West Coast Wing                           1997 Bob Wing
May 18, 1997         By Bob Wing



Last month I drove west of Santa Rosa, California on Sebastopol Road
looking for the Coherent Power shop. I had last been on this section of the
road 50 years ago to rent a house for my first job at Pacific Bell after
completing my Graduate Business School degree at Stanford. This part of the
road looks no different now except there are fewer cars, no trucks, the
railroad no longer operates as the tracks are up for a bicycle trail. The
freeway is 1/2 mile away leaving the original farm houses much as they were
when built.

Les Piper, business manager, met me and showed me around the shop. CEO
Volker Scholze then came in to discuss the technical details, I had met
Volker the previous year when he came to an EV Show in Point Reyes Station.
And I met Ellen James, CFO/chief designer. The Coherent HFXC 5000 charger
is the result of a successful five year R & D plan leading to production.

This Coherent charger is 5 kW and it's just what I have been waiting for.
It is mounted in a metal box 7" high x 12" x 17" and weighs 33 pounds,
isolated from the AC line by a high frequency transformer. It has the best
power factor correction I have seen on any charger, PF of 99.9+% and
current 3-5% THD (harmonic distortion) over the entire range of power from
500 to 5000 Watts, well below the limits proposed by IEEE 519 and the more
stringent requirements of the Electric Vehicle Association of the Americas.

It works on 95 -145 Vac at 1800 Watts and 200-275 Vac at 5000 Watts. The
output is for 120VDC nominal battery  packs to 312 VDC. There is an
optional version that operates from all of the above, plus 200-275 Vac

The charging cycle is automatically regulated for wet or sealed batteries
for current control, temperature compensation, gassing and equalization.
Output voltage thresholds, two upper and one lower, are adjustable. This
means that my Optimas can have on top setting for daily use and every two
weeks have an automatic 3 hour equalization charge, all thru my Rudman
regulators. Output current is programmable for adjustment for each of up to
nine sequential steps. Thirty HFXC are available for beta testing, of these
five have been delivered as of this writing. This certainly should be the
preferred charger by vehicle integrators and manufacturers. At $5000 per
unit it is pricey for home conversions but seeing the extreme care taken in
design and fabrication and the clean power factor it should certainly take
over a large share of the market except where the "Not Invented Here"
factor limits purchase of the best quality charger.

Leslie Piper
768 Brittain Lane
Santa Rosa, CA 94507
Ph  707-523-0335
Fax 707-546-4538

Bob Wing is West Coast Editor for EV News and an EV Consultant. He can be
reached at POB 277, Inverness, CA 94937-0277; Tel 415-669-7402, fax
415-669-7407 or bobwing@nbn.com .