50 Amp Circuit breakers & trailer plugs
Submitted: Monday, May 31, 2010 at 21:26
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Mark
Hi Guys
I am installing some 16mm2 cable from a smart isolator in the engine bay to a 12 Pin flat trailer plug to connect to charge a second battery in a camping trailer.
1. The Trailer manufacturer recommends a 50 amp breaker near the isolator. I have seen several types but the cheaper auto reset type seem flimsy & i'm worried about voltage drop. Are there any other alternatives for 16mm2 cable? (the trailer manufacturer recommended 8 B & S but i'd rather use the heavier stuff).
I have used a 75 amp (resettable) breaker from Jaycar in the past but found that it had a .5 volt drop from the input to output.
2. Does anyone know the max cable size for a 12 pin Britax B48 trailer socket (trailer has a B47 plug). I guess I'm going to have to step down the cable size at the socket. I'll be splitting the load across two pins which are 35 amp each.
3. Is it best to earth the return close to the trailer plug on the vehicle chassis or run a second 16mm2 cable back to the engine bay and as close to the alternator as possible. In other words would decent copper wire provide lower resistance than the vehicles steel chassis.
Thanks
Mark
Reply By: Member - Andrew (QLD) - Monday, May 31, 2010 at 22:04
Monday, May 31, 2010 at 22:04
Mark,
Most people use an anderson plug to supply power on a seperate system to the trailer plug. A typical diagram from the battery charging article on this site which may answer some of your questions:
Andrew
AnswerID:
419016
Follow Up By: ABR - SIDEWINDER - Monday, May 31, 2010 at 22:32
Monday, May 31, 2010 at 22:32
Hi Mark
We find auto reset breakers work
well, they have a set of contacts inside and can carry quite heavy current without voltage drop. Make sure to support the cable on each side of the breaker, don't use the breaker as a cable anchor.
Regards
Derek from ABR
FollowupID:
689179
Reply By: drivesafe - Tuesday, Jun 01, 2010 at 12:24
Tuesday, Jun 01, 2010 at 12:24
Hi Mark, it’s not uncommon to get a voltage drop across an unloaded set of contacts like a relay or circuit breaker.
But if you got a reading like that across the circuit breaker with even a small load of say 10 amps, you probably got an incorrect measurement because even at 10 amps, the amount of heat that needs to be generated to create a 0.5v voltage drop, your circuit breaker would literally glow in the dark.
Try measuring again, with a decent load and see what you get.
AnswerID:
419090
Reply By: Member - Graham H (QLD) - Tuesday, Jun 01, 2010 at 12:45
Tuesday, Jun 01, 2010 at 12:45
7 and 12 pin connectors are nowhere near heavy enough for that sort of wire
Use Anderson Plugs to do the job properly.
AnswerID:
419095
Follow Up By: Mike DiD - Tuesday, Jun 01, 2010 at 13:56
Tuesday, Jun 01, 2010 at 13:56
. . . and Anderson contacts are silver-plated so they'll still be working years later.
FollowupID:
689249
Follow Up By: drivesafe - Tuesday, Jun 01, 2010 at 14:48
Tuesday, Jun 01, 2010 at 14:48
Like Mike posted, not only are genuine Anderson terminals silver-plate but unlike trailer plugs and sockets which are friction fit and get loose with time, Anderson plugs are spring loaded so you get the same contact pressure over the life span of each plug.
FollowupID:
689256
Reply By: Mark - Tuesday, Jun 01, 2010 at 21:26
Tuesday, Jun 01, 2010 at 21:26
Thanks for the replies guys. I would normally use Anderson plugs as I have already used these on the connection to the fridge & tyre compressor in the 4WD. The problem is the trailer manufacturer has wired the trailer with the 12 Pin plug so I would have to modify it after I take delivery.
Cheers
Mark
AnswerID:
419170