Towed Battery Charger

[Rich-n-Linda]

Bflinn181 is absolutely correct. You do NOT need a charge controller for the toad! All you need is a piece of wire and a fuse! ONE fuse.

When you run a charge line from the motor home to the toad, all you are doing is putting the motor home chassis battery in parallel with the toad's battery. The motor home voltage regulator which controls the charging of the chassis battery is now also controlling the charge in your toad's battery. Electrically it is no different from adding another chassis battery in the motor home.

You don't need a "charge controller" for the toad, you don't need fuses on each end, all you need is to connect the black wire on pin #4 in the 7-pin plug (black wire) to your battery with a piece of 12 gauge wire and a 7 to 10 amp fuse in the line at the toad battery. Done.


Rich & Linda

[Bleclair]

This is what I installed 3 years ago. It is by break buddy


Accessories | BrakeBuddy - Braking systems for motorhomes towing a vehicle

Work great

Bruno L
Ventana 3634, 2014
Yaris with Blue Ox Aladdin

[BFlinn181]

And what does that $25 box do that a wire and a fuse or auto reset CB doesn't? I never said they don't work, I just don't understand what advantage they have over a wire. As Rich-n-Linda and I said, your alternator's voltage regulator is going to do everything that box does.

[Bleclair]

This what I am hoping to find !

What is inside that mystery box ???

Safety feature ? Or marketing feature ?

[ImagineIF]

Fuses are to protect the wiring and should be close to the power source. If you're going to install one fuse, install 2. There are two power sources, the coach and towed.

FWIW, I too have simply connected the coach and towed through the existing 12V feed from the coach on it's 6 pin connector.

The purpose built towed charger is simply a current limiter restricting what the towed can pull from the coach. If, for example, the towed's battery is discharge, it could draw more current from the coach than the coach's circuit could handle. That's one reason to size the two fuses properly.

[Rich-n-Linda]

Originally Posted by ImagineIF

Fuses are to protect the wiring and should be close to the power source. If you're going to install one fuse, install 2. There are two power sources, the coach and towed.

There are NOT two power sources in this situation. There is ONE power source consisting of three 12-volt batteries in parallel.

There is absolutely no need for two fuses in series...in the SAME WIRE! If current flow through the wire exceeds the rating of the single fuse, it will blow. Two fuses in series in the same wire is unnecessary and is actually bad electronic practice.

The likelihood of charging currents to the toad battery exceeding 10 amps is almost nil. I have measured the current flow in the charging wire when my toad battery was badly discharged and showing only 12.0 volts. As I recall, the charging current was just over 4 amps. It remained at 4 amps for only a short period of time before dropping as the toad battery charge level increased.

Using a charging wire to add the toad battery in parallel with the chassis battery will not overload the chassis charging circuits. You have an alternator on the coach that is capable of delivering many more amps than the toad could possibly draw.

There is a lot of "Snake Oil" being sold to unsuspecting consumers in the form of these so-called "Toad Charge Contollers." They are completely and totally unnecessary.



Rich & Linda

[Ret Syntst]

The most important part of those toad chargers is the diode which doesn't allow current to flow from your toad battery to the motorhome. If the motorhome battery is not up to snuff I don't want my toad battery trying to start the motorhome
RVibrake Towed Battery Charger
This is a relatively inexpensive insurance to ensure that the above cannot occur.

[BFlinn181]

I choose to have a auto reset CB on the wire from the RV battery to the 6 pin socket on the back bumper. Something stuck in the socket could ground the wire and the CB is there to protect it. The second CB is between the toad battery and the 6 pin socket on the front grill, again to protect the socket grounding out against the (+) pin. I don't consider it bad electrical practice, when the two are not connected, each CB serves a very important function. To have a 12 v (+) wire directly connected from battery to socket without a fuse or CB is an invitation to a fire.

]Ret Syntst, a 16 gauge wire (RVBrake spec) is not going to handle the amperage to start a V-10, 6 cyl. diesel, or anything else. That's another reason for the circuit breakers. After a day's drive hooked together and fully charged, nothing's going to happen to either battery system. If I'm parked for a few days, the chassis batteries are kept charged by the shore cord and the toad is disconnected and driven.By the way, my wires are 12 gauge, but still not capable of jumpstarting anything.

[Rich-n-Linda]

Originally Posted by Ret Syntst

The most important part of those toad chargers is the diode which doesn't allow current to flow from your toad battery to the motorhome. If the motorhome battery is not up to snuff I don't want my toad battery trying to start the motorhome...

That's not how it works!

When you connect a charging wire, all you are doing is putting three 12-volt batteries in parallel. If one battery is down a bit from the others, a little current will flow one way or the other through the charging wire...until you start the engine. As soon as you start the engine, the motor home alternator and voltage regulator fire up and develop 13 to 14 volts that results in charging ALL the batteries with the SAME charging voltage. Everything becomes equal, no matter what the state of charge in the batteries.

There has been a LOT of misinformation published on the internet about this, much of it by folks who want to sell you something you don't need.



Rich & Linda

[ImagineIF]

Fuses are there to protect the wiring. The 12V supply that may be prewired to your coach's 6/7 pin connector no doubt has a fuse or breaker already installed. It will protect that wiring or any sufficiently sized wire extend to your towed.

The wire from your towed's battery to the 6 pin connector is unprotected if not fused. If that wire has a short and is not fused it will burn. Spend a dollar or 2 and fuse that wire near the battery.

This setup is not a battery bank and should not be treated as one.

[alilly]

Originally Posted by Rich-n-Linda

... All you need is a piece of wire and a fuse! ONE fuse.

Rich & Linda

I beg to differ.

You need TWO fuses (or circuit breakers or diodes etc).

Take the case where the charge wire is shorted to ground on the towing vehicle, the towing vehicle fuse opens -now the current flows from the battery in the towed vehicle and will melt the wire unless there is a fuse installed near the battery in the towed.

The charge wire needs protection from both batteries.

[dennis45]

Originally Posted by alilly

I beg to differ.

You need TWO fuses (or circuit breakers or diodes etc).

Take the case where the charge wire is shorted to ground on the towing vehicle, the towing vehicle fuse opens -now the current flows from the battery in the towed vehicle and will melt the wire unless there is a fuse installed near the battery in the towed.

The charge wire needs protection from both batteries.

Sounds pretty logical to me. When the cord is unplugged, there needs to be fuse protection for each source. I also agree the Toad Charger is nothing but "Snake Oil"

[Ret Syntst]

Originally Posted by alilly

I beg to differ.

You need TWO fuses (or circuit breakers or diodes etc).

Take the case where the charge wire is shorted to ground on the towing vehicle, the towing vehicle fuse opens -now the current flows from the battery in the towed vehicle and will melt the wire unless there is a fuse installed near the battery in the towed.

The charge wire needs protection from both batteries.

This is my point exactly, put in a diode and a fuse and forget about it. Three batteries in parallel will draw equal current from all when starting the motorhome - the diode prevents a current draw from the toad so you won't burn out the wire. The alternator doesn't come online until the motor starts and it's that initial current draw that you're trying to avoid. A straight wire with nothing on it will work for awhile the same as bad electrical wiring works in your home for awhile. It's when something isn't equalized that a fire starts.

[Old Bounder]

Originally Posted by Rich-n-Linda

There are NOT two power sources in this situation. There is ONE power source consisting of three 12-volt batteries in parallel.

There is absolutely no need for two fuses in series...in the SAME WIRE! If current flow through the wire exceeds the rating of the single fuse, it will blow. Two fuses in series in the same wire is unnecessary and is actually bad electronic practice.

.....yada, yada, yada......

There is a lot of "Snake Oil" being sold to unsuspecting consumers in the form of these so-called "Toad Charge Contollers." They are completely and totally unnecessary.

Not sure where you learned your electronics, but there absolutely is a NEED for a fuse at both ends of a connection from a battery in the MH (tow vehicle) to the battery in the toad (towed vehicle), period.

(A diode at the toad end concept accomplishes the same thing protection wise, I just don't like the resultant voltage drop, since the path is already very long and resistive.).

I wouldn't exactly call the TOAD CHARGERS "snake oil", but they are more than is necessary for the job.