[Oeva-list] Lee Harts Battery Balancer

Theoldcars at aol.com Theoldcars at aol.com
Sun Mar 4 13:56:50 PST 2007

Hello Tim
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 
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. 
Thank you
In a message dated 3/4/2007 7:04:16 AM Pacific Standard Time,  
oeva-list-request at oeva.org writes:

Message:  3
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"

Hi Don,

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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