Toad Power Feedback discussion?

Morich · 12-30-2020, 10:56 AM

We got into a few thoughts on whether we need a diode in the line if we connect the RV to the towed car. We often read about feedback between the two but I do not understand the term and what it is feeding back and what it might do to us.
We do add diodes to the lights but that is a different issue as we are thinking about only connecting the power from the RV to the battery on the car.

If we connect power from the trailer connector which has 12Volt while the RV key is on through a wire directly to the towed battery without using a diode , how is it different than if we use the RV to jump start the car without using a diode?

We do connect the start battery to the coach battery as we drive and we do the opposite and connect the coach battery to the start when we use the boost switch and these are both just simple connections at the mode solenoid, so what is different in connecting the towed battery to the RV without diodes on the battery supply?

BobC · 12-30-2020, 11:42 AM

I installed one of these just to be on the safe side:

https://rvibrake.com/products/towed-...13115309260823

Winterbagoal · 12-30-2020, 11:48 AM

The concern centers around 12V DC draw from the towed's battery, back to the coach's chassis electrical system, when the 2 vehicles are parked, engines off, say if you're stopped for the night while still enroute. Some suggest the coach may pull current from your towed's battery in that situation, depending on what you have running in the coach off of the chassis battery. The one-way diode would prevent that from happening. I don't know if that happens or not, but it seems like it could.

**macnut** · 12-30-2020, 12:13 PM

Quote:

Originally Posted by BobC

I installed one of these just to be on the safe side:

https://rvibrake.com/products/towed-...13115309260823

If you have the RVi Command Center, it’s great to see when and how much the car battery is being charged while on the road. Since my CRV battery is undersized, (though I have since added a larger battery), this gives me extra peace of mind.

BobC · 12-30-2020, 12:59 PM

Quote:

Originally Posted by Winterbagoal

The concern centers around 12V DC draw from the towed's battery, back to the coach's chassis electrical system, when the 2 vehicles are parked, engines off, say if you're stopped for the night while still enroute. Some suggest the coach may pull current from your towed's battery in that situation, depending on what you have running in the coach off of the chassis battery. The one-way diode would prevent that from happening. I don't know if that happens or not, but it seems like it could.

RVI's Towed Battery Charger also prevents this from happening.

Morich · 12-30-2020, 01:52 PM

Quote:

Originally Posted by Winterbagoal

The concern centers around 12V DC draw from the towed's battery, back to the coach's chassis electrical system, when the 2 vehicles are parked, engines off, say if you're stopped for the night while still enroute. Some suggest the coach may pull current from your towed's battery in that situation, depending on what you have running in the coach off of the chassis battery. The one-way diode would prevent that from happening. I don't know if that happens or not, but it seems like it could.

We know that the coach can eventually run down the coach batteries, so they give us the boost switch to fall back on if we do need the help.
But since the trailer power connection is dead when the RV engine/key is off, is this actually possible?
It seems that if we cut the connection for battery power to go to the tow car, there is no way for the Rv to draw power from the car.

I asked the folks at RVI and got what seemed to be an evasive answer in that, "there are a lot of complex electronics in RV's". But I fully admit that I was questioning why I should buy their product and that does make people become less helpful in some situations.

I fell back to wondering why those electronics are more affected if I hook a towed car battery to the RV battery when driving down the road than when we connect two battery strings together when driving the RV and the start and coach batteries are connected for charging or if we do use a jumper cable to start the engine.

If we agree that the RV has two sets of batteries, start and coach connected together when driving down the road and those batteries are much larger, higher capacity batteries than the tow car battery, I wonder how a tiny little Honda battery can create problems for the RV electronics that the two strings plus alternator power can't? We know that the battery voltage goes low when we camp and then when we start the engine, that voltage suddenly goes high, so the voltage fluctuations seem out of the question.

Humm?? I still have some questions on the diode idea.

Winterbagoal · 12-30-2020, 02:29 PM

Maybe the problem is with trailers/fivers? I seem to recall someone saying that their tow vehicle might have been sucking battery power from the trailer's house batteries, overnght, when they stopped and parked it while en route.
Either way, it's probably possible that the coach could draw 12V power from the towed's battery if the draw was sufficient. What could cause that draw, I have no idea. Power steps? Dash radio or rear view camera? Cab lights?

Morich · 12-30-2020, 03:03 PM

I guess I should have been more specific and limited it to motorhomes towing car, etc. as that is where we were on the other post.
In the case of trailers, the diode is no help as it keeps power from being sucked from the trailer to the towing vehicle and has to let power flow in the other way car to tow to recharge the batteries and keep the lights on.
What makes it different on many motorhomes is that the trailer hitch power to charge the towed battery is only there when the key is on.
So it brings the questions what good the diode does if the wiring is disconnected with the switch off in the RV? With the ignition switch off, isn't the wire going to the hitch and on to the tow battery just left there dead?

It seems like the wire from the tow car battery to the ignition switch would still be hot from the tow car battery forward but with no connection to need a diode.

This question is based on using the 7 pin trailer connection which is 12 volt only when the ignition is on.

l1v3fr33ord1 · 12-30-2020, 03:59 PM

It depends on whether or not you want to leave the umbilical connected when the coach is shut off. If you disconnect, no need for a diode.

If you keep the coach and toad connected (we do), then it depends on the circuit. If it is ignition-switched, and the charge line is the only wire on the circuit, a diode is not needed. If it's not ignition-switched, then someone may want a diode in the circuit, to keep the coach from pulling starting current from the toad battery.

Or. it's coach-specific. Certain years of Monaco coaches (including ours) provide the charge line 12V from a bus off an ignition-switched relay. Applying 12V to the toad end of the charge line will supply 12V to any of the other circuits attached to the same bus. For those who may connect their coach-toad umbilicals before starting the coach, or leave their umbilicals connected overnight, this could be a problem. A diode at the toad end fixes this problem.

Here is a diagram of the problem, for my coach.

Winterbagoal · 12-30-2020, 04:25 PM

Quote:

Originally Posted by Morich

I guess I should have been more specific and limited it to motorhomes towing car, etc. as that is where we were on the other post.
In the case of trailers, the diode is no help as it keeps power from being sucked from the trailer to the towing vehicle and has to let power flow in the other way car to tow to recharge the batteries and keep the lights on.
What makes it different on many motorhomes is that the trailer hitch power to charge the towed battery is only there when the key is on.
So it brings the questions what good the diode does if the wiring is disconnected with the switch off in the RV? With the ignition switch off, isn't the wire going to the hitch and on to the tow battery just left there dead?

It seems like the wire from the tow car battery to the ignition switch would still be hot from the tow car battery forward but with no connection to need a diode.

This question is based on using the 7 pin trailer connection which is 12 volt only when the ignition is on.

Why not check the 12V pin on the coach side with a multimeter, engine/ignition off, and see if it's hot or not?

Morich · 12-30-2020, 06:15 PM

Okay, that makes sense as different RV will often be different and while mine is set so that the 12V power from the ignition is dead when key is off, some might not and that "could" mean the towed battery could feed back to run down at the same time as the RV start battery.
That would not be a bother to me as most of the time we will be hooked to shore power and running either down is not a problem.

But the idea of what might be on the same bus with the ignition wire which makes the trailer connection is also a good point as it would make it possible for the tow battery to wind up supporting something like the dash radio in the RV, even when the key was off.

I think I see the reasons for it to always be recommended for a couple reasons. One is that it takes less thought to just sell ALL RV tow packages with diodes to avoid having the question of whether it is needed or not.
So when simple also comes around at the same time as increased sales, it's sure to be a winner in the mind of the folks selling things!

I have wired in the box with diode for the battery maintainer but I can now see enough questions that if I were doing the tow car wiring, I would sell the diode idea, too!

Thanks for helping sort the questions.

Bobn1957 · 01-03-2021, 07:23 PM

The thing to remember about batteries connected in parallel is that the charging system will charge all the batteries to the same level and that would be the smallest or weakest battery level. So once the toad battery is full the coach battery will stop charging, hence the need for a diode.

Winterbagoal · 01-03-2021, 07:34 PM

Adding a dhe diode stops charge from being drawn out of the towed battery, back to the TV or motorhome, when travel and charging is stopped for the day. Unplugging the umbilical, or the standalone charging wire, achieves the same purpose.

JerryP · 01-03-2021, 11:19 PM

It's important to isolate the battery systems between your RV and Toad.

In my Tacoma, I installed the RVI Brake Towed Battery charger.
If I were to do it again, I might use The Toad-Charge from Trik-L-Start.
It looks like it provides a little more protection.

TOAD-CHARGE Dinghy Vehicle Battery Charger/Maintainer

I also use Trik-L-Start to keep my coach battery charged while in storage. This is used for Sprinter Van based RVs.

Regards,
Jerry