Unexplained Flat Battery - My Turn

[Ferret]

Read a few posts here from time to time about mysterious flat batteries in D4s. Had one myself today.

I tend to drive a lot of short trips. Always have and have not changed my driving habits over the 18 months I have owned the D4. Short trips have never caused a problem before in any car I have owned and I'm sure if it was a problem with the D4 it would have shown up before now.

Anyway jumped in the car this morning, foot on brake, press the button and I'm rewarded with a dash full of Christmas lights and a low battery warning. Battery had drained overnight. The car was parked up hard against a brick wall and I could not even release the hand break to push it away from the wall to open the bonnet.

I have one of Traxide's USI 160 dual battery systems, so a flick of the little toggle switch under the dash and I'm driving again after starting off the second battery. No need to open the bonnet - magic.

But I'd really like to understand why the battery discharged. Things don't just happen for no reason.

[drivesafe]

Hi Ferret and if you have a battery charger, I recommend you give your battery a good, LONG, charge.

What happened is actually common with Calcium/Calcium batteries.

They tend to slowly loose the ability to hold a charge.

This is not so obvious with the auxiliary battery continually putting some charge back into your cranking battery but as you have found, it eventually gets to the point where the auxiliary battery just can’t replace enough of the used capacity and the cranking battery falls below the cut-out threshold of the isolator.

This leaves your auxiliary battery with enough grunt to start your motor, but the cranking battery will be stuffed if you don’t either go for a good, LONG drive or give the batteries a good long charge.

Also, you will need a charger that has a boost or equalisation cycle, to get back the cranking battery’s capacity to hold charge.

If you don’t have a battery charger, a large solar panel can actually do a better job.

If you have an 80w solar panel, or can borrow one, connect it directly to your cranking battery every opportunity you get.

Note, you must bypass the solar regulator.

You need to connect the solar to the cranking battery because an 80w solar panel will progressively raise your cranking battery’s voltage up around 17v to 17.5v

Your cranking battery can tolerate this high voltage for a few hours but your Optima can not, BUT, you do not need to disconnect the Optima because the USI-160 not only has low voltage cut-out, it also has high voltage cut-out.

If you use the solar panel to charge the batteries, with the solar panel connected to your cranking battery, both batteries will be charged at the same time UNTIL the common voltage reaches 15.1v.

At 15.1v, the USI-160’s over voltage protection turns the isolator off and then only your cranking will continue to charge.

Let us know how you go!

[Ferret]

Drivesafe, does what you say about the solar charger apply to a battery charger as well. For instance if I'm using a battery charger with a specific calcium charging mode, say something like this

Projecta 8amp, 6 stage

Are you saying if I leave the Optima connected to the USI 160 controller then the Optima will still be charged safely and satisfactorily while using the calcium charging mode on the cranking battery?

[discojools]

Drivesafe,
Ferret mentions a toggle switch to change over to second battery for cranking. Do i have one of those on my Traxide or is this a new thing since mine was installed 18 months ago?
Also, if I connect a CTEK to my main battery do I have to disconnect the second battery or does what you say about the solar panel apply?

Jools.

[drivesafe]

Hi Jools and the over voltage protection does not apply to the standard SC80 or SC80-LR, and the USI-160 is the only isolator I make that has a cab control for jump starting.

The only the USI-160 and the NEW SC80+A have Over Voltage protection.

As to your set up, if you connect a battery charger to the cranking battery, you will still charge both batteries.

If the LED on the SC80 and SC80-LR is on constant, you can connect the battery charger to the auxiliary battery and both batteries will charge. This also applies to the USI-160 and the NEW SC80+A.

With the the SC80 and SC80-LR, if you want to try the solar fix for Calcium/ Calcium batteries, you MUST disconnect the EARTH off the AUXILIARY battery or you may damage the Optima.

You do not need to disconnect anything from the cranking battery as all the electronics will tolerate much higher voltages than the 17.5v the solar can get the cranking battery up to.

Even then, if you turn something on in the vehicle while the solar has the battery up at that voltage, the instant you turn on anything, the load caused by what ever you turned on will pull the voltage down again.