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Old 05-17-2012, 01:49 AM
sheik480 sheik480 is offline
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Question High battery voltage and controller longevity

My question is this: how will battery voltage near the controller's rated maximum affect its durability and longevity? The idea would be to allow high motor rpm while still being able to pull many amps to allow for a responsive motor in the efficient rpm range. The specific instance I'm thinking of is feeding a Soliton Jr. with a 95 cells in series, which would be right at it's rated limit with fully charged cells (342 volts to the controller at 3.6 volts per cell). All criticism, advice, sage advice, and schooling welcome.

-Christopher
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Old 05-17-2012, 05:48 AM
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Default Re: High battery voltage and controller longevity

Well, it's generally true that the closer you run anything to its limits the shorter its lifespan will be. More specifically, switching losses go up with voltage (and current and frequency) so the controller will run hotter at a higher voltage, all else being equal.

Thus, the maximum current is reduced by 100A if the battery pack voltage is above 310V in the Soliton1 and Soliton Jr controllers. If you don't intend to run your Soliton Jr above 500A then this won't affect you, otherwise you might want to reduce the number of series cells to 90 or less.
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Old 05-17-2012, 09:26 PM
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Default Re: High battery voltage and controller longevity

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Originally Posted by Tesseract View Post
Well, it's generally true that the closer you run anything to its limits the shorter its lifespan will be. More specifically, switching losses go up with voltage (and current and frequency) so the controller will run hotter at a higher voltage, all else being equal.

Thus, the maximum current is reduced by 100A if the battery pack voltage is above 310V in the Soliton1 and Soliton Jr controllers. If you don't intend to run your Soliton Jr above 500A then this won't affect you, otherwise you might want to reduce the number of series cells to 90 or less.
This is exactly what I would not have expected. I imagine it wouldn't be a problem with sufficient cooling, but it's good to know that not only amps make heat. I should have figured that stress goes up with power, however that power rises.
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Old 05-17-2012, 09:40 PM
sheik480 sheik480 is offline
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Default Re: High battery voltage and controller longevity

If you feel so inclined, could you roughly estimate how much hotter it would run compared to a 60s system?
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Old 05-17-2012, 10:22 PM
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Default Re: High battery voltage and controller longevity

You might also be interested to know, the elevation of the controller also affects it's lifetime, especially with respect to high voltages.

numerous studies have concluded that electronics are exposed to more cosmic radiation at high altitudes, and that high voltage electronics are affected the most. So it may be an important factor if you are running in high elevations.

When switching, the switching electronics inevitably switch some parasitic inductance. Switching off inductance creates a high voltage spike. Controllers have built in diodes (or the body diode of a MOSFET) which serve to shunt the reverse voltage spike. However, the higher the bus voltage is (or bus current), the more the diodes lose in terms of conduction losses, since they are not perfect conductors. So, more turn off voltage means more turn off current in the diode, thus more losses. So losses estimate..... P=I2R... though only in respect to the switching frequency and pulse width since the current is being switched.. higher frequencies means more losses.

Last edited by subcooledheatpump; 05-17-2012 at 10:28 PM.
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Old 05-17-2012, 11:10 PM
sheik480 sheik480 is offline
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Default Re: High battery voltage and controller longevity

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Originally Posted by subcooledheatpump View Post
You might also be interested to know, the elevation of the controller also affects it's lifetime, especially with respect to high voltages.

numerous studies have concluded that electronics are exposed to more cosmic radiation at high altitudes, and that high voltage electronics are affected the most. So it may be an important factor if you are running in high elevations.

When switching, the switching electronics inevitably switch some parasitic inductance. Switching off inductance creates a high voltage spike. Controllers have built in diodes (or the body diode of a MOSFET) which serve to shunt the reverse voltage spike. However, the higher the bus voltage is (or bus current), the more the diodes lose in terms of conduction losses, since they are not perfect conductors. So, more turn off voltage means more turn off current in the diode, thus more losses. So losses estimate..... P=I2R... though only in respect to the switching frequency and pulse width since the current is being switched.. higher frequencies means more losses.
The connection with high altitude is quite interesting. I spend almost all of my time below 1500 feet, so that would not be a problem, but I imagine it is a good factor to remember.
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Old 05-17-2012, 11:52 PM
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Default Re: High battery voltage and controller longevity

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Originally Posted by subcooledheatpump View Post
You might also be interested to know, the elevation of the controller also affects it's lifetime, especially with respect to high voltages.

numerous studies have concluded that electronics are exposed to more cosmic radiation at high altitudes, and that high voltage electronics are affected the most. So it may be an important factor if you are running in high elevations.

interesting. I wonder if it's noticeable? I mean to the average electronics user. If being at 5000 feet reduces the average piece of electronics lifespan by 1% no one but a statistician will notice, but if it's 10% it starts to make a noticeable difference.
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Old 05-18-2012, 12:12 AM
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Default Re: High battery voltage and controller longevity

I would think the biggest effect of high altitude would be reduced cooling due to thinner air. The main effect of cosmic radiation is typically bit flips in system memory which can cause system instability and BSODs.
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Old 05-18-2012, 05:39 AM
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Default Re: High battery voltage and controller longevity

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Originally Posted by sheik480 View Post
If you feel so inclined, could you roughly estimate how much hotter it would run compared to a 60s system?
I can calculate the losses out exactly for a given operating point (input voltage, duty cycle, switching frequency, output current) but EV motor controllers aren't operated at a fixed operating point.

Assuming an output current of 400A and a switching frequency of 8kHz:

If you adjust the duty cycle so that the output power is the same then the losses are 3% higher at 300V vs. 200V.

If you keep duty cycle the same so that output power goes up with input voltage then the losses are 24% higher at 300V than at 200V.

Overall controller efficiency is at least 98% in all cases above as the total losses range from 550W to 700W while the output power ranges from 40kW to 60kW.
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Old 05-30-2012, 03:46 PM
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Default Re: High battery voltage and controller longevity

Quote:
Originally Posted by Tesseract View Post
I can calculate the losses out exactly for a given operating point (input voltage, duty cycle, switching frequency, output current) but EV motor controllers aren't operated at a fixed operating point.

Assuming an output current of 400A and a switching frequency of 8kHz:

If you adjust the duty cycle so that the output power is the same then the losses are 3% higher at 300V vs. 200V.

If you keep duty cycle the same so that output power goes up with input voltage then the losses are 24% higher at 300V than at 200V.

Overall controller efficiency is at least 98% in all cases above as the total losses range from 550W to 700W while the output power ranges from 40kW to 60kW.
I know you probably don't want to dig into this too much, send me a PM if this is getting too application specific but I'm looking to run around 96 cells because I'm looking to get fairly close to 20kwh and the 90Ah and 100Ah cells are too large for a 20kwh capacity and to maintain voltage for peak performance with a Kostov 220v(nominal) motor which means I'm looking at 60Ah cells(hoping Sinopoly makes it to the US because their 60Ah B-size cell is light and relatively small).

I'm looking to be pulling 10kw with a very light and aerodynamic car while cruising most of the time. If I'm at 300v(rounding the number for easy math) pulling 10kw which is about 33.3 amps from the batteries, and the motor is cruising at Kostov's high RPM and around 150v(66.6 amps), I'm trying to get a decent guess on efficiency losses, mostly because I'm trying to build an extremely efficient car that is 1900 pounds pre-conversion weight with excellent aerodynamics. I went with Kostov because their efficiency with their higher voltage Kostov 9 looks great and my only other option would be to run a lower voltage system with 100Ah cells using an Impulse 9 as a compromise motor but it looks on paper like that is a lower efficiency option and I'd lose highway passing performance(and acceleration in general unless I upped to a Sol 1 but that would be overkill for the car and to 100Ah Chinese prismatic batteries), and put myself at a disadvantage to the stock transmission gearing of the car.

It sounds like the efficiency loss at cruising would be minimal but I'd still like to quantify it in my most common scenario. I've had people PM me from the 1st Gen Honda Insight forums telling me to AC50 but I'm seeing much higher losses through the Curtis AC controller itself than I would through both an interpoled series DC motor and controller together.

Last edited by MN Driver; 05-30-2012 at 03:49 PM.
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