Thread: Electrical Q; how many amps through 7-pin trailer socket?

Given the size of the wiring on the pump, a trailer plug should handle it fine. You should be able to connect the braking system to the stop light circuit through a relay (so as not to overload your brake switch) and assuming you have large enough wires to and from your plug, you should be fine. I don't know if there is an amps rating but you should be able to pull a fair bit through it.

A trailer plug should be able to handle 10 amps for a fair while, so long as the wiring to/from the trailer plug isn't too thin, resulting in big voltage losses. I would use at least 4mm2 wire if not 6mm2 to run from the brake controller to the socket, plus the earth return, and 4mm2 in the trailer plug cable.

A while a go (~2001) I fitted 2 electric/hydraulic units on 2 boat trailers, both with 4 wheel disks, both weighing around the 2.8t. Actuators used were 1200psi Carlyle Hydrastar. One of these rigs is still owned (and used heavily) by the family.

The 1st one was wired with the electrical feed through the 7pin plug. The 2nd one had an electric winch that was run through an Andersen plug (8mm2 cables) and we supplied the actuator power (and earth) from the winch. After a couple of outing with both, the 1st install was changed to get its supply from an Andersen plug as well because the 2nd unit performed so much better.

After that experience, there is no way I would ever install one of these unit with the power supply or earth through the 7 pin. The rotary pump takes time to build pressure and the better power source you can give it the less delay you will notice. There is a reason these actuators don’t draw their power supply from the controller – they want heaps – more than caravan drums

The switch wire on pin 5 is OK – there no need to run a heavy wire from the controller to the actuator – it is just a signal that supplies no current at all – electric caravan brakes are different as there draw all their power from the controller and do require something decent on pin 5 (and 3 for earth) – BUT it is a good idea to run something decent (as well as pin 3 earth) so it’s compatible with other systems.

You have picked a good controller – I have a P3 and it operates these brakes much better than any controller we’ve tried before (P2 should be the same)


Personally I wouldn’t use Electric/hydraulic on a camper, but I can see why your doing it...

Thanks for the responses, Harlies info prompted me to look at an online wiring diagram and it seems that the wire from the in-car controller does indeed only carry a signal, whereas the actual power feed to the pump needs to be at least a 30 amp circuit. As I already have a 50amp anderson plug running to the camper, I should be able to utilise this and run the signal wire through the 7-pin socket.
Seems these units use the controller differently to 'normal' electric trailer brakes, which get magnet power direct from the controller output.
The Prodigy P3 is not compatible with electric-hydraulic. The P2 has a dedicated setting for e/h brakes.

typically 5amps continuous 10 amp surge and 15 peak for a normal 7 pin flat or round, the large 7 pin round is rated for roughly double.

remember the limiting factor for the plug is usually the earth cable.

Originally Posted by POD

The Prodigy P3 is not compatible with electric-hydraulic. .

Not even close - Actually there is no such thing as a "Prodigy P3", so I can't really say that this statement is wrong.

There is a "P3" which has been out for several years, the box mine came in, and all its doco makes absolutely no reference to the name “Prodigy” – nor does the website.

There is a "Prodigy" which is no longer made, now replaced by the "Prodigy P2"

The "P3" CAN handle electric Hydraulic systems, mine has for at least 2 years now, by selecting “hydraulic” in the “Brake Type” setting - selectable via the multi line LCD screen.

The Original "Prodigy" CANNOT be used with Hydraulic systems, it will actually work but the test pulse (only difference between the two modes) will cause damage to the Hydraulic pump.

Seems I was misinformed about the P3 and it's compatibility with electric/hydraulic systems. One vendor website stated that the P3 was not suitable for this application. No matter, got the P2 at a good price and it looks the goods. Hoping my actuator arrives soon, keen to get on with this project now.

Originally Posted by harlie

Not even close - Actually there is no such thing as a "Prodigy P3", so I can't really say that this statement is wrong.

There is a "P3" which has been out for several years, the box mine came in, and all its doco makes absolutely no reference to the name “Prodigy” – nor does the website.

There is a "Prodigy" which is no longer made, now replaced by the "Prodigy P2"
<snip>

I have one of the original Prodigy controllers and am nothing but happy about it. Has saved me several times, however unplugging it to use in other vehicles caused occassional malfunctions when it was not plugged back in properly so I decided to get a second controller for my other RRc.

I purchased the P3 thinking it was the third upgrade of the Prodigy. Even though I haven't had any problems with the P3, I think I would rather have purchased the Prodigy P2.

Onto the current issue, the other option for powering the compressor for the trailer system is to use the 12pin (2 row) flat. The top row is the same 7 pins as the standard 7 pin flat and will recieve the 7 pin plug into the socket. The second row of 5 pins are designed to carry a higher current. You could use either of pins 8 (Batt charger/winch) or 9 (Aux Batt) for the battery feed and pin 10 an additional chassis ground.