Low battery warning - an investigation - Renault Z.E. Forum
 
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post #1 of 4 (permalink) Old 05-13-2014, 01:39 PM Thread Starter
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Low battery warning - an investigation

Your intrepid investigator has been examining the low battery range ...

So I had an extra errand today using up most of the battery, and so ended up just a couple of streets away from home when the final 3 miles showing disappeared into dashes, --, with the SOC needle around 1/3rd of an octal above the lowest point of the bottom octal.

There is a village and a gentle road that I know to be a 3 mile round trip, so I thought I'd just drive up there and see what happens. I reset the gauge and carried on.

At 0.6 miles past the loss of the range indicator, the regular low battery warning came on, the one that runs every 15 seconds or so. (You can turn the longer interval alarm off in the menus, which I have done, but you can't turn this very low indicator off.)

At 2.7 miles a 'performance limited' sign came up. By then I was already virtually back home, into the back streets near the house. I couldn't tell if the performance was limited, seemed OK for a while and could give 30kW (didn't try harder).

I was back home by 3.2 ish miles and everything still seemed normal so I drove around the block a few times. Just a little later the power seemed to limit to around 17kW. I suspect it'll give you that power but will limit speed, which I couldn't tell as I was doing less than 30 by then.

The needle was properly at the bottom of the lower bar by 3.5 miles or so. I pottered around a couple more times and reached 4.9 miles. Discretion being the better part, I parked up.

I kept an eye on the mi/kWh gauge throughout and it was fairly consistently, as makes any odds, around the 4.2mi/kWh range. Roughly, then, I had at least 1.2 kWh when the range disappears and the repetitive alarm goes off. Clearly, I had not stopped or even ended up crawling along, so there may still be a little margin beyond that even.

My further study I brought out the brick-lead to see how long it said it would take to charge up. Indeed, the first thing it said was 8:30hr (per a recent thread) but the time estimate was creeping upwards. 90 seconds later it said 9hr, and 5 minutes later it peaked at 10:10hr before falling back. (I'm sure I have seen 10:30 up on it before when I first got the car, hmm, wonder if that reflects a little battery loss?)

I shall be monitoring input energy tonight with an overnight charge, and we'll see how much energy the battery takes, back to full.

I was running the AC and ran it throughout. It did not turn the AC off at any time. I would've though that would be one thing the car would shut down automatically if it is already limiting the power output, but it didn't.


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post #2 of 4 (permalink) Old 05-13-2014, 06:18 PM
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RE: Low battery warning - an investigation

Once my battery was empty and had 15KM to go, the stripes appear in the KM indicator screen, later the interval alert appear, then the low performance message, later... the car goes only 50 km (30 miles), I need 3 more km, please please, then the car goes only 35 km/hr over a bridge, panic lights on... gravity helped me to the bottom of the bridge, chargepoint in view, 300 meters, poef, the green "go"light went off, headlights went off.... car in park, restart, work ! .... slow speed to towards the charger, poef, the lights off again, restart, not too much power so the car keeps powered on... I made it !

I will never take this risk again,
the manufacturer of the battery told me that it is not good for the battery to run it flat, some people think it's good to do it, but it's NOT !

why you test it? I can tell you what happen if the battery is empty
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post #3 of 4 (permalink) Old 05-13-2014, 06:34 PM Thread Starter
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RE: Low battery warning - an investigation

I've never had the battery that low before, at a point where I was in control of a fixed mileage ahead of me. The reason is to know what the car will really do and how far you can go when it really matters to know. Better to find out how my car functions when everything is under control, not when everything is a panic.

I've been into very low battery warning a couple of times before, but it was always anticipated and controlled and have not hit right at the bottom before so it is useful to know if the gauge is being optimistic, pessimistic, or accurate, and whether the car comes up with any little 'surprises'.

Note that I did not test it until it stopped! It is clear that I would have not had more than a fraction of a kWh, so there is no need to explore beyond that as far as I am concerned.

So, basically, it is so that it gives me the information I need to stay in control of my car, rather than the car being in control - like you have described for yourself. (Relying on public charging is a bad idea. Especially for the Fluence which is slow charge only.)
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post #4 of 4 (permalink) Old 05-15-2014, 12:45 AM
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RE: Low battery warning - an investigation

I understand, it is good to know how far you can go and what the real estimated distance is when the alerts sound.
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