Battery isolator relay

[KarlB]

I’m looking at hooking up a solenoid under the hood to recharge my rv battery.
The 7 pin wiring harness has heavier gauge wires (10 or 12 AGW) but is this heavy enough? I have checked set ups on YouTube and they route battery cable all the way back to the auxiliary battery.
Another concern is how would I connect this to the aux. battery; what type of heavy connector should I mount to the trailer that is removable when I unhitch the Trillium?
Am I complicating my life here? I tend to look too deep sometimes.
Thanks all.

[Byron Kinnaman]

FYI.... My 2005 Dodge Dakota Factory tow package connects directly to battery. I had a Chevy Brazer with a solenoid installed. It failed about a couple years. A solenoid is another not needed failure point, in my humble opinion.
I really don't know why it's worry for some people. I've seen trailers that the only to them comes from the tow vehicle. No lights, etc. until the trailer was plugged into the tow.

I have the same size of battery in the tow and the trailer. The trailer battery get recharged about every 4 to 6 days while camping. Is recharged from the tow or solar. If I can go 6 days on the trailer battery I could about 8 with it plugged into the tow. To the additional cost and failure point is a negative and no positives to be gained.

[Wayne Collins]

The 7 pin connector should have one 12 gage wire connected directly to the + post of your car battery with a 20 amp inline fuse. That goes to the trailer battery so whenever they are connected, and the engine is running you're charging both batteries. You should also have a wired ground.
Caution: with the car engine stopped, the trailer fridge can discharge the car battery. So, just pull the 7 pin plug if you are stopped for more than a few minutes.
For the Trailer Brake control you will have another wire with fuse from the battery
to the controller, then from controller to the 7 pin, then to the brakes.

[charlsara]

I ran # 6 cable directly from the tow battery to an Anderson plug under the back bumper. I have #6 wires from the trailer to another Anderson. I just plug in the extra harness when I need to charge from the vehicle. I chose to just unplug it when we are parked rather than use a solenoid. It works great.

[Stephen_Albers]

Depending upon your nerve and tolerance for memory items, in general, it is not good electrical practice to parallel vehicle electrical systems. They should be strictly isolated so that current flows only in one direction while charging. Latching solenoids are also not safe because various system configurations can allow backflow, overheating and even fire. Solid state low voltage drop isolation is the total solution. Properly configured Andersen connectors have proven reliable in commercial service.

[KarlB]

Originally Posted by Byron Kinnaman

FYI.... My 2005 Dodge Dakota Factory tow package connects directly to battery. I had a Chevy Brazer with a solenoid installed. It failed about a couple years. A solenoid is another not needed failure point, in my humble opinion.
I really don't know why it's worry for some people. I've seen trailers that the only to them comes from the tow vehicle. No lights, etc. until the trailer was plugged into the tow.

I have the same size of battery in the tow and the trailer. The trailer battery get recharged about every 4 to 6 days while camping. Is recharged from the tow or solar. If I can go 6 days on the trailer battery I could about 8 with it plugged into the tow. To the additional cost and failure point is a negative and no positives to be gained.

Thank you Byron for your reply. Absolutely right, I’ll simplify my life and follow your advice. So far I’m running a small fan and some LED lights on the battery... that battery will last weeks.
I did meter the wires at the vehicle end and I have a constant 12vdc there with engine running or not. That bothers me a bit.
Karl

[ehoepner]

If you want to isolate your camper DC power from the tow vehicle you can install an isolator in the camper. I have a West Mountain Radio ISOpwr. It is designed for 40 amps, it is electric and it automatically dilsconnects the tow vehicle from the camper when the battery voltage drops to 12.6v. It uses the Anderson Power Pole connectors. This thing works well.

[stevebaz]

I use the standard battery isolation solenoid but if I were to rewire again I would use this one from Cole Hersee.

https://www.littelfuse.com/products/...isolators.aspx

[Byron Kinnaman]

Originally Posted by KarlB

Thank you Byron for your reply. Absolutely right, I’ll simplify my life and follow your advice. So far I’m running a small fan and some LED lights on the battery... that battery will last weeks.
I did meter the wires at the vehicle end and I have a constant 12vdc there with engine running or not. That bothers me a bit.
Karl

If connected to the tow vehicle from the trailer you're looking at both batteries. If disconnected you're looking at the tow vehicle battery only. That would be expected. There are lots of devices in your tow vehicle that go through switches that there's 12vdc at the switches. Not to worry. In years gone by there was no house battery only the tow vehicle battery.

The connector on the tow vehicle should have a spring closing cover which will help prevent shorting battery connections. There should also be a 20 or 30 amp fuse in the tow vehicle's charge line going to the trailer. Mine in the fuse block. On my Blazer it was right at tow vehicle's battery.

[John in Santa Cruz]

with the vehicle engine running, and a fully charged vehicle battery, you should see around 14.2-14.4 volts anywhere in the vehicle electric system as long as the circuit you're on doesn't have a heavy load on iit.

every vehicle I've owned with a factory tow package has had an isolation relay in the charge circuit to the 7-blade RV connector, this relay shuts off the RV power when the vehicle is off. the trailer charging circuit is typically fused at 30 or 40 amps, depending on the size of the tow vehicle and the factory wire gauge. I would probably use 30A fuse in a 50A fuse holder, and 10 AWG wiring to minimize voltage drop if I was adding this myself, and I would use a 'smart' isolator like this: https://www.amazon.com/dp/B0741Y7YCZ..._t1_B00400IYTK which only switches on the trailer power when the vehicle power is above 13.3V, thus ensuring the vehicle battery can't be discharged by the trailer..

[Jann Todd]

Originally Posted by stevebaz

I use the standard battery isolation solenoid but if I were to rewire again I would use this one from Cole Hersee.

https://www.littelfuse.com/products/...isolators.aspx

We've used these type isolators more than once. When they fail then your trailer battery won't charge but at least your TV battery never gets drained. When the TV is not running the isolator closes the connection. I would never tow without an isolator. We had a camper with one when our electrical system shorted. Fortunately it only got a little of the charging wiring because the isolator stopped the shorting. These are an inexpensive good isolator.

[charlsara]

I forgot to mention that I use a 40 amp breaker on the positive cable. With my dual 6v Golf Cart house batteries I can’t see where draining the tow battery would be a concern. Of course it will only be plugged in when we have stayed overnight off the grid.

[John in Santa Cruz]

if your 220AH worth of GC batts were 50% discharged (12.1V at 68F), and you plugged it into your tow vehicle, drove a short distance then parked and left it plugged in, without an isolator, your vehicle battery would find itself pretty close to 50% before long without putting much pookah into the GC batts.

[charlsara]

Originally Posted by John in Santa Cruz

if your 220AH worth of GC batts were 50% discharged (12.1V at 68F), and you plugged it into your tow vehicle, drove a short distance then parked and left it plugged in, without an isolator, your vehicle battery would find itself pretty close to 50% before long without putting much pookah into the GC batts.

Anything is possible. I'll take that chance..I can pull out the gen and recharge the tow battery. A hassle but unlikely.

[gordon2]

Originally Posted by John in Santa Cruz

...vehicle battery would find itself pretty close to 50% before long without putting much pookah into the GC batts.

This is why I wish I had an Electrical Engineering degree. Then I might know what pookah was.

I doubt its any of the definitions from the Urban Dictionary

[John in Santa Cruz]

pookah, nerd slang for power.