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Originally Posted by Bill
I've looked at the article you mentioned, and I don't see any claim that it will actually limit current. And as you noted, they don't actually claim that it does. I apologize in advance for the techy-mathy stuff below, but it is real.
The third thing to notice is that the calculations above assume that your truck has #10 wire all the way from the alternator to the lithium battery. It doesn't. I traced the wire in the factory-installed towing package in my Ford Explorers, and found that at least half of it is #12 or smaller. That means even more resistance in the circuit, and even less available at the lithium battery.
So the SG35 is simply a conventional isolation relay with hefty contacts. It is very expensive, and you could do the same thing with a 30-amp or 40-amp relay for $15 or so from any auto supply store. I have used one for years, and it does just what you would want an isolation relay to do. In fact, your truck may already have an isolation relay as part of a factory-installed towing option, so that is the first thing to check. Just get a voltmeter or automotive test light, and press the probes onto the +12 VDC and Ground pins in the truck's 7-pin connector. If you find 12 VDC with the engine off, then you don't have an isolation relay. But if there is 12 VDC with the engine running, but it disappears when you turn the ignition off, then you already have one.
Bill
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Thanks Bill,
10 gauge wire seems inadequate for the task. Looking at the Trailmanor electrical diagram it even showed 12 gauge wire in the charging circuit so I hope that's been upgraded.
Great tip to do your test to see if I already have an isolation relay and I might because I have the tow package.
Thanks again.