Batterty Isolators - Is there a consensus?
There's another thread on battery isolators, and here is a quote from that thread on testing a diode type isolator: "Should be around 14 at the outer lugs and around 14.7 at the B+ lug" Presumably, ...
Forum Discussion
The way the old-fashioned silicon diode (finned) rectifiers worked was this way:
When the rectifier was not in use or lightly loaded, there was supposed to be a .7 volt junction drop across the rectifier. BUT, take the old Sure Power 70-2 for instance. It was normal for them to have a ONE POINT TWO VOLT DROP across the junction when an alternator was putting more than 50 amps through that rectifier.
It was assssssssssumed that the vehicle would have a remote voltage sensing voltage regulator. Connect to the vehicle battery and the regulator would compensate by boosting alternator voltage to "normal". This philosophy never worked right. Batteries were either chronically overcharged or undercharged.
So a silicon diode "isolator" is not a very good choice. Many years ago I touched the terminal on an old Chrysler squareback alternator and received what I later determined to be a 180 volt quasi-sinewave shock (some of the diodes had failed). The alternator was going nuts because the voltage regulator kept telling it to charge. The CHASSIS rectifier in the isolator had failed in the open position, and after boiling the house batteries, the alternator itself failed.
Could someone post a link to the FET type of isolator? The concept is really pretty.
What I can offer is this: A solenoid type isolator that uses a dash mounted switch has an awful lot of connectors that can fail and the control wire between the dash switch and solenoid is run beneath the vehicle and it is exposed. Count the connectors in this type of system...any guesses as to how many? Don't forget the fuse for the control wire and switch, and don't forget the ground wire for the solenoid.
I have seen dozens and dozens of can type constant duty solenoids fail because the owner did not connect the switch power source wire to IGNITION "B". An ignition switch has two "ignition" positions: The fist is for "the ignition" including fuel pump. Ignition "B" is connected to accessories like wipers, heater blower, radio, etc. The poor solenoids could not handle the massive current sent from the house battery bank over to the starting battery to assist it. Connected to Ignition "B" the isolator solenoid plays possum while the engine is cranked.
When the rectifier was not in use or lightly loaded, there was supposed to be a .7 volt junction drop across the rectifier. BUT, take the old Sure Power 70-2 for instance. It was normal for them to have a ONE POINT TWO VOLT DROP across the junction when an alternator was putting more than 50 amps through that rectifier.
It was assssssssssumed that the vehicle would have a remote voltage sensing voltage regulator. Connect to the vehicle battery and the regulator would compensate by boosting alternator voltage to "normal". This philosophy never worked right. Batteries were either chronically overcharged or undercharged.
So a silicon diode "isolator" is not a very good choice. Many years ago I touched the terminal on an old Chrysler squareback alternator and received what I later determined to be a 180 volt quasi-sinewave shock (some of the diodes had failed). The alternator was going nuts because the voltage regulator kept telling it to charge. The CHASSIS rectifier in the isolator had failed in the open position, and after boiling the house batteries, the alternator itself failed.
Could someone post a link to the FET type of isolator? The concept is really pretty.
What I can offer is this: A solenoid type isolator that uses a dash mounted switch has an awful lot of connectors that can fail and the control wire between the dash switch and solenoid is run beneath the vehicle and it is exposed. Count the connectors in this type of system...any guesses as to how many? Don't forget the fuse for the control wire and switch, and don't forget the ground wire for the solenoid.
I have seen dozens and dozens of can type constant duty solenoids fail because the owner did not connect the switch power source wire to IGNITION "B". An ignition switch has two "ignition" positions: The fist is for "the ignition" including fuel pump. Ignition "B" is connected to accessories like wipers, heater blower, radio, etc. The poor solenoids could not handle the massive current sent from the house battery bank over to the starting battery to assist it. Connected to Ignition "B" the isolator solenoid plays possum while the engine is cranked.
