Outer Limits 4x4 Board

Hi All,

My batteries are going flat after about 7 days of not driving my vehicle, all the accessories are off during this time.

Now I've noticed the SC40 (battery isolator) is warm to touch, it feels a couple of degrees above ambiant. Is this the likely reason my batteries are loosing voltage or is it normal for the battery isolator to be warm when the vehicle is not in use?

Cheers, Bucko.

With the vehicle off, the SC40 should be off, and there should be no heat generated in it - so it should not be noticeably warmer than ambient.

Disconnect the coil of the SC40 for a day or two, and see if that makes a difference to your battery life.

With the vehicle off disconnect your positive battery terminal and with a multimeter on the amps range check and see what current is being drawn, there should be a relatively small draw to power things such as radio memory and clocks etc. You could also then disconnect the battery isolator and see if the curent drawn decreases.

Not sure what would be considered excessive, someone on here would have a beter idea of that

Other possibilities could be if it is flattening your battery within seven days your battery may be on its way out or alternator may not be giving full charge.

Hi Bucko, ring me when you get a chance as there are so many reasons why your batteries are going flat but as far as the SC40 being warm, this is actually quite normal.

Next, what do you call flat?

The fact that you are leaving you vehicle for 7 days without driving it points more to the batteries probably not being charged fully before you leave the vehicle for a week.

Unlike ordinary battery isolators, the SC40 does NOT disconnect the batteries from one another when you turn your motor off.

The SC40 keeps the batteries connected until the batteries are down to 12 volts ( about 50% SoC ) when the batteries are then isolated and at this level you should still be able to easily start you vehicles.

One quick check, if the the SC40 has both batteries connected, the LED on the SC40 will be on constantly.

If the SC40 has isolated the batteries from one another the LED will be flashing and if you measure the voltage at both batteries, they should be at 12v or less and each battery should have a deferent reading.

If your cranking battery is stuffed, the SC40 will still keep the batteries connected until the batteries are down to 12v even when this voltage drop is caused by one battery being stuffed and this drags the good battery down to 12v, but you should then have enough power in the other battery to again, easily start your vehicle.

So under normal use, the the likelihood of both batteries being stuffed is very remote but having low charged batteries when you leave the vehicle for 7 days is more likely the problem.

BUT

This all doesn’t rule out the possibility that the SC40 itself is stuffed but there can be other causes, unrelated to the batteries or the SC40, so give me a call and I’ll try to sort it for you.

Hey,

Thanks for the help everyone. Drivesafe got me thinking about my driving habbits which are often short trips and most likely the reason for the lack of substantive charge in the batteries.

I also discovered a few more things since I've been testing:
SC40 cuts in and out exactly as it should and the LED responds accordingly.
One of my voltmeters is out by about 2 volts!!!
Charging the auxilary battery wont charge the starting battery when the isolator is cut out. (Yes I do feel stupid thanks for asking)

Thanks again, Bucko.

Bucko, nothing to feel stupid about, what would have been stupid is if you hadn’t asked for help.

If you have a battery charger, give both batteries a charge and then see how they go.

If your not doing much driving time, you may need to get into the habit of charging your batteries on a regular basis.

If so, put the charger on the cranking battery and even if the SC40 has isolated the auxiliary battery, once the cranking battery is charged, the battery charger will have the voltage high enough to get the SC40 operating and you will then charge the auxiliary as well.

Saves having to swap the charger form one battery to the other.

Cheers

Careful, drivesafe.

If the book writer and his mates discover this thread, they'll use it as proof that an alternator cannot charge a battery.

Not funny Scott, hilarious, but not funny