UPDATE 01 July 2012
Charlie was kind enough to send an update in the midst of a serious power
failure and heat wave. "Derecho" was a new word for me and hopefully will
remain an obscure one given the large-area consequences. At least
Charlie's ice cream is safe.
Our 2006 Prius
was totaled some years back. I tapped the
battery in our 2009 the same way but didnít
have much need for it until this weekend.
Washington DC area utilities were hammered
by high winds on Friday night and a million
and a half customers lost power. (See
Some of us donít expect it back for quite a
while. I write on Monday morning: the ice
cream is still good, and our Prius is still
idling as needed in our driveway. Itíd be
nice to have air conditioning for this heat
wave; Iím not sure that weíve got the juice
for that. Lights, fans, and suitable
refreshments will do just fine for a while.
that we needed a heftier bootstrap UPS and
use an APC Back-UPS (maybe a 900) for that
task. Cold-starting the Back-UPS takes an
extended button press but works fine. I
still donít entirely understand the startup
behavior of the bigger unit when running on
the Cherokees and bootstrapping from the
small UPS, but it seems to fire up after two
or three long presses of the ON button. I'm
still thinking about boosting the supplied
voltage with an additional 24-volt DC-DC
converter some day, but the system is
plainly doing exactly what I want it to do
as-is. (Info on boosting the
Prius battery voltage if necessary
here - Richard.)
Original entry from 2006: Although Charlie used the same major hardware components I did, his
implementation differs, and he ran into a few complications that I didn't.
He also is clearly a safety-conscious dude! Read his valuable comments on
DC fusing, which is more critical than AC. And he has his priorities
straightĖone of his main goals is to make
sure the ice cream doesn't melt.
Among the differences
- He found that the UPS would drop out on surge loads. That was
resolved by the addition of some capacitors as described below.
- I commented that I felt the 12/3 extension cord was a little light given
its length. Charlie: "I thought about going heavier than 12/3, but (1) for the draws I was expecting
the math said it ought to be ok, (2) if I was really drawing much more than 12/3
could handle I'd want my fuse to blow first, and (3) it's heavy enough to lift
as it is -- that length of 10/3 would have been much too heavy for my wife to
lift. This may indeed be a factor in the issues I experienced keeping up with
surge loads on the Cherokees."
- The relay terminals on his 2006 Prius aren't fully threaded as they are
on my 2005. See the photos below.
- I left my R3000XR with it's large and long factory power cord attached.
Charlie's (better) solution was to remove it to save weight and use a
light cord, since the only current it will need to carry is that required
for a restart. I should probably do this, too.
Charlie comments on the purpose and ultimate success of the project:
"Lastly, it might be worth saying why I chose the solution I did. My goal was to
have a reliable, quiet, long-running power source to back up my rather
unreliable neighborhood power circuit. I wanted to keep my fridge and my furnace
fan going during extended outages; interruptions that don't melt the ice cream
or make my house really cold in winter are ok. (Ok, it would be great if I could
power the central a/c too, but that just doesn't seem all that likely.) I
decided to mount the UPS in the house instead of in the car because (1) I hate
lifting heavy stuff even in good weather with the lights on, and (2) I have a
long distance from where I park to where my load center is and I preferred to
push fewer amps through that long cord. I used a mechanical transfer switch even
though I could have done without one because I didn't want to keep the UPS
powered up all the time. This way I didn't need to add a heavy circuit to power
everything via the UPS during normal operations-- everything stays on separate circuits just as it was before I had this
"I ran my fridge, furnace fan, and a few
lights on the power from our Prius for about an hour today, and I'm declaring
||If you look closely you can see that the main relay studs on my 2006
are different than yours; my options for fastening additional fittings
were a lot more limited.
|I used every bit of a 100' 12/3 lighted extension cord.
The male end is now sticking out of the R3000 XR, where it feeds the two
Cherokees modified per your specs. A bit more connects the Prius main
relay terminals to my new socket, and the rest stretches across our yard
and connects the other pieces. The neon pilot light in the female end is
convenient and quite happy with the Prius DC voltage.
I used a panel-mount Anderson PowerPak fitting as the socket in the
car and their plug-type fitting to mate with it. A KLKD 20 amp DC-rated
fuse protects the car from anything I might try to do to it. The socket
and its enclosure sit quite unobtrusively in the driver-side rear cubby.
(We do fold our seats down from time to time and preferred to keep the
socket safely out of the way even when the seats are down.)
|The transfer panel is a modified version of the cheap
panels that sell every day on eBay. The stock 4-circuit panels are wired
for 15 amp service, not quite enough. The stock 6-circuit panels use
twist-lock connectors and would not allow me to distribute load across
the R3000 XR's available load segments. I modified a 4-circuit panel by
removing the convenience outlet, adding another 15-amp inlet, and
splitting the device into a pair of electrically-independent 2-circuit
panels. Each pair of circuits now has proper 15-amp wiring and is
connected to a different load segment on the UPS. Interestingly, the
factory panel was wired incorrectly -- each of the 4 load-side circuits
has its own 15-amp breaker, but all of them were wired to draw though
the breaker for the first circuit, effectively making the other three
|Like you, I sacrificed the R3000 twist-lock connector
for ventilation. I added a wire cover for it and routed my DC input out
that way as well. I do use a pair of KLKD 15 amp fuses to protect the
Cherokees -- the little fuses they have internally would probably just
arc endlessly if they actually opened under DC load. I do have the
Cherokee's pushed up closer to their high limit -- my cheap DVM shows
The late addition of a pair of 800 μf caps connected to the external
battery port did make a real difference in the ability of the UPS to
handle peak loads (i.e., fridge compressor startup). One helped; two seem
better. I may experiment with adding more. They're out of view on top of
the main ups.
The little Belkin UPS is there for more reliable cold starting of the
I added a dummy mail slot to our side door to admit the extension cord
powering the UPS. Now all I need to do is write up instructions for my
wife and wait for the power to fail!