DC-DC charger and Emergency Breakaway

[Guest]

When I re-wired my rig for lithium power in the passthrough, I did not feel comfortable having an unprotected circuit inside the rig to the break away switch. On the TT in its original configuration, the break away is wired directly to the battery outside the rig. I inquired for the acceptable method and found that a direct connection has to be made but a breaker can be used on this circuit as long as no other components are connected to that circuit.

My break away is also wired through the main switch where I struggled with this initially. I was considering a frame mounted break away kit with aux battery and charger where the charger function could be protected via a breaker. I finally just left the break away switch configured through the main switch at the docking station and protected that circuit with a dedicated breaker. We travel with the fridge on and also need the switch on to operate the tongue jack so there is no possible way to forget to close the switch for the break away function during travel. My main switch was also replaced with a Sierra marine switch with a much stronger detent to be sure it stays closed during travel. This configuration is a compromise but one I am comfortable with.

Jim

[AlexPeterson]

I totally concur with Guest Jim above.

I don't have a 5th wheel, but the original wiring for the break-away was: Battery to automatic resetting circuit breaker on the frame, then a wire directly back to the break-away from the non-protected side of the circuit breaker. However, there was an in-line fuse about halfway in the break-away line. I brought all of this inside the pass through, documented in another thread. I would advise against running any unprotected wire directly from a battery. The original wiring on our TT did have a few feet of it, but it was all external and fastened to the frame.

I would advise testing the break-away regularly, just a quick pull and immediate re-insertion of the pin. It takes a lot of force to do these removal/insertions. You should hear a clunk in the brakes. Wear gloves - there are really sharp edges on the pin or switch (there was blood involved in learning this).

[epearce]

AlexPeterson I'm coming around to this point of view (no unprotected wire). Between the risk of a short, snagging a wire, mice, etc... and having a trailer fire, vs. the seemingly unlikely failure of a breaker or fuse on a single wire circuit, and a breakaway situation, it seems like a protected circuit is the way to go.

So, how big of a fuse did you use? Anyone know what the current draw on the electric breaks is?

[AlexPeterson]

epearce Seems it was a #10 wire, so IIRC it had a 30amp fuse. I might be wrong about this - will look next time I'm at the storage shed, sometime in the next week. I believe the amperage is around 3a per wheel, or about 16a total, at least for the axles on mine. I understand that this will vary with axle weight rating.

[Jlawles2]

I read somewhere so take it for that. Someone pulled the break away switch (not a good idea IMHO) to help with unhooking and setup on an incline. They forgot to reinstall the pin and after a brief (under 1 hr IIRC) either the owner remembered or smelled something. They found the wire from the switch to be extremely HOT and was starting to melt the insulation. No breaker or fuse on the circuit.

Problem: during emergency operation the is no regulation on the amount of voltage or amperage sent to the magnets as stopping the unit is the first priority. Fusing (or circuit breaker) the circuit may actually defeat the purpose of the system if the fuse blows due to current.

[Scott'n'Wendy]

Problem: during emergency operation the is no regulation on the amount of voltage or amperage sent to the magnets as stopping the unit is the first priority. Fusing (or circuit breaker) the circuit may actually defeat the purpose of the system if the fuse blows due to current.

To each their own I guess. But there should never be a fuse or breaker or a splice in the emergency brake system. I've never heard of a trailer burning down because of the emergency brake...I'm sure it has happened. In that rare event, that is what my insurance is for. But I'm not going to potentially help the emergency brake to fail, however remote the chance of that happening.

[Scott'n'Wendy]

Country Campers
About the only other way I could think of would be with a relay. With the relay connecting the original charge wire back to the +ve busbar. So when there is no signal to the DC-DC, the relay contacts (N.C) are closed and completes the cct back to the busbar. When the truck is connected and sending a signal to the DC-DC, that same signal would pick up the relay cutting off the bypass connection to the +ve busbar. The N.C contacts would be open with the 12v signal from the truck.
This will still have you with connections in the emergency brake system...but how comfortable you are with connections is up to you. It is a fail safe style of wiring the relay.

[AlexPeterson]

I read somewhere so take it for that. Someone pulled the break away switch (not a good idea IMHO) to help with unhooking and setup on an incline. They forgot to reinstall the pin and after a brief (under 1 hr IIRC) either the owner remembered or smelled something. They found the wire from the switch to be extremely HOT and was starting to melt the insulation. No breaker or fuse on the circuit.

Problem: during emergency operation the is no regulation on the amount of voltage or amperage sent to the magnets as stopping the unit is the first priority. Fusing (or circuit breaker) the circuit may actually defeat the purpose of the system if the fuse blows due to current.

Joe - I totally agree with "to each his own" regarding fusing various circuits.

In this and many other discussions on this forum, it can be helpful to think about the amperage a little differently: it is not sent to the brakes, but, rather the brakes draw a finite and knowable amount of current from the battery. The amount of this current, assuming the battery can supply it, is a simple Ohm's law result. Voltage divided by resistance = current. Of course, the brake pucks (coils) will heat up, and that is the real danger of leaving the brakes on for an extended period of time. If the brakes each draw 3 amps, the wattage is about 3 x 12 = 36 watts or so. Put that in a confined, relatively small volume like the brake puck and it will get hot. If the wiring to the brakes is getting hot, there is something else wrong with the system such as a short to ground in the wiring or puck, loose (corroded) connection in the switch, undersized wire, etc.

[Yoda]

You folks got me thinking about this - made my head hurt too

You would think in the design the engineers took into account the breakaway switch being pulled for a long time. In the case of a trailer separation, the brakes will activate and stay activated until someone disconnects the power (not probable), retrieve and re insert the key (not probable) or or the batterys god dead - most likely. Now with a stock 80 amp hour battery a 12A that is about 4 to 6 hours, but with today's upgraded battery system that could now be days. I would be curious is anyone has tested or would be willing to put an amp meter on the brake main power line and pull the key and watch for a period of time, taking temperature measurement where possible.

I wonder if the brake manufacturer has don this already in testing? But that would probably just be the brake assembly and not the support wiring. There also must be a reason the circuit is not fused - guberment regulation?

One would think that with the magnets activated and attached to the drum, that the drum becomes a huge heat sink. I would also like to believe the designers designed the brake wiring to withstand constant power, but who knows. On my unit the brake wiring at the drum seems to be a smaller gauge than the wiring crossing over between them and the power line feeding them from the battery. We all know the weak link will fail first, or fry in this case.

But we all know what happens when I think....I guess time to go back to my corner.

Keith

[epearce]

You folks got me thinking about this - made my head hurt too

You would think in the design the engineers took into account the breakaway switch being pulled for a long time. In the case of a trailer separation, the brakes will activate and stay activated until someone disconnects the power (not probable), retrieve and re insert the key (not probable) or or the batterys god dead - most likely. Now with a stock 80 amp hour battery a 12A that is about 4 to 6 hours, but with today's upgraded battery system that could now be days. I would be curious is anyone has tested or would be willing to put an amp meter on the brake main power line and pull the key and watch for a period of time, taking temperature measurement where possible.

I wonder if the brake manufacturer has don this already in testing? But that would probably just be the brake assembly and not the support wiring. There also must be a reason the circuit is not fused - guberment regulation?

One would think that with the magnets activated and attached to the drum, that the drum becomes a huge heat sink. I would also like to believe the designers designed the brake wiring to withstand constant power, but who knows. On my unit the brake wiring at the drum seems to be a smaller gauge than the wiring crossing over between them and the power line feeding them from the battery. We all know the weak link will fail first, or fry in this case.

But we all know what happens when I think....I guess time to go back to my corner.

Keith

Good points...

I guess I would add that you will have splices on your E-brake wiring, its unavoidable. My breakaway switch looks to be 12 AWG, although I have a big marine grade 10 AWG extending it to the battery. Rather unavoidably, there is a lug at the battery, and a splice at the breakaway switch. The other end has a lug and a post connector to the 7-pin junction box. The trailer brake wiring has multiple clamp style wire connectors. One more well done splice is not going to be a big addition to the failure risk. The breakaway switch wiring is unlikely to be long enough to get to an internally mounted battery bank. If this all was truly considered safety critical wiring it would be in a conduit, or steel braid, or something, not just some bare, not even marine grade 12 AWG hanging under the tongue of the TT.

Yoda as you point out, a big battery bank is likely to run the brakes for days. Hopefully the tow truck guys know to clip those wires or something when the load the wreckage up on the truck. I think the first thing that get warm is that 12 AWG at the switch. Although I think we would all consider it undersized for a continuous load like that, it is rated at 20 A, and would probably be just vaguely warm.

But lets think about the real risks here... (1) Trailer breaks away, which with a TT would require the hitch receiver to disconnect, and the safety chains to fail, and the breakaway switch to pull, and THEN somehow the fuse or breaker to be tripped on the e-brake, or (2) the unprotected e-brake wire gets snagged on a branch or something, shorts to the frame, arc welding itself there and killing your battery, or worse, causing a fire. I think (2) is much more likely. Has anyone ever heard of a complete breakaway, except while watching old episodes of CHiPS?

I cannot find any DOT regulation that says it should be unfused, or unprotected.

So, I think common sense applies: (1) used good solid connections, and minimize the number. (2) use a good marine grade durable wiring and route in as protected of a path as possible to the battery, independent of the rest of your 12+ distribution, (3) protected it with a fuse, perhaps a bit oversized, or a self-reseting breaker.

[AlexPeterson]

Mine had an in-line fuse from the factory, between the common battery connection and the break-away switch.

[Guest]

The standard is a 5ah supply which should hold the brakes for 15 minutes. The auto resettable breaker I use is never exercised and is mounted inside so it has an indefinite service life. A relay that is exercised regularly is subject to failure and should not be used. I would not recommend a fuse but rather an auto resettable breaker for the break away which should be the only item on this circuit. If folks are uncomfortable with this setup there is only one option. A break away kit with aux battery and charger mounted outside the rig where the charger circuit could be protected. Many of these kits have LEDs on the aux battery box that indicates the state of charge to be checked before towing.

No way I would run an unprotected circuit inside the rig just like I would not do so inside our home.

Jim

[Guest]

Good points...

I guess I would add that you will have splices on your E-brake wiring, its unavoidable. My breakaway switch looks to be 12 AWG, although I have a big marine grade 10 AWG extending it to the battery. Rather unavoidably, there is a lug at the battery, and a splice at the breakaway switch. The other end has a lug and a post connector to the 7-pin junction box. The trailer brake wiring has multiple clamp style wire connectors. One more well done splice is not going to be a big addition to the failure risk. The breakaway switch wiring is unlikely to be long enough to get to an internally mounted battery bank. If this all was truly considered safety critical wiring it would be in a conduit, or steel braid, or something, not just some bare, not even marine grade 12 AWG hanging under the tongue of the TT.

Yoda as you point out, a big battery bank is likely to run the brakes for days. Hopefully the tow truck guys know to clip those wires or something when the load the wreckage up on the truck. I think the first thing that get warm is that 12 AWG at the switch. Although I think we would all consider it undersized for a continuous load like that, it is rated at 20 A, and would probably be just vaguely warm.

But lets think about the real risks here... (1) Trailer breaks away, which with a TT would require the hitch receiver to disconnect, and the safety chains to fail, and the breakaway switch to pull, and THEN somehow the fuse or breaker to be tripped on the e-brake, or (2) the unprotected e-brake wire gets snagged on a branch or something, shorts to the frame, arc welding itself there and killing your battery, or worse, causing a fire. I think (2) is much more likely. Has anyone ever heard of a complete breakaway, except while watching old episodes of CHiPS?

I cannot find any DOT regulation that says it should be unfused, or unprotected.

So, I think common sense applies: (1) used good solid connections, and minimize the number. (2) use a good marine grade durable wiring and route in as protected of a path as possible to the battery, independent of the rest of your 12+ distribution, (3) protected it with a fuse, perhaps a bit oversized, or a self-reseting breaker.

Good points as well. Many do not realize the safety chain length should be set up so the break away activates in a TT situation when the trailer separates from the ball but not from the chains. I believe Howard did a post on this long ago which would be good reference material. I believe the fifth wheel would be set up similarly but I do not own one so perhaps Howard can chime in.

Jim

[Jlawles2]

The only reason the break away cable needs to be shorter than the chains has more to do with the way people attach. A lot (not everyone) uses the chain hook as the attachment point to the TV. This creates an issue. If something happens to the trailer and it becomes disconnected, where is the chain going to fail? The bent wire hooks may or may not be the weak link. With a shorter break away cable, it ensures the switch gets activated before the chain hook could possibly fail. This is also why there are no chain attachment points on the actual ball mounts. If the pin fails on the ball mount with the chains attached, you have no safety.

With trailer e-brakes, I always try to use a separate hook arrangement for the breakaway switch. Ideally using a completely separate attachment point would be the most ideal, however most TV and their receivers only have attachment points for chains in 2 places.