Poll: will it work? Prius as a generator, direct charging of 48V from traction battery

[sunshine_eggo]

With a Prius it's more appropriate to refer to the synergy drive system being ON, rather than to use the term "sit and idle".

Thank you for telling me how to refer to a platform I've been servicing for 8 years. Unfortunately, you are wrong. The most appropriate reference would be to say "in READY mode."

I've run an inverter off the 12 volt system many times and the ice engine doesn't turn on every time I put a load on the system. The IC engine only comes on occasionally.

The ICE runs when SoC drops to 40%.

I don’t know how well the IC engine is matched (efficiency wise) to the traction battery charging load when the car is sitting but it definitely outputs more power than can be drawn off the 12 volt system.

I've literally told you about 4000W above.

I totally agree but one must also consider the duty cycle that each engine must run and taking into account the often non constant load that is being powered.

Nope. We're comparing fixed rate 4kW power generation. Generator auto-start is a readily attainable feature, so duty cycle isn't relevant. A dedicated generator can be programmed to come on at X% SoC and shut off at Y% SoC. Or one can manually start/stop a traditional generator. I don't think anyone with an inverter and battery is going to run a 5kW generator when the load is only 100W.

Again, I totally agree, but for fuel efficiency determination one must take into account the duty cycle that each is required to operate under the load conditions, especially if the load on the 12 volt system is not constant.

See above.

 

[Consumerbot3418]

The Prius engine efficiency is optimized for commuter-type travel. It is NOT optimized for low rpm idle charging.

Appreciate your sharing of knowledge! I'd love to know exactly how much worse the efficiency is, but taking into consideration the benefits and versatility, it's hard for me to imagine a standalone generator being superior for rare/occasional use. It'll be one less piece of equipment to own and maintain, much larger tank, much more discreet, and lower emissions to boot, I'd wager. Feels like a win/win/win, even at a 25% fuel economy loss. At least I can eliminate two steps of (minor?) efficiency losses in the 200VDC -> 12VDC -> 120VAC -> 48VDC chain!

I'd really prefer a professionally engineered way to tap into the power, for safety reasons, but I'll do my due diligence and exercise caution whenever I end up pulling the trigger.

 

[AntronX]

I'd first test the concept with one converter at 2kW then add 7 more converters for 16kW load on the engine for best efficiency. You would need to program a CANbus controller to control converter modules and engine speed. And obviously your 48V battery has to accept 300A charge current.

 

[sunshine_eggo]

Appreciate your sharing of knowledge! I'd love to know exactly how much worse the efficiency is, but taking into consideration the benefits and versatility, it's hard for me to imagine a standalone generator being superior for rare/occasional use. It'll be one less piece of equipment to own and maintain, much larger tank, much more discreet, and lower emissions to boot, I'd wager. Feels like a win/win/win, even at a 25% fuel economy loss. At least I can eliminate two steps of (minor?) efficiency losses in the 200VDC -> 12VDC -> 120VAC -> 48VDC chain!

I'd really prefer a professionally engineered way to tap into the power, for safety reasons, but I'll do my due diligence and exercise caution whenever I end up pulling the trigger.

It's probably about 15-20% less efficient based on some bsfc estimates. It is worst at low rpm/power, and it's limited to 4000-5000W of continuous output at "idle". You can sit in the car, put it in "D", hold the brake to the floor and pin the throttle. This will force-charge, and I've observed about 15kW. This doesn't harm the car as it's not trying to propel the car by more than what is typical for "creep" while in "D". You wouldn't want to do this with the power supply attached as you'll definitely see > 250VDC.

A vehicle ICE MUST run at different rpms as speed varies. This complicates efficiency. For any given speed, there is an rpm and power combination that is optimal. The CVT-like operation of the transaxle helps, but it has limitations.

With a generator, they operate at constant rpm, so their thermodynamic efficiency is best at peak power. Running a generator at peak power will wear it out, so you shoot for 70-80% utilization. Inverter generators can be little more efficient at lower power settings because they can vary their rpm for peak efficiency for a given power, but again, this is for LOWER power settings. A regular 5kW generator and 5kW inverter generator will be about the same efficiency at peak power.

FWIW, I voted that it will work. My only concern is the power supply voltage and that you have a better understanding of how it all works.

As a generator, it's delightfully quiet and has two catalytic converters, so there are non-efficiency plusses.

 

[AntronX]

My only concern is the power supply voltage.

The Flatpack 48/2000 is rated for 250Vdc input but also for 250Vac as well. Peak of AC waveform will be 355V at 250Vac. I suspect it uses 400V internal bus voltage before step down transformer. Therefor it should work above 250Vdc up to 400Vdc.

 

[AntronX]

Another nice thing about these converters is they can operate as MPPT solar controllers as well with appropriate control strategy over CANbus. So they are like 3 devices in 1. Grid charger, Solar MPPT and Prius generator to 48V battery chargers.

 

[sunshine_eggo]

The Flatpack 48/2000 is rated for 250Vdc input but also for 250Vac as well. Peak of AC waveform will be 355V at 250Vac. I suspect it uses 400V internal bus voltage before step down transformer. Therefor it should work above 250Vdc up to 400Vdc.

I'm not smart enough to make that conclusion. If a device gives a range, I stick with that.

Another nice thing about these converters is they can operate as MPPT solar controllers as well with appropriate control strategy over CANbus. So they are like 3 devices in 1. Grid charger, Solar MPPT and Prius generator to 48V battery chargers.

Is this actually a charger, or a constant voltage supply?

 

[AntronX]

Is this actually a charger, or a constant voltage supply?

CC/CV supply controllable over CAN. You can program them into whatever you want them to be.

 

[AntronX]

I'm not smart enough to make that conclusion. If a device gives a range, I stick with that.

I got a couple of them. Maybe I will tear one down and test with > 250Vdc input.

 

[sunshine_eggo]

I'd first test the concept with one converter at 2kW then add 7 more converters for 16kW load on the engine for best efficiency.

This would require someone in the driver seat.

Unattended, it's limited to about 4000-5000W.

 

[AntronX]

Unattended, it's limited to about 4000-5000W.

Any way to bypass the seat sensor? Or does it require foot on gas pedal? That could be spoofed over CAN using MITM device.

 

[sunshine_eggo]

Any way to bypass the seat sensor? Or does it require foot on gas pedal? That could be spoofed over CAN using MITM device.

In "D", brake pedal depressed, throttle floored.

 

[Consumerbot3418]

CC/CV supply controllable over CAN. You can program them into whatever you want them to be.

FWIW, I’ve already got CAN control working on the Flatpack2, able to set voltage, current, and default voltage. Using ESPHome, and the code for multiple units needs to be modularized, but I’ve got it working with two units. If I can really feed up to 400VDC into these things and use them as charge controllers, that would be incredible!

add 7 more converters for 16kW load on the engine for best efficiency

I’d prefer to sacrifice some efficiency if it means preserving health of the engine and mags. Sustained 16kW seems borderline abusive, as there’d no doubt be lots of heat generated.

I’d be tickled pink to just get 4000W (2x2000W), and possibly try to hack the Prius’ CAN for a (slightly) higher RPM if it means fuel economy gain.

 

[AntronX]

Which model year is your Prius?

 

[Consumerbot3418]

Which model year is your Prius?

It’s a 2012 Prius V.

 

[AntronX]

So it's a 3rd gen Prius with 42kW MG1 up to 13500 rpm coupled to engine via 3.6 gear ratio, limiting you to 3750 engine RPM while stationary. @sunshine_eggo ?

 

[AntronX]

On another thought, maybe solar MPPT idea may not be healthy for that converter if constantly writing current limit values over CAN could wear out internal memory cells. I guess it would store those values every time you set them. After > 100k - 1M writes it could fail. That's only 2 - 18 months worth of use if CC is written every second for 12 hours/day.

 

[sunshine_eggo]

So it's a 3rd gen Prius with 42kW MG1 up to 13500 rpm coupled to engine via 3.6 gear ratio, limiting you to 3750 engine RPM while stationary. @sunshine_eggo ?

I'm less familiar with the Gen 3 specs, but it won't go above idle rpm without a foot on the gas. Still limited to about 4000-5000W unattended generator power, and it doesn't willingly engage the forced charging process I mentioned previously. It will do it briefly, but you have to cut the throttle and then re-floor it about every 5-10 seconds.

You'll want to pull the case cover and attach your feed wire at the main (+) and (-) terminals. The current sensor is integral to the relay, and

 

[McKravitts]

Thank you for telling me how to refer to a platform I've been servicing for 8 years. Unfortunately, you are wrong. The most appropriate reference would be to say "in READY mode."

I wasn't "telling you" you how to refer to anything. I don’t know the terminology that service professionals use, but it's clear that you understood what I was referring to.

Nope. We're comparing fixed rate 4kW power generation. Generator auto-start is a readily attainable feature, so duty cycle isn't relevant. A dedicated generator can be programmed to come on at X% SoC and shut off at Y% SoC. Or one can manually start/stop a traditional generator. I don't think anyone with an inverter and battery is going to run a 5kW generator when the load is only 100W.

In your original post, you didn't say that the "fixed rate" 4kwH generator was going to be charging batteries. Nor that it had to have programmable shut on/turn on and/or be manually started and stopped. All the things that a Prius does automatically.

The Prius doesn’t run a 5kwH generator to power a 100 watt load.
It runs the generator to charge the traction battery. The traction battery then supplies (via a dc to dc converter) 12 volt power to the car, which then can power an inverter which supplies the 100 watts.
Are you saying that when sitting idle in the "ready mode" the IC engine starts if one turns on the radio?

On the topic of fuel efficiency of gas powered engines, I have one question.

When powering a fixed 10 kwH load, what's more fuel efficient;
Two synconized genertaors optimized to run at 5kwH and each running at that output ?
Or one generator optimized to run at 10kwh and running at that output?

 

[sunshine_eggo]

Are you saying that when sitting idle in the "ready mode" the IC engine starts if one turns on the radio?

I've already answered this twice on the first page, and you even quoted the answer.

On the topic of fuel efficiency of gas powered engines, I have one question.

When powering a fixed 10 kwH load, what's more fuel efficient;
Two synconized genertaors optimized to run at 5kwH and each running at that output ?
Or one generator optimized to run at 10kwh and running at that output.

About the same.

 

[billvon]

Why not hook up one of the high voltage inverters directly to the drive battery system?

Because that AC to DC supply is isolated; your typical (non-transformer) inverter is not.

 

[McKravitts]

I don't think anyone with an inverter and battery is going to run a 5kW generator when the load is only 100W.

Unless they have a big battery bank to charge.

 

[Consumerbot3418]

constantly writing current limit values over CAN could wear out internal memory cells.

Based on behavior I’ve seen, the voltage and current limit isn’t stored in non volatile memory. If CAN comms is lost, or power cycled, it reverts to default voltage, which must be written to nonvolatile memory. At $50/unit, seems worth a gamble to experiment.

You'll want to pull the case cover and attach your feed wire at the main (+) and (-) terminals. The current sensor is integral to the relay, and

I’d sure like to know how this sentence ends!

So it's a 3rd gen Prius with 42kW MG1

I’ve seen close to 100 amps at over 200V while using regenerative braking… The behavior @sunshine_eggo described makes it sound like they’ve built in a duty cycle in software/firmware. Might be willing to push it if it was a salvage unit, airbags deployed, etc. But don’t want to risk exceeding specs on a vehicle used for commuting.

 

[sunshine_eggo]

Unless they have a big battery bank to charge.

Precisely my point. Generator charging is typically at a consistent power level, hence why I compared two generators running at 4kW thus negating duty cycle as a consideration.

 

[sunshine_eggo]

I’ve seen close to 100 amps at over 200V while using regenerative braking…

You're also charging with MG2, not MG1 when braking regeneratively. 90-100A is pretty typical if you hit the max regen braking conditions.

The behavior @sunshine_eggo described makes it sound like they’ve built in a duty cycle in software/firmware. Might be willing to push it if it was a salvage unit, airbags deployed, etc. But don’t want to risk exceeding specs on a vehicle used for commuting.

Just so I understand, what do you mean?