#148851  by pcm
 Sat Feb 09, 2019 12:37 pm
Hi

I've recently removed the 12v house batteries from my motorhome in order to have them tested. To my surprise, the 12v house system is still running, with a good voltage showing on the battery charge indicator. I can only assume that I'm running off the vehicle batteries now. My worry is that I might end up running these down.

In the cavity where the vehicle batteries reside there is VSR and a 12v batt isolator. (Pic attached) The isolator does not appear to make any difference to the vehicle or house 12v systems. Am I correct in assuming that the VSR will cut out and protect the vehicle 12v system (i.e I'll always be able to start!)?
truck batteries.jpg
Vehicle batteries
Would the isolator do something after the VSR cutoff perhaps?

If I plug in to AC, is it likely that the battery charger will charge the vehicle batteries too? How can I confirm this?

Many thanks
PCM
 #148853  by mattn
 Sat Feb 09, 2019 2:59 pm
The LED indicates the VSR is active, so yes you are connected to the main battery (Presuming that's what is on the other side). Its likely your solar panels are keeping batteries above the VSR cut off voltage and will so till the sun stops shining. Come this evening when the sun goes down, I expect the VSR will disconnect. Once disconnected, it will not reconnect (unless is a dual VSR and the solar controller produces more than about 13V without a battery - depends on the controller what will happen) until the engine battery goes above cut in voltage.

The battery isolator will probably be between the battery and the rest of the circuits, so the VSR-Solar link is not broken when you switch it off.

Without circuit diagrams all of this is obviously supposition....
 #148856  by Neddy
 Sat Feb 09, 2019 3:16 pm
"Removed the house batteries but the 12v house system is still running.
I can only assume that I'm running off the vehicle batteries now."

That's right, you are. You have got a Dual sensing VSR and it is switched ON (You can tell because the little red "ON" LED is lit). So, your Starter battery is linked to your house 12v electrics and would also be connected to your 12v House battery if it was there.

"My worry is that I might end up running my Starter battery down."
You are using it, but it will only stay connected until its voltage falls to below 12.8v, at which point it will disconnect, still retaining plenty of charge for starting purposes.

"Would the isolator do something after the VSR cutoff perhaps?"
This switch has been wired such that it disconnects your House electrics from the House battery. With the House battery removed it will have no effect either way.

"If I plug in to AC, is it likely that the battery charger will charge the vehicle batteries too? " It will initially charge the Starter battery only, but when it reaches about 13.4 volts (or whatever) the DVSR will turn on and the House batteries will begin charging too. If they are there!

"How can I confirm this?"
You can watch the progress of all this by tracking the voltages of your Sytarter and House batteries. When the DVSR is ON, though, they will always be exactly the same.

Neville.

PS: I have just now seen Matts similar reply but haven't got the heart to delete the end product of all my tedious, painstaking cellphone tapping.
 #148857  by pcm
 Sat Feb 09, 2019 3:29 pm
Thanks guys, I really appreciate the replies. I'll work on getting some schematics drawn up - I'm keen to trace the circuits and understand what's going on. You've given me some piece of mind too.

Cheers
PCM
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