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      06-19-2018, 01:06 PM   #1
crankieshaft
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DC gives more range than AC?

OK, so I'm definitely no sparky expert, so if this is a really stupid question then please forgive me.

I use my i3 REX here in Scotland for a daily 80 mile commute. Typical use around 60-70% of battery (fair bit of motorway involved). When I charge on my home unit (7.2 k/WH) I usually have an eco pro range of 117 miles showing when it's done charging.

There's now a public charging station available to me en route home (tiny detour, actually shortens the daily mileage slightly) and it struck me that I should really give the shiny new DC50 a go. It is free in Scotland after all!

I only intended to top it up to 80% but I kinda fell asleep (a post work nap really is a Very Good Thing) and was woken with the phone ringing; wife telling me dinner was ready.

I jumped out the car and stopped the session, noting when I got back in that I had 99.5% battery and eco pro range of 162 miles.

Repeated the exercise tonight and it was the same, give or take a mile or two.

Now what I find strange is that I'm still averaging 4.2 kWh/M and if anything the outside temperature is cooler than the last week or so.

What I also noted today was that the range stayed high this morning (didn't bother to pre-warm) and didn't drop off enormously during the commute.

So, I guess what I'm asking is: does a DC rapid charger give a better...ummm...quality charge? That reads as daft as I think it sounds!

Any explanation for why the range seems to be so much more from a DC than my AC home unit would be welcomed, especially given that all other parameters seems to be equal.
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      06-27-2018, 02:08 PM   #2
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Just read today that BMW only allows the 33kw battery back to charge to 90%, so perhaps for some reason these chargers your using is somehow charging it to 100%...
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      06-27-2018, 03:15 PM   #3
crankieshaft
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That's interesting. It always shows 100% when fully charged (either from DC public or my home 7.2).

I seem to remember reading that the actual usable capacity of the 33kw battery is actually something like 28ish...something about protecting the cells at other end (someone who knows better will no doubt confirm/correct me here. I guess that accounts for the 90% you mentioned. Does that mean that if I charge on DC until it can take no more, I could be inadvertently damaging the battery?
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      07-01-2018, 10:23 AM   #4
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Quote:
Originally Posted by crankieshaft View Post
When I charge on my home unit (7.2 k/WH) I usually have an eco pro range of 117 miles showing when it's done charging.
Please disregard on projected XXX miles value, and focus on battery % charge levels. The former are an approximation based on your recent driving pattern (identical to "range" function in ICE cars). The latter is the truth.

I know it's confusing, since BMW prominently displays the former, and downplays the latter.


Quote:
Originally Posted by crankieshaft View Post
[...]give the shiny new DC50 a go. [...]I had 99.5% battery and eco pro range of 162 miles.

Now what I find strange is that I'm still averaging 4.2 kWh/M and if anything the outside temperature is cooler than the last week or so.

[...]So, I guess what I'm asking is: does a DC rapid charger give a better...ummm...quality charge?
No it does NOT.
Just look at your battery % charged value, and you will see.

Quote:
Originally Posted by crankieshaft View Post
Any explanation for why the range seems to be so much more from a DC than my AC home unit would be welcomed, especially given that all other parameters seems to be equal.
Because "range" is an estimation, that fluctuates a LOT.
If you coasted downhill before starting charging, upon charge completion it will show much greater range, than if you hard braked before plugging in.

If you pre-conditioned the batteries during charge (usually the case during L3 DC charging) vs. not - "range" estimation will jump up.

Lastly, "range" is bull-shit, since it will fluctuate all-over the place during your trips depending on your speed and multiple other factors (that you already figured out). So you can't really rely on "range".

It's better than nothing, and perfectly adequate for people who want to keep it simple.

But if you want to know the truth, look at battery % complete value, realize that your usable portion of 33.2KWh battery is 27.2KWh (to avoid full discharge and damage of batteries), then multiple the remaining capacity by your real 4.2 kWh/Mile consumption average, and you will know how far you can travel.

More data here:
https://ev-database.uk/car/1104/BMW-i3

HTH,
a
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      07-01-2018, 10:31 AM   #5
crankieshaft
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Thanks afadeev - much appreciate the responses. I guess I just found it weird how the numbers suddenly took a significant jump after hooking up the DC!

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