Inverter on 12v battery

Don't connect there. The inverter is where the magic happens. It takes the HV DC from the traction battery and produces the 12v that runs down and charges the battery. The battery is used for nothing really. It gets a short ~1s burst of about 15A to 30A to prime the brake pump, then it flips a couple relay coils at a few tens of milliamps a piece, then the inverter kicks on the battery sits there as a load charging away until the next time it is needed for almost nothing. So the wires going back there are small because its work load is small.

Up front is where all the higher amperage systems drawn off of the 12v rail come from. The fuse box under the hood has the fusible link (100A in GenII, similar in GenIII I thought). So you can draw 100A continuously for your whole system.

I hooked up some low gauge wire to the 12v terminal under the hood and then a ground bolt in the same area. This then goes to a nice Anderson connector. When I need my inverter I just pop the hood connect the Anderson and off I go. The inverter is rated for 1500W continuous with 3000W peak. I have never tried to draw more than 800W continuous, but the Prius took it like a champ when I drew 700W to 800W continuously for almost a full day as my house was rewired for a new electrical panel service. I kept the fridge plugged in which was a large inductive load, and my rackmount server cabinet with its own UPS and server system.

 

The 12v "jumper" is the fusible link. It is a piece of copper bent into lots of funny shapes. They say don't jump because if you reverse the polarity of the cables, the inverter is toast. $4K repair.

If you are going to draw more than 125A (dereated for actual Prius load too) then you have to go off of the battery. But the inverter is where you want it 99% of the time. Why run high current low voltage DC from the front to the back of the car?

 

Well to preface, I do not have much stick time with the GenIII. However I would be surprised if they changed it substantially from what they had going on in the GenII.

Here is a pic of the GenII fuse box. A is the "jump point" and B is the fusible link:



This is a blown fusible link:


Closeup of the fuse box:


You can pretty clearly see the fuses on that piece, how it is supposed to look. That main one that is blown is the main 100A (in GenII) but it also has separate exits for other parts of the system also fused in the link at various amperages. Simple yet brilliant way of having multiple high current fuses, except a PITA to replace and not something you can buy at 3am when it explodes. Now I drew the current flow with some yellow:



The yellow at the bottom of the picture behind that black plastic piece (it slides off) comes directly from the inverter. That is the main Inverter->12v Rail connection in the vehicle. It's first stop is the jump terminal. which is essentially just another piece of copper that it can be bolted to, and big enough that you can clamp to in emergencies. It then goes through the fusible link and out to various other systems.

Growing tired of not finding the images I wanted on the internet, I just went outside and snapped a few of my own. Here is my main connection. The cover is flipped up. The large copper piece with lots of strands of crimped wire that then curves up on the bottom of the "pile" is the OE inverter->box connection. The large wire in the middle goes to my anderson connector for my 120vac inverter. The two smaller wires on the top go to my retrofitted headlights. You can sort of make out star here. They all connect to this big metal chunk where the screw is. Then a small piece comes up "above" the screw in the photo, towards the cabin in physical world, and that is the piece where you can jump from. Another similarly sized piece goes down and becomes the fusible link.



And from another angle:



And another angle to see the fusible link connection better:



Conclusion being, you should connect where the inverter connects. The only time this is not true, is if you have large cycling loads where the instantaneous power for a few cycles is greater than the max output of the inverter. In that case you connect it to the battery and when your circular saw or air conditioner is turned on and draws 3000W for a second, the battery is providing the excess 2000W. Then when it calms down to sub-1000W, the inverter then is supplying all the power and slowly recharging the battery too. But to draw 1000W in the back continuously, you will need to rewire from the front of the car to the back by the 12v battery. It is just not meant to do that.

The inverter connection however is meant to do exactly that. That nice low gauge wire to a nice terminal is perfect and just the way Toyota made it.

 

You might be correct that the white wire comes from the inverter. Just because the red box above the "number 4" in the big long part seems like the fusible link. It is #10 in the picture:



If you have 10AWG wire, you are going to get about 1mohm/ft. If you have 15ft of wiring (probably conservative since it is not a straight run, it is snaking around body panels) that is 15mohms of drop. If you are drawing 900W continuously, at 13.8v, that's 65A. You are going to get a 1v drop across the line, and the itty bitty 10awg wire bundled up in the bowels of the car with no air flow will be dissipating 65W of waste heat. That's too dangerous for my blood.

The NEC says that you should really only draw 30A through that wiring continuously with 60C insulation.

And really, 15mohms of resistance doesn't account for the connectors and other environmental factors.

You should use 4awg wire for 65A at a minimum. At 0.2485mOhms/ft, 15ft, that's 3.728mOhm. Only about 250mV drop over the 15ft, and 15.75W. That is a little better, but still personally above the comfort level. I don't want to be able to feel the heat even under high load. But that will get you by. The current wiring will not, the Prius was not designed to pull any sort of power from the AUX battery area to the hood. It draws 30A's for a second, then drops to nothing.





The Prius dynamically changes the charging voltage between 13v, 13.8v, and 14.4v depending on load and assumed state of charge of the aux battery, temperature of the aux battery, and so on. I am not sure if they still put a thermocouple in that big red thing over the + terminal, but they used to. So don't count on the higher voltage to offset some of the losses.

Correct that you do not have room for surge. This is where a good inverter comes in handy. The inverter should have its own fast blow fuse for 100A between the input of the inverter and the Prius. Then you buy one that has a surge rating higher than the continuous, by about double. Usually they just cram a bunch of capacitance on the output so that short inductive load like a motor can startup without problems. If you plan on running a 1000W resistive heater however though, that just won't work.

And just to throw it out there, the "optimal" solution is to actually connect to the HV battery. Then you get a 30KW system with a battery surge supressor. There are some Chinese products available that can take the variable 180VDC to 260VDC and output a nice stable 220VAC or 120VAC. This is still very new tech though...

You seem knowledgable with a thirst for real engineering, I encourage you to join the Prius Technical Group on the Yahoo Groups email list. Lots of brilliant minds as well as some good humour from loud mouths.

 

It does look like you are missing a cover, but again my area is in GenII Prii, not GenIII. It does look odd though to have downward facing contacts exposed.

As to your question about the fusible link, I didn't blow it. That's one of the very few images of a blown fusible link available online. One of the dangerous aspects of mounting my headlights and AC-inverter connections where I did, is that there is no protection from the fusible link. That is only for things downstream, like the aux battery.

 

my fusible link looks much the same except it has 2 printe on it instead of 4. We are RHD in Aussie.

 

I had some of the same concerns that you had considering the large size of the cables going to a 12V inverter and the proper fusing. I was really glad to see AHetaFan make his excellent post on using the AIMS 220V inverter that connects to the HV battery. I really liked the idea of using #10 cables versus the #4 cable or larger for the 12V inverter and using 15A fuses versus something less than 100A.

AHetaFan's write-up is excellent and the way he had good input in to the proper fuse selection is also excellent. I followed his advice and it worked out very well.

You just need to know the proper precautions to take when connecting to the HV battery. When the car is powered down the HV battery is disconnected from the DC leads going to the Inverter/Converter module by relay contacts. So when you are connecting the inverter cables to the HV battery output terminals there is no voltage present.

As for the missing cover, you are not missing anything. My Gen III looks the same.

 

That is the write up .

We found a minor issue where the 220V DC- connection was connected to case ground. I sent mine back to be repaired. AHetaFan repaired his own after seeing AIMS' repair. Any new inverters ordered from Jack Chen should be free from any ground now. Jack is just having AIMS supply their inverter with a DC input to range from 180-240 VDC to match the Prius HV battery.

Good luck with your install. Keep us posted on your progress.

 

If you have a multimeter you can get a voltage reading off the jumpstart tab in your fuse box or from the big white cable. I presume you mean 12 volt battery and with ignition off. If ignition is on then you will get the inverter charge voltage to the 12 volt battery.

If you mean the traction battery then I suggest buying a Scanguage which can be programmed to provide a lot of useful readings.

 

No way of knowing what code will be thrown without knowing how their fault conditions were programmed.

In a boost circuit (not necessarily a boost topology, but boost, SEPIC, flyback, half/full bridge, etc) you still have to maintain Pin = Pout. Really there is an efficiency derating in there too, that's where the heat comes from, and fans, and control circuitry, magnetic losses, all that jazz.

Lets say you supply 13.8v input and are getting

If you are pulling 683W output at 80% efficiency, you are drawing 853W at the input. At 13.8v that is 61A. We already know that with your wiring you are actually closer to 12v. 853W @ 12v is 71A. 900W continuous at 13.8v is ~65A.

So perhaps your inverter tests an output overload by measuring input current. In that case you would be over the limit.

Nobody knows, but even if it did work, you are at severe risk of melting your internal wiring. That would be a horribly un-fun weekend snaking a new 10awg cable into the stock bundle from the front to the back.

Having said all that, I don't think that's your problem.

An electric space heater is 100% efficient and usually 100% duty cycle. They also almost always draw 1500W. It just a beefed up toaster coil tied to the wall. You can derate the heat by duty cycling it. So if you turn the dial to 25% heat, you are drawing 1500W for 25% of the time and 0W for the other 75% of the time. It is not just drawing 375W.

So your 900W space heater is probably switching at 60% duty cycle. Probably 1500W for 60% of the time, 0W for the other 40% of the time.

And the time period can be nanoseconds or microseconds, or some even pulse at hertz wear you can see the bar glow and die, then glow and die.

So my guess is that you actually overloaded it.

 

Overload of what though? Input current overload? Output current overload? Saturation of the inductor? Different things can happen, and it is really hard to tell what the code means without knowing what the topology and coding is.

The KillAWatt is a very long average watt meter. Just like a DMM won't show you the oscillations either.


A cheap heater usually uses the PWM mode. It is super cheap and another heating coil is much more expensive then a penny worth of electronics.

It is still 65W of heat being dissipated. You can run your car without coolant too. It will work, until it overheats and dies. Running 100A through 10AWG wire will work until it gets too hot and then dies.

Running off of the battery you are going to be drawing most of the power through the battery since the voltage drop over the line would make the potential at the battery too low. However, because you are not replenishing the battery fully, eventually it too will drop. When it drops to the same voltage as the input now you'll be drawing the full load from the inverter, and that's where your 65W of waste heat in a tiny burred wire will come from.

It seems like you are only testing for now, so just make sure to keep the battery nice and charged for your testing. But before you use this to actually power your house, you need thicker wiring from front to back.[/quote]