Round or Flat trailer plugs?

Hi All
Soon to pick up an off road caravan and am
wondering what the pros and cons are for heavy duty round 7 pin or flat 7 pin trailer plugs.
ie does one hold in better than the other, does one fatigue more quickly than the other.?
Cheers Craig
Back Reply Expand Un-Read 0 Moderator

Reply By: Member - Stephen L (Clare SA) - Monday, Jun 22, 2020 at 23:40

Monday, Jun 22, 2020 at 23:40
Hi Craig

From what I have seen these days, a lot of campers and caravan are going away from the round and going to the flat......well that was the case when I got our camper.

I find the flat more compact and easier to connect. The only problem that I have had, is that from constant connecting and discovering, the male pins on the camper May lose contact, but takes seconds to fit with a small flat blade knife, but ever so gently slightly opening then up for a tight connection.

Best bet is to check what will be on your new van.

Cheers

Stephen
Roxby Downs Special

Lifetime Member
My Profile  My Blog  My Position  Send Message

AnswerID: 632257

Reply By: swampy - Monday, Jun 22, 2020 at 23:45

Monday, Jun 22, 2020 at 23:45
Hi
The larger pins in the 12 pin plug are an improvement if wanting more durable connection.
The standard pins should only carry lights and single axle brakes 12 pin preferred but 7 pin ok
Dual axle 4x brakes large 12 pin
Van earths multiple 12 pin large

Common box trailer 7 pin ok
AnswerID: 632258

Follow Up By: Nomadic Navara - Tuesday, Jun 23, 2020 at 07:43

Tuesday, Jun 23, 2020 at 07:43
There is an Australian standard for trailer connections - See This Link - Wire the brakes as per this standard. If you do not then it will be possible for someone to inadvertently couple a trailer with brakes to your vehicle and find out they have no brakes if you wire the brakes through the large pins in a 12 pin plug. Pin 5 is sufficient for four wheel brakes. In addition, if you wire the wire the brakes through the large pins then you can not tow another van that has only a seven pin plug (trailers with seven pin plugs can be connected to the 12 pin trailer sockets on the tug.)

Keep to the standard.
PeterD
Retired radio and electronics technician

Lifetime Member
My Profile  Send Message

3
FollowupID: 908819

Follow Up By: swampy - Wednesday, Jun 24, 2020 at 10:31

Wednesday, Jun 24, 2020 at 10:31
Hi
Use the largest pin and cable possible . All this to prevent volt drop especially on twin axle braking or use a more durable separate connector for brakes .
I have repaired ""just a few "" this way with great reliability and success.
1
FollowupID: 908841

Follow Up By: Nomadic Navara - Wednesday, Jun 24, 2020 at 12:28

Wednesday, Jun 24, 2020 at 12:28
I suggest that members stick to the standards and not to deviate from them. It takes a very sensitive voltmeter to measure any significant voltage drop across the trailer connector pins (unless of course you do not maintain your trailer plug properly.)

How many of you out there have had the trailer brake pin burn out?




PeterD
Retired radio and electronics technician

Lifetime Member
My Profile  Send Message

0
FollowupID: 908843

Follow Up By: qldcamper - Wednesday, Jun 24, 2020 at 15:47

Wednesday, Jun 24, 2020 at 15:47
Cant say I recall ever seing one melt a brake pin Peter,and I have replaced many dozens over the years. It is almost always the earth pin that melts.

The other big problem is a corroded tail light pin in the cars socket from it having 12 volts on it at night when the socket gets wet, mine it green at the moment too. Used to see pin 2 melt and corrode too but not often connected anymore.
0
FollowupID: 908844

Follow Up By: Nomadic Navara - Wednesday, Jun 24, 2020 at 16:12

Wednesday, Jun 24, 2020 at 16:12
Melted earth pins - If you have a 12 pin connection, make sure pin 10 is well earthed both in the tug and the trailer. Do this even though you may not use the large pins for heavy current. That will assist the small earth pin with current carrying.

That pin 2 problem - I got caught with it before I became aware of the low rating of the small pins. As a communications tech I am well aware of voltage drop problems. When I got my first 3-way fridge (the ones before were only 2 way - no 12 V) I attempted to improve the efficiency of the fridge whilst towing. I replaced the piddling thin manufacturers wire with 6 mm2 wiring in both the van and the tug. On the first long outing, I could not get the plug out. It had welded itself well and truly into the socket. I had to break the pin before I could uncouple. That's when I found out about about the real ratings of the connectors and 12 pin connectors. I have had 12 pin connectors on all vans over the 25 intervening years I have not had a pin burn out.

Many manufacturers have and still do, do not follow the standards. They still thieve pin 2 to power the fridges. They get away with it as the wiring is too light and the reduced voltage at the fridge due to voltage drop does not draw enough current to stress the connector. However, it also means the fridges do not work as designed on 12 V.



PeterD
Retired radio and electronics technician

Lifetime Member
My Profile  Send Message

0
FollowupID: 908846

Follow Up By: qldcamper - Wednesday, Jun 24, 2020 at 16:39

Wednesday, Jun 24, 2020 at 16:39
Had a run of problems with electric brakes not working very well when the fridges were turned on due to well greased towballs and light earth wiring to the car.
Some of the vans had a chassis voltage as high as 4 volts higher than the cars.

These days with LED trailer lights bad earths are not as easy to spot without the feedback glow from the other light circuits.
0
FollowupID: 908847

Reply By: Sand Man (SA) - Tuesday, Jun 23, 2020 at 07:16

Tuesday, Jun 23, 2020 at 07:16
There is no default standard.
Many people use a flat 7 pin plug and socket and a separate Anderson connector circuit for heavy duty connection to van for charging/12v fridge supply while in motion. The manufacturers usually ask which type of connection the buyer prefers and wire their vans accordingly.

The flat plugs and sockets provide a better locking connection. The spring loaded socket lid has a couple of lugs which hold the plug in the socket quite securely.
The flat plugs and sockets are quite robust and I find they are easier for maintenance, checking for loose or broken wires.
Bill


I'm diagonally parked in a parallel Universe!

Member
My Profile  My Blog  My Position  Send Message

AnswerID: 632260

Follow Up By: qldcamper - Wednesday, Jun 24, 2020 at 18:45

Wednesday, Jun 24, 2020 at 18:45
The round plugs both large and small have claws arranged in the cover flaps to hold the plug in also but the spring usually corrodes and renders it useless in time.
My preferance is a 7 pin flat but my present one hasnt got a flap, after doing such a marvelous job installing it above the rear step to make it more accessable the bloody flap didnt have room to open far enough to get the plug in so i took the flap off.
1
FollowupID: 908848

Follow Up By: Member - David M (SA) - Wednesday, Jun 24, 2020 at 20:38

Wednesday, Jun 24, 2020 at 20:38
So your travelling flapless Q/c. Are you sure that's legal. :)
Dave.
0
FollowupID: 908853

Follow Up By: qldcamper - Wednesday, Jun 24, 2020 at 21:12

Wednesday, Jun 24, 2020 at 21:12
Haa Dave, there is somewhere I am not brave enough to go lol.
0
FollowupID: 908854

Follow Up By: Nomadic Navara - Thursday, Jun 25, 2020 at 08:00

Thursday, Jun 25, 2020 at 08:00
If that flap does not lock properly then the plug is likely to work its way out. It will fall to the roadway so he then has to replace it. It will not be long before he has to do something about it.
PeterD
Retired radio and electronics technician

Lifetime Member
My Profile  Send Message

0
FollowupID: 908857

Follow Up By: qldcamper - Thursday, Jun 25, 2020 at 09:19

Thursday, Jun 25, 2020 at 09:19
Theoretically correct Peter, but it is a tight squeeze to get it in where it is and the top of the rear step rests firmly against it so it is a 2 hand operation to remove it, it wont go anywhere on its own.
I had no choice but to put it up there because the old position was not protected by the stone stomper and both it and the anderson plug got destroyed after a couple of days on gravel.
Luckily I had a 6 pin Deutsch plug and receptical in my "might come in handy" box.
The way the electrolysis is setting in to the flat socket I am considering replacing it with Deutsch permanently and keeping it sealed with a senson filled cap. Sort of half way to a military version, just means I will need a couple of adaptors on hand.
All this because my flap has been removed and I can see whats going on before I actually need to use it.
1
FollowupID: 908859

Reply By: RMD - Tuesday, Jun 23, 2020 at 08:58

Tuesday, Jun 23, 2020 at 08:58
Use a flat 7 pin setup. Properly positioned on the vehicle, Near the centre, not to the side as many are, means there is practically no drag on the wire cable when connected. If cable is fed through a retaining lug or loop near the hitch then it will never be pulled out or drop out and drag on the road. The connection is as reliable as any other, perhaps better reliability. Sometimes you do have to spread the pins slightly as mentioned above but that is the same for any plug. A prudent person always carries a spare plug so if any damage or failure happens you can simply replace it and still have everything working. These plugs are not of a size or capability to supply any significant power to a fridge or battery. Even the 12 pin variant, which does have large power pins, is sus for power and best an Anderson plug arrangement is used for any significant power transfer to caravan. Your van lights LED, and brakes don't take much current so 7 will do the job.

The whole thing is for light duty work not heavy at all. Heavy duty means what? What concept of heavy is thought of as being an advantage?
AnswerID: 632262

Follow Up By: Gronk - Tuesday, Jun 23, 2020 at 17:45

Tuesday, Jun 23, 2020 at 17:45
Even the 12 pin variant, which does have large power pins, is sus for power and best an Anderson plug arrangement is used for any significant power transfer to caravan.



The large pins on the 12 pin plug are rated at 35A........double them up and you have 75A. Pretty good compared to the anderson 50A plug.
'
I have 12 pin plugs, but both 4wd and van had andersons, so I have not bothered to use the 12 pin large pins.
0
FollowupID: 908831

Follow Up By: Member - peter_mcc - Wednesday, Jun 24, 2020 at 15:48

Wednesday, Jun 24, 2020 at 15:48
Gronk - Anderson SB50 connectors are actually rated to carry 120A. The 50A rating is a UL rating for hot plugging.

See the datasheet: https://docs.rs-online.com/cf13/0900766b81714eef.pdf

I'm not sure how the 35A rating on a 12 pin trailer plug/socket is calculated/measured - it is probably in AS4177.5-2004 but I don't have access to the standard.
0
FollowupID: 908845

Reply By: Frank P (NSW) - Tuesday, Jun 23, 2020 at 09:54

Tuesday, Jun 23, 2020 at 09:54
My van came with a large 7 pin round plug. I'm not impressed. They are difficult to plug in and remove without strong "wiggling". This seems to make the pins lose their tension relatively quickly, resulting in poor connections. My Redarc Tow Pro was especially susceptible to that, frequently reporting a poor earth. Fixed, of course by gently spreading the pins with a knife.

Until the plastic disk that hold all the pins breaks. Then it's a new plug.

After 4 or five replacements over the years and numerous campsite repairs adjusting pin tension I changed to 12 pin flat with standard wiring. It is MUCH easier to plug in and remove, so I suspect much easier on the pins. We'll see how that goes.
FrankP

Member
My Profile  My Blog  My Position  Send Message
Moderator

AnswerID: 632263

Follow Up By: rumpig - Tuesday, Jun 23, 2020 at 12:04

Tuesday, Jun 23, 2020 at 12:04
Can’t say i’ve had any issues in 10 years of owning our Kimberley Kamper with the large 7 pin round plug it came with, the plug has performed flawlessly over much of Australia and still going fine.
1
FollowupID: 908825

Reply By: Notso - Tuesday, Jun 23, 2020 at 10:39

Tuesday, Jun 23, 2020 at 10:39
Last Caravan I owned, the manufacturer wouldn't even consider fitting a flat 7. He insisted on the large round 7 pin. Larger Pins means better contact, less resistance etc. That was their story. I must say I had absolutely no issues with it, as opposed to 7 flat with the pins closing up and making poor contact etc.
AnswerID: 632264

Follow Up By: RMD - Tuesday, Jun 23, 2020 at 11:49

Tuesday, Jun 23, 2020 at 11:49
Hardly any caravan manufacturers tow caravans throughout Australia for any period of time so are not good ambassadors for lots of things. In a previous job I rewired trailers of a fleet and replaced/ fitted many many troublesome round 7 pin plugs which fell out or failed because of loose pins. The notion that large pins are better is flawed with the plug only passing electrical flow where the pins actually can touch their mating surface. Pull out a 7 round base or plug and look with a magnifying glass what contact there really is, you will be alarmed. An accurate 7 pin flat system can't be worse. 7pin flat fits into 12 pin base flat/2 row, so is handy if other vehicles are involved.

The reason the manufacturer wouldn't fit a flat one was because they had hundreds of round plug systems in stock and wanted to sell them otherwise they lose on the bulk deal purchase they made.
4
FollowupID: 908824

Follow Up By: Notso - Tuesday, Jun 23, 2020 at 12:51

Tuesday, Jun 23, 2020 at 12:51
Wouldn't know about any technical details really, but I do know I had no issues with the Large Round 7, whereas I have always had issues using the flat 7.
1
FollowupID: 908826

Follow Up By: Frank P (NSW) - Tuesday, Jun 23, 2020 at 13:46

Tuesday, Jun 23, 2020 at 13:46
Another issue that helped force my hand is the BT50 manufacturer's trailer wiring and the 12 pin flat socket they use. It is a Mazda-branded socket and has two extra wires in it that are connected to a reed switch which is operated by a small magnet in the dust lid. If you listen carefully you can hear the switch operate when you open and close the lid.

The BT50 has trailer sway control. I presume the reed switch tells the vehicle that a trailer is present, probably to turn off reversing sensors where fitted and also, perhaps, to activate trailer sway control. The manual gives no clues that I can find to confirm that. I have asked both my dealer and Mazda customer service about the trailer sway control component but have been unable to get a clear answer.

I took the precautionary approach and left the flat socket in place, in the hope that I get a better run out of it than I did with the large round.
FrankP

Member
My Profile  My Blog  My Position  Send Message
Moderator

0
FollowupID: 908828

Follow Up By: RMD - Tuesday, Jun 23, 2020 at 16:01

Tuesday, Jun 23, 2020 at 16:01
You are right Frank, the lid does contain a magnet and reed switch buried in the Base with two contacts. Isuzu tow bar bases have the same system to switch off reverse sensors when towing. Magnet closes reed with lid closed and the reed switch for camera and sensors and no magnet opens the reed, ie, an "NO" status reed, very small current through that though.

Not sure if the base lid magnet/reed has a bearing on sway control as any damage to the base would render sway inoperative. Pretty non techo is the base of most vehicles. I presume sway control is done by an inbuilt Yaw sensor in the vehicle, similar to Alko caravan sway detection, or rather Alko has used the tech for cvans.
0
FollowupID: 908830

Reply By: qldcamper - Tuesday, Jun 23, 2020 at 14:37

Tuesday, Jun 23, 2020 at 14:37
Whatever configuration you decide on make sure you use Utilux and if not a flat variety go for a metal bodied Utilux.
There are so many cheap rubbish brands out there sold by auto spares shops and even cheap shops like crazy clarks and dollar shop and so on, many fall apart when your trying to fit them.
Utilux has been around in Australia since before I was around and has never gone backwards in quality to stay compeditivly priced as did Hella when Narva flooded our market with cheap copies. Dont know if Hella still sell trailer plugs in Australia, they turned to crap probably when they moved manufacturing off sure, I stopped using them over 30 years ago.
AnswerID: 632267

Follow Up By: bellony - Tuesday, Jun 23, 2020 at 20:23

Tuesday, Jun 23, 2020 at 20:23
Yep, Utilux alloy large round, problem solved. Never falls apart, large terminals make it easier for breakaway battery feeds or piggy backing wires for extra signal lights. The one on our LC has been around since 1994, still going.
0
FollowupID: 908834

Follow Up By: Frank P (NSW) - Tuesday, Jun 23, 2020 at 20:32

Tuesday, Jun 23, 2020 at 20:32
i wish I had such luck with the round.

Now using Utilux Alloy 12 pin flat.
FrankP

Member
My Profile  My Blog  My Position  Send Message
Moderator

0
FollowupID: 908836

Reply By: Ausdigga - Tuesday, Jun 23, 2020 at 18:55

Tuesday, Jun 23, 2020 at 18:55
And it would be wonderful if the makers of these plugs and sockets used stainless instead of thinly plated steel fasteners that rust within weeks, after all they are meant to be out in the weather , yes ?
AnswerID: 632270

Follow Up By: RMD - Thursday, Jun 25, 2020 at 10:22

Thursday, Jun 25, 2020 at 10:22
I always use a Lanolin spray into the wires of bases and plugs so the green verdigris and any rust is severely retarded from developing. So a good idea, YES? Also means the screws are lubed to be able to service or replace whenever required. The Lanolin also tend to run water away from the innards of the plug to further assist with prevention.
4
FollowupID: 908866

Reply By: Grizzle - Tuesday, Jun 30, 2020 at 14:46

Tuesday, Jun 30, 2020 at 14:46
One thing which can be overlooked is with the Flat plug you can't wire incorrectly (based on following the conventions of course). Whereas with a round plug there are 5 wire and 7 wire configurations. With the 12 pin flat it should only be the power to your electric over hydraulic brake wire that goes into the larger pins. Then when you have a 7 pin flat your standard electric brakes will still work.

Lifetime Member
My Profile  Send Message

AnswerID: 632323

Reply By: LIFE MEMBER-snailbait - Thursday, Jul 09, 2020 at 11:56

Thursday, Jul 09, 2020 at 11:56
I f you live in NSW the round Aluminium 12 pin If you live else ware any thing wil do
Life MEMBER snailbait Oberon HF RADIO CLUB VKE237 mobile 7661

Lifetime Member
My Profile  Send Message
Classifieds: End of an ERA AVAN Owen ltd with adventure pack 2014

AnswerID: 632436

Sponsored Links

Popular Products (13)