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Old 10-09-2014, 10:15 PM   #1
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Battery Wire

I am going to run a wire from my MH ( round Connector ) to my toad jeep.

Do I need a diode to keep the flow only going from the MH to the toad?

Bob
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Old 10-09-2014, 10:21 PM   #2
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If it's just a charge wire , no diode required ; BUT ; should have a fuse in both ends. So , in the event of a short, the fuse at both ends will blow and prevent the wiring from a complete melt down, and possible fire.
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Old 10-09-2014, 10:27 PM   #3
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no diode required
Why no diode required for a charge wire when almost everybody insists that diodes are a MUST in tail light, brake light, and turn signal wiring?

Tim
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Old 10-09-2014, 10:46 PM   #4
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If it's just a charge wire , no diode required ; BUT ; should have a fuse in both ends. So , in the event of a short, the fuse at both ends will blow and prevent the wiring from a complete melt down, and possible fire.
I used 30 amp self resetting fuses at both ends and 8GA wire. The wire really isn't rated for 30 amps though but I know the draw is less than 30 amps just to keep the battery charged.
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Old 10-09-2014, 10:47 PM   #5
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Check this out

RVibrake Towed Battery Charger

It's $50 but it contains a fuse and diode in a weather proof case. Hook up is about 15 minutes. You should still put an inline fuse where the charge wire starts in the motorhome. The diode prevents the motorhome from drawing power from the toad battery when starting the motorhome.
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Old 10-10-2014, 10:33 AM   #6
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Why no diode required for a charge wire when almost everybody insists that diodes are a MUST in tail light, brake light, and turn signal wiring?

Tim
When you're feeding the tail and brake lights without a diode you are also backfeeding (powering) the entire toad electrical system through that connection. If you simply run a fused wire to the toad battery, the fact that the toad key is off will prevent any power from energizing the toad system, and the battery will charge until it's internal resistance is too high for current to flow through it (this is full charge). The toad system will not backfeed to the coach because when the coach key is off, the charge line is switched off. If you're still concerned about that, you can pull the plug to the toad when you stop overnight, but to me, that's a waste of time.

A final reason to NOT use the diode is that there are losses internal in the diode, that's why the big surface area and heat dissipating fins. When you pass current through the diode, you don't get the same current out the other end, and that's power that could keep your toad battery fully charged vs partially charged. You can buy all the fancy gadgets and super "things" but nothing beats a fused wire.
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Old 10-10-2014, 11:33 AM   #7
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When you're feeding the tail and brake lights without a diode you are also backfeeding (powering) the entire toad electrical system through that connection. If you simply run a fused wire to the toad battery, the fact that the toad key is off will prevent any power from energizing the toad system, and the battery will charge until it's internal resistance is too high for current to flow through it (this is full charge). The toad system will not backfeed to the coach because when the coach key is off, the charge line is switched off. If you're still concerned about that, you can pull the plug to the toad when you stop overnight, but to me, that's a waste of time.

A final reason to NOT use the diode is that there are losses internal in the diode, that's why the big surface area and heat dissipating fins. When you pass current through the diode, you don't get the same current out the other end, and that's power that could keep your toad battery fully charged vs partially charged. You can buy all the fancy gadgets and super "things" but nothing beats a fused wire.

X2 well stated and exactly correct.
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Old 10-10-2014, 12:00 PM   #8
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When >snip<he

A final reason to NOT use the diode is that there are losses internal in the diode, that's why the big surface area and heat dissipating fins. When you pass current through the diode, you don't get the same current out the other end, and that's power that could keep your toad battery fully charged vs partially charged. You can buy all the fancy gadgets and super "things" but nothing beats a fused wire.
It's a series circuit - you do get the same current out. You take a voltage hit somewhere between ~ 0.2 and 0.7 VDC across the diode plus whatever wiring loss.

If it is properly wired the 7 pin connector has a protected 12 V Line built into the spec.
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Old 10-10-2014, 03:37 PM   #9
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Why no diode required for a charge wire when almost everybody insists that diodes are a MUST in tail light, brake light, and turn signal wiring?

Tim
First: Why the diode in the lights.. Because the JEEP is not fused to light up the motor home.. Also without the diodes the turn signals would not work properly (Both right and left turn would turn both right and left lights both on the motor home and the jeep, and brake lights would disable the turn signals) use of diodes causes the lights to work more or less properly (there is one more step needed).

On the battery-battery line..... On my Motor home I originally put in the US-Gear Unified Brake Decelerator, I will give you PART o the wiring for that....

Chassis battery+----Breaker----Long wire--Breaker--Car battery

That is all they did chassis to car battery.

IF you put a diode in the line there is some voltage loss in the diode.

Why does this work?

Well, the breakers protect things when starting the coach, and the coach isolator prevents you from running down the car battery watching TV or running the Furnace (Same as it does for the chassis battery).

In short, it works great.

On my new towed I'm going with a different brake system but I still installed a "Tie line" for the battery so that if I am doing a cross country hike or if Im parked for a week and not starting the car I can "plug in" to either the front or back of the motor home with a jumper cable.. Anderson power poles instead of the US-Gear cable, but it works great.
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Old 10-14-2014, 09:57 AM   #10
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Mr. Pigman,

Since you answered my question first, I’ll address my reply to you. Your comments are >>>Bold.Others… Feel free to jump in.


>>>When you're feeding the tail and brake lights without a diode you are also backfeeding (powering) the entire toad electrical system through that connection.

Exactly how does that happen?

Without diodes, when the RV driver steps on the brake, the RV EMF comes into the towed and usually enters the towed’s electrical wiring at the tail lights. The EMF lights the bulb as it is grounded. The EMF also travels forward into the towed and what does it see? An open brake light switch. No chance of getting into the towed’s electrical system there.

When the RV driver turns on either directional signal, the RV EMF comes into the towed and usually enters the towed’s electrical wiring at the tail lights. The EMF lights the turn signal bulb as it is grounded. The EMF also travels forward into the towed and what does it see? An open turn signal switch. No chance of getting into the electrical system there.

When the RV driver turns on the RV head/park lights, the EMF comes into the towed and usually enters the towed’s electrical wiring at the tail lights. The EMF lights the turn signal bulb as it is grounded. The EMF also travels forward into the towed and what does it see? An open head light switch. No chance of getting into the electrical system there.

>>>If you simply run a fused wire to the toad battery, the fact that the toad key is off will prevent any power from energizing the toad system,

But for the vast majority of vehicles, while being towed, the vehicle’s ignition switch is not in the off position. It is in the ACC or Full ON position so that the steering wheel is unlocked to allow the towed vehicle to track the RV.

>>>and the battery will charge until it's internal resistance is too high for current to flow through it (this is full charge). The toad system will not backfeed to the coach because when the coach key is off, the charge line is switched off.

But while being driven, the coach’s ignition switch is always in the ON position.

If the fused wire is connected battery to battery, what mechanism switches the charge wire off when the coach’s ignition is switched off.

>>>If you're still concerned about that, you can pull the plug to the toad when you stop overnight, but to me, that's a waste of time.

>>>A final reason to NOT use the diode is that there are losses internal in the diode, that's why the big surface area and heat dissipating fins.


I Googled for 20 amp and 30 amp diodes and did not find even ONE heavy current diode with fins. Nearly all I found were plastic “barrel” diodes. Besides, we don’t need a heavy amperage diode here. The point is to keep the towed vehicles battery topped off, or at least from going dead. NOT go charge it up after a heavy discharge. A 5A or 10A diode will do it.

>>>When you pass current through the diode, you don't get the same current out the other end, and that's power that could keep your toad battery fully charged vs partially charged.

True, but the voltage loss through a diode is minimal (.6 to .7 V). The remaining voltage should keep the towed vehicle’s battery “nearly” fully charged. At least charged enough to start and run the vehicle, which is the reason for a charge wire in the first place.

I sometimes tow my Austin Healey and there is not a diode anywhere in the whole car and everything has worked fine for over 20 years.

Tim
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Old 10-14-2014, 05:54 PM   #11
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Quote:
Originally Posted by Healeyman View Post
Mr. Pigman,

Since you answered my question first, I’ll address my reply to you. Your comments are >>>Bold.Others… Feel free to jump in.


>>>When you're feeding the tail and brake lights without a diode you are also backfeeding (powering) the entire toad electrical system through that connection.

Exactly how does that happen?

Without diodes, when the RV driver steps on the brake, the RV EMF comes into the towed and usually enters the towed’s electrical wiring at the tail lights. The EMF lights the bulb as it is grounded. The EMF also travels forward into the towed and what does it see? An open brake light switch. No chance of getting into the towed’s electrical system there.

When the RV driver turns on either directional signal, the RV EMF comes into the towed and usually enters the towed’s electrical wiring at the tail lights. The EMF lights the turn signal bulb as it is grounded. The EMF also travels forward into the towed and what does it see? An open turn signal switch. No chance of getting into the electrical system there.

When the RV driver turns on the RV head/park lights, the EMF comes into the towed and usually enters the towed’s electrical wiring at the tail lights. The EMF lights the turn signal bulb as it is grounded. The EMF also travels forward into the towed and what does it see? An open head light switch. No chance of getting into the electrical system there.

>>>If you simply run a fused wire to the toad battery, the fact that the toad key is off will prevent any power from energizing the toad system,

But for the vast majority of vehicles, while being towed, the vehicle’s ignition switch is not in the off position. It is in the ACC or Full ON position so that the steering wheel is unlocked to allow the towed vehicle to track the RV.

>>>and the battery will charge until it's internal resistance is too high for current to flow through it (this is full charge). The toad system will not backfeed to the coach because when the coach key is off, the charge line is switched off.

But while being driven, the coach’s ignition switch is always in the ON position.

If the fused wire is connected battery to battery, what mechanism switches the charge wire off when the coach’s ignition is switched off.

>>>If you're still concerned about that, you can pull the plug to the toad when you stop overnight, but to me, that's a waste of time.

>>>A final reason to NOT use the diode is that there are losses internal in the diode, that's why the big surface area and heat dissipating fins.


I Googled for 20 amp and 30 amp diodes and did not find even ONE heavy current diode with fins. Nearly all I found were plastic “barrel” diodes. Besides, we don’t need a heavy amperage diode here. The point is to keep the towed vehicles battery topped off, or at least from going dead. NOT go charge it up after a heavy discharge. A 5A or 10A diode will do it.

>>>When you pass current through the diode, you don't get the same current out the other end, and that's power that could keep your toad battery fully charged vs partially charged.

True, but the voltage loss through a diode is minimal (.6 to .7 V). The remaining voltage should keep the towed vehicle’s battery “nearly” fully charged. At least charged enough to start and run the vehicle, which is the reason for a charge wire in the first place.

I sometimes tow my Austin Healey and there is not a diode anywhere in the whole car and everything has worked fine for over 20 years.

Tim
First point. Newer vehicles no longer have manual mechanical systems. These switches do not controll the toad electrical systems as they did in the past. Then now control an integrated circuit (mini-computer) that feeds these systems. Backfeed may be OK or may be very detrimental to the toad system, but those circuit boards cannot be repaired and are expensive. And no place to to find out if it's a problem or not.

Second point. Newer vehicles steering does NOT lock on turning key off. Key off=power off.

Third point. Charge wire on the 7 pin trailer plug on the rear of the RV is SWITCHED. RV key on, wire is hot, key off, wire is off

Your comments on diode losses are somewhat confused. In the first section you imply there are no diode losses and the second you talk about losses. Your Google returned electronics diodes. The diodes I have (3 different brands and sources) all are large, finned and set up for heat dissipation, and were sold to be used for tail light application on a toad.

Use what you like and discard what ideas you don't like, but don't think current toads electrical systems are anything like 20 year old units. To approach the topic with that preconception, can get expensive. By the same token, using an expensive and unnecessary charge controller is not indicated here unless you choose to buy into the pop advertizing for the poorly informed or subscribe to the approach of those who think expensive is better.
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Old 10-14-2014, 06:31 PM   #12
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Originally Posted by Healeyman View Post
Mr. Pigman,

Since you answered my question first, I’ll address my reply to you. Your comments are >>>Bold.Others… Feel free to jump in.


>>>When you're feeding the tail and brake lights without a diode you are also backfeeding (powering) the entire toad electrical system through that connection.

Exactly how does that happen?

Without diodes, when the RV driver steps on the brake, the RV EMF comes into the towed and usually enters the towed’s electrical wiring at the tail lights. The EMF lights the bulb as it is grounded. The EMF also travels forward into the towed and what does it see? An open brake light switch. No chance of getting into the towed’s electrical system there.

When the RV driver turns on either directional signal, the RV EMF comes into the towed and usually enters the towed’s electrical wiring at the tail lights. The EMF lights the turn signal bulb as it is grounded. The EMF also travels forward into the towed and what does it see? An open turn signal switch. No chance of getting into the electrical system there.

When the RV driver turns on the RV head/park lights, the EMF comes into the towed and usually enters the towed’s electrical wiring at the tail lights. The EMF lights the turn signal bulb as it is grounded. The EMF also travels forward into the towed and what does it see? An open head light switch. No chance of getting into the electrical system there.

>>>If you simply run a fused wire to the toad battery, the fact that the toad key is off will prevent any power from energizing the toad system,

But for the vast majority of vehicles, while being towed, the vehicle’s ignition switch is not in the off position. It is in the ACC or Full ON position so that the steering wheel is unlocked to allow the towed vehicle to track the RV.

>>>and the battery will charge until it's internal resistance is too high for current to flow through it (this is full charge). The toad system will not backfeed to the coach because when the coach key is off, the charge line is switched off.

But while being driven, the coach’s ignition switch is always in the ON position.

If the fused wire is connected battery to battery, what mechanism switches the charge wire off when the coach’s ignition is switched off.

>>>If you're still concerned about that, you can pull the plug to the toad when you stop overnight, but to me, that's a waste of time.

>>>A final reason to NOT use the diode is that there are losses internal in the diode, that's why the big surface area and heat dissipating fins.


I Googled for 20 amp and 30 amp diodes and did not find even ONE heavy current diode with fins. Nearly all I found were plastic “barrel” diodes. Besides, we don’t need a heavy amperage diode here. The point is to keep the towed vehicles battery topped off, or at least from going dead. NOT go charge it up after a heavy discharge. A 5A or 10A diode will do it.

>>>When you pass current through the diode, you don't get the same current out the other end, and that's power that could keep your toad battery fully charged vs partially charged.

True, but the voltage loss through a diode is minimal (.6 to .7 V). The remaining voltage should keep the towed vehicle’s battery “nearly” fully charged. At least charged enough to start and run the vehicle, which is the reason for a charge wire in the first place.

I sometimes tow my Austin Healey and there is not a diode anywhere in the whole car and everything has worked fine for over 20 years.

Tim
First point. Newer vehicles no longer have manual mechanical systems. These switches do not controll the toad electrical systems as they did in the past. Then now control an integrated circuit (mini-computer) that feeds these systems. Backfeed may be OK or may be very detrimental to the toad system, but those circuit boards cannot be repaired and are expensive. And no place to to find out if it's a problem or not.

Second point. Newer vehicles steering does NOT lock on turning key off. Key off=power off.

Third point. Charge wire on the 7 pin trailer plug on the rear of the RV is SWITCHED. RV key on, wire is hot, key off, wire is off

Your comments on diode losses are somewhat confused. In the first section you imply there are no diode losses and the second you talk about losses. Your Google returned electronics diodes. The diodes I have (3 different brands and sources) all are large, finned and set up for heat dissipation, and were sold to be used for tail light application on a toad.

Use what you like and discard what ideas you don't like, but don't think current toads electrical systems are anything like 20 year old units. To approach the topic with that preconception, can get expensive. By the same token, using an expensive and unnecessary charge controller is not indicated here unless you choose to buy into the pop advertizing for the poorly informed or subscribe to the approach of those who think expensive is better.
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Old 10-14-2014, 06:57 PM   #13
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I never use diodes to prevent back feed in a charge circuit. There are voltage losses across a diode PERIOD. Think about it, you have a length of wire that has losses and you are planning to charge your TOAD batteries. You need about 13.5 volts to charge a 12 volt battery. Less voltage takes more time to charge. Use a large charging relay instead of a diode. A Ford starter relay works well and no voltage losses. Fuse it coming right off the alternator then the relay, back to connector. Use 8 gauge wire which is rated for 40 amps and you will charge batteries quicker then if you use a diode. The reason for a break in the charge line is so low toad batteries don't discharge TV battery when every thing is off but hooked up.
-Paul R. Haller
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Old 10-15-2014, 12:47 PM   #14
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I initially ran the center pin of the connector on the RV to the toad battery via a 10 amp fuse. I didn't want/need to "charge" the toad battery -just "maintain" it.

I found, and this may be unique to my RV, that when parked I couldn't turn off one of the "salesman's" switches (it's "on" light stayed on), the electric awing would not extend nor could the RV steps be left extended.

I don't remember if it was the coach or chassis battery switch that remained on -suspect chassis. In any event a low ampere diode properly oriented installed in the center pin wire allowed me to leave the coach connected to the toad.

That's why I installed a diode, the 0.7 vdc loss across the diode is irrelevant.
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