Wiring electric tongue jack on trailer with DC-DC charger

[rubicon327]

Originally Posted by tdf-texas

The 60 amp fuse is fine. The only way that it would blow from the emergency brake circuit is that the wiring shorted to ground and the 60 amp fuse will prevent any wire meltdown.

If you are curious, attach a 10 ga wire to a 60 amp fuse and dead short it across the 12v battery. The fuse will blow before the wire even gets warm.

Using an additional fuse in the emergency brake circuit is not recommended. The emergency brake circuit is a safety system and should be designed for maximum reliability. Also, any failure of the power to the circuit should be readily detectible - blowing the battery 60 amp fuse will leave the trailer 12v dead and about as noticable as it can get outside adding a alarm horn that would sound when the fuse blows. ( idea for a new mod.)

I would suggest adding the trailer power jack to the 10 ga for the emergency brake circuit at the 7 pin junction box with a inline 30 amp fuse on the power to the jack. The two circuits are never used at the same time so it should be fine.

Thanks for this insight. Only issue is with the jack connection. With my inline DC-DC charger I don’t think I have power at the 7 pin junction box 12V+ unless I’m connected to the tow vehicle. See my initial post. I’ll check but I think I need to terminate on the trailer side of the DC-DC charger.

[MVA]

When I install a power jack, I will probably terminate at one of the two 30A terminals in the WFCO power center. That way the jack will operate both when the trailer is on shore power (and the battery disconnected/removed), and on battery power.

[rbryan4]

Originally Posted by MVA

When I install a power jack, I will probably terminate at one of the two 30A terminals in the WFCO power center. That way the jack will operate both when the trailer is on shore power (and the battery disconnected/removed), and on battery power.

It's much simpler to connect directly to the batteries in a 19, or to tap in to the terminal under the rail for the 7 pin. There's only one wire on most power jacks, and the bolts that hold it to the frame provide ground. The jacks (most of them anyway) have their own inline fuse on the power wire. In any case, a power jack should always be wired (logically) directly to 12V battery power.

[MVA]

Originally Posted by rbryan4

It's much simpler to connect directly to the batteries in a 19, or to tap in to the terminal under the rail for the 7 pin. There's only one wire on most power jacks, and the bolts that hold it to the frame provide ground. The jacks (most of them anyway) have their own inline fuse on the power wire. In any case, a power jack should always be wired (logically) directly to 12V battery power.

Understand. Depends where the battery is located. I could not remember from previous posts if rubicon327 had moved his battery inside (like I did). Given the three options he outlayed earlier, I suspected he may have.

[rubicon327]

Originally Posted by MVA

When I install a power jack, I will probably terminate at one of the two 30A terminals in the WFCO power center. That way the jack will operate both when the trailer is on shore power (and the battery disconnected/removed), and on battery power.

Your 7 pin charge line terminal in the junction box should be hot too at all times even without a battery because the converter would backfeed power. I have custom wiring and components so this is not true for me. My lithium battery and 7 pin junction box are inside. DC-DC charger on the 7 pin charge line is a one way device which makes my charge line terminal on vehicle side dead unless plugged in to tow vehicle. Also my WFCO converter was replaced with Xantrex inverter/charger wired direct to the battery so I need to have a battery installed to have any 12V power for the jack or any other devices. I need to come inside for any of my options so just deciding which is best.

This has gotten convoluted but for most owners with standard wiring landing on the 12V+ terminal with the charge line in the 7 pin junction box is probably the easiest since it is typically outside on the frame rail. You should have power there in all circumstances.

[rubicon327]

Finally got around to installing the Bulldog electric tongue jack. It fit perfectly and installed quickly with three bolts. Rotated it to face the driver’s side for better clearance. Had to rotate the emergency breakaway module slightly to clear larger round base. Propane cover is snug but it works. Ended up running the power to one of the 30A slots on the WFCO DC board since my wiring required me to go inside for power anyhow. Etrailer says the normal draw for the Bulldog jack is 15 amps, but can surge to 30 amps when under maximum stress. I ran a 10AWG wire and used a 30A fuse. For those that don’t know only the lowest two slots on the WFCO DC board are rated for 30A. The rest are rated for 20A. I did a speed test and it matched the etrailer numbers almost exactly (extends about 6" in ~28 seconds
and retracts 6" in ~24 seconds) even with less load (they tested with 1000# tongue weight). This is faster than most jacks and it is also very quiet. The 8” drop leg design is a nice feature. The manual override was tested and it moves the jack quickly and smoothly without much effort to overcome the motor. Time will tell but based on initial impressions I highly recommend this jack.

[rubicon327]

Granted it was not covered but a little disappointed in the fading away of the button labels on the Bulldog jack in only a year and a half. Nothing a label maker couldn’t fix. Jack is still functioning perfectly.