Batterty Isolators - Is there a consensus?

The Delco 11880 solenoid has silver inlay contacts. You lucked out. Drain your house batteries down, start the engine on fast idle, then take voltage readings.

At the alternator. From battery stud to case ground.

Across the battery lead posts.

Across the battery isolator solenoid, post to post.

What do you get?

I accumulated a 5 yard dumpster's worth of solenoids that were burned out via their power contacts.

MEXICOWANDERER wrote:
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.

Hmmmmm. My RV, built in 1973, still has its original (constant duty) can-type solenoid installed. It's wired to parallel the engine battery and the RV batteries. I can lock it down for charging, press it momentarily to help only with starting, or disable it to isolate the engine and the RV.

I would estimate that at least 90% of the starting cycles (and probably more than 95%) in the last 40 years were with that solenoid engaged to assist the engine battery during starting. Many, if not most of those starting cycles, the engine battery was marginal for starting, so the solenoid was carrying a hefty current. The solenoid has gotten lots of use - we're on our third engine in the chassis.

I looked up the number of the solenoid, and it wasn't anything particularly fancy. I think it was a Delco (400A short duration) rated for continuous duty at some lesser current, but don't hold me to those numbers. Part of the reason I asked for comments was because I thought I should carry a spare, but wondered if I might want to modify the system to something more modern.

Here is the link to solid-state isolators:

Solid State Isolator

I had this in my old Suburban and installed it in my current Suburban (I have dual batteries for audio, video, etc.)

I can vouch that it works exactly as promised and the current one is still working after 10 years.

It also has various other functions.

Steve

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.

Many of the new Isolator devices have bi-directional charge control and use FET's which have a very low voltage drop when on, and almost zero current draw when off or disconnected.

Just an FYI if you want one and have the funds.

When charging todays deep cycle batteries the difference between BOOST CHARGE 14.4VDC and NORMAL MODE 13.6VDC is 0.8VDC. When you add in the standard voltage drop for the DIODE BASED Battery isolators which is 0.7VDC it sure messes up what what you are trying to do when charging a deep cycle battery in a quick three hour time frame..

In other words it would be hard to use BOOST MODE smart mode charging going through an battery isolator.

consider these times determined by Progressive Dynamics on the amount of time each of these charging voltages will take to re-charge a deep cycle battery

"Progressive Dynamics ran this test on the amount of time it took a PD9155 (55-amp) converter/charger set to three different output voltages to recharge a 125 AH (Amp Hour) battery after it was fully discharged to 10.5-volts.

14.4-VOLTS (Boost Mode) – Returned the battery to 90% of full charge in approximately 3-hours. The battery reached full charge in approximately 11 hours.

13.6-VOLTS (Normal Mode) – Required 40-hours to return the battery to 90% of full charge and 78-hours to reach full charge.

13.2-VOLTS (Storage Mode) – Required 60-hours to return the battery to 90% of full charge and 100-hours to reach full charge."

If your 14.4VDC battery charging voltages drops by the 0.7VDC voltage drop when using an DIODE BASED high current ISOLATOR it will take the times stated in the 13.6VDC test shown above to re-charge that battery. It will charge your second battery but certainly will not re-charge that battery in a three hour period of time.

What they use today is SMART RELAYs verses ISOLATORs which monitors the DC VOLTAGES and when the truck alternator goes to its BOOST CHARGE mode it switches in the extra battery to be charged. Or you can do all of this manually by just switching in the RELAY CONTACTOR...

Battery DIODE BASED ISOLATORs worked great in the past when standard start batteries were being used but not so good these days meeting the required DC CHARGING voltages for the deep cycle batteries.

just my two cents...
Roy Ken

I used a isolator on the alternator and had two marine chargers one for each battery.

Manual override / control works for me as well

Winni wired my monentary "Boost" switch as they typically do
1 - The house battery supplies the needed current to drive the 100% Duty Cycle relay when the switch is held active. This enables the house batteries to help start the engine when the engine battery is low. Ok for me so far
2 - Wired the engine battery through the igintion switch to activate the relay when the engine is running. Thus both batteries were always connected while under way. This did NOT work for me thus required some modifications

Modified the system by adding a couple dash mounted switches and a 3rd switch
1 - A disable toggle switch that inhibits the ignition switch control of the relay. This switch has a nice little green LED inside the switch to help me visually see the system status
2 - A Manual on/off switch that I can toggle when I want the banks connected
3 - A heavy duty rotary switch in the battery compartment that connects the two banks together. Only used during winter to lock the two battery banks together as one while the converter keeps them alive with 13.1 volts for months at a time

My typical operation includes
560watts of Solar that charges the house battery bank and if needed the engine battery via above switch settings
When on shore power or genset power the 75amp full manual control w/ pendant converter charges the batteries depending on the state of the switches
The 130amp alternator typically only charges the engine but can be connected to the house batteries if need be

Did pretty much the same setup in my fishing boat with it's engine battery and trolling motor batteries. We tend to be way out in the woods for a week or more at a time so needed some addition method of charging the trolling motor batteries. Added a connection from the RV solar system with 50ft of flexible 8awg cable to charge the battery bank. When the boat is at home it gets connected to one of the dozen or so converters hooked up around the place.

Works for me but might not for others since it requires manual intervention with an eye on the battery metering / monitoring systems

I have never used the expensive diode isolators. A simple continuous duty relay for $15 has always worked fine for me.

When I had a TC I had it almost the same as you. When the alt was charging the relay had the batteries hooked together, when the alt wasn't charging the the camper battery was not hooked to the truck battery. The continuous duty relay only has a draw when the alt is charging.