12V System On Auris Hybrid

[Lesolee]

I have only had my Auris Hybrid for a month and I have been trying to find out all the relevant technical information during that time. In the process I have come across some “techno-drivel” which I would like to correct.

Here is an example from this site, although it is just an example; I don’t want to start a fight, so I am not stating who wrote it. It is, however, worth correcting these errors. Here is the quote :

"… unless you run the car EVERY DAY in daylight, in good weather for at least 20 miles, the design of the inverter based charging circuit and the battery capacity is pitifully inadequate to keep a reasonable level of charge in the battery, as a result, the car becomes completely unusable"

The poster had a problem with the 12V Battery going flat because there was an undetected software/firmware fault --- which eventually got fixed in 2014. However, there are still several important errors to correct.

Let’s take a trip back in time to my first car, a Reliant Regal three wheeler. It had a dynamo charging system so that when you came up to traffic lights, with your headlights on, the charge gauge would slam over to -20A. That car was scrapped one year after I bought it as an unrepairable MOT failure due to chassis rot. The “spec” for my next car was “must have 4 wheels; must have an alternator”. The point is that an alternator provides a constant voltage output around 14.2V, even when the engine is idling, and even when the headlights and heated rear window are on. When I bought my Corolla 14 years ago that was a primary test. Put a voltmeter across the Battery terminals when the engine was idling and turn on everything electrical. If the voltage drops below 13.8V the alternator is no good.

Naturally I have done the same thing with my Hybrid, and sure enough with the Hybrid system ON the inverter puts out enough power to keep the Battery up at 14.7V. The charging circuit is totally up to the job. Don’t take my word for it, try it! A handheld DVM costs less than £10, or you can just switch ON in Service Mode and read the battery voltage off the screen.

So it doesn’t matter if you drive in daylight or at night, the 12V battery will get charged at the same rate. Now, what about this arbitrary 20 miles? Look, if the car is stationary with the Hybrid system ON then the battery will be charging. DISTANCE has nothing to do with charging the 12V battery. It is only a question of TIME.

My regular commute is 3.5 miles each way to work, with another 6 miles each way at lunch time. That is not a lot on ON time, so I checked my battery today, after 2 days standing, and it was 12.2V. That is not especially healthy. So I put a clamp-on ammeter around the negative battery lead.

But therein lies the problem. How do you measure the “off state” current? The boot is open so the light comes on, and takes 8W according to the handbook; that’s about 0.7A on its own. Having just unlocked the car, the battery drain was 2.9A. That’s quite a lot for a weedy little 35Ah battery. It probably drops after a while, but even so, not nice.

So I turned it ON into Accessory Mode. A whopping 4.7A! This, from a battery which states that you mustn’t charge it at more than 5A. I wasn’t happy with taking that much current from a half-flat battery so I turned on the Hybrid system. Initially the charge current went up to 7.3A. Happiness. For a partially charged battery that seemed pretty reasonable. But that current very rapidly dropped to 2.5A and then 1.3A. So, here’s the real problem. If the battery will only take a 1A charge, even at 14.7V, it is going to take 20 hours of running to get it from half charged to fully charged. That’s never going to happen. The fact that the battery won’t take a reasonable charge current, even when half-discharged, suggests to me that it is on its way out. Of course it could have been damaged by being left flat for several weeks, but I have no way of finding out. After all, the last owner was Toyota UK, so they are unlikely to admit anything!

[kithmo]

Sorry, what was the question ?

[RunningInPleasePass]

'How do you measure the “off state” current?'

If you put a screwdriver, or similar, through the boot lock to imitate the boot being closed the light will go out.

Then key has to be out of range, so all the interior lights are off.

Then you have to wait and the background current draw drops to mA.

[RunningInPleasePass]

'So I turned it ON into Accessory Mode. A whopping 4.7A!'

As you say, you cannot leave the car in Accessory Mode for long.

[RunningInPleasePass]

'Initially the charge current went up to 7.3A. Happiness. For a partially charged Battery that seemed pretty reasonable. But that current very rapidly dropped to 2.5A and then 1.3A. So, here’s the real problem. If the Battery will only take a 1A charge, even at 14.7V, it is going to take 20 hours of running to get it from half charged to fully charged.'

Your Battery cannot have been as flat as you thought if the charging current dropped as fast as this.

[RunningInPleasePass]

'Of course it could have been damaged by being left flat for several weeks, but I have no way of finding out. After all, the last owner was Toyota UK, so they are unlikely to admit anything!'

Take the car back to the Dealer and ask the question?

[Lesolee]

How do you measure the “off state” current?

If you put a screwdriver, or similar, through the boot lock to imitate the boot being closed the light will go out.

Then key has to be out of range, so all the interior lights are off.

Then you have to wait and the background current draw drops to mA.

Excellent idea.

Thanks.

There is of course a little wrinkle, there always is! We really want to measure the current when the car is locked and the intrusion detector is running. I doubt that I could see the ammeter screen from outside the car. Maybe I need to leave a camera looking at the ammeter and then lock it all up. Or maybe i just need to get a life.

[RunningInPleasePass]

The car will lock with the boot open if the screwdriver is through the lock.

[Lesolee]

'Initially the charge current went up to 7.3A. Happiness. For a partially charged battery that seemed pretty reasonable. But that current very rapidly dropped to 2.5A and then 1.3A. So, here’s the real problem. If the battery will only take a 1A charge, even at 14.7V, it is going to take 20 hours of running to get it from half charged to fully charged.'

Your battery cannot have been as flat as you thought if the charging current dropped as fast as this.

My thought was that the internal resistance of the Battery is high (because it's faulty) and that makes it refuse to take the charge. But I was assuming (falsely) that I was measuring a non-load voltage. Since the current draw was actually substantial when I measured the voltage that would make the state of charge higher, and maybe much higher. That would have been an embarrassing mistake to have made to the service department. Much appreciated

[Lesolee]

The car will lock with the boot open if the screwdriver is through the lock.

True, but what about the alarm? I did an "unintentional experiment" a couple of weeks ago where I locked the car with the passenger window open. ( I have to fold at least one mirror in to get the car in the garage.) When I went back to the car some minutes later the alarm went off, loudly, and I had to fumble around to find the key to shut it off. So disabling the boot lock will allow the alarm to be set, but then i have to stand still at an odd angle for several minutes in order to test with the alarm active and without setting it off. I'm not liking that. But I now have an additional "mission" to measure the no-load Battery voltage (without disconnecting the battery). I'm thinking ammeter and voltmeter inside the car with a torch and camera. Set follow-me-home headlights to give the Battery a good dip, since I will have to get the car out of the garage, and that will run the hybrid system, and I don't want a freshly charged Battery reading. The reading would ideally be taken 20 minutes after any charge/discharge activity to be valid.

[RunningInPleasePass]

You could measure the voltage from the jump start terminals under the bonnet?

[Lesolee]

You could measure the voltage from the jump start terminals under the bonnet?

You sir, are full of excellent ideas.

Anyway, I went out in the cold, the dark, and the rain (before reading your post) set up my ammeter, voltmeter, torch and camera, with considerable difficulty because they didn't want to stay in the field of view of the camera. Anyway after 4 minutes the voltage had risen to 12.39V which means something like 77% charge. I'm happy with that. It's a pretty crude approximation, but it does suggest a lack of problem. Sadly my emergency torch, which had been on charge today for several hours, failed after 4 minutes of recording time and the ammeter had no contrast at the viewing angle achieved so I got no current readings

The good news is the Auris is back out of the doghouse.

I will have to have another go at measuring the current during the daytime, and when it is not raining!

PS: I looked for somewhere to stick a screwdriver to shut off the door-open switch, but I couldn't find anywhere. Could you elaborate on where to poke the screwdriver please?