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

[sunshine_eggo]

What do you mean by "typical idle charge rate"?

With the vehicle sitting idling and charging, it sends about 20A to the HV battery.

Comparing a typical 1.5 L engine to a similarly constructed .5 L engine is an unfair comparison.

It's very fair to compare the relative sizes of two gas burning engines at the same power output level. Thermodynamics still applies. Pulling the same power out of a notably larger engine has mechanical and friction losses larger than the smaller engine. More power is required to simply spin the larger engine.

The prius engine has a lot of controls (electronic and mechanical), which may produce higher efficiency than a standard gas generator engine. Even at less than max power output.

The smaller engine is optimized for CONSTANT RPM. It is much easier to maximize single-point efficiency than dealing with a multi-speed/variable power application.

The Prius engine efficiency is optimized for commuter-type travel. It is NOT optimized for low rpm idle charging. I'm not saying it sucks, but it's not going to use more gas per kWh produced than a suitably sized generator.

 

[sunshine_eggo]

However, pulling a given wattage out of the battery like say 1500watts and then letting the engine cycle every few hours means the engine is seeing a decent enough load during the recharge that it starts to make more sense from a fuel consumption standpoint.

Ummm... 1500W is going to cause the engine run quite a lot. Usable HV battery capacity is about 0.5kWh, and it's going to cycle charging on/off about every 200Wh. A Prius with a very healthy battery operating at the typical running SoC (57-60%) will run the A/C maintaining cabin temp (not full blast) in 90°F ambient for about 4-5 minutes before the engine lights off. Then it will cycle on/off every 1-2 minutes.

 

[Checkthisout]

Ummm... 1500W is going to cause the engine run quite a lot. Usable HV battery capacity is about 0.5kWh, and it's going to cycle charging on/off about every 200Wh. A Prius with a very healthy battery operating at the typical running SoC (57-60%) will run the A/C maintaining cabin temp (not full blast) in 90°F ambient for about 4-5 minutes before the engine lights off. Then it will cycle on/off every 1-2 minutes.

This is the worst thing I have ever read.

I'm confusing the Prius with the Prius Prime.

 

[sunshine_eggo]

This is the worst thing I have ever read.

I'm confusing the Prius with the Prius Prime.

Given that the original Prius Prime had a measly 12 mi range, I doubt it would be substantially better. The initial run would be longer, but once capacity is depleted, it reverts to a standard hybrid configuration, so it would still cycle the engine on and off about as frequently.

Also, the Prime is Lithium-ion and 351V-ish, so it's a completely different beast.

 

[McKravitts]

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".
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.
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.

It's very fair to compare the relative sizes of two gas burning engines at the same power output level. Thermodynamics still applies. Pulling the same power out of a notably larger engine has mechanical and friction losses larger than the smaller engine. More power is required to simply spin the larger engine.

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.

The smaller engine is optimized for CONSTANT RPM. It is much easier to maximize single-point efficiency than dealing with a multi-speed/variable power application.

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.

 

[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.