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eggpie

Shoreline fridge trips 15a fuse

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What would make a 12v fridge trip a 15a fuse? Yes, another fridge thread. It must be summer. 

 

Essentially, my neighbours fridge has been repeatedly tripping the 15a breaker since yesterday. It runs for up to a minute, then blows the breaker, so at least the compressor definitely starts.  I've temporarily replaced the breaker with a 15a blade fuse,which doesn't blow,  but it definitely gets warm. My clamp ammeter suggests its drawing around 20a when running (may not be entirely accurate due to survival of 15a fuse). I've checked the connections from the isolators forwards, and remade all of them (except for some previous soldered ones where the 16mm2 cable joins a short piece of 6mm2 cable behind the fridge). Could those be creating resistance? 

 

Shoreline told me earlier that the danfoss compressors never draw above 13a when theyre running, which might be enough to make the blade fuse warm? Also there are no flashing lights on the fridge to suggest faults, and I've tested it with the engine running at >13v, and there's still no obvious voltage drop at the fridge due to wiring.

 

Any suggestions what I'd try next?

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3 minutes ago, eggpie said:

Shoreline told me earlier that the danfoss compressors never draw above 13a when theyre running,

Ask them about startup surge currents and they will go very quiet ...

 

Also, check that the radiator grill is cleaned off and the fan(s) are cleaned.  Just dusting them with a vacuum cleaner or a dry paintbrush is enough.

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38 minutes ago, eggpie said:

What would make a 12v fridge trip a 15a fuse?

That is only 180 watts.

 

I have read that a 75 watt fridge can pull over 600w on start up - I have no idea if that is an estimate or an actual figure.

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This is in no way meant to be advice, but I run a Shoreline 12v fridge. It is an odd setup, running constantly for 5 years plus. In it, I have a 30 amp fuse. The setup consists of a computer PSU of 650 watts, so, not massive. It is rated at around 32 amps. Honestly, I've had no problems, using the 30 amp fuse. Yours, at 15 amp is not enough, imho.  

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1 hour ago, eggpie said:

Shoreline told me earlier that the danfoss compressors never draw above 13a when theyre running, which might be enough to make the blade fuse warm? 

Yes, 13A would definitely make a 15A fuse warm, and would trip a tired 15A mcb 

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My 12V Shoreline fridge draws about three amps when running (for the compressor - no fan).

If you fride is starting and running for a minute, it is not the startup load that is tripping it, so as Mike says, suspect the breaker.  Doesn't explain why you are measuring 15 - 20 amps though.

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MCBs derate with use. The closer they are run to break current, or the more often they are tripped, the faster the derating. We knew it as the breaker "getting soft"

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8 hours ago, eggpie said:

I've checked the connections from the isolators forwards, and remade all of them (except for some previous soldered ones where the 16mm2 cable joins a short piece of 6mm2 cable behind the fridge). Could those be creating resistance? 

Anything such as a bad connection which adds resistance into the circuit will reduce the current draw not increase it. Both my Shoreline fridge and freezer each run on a 15A breaker without problems.

My money's on a tired breaker as stated earlier.

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if after starting and running for several minutes and the fuse is warm and coupled with the current measurement of 20A after one minute (so not start-up surge) then something is wrong.

 

Does the fridge fuse supply ONLY the fridge or is something else also running from that circuit?  Turn the fridge off at the fridge and measure the current at the fuse.  Let us know what you get

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It's a dc breaker, attached to an old switch panel. I've given up on the breaker. What still concerns me is the warm 15a blade fuse, and the high reading on the clamp meter. 

 

My shoreline draws somewhere around 5a when running, and the 15a fuse is definitely not warm. Neighbour says his was working perfectly, but his definition and mine may be different.

 

I'll check the fan and grill for dust  though.

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8 minutes ago, Chewbacka said:

.....the current measurement of 20A after one minute (so not start-up surge) then something is wrong.

This ^^^^

 

My Shoreline fridge draws around 3 Amps once running and it's 15 amp fuse copes with the startup surge - I suspect this is the same in most of our 12v fridge  installations.  If this fridge is similar and drawing 20 Amps in the steady state there's a fault. Changing breakers or fuses may well mask the symptoms but it won't do anything to fix the cause. 

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1 hour ago, Stephen Jeavons said:

Anything such as a bad connection which adds resistance into the circuit will reduce the current draw not increase it. Both my Shoreline fridge and freezer each run on a 15A breaker without problems.

My money's on a tired breaker as stated earlier.

Are you sure about that? Into a resistive load I agree but a motor tends to be a speed dependant inductive load so the faster it runs the lower its effective resistance. That may well give a higher current flow at lower voltages. Water pump motors have been known to burn out with undersized wiring. Not sure about the Danfoss setup though.

 

Still does not explain that 20 amps runnng though.

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18 minutes ago, Chewbacka said:

 

Does the fridge fuse supply ONLY the fridge or is something else also running from that circuit?  Turn the fridge off at the fridge and measure the current at the fuse.  Let us know what you get

 

Its a dedicated fridge circuit. I traced the cables to look for stray connections and there's nothing else. If I turn the fridge off there's no current. This makes me suspect the fridge..

 

 

The 20a was measured with a clamp ammeter and may not be exact. Its not enough to blow a 15a blade fuse. I probably need to make a more accurate measurement

Edited by eggpie

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I suspect the fridge as well.  However one final check is to measure the voltage across the supply cables at the fridge, if it is reasonable (it will be down a bit because of cable losses at 20A) then you can forget about dodgy connections etc.

I have never had a 12V fridge but my understanding is that they alarm or switch off if the supply voltage is low, so if you did have a bad connection in the circuit dropping the voltage enough to cause the fridge to draw 20A then I would have expected the low volt alarm (assuming it has one) would activate.  As you have not mentioned one activating and assuming the fridge has one, then I expect the supply voltage to be ok.

 

If the supply voltage at the fridge is within spec and it is drawing 20A something is wrong with the fridge and a call to their tech people would be my next job.

Edited by Chewbacka

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Yep. The breaker was tripping long before the voltage dropped enough to set the !ow voltage light off. There's still around 12.5v with it running, so it has to be the fridge.

 

Shoreline said they'd only ever seen a handful of compressor failures. They were more evasive when I asked about the controller though.

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1 hour ago, Stephen Jeavons said:

Anything such as a bad connection which adds resistance into the circuit will reduce the current draw not increase it. Both my Shoreline fridge and freezer each run on a 15A breaker without problems.

My money's on a tired breaker as stated earlier.

My understanding is with AC motors the speed is not voltage dependant. They will strive for synchronis speed regardless. The load will be dependant on speed. So depriving a synchronous motor of voltage will just up its demand for current to acheive its rated speed, typically 1440rpm for a 4 pole motor on 50 htz.  Inverter variable speed motors is a different ball game.

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1 minute ago, eggpie said:

Yep. The breaker was tripping long before the voltage dropped enough to set the !ow voltage light off. There's still around 12.5v with it running, so it has to be the fridge.

 

Shoreline said they'd only ever seen a handful of compressor failures. They were more evasive when I asked about the controller though.

 things to bear in mind - 

1) At 12.5v and 20A the fridge is 'consuming 250W which is going to be mostly heat, so something is going to get very hot, which might help you to identify the faulty part.  Don't burn your fingers looking for it.

2)  I would not run it for long as if whatever is faulty is small or not well cooled it might catch fire

3)  If running on batteries, the batteries wont last long supplying a constant 20A

3 minutes ago, DandV said:

My understanding is with AC motors the speed is not voltage dependant. They will strive for synchronis speed regardless. The load will be dependant on speed. So depriving a synchronous motor of voltage will just up its demand for current to acheive its rated speed, typically 1440rpm for a 4 pole motor on 50 htz.  Inverter variable speed motors is a different ball game.

This is an old 12V fridge, so probably a DC motor, though I could be wrong

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8 minutes ago, Chewbacka said:

 things to bear in mind - 

1) At 12.5v and 20A the fridge is 'consuming 250W which is going to be mostly heat, so something is going to get very hot, which might help you to identify the faulty part.  Don't burn your fingers looking for it.

2)  I would not run it for long as if whatever is faulty is small or not well cooled it might catch fire

3)  If running on batteries, the batteries wont last long supplying a constant 20A

This is an old 12V fridge, so probably a DC motor, though I could be wrong

Not an absorption fridge? No motor just a 3 way heater, 12v 230v or gas flame

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8 minutes ago, DandV said:

Not an absorption fridge? No motor just a 3 way heater, 12v 230v or gas flame

The op did say in post #1 "the compressor definitely starts"

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25 minutes ago, DandV said:

My understanding is with AC motors the speed is not voltage dependant. They will strive for synchronis speed regardless. The load will be dependant on speed. So depriving a synchronous motor of voltage will just up its demand for current to acheive its rated speed, typically 1440rpm for a 4 pole motor on 50 htz.  Inverter variable speed motors is a different ball game.

This is why I said I am not sure about the Danfoss units. Definitely 12V DC into the control box but what happens in there and what is sent to the motor is open to question. It might be AC but the number of motor wires makes me suspect its more like a stepper motor, especially as it seems to have settings for motor speed.

 

I would love to get some definitive info on how the Danfoss units work.

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11 minutes ago, Tony Brooks said:

This is why I said I am not sure about the Danfoss units. Definitely 12V DC into the control box but what happens in there and what is sent to the motor is open to question. It might be AC but the number of motor wires makes me suspect its more like a stepper motor, especially as it seems to have settings for motor speed.

 

I would love to get some definitive info on how the Danfoss units work.

Look up Danfoss on the net and you will find it is a 3 winding  motor, the control box produces the 3 voltage outputs in sequence to run the motor, not like a conventional motor with run and start windings. Nor is it a DC brush motor.

 I suspect the control box.

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1 minute ago, Boater Sam said:

Look up Danfoss on the net and you will find it is a 3 winding  motor, the control box produces the 3 voltage outputs in sequence to run the motor, not like a conventional motor with run and start windings. Nor is it a DC brush motor.

 I suspect the control box.

That figures, something like a 3 pole stepper motor. Agree, the control box is a fair bet.

 

A wile ago I posted a control box to a London boater Member who did not use it but they seem to have disappeared but if they read this perhaps they could contact the OP and post it to him.

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12 minutes ago, Tony Brooks said:

That figures, something like a 3 pole stepper motor. Agree, the control box is a fair bet.

 

A wile ago I posted a control box to a London boater Member who did not use it but they seem to have disappeared but if they read this perhaps they could contact the OP and post it to him.

There’s a rough and ready check that can be done for the compressor using a multimeter but as it runs then I’d guess it’s a fair bet that the compressor isn’t faulty:

 

Those folk might also be worth a phone call as they appear to know the Danfoss system well - perhaps they’ve seen high running current before: 02392 453430

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