Xantrext Truecharge 20 and fuses

[David W]

I installed a Xantrex Truecharge 20+ on the weekend. I have a Trojan group 24 deep cycle and a starting battery.I used #10 wire for the DC wiring and #14 for the AC as per the manual. I fused the positive DC circuits with two 25A fuses (one for each battery) and the AC with a 15A breaker as per the manual. Settings set to warm temperature, flooded batteries and three stage charge.Plugged in the charger and all seemed exactly normal, just as it was when I connected it at home using the same configuration.We went sailing yesterday and when I returned to the dock and plugged in my shore power again, I checked the lights & fuses and noticed that one of the 25A DC fuses was blown. The fuse on the house battery was fine.What could have caused this to occur?The only thing I can think of is that I started the engine with the battery switch in the "Starting" position and the shorepower was still connected, therefore the charger suddenly had to produce more than 25A. How it might have done this I am not sure.Or did I backfeed more than 25A when the alternator started putting out its rated 35A, so the fuse blew to protect the charger?Thanks!David

 

[Stu Jackson]

Two sources

David: "The only thing I can think of is that I started the engine with the battery switch in the "Starting" position and the shorepower was still connected, therefore the charger suddenly had to produce more than 25A. How it might have done this I am not sure."I am constantly amazed at how many people do this. Why chance the possibility that someone will forget to unplug the yellow cord before you back out of the slip?The charger didn't have to put out any more, because the alternator was try to do the same thing. It's hard to answer your question without having a wiring diagram of your setup.What was the charger connected to when you "tried it at home?"Best and safest bet: do this: Unplug your shorepower cord. Replace the fuse. Start the boat. Then turn off the engine, replug the shorepower after replacing the fuse and see if that works. If it works, then you're OK and have some time to figure it out. Make sure you have spare fuses on board, too.Good luck.StuPS good choice for the charger

 

[David W]

Thanks Stu

I start first because I like to have let her warm up before we slip the lines. I agree this is probably not the best idea, I will change our departure procedures... Thanks! Last night I replaced the fuse, connected the shorepower and all was well, as it was when I installed the system. But I did not try starting the engine again.Could the momentary drop in starting battery voltage when starting the engine(the engine cranks for 4 or 5 secs before it fires) have caused the charger to supply more than 25A of current for a moment or two thus blowing the fuse?I can see how starting and running the engine with the charger discnnected from shorepower would have no effect on the fuses as every boat out there with one of these would have essentially the same set-up. The alternator output has to go to the batteries or they don't get charged. The charger is connected to the batteries so that is the common point.BTW Xantrex was of absolutely no help. The best explanation was that the fuse might have not been a 25A fuse... maybe it was a smaller rating. Too bad I threw it away like a dummy...Thanks Stu (glad I made the right choice on charger!)

 

[David W]

Sorry the home setup

was essentially AC power in, DC power out to a single group 27. I did not have a fuse in the positive DC circuit, only the AC side.