Voltage drop.......what am i doing wrong...

[mangoat Lurker Find all posts View Profile Close mangoat]

I have the new 2.8....... ive installed a idc25 projecta dcdc charger.
Run 6 b&s cable for the charging circuit.
I ran 6mm dual core from the secondary battery to the rear of the luggage area via the chassis rail and installed an engel style socket in the rear luggage area.
12.65v on the battery but only 11.9v when the fridge is running at the fridge end.....
Do i need to go heavier cable again than the 6mm ive already run?
Why so much drop?

[pradosteve97 Junior Member Find all posts View Profile Close pradosteve97]

http://www.solar-wind.co.uk/cable-sizing-DC-cables.html
try play with the cable sizer on that page and compair what size cable it comes up with ,

[nudgebar Member Find all posts View Profile Close nudgebar]

might be normal , what is the reading with the fridge not running?

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

Sounds a little high, try reading the voltage drop across the positive side ie positive battery
terminal to positive at fridge and the same for the negative side and see if there the same.

Other tests would be battery terminal to clamp, battery terminal to wire, battery terminal to fridge plug
etc or you could do each individual section.

[cuda Advanced Member Find all posts View Profile Close cuda]

This sounds like a 0.7v drop. Have you got a diode in the circuit?

[andoland Senior Member Find all posts View Profile Close andoland]

Test across the fridge plug at your socket, i.e. on the battery side of the socket and the fridge side of the plug. Some fridge plugs are notorious for poor connection causing voltage drop.

[Mr ok Lurker Find all posts View Profile Close Mr ok]

That volt drop would be correct. It depends on the length of the cable, area of the cable and the current passing through it. From the battery at the front to the back you probably used at least 7m of cable of cable, pulling 6 amps through a 4.5mm2 (6mm) square cable it will drop by 0.3 to 0.35 of a volt. Then you have the earth return back to battery so you have 14m of cable to complete the circuit. Hence 0.7v drop you are seeing.

A simple fix would be to earth the negative to the body at the back of the car. See if that eliminates half the drop. Next step will be to increase the size of the cable but voltage gains will be minimal. One length of 6B&S earthed at the rear will still drop 0.1 to 0.2 of a volt 6 amps. If your fridge has a voltage setting at which it cut off, set it on the lower one because the voltage at the supply (battery) will be higher than what the fridge sees.

[adrian5800 Advanced Member Find all posts View Profile Close adrian5800]

That volt drop would be correct. It depends on the length of the cable, area of the cable and the current passing through it. From the battery at the front to the back you probably used at least 7m of cable of cable, pulling 6 amps through a 4.5mm2 (6mm) square cable it will drop by 0.3 to 0.35 of a volt. Then you have the earth return back to battery so you have 14m of cable to complete the circuit. Hence 0.7v drop you are seeing.

A simple fix would be to earth the negative to the body at the back of the car. See if that eliminates half the drop. Next step will be to increase the size of the cable but voltage gains will be minimal. One length of 6B&S earthed at the rear will still drop 0.1 to 0.2 of a volt 6 amps. If your fridge has a voltage setting at which it cut off, set it on the lower one because the voltage at the supply (battery) will be higher than what the fridge sees.

I would connect the neg to the body as the earth return and combine the both 6mm cables to be +ve. That'll double the cross sectional area and reduce your voltage drop. Add a 30 amp fuse to both positives at the source to protect each cable

[Mr ok Lurker Find all posts View Profile Close Mr ok]

Now that's thinking. As long as they are the same length there shouldn't be an issue.

[Rdae1981 Junior Member Find all posts View Profile Close Rdae1981]

6mm is really only (4.5mm) and is quite undersized for such a run, l have run 6 b&s (13mm) and have zero voltage drop

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Hi Mangoat, as others have suggested, you need to do some testing because 6mm AUTO Twin ( 4.5mm2 x 2 ) is well and truely large enough to power a fridge over about 6m, and you should be seeing no more than about 0.3v voltage drop over that sort of distance.

Are you sure the cabling is 6mm AUTO Twin, because the next size down, 5mm AUTO Twin ( 2.5mm2 x 2 ) would still have slightly less voltage drop over that distance.

[mangoat Lurker Find all posts View Profile Close mangoat]

This sounds like a 0.7v drop. Have you got a diode in the circuit?

diode?????

[mangoat Lurker Find all posts View Profile Close mangoat]

Hi Mangoat, as others have suggested, you need to do some testing because 6mm AUTO Twin ( 4.5mm2 x 2 ) is well and truely large enough to power a fridge over about 6m, and you should be seeing no more than about 0.3v voltage drop over that sort of distance.

Are you sure the cabling is 6mm AUTO Twin, because the next size down, 5mm AUTO Twin ( 2.5mm2 x 2 ) would still have slightly less voltage drop over that distance.

YES i am sure its 6mm auto twin i sell it for a living.