What is the largest dc ac inverter that I can safely use on my Prius?

The 12V system is limited by the DC to DC converter. If you want a large inverter, don't draw power from the 12V bus, but instead take it from the HV system.

Tom

 

The DC to DC converter can deliver about a 100 amps, so the biggest inverter you should consider is around 1000 W. You could go a tad more, but that would be pushing it.

You will need to connect directly to the 12V bus. Some sort of circuit protection should be used, whether a fuse or circuit breaker.

Tom

 

I can tell you that I connected a small (not the smallest but no where the largest dc / ac inverter) to the cigarette lighter port. I blew the fuse... twice. I would now consider connecting to the 12 volt battery terminals. However... I have had enough problems with the 12 volt battery. So I will be watching this thread closely.

 

I have run a 3kw inverter from the 12v battery the 100amps available from the dc to dc in the prius is just a charger for your 12 volt battey. Just don't let the volts get low as more will come from dc to dc inverter. The inverter I used was a 230vac supply from ebay wired directly to the battery I monitored this with a voltmeter. don't forget to use correct rated leads on the low voltage side of inverter. I upgraded mine as they would get warm under heavy load. I guess the fool-proof way to connect it would be to use an auto-disconnect like in some solar regulators. this would automatically disconnect supply should you take too much out of the battery. I didn't need to use mine for too long so have no idea how much it would deliver, in the KWH's range though

 

Simtronic makes a good point. I was assuming a steady draw at maximum power when I recommended a 1 kW inverter as the largest you should use. That limitation is based on the ability of the Prius to supply 12V power continuously.

If you are willing to draw from the battery you can use a bigger inverter, but keep in mind that the Prius battery is very small. Used in short bursts, such as starting a motor, the extra draw is fine. Steady state a 3 kW inverter will flatten your battery in minutes, not hours. The DC to DC converter will extend that time, but not prevent the inevitable.

In addition, the charging system on the Prius is primitive. Instead of using a three step smart charger, the Prius applies a steady voltage to the 12V battery. It's almost like trickle charging. This works okay for normal use, since the 12V battery isn't required to do much, but it means that it takes a long time to recharge the 12V battery if you draw it down with an inverter.

Tom

 

I'm wondering if this may help:

I wired an amateur radio 2meter FM transceiver directly to the 12v battery with 12 gauge wire and a fused connection, and using Anderson PowerPole connectors.


this has worked fine for the duty cycle of 2 minute max transmit on 5 or 10 watts output power.


One time the 12v battery did die cause an occasional driver forgot to power down the Prius when left in the garage, and I was able to jump start the 12v with an Optima blue top marine battery using the PowerPole connectors.


What would happen to the capability of emergency household power if that extra big 12v batttery were left jumped to the 12v aux battery? Or is that even advisable?

 

It would only increase the AH available for use, it is a shame the standard battery isn't bigger in the first place. After doing a little maths I realized my setup wouldn't of lasted very long but a 1kw inverter should in theory run on 100A allowing for losses meaning the battery is just a buffer. The only real danger from adding a very much larger battery is the fact that the Prius charger is just a constant voltage supply and it's current could go above it's rated limit just by connecting the extra battery if not fully charged. Possible blown fuses or even burning the dc to dc converter.

Getting back to the original question I agree with qbee42 as to the largest inverter for continuous use on a standard Prius

 

The highest wattage that you can contuously draw is 1.2 KW. (100 amps x 12 volts). Actually it is less, since the car draws some current at 12 volts, which I have not measured. I do know that it uses 2 amps at 220 volts when sitting at ready in park. So maybe 200 watts at 12 volts, or 1 KW is actually available. However, another key factor (and maybe more important) is inrush current. If you want to run a refridgerator, it may draw 20-30 amps on start up for a fraction of a second. So, you really need an invertor capable of 3 or 4 KW peak, which normally is 2x the average, so I would recomment getting a 1.5 to 2 KW invertor, and limiting your average demand to under 1 KW. Some of the invertors have power monitoring meters, or you could use a Kill-A-Watt to monitor your useage. I have a 1.2KW invertor, and it barely starts the fridge, and only when it is first turned on, since the inrush is reduced then. When it restarts after running, the invertor shuts down, and then restarts and ther fridge then starts OK.

 

I have been advised by other members of this forum that the Prius only supplies a trickle charge to the 12V battery because it's function is mainly to "boot" the electronics. If you wanted to see how much amperage it will supply under load you would need to take a page from the solar crowd. They put a calibrated shunt meter in line with the charging supply so that current moving thru can be measured against a standard.

 

A quicker way might be to look for posts from Bob Wilson here from a decade or so ago where he gathered the data you're thinking about.