Can I get voltage sensitive power control?

[Commutator]

I'm putting a wireless backup camera on my car hauler trailer and I want it to be powered up only when the truck is running. So I'd like to use the hot feed coming from the truck to power the trailer camera but through some circuitry that works like a voltage sensitive relay. The camera should only get power when the voltage is over 13.7 or something like that to indicate the alternator is running.

I don't have or want a battery in the trailer. The VSRs I've read about seem to require a battery on both sides of the relay to operate, whereas I'm looking for something that has the power source on one side and the load on the other, but only passes power at charging voltages.

Any suggestions how to accomplish this?

Thanks,
Fred

[ve7prt]

copeland343 wrote:
I connected our camera to a running light. Headlights on camera on lights off camera off. Power is already at the rear of trailer for this easy to connect. Works for us as I always tow with my headlights on.

X2. Easiest solution since I always have the running/headlights on when the truck/trailer moves. Then I just turn on the monitor when I need to see what the camera sees.

Cheers!

[copeland343]

I connected our camera to a running light. Headlights on camera on lights off camera off. Power is already at the rear of trailer for this easy to connect. Works for us as I always tow with my headlights on.

[Commutator]

wa8yxm, I should have pointed out the 7-way on the back of my truck is not on an isolator. It is always live and I won't use that hot feed without the fancy electronics. It's not that I *can't*, it's that I *won't*. My rig sits with the trailer connected to the truck for days at a time when we are camped. I don't want to disconnect nor do I want the camera always-on. I will gladly buy the Sure Power for the hands-off convenience.

Thanks again to all for the suggestions.

...Fred

[Commutator]

My trailer is buried in a rented winter storage spot and inaccessible so I can't check my facts on this. However I'm pretty sure the breakaway battery is already isolated to the brakes by a small charger like this. If that turns out to not be the case I do plan to install a diode to prevent the breakaway battery from powering the camera so all will work as desired.

...Fred

[Chris_Bryant]

wa8yxm wrote:
Ok, in that case, take my last post and remove all reference to "HOUSE".

Just charge the brake battery when parked using a battery tender

And use the charge line from your towed to power the camera.. TWO independent systems, one powered by the truck and the emergency brake battery operated.

No need for any fancy electronics, just the already existing isolator in the truck.

You could still charge via the truck- just add a diode in the charge line after the camera feed. As long as the charge line was switched, it would work fine.

[wa8yxm]

Ok, in that case, take my last post and remove all reference to "HOUSE".

Just charge the brake battery when parked using a battery tender

And use the charge line from your towed to power the camera.. TWO independent systems, one powered by the truck and the emergency brake battery operated.

No need for any fancy electronics, just the already existing isolator in the truck.

[Commutator]

OK, now I think I get why some are confused. My trailer is a car hauler, not a toy hauler (with living quarters) or a race car trailer (with work area). It's just a bare cargo trailer with a handful of 12v lights and some tie down rings - not even a winch. Hence no point having a "house" battery.

Also, I use the term "car" loosely. I carry a pair of Model T's in the trailer. More like buggies than cars really, but lots of fun.

...Fred

[Commutator]

Chris, I believe you are correct, at least for the 1314 model which I was just reading about. The other isolator brands I'd looked at had a low voltage check on the "house" battery connections and wouldn't close the relay if the voltage was too low to be deemed suitable to charge. The voltage of my camera would be zero so the relay would never close on those, but I don't think the 1314 has this feature so I'll give it a try.

smketter, the ALS unit is a charger and they typically don't function well for a static load, i.e., trying to "charge" my camera.

OnaQuest, that relay uses an ignition feed as a trigger, which I won't have in the trailer, and if I fake it somehow then it won't disconnect until the camera has run down the truck batteries (or fried itself from being on for a week or so).

I appreciate all the suggestions of alternatives, but really I only wanted to see if I could easily make it come on with the running truck. I know a bunch of ways to do it with manual intervention. So Sure Power 1314 it is!

...Fred

[Chris_Bryant]

This Sure Power unit does what you want- closes the relay when the battery is above 13.2 volts. You don't need an ignition tag line (even though it has a connection for it).
As long as the camera draws under 100 amps, it should be fine 😄

[wa8yxm]

Let's see if I have this straight.. You do not want a 12 volt SERVICE (house) battery, only the break-away battery for the brakes.. You will run your 12 volt systems in the house only off the converter (park model style).

Ok, this is easy

For the break-a-way battery use a Battery Minder, or Battery Tender to maintain it, These are very very slow chargers.. but you have weeks to bring 'em up to charge so that battery should, in theory, last a long time.. Make sure the unit you have does not have a time out function though.. (one of mine does). The time out function. if the battery is not fully charged within the time out period, it shuts down instead of continuing charge, you want one that continues charge till the battery is FULL up.

Now, do not connect the house 12 volt lead to the battery.

Isolate the Alternator (Tow vehicle) charge lead and use it to feed the camera.

The isolator in the tow vehicle will now control the camera's power.

This leaves you with 3 independent 12 volt systems in the trailer

1: Brakes (With battery)
2: House (Converter powered)
3: Camera (Tow vehicle powered).

[naturist]

The second cheapest solution requires a $1 toggle switch. The cheapest involves disconnecting a wire.

[dougrainer]

Commutator wrote:
Of course there's a breakaway battery, but it's not relevant. I'm not going to use it to power a camera for the obvious safety reasons, plus that would make the camera always-on which is worse than just having it on whenever the truck is connected. I only want the camera on when the truck is connected AND running.

I'm not going to rework the 7 way connector to get an ignition-hot feed to the trailer so I can use a relay. If I can't find the equivalent of a vsr that works without a battery on the load side of the relay, then I'll just feed the camera from the running lights. But my strong preference is to have it automatically on when truck is running, and off when truck is not.

Thanks,
Fred

I connected the Camera to the rear Running lights on the rear of the trailer. You just turn the Truck headlights OR just the running lights ON to activate the Camera. Doug

[Commutator]

Of course there's a breakaway battery, but it's not relevant. I'm not going to use it to power a camera for the obvious safety reasons, plus that would make the camera always-on which is worse than just having it on whenever the truck is connected. I only want the camera on when the truck is connected AND running.

I'm not going to rework the 7 way connector to get an ignition-hot feed to the trailer so I can use a relay. If I can't find the equivalent of a vsr that works without a battery on the load side of the relay, then I'll just feed the camera from the running lights. But my strong preference is to have it automatically on when truck is running, and off when truck is not.

Thanks,
Fred

[enblethen]

A heavy duty relay installed with coil operated off a "run" hot location.
Relay
Trailers with brakes must have a battery to operate the breakaway function.