| Re: Testing the battery isolator [message #189256 is a reply to message #189146] |
Mon, 05 November 2012 14:12   |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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Senior Member |
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| Kerry Pinkerton wrote on Sun, 04 November 2012 06:04 |
... Seriously, based on what I THINK I know (as opposed to what is the actual facts). This is how I would test the isolator.
1- Disconnect from shore power.
2- Set my meter to 25VDC (over 13 V) range
3- Put the negative lead (black) of my meter on a good ground.
4- Verify the ground by putting the positive lead of the meter (red) to the Positive terminal of the engine battery. Should read 12+ volt depending on battery state.
5- Start the engine. The voltage on the battery should increase by about 3/4 Volt. Perform same test on house battery.
If voltage does not increase at the battery (s) and the alternator is working, either the isolator OR the wiring is suspect. To test the isolator:
1- With engine running, check voltage at center lug of isolator. It should be 13.5 V or so (alternator output V)
2- Check voltage at the other two lugs. If voltage is not the same on the top and bottom lugs, then the corresponding diode has failed and the unit should be replaced (repaired??)
3- If voltage is present on the output lugs but not at the battery, the wiring or connection is bad.
To verify the shore power 120 to 12V power supply is working, shut off engine, plug into shore power (or start generator), and measure voltage at center terminal. Again, should be about 3/4V+ more than battery voltage.
OK, that is what I think I know. Until confirmed, please don't run out and rip apart your coach based on this process.
Now a question. How does battery condition effect measured voltage? Again, what I think I know is that the original BUZZ box converter will always put out the same voltage to the battery regardless of battery state (fully charged or not). I have a new 'smart' converter that is supposed to charge at lesser and lesser rates as the battery comes up to full charge. I THINK that the alternator will also charge at different rates but am not sure.
Ok, pass, fail, what?
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I finally had time to read again...
I would say "pass." But with the following comments:
-- The measured voltage on the center post should be a little higher than 13.5v as you should be around that (as charging voltage) on the outer posts.
-- I would also check the center post for zero volts with the engine not running to ensure that the isolator has not been by-passed (relatively common) or shorted (not so common).
-- From the factory the converter only charges the house battery. So you should NOT have anything on ethe input to the isolator if the engine is not running... pugged in or not. Some have added a "battery combiner" to connect the house and engine batteries when either battery has a charging voltage, but I suspect there are more coaches without than with combiners.
-- "How does battery condition effect measured voltage?" A bad battery can cause lower measurements, mostly noticed when no other voltage is being applied but can draw down even normally good charging voltages.
-- A good modern converter/charger is always a good idea over the old buzz box.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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