[pariah]

I was trolling You Tube lately and saw a device aptly named a voltage doubler. Could a stout enough one be used to double the voltage on an EV? I now have to admit that at best I'm more lurker than builder. It seems too good to be true that theoretically you could use 144 volts or so and double it to use possibly an OEM AC motor with the proper controller. I admit to just knowing enough to be dangerous!!!

 

[brian_]

I was trolling You Tube lately and saw a device aptly named a voltage doubler. Could a stout enough one be used to double the voltage on an EV?

Yes, Toyota uses a voltage-doubling technique in their inverters (in hybrids) to run (at least some of) their motors at up to twice battery voltage.

I now have to admit that at best I'm more lurker than builder.
...
I admit to just knowing enough to be dangerous!!!

This really doesn't seem like beginner or DIY stuff to me; it seems better suited to a major manufacturer with massive development resources... but maybe someone with hands-on experience has a different view.

It seems too good to be true that theoretically you could use 144 volts or so and double it to use possibly an OEM AC motor with the proper controller.

Keep in mind that you never get something for nothing. In this case, the current out of the battery will be at least double the current into the inverter.

What is likely to be worse for performance:

• The limitation on motor torque due to the current limit of the battery with the doubler?
• The limitation on motor speed (or power at high motor speed) due the voltage limit of the battery without the doubler?

I suspect that it might be more reliable and cost-effective - especially in a single DIY project - to use less than the full capability of a relatively large 360 V motor (by running it at lower voltage) than trying to optimally drive a smaller 360 V motor. I haven't done the math with any battery and motor combination to test this.

 

[onegreenev]

If you want/need the extra voltage just add in more batteries. Doubling the voltage will decrease your available amperage by half as well. No gain because the process of changing the voltage will result in some losses. Just use the proper voltages from the start with the proper amount of batteries. Using a doubler only inserts another complex process and more electronics that don't need to be there. However if you need to double 12 volts to run your 24 volt contactor then you can use a doubler and have be able to run your 24 volt contactor. This is where the doublers come into play.

 

[brian_]

If you want/need the extra voltage just add in more batteries.
...
Just use the proper voltages from the start with the proper amount of batteries. Using a doubler only inserts another complex process and more electronics that don't need to be there.

I agree in general, but in some circumstances it can make sense. After all, has Toyota failed to use "the proper amount of batteries"?

In this case, the desire appears to be to use an OEM motor and inverter. To use OEM modules without modifying them at the lowest level of connections, reaching the OEM design voltage means using the entire pack, and that's not always practical. Even if using aftermarket cells, stringing 96 of them together isn't a trivial fabrication exercise, and connecting (and monitoring) half the number is appealing. Not likely worth the issues of a huge doubler, but not an unreasonable question, in my opinion.

 

[onegreenev]

In what situation does Toyota use a Doubler on the Main Pack?

 

[brian_]

In what situation does Toyota use a Doubler on the Main Pack?

My understanding is that the doubling is integrated in the Power Control Unit with the inverter. I've seen references to this starting in model year 2010. Here's some text from Toyota Global > Technology File > Hybrid > Power Control Unit

The power control unit converts AC/DC power and appropriately adjusts the electrical voltage. Hybrid vehicles powered by motors are equipped with a power control unit that consists of an inverter, a boost converter, and a DC/DC converter.

The boost converter controls the voltages of the motor and generator. It steplessly increases the normal roughly 200 V DC supply voltage to a maximum of 650 V DC as required. This means more power can be generated from a small current to bring out high performance from the high output motors, enhancing overall power control unit efficiency.

There are references in this page to changes for 2015, but the voltage 'doubling' (the boost converter) is not flagged as new. A non-authoritative set of Prius Specifications for 2004-2009 show a battery nominal voltage of 201.6 V and a motor voltage of "500V maximum". Authoritative specs from Toyota (but for an unknown year, 2010 or later) show similar voltage levels.

There is little design difference between Toyota hybrid models of the same generation (other than the obvious transverse or longitudinal powertrain arrangement, and presence or not of an electric drive unit for the rear axle of AWD transverse models), so if a Prius is doing it, it is likely that everything else is.

 

[onegreenev]

Ok, low current applications. I can see this as a help so the manufacturer can utilize the high voltage motors rather than build low voltage motors. Usually the higher the voltage the lower the amperage needed. I can see this on a Hybrid but maybe not on a 100% Electric vehicle. But its not out of the question. I thought the doublers were best suited for things like kicking the voltage up to utilize higher voltage components like I had mentioned yet keep the main voltage low. Got it.

As for a DIY build! I'd would most likely use a motor suited for my voltage range and current range. Like Im doing with my DC setup and my AC setup from HPEVS. 120 volts for that one. Utilizing OEM recycled batteries from wrecked vehicles. Cheaper than buying new LiFePO4 cells.

 

[brian_]

I can see this on a Hybrid but maybe not on a 100% Electric vehicle.

I think that's a good point: Toyota probably wanted to keep the cell size up but in a relatively small battery (because it's only a hybrid, not a battery EV) so the cell series count and voltage are relatively low, yet they wanted the low-current advantages of a higher motor (and inverter) voltage.