Thread: Cranking battery State of Charge test feedback

Hi Dave and for a vehicle in daily use, no, it make no difference.

But with more and more people leaving their vehicles unused for weeks at a time, yes it can be.

There is a simple fix. If you have an SC80 and if you do not use your vehicle for long periods of time, there is a thin earth wire coming from the SC80, this wire is either Green with a Yellow trace, or Brown.

You can cut this wire and fit a small switch in the wire.

The switch can be turned off when you know you are not going to be using your vehicle for a while and then turn it back on when you are going to be doing some driving.

NOTE, this is only for the SC80.

The USI-160 ( post 2012 ) and the DT90 have the TIME-OUT feature incorporated into their programs and they shut down automatically if the vehicle’s motor is off for more than 3 days.

I have the SC80 yet to install it. Why can't this have the "go to sleep" function like the others?

Hi again Dave and the next generation of the SC80 will have the TIME-OUT feature but because of the huge number of orders I have been receiving for the last 7 months, all R&D is now shelved.

The next generation of SC80 isolators was to go into production some time next year but this too is now shelved.

Originally Posted by drivesafe

Hi Again Peter and I’ll take a guess here and say you have a 75Ah cranking battery and a 55Ah auxiliary battery.

If this is the case then you have other factors to be taken into consideration.

For those batteries to loose 40% of their capacity in 24 hours, they would need to have a constant load of at least 4 amps.

This is because “if” the batteries were in a good state of charge, meaning at their maximum capacity, not just fully charged, you would need to use more than 50 amperes of capacity to get them down to 12.2v ( 60% SoC ).

My USI-160 isolator draws less than 0.15A or less than 150 milliamps and at that current draw, it should take around 14 days to discharge your batteries down to 12.2v and this is normally the case, not 24 hours.

Lets see if we can sort this out for you.

What sort of driving are you doing?

Also, have you measured the voltage after 48 hours. I suspect you will still have 12.2v in the batteries.

This then would be their settled voltage and would indicate they need the charge cycling I posted about earlier.

Hi Tim, referring back to my post no.27 I can tell you the following. The red top (cranking battery) is only a 50amp hour, the yellow 55amp hour, so red is on the low side but it was recommended to fit ok. I have left the aux disconnected and the main connected. On Sunday I charged both to approx 12.8v with Ctek as stated. 3 days later red top (connected) is reading12.56v yellow top (earth lead disconnected) still 12.72v.

Now (deep breath) previously after a long run and with everything connected both batteries down to 12.2v within 24 hours.

My driving is usually a couple of long runs per week. I do not do stop start driving in vehicle.

The draw from red top is according to my measurements approx .04amp the yellow 0. As there is nothing connected that draws power when not in use.

I will connect all back up go for a long drive, check voltage after 24 and 48 hours and see what happens again.

Hopefully this makes sense to you

Thank you. Pete

Hi Pete and first off, with no load, you do not get a real idea of the actual SoC of the batteries, but that is a simple fix, just turn your headlights switch to PARK and leave them on for about ten minutes and you will get a fairly accurate of the SoC.

Next, I am not quite sure what you mean by you charged the batteries to 12.8v?

When charging batteries with a battery charger, the charge terminating voltage should be no less that 14.4v.

If your charger is not getting the batteries up to that voltage level, there is something very wrong somewhere!

Even if you leave the charger on and in fully charges the batteries and then goes into FLOAT mode, the minimum FLOAT voltage should be at least 13.5v.

I went away camping last weekend and gove my batteries a hammering. What is not known is the state of charge before I left but I know the crank dropped below 12 at the camp site as the SC80 kicked in. After the drive back the batteries were at 12.34 after sitting twelve hours. I decided to plug in the ctek 5amp charge and give them a topup.

I only managed to give them 4 hours on the charger as I had a couple of errands to run (short trips). The charger did cycle all the way to stage 7. I used AGM mode.

Measured this morning and I am 12.3. Not real good. I think I need to do the 8 hours on 8 hours off and 8 hours on trick that Tim came up with (need to find that thread though).

Originally Posted by drivesafe

Hi Pete and first off, with no load, you do not get a real idea of the actual SoC of the batteries, but that is a simple fix, just turn your headlights switch to PARK and leave them on for about ten minutes and you will get a fairly accurate of the SoC.

Next, I am not quite sure what you mean by you charged the batteries to 12.8v?

When charging batteries with a battery charger, the charge terminating voltage should be no less that 14.4v.

If your charger is not getting the batteries up to that voltage level, there is something very wrong somewhere!

Even if you leave the charger on and in fully charges the batteries and then goes into FLOAT mode, the minimum FLOAT voltage should be at least 13.5v.

Hi Tim, my fault, my lack of terminology is showing. When attached to batteries voltage reads 14.8v on Aux and 14.75v on starter. 13.8v was my reading some time after removal of Ctek charger.

After a 15 Km trip, with the car left for 12 hours, the voltage read 12.61

It's a Defender Xtreme 2004 (TD5), & the battery is the one which was in the car when it was purchased as a demonstrator with 1200Ks on it.

It is a Supercharge MF31-931. 10 years & still counting!

Cheers,

Lionel