Inverter: How much power? and how?

Andrei,
Please be careful as the battery voltage can kill. Make certain that you have the skills (or learn them) to deal safely with high voltages before starting this project.

JeffD

 

Up to around 1000 watts, connection to the 12 volt aux battery is practical, and those inverters are common and easy to get. I've seen people push that and put a 1500 or even 2000 watt inverter there, though they are unlikely ever to get that much out of the car's 12 volt system. Sometimes it's just because they got a good deal on that inverter.

For attaching to the traction battery, there's a lot more power available, but that's a much less cookie-cutter procedure. Inverters that can handle that input voltage are harder to find, and designing a safe way to cable one in is more challenging. The original iteration of Randy Bryan's inverter business sold 2000, 3000, and 5000 options. 5000 watts is less than 25 amps from a 202 volt battery, so even that's no sweat for the car, but those inverters are chunky.

Randy's current business sells (newer, different) 3000 and 5000 options, but I can't find very much about them on the web site. There was a recent PriusChat post by someone who had bought one, if you can find it. Had pictures. Not a small package.

 

It's 202 volts nominal—that is, 28 modules ✕ 6 cells/module ✕ NiMH nominal 1.2 V/cell, 201.6. Keep in mind that when charging, that can rise to 1.6 per cell or so, therefore anything you connect had better be comfortable to at least 270 volts input.

The car will happily use up to 100 amps or a bit more, in or out, in normal operation. Lay a metal tool across the terminals inadvertently and you'll find out what the real max is it can put out, and you won't like it. There's a fuse built into the service plug, so you could look at that for the actual max-that-won't-blow-the-fuse.

Here's hobbit testing one of Randy's earlier 3000W offerings, after removing the casters from the bottom to reduce the height a bit.

 

What you want is not common at all, and that specific availability is (probably) what gave rise to the Converdant business model.

If an inverter's data sheet specifies x volts input, there is a range, but it will have limits and you cannot expect identical behavior at or beyond limits from different devices. This makes system design a bit of a challenge. Charger X may need to take the system up to 285 volts for its daily test program while inverter y may go into safety shutdown if it ever sees a peak above 279 volts. The numbers are made up to illustrate the point. You get to navigate a lot of awesome things like that.

There is safety in numbers. I don't mean the inherently safer low voltage of 12v, I mean there's way, way more automotive & alt energy hobbyists working with 12v systems. Many more problem-solving parts and a lot more experience to draw on.

You can get much more compact inverters in the "popular" DC voltage ranges. I suspect the converdant ones are that large because the expected sales volume meant using off-the-shelf casing and components rather than optimally sized items.

Consider the demand side before you commit to building a huge system. What's going to draw all this power, and is there a smarter way to do reach the end goal?

 

For camping trips, traction battery connected inverters are overkill. How much electric load are you needing to run? Do some math and if your need is less than say 1.5Kw, then the 12v system may be far easier and cheaper.

Randy's PLUGOUT POWER, LLC (formerly known as ConVerdant Vehicles) has a 3kW and a 5kW system for sale now. But they are more for running a whole house as a back-up generator. The system is not portable size at all. See my photo and comment in the thread linked below as well as attached sales docs from PlugOut I got from my recent visit with Randy. In the end, the price tag was too high for the smallish power I get from it as a back-up generator, I decided not to get it.
Prius Whole house Converdant Inverter | Page 3 | PriusChat

 

The bad news is transformers depend on Faraday's law, which says the voltage induced by a magnetic field depends on the rate of change of the field, so the field has to be constantly changing for the transformer to work, so a transformer has to be fed AC, and it produces AC. A transformer connected to DC is just a space heater that you might also be able to pick up nails with if you spilled a box.

To get one DC voltage to a different DC voltage you need not a transformer but a converter. You've got one of those under the hood already, taking the traction battery voltage down to 12, but as mentioned elsewhere that one's only sized for around 1000 watts.

The insides of a converter are pretty much the same as the insides of an inverter. It needs to take the DC input, make a changing waveform out of it, and get (by a transformer or otherwise) a waveform around the desired output voltage from that. It doesn't need the parts of an inverter that shape the output into beautiful sine waves; instead of those, it just needs to rectify and smooth the output back into DC.

Needless to say, using a converter to change the DC input voltage to an inverter would make Rube Goldberg proud.

 

Andrei,

I am fully capable to install a HV connected AC inverter, but have an 8 kw ICE driven generator to handle my emergency electrical needs at home (except the air conditioner) and use a 12v inverter on the road as those needs are normally lower wattage. I agree with the Salamander_King.

JeffD

 

Interesting, just yesterday you were super confident but today not so much. The reality is "playing with electricity" is different than throwing together parts to take high voltage dc to clean sine wave ac voltage. Even Toyota did not have reliable high power mobile inverters until about 2016. Plus, the Toyota inverter requires active liquid cooling. All electrical conversions lose energy as heat. High power means high waste heat loads.

If you are a well capitalized entrepreneur, you hire an experienced design contractor and eventually you get there. Or you buy someone else's prototype. For cost effectiveness, a 1000 watt inverter running off a paralleled Prius 12v battery would be my choice. Even then the Prius will be starting up many times an hour at a louder db than a decent Honda inverter generator.

For whole house backup I would use a 14kw LP or Natural gas generator and transfer switch.

Often we "don't know what we don't know" and as a result, don't know the questions to ask and are not well equipped to make good value judgements. Yes, anything can be prototyped and used for a variable amount of time. But it might cost five times more than a quiet Honda inverter generator and the Honda won't fry your loads and perhaps your Prius.

 

I agree on all points and suggestions. But this person is either going big or go home, and he ain’t going home.

 

If they can handle that kind of discharge rate. Just because the energy is in there doesn't mean you can get it all out on the schedule you're hoping for. I'm not familiar with any photo or cine batteries that would handle this load gracefully.

Run an extension cord out to the car and cook in it for a weekend on shore power and ask yourself if you're really going to keep that up for long. There are some innovative and useful ways to heat at least certain foods in a car and many of them don't use much electricity. Crockpots and warmer ovens are cheap and easy to live with.

The amount of power needed to run a blender and to heat wash water to sanitize it is a really serious commitment energy wise.

 

I believe those batteries are 6.6ah.

 

I'm a deliriously satisfied Instant Pot customer, and the three-quart models pull 700 watts.

 

I think you are on the right track now but those 100wh / 6.8 amp hour batteries won't run a 1500w inverter at any kind of load. An inverter that big needs at least 125 amps of 12v at full load. If the Prius 201v to 12v dc to dc is used it is fused at 125 amp 12v current. The car needs 12v power to operate so most suggest limiting an external inverter to about 1000w which is still over 85 amps at full load.

To handle short term high current a decent solution is to add a high amp hour agm with proper isolation to protect the 40ah hour 12v car battery. A 100ah battery can drive a 1500w inverter for 30-60 minutes at full load, much longer at part load. Most of the equipment can be found at off grid suppliers.

 

Yes, it can absolutely be done. An AGM battery similar to the 12v Prius battery would be a good starting point. I'd probably go larger to gain access to more commonly available and possibly cheaper (by the w/hr) sizes with deeper reserves.

That load is going to be described in amps. A common storebought inverter is likely to deliver 80% efficiency. While handling the start surge of a blender labeled as "1600w" it will probably tax the battery for ~230 amps at first, falling to 150 or so once it gets up to speed. That's somewhere between "motorcycle starting" and "car starting" kinds of electrical demand, so it should give you an idea of the battery needed to back it. You'll probably run the blender longer than you would need to start a car engine, so think about that too.

Then you need to choose whether you drive the inverter from the built-in 12v battery, or add a second one with its own charging scheme.