AC outlet

The Prius 12 Volt system stays near 14 volts when READY. I would not be surprised if it drops below 13 Volts under heavy load.

Just so you know, 30 Amps at 13 Volts is 390 Watts. If you really plan on getting 600 Watts out of that thing you will need about 46 Amps at 13 Volts. At 600 Watts it should not take very long to blow your 30 Amp fuse. This is good because I'm not sure I would use #10 wire for more than 30 Amps anyway.

I assume the seat frame is a solid ground but I'm not sure.

I once heard that the Prius DC-DC converter is rated at 100 Amps. I think this sounds small. I wish I knew the real number. If I look at my owners manual I see 42 fuses listed. If I add all 42 fuse ratings together (not a smart thing) I get a total of 765 Amps. The real answer is probably between 100 Amps and 765 Amps (but I would guess closer to 100 Amps).

Let's stick with the 100 Amps. If you draw 30 Amps you are taking 30 percent of its rated current. At 50 Amps you are taking 50 percent of its rated current. I'm not sure how much margin the DC-DC converter has.

You may want to consider NOT using some accessories (like climate control blower fans, and hi beam lights) when you are using your 300 Watt gizmo.

If you ask Toyota I'm sure they will say only use the 120 Watts provided by the power outlet. You should be able to easily conserve the other 180 Watts by avoiding use of the hi beams and the climate control blower fans.

Good luck.

Ed

> I once heard that the Prius DC-DC converter is rated at 100 Amps.
> I think this sounds small. I wish I knew the real number.

Ed,

I've just done a bit of tracing my way around the wiring diagram.

There are three paths by which current may leave the DC/DC converter. One is fused at 100 amps, one at 10 amps, and one at 5 amps. Although this doesn't give us a definitive answer, it is at least a pointer to the maximum current that the designers expect to be drawn from the converter.

Regards,
Julian.

ps. Continuous current, that is. I'm witholding any judgement on what the transient currents might be.

Details on using a Prius as a backup generator for your house can be found in the Yahoo group "Prius_Technical_Stuff" message 2584. I won't post a link, because you would have to be signed into the group to read the message, but I have included the relevant sections of the message below.

Note: there is a current limitation, because the Prius' DC-DC convertor can pump a maximum of 60 A to the 12V battery (which is where this person wired in the inverter). If I am doing the math correctly, 60 A at 13.8 V is 828 W. Assuming the inverter is 100% efficient, 828 W gives you 6.9 A at 120 V. Inverters are not 100% efficient, so maybe you will have 5 A of power available in the extension cord running to your house. This is insufficient for major appliances (heater, AC, refrigerator), but it would run electronics and lights.

Douglas (2002 Silver, Wisconsin)

---------------------------------------------------------
...
2002/05/03 ... This weekend I'm hoping to wire in my 1kw inverter and test using the car as a backup generator/power source for the house in the event of power outages. I expect that a twist of the key will have the quiet, low emission ICE run to recharge the NiMH pack that will keep the 12v battery charged via the 70a? dc/dc. Everyone will want one of these hybrids when they realize they can have backup power without the noisy, smelly, 500 hours to rebuild typical backup generator. In fact, short sell your generator manufacturer stock now!


2002/05/04 I wired in the 1kw inverter as a test, direct wired to the 28ah 12v battery in the trunk. Ran a few quick tests first, checked the resting voltage of the battery - 12.54v. Turned the ignition key to on, all controllable loads except for the ventilation fan was off, the voltage crept downwards into the 12.3's fairly quickly. Didn't expect that, thought the DC/DC would keep it up, but apparently it wasn't on. 'Started' the car, and the DC/DC switched on, the voltage climbed right up to approximately 13.8v, then to 13.84v when I switched the fan off. Guess I'll make sure we 'Start' the car before letting it sit with a radio or lights on. I noted that the 12v system battery negative cable was bolted to the chassis, with just a positive cable running elsewhere. I'll have to measure voltage at a few
points in the car just to see where it's at.

So, time for the real test. I plugged my Fair Radio 'charger' into the inverter, switched the inverter on, and dialed up about 5 amps into the Elec-trak's 36v battery pack. The inverter registered about 15amps, and the Prius 12v battery read 13.8v at the battery posts. So I dialed the Fair Radio unit up to 7, then 10, then 12amps, so that the inverter was drawing about 40amps from the Prius. The voltage held steady at about 13.8v, with about a 0.1v drop through the 6AWG cables I used to connect the inverter to bolted on screw terminals on the Prius battery -- yes, no fuse for this test. I plan to install either a fuse or a breaker after I determine maximum continuous current I want to draw from the Prius. On the fused connector next to the battery, it showed a 50A rating for the fuse, and a separate 5A rating for some 'other' fuse. Since I don't even have the owner's manual yet, I don't know the purpose of the 5A. So I limited my inverter draw to less than 50A.

I didn't watch the clock, but after a few minutes, the Prius traction pack depleted enough that the ICE started and began charging it. The 12v system voltage didn't change at 13.8v. The inverter and Fair Radio charger was left running at the approximately 40A draw. After a few minutes, the ICE shut down, while the traction pack via the DC/DC maintained the 12v system at 13.8v. Success! After I permanently mount the inverter, I'll have at least 600W continuous mobile and backup 120Vac power, with SULEV emissions, no noise or very little noise with the ICE running, and no generator to maintain.
...

I realized later: it's not a hard limit of 5 or 6 A, but rather a continuous limit. Because the 12V battery serves as a big capacitor, you can draw more than 6 A for short periods (for example, the spike current of a compressor or fan starting up, or even a big heater element running for a few minutes every hour). As long as the Prius' DC-to-DC converter doesn't need to provide more than 60 A to recharge the 12V battery, there isn't a problem there.

Of course, the 12V battery is rather limited. IIRC, it is rated for 28 amp-hours, which (I think) means if you pull 28 A, it will be dead in 1 hour. This means it could provide 28 * 12 = 336 A of additional current for 5 minutes. That is 4032 W at 12 V, which is 34 A at 120 V (assuming 100% inverter efficiency) or more likely 27 A (at 80% efficiency).

This is a better number, because it means the Prius could provide emergency power given a complete loss of the utility grid, but you'd have to manage it carefully. You could probably leave it connected to your refrigerator, and it would safely keep your food cold indefinitely. But, if you connected it to an electric furnace, I think you would have to turn the furnace on for a few minutes (ideally while monitoring the current with a meter), and then turn it off for the rest of the hour.

Douglas (2002 Silver, Wisconsin)

Jeff Hatton opened this thread (2002!) with a title that I thought would have gotten much more attention over the years~

Regardless, I bought a sine wave output inverter to address the noise produced in the audio system by the cheaper "modified sine wave" inverters (read 'stepped square wave'!)~

I plan to mount a home-style wall outlet (they make a nice gray one to match the carpet) ankle high, below the back seat at the center of the kick board, and run the heavy 12V leads the short distance back to the 12V battery terminals~

The two questions I have are: How do I get to under the back seat? (it doesn't seem to pull up like all other back seats ever created), and should I power-up the car while the 12V battery terminals are disconnected so as not to loose the various radio station settings, etc? (I need to disconnect the terminals to properly attach the inverter leads)~

Anyone?...

Much obliged,
jeroboambramblejam

To remove the rear seat bottom pull up on the front of the seat. There are two "snap in" fasteners at the front of the seat. Then you just pivot it up and pull away from the seat back. Before installing the seat bottom fasten all the belts, so you don't loose one under the seat.

As for the inverter, I wouldn't install one with more than 300W capacity, and I wouldn't install one except on "switched power" (accy). You can find that in the console. The 12V battery in the Prius is only 38 or so A-hr. and if you drain it you won't be going anywhere! If you use accy. use the feed in the console to control a relay that connects the inverter directly to the battery.

It's safe to disconnect the 12V battery, but I wouldn't do it with the car in "ready". Leave the car off when messing with it. Disconnect the -ve lead first, and reconnect the -ve lead last. You will loose the radio presets and if you leave it disconnected long enough the car will have to relearn a bunch of stuff. It's not a big problem. It will be fine (back to normal) after a day or two, and before that will run just fine.

There is a charger for the 12V system built into the HSD electronics. It can safely supply about 40 Amps continuously. It tries to maintain 13.8V on the system bus, and I've heard (but not measured) that it actually goes a bit higher if you start to draw a lot of current.

40A to an inverter will give you about 400W (hence my recommendation of a 300 W inverter). The amount used to keep the battery charged is rather small. Perhaps 1 Amp after a few minutes of running. The car itself will probably draw 8-10 Amps without the headlamps on, and double with them on. The cars electronics is liquid cooled, so I doubt you could overheat it. Besides, the hybrid drive uses much more power than the charger. You would need rather substantial cable to handle 40A without excessive voltage loss. I'd use #6 or perhaps even #4 - finely stranded to reduce stress on the connections.