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Prius inverter?

I have been researching posts on how an inverter can be added to a Prius. Apparently, if I keep it below 1000w, I can use the 12v feed to the starter battery and not get involved with the main drive battery. I have several questions:

  1. has anyone here done this and what has your experience been?
  2. What sort of shop might do this kind of work (Toyota won’t)? Is this a regular mechanic, or a car stereo installer, or body shop?
  3. The work consists of attaching the inverter across the battery posts, with fuses, and running the 110v line into the passenger compartment. What sort of ballbark range should I consider reasonable for labor?

My application is multifold. First, it is just cool. Second, we go on alot of long trips and have my wife and daughter have more computer equipment plugged in than the cigarette lighter can handle, and third, I am doing some boatbuilding in a barn with no electricity and would like to run some lights and recharge the batteries for my cordless tools.

1000w? Really? That’s VERY high for a 12 v system. If you’re overtaxing the cigarette lighter, that’s the 12v system, you’ll be overtaxing it, too. The Prius has a very limited 12v system. The uses you plan for the inverter are far beyond what the Prius can do. Get a portable generator.

You don’t need any special wiring for your purposes. Get an inverter with battery clamps. In your barn you simply raise the hood and attach your inverter. When finished you remove the clamps.

For the car’s interior, go to WalMart and buy a power outlet accessory. It plugs into the lighter socket and provides you with three outlet ports. I have one – I use it for GPS, radar detector, and lighter. Costs about $10.


The issue is that I need more than the cig lighter can provide in the car interior. I believe the cig lighter is fused at 20A, which is 240w. My daughter’s laptop is a monster and can draw almost 200w, plus my wifes draws 65, plus the GPS, phones, bluetooth, etc. I can just run an extension core from the trunk into the interior, but it isn’t very pretty.

So, I would prefer a permanent inverter mount and wiring under the carpet to the 3 prong outlets in the interior. Of course, if that is going to cost me $1000, then I will go with the bright orange extension cord :slight_smile:

Gardner, all of these devices are intended to run off their own battery power. Get them fully recharged at home and recharge only the essentials when you drive. I urge you not to become a slave to family demands for More Power.

If you feel you must… one possible solution may be to keep two or three spare 12v car batteries in the trunk. Attach them in parallel, and run your heavy-duty inverter off of them. Bring the extension cord into the cabin and you will have your requisite power source. Using this method you will not have to worry about compromising the Prius electrical system. Of course, you will have to recharge these batteries at home using a standard battery charger. How’s that?

I am unclear on the source of the concern with permanently connecting an inverter to the starter battery. The drive battery is designed to supply up to 100A of 12v power to the starter, so tapping off it does not seem that it would be an issue, provided you have it connected with an appropriate fuse and have it tied to the ignition so that the inverter does not drain the battery when the car is off.

What problem are you cautioning me to avoid?

The starter battery is the main power battery for the electric motors, the hybrid system. It is not a 12 v battery, it is a 288 V battery. There is no practical way (not to mention no prudent way) to tap into the hybrid battery. The only 12v battery is the small one in the trunk, completely unsuitable for what you plan.

1000w at 12 V is about 80 amps, far beyond what your 12V system (or most 12V systems) is designed to deliver to an inverter.

1000 watts is too much, you will be placing a high load on the DC/DC converter. Try a 400W inverter.

From the service manual; (2005)

The DC/DC converter reduces the nominal voltage of DC 201.6 V to DC 12 V in order to supply
electricity to body electrical components, as well as to recharge the auxiliary battery (DC 12
This converter maintains a constant voltage at the terminals of the auxiliary battery.

I don’t mean to argue; I just want to make sure that I understand what is going on. My understanding of the prius electrical system agrees with what you say; there is a main 288v drive battery and it has its own DC step down which is responsible for maintaining the small 12v battery in the trunk. This step down can provide 100A of 12v (actually I think it is 14v).

If I put the inverter across those 12v terminals, that wires it in parallel with the 12v battery, so no current should actually be drawn from there until the voltage drops, at which time the main battery bank and the engine will kick in to pump out the 100A to maintain the voltage. If I was actually drawing anywhere close to 1000W, the car’s gas engine would be on continuously to provide the power.

The only concern I can see is if there is a momentary excessive draw on the 12v battery before the system kicks in. It would certainly be a problem if the car was off; that would drain that battery in a trice.

The limit, AFAIK, to the 12v system is the wire gauge run from the battery terminals to the devices. The wire to the cig lighter is far too small, but the cables from the 288v to the 12v batteries are something like 0 gauge, which is the same that would be used for the short (1’ or so) run from the 12v battery to the inverter.

What am I missing?

I just wouldn’t want to play around with my $3,000 main battery to power stuff. The system is set up to carefully monitor charge levels to keep that battery in the correct operating range. What you’re proposing at a minimum sidesteps those monitors and controls. Not worth it to me.

That is a good point, and one I had not considered. If they have some sort of monitoring that says that the 12v system is drawing too much power, it might trigger consequences that I can’t predict. There might not be actual harm, but some computer somewhere might decide that it knows better that me .

Maybe some other fool has tried this already and can save me from myself! Please hop in if you have done this.

The normal continuous load on the DC converter is 10 to 35 amps for the lights, blower motor, fuel pump, wipers ect. The system was not designed to operate near the 100 amp limit for periods of time to operate shop lights/equipment. It will work but for how long?

Here’s a line of inverters that converts 12 VDC power to 110 VAC power. The output wattage of the inverter dictates the price,


If you are looking for 1000 watts of power, look at one of the small, quiet, lightweight generators offered by Honda and others. Don’t ask the very expensive DC-DC converter in the Prius to provide that kind of power…

Good Lord! What the $%&# kind of laptop does your daughter have! Most of them don’t even pull 100W. I think it would be easier and cheaper to buy her a more efficient laptop. GPS and cell phones probably don’t draw a significant amount, but heck, I can charge my cell phone at home and use it for 3 days. Can’t they charge some of that crap at the hotel room?

It might be cheaper to buy spare batteries for all the devices and just change them as required. Replacements are available that provide longer use times than the typical laptop. The other items should not draw much power.

WOW! You can go up to 375 watts for a standard inverter that plugs into a power point. I would give you a 99% probability that will be fine. $50.00
If your stuff draws more than that replace it.

375 watts/12 volts = 31 amps. Need to check if it’ll handle that.

It’s 375 watts @ 110 volts output. So that equals 3.4 amps.


* 12V DC input; 120V AC output; 2 outlets
* 375 watts continuous output
* 600 watts peak output (instantaneous)
* Convenient cigarette lighter plug

I have not had one blow a fuse yet. I am thinking 15 or 20 amp circuit. Laptop, 15" touchscreen lcd monitor and gps antenna is our typical load.