RV 12V power wire

**deerewright** · 05-31-2009, 03:36 PM

I have a 2006 LE that I already have wired for a brake controller, but want to run 12V out to the camper for the Aux battery. I also only want it to be powered off of an ACC line (not hot), so it only draws power when the van is on. Anyone have any suggestions for where to tap into an accessory line?

Thanks,

**robo5** · 05-31-2009, 05:03 PM

There is a "power outlet" in the cargo area. Do you need something more heavy duty than that?

**deerewright** · 05-31-2009, 07:59 PM

There is a "power outlet" in the cargo area. Do you need something more heavy duty than that?

I don't know. I know that the aux power wire on the trailer is 10ga., and I'm afraid of pulling too much amperage through that power port line. I don't know what the requirement is (amperage wise) for that line

? The 12V system on the trailer is a 20amp system, so I guess I should plan on 20 amps? What is the amp rating on the power port?

**robo5** · 05-31-2009, 08:17 PM

I just went out to my van. The power outlet is good for 120 watts(sorry i don't know if that helps you??) There is only 1 fuse that i can see as far as "power outlet" and it is an 15 AMP fuse.(now this fuse does all 3 power outlets so this i split between 3 outlets)

What will be running on the trailer while the van is i motion

Fridge? Or are you just using the convertor to top up the battery?

Sorry this is all the help i can give you at this time. Hang tight.. We have some great guys on here that will give some great info!!

**deerewright** · 05-31-2009, 09:40 PM

Just looked at it myself. 120 watts on a 12V circuit means 10 amps (Volts * amps = watts), so the line is rated for 10amps. You are also correct I think on the 15amp fuse. Each port is rated for 10amps max, probably, but the entire circuit (all three) together for a max of 15amps. The only thing I would be running would be the fridge and keeping the battery topped off, I'm going to try to find the amp rating for the fridge and go from there. I would like to run a dedicated circuit for the trailer aux power, so I'd like to avoid tapping into an existing circuit. I don't mind running wire from the front all the way back (already did that once for brakes). Hopefully someone will have a good solution. Thanks for the help.

**robo5** · 05-31-2009, 09:56 PM

The only thing that i can add to this is. What "camper" are you towing? Size? This will help on other comments on this. How long from point "A" to point "B"

**tcp** · 05-31-2009, 10:06 PM

I suggest you run a 10guage wire from the battery, through a 30 amp fuse near the battery to the back of the van. Back there I would interrupt the wire with a normal auto relay and use the accessory socket power wire to trigger the relay and close the connection when the van is on. Then finish the wire run back to your 7 pin connector.

Originally Posted by deerewright

Just looked at it myself. 120 watts on a 12V circuit means 10 amps (Volts * amps = watts), so the line is rated for 10amps. You are also correct I think on the 15amp fuse. Each port is rated for 10amps max, probably, but the entire circuit (all three) together for a max of 15amps. The only thing I would be running would be the fridge and keeping the battery topped off, I'm going to try to find the amp rating for the fridge and go from there. I would like to run a dedicated circuit for the trailer aux power, so I'd like to avoid tapping into an existing circuit. I don't mind running wire from the front all the way back (already did that once for brakes). Hopefully someone will have a good solution. Thanks for the help.

**scubajoe** · 05-31-2009, 10:50 PM

I think that you'd need a relay controlled by an accessory power line, which ran the 12V line directly form the battery. I've heard that you also really need a boost regulator in order to get enough voltage back there to actually be able to charge the battery when you're driving. For these reason (and because we pretty much always have hookups) I haven't bothered running the power back there for the AUX.

I'm not sure what the drop will be, but if you did it, you'd need to check the voltage as it enters the trailer to see how much drop you get. If it's not 13.6V to 14.7V then it won't charge your battery. 'Course, your alternator is typically only 13.8V, so you'd need a large wire, and low enough current draw to prevent it from dropping too much. Here's a chart (not sure how accurate) that talks about 5% drops for given distance and wire gauge.
http://webmaster10.com/ldr/wire_size.htm
Remember, you need 13.6V minimum to slow charge your battery. 5% drop of 13.8V (i.e. coming off your alternator), is 13.11V. Actually, you need a drop of 1% or less at the battery! This is why a boost regulator is really what your need.

Here is a product sold for ham radio use, but should work here as well. Not sure where to find a more "commercial" product to do this.
http://stores.tgelectronics.org/Detail.bok?no=7

**brian_bp** · 06-01-2009, 03:21 PM

I agree that it is better to run a dedicated circuit than to extend the already marginal accessory socket circuit, for two reasons:

too much load
- The typical use of a travel trailer "battery" or "charge" line is to charge the trailer's battery by simply connecting it directly, and a discharged trailer battery will get a lot of current from the running Sienna's charging system.
- The other common use is to run a refrigerator while on the road, and even the smallest RV refrigerator will use almost 10 amps by itself.
accessory use
- The accessory sockets are on in the ignition key's accessory position, which means even while the engine is not running if someone leaves the key in for uses such as listening to the radio; it would be easy to run the Sienna's battery flat this way.

Some sort of relay or other isolating device is required as far as I am concerned, but many people (not necessarily Sienna owners) just wire to the battery with only a fuse or circuit breaker, and apparently remember to unplug the trailer every time they stop the engine and thus avoid accidentally discharging the tug's battery.

If you really do want operation in the accessory key position, then placing the accessory-controlled relay at the back of the van makes sense; if you want to use ignition-switched power, the source of that power will only be at the front, so the relay might as well be up there.

As far as I know there are no spare accessory or ignition-switched circuits to use in my Sienna... at least not readily available under the hood.

I wanted the power to be on to the trailer only when the Sienna's engine is running. Not having any technical documentation at the time, and wanting to avoid running wires through the firewall, I went hunting for a candidate in the underhood fuse box. Although the layout is clearly shown in a diagram on the underside of the box, there was not an obvious circuit to use. In the end, I just probed the fuses for a circuit which was on only with the ignition; what I found was was a fuse labeled "EFI NO.2", with a 10 amp fuse. I used a Littelfuse Add-A-Circuit to tap that fuse box socket, which leaves the original 10 A fuse for the original circuit, and adds a wire fed by an additional fuse (I used the smallest I had, which was 5A) which I used to feed the control coil of my trailer power relay.

I also added a switch in series with this control line to the relay, so I can turn the trailer power off regardless of the ignition key state. This way, I only turn it on when I hook up the trailer at the begnning of a trip, and turn it off at the end of the trip (even if that's a week later), so the relay isn't even turned on the vast majority of the time I'm driving (since towing is very little of the Sienna's use).

The attached photo shows the Add-A-Circuit (containing 10A and 5A fuses) and its red wire pigtail, plus the red wire I spliced onto it, running out of the underhood fuse box through a hole which I drilled for this purpose.

A long-standing item on my endless To-Do list is to check the wiring diagrams and find a better circuit to tap. As you can see from the photo, underhood cleaning is also on the list, and when I looked at this stuff to take the photo yesterday I realized that I also need to replace the tacky attempt at sealing the hole with a proper grommet!

Caution: I got a check engine light indication when I first ran the Sienna after this addition, presumably because I confused the engine control computer with extra load on the EFI No.2 circuit; however, it cleared, has not recurred, and does not seem to have caused any problems.

**scubajoe** · 06-01-2009, 06:22 PM

Nice job Brian. I would be more inclined to think you pulled power off something that would typically have it all the time, but then you said this is a ignition only circuit. Still I'd be really surprised if it were sensing an extra load, especially since that is negligible to just power a relay. What reason would there be for them to have any kind of "current meter" on that circuit (or any other, for that matter)?

**brian_bp** · 06-01-2009, 07:19 PM