Tuesday, 24 May 2016

The art of electricity and the poorly performing fridge !

Last year - yes it really was last year I had some beer issues.

The issues being the Waeco fridge would keep John and my beer cold during the mini heatwave we endured taking Percy to be repainted on the Stourbridge canal - whule the engine was running. However in the late PM it would retire disgracefully allowing much needed beer to get warm.

I have concluded this is an issue with voltage - or voltage drop. The charging batteries would cope with the challenge of too thin cable when under charge but give a few hours of battery use the compressor start up would require more than the cable would allow resulting in a fan running but the compressor not kicking in.

So based on some studious internetting I have concluded that the voltage drop on a 6mm2 cable on a 12v circuit with a 4 amp load at a generous 8 meters (it is actually 40watts/12v = 3.33 amps) is 0.18v or 1.5%. I understand an acceptable drop of up to 3% is the norm.

Cable is very expensive compared to other things so whilst tempted to go for 10mm2 (which gives a 0.11 drop or 0.92% ) I'll risk the 6mm2 plus it will be easier to install/replace the current *ouch*

Only two things I cannot define is the present cable size, I think about 1.5mm so getting an unhealthy and risky .75v drop, plus a definitive compressor start up voltage for the Waeco.

I think I'll also follow Halfie's venting approach by drilling some holes in the floor to draw up cool air from the bilges, giving the added benefit of some bilge ventilation. I recently treated myself to some nice sharp flat bits to do the work.

Watch this space but if you think I have anything calculated wrong please let me know  !!


ditchcrawler said...

Its not the running current for the fridge that causes the problem its the start up current which for a few seconds can be much higher which means just when the fridge requires the maximum power the volt drop is at its worst and the terminal voltage at the fridge the lowest. I think you will find that some manufacturers of low voltage fridges recommend 1mm sq per meter run. I think that is for both positive and negative

Tom and Jan said...

Nev, I'd look to buying 8mm2 twin cable. Something like this

Nev Wells said...

I am never let down by my blogging friends. Thank you both for your advice - I have ordered 9m of 8.5mm2 thinking I only need about 7-8m but better be safe than sorry. Thanks again I'll report back but at least I am on the right side and hopefully you have saved an expensive underestimate.

Halfie said...

I've just tried to look up the cable suggested by Tom and found the eBay listing has been removed.

Nev Wells said...

Hi John, I saved the planet a little bit of carbon by buying from Essex rather than Australia plus the 8.5mm I purchased is single cable so using the existing to pull through may be a bit easier. The advice is spot on and hopefully I should get this done next week before the next heatwave !!