Electrician in Worcester area required

[Iain_S]

The negative supply for the BMV probably comes from the shunt, but I'd expect a separate positive supply to a battery terminal. (My equivalent meter is certqinly connected up like this)

 

Another thought is : where does the engine battey negative go to? It should be to the "boat" side of the shunt, but is quite often found connected to leisure negative, which means that very little of the charging current from the alternator passes through the shunt, which might explain the "---"  on the SOC display.

[WotEver]

16 minutes ago, Iain_S said:

... which might explain the "---"  on the SOC display.

That’s actually probably the most useful thing for a BMV’s SoC display to show... at least it’s not lying

[Tony Brooks]

3 hours ago, celiaken said:

If, despite all the exellent help from posts on here, you are still having problems, I have had a couple of visits from Paul at Loom-Tech who is operational in the Worcester area. I am one of his very satisfied customers and have no hesitation in recommending him.

Now, I wonder who the company was the thought they knew better than Danfos (the 12V compressor maker) and insisted their cable size calculation were correct. In the end a reader with a new boat had to get Shoreline to move the jumper lead on the fridge control box to cut out at a lower voltage than normal. I had an email from Danfos stating the cable was undersized.

 

Fit undersized fridge cables at your peril, the fridge may work  with well charged batteries but refuse as they get flatter. The cable conductor (not including the insulation) should have 1 sq mm of cross sectional area for each metre between batteries and fridge so that is 0.5sq mm for each meter of total out and back run. The cables on my fridge just over half way up a 55ft boat were about the size of car starter cables and never had a low voltage lock out even with fairly flat batteries.

 

Once you get the BVM sorted think about rewiring the fridge using the manufacturer's recommended cable size.

[Eeyore]

 

It might not be a "ball of corrosion"; but that all (including the ones on the hull mounted stud) needs disconnecting and cleaning up with a "scotch pad". The washers on the main terminals appear to be steel; but should be brass or stainless steel. Remove the RJxx plug and the red lead, then the circuit board can be removed by removing the two mounting screws. The contact pads and connectors on the circuit board are best cleaned using a contact cleaning spray; you can also clean the plug using the same spray. Might not cure the problem; but certainly won't do any harm.

[nbBox12]

So I managed to test the fridge with the multimeter this morning. With the mains disconnected, inverter off, and the lights and fridge running just on batteries, the voltage reading from the back of the fridge said 12.6v.

 

I've included a picture of the fridge wires below. As you can see, they're pretty thin - about 1.5mm I reckon, but the compressor still feels warm, and the fridge is still buzzing like it normally would. But even with it turned up to maximum it's barely even cold inside, whereas it would normally be totally iced up along the back wall.

 

I also noted that the main Voltage Reading off the batteries at the time was 12.6v (whereas the BMV said 1.96v).

 

So I'm guessing I maybe do have 2 separate issues, with both BMV and fridge playing up at the same time. Still not totally convinced though.

 

Edited March 4, 2020 by nbBox12

[ditchcrawler]

14 minutes ago, nbBox12 said:

So I managed to test the fridge with the multimeter this morning. With the mains disconnected, inverter off, and the lights and fridge running just on batteries, the voltage reading from the back of the fridge said 12.6v.

 

I've included a picture of the fridge wires below. As you can see, they're pretty thin - about 1.5mm I reckon, but the compressor still feels warm, and the fridge is still buzzing like it normally would. But even with it turned up to maximum it's barely even cold inside, whereas it would normally be totally iced up along the back wall.

 

I also noted that the main Voltage Reading off the batteries at the time was 12.6v (whereas the BMV said 1.96v).

 

So I'm guessing I maybe do have 2 separate issues, with both BMV and fridge playing up at the same time. Still not totally convinced though.

 

You did manage to read that voltage with the compressor actually running didn't you? I cant see where you would get a meter probe in to do that

[nbBox12]

No, I couldn't do that. The plastic sheaths completely cover the connectors, so I had to unplug the wires to check the voltage that was coming through them. 

 

[ditchcrawler]

3 minutes ago, nbBox12 said:

No, I couldn't do that. The plastic sheaths completely cover the connectors, so I had to unplug the wires to check the voltage that was coming through them. 

 

In that case the reading is pointless, it must be made under load so you can see how much volt drop you have, You may need to pull the connector back a bit so you can get your probe on there or even push a needle through the insulation or the wire so you can get a reading

[nbBox12]

OK, thanks for the info. I'll give it another go then, and see what it says under load if I can.

 

[Alan de Enfield]

13 minutes ago, nbBox12 said:

No, I couldn't do that. The plastic sheaths completely cover the connectors, so I had to unplug the wires to check the voltage that was coming through them. 

 

If there is no load then there is no volt drop. It is the 'load' that pulls down the voltage.

 

Red Pre-insulated terminals are designed for 0.5mm² to 1.5mm²  so at best the cable size is 1.5mm2

 

As mentioned above you need to work on  1mm2 of copper (not diameter of the wire) per metre of cable run to the battery (remembering that the leccy has to go in a circuit, from the battery to the fridge to the battery)

[Graham Davis]

31 minutes ago, nbBox12 said:

OK, thanks for the info. I'll give it another go then, and see what it says under load if I can.

 

Generally you can stick a narrow probe between the plastic of the connector and the wire, and that will touch the crimp around the wire.

[WotEver]

How misleading reports can be...

2 hours ago, nbBox12 said:

fridge running just on batteries, the voltage reading from the back of the fridge said 12.6v

Followed a couple of posts later by...

1 hour ago, nbBox12 said:

I had to unplug the wires to check the voltage...

So the fridge wasn’t running. 
 

It couldn’t have been running anyway with the voltage at the fridge being identical to battery voltage. 

[Alan de Enfield]

3 minutes ago, WotEver said:

How misleading reports can be...

Followed a couple of posts later by...

So the fridge wasn’t running. 
 

It couldn’t have been running anyway with the voltage at the fridge being identical to battery voltage. 

 

It does make diagnosis difficult when the questioner doesn't have an understanding of the subject (which is why he asked the question in the first place)

The problem is that when questions are asked to try and identify the problem the OP often takes offence and thinks that 'he / she is being bullied' or 'disbelieved'.

 

This thread is a good example of why follow up questions should be answered.

[nbBox12]

Yes, thanks for the clarification. I'm a compete noob at this so please forgive my misunderstandings of some of the suggestions and terminologies being used and so on. That's why I originally asked for an electrician!

 

Edited March 4, 2020 by nbBox12

[ditchcrawler]

Just now, nbBox12 said:

Yes, thanks for the clarification. I'm a compete noob at this so please forgive my misunderstandings of some of the suggestions and terminologies used and so on.

Yes, thanks for the clarification. I'm a compete noob at this so please forgive my misunderstandings of some of the suggestions and terminologies used and so on.

Thats, fine. Its just some people get upset when we keep asking them questions on how they are testing things, you are not one of those people so just keep plodding away at it and tell us exactly what you are doing

 

[Alan de Enfield]

3 minutes ago, nbBox12 said:

Yes, thanks for the clarification. I'm a compete noob at this so please forgive my misunderstandings of some of the suggestions and terminologies used and so on. That's why I originally asked for an electrician!

 

It is not a problem (as Ditchcrawler explains)

 

It is far better to try and learn how to do it yourself and get a working relationship with the 'guts of your boat', that way when you are out in the wilds and no help forthcoming you may be able to bodge something up and limp to civilisation.

 

Keep asking and you'll keep getting answers.

 

Learning to produce, manage and use electricity on a boat is one of the hardest thigs to get your head around - start with remembering :

1) that as 12v battery is virtually flat at 12 volts and full at 12.8 / 12.9 volts.

2) you need to put back into the battery 1.25 x the amount you have used.

3) a battery will take upwards of 10 hours to recharge from 50% state of charge to 99.99% state of charge (irrespective of how big your battery charger is)

[WotEver]

2 hours ago, Alan de Enfield said:

This thread is a good example of why follow up questions should be answered.

Yep absolutely. Fortunately the OP hasn’t taken offence (not even the garden gate)

[WotEver]

1 hour ago, Alan de Enfield said:

It is far better to try and learn how to do it yourself and get a working relationship with the 'guts of your boat', that way when you are out in the wilds and no help forthcoming you may be able to bodge something up and limp to civilisation.

Agreed 100%. You don’t need to become an expert but it will make your life far more enjoyable if you have a little more than a passing familiarity of all of your boat’s systems.

[TheBiscuits]

5 minutes ago, WotEver said:

Yep absolutely. Fortunately the OP hasn’t taken offence (not even the garden gate)

Yes, he is quite chilled about it, unlike his fridge. 

 

[WotEver]

A good example might be: When you switch a light on and it works, ‘why’ does it work?

[nbBox12]

I managed to read the voltage off the running fridge this morning, and it gave a reading of 12.2v. At the time, the voltage reading directly off the batteries was 12.8v. I'm guessing this is just outside the generally accepted voltage drop of 3-4%?

 

 

[Alan de Enfield]

3 minutes ago, nbBox12 said:

I managed to read the voltage off the running fridge this morning, and it gave a reading of 12.2v. At the time, the voltage reading directly off the batteries was 12.8v. I'm guessing this is just outside the generally accepted voltage drop of 3-4%?

 

 

Was that with the engine running or the battery charger on ?

 

Mine was fine until there was nothing charging the battery (no solar, no engine and no battery charger), for example overnight - when the ice box would de-frost and everything get 'wet', soggy and 'warm'.

Edited March 6, 2020 by Alan de Enfield

[WotEver]

20 minutes ago, nbBox12 said:

I managed to read the voltage off the running fridge this morning, and it gave a reading of 12.2v. At the time, the voltage reading directly off the batteries was 12.8v. I'm guessing this is just outside the generally accepted voltage drop of 3-4%?

Yes, 5% is well outside the tolerance for a fridge. If it’s dropping 0.6V just running then with 10 times the current when it’s starting up you’d be dropping 6V. 

[nbBox12]

33 minutes ago, Alan de Enfield said:

Was that with the engine running or the battery charger on ?

 

Mine was fine until there was nothing charging the battery (no solar, no engine and no battery charger), for example overnight - when the ice box would de-frost and everything get 'wet', soggy and 'warm'.

That was without the engine running, battery charger off, and plug disconnected from the shoreline.

[Tony Brooks]

1 hour ago, nbBox12 said:

I managed to read the voltage off the running fridge this morning, and it gave a reading of 12.2v. At the time, the voltage reading directly off the batteries was 12.8v. I'm guessing this is just outside the generally accepted voltage drop of 3-4%?

 

 

To emphasize:- forget any generally accepted volt drops as far as 12V DC is concerned. there is absolutely NO  "generally accepted" voltdrop for such fridges because its the very high current but transitory starting surge that causes the problems. Any equipment a normal boater has is incapable of measuring that transitory current surge or the voltdrop it causes. This is why the compressor manufacturer specifies the cable size required and not a voltdrop. Deviate from that recommendation is very likely to cause you problems. Because of the starting surge and the cable size needed I would suggest any fridge motor running voltdrop should be not much above zero volts so your voltdrop just confirms badly undersized cables.