Battery Isolator Question

[digitboy123]

I understand the function of a battery isolator during the charging phase, so no problem there.

I was under the impression that another function of the isolator is to automatically switch the vehicle's electrical system to the AUX battery when the vehicle's engine is off. Some dealers (and manufacturers) have told me this is not true, that any components I wanted to run (in-dash stereo, amplifier, lights, cigarette lighter connector, etc.) when the vehicle is OFF, would need to be directly connected to the AUX battery.

This would require new wiring to these components, separate from the regular vehicle electrical system. I thought one of the features of an isolator was to not drain the main battery if, for instance, I left the headlights on accidentally.

I don't understand how both of these statements can be true. Can someone who has used these isolators provide insight?

BTW, I am considering one of the relay-type isolators such as the True Smart Battery Isolator, Stinger SGP32 200 AMP Battery Relay Isolator and Relay, 140 Amp Dual Battery Smart Isolator by KeyLine Chargers, or similar. In other words, NOT a diode-based isolator.

Thanks in advance!

Click to read more...

 

[wew lad 5,000+ posts]

The isolator will isolate whichever circuit you put on the output pole, if your vehicle is wired so most of your electronics are on the primary battery and not the auxilary, then you will need to rewire them accordingly or accept that when you turn the key on the circuit will equalize for a moment before both batteries are at the same level again. your car will very likely start every time unless you really kill the other battery.

some switches allow you to pick between battery 1, 2, or both but its not gonna be a small switch unless you're talking about small loads less than 10-20a

the reason why dealers are telling you that is because all of your primary wiring for the equipment you just mentioned is integrated in the factory harness wrapped up neatly all the way to the main battery or fuse box

 

[garychurch84 10+ year member]

I have one of these I've never used,pretty much a paper weight for me. I'm tuned in on this topic,i would love some info as well.

 

[digitboy123]

The isolator will isolate whichever circuit you put on the output pole, if your vehicle is wired so most of your electronics are on the primary battery and not the auxilary, then you will need to rewire them accordingly or accept that when you turn the key on the circuit will equalize for a moment before both batteries are at the same level again. your car will very likely start every time unless you really kill the other battery.
some switches allow you to pick between battery 1, 2, or both but its not gonna be a small switch unless you're talking about small loads less than 10-20a

the reason why dealers are telling you that is because all of your primary wiring for the equipment you just mentioned is integrated in the factory harness wrapped up neatly all the way to the main battery or fuse box

I've since spoken to another technician who was able to describe the operation, and was even able to give an acceptable (I think) way to accomplish what I'm looking for.

Normally, an auxiliary battery is installed to power external accessories connected directly to it (i.e., not through the vehicle's standard wiring). Placing an isolator between the batteries (rather than wiring them in parallel) is what 'isolates" them and prevents draining both batteries with the external accessories. However, accessories inside the vehicle on the existing wiring will still get power from the main battery. And rewiring internal vehicle components to power from the auxiliary battery would be a great deal of work.

The other feature of the invertor is to regulate the charging phase so that the second battery only gets charged once the main battery is fully charged.

In my case however, I'm not looking to add any external accessories. I want to use accessories inside the vehicle using the existing wiring while the engine is off, and still be confident I can start it afterward.

So a way to accomplish this would be to first wire the the isolator as usual. I would use the inside accessories with the engine off and they would receive power as normal, from the main battery. Now, the isolators have an "override" connector (usually a yellow wire or post). Connecting the override connector to the (+)auxiliary battery effectively removes the isolator from the circuit, putting the batteries in parallel. Placing a switch on the connection allows you to temporarily control this action. With the switch off, it will attempt to start from the main battery. With the switch on, it will have the cranking power of the two batteries combined.

So, turn the switch on, start the engine, then turn the switch off once the engine is started. Don't forget! This would defeat the whole purpose of the setup. Perhaps even get in the habit of starting the engine this way all the time.

Installing one wire and one switch on a low amperage (

Brilliant, I think. Thanks to Matt at Powerstream. Injection molding, Batteries, Battery Chargers, Custom UPS, and power supplies for OEMs in a hurry from PowerStream

 

[digitboy123]

Better yet, use a normally off push button switch. Then you won't forget to switch it off.

 

[wew lad 5,000+ posts]

You don't really need a switch, I'd imagine you can tap into remote 12v somewhere along the way to activate and deactivate the relay per your requirements

You've said pretty much what Ive said about using the main battery by itself when the relay is off and connecting the two in parallel when it's on for starting/running

 

[digitboy123]

If we're saying the same thing, then I'm just dense. Or maybe we're talking about two different types of isolators. But I think we're saying something differently, so I'm happy to try again.

In my admittedly non-typical use of an isolator, I will require the switch in order to connect the starter to the batteries in parallel in the event the main battery has been sufficiently depleted by the vehicle's internal accessories while the engine is off.

The isolator has two output poles, one connected to the main battery (and thus to the alternator) and one connected to the auxiliary battery. While the engine is running, it automatically isolates the batteries so that the main battery is charged first. Once the main battery is charged, then the isolator "de-isolates" the batteries, putting them in parallel to initiate the charging of the auxiliary battery. If the main battery gets depleted by a certain small amount, due to the normalization of the batteries in parallel, the isolator will sense this and isolate the batteries once again until the main battery is fully charged. This is the normal function of the isolator.

When the engine is turned off, the isolator once again isolates the batteries from each other. Loads placed on the main battery, i.e. the internal electrical components of the vehicle, run off the main battery. This includes the vehicle starter. In the typical setup, loads to be used when the engine is off would be placed on the auxiliary battery, and there would be no concern about the ability of the main battery to start the engine. But I want to be able to use the vehicle's internal electrical components while the engine is off--without doing a major rewiring of the electrical system. This is not the typical setup, as I won't have any loads on the auxiliary battery.

In my case, the switch is necessary to override the isolator's function while starting the engine, so that the batteries are put in parallel during the starting process. Once the engine is started, the override switch should be turned off, (again, a normally-off push button is ideal) in order to return the isolator to its normal engine-running operation.

The override switch is not placed inline with a battery cable, which as you correctly noted above, would need to handle a large current. The override switch is placed inline between the (usually) yellow override pole on the isolator and the auxiliary battery, which merely changes the isolator's function to "de-isolated" during the engine starting process. This circuit does not need to handle a large current because it is only changing the position of the switch within the isolator, and not carrying the full current from the battery.