Peter Gabrielsson via EV wrote:
One relatively cheap way of doing high power cycle testing is to cycle
power between a large battery bank and the test battery using a
bidirectional DCDC converter.
The DCDC is simple since it's just a switching pole with an inductor and
some controls. A DC motor controller with regen capability can be used as
the DCDC converter, the controls should have a constant torque (current)
mode for it to be useful.
I've tried this. A motor controller has a significant amount of input
ripple current, and a *huge* amount of output ripple current. You have
to add inductors on the input and output to approximate DC. Since motor
controllers handle high currents and switch at relatively low
frequencies, these inductors are *big*.
What I used instead were Vicor modules. They switch at high frequencies,
so the input and output filters are far smaller. Their internal filters
are already adequate for battery testing. The output voltage and current
can be adjusted with their TRIM pin. The output voltage can be higher or
lower than the input voltage; important if you're "ping-ponging" power
between two same-voltage batteries. For example, a VI-202 has a nominal
12vdc input (10-20v), nominal 15v output (adjustable 7.5-16.5v), and 6.7
amp max current. When I got mine, the VI-202 was $158 direct from Vicor.
Vicors are built to operate in parallel, so you can use as many as
needed for high power. PS: I just checked eBay and see that someone has
VI-202 modules for $99 each or 15 for $479 if anyone is interested. I
have no connection with the seller.
The DC/DC doesn't have to be bidirectional; it's much easier to simply
include a reversing relay that swaps input and output.
--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
-- Antoine de Saint Exupery
--
Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
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