13V is a tad low, it ought to work, but if you could get another half volt or so you'd be better off, especially after you deal with the drop in the wiring all the way back to the battery in the camper. The alternator does indeed have an internal regulator, I don't recall if this year has a Bosch or Denso alternator, but if it's the Bosch, IPD sells an adjustable regulator you can install. I've never looked closely at the Denso alternator in some later cars so I don't know the details of the regulator. Either way, you should avoid going above about 14V at the fuse box in the car or things like lamp life will start to suffer.
Alternator voltage : min. needed?
Oct 28, 2008
2 Replies
I am adding a 12V external connection to my Volvo 92 740 to be able to run/charge the DC system on my pop-up camper, which has a 12 V deep cycle battery. So I got one of those three-terminal battery isolators. The alternator output goes to the center terminal, and the car battery and the pop-up battery go to the other two terminals. The alternator puts out abt 14 V measured with my fluke. However, each of the isolator diodes has about a 1 volt drop across it, so now there is just 13 volts available to charge either battery....at the battery terminals. Question is, is this going to be sufficient to keep the batteries topped off? I was expecting to have something less of a drop than what this diode isolator has, since a silicon diode junction when forward biased has a .6 volt drop. I have heavy gauge wire and tight connections, so I am sure that the voltage drop is at the diode junctions. I believe the alternator, which is OEM, has an internal regulator, and probably no way to tweak the voltage up to compensate for this. Do I have a problem, or not?
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13.8 is needed to get to a peak,
14 is a peak voltage and works. 13 is not going to saturate cells but will do if you use a seperate charger at home and this is just a vaction set up. 12.8 is a fully stabilised charge, but it needs to peak for a while at 13.8 or so. That is a hard load on an alternator to run it as a charger, an easy way to burn one out is what you propose.
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