First project - extra 12V socket - a cable mystery!

[gdhgdh]

Hullo!

I've just joined the MoHo brigade with a 2006 Dethleffs Advantage and I want to put a 12V cig socket in the 'stuff' area that the central table hooks onto. The Elektroblock is very close by. I've verified simple hookups using Mate-N-Lock connectors onto block 5 'Spare 2' to run the 12V TV, and that's working fine. The question is less about the actual electrics and more about sensible cable routing.

Is anyone familiar with this layout of Dethleffs MH as to how I can neatly run the 25A cables from the EBL 99 under the driver's seat across to the INSIDE of that side-table / console?

I need a 30mm diameter hole with about 10cm space behind for the 12V cig socket, so surface mounting it on that 'marble effect' area seems to make sense, but I have no idea how to disassemble the side-table unit without potentially just unscrewing everything and making a terrible mess.

Answers on a postcard to the usual address!

Cheers,
Gavin.

 

[donkey]

I know nothing of your specific van layout but that positive battery terminal looks like an accident waiting to happen. Unless it is covered and you have removed cover for exploration.

Geoff

 

[Lenny HB]

I know nothing of your specific van layout but that positive battery terminal looks like an accident waiting to happen. Unless it is covered and you have removed cover for exploration.

Geoff

It s the negative terminal so no problem., although it doesn't look good.

 

[Lenny HB]

Looking at your drivers door it looks like an A Class if it has a double floor run the cable in the floor void.

 

[gdhgdh]

donkey haa yes it looks ugly and represents no safety hazard - I'm comfortable enough working with power, and yup I'm very familiar with 'the volts what jolts, but the mills what kills' ! A future LiFePo4 project will replace that entirely with its own sealable battery box.

Lenny HB yea it's an A-Class but only just No double floor, alas. The manual is peppered with 'If your model has a Double Floor fitted then (really easy convenient thing) - for all other models (more awkward thing usually involving being outside)'

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[MisterB]

why do you need a cig socket there with 25A rated cable? i recently installed an additional 12v socket for my tv to be used in the lounge area but only used 10A cable, i am hoping i used the right sized cable !!!

 

[gdhgdh]

MisterB Cable costs almost nothing, so there's zero harm in overspeccing it. From my recent tests of the BRAUN 12V TV in our van, it's only drawing maybe 2A, so 10A is perfectly cool even including any momentary 'jolt' when it powers on.

I will be attaching this which will be the focus for charging, occasional inverter, who knows what else, so I am running it close to the rated fuse for the Spare 3 circuit on Block 5. It will be drawing a lot of power, but not often.

 

[Lenny HB]

why do you need a cig socket there with 25A rated cable? i recently installed an additional 12v socket for my tv to be used in the lounge area but only used 10A cable, i am hoping i used the right sized cable !!!

You are obviously not concerned with volt drop which is very important on low voltage (12v) circuits.

IMO 25 amp cable is too small, to keep the volt drop to recognised levels for a 5m cable run feeding a 10 amp socket I would use 6mm sq cable which is rated at 48 amps.
If the cable run is longer than 5m you need to increase the cable size to suit.

Never any harm in oversizing cables but it's a complete no, no to under size.

 

[MisterB]

You are obviously not concerned with volt drop which is very important on low voltage (12v) circuits.

IMO 25 amp cable is too small, to keep the volt drop to recognised levels for a 5m cable run feeding a 10 amp socket I would use 6mm sq cable which is rated at 48 amps.
If the cable run is longer than 5m you need to increase the cable size to suit.

Never any harm in oversizing cables but it's a complete no, no to under size.

Thanks, it's a cable run of less than 1 metre AND it's 6mm cable which I assumed was 10A cable.

 

[Lenny HB]

Thanks, it's a cable run of less than 1 metre AND it's 6mm cable which I assumed was 10A cable.

Just had to give that a funny I think you know why.

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[MisterB]

6mm cable may be a little over the top LOL ...

Though it was def 10amp on the packet!

 

[Lenny HB]

6mm cable may be a little over the top LOL ...

Though it was def 10amp on the packet!

Exact rating will depend on the copper purity and type of insulation.
0.5mm sq cable is approx 10 amps but you wouldn't want to use that as even over 1m the volt drop would be over 6%. 3% is the max volt drop to aim for the lower the better.

The current rating on a cable is the max current that can be passed through the cable in normal conditions (in free air) without overheating. Nothing to do with its suitability for the job.

Good cable size calculator here.

Voltage Drop Calculator | 12 Volt Planet

Use our Voltage Drop Calculator to select the correct Cable for your campervan, motorhome or boat wiring application. Auto and Marine Electrical Components from 12 Volt Planet - Cable Size Calculator

www.12voltplanet.co.uk

 

[autorouter]

On my Hymer there is a channel covered by an aluminium plate, just at the junction between the cab and hab area, under the carpet. Maybe there's something like that in yours.

I don't know how to dismantle that side-table unit, but for example in the Hymer bathroom the cupboard under the washbasin is held in by four screws from the inside of the cupboard, and the whole unit can be removed easily.

I note you are using the 'Spare3' circuit. I'm sure you know that it's 25A rated because the pins are doubled up, each pin is only good for about 15A, so the amps has to be able to flow through both pins. Working with 12V the main concern is voltage drop. Normally kept to less than 3%, which is only 360mV. If the voltage drop is OK, the amps will always be well within the cable spec.

 

[gdhgdh]

Excellent info, all - thanks autorouter and Lenny HB.

Whilst I haven't figured out how to get access to the side table, I have at least made a 12V extension available from Block 5 to that corner of the floor and insulated it well.

That's a great titbit about 15A per pin. I've installed a 15A fuse onto Spare 3 with a matching 15A in the cig plug itself. I'd rather pop a fuse than heat up the cables or damage the EBL 99.

Now, a question; the volt meter built into this:

is showing a (high?) 14.0V from Spare 3. I need to get the multimeter out to verify if that's accurate. If so, is providing 14V to 12V appliances something to be worried about?

I can imagine a TV simply drawing less current, but I'm worried that a Whale pump would be run too hard and greatly reduce its working life.

 

[autorouter]

'12V' supplies in a vehicle vary from 11V to 15V quite normally. Anything with a cigarette-lighter plug will be designed to adapt to that variation. More of a problem is items like routers, TVs etc that normally run from a 12V brick adapter from 240V mains. They normally expect 12.0V +/- 0.5V, and have problems with a standard vehicle supply.

You can get a 'voltage stabiliser' that will keep a vehicle supply within the required range. Also called a 'buck-boost converter'. Note that a 'buck' (= reducing) converter or a 'boost' (= increasing) converter is not suitable, because the supply voltage is not always above or below the required output voltage.

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[gdhgdh]

'12V' supplies in a vehicle vary from 11V to 15V quite normally.

Cool, cool. I'm actually a bit surprised that the elektoblock doesn't, you know, regulate that with a fixed output voltage. Every day is a school day! =)