Batterty Isolators - Is there a consensus?

[DryCamper11]

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, the 0.7v difference in voltage is due to the voltage drop over the diode in the isolator. That's a lot when charging a battery.

1) I know there are some modified alternators/voltage regulators that put out 0.7 more voltage than the batteries need to compensate for the diode isolator voltage drop.

2) Others just ignore the diode drop.

3) A different isolator design is to use relays - they have no voltage drop.

4) My 40 year old RV uses a continuous duty relay and I manually engage it when on the road if I want the coach batteries charged by the engine. If the ignition switch is off, it's off, too. I like having control over whether the engine alternator is trying to charge the house batteries (there are times when I don't want the alternator running maxed out). I've occasionally left the ignition on and the dual switch on when I'm parked and plugged into 120VAC to get the engine battery charged by the converter/charger.

Is there any consensus on the preferred system and the advantages/disadvantages? Does anyone have a system they particularly like?

[ken_white]

DryCamper11 wrote:

ken white wrote:
I have had FET battery Isolator devices for years in a few different campers and never had any issues - no contacts to burnish...

The cost was $170-$200 for a suitable FET isolator, when I checked. I can replace a lot of mechanical solenoids for that price, particularly when mine has been running for 40 years.

Depends on what you need, or want, and are willing to pay - BTW I did not pay anywhere near your estimates.

If you are happy, then stick with solenoid technology.

I opted for lower losses and automatic operation, YMMV.

[DryCamper11]

ken white wrote:
I have had FET battery Isolator devices for years in a few different campers and never had any issues - no contacts to burnish...

The cost was $170-$200 for a suitable FET isolator, when I checked. I can replace a lot of mechanical solenoids for that price, particularly when mine has been running for 40 years.

[DryCamper11]

CloudDriver wrote:
The Winnebago supplied solenoid is a Trombetta #936-1215-011-21. Anyone have a suggestion for a more reliable replacement?

Mex thinks I have the Delco 11880 solenoid with silver inlay contacts. I suspect he's right, but all I really recall is that it was Delco continuous duty. Mine has lasted 40 years, unless my father replaced it in the first 10 years of RV use.

[ken_white]

MEXICOWANDERER wrote:
...Unless a Field Effect Transistor type power relay is manufactured incorporating a host of protective circuits (over, under voltage, transients, short circuit, reverse polarity and thermal shutdown, it cannot be as reliable and rugged as a mechanical relay. No way in hell. The insane amount of transient voltage spikes generated when a starter motor solenoid collapses the field inside a starter motor is the bane of any electronic device. DO NOT DO THE FOLLOWING! If a person should be touching a starter motor battery post connection when the ignition key is relaxed, the resultant transient voltage will knock them on their ass. It is far worse a jolt than a spark plug shock. It is not the POSITIVE transients that do damage in a starter motor circuit. It is the negative transients, and guess what...the ground side of a starter motor is not switched.

The newer FET designs are very robust, as are all of the electronics in newer vehicles.

I have had FET battery Isolator devices for years in a few different campers and never had any issues - no contacts to burnish...

[CloudDriver]

Interesting reading here and perhaps someone can suggest a proper replacement for the battery isolator solenoid that came with my Winnebago Minnie. In the ten years we have owned this MH, I have replaced the solenoid twice, with the same model obtained from Winnebago. Last time was only a year ago, and already I'm having problems again. The problem I have is that the solenoid doesn't always pull in when the ignition is turned on and the engine running. With the ignition on, I get voltage at the coil terminal, but no action from the solenoid. I can see the house battery voltage readout on our inverter display when sitting in the driver's seat, and sometimes after driving over some rough road, I can see that the solenoid has pulled in so that the alternator is then charging the house batteries. After the solenoid pulls in the first time, I can use a jumper with the ignition off to connect the coil terminal to one of the heavy battery terminals and the solenoid pulls in and drops out normally, with a loud clunk in either direction. A day or so later I can't count on the solenoid working though. It seems that it gets stuck after sitting for a while.

The Winnebago supplied solenoid is a Trombetta #936-1215-011-21. Anyone have a suggestion for a more reliable replacement?

[MEXICOWANDERER]

Yes I autopsied too many to count. Drilled out the spot welds holding the lid to the can. Many died because they were junk to start with. A quick and dirty lesson. Solenoids must use a spring to pop the contact disc (copper) away from the two stud contact points QUICKLY after the solenoid is de-energized. If the disc lollygags it's going to get burned all to hell. OK a strong spring means a strong magnetic field is needed to overcome the spring tension then clamp the disc hard against the two copper studs.

A lot of magnetic energy is needed. Not just amps. A solenoid can be wound two ways. One is with fewer turns of lighter gauge magnet wire the second is with a lot more turns of heavier gauge magnet wire. Both may yield a resistance of let's say 7.0 ohms when measured with a meter. But electromagnetic coil winding function is a measure of AMPERE TURNS. Turns of wire. A "heavily wound" magnet coil may draw the same amount of amperes but have TWICE the magnetic pulling power. Yes, longer wire means more ohms (a higher resistance) but what happens when that "more wire" solenoid uses a larger gauge wire...the resistance difference is offset.

Think of a cheap solenoid as being "A Loose Connection In Sheep's Clothing".

Too many amps (watts) will overheat and burn out a solenoid coil winding. So this is why a Ford Type starter solenoid can carry 400 amperes - for 1 minute.

And too many amps will melt a solenoid's power contact disc and stud contact points. If the "connection" is loose as a goose because of a poor magnetic field then the solenoid went into my dumpster.

I found out the hard way that even small relays like the BOSCH (now TYCO) have many worthless junk copy-cats. Comparing a Bosch relay to a counterfeit is like comparing a Rolls Royce to a Yugo.

The newer "Tower Type" solenoids like the ESSEX are far superior to the earlier can type solenoids. They run cooler, use less current, pass more current safely and last longer.

Unless a Field Effect Transistor type power relay is manufactured incorporating a host of protective circuits (over, under voltage, transients, short circuit, reverse polarity and thermal shutdown, it cannot be as reliable and rugged as a mechanical relay. No way in hell. The insane amount of transient voltage spikes generated when a starter motor solenoid collapses the field inside a starter motor is the bane of any electronic device. DO NOT DO THE FOLLOWING! If a person should be touching a starter motor battery post connection when the ignition key is relaxed, the resultant transient voltage will knock them on their ass. It is far worse a jolt than a spark plug shock. It is not the POSITIVE transients that do damage in a starter motor circuit. It is the negative transients, and guess what...the ground side of a starter motor is not switched.

[DryCamper11]

wa8yxm wrote:
Dang few alternators have a voltage sense lead now days.

Mine does, but then again, it's not a "now days" design - it was installed in 1972 (or rather, its great, great grandaddy was 🙂 )

[DryCamper11]

KJINTF wrote:
What caused them to die?

That's my question. I assume Mex wants me to measure voltage drop across the relay contacts to see how bad they have gotten in 40 years. I'll do that eventually, but I pulled my batteries for the winter last weekend.

What voltage drop would be considered too much? At what charge amperage?

I don't like to let the house batteries run down for long, so while camping, I tend to keep the charge up with gen charging. I'm optimized and balanced so that I can usually get back to 90-95% SOC every couple of days with normal gen usage to run the WH and the microwave.

I tend to think of the constant duty relay as primarily serving the purpose of making it easy to start the engine by adding in the RV batteries, not as a means to recharge the RV batteries while driving.

[KJINTF]

A solid well built 100% Duty Cycle mechanical solinoid with at least 200amp continous current rating (coil current is small enough to not worry about) is my choice any day over a solid state FET device. I too have had several relays last 20 plus years come to think of it never had one fail.

Mex have you taken the defective ones apart?
What caused them to die?
Did the connector assembly stop turning as they should?
Dampness rust excessive heat etc can kill them

[wa8yxm]

I have seen diode isolators with 3 output terminals, two big, one small.

Here is how they work

The big ones go to battery one or battery two.. The small one to the voltage sense terminal on a voltage regulator.. Thus automatically adjusting for it being there.

The problem.

Dang few alternators have a voltage sense lead now days.

[MEXICOWANDERER]

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.

[DryCamper11]

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.

[subcamper]

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

[MEXICOWANDERER]

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.