Volt sensitive dual battery setup

[Jacko]

Hi Guys,

I am finally looking to setup my dual battery. I purchased a 100 a/h battery and battery box to sit in the boot. After reading all the threads and everything I can find online, my preference is for a Volt Sensitive Relay with override switch in the cabin.

My problem and question is that after fixing a volt meter in the car to monitor my battery voltage, I have realised my system sits somewhere between 12 and 13 volts when the engine is running and around 11.5 to 12.5 when the car is off.

The VSRs usually have a cut-in at 13.2 and cut-out at 12.7 so to me it seems my second battery would rarely get charged?? Are my numbers too low and should I presume my battery or alternator need a check? Or is this usual for a Forester and a VSR is not the way to go?

Cheers,

Jacko.

 

[Ratbag]

Jacko

A lead/acid battery with a nominal voltage of 12V should always be 12V or slightly over if charged properly and after having stood for a while for the surface charge to dissipate. 11.5V standing voltage indicates that either the battery is not properly (fully) charged, or charging fully; or is cactus (unlikely with a new battery).

 

[Jacko]

Hey Ratbag,

Those figures are just for the primary battery, not the auxiliary (I haven't installed a dual battery system just yet).

So I guess I should presume either my primary battery is cactus or my alternator is not producing enough charge to fully charge it?

If that's the case, a Volt Sensitive Relay should work just fine once I correct my initial problem with the main battery?

Cheers.

 

[Kevin]

^ yes, your charge should be around 14.2 volts when running. I still have a VSR in my Foz but opted for a DC-DC charger in the Triton. Matson have a VSR with an override switch on the unit itself - had this in the Triton and am handing it over to my son. e.g. https://www.australiandirect.com.au...battery-isolator-with-override-switch/MA98404

 

[nipper]

What is your alt output at 1800 RPM with everything on, that is the true test of the Alt. Output at idle isnt a good load test.

Have you thought about a battery isolator that is already built for this purpose?

 

[Jacko]

So after your responses I did a better test, at the alternator I get close to 14 and just under that at the main battery. Seems the point I was reading from in the cabin may have some voltage loss somewhere.

Got the VSR today and works a treat Ran 6 B&S cable to the back of the car and get no voltage drop. Installed the VSR inside my aux battery box so I can take it with me in the future.

Just waiting for a couple of Anderson Plugs to make removal easy.

Thanks guys.