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12v fridge


Jo Green

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Hello,

 

Looking for some advice on a 12 v fridge. It was working last summer. I disconnected it from the 12v power over the winter but it now doesn't seem to be working. I didn't buy it, it came with my boat and it seems to be made by 'The Fridge People'.

 

When I connect it up to the power it makes a sound like it's starting up and the right light flashes on momentarily and then it dies. Every minute or so it tries again to power up but fails.

 

It is quite old but it was working perfectly when I disconnected it last autumn.

 

Do you think there's hope for it or should I get rid of it and look for a new fridge- big expense!

 

Thanks

 

Jo

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Try charging batteries fully first.

Yes. I'm not certain but I think my 12v fridge has a cut out which will not power up if the volts drop below 10.5v. The instantaneous draw when a fridge kicks in can be quite large and less than optimal batteries can give the fridge the wrong message.

 

Then again, I could be talking complete b.....ks!

 

George ex nb Alton retired

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Yes. I'm not certain but I think my 12v fridge has a cut out which will not power up if the volts drop below 10.5v. The instantaneous draw when a fridge kicks in can be quite large and less than optimal batteries can give the fridge the wrong message.

 

Then again, I could be talking complete b.....ks!

 

George ex nb Alton retired

 

Not B..ks, but I think in those circumstances the ops fridge should be flashing or beeping in a series of groups of 1 flash/beep. That is unless the battery is so flat there is even less that the 10.5 volts.

 

I agree the battery voltage is the first suspect. Try it again with the engine running and revving at about 1500rpm.

 

Could be a poor connection but then I do not understand why it does not keep flashing in groups of 1 until it tries to start again.

 

Jo - exactly how the fridge flashes or beeps is important because it provides a diagnostic code.

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Also check that you have at least 4 mm2 cables feeding the power to the fridge. The voltage drop across smaller cables is significant when the fridge tries to start. We had similar problem on an old fridge, which was cured by replacing thin cables. If it works when the engine is running, but misbehaves when only running on batteries then check the cables.

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Also check that you have at least 4 mm2 cables feeding the power to the fridge. The voltage drop across smaller cables is significant when the fridge tries to start. We had similar problem on an old fridge, which was cured by replacing thin cables. If it works when the engine is running, but misbehaves when only running on batteries then check the cables.

And that would be quite a short cable run at that.

 

I think I used 10mm2 cable on my run from engine room to galley area to be sure.

 

George ex nb Alton retired

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The rule of thumb is 1mm squared cable for 1metre run so 4mm cable would cope at 4 metres from batteries but

if it was working perfectly last year it cant be that.

 

Neil

Agreed on the fact that is was working OK last year.

 

Regarding cable size, I would appear to be overspecified, but I did use a cable calculator. Anyway, the job is done and I shouldn't have any volt drop problems!

 

George ex nb Alton retired

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Our fridge had what looked like speaker cable and we had similar problems. We changed the batteries and the cable to 10mm which was probably overspec for our little boat we subsequently found the batteries were OK so think the cable has made a major difference. It's been fine since.

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The fridge seems to work perfectly when the engine is running however once the engine is switched off it goes back to intermittently trying to power up. I am thinking this means I need thicker cable?

 

Thanks

 

 

Not necessarily. Given that it worked fine last year I'd say your batteries are too deeply discharged to run the fridge.

 

Try running the engine for a couple of hours to charge the batteries, THEN try the fridge again with the engine off.

 

Presumably when it was working last year conditions were the same? Was it engine-charged battery power you were on, or were you perhaps plugged into a shore line?

Finally you say you have new batteries. I'm wondering why you changed them. If the old ones seemed dead this could possibly be because your charging regime is not adequate for the power you draw, rather than them being genuinely knackered. If this is the case, the new ones will decline pretty rapidly too and eventually display the same symptoms.

Do you have a multi-meter? If so, measure the battery terminal voltage while the fridge is connected but failing to work, and post the result here...

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Not necessarily. Given that it worked fine last year I'd say your batteries are too deeply discharged to run the fridge.

 

Try running the engine for a couple of hours to charge the batteries, THEN try the fridge again with the engine off.

 

Presumably when it was working last year conditions were the same? Was it engine-charged battery power you were on, or were you perhaps plugged into a shore line?

Finally you say you have new batteries. I'm wondering why you changed them. If the old ones seemed dead this could possibly be because your charging regime is not adequate for the power you draw, rather than them being genuinely knackered. If this is the case, the new ones will decline pretty rapidly too and eventually display the same symptoms.

Do you have a multi-meter? If so, measure the battery terminal voltage while the fridge is connected but failing to work, and post the result here...

+1 for MtBs diagnosis! I need to run my engine for three hours every day to replace what I consume and eight hours once a week to maintain their capacity, both at much more than 'tickover'.

 

Alan

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Also check all terminations and connections are "bright and tight" no use having well charged batteries and correctly specified conductor size if you have corroded and or loose connections causing massive volt drop, this often happens with heaters, symptom heater will not start because of high initial draw from glow plug / pin but running the motor raises the voltage enough to start it. Just renewing or cleaning and tightening the connections restores starting OK with no engine running.

Edited by NMEA
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We have been through this pain...

 

Do the simple thing before you move on to the difficult thing. I was contemplating having to upgrade the supply cables which would have been majorly disruptive, when, following the advice from the good people on this forum I checked the batteries first...

 

Result - new batteries fitted - fridge works perfectly.

 

Bad batteries will run lots of things around the boat perfectly ok, thus giving the impression that they aren't the cause of the fridge failing. But 12v fridges are really sensitive and need best quality power.

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The fridge seems to work perfectly when the engine is running however once the engine is switched off it goes back to intermittently trying to power up. I am thinking this means I need thicker cable?

 

Thanks

 

Measuring the voltage being received by the fridge with a multimeter (whilst its compressor was running) would explain everything. As a rough guide though, if your batteries are at the back of the boat and fridge is anything further than midship, I would ensure that 10mm2 cable is used for both positive and negative cable runs - you can't have too thicker cable.

 

Note that having new batteries is no assurance if they are not fully charged, particularly regarding your comment that fridge works fine with engine running but otherwise not.

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The rule of thumb for 12v fridges is 1mm2 of cable cross section per metre between fridge and batts.

 

So a fridge 6m from the batts must have 6mm2 cable. Seems even some reputable boat builder don't follow this...

 

As mentioned duff fuseholders/isolators/connections can be a source of problems.

 

cheers, Pete.

~smpt~

Edited by smileypete
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The rule of thumb for 12v fridges is 1mm2 of cable cross section per metre between fridge and batts.

 

So a fridge 6m from the batts must have 6mm2 cable. Seems even some reputable boat builder don't follow this...

 

 

 

Red herring. The fridge worked fine last year, but not this year according to the OP.

 

Cables don't shrink in cross section as they get older, do they?!

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The rule of thumb for 12v fridges is 1mm2 of cable cross section per metre between fridge and batts.

 

So a fridge 6m from the batts must have 6mm2 cable. Seems even some reputable boat builder don't follow this...

 

As mentioned duff fuseholders/isolators/connections can be a source of problems.

 

cheers, Pete.

~smpt~

 

Just on this theme - Our Waeco 12v Fridge installation manual gives a graph of the MINIMUM cable size by distance from the batteries - remembering that the 'electrical' distance is twice the actual distance.

The fridge does not give a wattage, just an 'average power consumption' of 40 watts, but specifies that a 15 amp fuse should be fitted.

It does state :

Current Consumption :

1.8 Ah/h at +25°C ambient temperature,

2.1 Ah/h at +32°C ambient temperature,

both at +5°C interior temperature and -18°C in the freezer compartment

 

Translating the cable size graph into figures :

 

Distance 2 metres 4mm2

Distance 4 metres 8mm2

Distance 6 metres 10mm2

Distance 8 metres 12mm2

Distance 10 metres 14mm2

Edited by Alan de Enfield
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Red herring. The fridge worked fine last year, but not this year according to the OP.

 

Cables don't shrink in cross section as they get older, do they?!

 

Well, just because something works OK - for a time - doesn't mean it's installed to manufacturers instructions. :unsure:

 

Mayyyybe the cable is marginal but works OK with fresh or well charged batts.

 

In the absence of more info (such as batt voltage when failed start occurs), the best one can do is point to statistically likely causes, ie common problems. :)

 

cheers, Pete.

~smpt~

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