12 Volt Wiring Question - Voltage Drop

Submitted: Tuesday, Jan 20, 2009 at 21:18
ThreadID: 65295 Views:6489 Replies:10 FollowUps:13
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I have had a problem with a voltage drop in the wiring in my camping trailer. Basically I was getting 12 volts plus at the top end of the connection but only 9 volts at the cig sockets in the camper.

As a result I chose to replace the cable in the camper for a larger diameter in case there was some sort of break in the integrity of the wire where I could not see it and to ensure the chance of voltage drop because of wire size was illiminated.

After running the new wire I found I still had the same issue happening.

After lots of mucking around I think the problem is the earthing.

The earth from the battery is onto the chassis and then from the cig socket the earth is again on the chassis.

What I did was run a earth from the battery to rear of the trailer and then found that I had full voltage and the fluro lights started with no problem?

Is the best way to resolve this problem just to run the earth from the battery?

Thanks in advance.
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Reply By: Member - Graham H (QLD) - Tuesday, Jan 20, 2009 at 21:24

Tuesday, Jan 20, 2009 at 21:24
Yes
AnswerID: 345287

Follow Up By: Cram - Tuesday, Jan 20, 2009 at 21:28

Tuesday, Jan 20, 2009 at 21:28
thanks for that I kind of figured it out but just wanted it confirmed by the knowledge base on this site.....
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Follow Up By: Member - Graham H (QLD) - Tuesday, Jan 20, 2009 at 21:34

Tuesday, Jan 20, 2009 at 21:34
Im not part of that really, but as you said doing that fixed the problem it seems the sensible thing to do. Just use the same gauge wire for both.
Chassis earths between trailers and cars are not usually the ideal thing.
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FollowupID: 613262

Reply By: Grungle - Tuesday, Jan 20, 2009 at 21:32

Tuesday, Jan 20, 2009 at 21:32
Chassis earths cause more problems than anything else so it always pays to run both power and earth for all accessories and batteries.

Second would be incorrect selection of wire gauge.

Regards
David
AnswerID: 345288

Reply By: Crackles - Tuesday, Jan 20, 2009 at 21:36

Tuesday, Jan 20, 2009 at 21:36
Cram it pays in the long run to install earths from the battery to all assesories & never use the body. In particular the tow hitch & trailer chassis should never be used as an Earth from the car. Both the negative & positive wires need to be the same size & to avoid voltage drop heavy wiring should be used for large loads (like fridges) or for long lengths. Additionally I'd toss the Cig lighter plugs away & replace with high amperage plugs (like Anderson or Clipsal) that can't rattle loose.
Cheers Craig.............
AnswerID: 345291

Reply By: kcandco - Tuesday, Jan 20, 2009 at 21:47

Tuesday, Jan 20, 2009 at 21:47
Hi Cram

In my opinion yes. I always run a earth wire. I have found chassis earths to be unreliable due to corrosion of the connection to the chassis. Some will say it is overkill but I also solder and heatshrink all connections. it takes longer but i never have lighting problems on my trailers. Cig sockets are notoriously bad for voltage drop especially if drawing anything more than a couple of amps. If you are drawing more, say for a fridge, use andersen plugs for a good connection. A formula I found for calculating Voltage drop is length of run including earth return x max amperage x 0.017 divided by cable wire size in square mm. This is from one of Collyn Rivers books which make excellent reading if you intend to do more wiring. Hope this helps.

regards Kc
AnswerID: 345296

Follow Up By: Cram - Tuesday, Jan 20, 2009 at 21:59

Tuesday, Jan 20, 2009 at 21:59
Thanks for the replies. I will buying the extra wire tomorrow and have just found some very cheap anderson plugs on ebay.....got ten for $45.00 including postage....so I will be camping at Lostock Dam this weekend and guess what I will be doing.....lol
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Reply By: Member - Tony S (WA) - Wednesday, Jan 21, 2009 at 02:18

Wednesday, Jan 21, 2009 at 02:18
Cram,
You most probably already know this.
When you get your thicker cable, don't go by the mm size on the sticker.That is the overall thickness of cable and insulation.
There should be another size indicated. ie 16/0.25. showing the actual wire thickness is a 1/4 of a ml. It might also show an amperage. This has a big question mark.
Overall it may look like this:-
3mm 10amp 16/ 0.25mm
go to this site it should give you all the answers :-
http://www.kayjayco.com/wiretables.htm

Tony
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AnswerID: 345316

Reply By: Sand Man (SA) - Wednesday, Jan 21, 2009 at 09:39

Wednesday, Jan 21, 2009 at 09:39
Cram,

I would rethink trying to do the wiring job whilst camping, especially for the the Anderson Connectors.

Run both positive and negative wires from your battery and fuse the positive side close to the battery.

The connection of the wires to the Anderson connectors can be either crimped or soldered, but if crimping, you need a "professional" crimping tool.

I "wire wrap" the cable ends with a single strand of copper wire to increase the diameter if necessary, tin and then solder the joint using a butane torch, but I do this in the workshop. I have never had a joint fail.

These are the two methods, recommended by the Manufacturer.

Bill

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AnswerID: 345328

Follow Up By: Sand Man (SA) - Wednesday, Jan 21, 2009 at 09:58

Wednesday, Jan 21, 2009 at 09:58
Data Sheet download (PDF format)

Assembly Instructions

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Follow Up By: Cram - Wednesday, Jan 21, 2009 at 13:28

Wednesday, Jan 21, 2009 at 13:28
Yeah thanks for that....I have a suitable crimper and have made some up before however, it's probably a bit ambitious to try and do it over the weekend.

thanks for that link and your suggestions.

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Reply By: Geoff (Newcastle, NSW) - Wednesday, Jan 21, 2009 at 10:23

Wednesday, Jan 21, 2009 at 10:23
Hi Marc,
Where are you going for the cable?

I was in Bambach Cables at Lambton before Christmas and they had multi-strand cable well suited to your needs at 70% off list.

It wasn't saleable any more as new stock due to the change in rules regarding the insulation. Older PVC insulation oddly enough has a small lead content.

The addition of lead is now illegal.

I'd give them a call and see what they have left,

Bambach Wires & Cables Pty Ltd
Specialist Industrial Cables

(02) 4956 204464
Orlando Rd
Lambton NSW 2299

1800 333 291FREECALL

Bambach Cables

Note: The cable they sell will be sized in SI units (metric), ie, Something like 2.5sqmm, 4sqmm, 6sqmm, 10sqmm, 16sqmm etc. This is the cross sectional area of the copper, the only way to measure a cable if you actually know what you are talking about.

This bizarre and dangerous notion of measuring the OD of the copper and the insulation then declaring a blanket current carrying capacity should result in the perpetrators being shot with a ball of their own droppings.

Geoff

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AnswerID: 345334

Follow Up By: oldtrack123 - Wednesday, Jan 21, 2009 at 11:23

Wednesday, Jan 21, 2009 at 11:23
HI Geoff
"This bizarre and dangerous notion of measuring the OD of the copper and the insulation then declaring a blanket current carrying capacity should result in the perpetrators being shot with a ball of their own droppings.Geoff"

Well said Geoff ,It is the most riduculous wire size system anyone could invent & to make it worse to then quote an amp rating,with no qualifications re cable length/ voltage drop.
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Follow Up By: Member - Tony S (WA) - Wednesday, Jan 21, 2009 at 11:58

Wednesday, Jan 21, 2009 at 11:58
Yes Geoff , again well said. I forgot to mention it was measured in sqmm. Got "CRAFT" these days.
A lot of people get caught.

Tony
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Reply By: Gronk - Wednesday, Jan 21, 2009 at 10:33

Wednesday, Jan 21, 2009 at 10:33
If your gonna make the anderson connections away from home you will need a couple of soldering irons ( big ones ) to get enough heat into the lugs !!
AnswerID: 345335

Reply By: Mark Taylor - Wednesday, Jan 21, 2009 at 13:48

Wednesday, Jan 21, 2009 at 13:48
When I was an apprentice auto electrician, we were taught that current carrying capacity for automotive wire was for a distance of 3 and one third yards... or in other words 3 metres.

Once you go over this length, you go up to the next size.

It was an interesting thing because every auto electrician I knew at the time knew this (including our tech teachers) but I never actually saw it in print in any of our text books.

When I was wiring my own CT for a battery to run lights etc, my neighbour came over for a gander. He told me I shouldn't use heavy cables as it took "more electricity" to fill up the extra strands in the wire and so my battery would go flat faster.

He was very serious. Also told me that headlight realys worked by "transformer action" to boost the power to the lights.

All very interesting stuff! I wonder how many other people he has imparted his "knowledge" to!!

Cheers

Mark T
AnswerID: 345350

Follow Up By: Gronk - Wednesday, Jan 21, 2009 at 14:13

Wednesday, Jan 21, 2009 at 14:13
Thats why you don't tie a cable in a knot ....it restricts the current flow !!!!!!!!!! ha , ha ...
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FollowupID: 613320

Follow Up By: Rolly - Wednesday, Jan 21, 2009 at 14:31

Wednesday, Jan 21, 2009 at 14:31
Sounds about as expert as some of the 'technical' writers in popular caravaning and camping magazines.
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FollowupID: 613324

Follow Up By: Geoff (Newcastle, NSW) - Wednesday, Jan 21, 2009 at 17:26

Wednesday, Jan 21, 2009 at 17:26
That's tied up with the reason you should fully un-roll welding cable.

Everyone knows coiled welding cables get hot!

Very few people understand why!

It's to do with centrifugal force, as the electrons go around and around the coil the bigger heavier ones get pushed to the outside.

They then rub up against the insulation causing friction. Friction causes heat and heat causes things to let the smoke out.

As we all know everything electrical contains smoke, a key component of its operation.

Once the smoke escapes it doesn't work anymore!

Geoff

Geoff,
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Follow Up By: Gronk - Wednesday, Jan 21, 2009 at 23:58

Wednesday, Jan 21, 2009 at 23:58
Yeah sure.......electrons rubbing against the insulation ?? Will have to remember that one....at least it's original ????
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FollowupID: 613434

Follow Up By: Member - Tony S (WA) - Thursday, Jan 22, 2009 at 00:12

Thursday, Jan 22, 2009 at 00:12
Heard everything now. Yeaa pigs might fly

T
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Follow Up By: Nisby - Friday, Jan 23, 2009 at 21:51

Friday, Jan 23, 2009 at 21:51
You can always check if a wire is "live" by sticking both ends on your tongue.
This is especially useful if the wire is short.
Long cables are a bit heavy to lift.
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FollowupID: 613666

Reply By: Nisby - Friday, Jan 23, 2009 at 22:01

Friday, Jan 23, 2009 at 22:01
Always. Run positive and negative cables of the same diameter.

As suggested, welding cable for the full length of a vehicle.

When wiring for an accessories battery, always use same thickness or greater cables between batteries.

If you're ever stuck with a flat main battery, the accessory battery can be used for an emergency starter battery. This assumes that the accessory battery is large enough capacity and you have a solenoid/relay in the circuit.

If your accessory battery is fitted on your trailer/caravan, suitably hefty connectors across the towing link are a must.
AnswerID: 345684

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