Mini BMS Calibration

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Mini BMS Calibration

Mike Beem
I had the opportunity today to take the Escort EV (
http://www.evalbum.com/4181) for the longest sustained trip I have made in
the 14 months since I changed to Lithium. I have not re-balanced since I
put this pack on the road in December, 2012; recent checks at full charge
showed all cells within 0.02v, and at 70% discharge within 0.04v of each
other, so I consider the pack to being staying balanced. If I am missing
something here, please speak up.
After charging Thursday night, I ran the charger again Friday until the
mini BMS shut it down, with me watching. Pack voltage ran up to 146v, all
red led's were well lit, so I know that the pack was as fully charged as I
was going to get it. I didn't need to go anywhere yesterday, so it sat
without being turned on at all. My drive today was country roads, up and
down hills, frequent stops and subsequent acceleration up to 50-55mph. When
I got home and looked at my usage according to the Mini EV Display, I had
used either 306 Watt hours per mile, or 2.273 Amp hours per mile, which is
lower than my normal driving into town/in-town driving going to work, etc,
which seems to average (Winter temps) 2.4-2.77 Ah/mile.

Are these numbers reasonable? This EV is *totally* different from my
previous +/- 200 volt AGM powered with reptilian controllers (T-Rex,
Godzilla) EV's, one of which had the license*QUICKEV*, so I still am
learning a new driving style. I was getting up to 55 from traffic lights as
slowly as I felt I could get away with depending on the cars behind me,
keeping the amps below 200 whenever possible, and staying to the right when
there was a passing lane. The real number I came up with today for Winter
driving without using the heater based on what I experienced is that I have
a real 40 mile range, which is what I estimated and aimed for when I
changed to lithium at the end of 2011. The pack is 40 CALB 100 Ah cells.
I think I may need to re-calibrate EV Display; I have it set for 20% for
minimum SOC, full pack @ 100 Ah, 13500 Wh.
Thanks for helping me drive electric!
Michael B
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Re: Mini BMS Calibration

Cruisin
Re-calibrate after a known full charge and change to a more realistic reserve of 10%. Drive the car normally and enjoy. If not enough range, increase battery AH as 100ah is too small anyway.
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Re: Mini BMS Calibration

Martin WINLOW
In reply to this post by Mike Beem
Hi Michael,

You might find it helpful to put a Watthour meter between your mains socket and charger as these are very cheap and reasonably accurate.  Whilst it will not take into account the efficiency losses in the charger and battery pack (no more than 10% and possibly less than 5%), it will at least give you some idea of how accurate your MiniEV Display is.  Besides, there is no getting around these losses so really you (and everyone else) should be quoting your Wh/mile figure including them anyway... IMO!

Something else worth mentioning, as with Dan P's Jeep, I feel you may be exercising your 100Ah LiOn cells a bit too hard for good longevity.  I understand entirely that with the price of Lithium still high you are a bit stuck in your cell choice but 160Ah would have been a more suitable choice, plus, of course, you'd get much better range. I would try to avoid discharging them below 60 or 70% to try and make up for stressing them at relatively high 'C' (discharge rate relative to their capacity) continuous discharge.

It will be interesting to see how they do in time.

Regards, Martin Winlow
Herts, UK
http://www.evalbum.com/2092
www.winlow.co.uk


On 9 Feb 2013, at 23:23, Mike Beem wrote:

> I had the opportunity today to take the Escort EV (
> http://www.evalbum.com/4181) for the longest sustained trip I have made in
> the 14 months since I changed to Lithium. I have not re-balanced since I
> put this pack on the road in December, 2012; recent checks at full charge
> showed all cells within 0.02v, and at 70% discharge within 0.04v of each
> other, so I consider the pack to being staying balanced. If I am missing
> something here, please speak up.
> After charging Thursday night, I ran the charger again Friday until the
> mini BMS shut it down, with me watching. Pack voltage ran up to 146v, all
> red led's were well lit, so I know that the pack was as fully charged as I
> was going to get it. I didn't need to go anywhere yesterday, so it sat
> without being turned on at all. My drive today was country roads, up and
> down hills, frequent stops and subsequent acceleration up to 50-55mph. When
> I got home and looked at my usage according to the Mini EV Display, I had
> used either 306 Watt hours per mile, or 2.273 Amp hours per mile, which is
> lower than my normal driving into town/in-town driving going to work, etc,
> which seems to average (Winter temps) 2.4-2.77 Ah/mile.
>
> Are these numbers reasonable? This EV is *totally* different from my
> previous +/- 200 volt AGM powered with reptilian controllers (T-Rex,
> Godzilla) EV's, one of which had the license*QUICKEV*, so I still am
> learning a new driving style. I was getting up to 55 from traffic lights as
> slowly as I felt I could get away with depending on the cars behind me,
> keeping the amps below 200 whenever possible, and staying to the right when
> there was a passing lane. The real number I came up with today for Winter
> driving without using the heater based on what I experienced is that I have
> a real 40 mile range, which is what I estimated and aimed for when I
> changed to lithium at the end of 2011. The pack is 40 CALB 100 Ah cells.
> I think I may need to re-calibrate EV Display; I have it set for 20% for
> minimum SOC, full pack @ 100 Ah, 13500 Wh.
> Thanks for helping me drive electric!
> Michael B




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Re: Mini BMS Calibration

tomw
In reply to this post by Mike Beem
I think you mean the EV Display rather than minibms no? You would be better off emailing Dimitri at cleanpowerauto, since he knows more about his display than anyone here and usually answers questions quickly. If it was a significantly warmer day than you have typically had since 12/12 that might explain lower Wh and Ah usage.  
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Re: Mini BMS Calibration

Tom Keenan
In reply to this post by Mike Beem
Hi Mike -

I also have an Escort EV, converted by US Solar/US Electricar back in 1992.  It is powered by 18 US-125 lead acid batteries, and is quite heavy - 3,400 pounds as weighed on a certified scale (vehicle empty/ready to drive).  http://www.evalbum.com/4331

I typically use about 450 Wh/mile for my normal 10 to 15 mile days, measured while charging.  

Longer runs (deeper pack discharge) tend to use the charger more efficiently since more of the charge time is in the Bulk phase as opposed to the Finishing phase of charging.  I have seen as low as about 400 Wh/mile while charging after 30 to 40 mile runs.

With my previous EV, I could measure energy used while driving, and the difference was about 200 Wh/mile reported while driving, and about 250 Wh/mile as measured at the plug after charging.  Of course, much of the difference can be attributed to charger losses.

Since your EV is likely much lighter than mine, I would say that about 350 Wh/mile is what you can expect for shorter (10-15 mile) charges, and perhaps 300 Wh/mile for deeper discharges, so your 305 Wh/mile number doesn't seem to be implausible, especially if you are measuring at the battery pack, and not from the wall.

Tom Keenan
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