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Author Topic:   Testing Battery Chargers
cswesq posted 05-05-2008 12:40 PM ET (US)   Profile for cswesq   Send Email to cswesq  
I am told my battery charger is done on my Larson Cabrio 290. Before I replace it (its in a tough spot to get at), I was wondering if there is a way of testing it to see if it works or not.
jimh posted 05-05-2008 02:58 PM ET (US)     Profile for jimh  Send Email to jimh     
To make a rudimentary test of the battery charger, connect a resistance which will cause the rated output current to flow at a voltage of 14.4 volts, and then measure the output current and voltage.

What is the rated output current of the charger you wish to test?

cswesq posted 05-05-2008 05:42 PM ET (US)     Profile for cswesq  Send Email to cswesq     
I will check and follow-up on this topic. It is designed to charge the 2 batteries on board and worked fine until last year, when the boat mechanic I was using, disconnected it, saying it was drawing power from (and discharging) the batteries when it was not connected to a dock power source.

What kind of device are you talking about to test it? Can one be purchased? Are they known as something (like a battery charger tester?). I know I sound ignorant, but wha I have found is that most mechanics (car and boat) don't know much about the electrical systems...

Chuck Tribolet posted 05-05-2008 08:59 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
What year is your Larson? Is the charger original equipment?

Who REALLY made it? Do some homework, first stick your head
into wherever it is, and see what's stuck on the side. It
might say Larson, it probably doesn't. Then find out whether
it has a reputation for doing what your mech says. That's
possible, but really really bad design.


Chuck

Chuck Tribolet posted 05-05-2008 09:12 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
JimH:

the rated output of the charger is pretty irrelevant
here. If the charger doesn't disconnect itself from the
battery when it doesn't have shore power, it's a problem,
the only question is when. Given that disconnecting without
shore power is trivial (a relay energized by the shore power),
there's no excuse.

And how many of the folks out here have a device that can
absorb the rated output current at 14.4V? If it's over about
a quarter amp, I sure don't, and can't think offhand of how
to jury rig something.


Chuck

jimh posted 05-05-2008 10:01 PM ET (US)     Profile for jimh  Send Email to jimh     
A car headlamp is a rather inexpensive way to absorb 12-volt current. Hook your charger up to a sealed beam incandescent headlamp. It will absorb several amperes of current.

Here is one for $3.39 at my local auto part store:

http://www.partsamerica.com:80/productdetail.aspx?MfrCode=SYL& MfrPartNumber=4000&PartType=301&PTSet=A

Just measuring the output voltage of a charger is also a simple test, but it really does not prove it will deliver current.

If the charger has a blown diode it will tend to discharge a battery. You can easily check for that if you know how to use a multi-meter with a diode test function.

where2 posted 05-07-2008 11:23 PM ET (US)     Profile for where2  Send Email to where2     
Even a resistance test function (unit=Ohm) on a multi-meter will work in a pinch for testing a diode. The resistance measurements should be drastically different when you flip the leads. Testing the diode in the circuit can be questionable. Sometimes you need to detach one leg of the component to get a real measurement.
seabob4 posted 05-08-2008 09:32 PM ET (US)     Profile for seabob4  Send Email to seabob4     
Sometimes it's best just to get a new charger! Larson's (part of the Genmar group) we're never known to make things watertight. I can get you a ProMariner 2-bank ProSport for $175, a 3-bank for $210.

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