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Testing Isolator

To test Isolator.

Use a good meter with a diode setting.

Remove wires from center and one side (or both sides).
Touch test probes to center and one side.
One-way is red probe on center & black probe on side.  Other-way is red on side & black on center.

Then repeat test with probes to center and other side of isolator.

If isolator is ok,
Probes one-way (called forward bias) will typically read between 400 & 1000.
with probes the other-way, meter will read "1"

If isolater is bad,
Shorted side will indicate near "0" and there will be continuity.
Open side will read "1" with probes either way.

Re: Testing Isolator

Reply #1 –
Very true, but for a basic "does it work or not" test, you don't need to remove the wires.  Let the batteries rest for a while without any charging from either the inverter/charger or the engine alternator, then measure the voltages at the chassis battery terminal and at the house battery terminal.  Turn on the house battery charger, and the house battery voltage should rise but the chassis battery voltage remain unchanged.  Then turn of the charger, find the rest voltages again, and start the engine -- now the chassis battery voltage should rise but the house battery voltage remain unchanged.
Tom Lang K6PG (originally  KC6UEC)
and Diane Lang
2003 38 U295 build 6209
2016 Jeep Grand Cherokee Summit Ecodiesel
still have tow-ready 2006 Acura MDX 
Temple City, California
Motorcade 16681 California Chapter President
SKP 16663 member of SKP Park of the Sierra, Coarsegold California
FMCA F071251
Retired electrical and electronic engineer

Re: Testing Isolator

Reply #2 –
Quote from: Tom Lang –
Then turn of the charger, find the rest voltages again, and start the engine -- now the chassis battery voltage should rise but the house battery voltage remain unchanged.

I don't think this statement is correct since the alternator charges both the chassis and house batteries through the isolator.  That is why the isolator is there.  Voltage should rise on both batteries.
Jerry Whiteaker former owner 96 U270  36' #4831 Austin,TX-Owner Mods LCD TV w/front cabinet rebuild - LCD TV bedroom - Dual Central AC, either can cool coach w 30 amp - Skylights at roof AC openings - Drop ceiling for ducting of AC - Shower skylight white gelcoat/wood/epoxy frame - Air Springs/Shocks replaced - 2014 CRV - 8K Home Solar - Chevy Volt

Re: Testing Isolator

Reply #3 –
But... Remember that the chassis battery gets a 'direct feed' from the alternator while the house battery bank feed gets a half volt less due to the diode drop across the isolator.
The selected media item is not currently available. Dave Head & Megan Westbrook
Titusville, FL - The Great Outdoors
'98 270 buying this month
Toad is a 2018 F150 XLT
 

Re: Testing Isolator

Reply #4 –
Gee, on my isolator, it has the same diode reading on BOTH sides, so both chassis and house batteries get the same voltage charge.  Why I raised the voltage on the belt driven alternator.
On my setup, I get a higher volt reading on the alternator terminal than either chassis or house side.
Both chassis and house side read real close the same.