Followups set to sci.electronics.components.
In sci.electronics.components David Lesher said:
For that, we are seeking a digitally controllable switcher supply
with ~120V output, at up to 20-30A.
Isolation transformer, Variac, bridge rectifier, stepper motor?
(hides)
The real classic way is a phase angle dimmer made of a a bridge
rectifier followed by an SCR; turn the SCR on sooner in the half-cycle
for more current. Use a microcontroller to pick the turn-on point and
you have a digital input. (You could argue that this is a switching
supply, but it isn't what is normally meant by "switching".)
Obviously new this will be $$$$, but I wonder if anyone knows of
a surplus candidate.
The power supplies I have used in the past with this kind of juice have
been from Sorensen (formerly a tentacle of Raytheon, now owned by
somebody named Ametek) and Zivan (an Italian company with US sales).
The Sorensen ones are general-purpose supplies and are usually available
with both front-panel knobs and remote control. Zivan makes ones that
are specifcially designed to be battery chargers for traction
applications; the controller is already built in. I don't think the
Zivan had any kind of data bus; it did have a few discrete inputs and
outputs for things like start/stop, status, and remote sense. It came
with a temperature sensor you could put somewhere in your pack to both
tailor the charge rate and act as a safety. It also had a blinkenlight
to indicate charge states and problems.
One Sorensen supply I used had to send about 48 V at 10 A down several
hundred feet of wire to some DC-DC converter bricks that output 5 V and
12 V. Something in this setup broke the regulation in the Sorensen; it
would still put out something but it wasn't related to where the knobs
were. At least they fixed it reasonably quickly under warranty, and
the repaired unit seemed to work OK. I think it had a data bus, but in
the prototype stage, the operator just tweaked the front-panel knobs to
get "enough" input voltage at the DC-DC bricks.
The Zivan charger I used did just fine at charging a series string of
twelve 12 V lead-acid batteries (144 V), but for some reason, had a
high leakage to ground on the AC input. It would sometimes pop GFCI
outlets or breakers, even when everything was otherwise sound. Non-GFCI
outlets/breakers were fine. Other people who had used Zivan chargers
reported similar problems. I suspect it may have been designed to a
European standard that allows higher leakage current.
I have seen Sorensen power supplies show up at used and surplus
electronics dealers. A Zivan probably won't show up used in these
places, but a group of electric car home-brewers might be a good place
to look. Both are available new, which might help set an upper bound
on time or money for a home-made solution.
Some other random things that you probably have already thought of:
Put a simple (maybe electromechanical?) timer somewhere to shut off the
charger as a last ditch defense against overcharge... it depends on the
pack size, but if you haven't gotten the battery charged in (say) 8
hours, you're probably not going to. This is more important with a
home-made charger; commercial chargers often have something like this
already.
Give a little thought to interlocking the charger power (AC input must
go away before DC output can be disconnected), or select a charge plug
that can stand being disconnected under load. Also, interlock the
"ignition" of the car and the charger input... the first electric car
charger probably got dragged down the street a few days after the first
electric car was invented. The "ignition" interlock also helps prevent
overloading the charger by trying to run the drive motor while the
charger is connected.
{Question: If you have 3 EE's is that 6E, or (EE)^3?}
A really wide shoe?
Matt Roberds
