Where to find a diode?

[Gary RVRoamer]

He needs a diode rated for a minimum of 10 amp for the Toad Charge line.

But I'm pretty sure the Toad Charge already has built in circuitry to prevent reverse current flow. Their FAQ age even describes it. Not clear if the OP is using a Toad Charge or a DIY connection this time. He says he had trouble with TC wiring.
TOAD-CHARGE Frequently-Asked Questions

[mhbell]

This is what you would need if you are trying to charge the battery in the toad and keep the starting battery in the motor home Isolated and prevent feed back. It is called a battery Isolator. here is one for $16 on amazon com. Stinger SGP38 80-AMP Battery Isolator and Relay.
Mel

[Pigman1]

I guess you can put all that stuff between the toad and MH if you want to waste your money, but we don't. My 7 pin connectors at the back of the MH have a pole called BAT +12V. Wire from there to the toad battery with a 10ga wire and put a 25A fuse within a few inches of the toad battery. The MH connection is on the IGN switch, so no connection until the key is on and no back feed. It's also fused at the MH end. We've been pulling 3 different toads with three different class A's that way for almost 200,000 miles and never had a problem.

[Rich and Cork]

You don't want diodes for what you are wanting to do. You just need fuses to protect from shorting.

[nothermark]

To do it correctly there should be isolation between the batteries. It's true that most of the time it works without it. The diode is there for when it does not. This looks like a reasonable device:

Battery-Related Products | Battery Isolators48051 | Cole Hersee - Littelfuse

Anything similar will work.

The ~0.3 VDC drop may prevent the battery form being maintained at 100% but it will maintain it at a high level of charge. If the alternator output is high enough it will not matter at all. The normal situation is that there is a low current flow to equal the phantom drains not the high capacity needed if there is a big difference in charge levels.

[maxwell18]

I am the OP, I have tried Toad Charge, if you used it or seen it you could see the connections are mickie mouse. My toad requires to have the key on to tow and draws alot of juice. I already have a CB in line all I wanted was diode in line to protect the expenesive MH circuits, cheap insurance. I know if anying can go wrong, IT WILL. Thanks for all the help and I did learn something.

[mel s]

Originally Posted by wa8yxm

A diode isolator (Battery isolator) comes with a pair (or 3) diodes.. Two are big mothers, encased in epoxy and aluminum they can pass easily 70-80-90 amps depending on the model
The third (if present) is smaller.

BUT there is a problem... THe voltage drop may prevent proper towed charging.

US-Gear (unified brake decelrator) puts a line from the motor home battery to the towed battery 20 amp breaker at one end 40 at the other (I'd use 20's both ends for your install) the self resetting thermal kind.

Now that works.. Very low voltage drop.. It is how I handle my towed.

wa8yxm
The 2 breakers are a good idea.
However, I believe a single diode should also be used in a charge line... (to prevent toad battery voltage from flowing into the 12V electrical system of the coach).

Mel
'96 Safari

[dpinvidic]

Originally Posted by maxwell18

I am the OP, I have tried Toad Charge, if you used it or seen it you could see the connections are mickie mouse. My toad requires to have the key on to tow and draws alot of juice. I already have a CB in line all I wanted was diode in line to protect the expenesive MH circuits, cheap insurance. I know if anying can go wrong, IT WILL. Thanks for all the help and I did learn something.

A diode is a one way switch. It does not protect against voltage spikes.
It is not perfect, so depending on the material, it can have up to .75 volt drop.
When your motorhome is putting out 14v charge voltage your toad will be see less.
13.8v is the normal float charge voltage. About 14.5v is a fast charge voltage.

Inside your motorhome, the charge solenoid actually ties your house and chassis batteries together (no diode).

If you have a Freightliner chassis, the 12v line on the trailer connector is ignition controlled and runs through a relay. So the worst that can happen is if the key was left on, engine off, your toad and chassis batteries would be in parallel.

If you want a well functioning charging circuit, don't use a diode.
If your concerned about draining the toad battery, put a relay in the charge line (if not Freightliner).

As far as protection against voltage spikes, the diode will only block negative spikes from the coach.

You are sacrificing having a fully charged toad for a false sense of protection.

Good luck.

Regards,

Dan

[YC1]

I'm a Certified Electronic tech with 40 yrs working on 12 volt systems in every imaginable type of vehicle.

IF the MH only charges with the ignition on then don't wast time, money, and the energy lost on using a diode. You are gaining zero protection.

A diode capable of handling a lot of current is big and not cheap. If you must, then consider buying a small battery isolator that can handle heavy currents and has a heat sink.

Here is an example. You can probably buy one at most automotive stores. You could even jumper the two output post.

http://www.boatersland.com/gue2501.h...FUERHwodp5EAOg

[nothermark]

You are missing the point of the diode. It is only there to keep the towed battery from discharging through the motor home while keeping the towed battery somewhere near full charge when driving. To do that it does not have to put full float charge on the towed battery though it may. The current is significantly lower than the diode rated maximum current when in float mode. Forward bias lower current will be less than the maximum drops being tossed around. The only reason the current capacity on the diode needs to be high is in case the battery on the towed is low compared to the battery on the coach when everything is hooked up. Then the current can be higher but the drop does not matter because of the differential in voltage. If anything it is a better way to charge as it is not slamming the towed battery with a high charge current. The latter is not a good idea as it can damage the battery or shorten it's service life. That is exactly what a relay will do.

[dpinvidic]

Then order one of these from Amazon for $21 and call it a day.

Towed Vehicle Battery Maintainer

Dan

[Pigman1]

Originally Posted by nothermark

You are missing the point of the diode. It is only there to keep the towed battery from discharging through the motor home while keeping the towed battery somewhere near full charge when driving. To do that it does not have to put full float charge on the towed battery though it may. The current is significantly lower than the diode rated maximum current when in float mode. Forward bias lower current will be less than the maximum drops being tossed around. The only reason the current capacity on the diode needs to be high is in case the battery on the towed is low compared to the battery on the coach when everything is hooked up. Then the current can be higher but the drop does not matter because of the differential in voltage. If anything it is a better way to charge as it is not slamming the towed battery with a high charge current. The latter is not a good idea as it can damage the battery or shorten it's service life. That is exactly what a relay will do.

Huh? Just what do you think the voltage regulator on any vehicle does? Damage a battery and shorten it's life? Since you're bound and determined to spend your money on something that's not needed, go right ahead, but don't try to justify it by claiming some of the manufacturers propaganda is The Gospel.

[TQ60]

Many options are provided but before doing anything just get a voltmeter and check the interface to see if you need to do anything at all.

If it is constant hot maybe but if only hot with key on you are set to go.

[azpete]

frys electronics has what you need.