Battery Isolator design / operation

Submitted: Tuesday, Aug 30, 2011 at 15:59
ThreadID: 88771 Views:3501 Replies:6 FollowUps:18
This Thread has been Archived
Hi all - been a while.

My question is "should I be concerned that my house batteries are continually being used for short high current discharges when starting the car or should I find a way to positively isolate the house batteries when the engine stops" - because on short stops the battery isolator is not dropping out - please read on on for explanation??

I expect the question I am asking here applies to all battery isolators (or voltage sensing relays by another name).

I have a major brand VSR which by specification cuts in at 13.3V and drops out at 12.8V and it does function properly within these limits - this one has no Override option so has only 3 connection points - Batt1, Batt2, and Earth - but that is proably beside the point of this discussion.

What I am finding is that on short stops the voltage of the batteries remains above 12.8V and so the VSR is not disconnecting - hence when starting the car again it is drawing from both the house and car batteries together (at least for a short time).

I would not have thought this was a good thing for the house batteries which are 2 x 120AH AGM Deep Cycle. If it is not a problem I guess I should not worry about it - but the cost of the batteries makes me want to know I am treating them the way they should be treated.

I can understand that the VSR is not going to drop out until the voltage drops to the pre-set level and this is by nature of the design and I am sure many of the Auto Engineers or similar people would be well aware of this situation.

For those with more pratical experience and knowledge of such VSR's, I was contemplating doing something that would momentarily disconnect the Earth from the VSR when the engine stops so the relay should drop out and not cut in again until the car starts and voltage comes up on the alternator side. This would effect immediate isolation of the house batteries. Not sure this is a practical solution and so looking for comments.

Ken

Back Expand Un-Read 0 Moderator

Sponsored Links