Battery Isolator Questions.

[shadow]

The battery isolator on my rv is over thirty years old.
Do they wear out over time or from age ?, and at this point should I replace it ?

At the very least, the terminals on mine need to be cleaned, but otherwise I don`t know
anything about them, or how long they last before needing to be replaced.

Thoughts or opinions would be appreciated.

[Scott7022]

The battery isolator on my rv is over thirty years old.
Do they wear out over time or from age ?, and at this point should I replace it ?

At the very least, the terminals on mine need to be cleaned, but otherwise I don`t know
anything about them, or how long they last before needing to be replaced.

Thoughts or opinions would be appreciated.

This is really Sternwake's area of expertise. 

I will add my two cent's but differ to him if he posts. 

I love BlueSea. It's built for marine applications and it is a little expensive but never heard or had one fail. They make an isolator and I like it as it is a latching relay. So it doesn't use any power when engaged. I love them.

[sternwake]

What does your Isolator look like/ say on it?

If it has big finned heat sink, it is a diode based isolator. A diode is like an electrical check valve, allowing flow in one direction.

The Diode drops a certain amount of voltage across it, and in doing so creates a lot of heat, slowing down battery charging. The diode based isolators are notorious for undercharging batteries as they will significantly slow the rate at which it charges, and the lower overall voltage reaching the battery pretty much insures it will NEVER fully recharge no matter how long the vehicle is driven.

A simple solenoid can and does wear out, the contacts inside develop high and higher resistance, creating more and more heat to the point they might fuse together resulting in NO isolation of engine battery from house loads.

The Blue seas products are great, but them make both a latching voltage sensing relay, and a super heavy duty solenoid switched by another 12v Ignition source.

There are so many different styles and brands and methods to achieve battery isolation. The topic can be vast, to encompass the benefits and dfetractions of all the methods/products available to achieve 'isolation'.

So A picture of your isolator or a link/ part number will help answer your question.

[shadow]

The battery isolator I have is a diode based isolator with the big finned heat sink.
The name on the side of the battery isolator is Protector 3 - 70 amp battery isolator.

I don`t know if I can get a picture, its mounted in a very tight spot that is hard to see and get to,
but I will try

[Optimistic Paranoid]

Thirty years ago, these diode type isolators were pretty much the only thing used on RVs.

There really are no moving parts to wear out.  The diodes are solid state one-way valves that permit dc current to flow in  one direction, but block it from flowing in the other direction.

Usually, the center post is where the wire from the alternator puts charging current into the isolator, and the two outer posts distribute this current to both battery banks.  Some have a fourth post, marked ignition, or sometimes e for engine that provides power to the ignition system.  You may not have that, it all depends on the way the original factory system was designed.

If you have a multi-meter that includes a diode test function, it's really easy to test one of these.  You can find Youtube videos that show you how, here's one:

[rvpopeye]

I'd replace with a quality solenoid type .
You can run an "activation" wire from a separate switch for manual control .
IMHO the only way to go.

[sternwake]

oK, NO pic needed.

Isolators are fine as long as one is not expecting a lot of alternator contribution to the house battery bank.

Usually these diode based isolators frop about 0.5 to 0.7 volts across them.

Many vehicles will naturally drop the voltage as the alternator/ voltage regulator warms as this will help prevent overcharging the starting battery.

BUt when the voltage drops to 13.8, and the diode takes out anbother 0.7v, well much less charging will occur.

Voltage is electrical pressure, so the less voltage the less amperage flow, and since a depleted battery, especially below 80%, can accept rather huge amperages, the diode based isolators will severely limit charging amperage/ speed/potential.

But they will keep house loads from draining starting battery.

A simple continuous duty solenoiid rated at no less than 90 amps continuous will charge the same battery much faster. The solenoid trigger requires 12v be applied to the electromagnet which closes the circuit, from the ignition, when the engine is running. On can put a manual switch on this circuit.

There are voltage sensing solenoids/relays. If solar is involved I recommend a single sense unit. Dual sense will combine batteries anytime either battery sees charging voltages, single sense will combine only when starting battery receives charging voltages. Single sense relays will not waste any solar wattage trying to bring the engine battery upto absorption voltage. The engine battery should not require any solar input, and even if it is fully charged it can consume 8 to 20 watts just to be held at absorption voltage. I'd rather those watts goto the depleted house battery.

testing your isolator, well get a voltmeter, measure voltage at house battery terminals, and engine battery terminals with engine off. Put on a large load on the house battery to drop it if they are reading very similar. A big load on house battery should not affect voltage on engine starting battery. If it does, then the isolator is not working

Then start engine, Both batteries voltage should climb with the engine battery at least 0.7v higher than the house battery, but in all likely hood even if working properly the voltage difference will be much greater, but the house battery voltage should climb. If it does not, then the isolator is not working.

There are so many different methods and products to achieve battery isolation. My opinion is the simple heavy duty solenoid whose trigger circuit is hooked to the ignition, and has an inline switch for optional manual control, is best.

That said, my own system is wired with a manual 1/2/both/OFF switch. As my charging systems are pretty well optimized, and i can regularly plug in at my current location, I am only running one battery for both engine and house duty and my switch is just left on 2. ther eis no battery on 1. With these switches it is important to not switch them to OFF when the engine is running. Removing the load like this can blow the diodes in the alternator.

Never remove the battery cable from a running engine, this alternator 'test' of long ago, can blow out the alternator on older vehicles and likely will blow it out on anything newer than 1994's.

[shadow]

I did manage to get a picture of the battery isolator

   
   

[shadow]

Thanks for all of the information.
I wish I knew enough about electrical to make the changes needed to
make the charging more efficient, but I don`t.

I will do some testing to make sure everything is charging, and leave it at that.

[rvpopeye]

When you get a chance ,replace the wires with something heavier (much heavier) !