Making the PriUPS work
Live from Tour de Sol: a UPS rig from bits and pieces. Richard Factor
was kind enough to send up one of his smaller PriUPS prototypes, in case
someone wanted to connect it to a Prius battery and make it work. But it
also happened that Jim Dunn brought along a salvaged Prius pack, which
would save the work of unearthing the battery connections in someone's
Each picture is a link to its larger version.
We moved the project into the Big White Tent and scrounged up a bunch of
other miscellaneous parts... Jim had also brought a 300VDC step-up power
supply, so to use that as a charger we'd need to drop its voltage down by
quite a bit -- however inefficiently, maybe, but we really didn't want to push
much more than 5 amps into the battery. He wanted to velcro all this into a
convenient box, with a voltmeter and a blocking diode and a series outlet [on
the DC side!] to plug a halogen worklight into as a current limiter.
Much soldering and taping and kludgery and polarity-checking happened...
and we wound up with a fairly workable system that could charge the pack
at about 4 amps. Note that where the service plug connects into had to
be bypassed [with a 5A fuse in a holder, in this case] because the actual
service plug wasn't available...
Let the major point be emphasized right here, that it is NOT hard to throw
together a rig to push some charge into a 200V battery pack -- no matter
what Toyota says about needing their whoop-de-do special charger to recover
an excessively drained NiMH hybrid battery.
We also didn't have 12V handy to fire the relays, so everything simply
connected to the hot sides. Most wires were tinned, bent, and mashed down
under the battery-lead lugs for solid contact.
We got it to about this state and then decided to call it a night.
The next day Jim was called away and left the whole mess with me to neaten
up and test some more, and lacking any sort of rolling cart I simply
loaded it all into the back of my car. The 90-odd pound battery pack went
across the seatback [like I need *more* ballast to cut my mileage]...
and the UPS itself in the way-back, with the outlets available at the rear.
The 200 volts from the pack is first downconverted through a switching supply
to 48VDC, which substitutes for the "battery" that the UPS originally had.
The result? I was able to boil water in the thousand-watt coffee urn, and
the UPS was showing about half load. You can just barely see some steam
at the top of the pot; it was slightly breezy so it didn't stay long.
The other UPS on the right is my 400-watter tied into the 12V system, and
since experimentation had drawn the pack down to around 200V I wanted to use
our little charger to bring it back up again. The work-light series load
turned out to be just a bit much for my UPS, so I dug up a 75W light bulb
to use instead. Then I could have the whole thing hooked together, with the
spare Prius pack ultimately charging from my car -- the hybrid system feeding
the 12V system to parallel into my UPS, that in turn feeding the step-up supply
to charge the Prius pack. The DC from the Prius pack feeds the 48V supply
into Richard's heavier-duty UPS, which finally produces AC. No connection
to my own HV battery other than via my 12V DC/DC. Talk about horrendous
conversion loss ... but by the time I was through fooling around with the
coffeepot and had actually taken the whole thing out on the road briefly while
fueling up, Jim and the others had came back from the offsite function and the
pack was back up to 235V or so. Jim then used it for a demo that afternoon.
-- Richard's PriUPS pages
-- my lower-power 12V based system
-- Vicor [makers of the step-up supply]