses

If your reported voltage droop was correct then he’s wrong. 

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1 hour ago, 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 ?

I have a 12v panel which has 12 switched  breakers on it but my Shoreline fridge is not supplied from it. The fridge goes via a separate 40 amp fuse and 10mm cable direct to the positive and negative buss bars. The buss bars are fed from 70mm cable. The volt meter is fed from the buss bars. When the fridge starts I only see a momentary voltage drop of about 0.1 to 0.2v. I'd reckon if you look at the wiring on the back of you power panel you won't find any wire bigger than 2.5mm.

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1 hour ago, 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 ?

It’s there for powering a fridge. But that’s just a label, it says nothing about the wiring. What size cables feed the distribution panel? How long are they? What size cable goes from dis panel to fridge? How long are they?

2 minutes ago, Flyboy said:

I have a 12v panel which has 12 switched  breakers on it but my Shoreline fridge is not supplied from it. The fridge goes via a separate 40 amp fuse and 10mm cable direct to the positive and negative buss bars. The buss bars are fed from 70mm cable. The volt meter is fed from the buss bars. When the fridge starts I only see a momentary voltage drop of about 0.1 to 0.2v.

A perfect description of a good installation :)

Edited by WotEver
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1 hour ago, Dave Bebb said:

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 

I have no wish to play with semantics but I very much doubt he was an electrical engineer, marine or otherwise. If he was I doubt that you could afford him, he would be unlikely to want to get involved with such trivial tasks and his practical experience at this level is likely to be suspect. Hew as possibly a marine electrician but that covers a multitude of sins.

If he listened to what you told him and you told him much the same as your question here he would have needed a oscilloscope (possibly a storage scope) to see and measure the instantaneous voltdrop on fridge motor starting. Although such things are now available in multimeter sizes I very much doubt he had or used one. 

I doubt anyone here would expect any signs of burning or overheating cables to be present based on what you told us because the fridge running load is so small when compared with the start up load. Unless your man made lots of measurements with you starting and stopping the fridge I, and I suspect many others, would not expect him to find anything.

If you had called me out the first question I would have asked is "have you wired the fridge in strict adherence to Shoreline's instructions ?" Then " did you understand those instructions ?" If the answer to either question is "no" then it is very likely your boat's wiring has problems, exactly as you have been told several times on here.

 

Next question - "how did he check the electrics?" "What meters were used and how?" Then "what were the readings for the voltdrops he tested for?" He did test for voltdrops didn't he?

 

Quote from D Bebb "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 ?".

 

I am afraid that you exhibit a very naive view of boat systems, especially narrowboat systems. Remember it is perfectly possible that any boat was wired by a carpenter or welder rather than a n experienced electrician.  The control panel is there to allow you to control and hopefully to protect the electrical circuits. The fact its there does not mean the correct sized cables have been used - ESPECIALLY when you add a 12V fridge that has an absolutely huge start up current demand  without upgrading the cables from battery to fridge, via the control panel if that’s how it is wired. It is even possible that the fridge switch/circuit breaker is now not man enough for a 12V fridge although that should not normally give a voltdrop on a properly installed voltmeter.

 

Read and understand what Flyboy wrote about his 12V fridge installation and see how yours compares.

You have been asked questions about what the voltmeter does when you put a high domestic current load on the system. You have not answered but you have asserted that the system is right. I can see no evidence to support that assertion and plenty of evidence to suggest the chap you paid to look at it has missed something and that the system is far from right. maybe its best to ignore us on the forum and go with your assertions. Then if we are right and you do have a voltdrop problem don't come asking for help here, just pay your Marine Electrical Engineer to sort it. I am aware that he has been on the boat but the rest of us have not but something seems very wrong to me.

 

 

 

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3 hours ago, Dave Bebb said:

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 

My Shoreline fridge takes about 3amps when running. I have not measured the starting current draw but it could be as high as 30amps for 1 -2 seconds.  This is not enough to cause a 3.1V drop from a healthy 440Ahr battery.  If your "Marine Electrical Engineer" tells you that everything is Ok, then how did he explain to you the reason for the excessive  voltage drop?  

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4 minutes ago, Flyboy said:

My Shoreline fridge takes about 3amps when running. I have not measured the starting current draw but it could be as high as 30amps for 1 -2 seconds.  This is not enough to cause a 3.1V drop from a healthy 440Ahr battery.  If your "Marine Electrical Engineer" tells you that everything is Ok, then how did he explain to you the reason for the excessive  voltage drop?  

I think Danfoss suggested a transient 70 amps or more on start up, that's why they need such huge cables. I am not sure I have ever seen an actual figure quoted in print though.

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2 hours ago, Tony Brooks said:

I think Danfoss suggested a transient 70 amps or more on start up, that's why they need such huge cables. I am not sure I have ever seen an actual figure quoted in print though.

I don't think my Shoreline has a Danfoss compressor, it has a ACCGD30FDC.  I know they use a Danfoss BD35F as well.  The installation instructions are common to both but with different fuses called for.

For Danfoss BD 35F :- Fuse rated at 15 amp for 12v and 7.5 amp for 24v.  20 amp isolation switch close to fridge. Cable size :- 10mm, up to 10 metres to 12v fridge (20 metres for 24v fridge).  

For ACCGD30FDC :- Fuse rated at 30 amp for 12v and 15 amp for 24v,. Cable size :- 10mm, up to 6 metres to 12v fridge (12 metres for 24v fridge).

This suggests to me that the start up current is a lot less than 70 amps with the recommended fuses. No start up currents are quoted.

All figures quoted from manufacturers data. I've found more ACCGD30FDC  data here and it quotes A rotor locked current of 11amp on 12v

https://www.huayicompressor.es/phocadownload/user-manuals/user_manual_gd30fdc.pdf

http://files.danfoss.com/TechnicalInfo/Dila/06/bd_compressors_04-2007_pk100c802.pdf       BD 35F has a max consumption of 100W ( 8.33 Amp at 12v)  I assume this would be with the rotor locked.

Edited by Flyboy
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Dave Bebb   re your panel #36. The logic that the volts drop to the new fridge was due to the cables between the batteries and control panel being undersized seems flawed to me. I would have thought that the boat-builder would have sized the power cables to carry the whole load of all the external circuits connected to the panel. But I am not a boat builder - so what do I know!

But even with cables large enough, resistance could be due to corrosion in the battery lugs, that occurs slowly and goes unnoticed until something happens - like adding a heavy load.

There is high resistance somewhere in the circuit.  I still guess it is the cable from the panel to the fridge that is undersized.

Having said that, high resistance is misleading - in 12 volt boat wiring we are talking of problems caused by much less than one ohm, which is probably not accurately measurable if looking for it with a simple pocket multi-meters. 

 

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4 minutes ago, Horace42 said:

I would have thought that the boat-builder would have sized the power cables to carry the whole load of all the external circuits connected to the panel.

Would you? I wouldn’t. Particularly as the boat was fitted with a 230V fridge. 

5 minutes ago, Horace42 said:

I still guess it is the cable from the panel to the fridge that is undersized.

That wouldn’t show a voltage drop at the panel so no, it’s not that. (Although it’s probable that those cables are undersized too.)

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48 minutes ago, WotEver said:

Would you? I wouldn’t. Particularly as the boat was fitted with a 230V fridge. 

That wouldn’t show a voltage drop at the panel so no, it’s not that. (Although it’s probable that those cables are undersized too.)

The volt drop at the panel is a clue (made worse by the fridge?) - but it is the voltage at the fridge end of the cable that really matters.

Where the power cables feeding the panel and onwards circuits should have been sized for the designed load. Omitting a full sized cable for a 12v fridge is a bit petty. Perhaps I should say what do I know about boat-builders, rather than boat-building, especially of other people's boats.

 

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The wires from the back of the new 12 volt fridge are the same size as the wires running to the fridge from the control panel ,and the voltage drop is only for one second until the fridge starts up i can live with that 

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3 minutes ago, Dave Bebb said:

The wires from the back of the new 12 volt fridge are the same size as the wires running to the fridge from the control panel ,and the voltage drop is only for one second until the fridge starts up i can live with that 

Dave, you are still missing the point, the volt drop is between the panel and the batteries, just a short run, Yes the volt drop is only while the high current is flowing so you are not bothered about the low voltage. What you should be bothered about is what is causing that volt drop. It could be a poor crimp, a lose connection, a faulty master switch, corrosion on any connection or the battery terminals. The volt drop is just a symptom and its only present while the high current flows. 

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Just seen the photo.

I can categorically state that I had a reader with a new boat from the same builder who was having battery problems. The builder even replaced the batteries with new ones. I visited the boat and within seconds it was clear the problem was the fridge complaining about low voltage that both the builder and owner had taken at face value. A quick look behind the fridge showed it was undersized cables. I later learned that rather than run new thicker cables the  boater ran a parallel pair, used both and cured the problem - not sure about the fusing though!

I would not trust the wiring sizes from that builder. Budget builders have to get their lower prices from somewhere, I think I know one place that is likely to be skimped.

 

If the OP is running on a shore-power charger at the moment then as soon as he goes off grid he is likely to suffer fridge "flat battery" problems so the voltdrop needs sorting.

If the OP is engine/solar charging only then I have no idea why the fridge has not shut itself down with the battery voltage falling to 9 volts on start up. The fridge cut out is set to around 10.5 volts or higher.

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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 PS the next time I am on the nb I will take a video of what happens , I am not connected to shore line all the time only when I want to charge the battery's once a month .Just had a thought I am going to put a volt meter where I have connected to the fridge to the wires from the control panel and see if I get a voltage drop from there 

Edited by Dave Bebb
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