Xref: utzoo rec.boats:4165 sci.electronics:13069 Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!ames!krypton.arc.nasa.gov!laforce From: laforce@krypton.arc.nasa.gov (Soren LaForce) Newsgroups: rec.boats,sci.electronics Subject: Re: Battery-charger tap from outboard motor Message-ID: <54677@ames.arc.nasa.gov> Date: 24 Jul 90 23:42:40 GMT References: <1990Jul24.153632.27480@phri.nyu.edu> Sender: usenet@ames.arc.nasa.gov Reply-To: laforce@krypton.arc.nasa.gov Followup-To: rec.boats Organization: NASA-Ames Research Center Lines: 74 News-Software: VAX/VMS VNEWS 1.3-4 In article <1990Jul24.153632.27480@phri.nyu.edu>, roy@alanine.phri.nyu.edu (Roy Smith) writes... > > A boat I'm looking at comes with a 5-HP Mariner outboard that has an >electrical output jack that is supposed to supply about 5A for recharging a >12V battery. The current owner says he tried to use it once but ended up >blowing out some of his electronics because the voltage output goes all over >the place. He tried changing the regulator in the motor, but that didn't >help. Anybody have any experience with these sorts of things? Any >suggestions on putting together some sort of external regulator that would be >hefty enough to handle the current load and voltage fluctuations, withstand >the marine environment (i.e. salt air, spray, etc), and have a small enough >voltage drop that I still got something useful out (about 14V for charging >purposes, I would guess)? I doubt a 78xx would do the job. >-- >Roy Smith, Public Health Research Institute One of the best voltage regulators I know of is.... A lead-acid battery!! Well... think of it as a **VERY** large capacitor. Do you know if the previous owner tried to use the motor as a battery charger, or if he tried to power the electronics w/o the battery in the loop? Were I in your position, I would assume stupidity (on part of prevoius owner), or at least a bad battery connection, and try the following: 1) Determine that the output is DC. Oscilloscope is the best method. 2) Connect battery to output. Check waveform. If voltage observed in 1) is above (about) 14 volts, the battery should charge and the waveform across the battery should be pretty darn flat. We are talking about several farads of effective capacitance. If in 2) there is no significant difference between the battery alone and the battery charging, I would suspect a wiring error on the part of the previous owner. Or, just insuficent understanding of the physics. I would **NOT** try to power anything semi-sensitive from a battery charger w/o a battery in circuit to act as a filter (and maybe not even then ;-). If the voltage is much higher than the battery voltage, i.e. above about 14 volts, you probably should put a resistor in serries with the battery when charging. This should provide correct voltage across the battery. R1 -------------/\/\/\--------------- + | |+ | G B Stuff - | |- | ---------------------------------- The charge current will then be a function of R1 and Vg-Vb. Be sure to work out the power requirements for R1. Anyway, this is what I would try first. It has lots of my favorite features, i.e. cheap and simple. --Soren "laforce@krypton.arc.nasa.gov" p.s. No, I don't have any idea how you will get a 'scope down to the dock. -S.