Which conditions produce the strongest regen? - Renault Z.E. Forum
 
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post #1 of 7 (permalink) Old 02-24-2014, 04:23 PM Thread Starter
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Which conditions produce the strongest regen?

Sorry for the slightly clumsy thread title - couldn't think of a better way of putting it.

Yesterday I was in Cambridge and parked at the Grafton Centre car park. On the way out, I was looking forward to descending the spiral exit ramp through eight levels to see what I could get back into the batteries through regen. I set off down the ramp and found that by keeping my feet off both the brake and the accelerator, the car descended at a nice safe comfortable constant speed.

To my surprise, though, according to the kW gauge, this was almost neutral from a regen point of view - the indicator fluctuated between zero and 1kw on the regen side, nothing like the 20+ kW I often get slowing from A road speeds when, say, approaching a roundabout.

So what conditions provide the most powerful regen effect? Uphill? Downhill? What are the other parameters?
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post #2 of 7 (permalink) Old 02-24-2014, 06:28 PM
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RE: Which conditions produce the strongest regen?

Hi ED, well it's a good question and to my mind there has to be quite a bit of speed / inertia involved in the first place. The most noticeable regen I've ever had only gives me one visible mile extra on the famous range guide, so unless I'm way off I don't think many of us will be experiencing huge benefits. It does of course make a big difference on slower country roads over time but I think that's a different question to the one you're asking? Conditions - with speed coming down from 70 to 20 on an A road, downhill with wind following behind a nice big wagon in the dry in summer with slightly over-inflated tyres, I suspect!! Will gain you 1 extra mile indicated for about 20 seconds.... Chris
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post #3 of 7 (permalink) Old 02-24-2014, 06:44 PM
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RE: Which conditions produce the strongest regen?

AFAIK - easy question to answer, it is simply a function of speed, and max regen is got at >40mph.

As far as I could tell when first driving it, and I have had no reason to look more closely ever since, is that you get maximum, i.e. 30kW, regen at or above 40mph and it tails off linearly down to 0. So at 20mph you get 15kW regen, 10 you get 7.5kW regen, etc..

..something like that, approximate figures offered here ...

I would guess the idea is that it is unnecessary, and less good for the battery to regen over 30kW. But to regen at 30kW lower than 40mph-ish then you'd be slowing too quickly, so below that speed by keeping it proportional to speed then you get a linear, steady deceleration. If you had 30kW of regen at 5mph you'd be head-butting the steering wheel![hr]
Quote:
Originally Posted by ElectricDave
To my surprise, though, according to the kW gauge, this was almost neutral from a regen point of view - the indicator fluctuated between zero and 1kw on the regen side
You lose energy during cornering, so most of the potential regen was being scrubbed off in the cornering action. Had it been a straight slope you were following down then you'd have got more regen.

Imagine free-wheeling on a flat quiet road from 10mph, now imagine doing that around a mini roundabout. Do you think you'd keep free-wheeling around the roundabout just as far?

Also bear in mind that you were probably running the heater at the same time (if you'd just set off) and the regen power goes straight into the heater. If the heater had been consuming 5kW and you were getting 5kW regen then you'd see 0kW come up on the gauge because that gauge is showing what's going in/coming out of the battery, not what the motor is doing.

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post #4 of 7 (permalink) Old 02-25-2014, 07:29 AM
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RE: Which conditions produce the strongest regen?

Maybe my memory is failing me but I'm sure I've noticed when holding the car back by regeneration only on a steep downhill stretch I've seen the regen figure go way above 30kw. I'll try it today and check.
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post #5 of 7 (permalink) Old 02-25-2014, 09:35 AM Thread Starter
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RE: Which conditions produce the strongest regen?

Quote:
Originally Posted by william
Maybe my memory is failing me but I'm sure I've noticed when holding the car back by regeneration only on a steep downhill stretch I've seen the regen figure go way above 30kw. I'll try it today and check.
Maybe it's the difference, as Donald says, between running in a straight line and scrubbing off speed by being in a cornering state?

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post #6 of 7 (permalink) Old 02-25-2014, 01:12 PM
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RE: Which conditions produce the strongest regen?

It will nudge up to 35kW or so in a straight line downhill no heating, but not much higher. A bit like it actually pulls 75kW if you floor it, but only for a moment then it backs off. I get the impression its regen 'target' is 30kW, though it might be 35kW of course (half the nominal power?) and perhaps it doesn't usually quite make that? In any case, one way or t'other, it is a fairly constant regen power above 40mph within a small margin of variability.
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post #7 of 7 (permalink) Old 02-26-2014, 04:47 AM
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RE: Which conditions produce the strongest regen?

Quote:
Originally Posted by william
Maybe my memory is failing me but I'm sure I've noticed when holding the car back by regeneration only on a steep downhill stretch I've seen the regen figure go way above 30kw. I'll try it today and check.
Now I suspect that my memory IS failing me. I reckon the 75 figure I saw was when putting my foot down, not taking it off. Sorry.
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