I'm wondering how much capacity the capacitors are adding to the system,
as the voltage of the capacitors can never go below the sag voltage of
the LiIon cells under load, and can never go above the LiIon cells
voltage during regen.
I'd love to see a comparison graph of the voltage of the system battery
bank during a hard acceleration and a hard regen event both with and
without the capacitors installed to see the voltage regulation effect.
Jay
On 2/27/19 10:40 AM, Lawrence Rhodes via EV wrote:
Thank you Steve,
This is what I am talking about. A simple system. Is it possible you can
provide a diagram of your setup? I was going to put two 16v modules in series
to feed and take from my 24volt system which would be connected in parallel.
I think the Maxwell modules might be better as they have built in hardware to
support some functions.I would use a sacrificial tether to hook them up.
Thanks for the warning. Lawrence Rhodes
On Wednesday, February 27, 2019, 2:18:58 AM PST, Steve Heath
<[email protected]> wrote:
I have 22x2600f super caps in series in my ev. They are simply
paralleled with the battery pack and perform two functions: the first is
that they take all the heavy grunt in terms of initail power start up
much means that the batteries don't see the big spikes and are treated a
lot better therefore prolonging their life. The second point is that the
caps can take far higher charge currents compared to the battery so when
regen is active, higher regen currents can be extracted. The charge goes
into the caps first which then feed it out to the batteries.
Anything else and the capacitors will need a dc-dc converter(s) that is
bidirectional to allow the rising and falling voltage to be allowed for.
These are not cheap. This is why I opted for the simple parallel them
up. Take care with them - they can source and sink thousands of A albeit
for a second but it is enough to weld wire/contacts. When connecting
them to batteries, the caps need to be charged up with a constant
current supply until the voltages match. Otherwise it is arc welding time!
On 26/02/2019 22:56, EVDL Administrator via EV wrote:
On 26 Feb 2019 at 21:48, Lawrence Rhodes via EV wrote:
I think the 300 dollars of caps would protect the pack and increase
performance.
Probably not all by themselves. The problem with capacitors is that, unlike
batteries, their voltage falls rapidly as they discharge.
What you're trying to do is exactly what Solectria did experimentally in
2000, but what they had that you haven't mentioned is the wide-range input
DC:DC boost converter that kept the caps' voltage up where it needed to be
as the caps discharged.
http://www.evdl.org/docs/supercap_leveler.pdf
The EEs here can correct me if I'm wrong, but I'm afraid that a DC:DC with
that wide an input voltage range is going to cost you a bundle. And you
will probably find, as Solectria did, that its efficiency isn't all that
great.
But you might scout around where the small Chinese industrial and hobbyist
electronics manufacturers hang out (Ebay, Aliexpress, maybe Banggood) and
see if you can find something usable, reliable and/or affordable (pick two).
I've seen a few constant voltage regulator boost and buck/boost modules
offered. Maybe you can find one that would work for you, at least until its
magic white smoke escapes. :-)
David Roden - Akron, Ohio, USA
EVDL Administrator
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