Additional solar system & B2B for compressor fridge

Markd said:
As you say any battery that gets down that low has used a few life cycles!
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The thing is the heater may see a voltage that low, but the Battery itself maybe nowhere near that low level if the device was not installed right.
For example, at shows, I used to get lots of people asking about why their 12V Compressor Fridge wouldn't turn on properly and had the "low voltage" light on. Reason is lots of people - including professional convertors - wire up the fridges using wire suitable for the running current of the fridge (under 3A) but ignore (or more likely just don't know) that the fridges may pull 50A or more on the in-rush when the compressor kicks in.
Instant massive voltage drop with thin wire resulting in a voltage well over 12V at the battery end, but under 10A at the fridge end.
Heaters not so dramatic but if wiring is substandard, a battery at 60% SOC may not be enough to start the heater.
 
wildebus said:
The thing is the heater may see a voltage that low, but the Battery itself maybe nowhere near that low level if the device was not installed right.
For example, at shows, I used to get lots of people asking about why their 12V Compressor Fridge wouldn't turn on properly and had the "low voltage" light on. Reason is lots of people - including professional convertors - wire up the fridges using wire suitable for the running current of the fridge (under 3A) but ignore (or more likely just don't know) that the fridges may pull 50A or more on the in-rush when the compressor kicks in.
Instant massive voltage drop with thin wire resulting in a voltage well over 12V at the battery end, but under 10A at the fridge end.
Heaters not so dramatic but if wiring is substandard, a battery at 60% SOC may not be enough to start the heater.
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The peak current is 6.5 amps on a Truma, and that isn't a sudden peak: the fan gently ramps up. A battery that drops to, say, 11v under that sort of load needs charging or replacing.
To lose another 0.6v over five metres of cable at 6.5A would mean the resistance is about 18 ohms per kilometre, which is what you'd expect from 1mm copper wire. Nobody wires a Truma with wire that thin.
 
Happens on Fridges; Happens on Diesel Heaters, especially the chinese ones with incorrect voltage readings to start with. Who knows what wiring may have been used to wire a Truma heater? You could say nobody would wire a Fridge with 1.5mm wire - but they do.
 
I will check the wiring to the heater in my van - I'm not optimistic because when I put the original build extractor fan over the hob on high speed it dims the built in down lighters noticeably.
I opened it up and he wiring is desperately light and the van loom is the same.
The over sofa spotlights are similarly skimpy supplied but at least these can be replaced with Leds at one third the rating - same goes for most of the other lights!
As you said earlier despite the otherwise good build quality of my 2004 Bessacarr the wiring and electrics are 'down to a price' for their whole range.
 
wildebus said:
Happens on Fridges; Happens on Diesel Heaters, especially the chinese ones with incorrect voltage readings to start with. Who knows what wiring may have been used to wire a Truma heater? You could say nobody would wire a Fridge with 1.5mm wire - but they do.
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I'm pleased to say that my fridge does at least have a 10mm feed - which it does need because the run must be getting on for 8m from the relay above the engine!

Edit to reflect that I didn't read Wildebus correctly - he was talking about compressor fridges and I was referring to absorption which obviously need a lot more current.
I have heard that some vans feed absorption fridges off the hab battery via main loom which can be pretty low on voltage.
 
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in h said:
Oh, having a B2B will make a big difference. When you have a battery that you can only discharge to 50%, starting at 100% is very different to starting at 85%.
I think that AGM is very suitable for leisure use. In fact my batteries (which are proper deep cycle batteries, not leisure) are AGM.
I agree about Varta being a good buy.
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When I said AGM not suitable I should have been a bit more specific.
As leisure batteries they do a good job but do as you have provided require the correct charging regime.
An awful lot of motorhomes don't provide the correct voltages to do a good job in their on board chargers and if the base vehicle doesn't have AGM neither will the alternator.
Added to which we see the marked deterioration of AGM batteries if they are used in hot environments such as sunny Spain or Portugal for any length of time.
It's also my understanding that VAG have stopped putting AGM batteries in cars because of the failure rates in hot countries.
BMW used to put them in the boot and provided cooling fans but may well have moved away from AGM.
 
wildebus said:
You could say nobody would wire a Fridge with 1.5mm wire - but they do.
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No, I said 1mm, not 1.5mm.
I seriously doubt any professional would use that.
Not many Truma heaters are installed by DIYers at all, let alone ones stupid enough to use 1mm cable - even assuming they could buy any.
 
in h said:
No, I said 1mm, not 1.5mm.
I seriously doubt any professional would use that.
Not many Truma heaters are installed by DIYers at all, let alone ones stupid enough to use 1mm cable - even assuming they could buy any.
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And I said Fridge, not heater.
Stop trying to constantly pick holes in discussions.
 
Markd said:
I will check the wiring to the heater in my van - I'm not optimistic because when I put the original build extractor fan over the hob on high speed it dims the built in down lighters noticeably.
I opened it up and he wiring is desperately light and the van loom is the same.
The over sofa spotlights are similarly skimpy supplied but at least these can be replaced with Leds at one third the rating - same goes for most of the other lights!
As you said earlier despite the otherwise good build quality of my 2004 Bessacarr the wiring and electrics are 'down to a price' for their whole range.
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In my experience, the problem is as likely to be a half-melted fuse somewhere in the line. Shouldn't be, but all too often is!
Yes switching to LED lights is a smart move, but one third the rating of spotlamp bulbs will leave you with over-bright lighting.
 
Truma specify 2x2.5mm² supply to the heater 12v terminals - I've not checked yet but I'm not expecting to find them as I don't recall seeing anything that size coming out of the psu.
Will update in the next couple of days.

Thank you for approving my change to LED lighting - I'm happy with the level of illumination I've chosen!!
 
in h said:
This discussion is about heaters.
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Look at the title -
"Additional solar system & B2B for compressor fridge"
Heaters may have started to be discussed but the thread is meant to be primarily about about Solar, B2Bs and COMPRESSOR FRIDGES, so comments abiut Fridges are equally - and probably more - valid than comments on heaters
 
I guess I'm responsible for dragging heaters into the discussion 😀
My excuse is that I was vaguely on topic of B2B and current drawdown.
What we are finding is that some motorhome wiring even installed by professionals and manufacturers leaves a lot to be desired.
I've a feeling that manufacturer's looms are based on the smallest lowest specced vehicle and then just extended and added to.
My van has a 20A main battery fuse and then runs 80A of fuses from the psu. I know the reason for that and it's just the same as a consumer unit in a house.
However I've just reviewed the fuse sizes and halved many of them - for example I can't imagine even with halogen bulbs that each of the two lighting circuits needed 10A fuses!
My cooker hood (dimming its lights at high speed remember and it only draws 30w apparently!) had a 15A fuse and the wires were probably 0.5mm² in the unit. I'll bet the loom was designed for a couple of downlights but then someone decided to go up market with an extractor.
And so on and on and on - so I'll stop ranting 😀
 
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wildebus said:
Look at the title -
"Additional solar system & B2B for compressor fridge"
Heaters may have started to be discussed but the thread is meant to be primarily about about Solar, B2Bs and COMPRESSOR FRIDGES, so comments abiut Fridges are equally - and probably more - valid than comments on heaters
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The thtead started about fridges, but this discussion was specifically about power to a Truma heater.
 
Actually all I said was that my battery had enough voltage to run my Truma and that demonstrated the ability of my solar to keep it topped up over a few days.
I own up to expanding on voltage drop more generally than fridges 😀
 
OK - what was anyone's money on with regard to the supply wiring to my Truma?

No prizes for guessing that it's not 2.5mm²
It measures 1.5mm diameter/thickness overall so even if 'no wall' insulation area is c1.7mm².
Apparently if thin wall this od is 0.5mm² flex.

So I have a Truma heater installed by Bessacarr that doesn't meet the manufacturer's specifications!
In fact because of the distance from hab battery to heater it should be 4mm².
Maybe because the first 5m are 3mm² they think the next 2 can be 0.5 and the average is >2.5??

Yes the main cables from hab battery to psu are 3mm² so no wonder things go dim when a few circuits are in use!!

For the record the voltage] drop from battery to Truma at full power is 0.6v.

I'm disappointed but not surprised 😀

Did someone say no supplier would install one with such thin wire?!

20200430_115509.jpg
 
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Is Hairydog back? Not sure I missed him.
 
Markd said:
OK - what was anyone's money on with regard to the supply wiring to my Truma?

No prizes for guessing that it's not 2.5mm²
It measures 1.5mm diameter/thickness so even if 'no wall' insulation area is c1.7mm².
Apparently if thin wall this is 0.5mm² flex.

So I have a Truma heater installed by Bessacarr that doesn't meet the manufacturer's specifications!
In fact because of the distance from hab battery to heater it should be 4mm².
Maybe because the first 5m are 6mm² they think the next 2 can be 0.5 and the average is >2.5??

I'm disappointed but not surprised 😀

Did someone say no supplier would install one with such thin wire?!

View attachment 54283
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I would say that is not a thin-wall insulation wire and is probably 1mm2 and possibly, just possibly 1.5mm2.

If you do end up replacing it, or even cutting it to do something, you can count the number of strands to determine the gauge.
There are, of course, some variations in the following depending on the manufacturer, but the general rule for multi-strand wire is the strands are the same thickness for "sets" of cable gauges, and it is the strand count within that "set" that determines the gauge as follows:
Gauge (mm2) = n Strands x strand thickness (mm)
Some examples
  • 0.5 mm2 = 16 strands x 0.2mm
  • 1.0 mm2 = 32 strands x 0.2mm

  • 1.5 mm2 = 21 strands x 0.3mm
  • 2.5 mm2 = 35 strands x 0.3mm
  • 4 mm2 = 56 strands x 0.3mm
  • 6 mm2 = 84 strands x 0.3mm

  • 10 mm2 =80 strands x 0.4mm

It really is more common than is realised to see under-sized cable as the people installing the wiring are not electricians any more than the people who fit tyres are Rubber Technology experts. They may read the specs, see what the running power of the Device is (which is always quoted as the minimum 'up to speed maintenance' number as it looks best to the buyer) and see what size cable can support that current. 1.0mm2 cable can support 16A in free air - why would you need more for a heater? in fact 0.5mm cable is ok for 11A so use that instead!

What they don't pick up on is voltage drops and surges & start-ups.
Take the Compressor Fridge - The specs of a Weaco quote the average current draw as between 1.29 and 2A. So why the hell do you need to run a 6mm2 cable? (that is a rhetorical question if anyone wonders :) )

And that is why you see fridges with 1.5mm wiring (as they probably had no 1.0mm to hand), heaters similarly installed and 140A Split-Charge relays with 4mm2 or sometimes even 2.5mm2 cable

(PS. I actually supply a lot of 1.0mm2 cable as it happens as it is suitable for many applications, just not heaters and fridges!)
 
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