Fridge power requirements
- Thread starter Jamie Gates
- Start date
Hi Folks
After some clarification on cable sizing...
I've just got a Dometic CRX50 compressor fridge and getting stuff together for the install.
When it comes to cable sizing, the tech specs for the fridge state 40w consumption and rated 5A.
So on that basis, I've bought this cable from 12v planet. It's rated for 16.5A so my assumption was more than enough.
So the fridge arrived and the manual suggests a 10amp fuse which id expect, but a much thicker cable (4mm2).
I read @Dellmassive's useful guide on cable sizing and 4mm2 cable is good for 39A which seems way over the top...
Where am I going wrong here, the fridge manual suggests I'd need the below cable from12v planet??
I get the idea of belt and braces and over rating the cable etc but if the draw is really closer to 5A for the fridge isn't that way OTT??
Sure I'm missing something stupid here, can someone please set me straight?
After some clarification on cable sizing...
I've just got a Dometic CRX50 compressor fridge and getting stuff together for the install.
When it comes to cable sizing, the tech specs for the fridge state 40w consumption and rated 5A.
So on that basis, I've bought this cable from 12v planet. It's rated for 16.5A so my assumption was more than enough.
So the fridge arrived and the manual suggests a 10amp fuse which id expect, but a much thicker cable (4mm2).
I read @Dellmassive's useful guide on cable sizing and 4mm2 cable is good for 39A which seems way over the top...
Where am I going wrong here, the fridge manual suggests I'd need the below cable from12v planet??
I get the idea of belt and braces and over rating the cable etc but if the draw is really closer to 5A for the fridge isn't that way OTT??
Sure I'm missing something stupid here, can someone please set me straight?
Cable has volt drop, a 6m run of 1sqmm cable pulling 4A will drop about 1V
If the fridge has a low voltage cutoff (to protect the battery), 12V at the battery will give 11V at the fridge, this may cause the fridge to cut out.
On switch on the fridge may pull much more than 4A for a short time (inrush), this make the situation even worse.
A 6m run of 4sqmm cable will only drop about 0.25A
Of course your installation may be a really short run of cable, and you may be ok with 1sqmm, do you want to do the maths, or just use 4sqmm?
Hope this helps
If the fridge has a low voltage cutoff (to protect the battery), 12V at the battery will give 11V at the fridge, this may cause the fridge to cut out.
On switch on the fridge may pull much more than 4A for a short time (inrush), this make the situation even worse.
A 6m run of 4sqmm cable will only drop about 0.25A
Of course your installation may be a really short run of cable, and you may be ok with 1sqmm, do you want to do the maths, or just use 4sqmm?
Hope this helps
So the leisure battery is under the driver's seat and the fridge is going directly behind that so the cable run will be about 2m max. If I've got a 1mm2 cable that's rated to 16.5A is that likely to be fine??Cable has volt drop, a 6m run of 1sqmm cable pulling 4A will drop about 1V
If the fridge has a low voltage cutoff (to protect the battery), 12V at the battery will give 11V at the fridge, this may cause the fridge to cut out.
On switch on the fridge may pull much more than 4A for a short time (inrush), this make the situation even worse.
A 6m run of 4sqmm cable will only drop about 0.25A
Of course your installation may be a really short run of cable, and you may be ok with 1sqmm, do you want to do the maths, or just use 4sqmm?
Hope this helps
Their 4.5mmsq is out of stock but I can get the 3mm which is good to 33A, that's surely got to cover it right?
Thanks Pete makes sense, will try and find some 4mm somewhere. Just wanted to understand where the maths fall down, technically the thinner cable should be sufficient but assuming the startup Amps must be much higher than 5A hence the need for the thicker cable.
Listen to Pete.
2m of 1sqmm drawing 4A will drop about 0.3Volts.
At inrush it may draw 16A, volts will drop by 1.2V then, will your fridge cope?
Want cold beer next summer on a hot day? Fit 4sqmm.
My fridge/fusebox are in the same places yours are, I used 4sqmm.
Page 22; automatic battery protection feature stops the fridge at 10.4v.
Out of interest, the maths does not fall down, 1sqmm will carry 16A continously, as you say, it would also cope with any inrush a fridge may cause. The current rating is NOT the issue.
The issue is VOLT DROP. In a house with 240V, we don't care if a 1mm cable drops 2/3/4 Volts, your house fridge will be fine with 236V. In a van we are starting with only 12V, we don't want to even lose 0.5V if we can help it.
Good prices, quality gear and a good section on electrical safety and choice of cabling.
Auto & Marine Electrical Components & Accessories | 12 Volt Planet
Huge range of 12v & 24V wiring products, components and accessories for vehicle electrics, marine & leisure electrical projects. FREE delivery on orders over £100
www.12voltplanet.co.uk
Have bought quite a few bits from Travelvolts and the stuff is great but the shipping costs are nuts.
£15 for the cable but another £10 for shipping??
Edit: I've gone for the Travelvolts one but that website isn't half annoying. Everything is listed ex VAT, so what's listed as a £15 cable set actually costs £30 at the final stage of checkout after shipping and VAT!
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Get some 4mm tri rated from ebay.
Yes, I thought when selling to public prices displayed should include vat.
They do at checkout before you pay.
It's about annoying to get all the way to the final page before you see the actual price. Just comes as a bit of a shock when the price for the item doubles with shipping at final stage.
Most sites that sell direct to consumer display prices including VAT at the first instance.
Not knocking them, they've been a great help throughout my build but I wish they'd get a better website!
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