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Discussion Starter · #1 ·
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,
 

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Discussion Starter · #3 ·
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?
 

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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!!
 

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Discussion Starter · #5 ·
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.
 

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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.


deerewright said:
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.
 

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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
 

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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.
 

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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)?
 

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scubajoe said:
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.
I really just checked with a meter... turning the key on an off and seeing which ones powered up and down. It makes sense to me that anything to do with fuel injection would only be on in the ignition mode. I would have really preferred a circuit which was live only with ignition on, and not when cranking, but fuel and ignition circuits need to be live during cranking. Some accessory circuits in normal vehicles switch off during cranking to leave power available for the starter motor, and to minimize voltage spikes to accessories.

scubajoe said:
Still I'd be really surprised if it were sensing an extra load, especially since that is negligible to just power a relay.
I, too, thought that the relay control load would not be an issue, and it has not been in the long term. All I really know is that I got the only check engine light to have occurred in the life of the vehicle the first time I started it after poking my nose into this circuit. That freaked me out a bit.

scubajoe said:
What reason would there be for them to have any kind of "current meter" on that circuit (or any other, for that matter)?
My guess is for diagnostics... to know when something (particularly something which is related to exhaust emissions) is not behaving as expected.
 

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That's why I would suggest using the rear accessory socket. You've tapped into the Fuel injection computer's for bank two. I would think the spikes from an inductive source like the coil of a relay would be a bad thing to have happen on that circuit. If you run a fused wire to the back, you can just tap your relays trigger wire onto the live circuit of the rear accessory socket and the ground to its ground as well. The accessory socket circuit isn't going to have issues with spiking from the coil. The

brian_bp said:
scubajoe said:
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.
I really just checked with a meter... turning the key on an off and seeing which ones powered up and down. It makes sense to me that anything to do with fuel injection would only be on in the ignition mode. I would have really preferred a circuit which was live only with ignition on, and not when cranking, but fuel and ignition circuits need to be live during cranking. Some accessory circuits in normal vehicles switch off during cranking to leave power available for the starter motor, and to minimize voltage spikes to accessories.

scubajoe said:
Still I'd be really surprised if it were sensing an extra load, especially since that is negligible to just power a relay.
I, too, thought that the relay control load would not be an issue, and it has not been in the long term. All I really know is that I got the only check engine light to have occurred in the life of the vehicle the first time I started it after poking my nose into this circuit. That freaked me out a bit.

scubajoe said:
What reason would there be for them to have any kind of "current meter" on that circuit (or any other, for that matter)?
My guess is for diagnostics... to know when something (particularly something which is related to exhaust emissions) is not behaving as expected.
 

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brian_bp said:
I, too, thought that the relay control load would not be an issue, and it has not been in the long term. All I really know is that I got the only check engine light to have occurred in the life of the vehicle the first time I started it after poking my nose into this circuit. That freaked me out a bit.
I had that happen after I ran the power through the firewall, and my wife called me to tell me the car was shifting funny, running horrible, and the check engine lamp was on. All day at work I'm thinking I hit the shifter cable when running the power through the grommet, and trying to figure out what a nightmare that was going to be to fix. Then I remembered that I forgot to plug in something under the hood (I actually know exactly what I forgot to plug in, but I'm having a mental block).
 

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Discussion Starter · #14 ·

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You all are very knowledgeable and are talking waaaaaay over **my** head......8)

A few of you mentioned something about being careful to not kill the Sienna's battery when charging a trailer/accessories. Just thought I'd suggest/remind you of the PriorityStart device that will cut-off other loads to maintain the charge of the vehicle's battery once it reaches a specified lower voltage level. It proved to be useful for many 2004 owners who do not have the properly functioning factory "battery-saver" feature that got fixed in later models.

I do not know if it would be useful/helpful for your purposes.... ??? ??? ???

Try here:
http://www.prioritystart.com/

and mentioned here:
http://siennachat.com/forum/index.php/topic,342.msg3359.html#msg3359

Good Luck!! 8)

EDIT: Based upon the knowledgeable experience and analysis of several members and their discussion occurring after this post, using the PriorityStart device I mention here is probably not a good choice for this particular application. YMMV.
 

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That isolator is generally not the best idea. All those things are is a couple of LARGE Diodes inside a heat sink. The alternator power goes through from the anode of both and current flows out through each one into the two batteries(one being the regular sienna battery and one being the trailer battery) since diodes don't let current flow from cathode to anode, they isolate any current flow back.

Here's the issue:
The alternator creates AC voltage/current that is regulated and rectified to a DC value with a great deal of ripple. Being attached to the battery "flattens" the ripple and if the average DC value is high enough it charges the battery. To do all this the regulator reads the battery voltage and the output of the Alternator and adjusts itself accordingly. when you put this Diode between the two, the regulator needs to adjust the alternator voltage upward to overcome the voltage drop of the diode(typically .5 to .7 volts in these units) so that the voltage being put to the battery can charge it properly. Here's the math:

Without the isolator:
Alternator output voltage: 13.8-14.4 depending on how much it needs to charge the battery.
Battery voltage is the same as they are directly connected.

With isolator:
Alternator voltage is 14.3-15.1V minus the 0.5 to 0.7 Volt drop of the diode = 13.8-14.4V at the battery so it can charge properly.

You are now pushing the alternator into a higher voltage than designed and the regulator as well. In an old chevy/ford chassis, that wasn't a problem as the regulator was just a couple of diodes anyway, but modern alternators have more brains and don't like to see this difference. Not saying it won't work for you...at least for a while, but you are pushing things out of their tolerance levels.

Again, The best way would be what I've shown in the attached image. The battery is the sienna's battery. The relay has the coil attached to one of the cigarette lighter sockets as switched power.

deerewright said:
Thanks guys for all the suggestions and help. I also had thought about the relay solution, then I decided to just run the wire direct from the battery and just rememeber to unplug. Then I found this battery isolator: http://www.bellrpg.net/hilltop/RV/grouppart.asp?MAJ=011&PRI=010&SEC=055&GRP=1263
it isolates the main battery from the aux when not being charged by the alternator.
 

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Like others have suggested, I used a 30/40 amp relay to control the trailer charge line. I tapped the rear accessory socket (cig. lighter socket) to control the relay and ran the wire under the rear seat well trim (below the rear hatch opening) to the jack compartment where I mounted my relay.

If you really want to charge your trailer battery then you need a pretty hefty wire coming from the van's battery to avoid voltage drop - I know some people that have suggested 8 gauge wire is needed, but I ran two 10 gauge lines in parallel (actually a marine rated 10-2 cable). You also need a good ground return (voltage drop occurs on both sides of the loop, not just the power feed), so in addition to grounding the trailer's ground line to the van's chassis I ran a dedicated ground wire back to the battery (also two 10 gauge wires). The trailers ground line supplies the ground for not only the charge line, but the lights and the electric brakes (if equipped), so I felt the less resistance in the ground path the better.

FYI, if your trailer has (or you want to add) reverse lights (back-up lights) you can add a relay for that as well. While I had the panel pulled back to tap the rear accessory socket power I also tapped a line into the reverse lights power; it feeds a second relay in the jack compartment that controls power to the center pin on the 7-way socket (technically the Aux pin but often used for reverse lights on the trailer). The power for this pin does not come from the dedicated charge line, but another 10 gauge wire that runs from the van's battery to the jack compartment to feed the reverse lights relay and my Modulite powered tail light converter. All circuits are protected by self-resetting circuit breakers near the van's battery - 40 amp c.b. for the charge line, 30 amp c.b. for the trailer lights (stop/brake, markers, and reverse lights), and a 20 amp c.b. for the brake controller.
 

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I agree that the diode-based isolators are not the best idea. I don't like the idea of interposing anything between the components of the Sienna's original charging system, but if anything is going there is should not create a voltage drop, as any semiconductor junction (such as a diode) will do.

There are also devices called Automatic Charging Relays (such as those from Blue Sea) which connect and disconnect the vehicle and RV batteries as appropriate to conditions; when they are connected, there is no significant voltage drop. This seems like a better solution, but I still don't want to break the stock charging system to battery connection.

My approach is to only manage the RV battery charge line.
 

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tcp said:
That's why I would suggest using the rear accessory socket. You've tapped into the Fuel injection computer's for bank two. I would think the spikes from an inductive source like the coil of a relay would be a bad thing to have happen on that circuit...
The accessory socket circuit isn't going to have issues with spiking from the coil.
True, and a reason that my to-do list includes searching for a better source to tap; however, I don't want an accessory-switched signal. If I did, then I think the rear-mounted relay idea would be great.
 

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topspy said:
A few of you mentioned something about being careful to not kill the Sienna's battery when charging a trailer/accessories. Just thought I'd suggest/remind you of the PriorityStart device that will cut-off other loads to maintain the charge of the vehicle's battery once it reaches a specified lower voltage level...
That's an interesting idea. :)

I have a cheap portable version of this type of cutoff relay, as a short extension of the lighter-socket style. I used it on our first trailer camping trip, with a rented tent trailer having no power... I ran a portable cooler from the Sienna, through this device to protect from flattening the battery. Unfortunately, it would cut off, then the battery voltage would rebound a bit when the load was removed and this thing would connect again, and the whole setup cycled until the Sienna battery was so flat it would not start. In technical terms, the deadband between the switch-off point and the switch-on point was too narrow. A properly designed equivalent might be useful.

I've read the material from the PriorityStart people, and I'm not sufficiently confident in the operating principles or design either to put it between my Sienna's battery and the rest of the Sienna, or to depend on it to cut off a trailer which is connected regardless of ignition switch position. A simpler low-voltage cutoff device in the control wire for my basic trailer power relay would suit me better, and make me more likely to use an accessory circuit (instead of ignition-switched circuit) for control.
 
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