backchannel: thoughts on gnomad home’s INSTALLING A SMART BATTERY ISOLATOR

From this article:

As I whined earlier, Keyline’s use of the “smart” descriptor is misleading.  It’s not smart in the normal sense;  it’s a voltage sensing relay (VSR).

A battery isolator is a great way to supplement your solar panels


and make sure your batteries stay topped off no matter the weather

Topped off != fully charged, and the difference kills lead batteries.

And if you’re on a tight budget, you can even skip the solar and still have basic electricity with nothing but a good isolator and a deep cycle battery.

At least until you murder the battery

Battery isolators are essential for vanlife.

Well, I’d say “useful”.  An overbuilt solar config can do it on its own, but it’s not cost effective.

having the ability to charge your batteries from your engine is a great way to increase your power efficiency

Efficiency isn’t the right word here.   Production or generation might make more sense.

since [solenoids] have moving pieces, they also come with some risk of mechanical failure

So do VSRs, which are solenoids with a bit of electronics added..

[solid state isolators]  are not nearly as efficient, introducing about 0.7A of voltage drop.

There’s that word efficient again.  The “price” of solid state isolators is measured in volts.  The price of solenoids/VSR is in amps. I agree we can afford the amps much more than the volts, but you might want reduced voltage when feeding non-LFP li-po, for example.

When the voltage reaches 13.3V (meaning the engine is on and the battery is fully charged),

Well, being charged at least.

the isolator “cuts in” and sends 100% of the alternator’s current to your auxiliary battery

That’s just wrong.  It connects the two circuits and power flows.

A smart isolator will run you about $60-$80+, but the efficiency, reliability, and ease of installation are definitely worth it.

I’d agree with the ease of installation part, compared to a solenoid.

We think a battery isolator should be one of the first things you add to your van’s electrical system.


having a battery isolator ensures that you can keep your batteries charged in all conditions

No, it means you can charge your batteries in all conditions.  There is a significant gap between “charging” lead batteries and fully/correctly charging them.