[ausev] discrete charging

[Gary Ellis]

>From a circuit point of view, there is no reason why you cannot recharge
each battery in parallel like this, although all of the batteries are
connected in series.  Each charger, of course, must be isolated and cannot
share a common ground.  This was an accepted method decades ago, before the
higher voltage EV-specific chargers were developed.  The reasoning to not
continue with parallel charging was that it was cheaper and more reliable to
have one isolation transformer and control circuit than to have N repeated.
Not to mention the added wiring, space and weight.

And one critical point that is missing here is the time required to
recharge.  It is hard to find cheap 12V chargers that deliver much more than
5 to 10 amps, so your recharge time is going to be 2X to 3X longer than a
typical higher current EV pack charger.

But you're right that the EV-specific pack chargers are getting pricer with
this latest growth in the EV market.  To some degree this may just be a
premium that they are getting with higher demand, especially when you
price-out the components that comprise these chargers.  Some less expensive
units (about $600) can be found at Quickcharge, and closer to Texas:
http://www.quickcharge.com/Select%20a%20Charge%20portable.htm

And you're right about getting efficient battery equalization out of it.
However, the equalization only takes place while charging and there is no
dynamic equalization while driving.  Some good charge shuttling switched
capacitor circuits are available to do this, while charging, driving, or
just parked:
http://www.smartsparkenergy.com/Publications_+26_Whitepapers.aspx

So the best and most versatile charging & battery management system may well
be:
- an EV pack charger, with 120V/240V options
- a charge shuttling circuit for battery equalization
- PakTrakr to alert you to any trouble batteries

I've run my car for a few years without any battery equalization (beyond
over-charging once in a while) and I'm seeing bad mismatch now and a few of
my batteries dying a slow and early death.  I'm now installing the charge
shuttling circuits to see what improvement they really make and I'll report
more later.

Gary
ReinCarNation
RCN Motors, LLC
http://www.rcnmotors.com


On Mon, Mar 2, 2009 at 6:49 AM, Joby Wieser <sleeper02_14_06 at yahoo.com>wrote:

> Tom,
>
> I am doing this, kind of.  When I got my little E-truck it ran on 48 volts,
> i replaced the home made charger with a 16 amp 48 volt charger from
> Japler-Schauer.  I quickly found out 48 volts was not enough to keep up with
> normal city traffic and it felt like i was mentally pushing the truck
> around, always concentration on getting the maximum acceleration possible.
>  I added 4 more T-105 6 volt batteries in the trunk.  At 72 volts the little
> guy became zippy and fun to drive.  Not wanting to waste my investment in
> the 48 volt charger I bought two 12 volt smart chargers ($35.00 each) for
> the new battery's each one charges two of them.  Later I added one more
> T-105 with its own 6 volt charger because I had room for it and I knew my
> Altrax 72 volt controller is ok up to 90 volts. I do notice the difference
> with the extra 6 volts.
>
> The only thing you have to make sure of is that there is no input to output
> continuity on any of the chargers. Some bond the AC neutral or ground wire
> to the negative output contact believing this makes it safer.  Most people
> recommend keeping the traction voltage isolated from the car frame since the
> 12 volt system uses it as the negative connection.
>
> If the old Jack and heintz motor ever burns up I’m going to switch to 12 ,
> 12 volt batteries and just buy 12 individual smart chargers for them.  That
> would cost less than $500 and as you noted inherently have individual
> battery management.
>
> Maybe one of the professional retrofitters has a good reason not to but it
> seems to be working for me.
>
> Joby in Fredericksburg
>
>
>
>
>
>
> > Hi,
> > I was wondering if anyone has built or thought of
> > displacing the cost of a large high voltage pack charger
> > with multiple smaller 12V battery chargers that could run in
> > parallel on a series connected pack, each with
> > microprocessor controlled independent three stage charge
> > regime (either IUU, IUI).  On the surface it seems doable: A
> > 30 A vector charger can be had for less than 80 bucks.  12
> > of those would be $960 - far less than a Manzanita, and with
> > implicit charge equalization.
> > What am I missing?
> > Regards,
> > Tom
> >
>
>
>
>
>
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