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Old 06-18-2015, 04:36 PM   #1
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Do I need a diode on towed wiring?

Changing wiring on towed from 4 wire flat to 6 wire round so I can charge towed battery while towing. Wiring from MH alternator to 6 wire round with 10 ga wire and 20 amp fuse. Wiring to towed battery is 10 ga wire with 20 amp fuse. The question is do I need a diode in circuit for when MH is not running and they are wired together. Will the backfeed to the alternator on MH cause any problems? If I do need a diode, what should I buy and where would I get it? Thanks for the help.

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Old 06-18-2015, 04:46 PM   #2
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Ron,
Why did you wire to the alternator? Aren't your chassis batteries in back, like mine? I wired my toad charge wire with a 20 amp auto reset circuit breaker, the wire goes right to the battery post. If I would draw too much power through the wire starting the engine, the CB trips and then resets. Never have had an issue with it hooked up this way.
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Old 06-18-2015, 04:53 PM   #3
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I wired in a simple relay that turns the power to the toad on when the motor home key is on and turns it off when ... (well, you get it!)
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Old 06-18-2015, 04:53 PM   #4
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The purpose of the diode is to prevent current flowing from the toad to the MH. Practically speaking, when MH is running, your MH alternator will be producing more voltage than the static toad battery, so it is not backfeeding into the MH alternator. When you turn off the MH, there should not be any significant voltage difference, and even if there were the MH and toad batteries would quickly equalize.
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Old 06-18-2015, 05:01 PM   #5
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And, without a diode, you can charge the MH from the toad in an emergency.
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Old 06-18-2015, 05:04 PM   #6
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38Chevy454 is exactly correct. It's also exactly what happened to mine when we had a bad battery in our Jeep on our way to Quartzsite. The toad battery drew down the engine battery in the coach so nothing would start the next morning! The relay went in right after the new battery!


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Old 06-18-2015, 05:10 PM   #7
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Quote:
Originally Posted by 38Chevy454 View Post
The purpose of the diode is to prevent current flowing from the toad to the MH. Practically speaking, when MH is running, your MH alternator will be producing more voltage than the static toad battery, so it is not backfeeding into the MH alternator. When you turn off the MH, there should not be any significant voltage difference, and even if there were the MH and toad batteries would quickly equalize.
Exactly!! If you turned the lights on in the toad, I guess you could discharge the RV chassis battery, but it's never been an issue in my set up. The only time there's a significant difference in voltage, as in starting the RV, the auto reset circuit breaker will trip if too much current is drawn through the wire.
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Old 06-18-2015, 06:07 PM   #8
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I hooked our charge wire from the coach chassis battery to the toad battery with 20 A reset able breakers or you can use 20 a fuses and also installed a diode at the toad battery so it can't back feed.
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Old 06-18-2015, 06:15 PM   #9
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Never thought of needing a diode or relay. I just wired two 30 amp auto reset fuses in and ran from the MH chassis battery shut off on the Dutch Star.
The dealer wired it in on the Magna and went through the spare wiring already in place.
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Old 06-18-2015, 06:38 PM   #10
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You really should run a diode and you can wire it yourself if your a DIY guy. If not, they make charge kits that have the connectors, fuses and diodes already incorporated.

Here is a charging system LSL Products TOAD-CHARGE-40 Dinghy Vehicle Battery Charger 40' Wire Harness
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Old 06-21-2015, 05:21 PM   #11
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Thanks all for the feedback. I originally ran from MH alternator because that was the easiest, most accessible route. Then after hooking that up is when I began to wonder about needing a diode at the alternator. So I will change the feed on the hot wire to the chassis motor starting batteries with a 20 amp fuse. Some have said I need a diode. Can anyone tell me which diode to buy and where to buy? I looked at Dutch Star Don's link and $80 is more than I want to spend.

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Old 06-21-2015, 06:12 PM   #12
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As others have explained, the diode isn't really needed. If you fear that there will be an imbalance and you'll drain the batteries while stopped, just get out and disconnect the umbilical between the two vehicles. If you stop at a campground where you're hooked to shore power, the on board charger in the RV will not only charge the RV batteries but through the umbilical it will maintain the Toad battery. Diodes can be had for under $20, but they're only 4 amp rated, don't know the capacity of the $80 one you mentioned.
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Old 06-21-2015, 06:56 PM   #13
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A voltage sensing relay called a Victron, Cyrix Battery Combiner, will do it all, for 50 bucks

No current passes, unless the voltage excesses 13.4.
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Old 06-21-2015, 06:57 PM   #14
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Quote:
Originally Posted by ronspradley View Post
Thanks all for the feedback. I originally ran from MH alternator because that was the easiest, most accessible route. Then after hooking that up is when I began to wonder about needing a diode at the alternator. So I will change the feed on the hot wire to the chassis motor starting batteries with a 20 amp fuse. Some have said I need a diode. Can anyone tell me which diode to buy and where to buy? I looked at Dutch Star Don's link and $80 is more than I want to spend.

ronspradley
Ron I bought my Diode from radio shack and the biggest I could get at the time and enclosed in shrink wrap. Price was about $1 maybe 2 and I have never had a problem keeping the battery up and In use a braking sys that mashes the toad brake lighting the toad brakes
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