Fuses

[wanderer]

A fellow camper is having a problem with his fridge it looks like the 3 amp fuse has blown , can you replace with a 5 amp fuse as I can’t find another 3 amp or is it no no

 

[MC 55 FUN]

Replacing a blown fuse with one of a higher value is not advisable.

Finding out why the fuse has blown is the first course of action.

 

[MikeD]

The fuse protects the cable and it is not a great idea to change it for a higher rating.

I wonder why it blew? You need to find that out first.

Check the supply voltage on site as if much below the 240v it will push the fridge amperage up.

 

[Richard n Ann]

Check the supply voltage on site as if much below the 240v it will push the fridge amperage up.

No it won't, if the voltage falls, the amperage (and wattage) falls with it...

What your thinking about is - To maintain the same power consumption (wattage) with less voltage the amps must rise.

Just saying

 

[Charlie9038]

3 amp fuse seems a bit low, might be worth checking in the wiring diag and manual if this is right, does it work on gas or is it just the 240v side that has failed?

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[MikeD]

No it won't, if the voltage falls, the amperage (and wattage) falls with it...

What your thinking about is - To maintain the same power consumption (wattage) with less voltage the amps must rise.

Just saying

Always happy to learn and that was what I was thinking. Not being a electrical guy but I thought the wattage stays the same?

 

[Charlie9038]

Always happy to learn and that was what I was thinking. Not being a electrical guy but I thought the wattage stays the same?

No it drops, watts = amps x volts
Formula p= A x V so 3 amp x 240= 720 watts.

 

[Richard n Ann]

Always happy to learn and that was what I was thinking. Not being a electrical guy but I thought the wattage stays the same?

No the only constant is the elements resistance. Let's say for example it's 150 ohms.
To work out the current flow(I) for any given voltage i=v/r

So at 240v current = 1.6 amps
And at 230v current = 1.53 amps

So at 240v power = 384 watts
And at 230v power = 351.9 watts

 

[wanderer]

3 amp fuse seems a bit low, might be worth checking in the wiring diag and manual if this is right, does it work on gas or is it just the 240v side that has failed?

Not working on gas plus no power to the cooker igniscion .

 

[Richard n Ann]

Not working on gas plus no power to the cooker igniscion .

Now you mention it, our fuse blew once. It was a 5a one, not at the fridge but in the fuse box. Never did find out what caused it but it's been alright since.

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[pappajohn]

No the only constant is the elements resistance. Let's say for example it's 150 ohms.
To work out the current flow(I) for any given voltage i=v/r

So at 240v current = 1.6 amps
And at 230v current = 1.53 amps

So at 240v power = 384 watts
And at 230v power = 351.9 watts

So why is an American 110v hookup system rated at 50amps if 230v 16amp is more than sufficient.

 

[Charlie9038]

Not working on gas plus no power to the cooker igniscion .

Sounds like your possibly on site at the moment? If that's the case I would consider 2 options:
A Use the outdoor fridge if in the uk and drink the beers & look at it in the morning.
B If your in a warmer climate pop the 5A & hope its not going to do further damage or make some space in yours and go back to option A.

 

[Richard n Ann]

So why is an American 110v hookup system rated at 50amps if 230v 16amp is more than sufficient.

Err, I don't know you'll have to email them and ask. One possible explanation is that yanks use a lot more power than us - 5500w

 

[pappajohn]

Like MikeD I believe watts are a constant... A unit of power produced
A 55watt headlamp bulb require the same amount of energy at 11v or 14v.... So the amps vary.
If the amps and volts were reduced the brightness of the bulb would also be reduced.

 

[MyrtleGuru]

3 amp fuse seems a bit low, might be worth checking in the wiring diag and manual if this is right, does it work on gas or is it just the 240v side that has failed?

On some models there will be a relatively low-power 12v connection (2 or 3 amps) that powers the electronic controls and the light. This is separate from the connection that actually powers the fridge when in 12v mode (usually controlled with a relay so that 12v mode can only be used with the engine running). But without the controls working, it won't work in any mode (mains/gas/12v).

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[MikeD]

Sounds like your possibly on site at the moment? If that's the case I would consider 2 options:
A Use the outdoor fridge if in the uk and drink the beers & look at it in the morning.
B If your in a warmer climate pop the 5A & hope its not going to do further damage or make some space in yours and go back to option A.

I would definitely pop across to his new best friend/fellow camper and offer to help him drink the beer before it gets warm.

ps: I thought the cooker ignition worked off the 12v leisure battery circuit.

 

[MyrtleGuru]

Not working on gas plus no power to the cooker igniscion .

So it sounds like the fuse is protecting not just the fridge controls. So it may not be the fridge that blew the fuse. Is there another 3 amp fuse not powering something vital that you can swap out until you can find a replacement?

 

[Richard n Ann]

Like MikeD I believe watts are a constant... A unit of power produced
A 55watt headlamp bulb require the same amount of energy at 11v or 14v.... So the amps vary.
If the amps and volts were reduced the brightness of the bulb would also be reduced.

OK, that's fine you can believe what you want.
But a 55w bulb is only 55w at its rated voltage. The amps reduce if the volts reduce.

Voltage can be defined as pressure between two points, as the pressure decreases it pushes less electrons (ie less current). Get it?

 

[MikeD]

OK, that's fine you can believe what you want.
But a 55w bulb is only 55w at its rated voltage. The amps reduce if the volts reduce.

Voltage can be defined as pressure between two points, as the pressure decreases it pushes less electrons (ie less current). Get it?

Nope but I believe you

 

[pappajohn]

I shall retire to my secret laboratory tomorrow and set up my highly technical equipment to prove your theory for myself.

I'll nip out to the garage with my multimeters, a battery and a bulb and have a shufty for myself. .

Only to prove this to myself of course as I've always been told as volts rise or drop amps do the opposite.

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[Richard n Ann]

your theory

Thank you how flattering... But although I am technically a genius... I'm afraid it isn't mine it was James Prescott joule (not Mr ohm either)

This explains it well, and a bit of history to boot:
https://www.allaboutcircuits.com/textbook/direct-current/chpt-2/calculating-electric-power/

 

[pappajohn]

Nooooo....... Wasn't at school the day they did algebra.
I'll take your word for it..... I believe you.

 

[autorouter]

Check the supply voltage on site as if much below the 240v it will push the fridge amperage up.

No it won't, if the voltage falls, the amperage (and wattage) falls with it...

Actually you are both right. It depends on what type of device it is.

A standard dumb device like a heater element or a light bulb has a more or less constant resistance. As the voltage goes down, the amperage goes down, so the watts goes down too.

A smart device like a laptop power supply or charger actively compensates for lower voltage by changing its resistance. As the voltage goes down, the amps increases, just enough to keep the watts constant.

On a fridge, the control board is smart but both the heater elements are dumb.

 

[autorouter]

So why is an American 110v hookup system rated at 50amps if 230v 16amp is more than sufficient.

110V 50A is equivalent to 230V 24A. The round blue plugs come in two ratings, 16A and 32A. The 32A version is slightly bigger and has the polarising notch at the top instead of the bottom. 32A hookups are rare on camp sites but are available at some marinas for the larger boats.