voltage cut out/in for dual batts

Posted: Wed Oct 08, 2008 4:32 pm

hi all,

have had a look in the search function and without going thru 43 pages of tripe, can anyone tell me what voltages the dual battery isolator should cut in and out.

My dual battery isolator has 14.2 volts on the side of the main battery and only 11.8 volts on the side that hooks up to the second battery.

I would have thought that at 14.2 volts, the isolator should have 'closed' and be charging the second battery by now.

this is the isolator

any advice

Joined: 11 Dec 2004 Location: Gold Coast

Hi mate, with those voltages, your isolator is not working.

Cut-in voltages can vary from one type of isolator to another but any isolator should cut-in by the time the alternator voltage reaches 13.5.

Cheers

Posted: Wed Oct 08, 2008 5:18 pm

yeah I thought the isolater was buggered, thanks

I thought that the isolator is open circuited once the main battery drops to a certain voltage like say 12 -13 volts (to stop the main battery droppig voltage too low) and once the engine/alternator starts back up and the main battery reaches say 14 volts, it closes again so the alternator charges the second battery...is that the basic principle?

Joined: 07 Aug 2003 Location: Happyrock

That doesnt actually look like it has a voltage control module attached, looks like its only the solenoid part which consists only of a magnetic coil which pulls a busbar onto the terminals. These are usually wired to turn on with a manual switch, or sometimes people hook them up to the oil pressure sensor or any number of other interesting places through some seriously dubious wiring. Id be looking for the manual switch though. Check the solenoid for operation by working out which of the small terminals is hooked up to ground or neg battery terminal and make sure that connection is good. Then supply power to the other small terminal, you should here a loud click. If you dont, then you can chuck it. If all goes well there you can leave it hotwired and recheck the voltages on each of the big terminals.

If it is voltage controlled from somewhere, doing this test shouldnt damage the controller at all.

Sam

Joined: 04 Oct 2008 Location: Canberra

agree with the general here
its definately a manual isolator controlled by some switching device like he said, possibly ignition or some sort of sender that engages it when the vehicle is running.
if you want a voltage sensitive isolator, the matson and redarc brands are common tho the redarc ones cut out at a lower voltage. i perfer the matson type as they isolate from around 12.8 volts from memory and iv not had many issues with them.

Posted: Wed Oct 08, 2008 6:58 pm

thanks sam.

I had a bit more of a poke around and traced out the smaller wires on the solenoid.

There is an over-ride switch on the dash that is wired up to the smaller connections on the solenoid. I dont think it was done right because there was another seperate +ve feed wire from the ignition to the small terminal on the solenoid, so when over the engine was running, the solenoid override was automatically powered up.

I disconnected that wire all together and fed the override switch from the main battery side, thru the switch and back to the small +ve terminal on the solenoid. Now the solenoid opens and closes whe I activate the switch.

BUT, the solenoid is intermittent and doesnt always close when you push the momentary over ride switch on the dash, so I a thinking that it is buggered by being powered all the time through the constant feed.

For the sake of about $85, I can buy another solenoid, maybe a redarc one or something and see how it goes.

what do you reckon?

Posted: Wed Oct 08, 2008 7:02 pm

sorry Presto, I was typing my response while yours was being posted.

yeah, you are right, it had a constant feed from the ignition but I think I will just replace it as its unreliable. Its a cheap part and for about $80 it isnt worth messing around with.

my drinks and food went hot last weekend and I was pissed off because the fridge wouldnt work with a flat aux battery. have another trip this weekend so I want it right and not be buggerising around with it.

thanks guys, you input has been invaluable.

cheers

Joined: 04 Oct 2008 Location: Canberra

i wouldnt disconnect it from ignition if you plan on using the same style isolator again, because if you forget to flick the override switch then your second battery wont get charged by the alternator, and if you leave the switch on then you may drain your starting battery. id suggest leaving it how it is and use the override for jumpstarting and leave the ignition feed so that it always charges when the vehicle is running. obviously dont leave it sitting around with the ignition on or you'll drain both Razz

Joined: 25 Jan 2006 Location: Stuck in Adelaide

What ive found with these type of solenoids is this.

The bridging piece that is activated by the solenoid, and closes the contacts side to side into the circuit, gets carboned up, and dirty.

A bush fix is this.

prise off the crimped top gently with some pliers so the top comes off.

remove the spring, and conducting bridging piece, clean with file or paper.
Do same to the contacts each side. *remove batt power first*.

Put back together.

rekon your voltage drop will now dissapear.

Trains

Posted: Thu Oct 09, 2008 4:15 pm

thanks guys.

I bought a redarc isolator this morning and will fit it tonight, so hopefully problem fixed.

cheers

Joined: 07 Aug 2003 Location: Happyrock

good choice, the redarc products are sweet sweet units. You can still keep the override switch on the dash, just wire it into the trailing wire from the redarc control box, good for running power back into the starter batt from the aux for winching and or if you somehow run down the main a bit. Does not substitute for jumper leads however if you completely flatten a battery, they do have their limits.

Cheers
Sam

Posted: Fri Oct 10, 2008 7:32 pm

redarc fitted and hey presto, aux battery now gets full charging voltage.....