Anderson Plug

Glen, you would be trying to charge the battery to achieve the same result to get it up from the 12.6 that you are reading at the plug. You may be inputting 14.2 until the plugs are united, but then the voltage drops. You will be required to put in more amps to get the voltage up.

With a lot of the charging systems there is only a small cable that connects the tralier to the car charging system. That small cable restricts the amps that can be transferred. With that restriction, the voltage drops and it will take a lot longer to actually charge the battery and get it to required voltage if the size of the cable is too small.

I have the cable to the back of the car at about 8mm for the actual diameter of the copper within the insulation. The cable is as big as your finger to the back of the car.

There are sites on the web that give the voltage drop over distance as you try to poke more amps through. Just part of the physics of electricity.

Hi Glenn

Was`a little hard to follow your description.

To read a lower voltage you have to be drawing current (perhaps charging the Tvan battery).

Resistance in the leads or connectors causes the volts drop.
(can also be weak battery,faulty fuse holder etc )

So if on car side of the A plug you have your 14.2v then abnormal resistance is on the Tvan side.

If on car side of A plug you have your 12.6 then abnormal resistance is on the car side.

1/2 V drop is normal if using leads of 8mm sq copper cables which should be minimum size.

(I note John used 8mm cable size to Great minds........)

Could be dirty connectors in the anderson plugs, get some CO Contact cleaner and spray them.

Or the contacts in the a/plugs crimped only not soldered on to the cable and get moisture in them which causes corrosion and thus bad connection, pull them apart and solder cables to contacts.

Or cable size too small, use a bigger cable should be at least 6mm square.


Cheers
Ross

Nope...

Just had this on a Pirahna system my son installed.

The 12.6v your reading when the plug is connected is comming back from the fully charged battery in the van, while the 14.6v at the anderson plug is comming from the alternator on the vehicle.

You have a bad earth somewhere - maybe to the TVan chasis and thats stopping the alternator 14.6 volts getting to the TVan battery - it's stopping at the anderson plug or bad earth there abouts..

Least that was the cause with ours, turned out to be paint on the panel on the spot we connected the earth strap, when we bared the spot down to fresh metal we suddenly got 14.6v at the second battery...

Trust me, I'm from the government and I'm here to help you! he he he.

Cheers!

Gentleman

Thanks for all your help gota love this forum I should have said in the 1st tread.
Both Anderson plugs are brand new we bared the wire solded the wire then crimped on the terminal and sealed the ends with solder .
The cable from the 2nd battery running though the car is about 8mm or so might be bigger its huge its about the same as a set of jumper cables got it off some sparky he knows it is earth via the same cable to the towbar we ground off all the paint and stuff i know we should have run it to the 2nd battery but it wasn't long enough im thinking might be the earth on the T-Van cause there 14.2 at the plug on the 4by maybe might look at the cable on trailer too cause its a gal dripped chassis bet they didnt grind it off were they earth it and the trailers 6 years plenty of time to get all grotty
But thanks again for all your help

Glenn..

Hi Glenn,

Have you an ARRID Twin Charge in the T-van? This boosts the incoming voltage from the vehicle plug up to ~14.2V and ensures the van battery is properly charged (compensates for voltage drop from the vehicle). This would be one explanation for the higher van voltage than the trailer connection plug voltage.

Cheers

Captain

Hello Gentleman

Well just got back home from my mates place we put a dirty great big earth on the T-Van battery and in doing that halved the voltage drop we got the trailer up to 13.9 im thinking know is just the extra distance it has to travel in the trailer to get to the battery so we have a .3 different my mates more than happy with that and thanks again for all your help

Glenn...