Prius Prime plug-out, backup power supply for house

Lol, are you all smyles when you do it ?



Rob43

 

Should work fine.

 

I set this rig up for a 2015 Standard Prius. Now have a new Prime and am considering the same thing. I had (still have) a ballast battery (probably not the correct technical term) connected to a float charger and a 2000 Watt Costco Inverter. (There is a 75Amp circuit breaker in between) When AC power went down I backed up the original Prius to the rig and clipped on ballast battery terminals to the 12V battery on the car with standard jumper cables. I ran a heavy cord from the inverter to the refer as well as some minimal LED lighting in the house. The current draw never got too much over 300 Watts. It apparently worked as intended. I left the car “on” in the driveway. When the voltage in the car battery dropped sufficiently the car would start, run quietly for a few minutes and then shut off. There was no apparent damage to the car in the course of 3-4 overnight sessions - and the only visible evidence were some very light “normal” jumper clip marks on the battery terminals. Refer works fine and shows no particular signs of distress (after 3 years). I had some worries because of the ragged wave form generated from the “standard” (not true sine wave) unit.

Wondering if this raises flags with any in the group more versed with the technical electrical aspects of these cars?

I plan to use the same set up with the Prime, though I notice the 12 V battery is located in the front. Is it otherwise a similar set up or am I barking up a risky tree?

Wondering if the Low Voltage bat (12V) and the High Tension “traction” battery are connected. I assume they are but is the set up different than the older regular model. My uninformed assumption is that the Prime is more or less a regular Prius with a more robust traction battery and associated beefier regeneration and drive system.

Thanks for any help/ advice you can offer.

 

They are connected, so to speak, when the car is in READY, by a gizmo called the DC/DC converter, which (you would never guess from the name) deals with the difference in voltage between them.

Essentially, whenever the car is in READY, all of the power being used by 12 volt devices will be coming from the converter, because its output voltage is slightly above that of the 12 volt battery.

 

There should be no need for an additional "ballast" battery if you keep the load small enough. My understanding is the Prime measures the current into the 12V battery and controls the DC-DC converter output so that the battery isn't depleted. A ballast battery might confuse the system that maintains the 12V battery state of charge. And using jumper cables adds risk. You should have a fuse on anything coming off the battery, and jumper cables typically have no fuse.

There is a DC-DC converter that powers the 12V system and charges the 12V battery from the HV battery. That is active when the car is in "ready" mode. Apparently it has a current limit around 100A, but the car always uses some 12V power, so keep the load well under 100A to be safe.

There is a current sense element near the battery, and the load should be connected on the correct side of that. I think the side away from the battery is correct, but I'm not sure. If you connect it on the wrong side you might drain your battery. Or maybe not since it sounds like it worked fine for you.

If the ballast battery is big enough and the power outage is short enough, you can just run everything off that.

Modified sine wave is not great, but probably fine for most things.

 

Be careful. 8-10A at 120V is 80-100A at 12V, or even higher because the inverter is probably 80-90% efficient (could be as high as 100-125A). That's a serious amount of current. You need heavy wiring and careful thought about wire lengths and connections to prevent too much loss in the wiring. And of course a fuse (or maybe a DC circuit breaker) near the battery to prevent damage if anything goes wrong.

I don't know the details of where to hook up to the 12V system or what the car does if you get that wrong. I plan to figure it out later, but I think there is some old information around here somewhere. The Weber auto youtube channel has a little info about the 12V system, but from what I remember maybe not quite enough for me to fully understand how to hook up a load like an inverter.

If you're not 100% sure of what you're doing, it would be safer to start with a standalone deep cycle battery, or even just a car with a less complicated electrical system. Or just a good generator as someone else mentioned.

You can read about car audio installations to get some ideas about how to do a good job of the wiring. Some amplifiers use as much power as we are trying to get from an inverter. But I don't think you'll find many people installing huge amps and speakers in a Prius, so you'll likely have to read about prius-specific details elsewhere.

The wiring doesn't have to be complicated. Just some short wires positive and negative to a high current DC connector under the hood would do it, and you could wire a corresponding connector to the inverter. It's best to keep the wiring short to reduce loss (and expense of heavy wire), but if you wanted to put the inverter in the trunk that's probably possible too.

Proper grounding on the inverter is also important to keep the AC side safe. That's another one where I need to do more research to see whether it grounds itself to the vehicle ground and if that's safe or good enough. My inverter has a GFCI outlet, so my understanding is that it's safe no matter how it's grounded. I don't think I've heard of anyone driving in ground rods for an inverter or portable generator, so maybe I'm overthinking it.

 

The DC/DC converter continually replenishes the 12v battery from the big traction battery. When the traction battery runs low, the engine starts to maintain it as needed.

You’re on the right track as far as connection type & ratings. That DC/DC converter is believed to be able to supply about 100A continuously, but the car needs a little for its own computers. So if you think your inverter is going to present a 75A surge load and closer to 40A continuous load… it will work, provided you wire it fat enough.

 

We sometimes lose power from half a day to two days maybe once or twice a year in winter storms. Although a generator to power a few lights, refrigerator and microwave (about 2KW capacity) can be bought for about $500, the best one appears to be the Honda EU2000i or EU2200i selling for a little over $1000. However many local people buy them and they get very little or no use before the owner sells his house and moves to Florida or an assisted living facility. Then they can be bought for $400 to $500. I bought one two years ago in like new condition and used it once last winter. It sits in my garage ready for the next big storm. For me, that is a better solution than buying an inverter and modifying my $30K automobile to do the same thing.

 

Yep, a number of people here have done it. Works fine. Haven't heard about any problems, and folks here are not shy about discussing problems. Some of it traces back to the ability of the car to idle for extended periods in an economical manner and without harm.

You don't really need a kit. You pick up an inverter that is sized right for the car, hook it up positive to positive and negative to negative. Next turn it on, then plug in your load. All done. I used a pair of Anderson Powerpole connectors so I can plug it in or out without fuss. There are various details, but we have existing threads that cover the fine details nicely.

The Japanese setup is that you can plug into the recharging port and tell it to send electricity back out to you. I believe that connector is orange rather than blue. They have some kind of internal wiring available that we don't have. They probably don't trust it with us, which is only sensible.

I have never seen Toyota corporate get involved with this. No need really, it would be like if they offered support for people who wanted to add fog lights to their car - too easy to be worth their notice.

 

The chief disadvantages of a PRIups setup are that you can only get a modest amount of power out of the 12 volt battery - you can run a fridge or a circular saw or something, but not your whole house - and in some places you might have to worry about drunks or something coming around at three in the morning and taking your idling car for a spin.

 

I think the kit was to get power directly from the HV battery. You could theoretically get a lot more power that way. With a peak output around 68 kW the Prime could completely power a medium home with the right inverter. I think charge mode runs at about 12 kW, so it could theoretically even meet the continuous demand most of the time.

I don't think anyone makes a 68kW vehicle to grid inverter, but it's something auto makers could add if the right pricing structure from the utility companies was in place to take advantage of it. It could be part of a storage solution to support an increasing amount of renewable energy.

 

Do yourself a favor, get a pure sine model. They can power anything.

When the car is on, it is always monitoring the state of the 12 volt battery. If the charge on the battery starts to drift down, the car will top it back up. It calls for power from the traction battery first, and if the traction battery starts to get a little low, it will call for the gas engine and top everything back up.

The car does not see this as odd or abusive, this is the exact same thing it does during the day when you are driving down the road. We had someone here who measured how much gas it takes to run an inverter in a third gen. all night and it wasn't that much.

Go to the site search box for third gen Prius and tell it "PRIups". All the plans, details, concerns, and after-action reports you could possibly want.

 

Ah, that is a different story. If you make a mistake working with a 12 volt battery about the worst that can happen is you flash weld all the links on your watchband. Now they are $#@! HOT and you are $#@! STUCK. Working with, what is a traction battery, 400 Volts? you can do yourself real harm.

We did have a fellow who tapped into the traction battery to run a high capacity inverter, but he was way more knowledgeable than I am, and unless you are a licensed electrician (or something similar) I recommend that you just leave that big boy alone...

 

Does anyone see a potential problem here where your car starts in the middle of the night in your garage? Where does all of that carbon monoxide go if your garage door is closed?

 

There’s an old rule: never, ever run a generator indoors. Doesn’t matter if it’s a Briggs & Stratton portable or a Toyota car being creatively adapted.

 

You should never leave the car running with the garage closed, even if you have plenty of battery power. The engine could start at any time for a variety of reasons if the car decides it needs to.

If I were to use this for backup power I'd leave the car in the driveway and lock the doors from outside (if that's possible?). I think it's technically illegal to leave a car idling unattended, but this would only be for emergency use to run the heat and keep my house from freezing.

A more likely application is to power electronics while camping, in which case I'd be outside and I wouldn't leave the car unattended.