[Oeva-list] Lee Harts Battery Balancer
gary.graunke at intel.com
Mon Mar 5 09:54:05 PST 2007
I'll be glad to support building a run of Lee's balancer as well. We
should make these available at very low cost for EV newbies (along with
Lee's incredibly elegant and inexpensive batt bridge) so they don't kill
their first pack (quite so often) and give up. A good BMS (or two) to
automatically care for the batteries and tell us when service is
required is the key to having an economical and dependable EV.
I've been buying relays (including solid state for a data acquire only
version) for a design for years-but no time to build it. I also use
Rudman MKII regs, powercheq (beta), and (when I really want to see
what's happening) Agilent data acquisition systems. I use both a Rudman
PFC50 and Brusa chargers (but not at the same time).
I was recently impressed that someone (whose name I can't recall) at the
EAA meeting in Florida was using this style balancer for 100AH 3.6V
Kokam LiIon cells.
This would be a great topic for a meeting. Perhaps I'll put together a
presentation just to start the discussion, and I'm sure many of our
local members can add their experiences and other alternatives that they
have tried (or are thinking about). We also have a number of different
battery chemistries that people are using.
From: oeva-list-bounces at oeva.org [mailto:oeva-list-bounces at oeva.org] On
Behalf Of John RA Benson
Sent: Sunday, March 04, 2007 9:01 PM
To: Don Blazer; Oregon EV
Cc: Lee Hart
Subject: Re: [Oeva-list] Lee Harts Battery Balancer
Well, you know I'm in!
If you look at the alternatives, there isn't much there at a reasonable
price point. Powercheqs are $58.00 from
http://www.evsource.com/tls_powercheq.php, but aren't really good for
long battery strings (12+). Rudman regs are $75. The mk2's are being
phased out at only $45. So from a purely financial standpoint,
$30/battery would be fantastic. $50/battery would still be pretty good.
They all have their advantages and disadvantages, of course. What I like
about Lee's is that it's not dumping energy away, and it's easy to
monitor the voltages. If you put good batteries in the vehicle, I hope
it pays to take care of them.
On 3/4/07 1:56 PM, "Theoldcars at aol.com" <Theoldcars at aol.com> wrote:
I want to state right off I am not an expert on electronics or
manufacturing them. My profession for over thirty years has been
collision repairs. My automotive hobby has been stock and modified 1955
Chevrolets. I have always been a car nut but only four years ago did I
take a serious look at electric vehicles.
I considered building an electric vehicle but decided not to for several
reasons. After adding up the cost I could buy a factory made vehicle for
less than I could buy the parts. I would have an electric vehicle right
away instead of who knows how long it would take to finish. Plus not
knowing anything about them I felt it would be a good way to start.
In the last four years I have learned a lot about batteries and the
factory electric vehicles. Using the factory service tools with the BMS
has shown me how difficult it is to keep from killing lead acid
batteries. Lee's balancer would solve some of the major challenges I
have seen with Lead acid and NiMH batteries. If I could buy the balancer
already done I would be using it.
Right now I am not up to speed enough on electronics. I rely on everyone
who knows more about this than I do. From the feed back it sounds like
if I backed building 100 of the balancers I might still have most of
them 5 years from now. I think a price range of 25 or 30 dollars a
battery on a 12 battery pack might be in reach if a high enough number
was built. This is just a wild guess with no research as to how many
would really take to reach that price.
The size of the run would depend on the price breaks. If it makes sense
to manufacture 10 or 1000 would come down to two factors. How much is it
going to save and are there enough EV drivers who see the value of it.
Can the price be brought down to what most people consider affordable? I
wonder how many EV drivers understand the value of the balancer? Without
being able to see all your batteries voltage under power demands how
would an EV driver ever know? There are a couple of EV drivers out there
who have made battery monitors but not very many.
The power supplied by Lee's balancer would make a real difference.
Trying to get by with 1.5 amps would too much of a compromise. I have
observed the out of balance in a pack is greatest in higher states of
discharge under load. As the load on the batteries increases the greater
the balance difference between batteries. As the pack ages this
condition occurs more and sooner. The 1.5 Amps is not going to be enough
on older batteries.
If you or anyone else would like to work with me on moving forward with
Lee's balancer let me know.
In a message dated 3/4/2007 7:04:16 AM Pacific Standard Time,
oeva-list-request at oeva.org writes:
Date: Sun, 4 Mar 2007 07:00:41 -0800 (PST)
From: Tim Kutscha <tim_kutscha at yahoo.com>
Subject: Re: [Oeva-list] Battery Balancer
To: oeva-list at oeva.org
Cc: sorefeets at yahoo.com
Message-ID: <955498.63905.qm at web36913.mail.mud.yahoo.com>
Content-Type: text/plain; charset="iso-8859-1"
Thanks for the excellent feedback you forwarded from Lee Hart
regarding the flying capacitor balancer. Having years of experience
can provide valuable information that a theoretical or prototyped
approach would not. I think all of Lee's points are correct. The
charge transfer as the batteries get closer together in voltage becomes
very slow. There are definite losses in the FETs, caps and batteries.
What I liked about the design was its simplicity (no STAMP controller
or DC-DC converter).
My main goal is to make something effective that costs around $10 per
battery. The modification that Paul Compton did sounds very
interesting to me. If we could upgrade the single DC-DC converter to
20-Watts, then we might transfer 1.5 amps instead of 0.3 amps.
I'd be happy to help you do research on this. Do we have access to
the plot files for the boards? How do you plan on creating the
PC-boards? Are you planning any modifications from the original
design? When you say "large run," how many are you thinking of?
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