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#11
 
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Re: OT: electric supercharging -
09-24-2009
, 11:19 AM
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*A turbocharger prespin setup would be much more effective, and simpler - but does play havoc with emission controls. (it consists primarily of a small injector feeding fuel into the exhaust ahead of the turbo) NO turbo lag. |
solution -- NO havoc for the emissions.
Yousuf Khan
#12
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JD wrote: It would still take WAY more electricity than the car's electrical system can deliver. Guess that depends on how many amps your alternator can put out, how much is consumed during driving (after startup), and the difference left over for reserve (usable to other devices). I doubt that the load by this pre-booster is large or sustained. Just a short burst (surge) of boost is all that is needed to compensate for turbo lag. Even if it could, the electrical losses would limit how much boost could be provided at any range. All the blower has to do is pressurize the exhaust from the fan. Doesn't take much horsepower to run an electrical motor even at 70K RPM. I do doubt that it provides as much boost as the turbocharger. It just provides SOME boost before the turbo kicks in (i.e., to eliminate the turbo lag). That's why I said you need to look at their chart and then create a NEW chart that shows the *differential* between the boost afforded from the start of the curve to when the turbo takes over. That differential shows the pre-boost isn't that high. If you look at their chart, their pre-boost unit only provides half the boost and only over a small 500 RPM range (between 1000 to 1500 RPM). |
Assume 2000 RPM
Assume 100% Volumetric efficiency.
That is 250 CFM of air required at atmospheric pressure.
To provide 8PSI boost at this airflow reqiuires something in excess of
5HP with a centrifugal blower. As the air demand increases, and
therefore the blower speed, the power rquirement escalates extremely
quickly to over 20 HP at 5500 engine RPM.
A positive displacement supercharger like a Whipple requires
considerably less horsepower - and boost is constant, while boost
rises with speed with an engine driven centrifugal blower.
To get any kind of effect on a turbo 3.8 with an electric supercharger
at low engine speeds, I would expect a minimum requirement of 5HP, or
aproxemately 5Kw of electrical power. On a 12 volt system (14 volts
running voltage) that is over 350 amps - significantly more current
than the average starter motor draws (over twice, being optimistic).
Starting current on a series wound motor (almost a requirement to get
the accelleration required to get the blower up to speed quickly)
would be in the range of 3 to 10 times running current - so to be
optimistic again, roughly 1000 amps starting surge.
Using a "softer starting" motor would give you the "turbo lag" you are
trying to get away from.
If the system could "anticipate" your throttle opening and start ahead
of time, the 350 amps would be adequate - but that is certainly not
within the realm of feasibility.
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A direct-drive supercharger would be FAR more efficient in combination with the turbo. But is still dependent on engine RPM whereas there is no RPM dependency for an electrically controlled supercharger. |
a Whipple, there is no speed dependency. Full boost, within a few
percent, is on tap at all times. Boost is determined by the ratio
between engine displacement and supercharger displacement and the
drive ratio.
Quote:
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Turbochargers have a definite lag before there is enough exhaust flow to spin its fan fast enough to pressurize its output. Supercharger boost (for dynamic compressor types) are dependent on the engine RPM. This VTES pre-boost supercharger isn't to add more horsepower but simply move the curve of when it is available. I don't think the point of the experiment was to create a monster horsepower car but to eliminate the turbo lag. Nowadays the throttle response for turbochargers is nearly the same to mechanically powered superchargers. Both still have lag. The VTES description says it is a compressor type supercharger so there would also be lag if it were dependent on the engine RPM; however, since it is electrically controlled, it can be made to provide boost faster than for the increase in engine RPM. Having this pre-booster handle the low RPM range also means a larger turbocharger (with more lag) could be put into the car to provide even more horsepower. "The supercharger¢s speed can increase from zero up to 70,000rpm in less than 1/3 of a second. |
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So how much lag is there with a compression-type supercharger? How much does the RPM have to come up before there is effectual pressurization? An electrical supercharger doesn't have lag but might not be able to handle as large a load for sustained periods - but then it doesn't look like this was a standalone solution, either. With your turbocharged car and mashing down on the accelerator, how long before you feel that rush of power kicks in? With your supercharged car, how long after mashing the accelerator before you get a significant increase in horsepower? Does a mechanically-driven supercharger based on the engine's RPM not have any lag? The article says they are using a 25kW electrical motor at 12V. There's no way they're going to get over 2000 amps from the alternator. I doubt their motor is consuming 25kW but is instead simply designed to operate at that current load for a sustained period because it makes for a motor that can handle a large surge current. It's a peak (or spike) rating, not a sustained rating. It might be that, yes, this motor can take a high surge current for quick spin-up but it cannot be sustained. Maybe it's only designed to handle the pre-boost load for a couple of seconds (until when the turbo is expected to kick in). |
second to spin it up.
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With that short blurb of a "news" article, there are just too many variables in implementation that are unknown. More info is definitely needed. |
#13
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On Sep 23, 7:55Â*pm, cl... (AT) snyder (DOT) on.ca wrote: Â*A turbocharger prespin setup would be much more effective, and simpler - but does play havoc with emission controls. (it consists primarily of a small injector feeding fuel into the exhaust ahead of the turbo) NO turbo lag. Well, I guess that's exactly the reason they came up with this solution -- NO havoc for the emissions. Yousuf Khan The tradeoff is large current spikes being drawn from the battery - |
The electrical efficiency will be quite low - convert engine power to
electrical using innefficient automotive alternator, store generated
power in lead acid battery, then pull it out and run a low-efficiency
high power electric motor..
I don't buy it.
#14
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Assume a 3.8 liter engine. |
thing is obviously intended for small engines in the 1 L range. A 3.8
will have quite a bit of torque without needing this supercharger.
Yousuf Khan
#15
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So it is over a very short burst or surge that the VTES gets used. *At 1000 RPM, isn't that around 2.5 seconds? *I also suspect that with the 0.3 second ramp up to 70K RPM that there isn't a huge air flow involved so it's just for small engines, like 1.2 liter. |
combustions, which a four cylinder has 2 of on each crank rotation. So
in the first five crank rotations. Or it mean combustion events per
cylinder, which would be 20 rotations for any piston engine.
Regardless, even at 1000 RPM it is much quicker than 2.5 seconds.
The 5 rotations happen in 1/200 of a second at 1000 RPM, which is 0.3
seconds. Even if it were 20 rotations, it would be 1.2 seconds. At say
3k RPM it woudl be 0.1 to 0.4 seconds.
#16
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As for an electric boost - I have doubts it's efficiency would improve over the use of fuel to keep the turbo spinning. But perhaps a large capacitor bank could be used to dump the required energy into an electric blower. I suppose it's only intended for starts from near idle, so recharging the caps could occur over time at cruise speed. Still, dunno under what driving conditions this would be useful. Autocross? drag racing? Daily driver? They all would need different configurations I guess. |
something like a 1L engine, then turbocharging takes care of the high-
end power problem, but low-end power would require a supercharger.
Once the turbocharger takes over, then the supercharger is no longer
needed, so an electric supercharger can be shutoff completely.
Yousuf Khan
#17
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JD wrote: It would still take WAY more electricity than the car's electrical system can deliver. Guess that depends on how many amps your alternator can put out, how much is consumed during driving (after startup), and the difference left over for reserve (usable to other devices). I doubt that the load by this pre-booster is large or sustained. Just a short burst (surge) of boost is all that is needed to compensate for turbo lag. |
and the reason they don't generally build electric superchargers is for that
very reason. Power is not free; to make it, requires gas.
Quote:
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Even if it could, the electrical losses would limit how much boost could be provided at any range. All the blower has to do is pressurize the exhaust from the fan. Doesn't take much horsepower to run an electrical motor even at 70K RPM. I do doubt that it provides as much boost as the turbocharger. It just provides SOME boost before the turbo kicks in (i.e., to eliminate the turbo lag). That's why I said you need to look at their chart and then create a NEW chart that shows the *differential* between the boost afforded from the start of the curve to when the turbo takes over. That differential shows the pre-boost isn't that high. If you look at their chart, their pre-boost unit only provides half the boost and only over a small 500 RPM range (between 1000 to 1500 RPM). |
the engine) takes a BIG electric motor.
Quote:
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A direct-drive supercharger would be FAR more efficient in combination with the turbo. But is still dependent on engine RPM whereas there is no RPM dependency for an electrically controlled supercharger. |
electric motor. In addition, the electric supercharger would draw enough
power that even at idle, the car would be a considerable gas hog just to get
to ambient pressure. You would be better to size a direct-drive
supercharger and a wastegate for the application.
Quote:
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Turbochargers have a definite lag before there is enough exhaust flow to spin its fan fast enough to pressurize its output. Supercharger boost (for dynamic compressor types) are dependent on the engine RPM. This VTES pre-boost supercharger isn't to add more horsepower but simply move the curve of when it is available. |
applications.
Quote:
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I don't think the point of the experiment was to create a monster horsepower car but to eliminate the turbo lag. Nowadays the throttle response for turbochargers is nearly the same to mechanically powered superchargers. Both still have lag. The VTES description says it is a compressor type supercharger so there would also be lag if it were dependent on the engine RPM; however, since it is electrically controlled, it can be made to provide boost faster than for the increase in engine RPM. Having this pre-booster handle the low RPM range also means a larger turbocharger (with more lag) could be put into the car to provide even more horsepower. |
electric motor would lose 10% over direct-drive drive and the size of the
motor would be a limiting factor. A direct-drive supercharger requires a
belt or chain. An electric supercharger of that size would require a huge
motor and monstrous cables to conduct the electricity. Its all about
conservation of energy and you can't beat the physics yet.
Quote:
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"The supercharger¢s speed can increase from zero up to 70,000rpm in less than 1/3 of a second. |
lire engine just to ambient, would require a fan to move more than 600 cubic
feet per minute of air. That is a lot of air.
Quote:
|
So how much lag is there with a compression-type supercharger? How much does the RPM have to come up before there is effectual pressurization? An electrical supercharger doesn't have lag but might not be able to handle as large a load for sustained periods - but then it doesn't look like this was a standalone solution, either. With your turbocharged car and mashing down on the accelerator, how long before you feel that rush of power kicks in? With your supercharged car, how long after mashing the accelerator before you get a significant increase in horsepower? Does a mechanically-driven supercharger based on the engine's RPM not have any lag? The article says they are using a 25kW electrical motor at 12V. There's no way they're going to get over 2000 amps from the alternator. I doubt their motor is consuming 25kW but is instead simply designed to operate at that current load for a sustained period because it makes for a motor that can handle a large surge current. It's a peak (or spike) rating, not a sustained rating. It might be that, yes, this motor can take a high surge current for quick spin-up but it cannot be sustained. Maybe it's only designed to handle the pre-boost load for a couple of seconds (until when the turbo is expected to kick in). With that short blurb of a "news" article, there are just too many variables in implementation that are unknown. More info is definitely needed. |
can handle 25KW, and most 25 KW motors are several hundred pounds.
#18
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On Thu, 24 Sep 2009 08:19:19 -0700 (PDT), YKhan <yjkhan (AT) gmail (DOT) com wrote: On Sep 23, 7:55 pm, cl... (AT) snyder (DOT) on.ca wrote: A turbocharger prespin setup would be much more effective, and simpler - but does play havoc with emission controls. (it consists primarily of a small injector feeding fuel into the exhaust ahead of the turbo) NO turbo lag. Well, I guess that's exactly the reason they came up with this solution -- NO havoc for the emissions. Yousuf Khan The tradeoff is large current spikes being drawn from the battery - and the emission hit would be very short too - like the current draw. The electrical efficiency will be quite low - convert engine power to electrical using innefficient automotive alternator, store generated power in lead acid battery, then pull it out and run a low-efficiency high power electric motor.. I don't buy it. |
#19
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On Sep 25, 8:21Â*am, 1 Lucky Texan <alcky... (AT) swbell (DOT) net> wrote: As for an electric boost - I have doubts it's efficiency would improve over the use of fuel to keep the turbo spinning. But perhaps a large capacitor bank could be used to dump the required energy into an electric blower. I suppose it's only intended for starts from near idle, so recharging the caps could occur over time at cruise speed. Still, dunno under what driving conditions this would be useful. Autocross? drag racing? Daily driver? They all would need different configurations I guess. I'd say they're mainly aiming it at the daily driver. If you've got something like a 1L engine, then turbocharging takes care of the high- end power problem, but low-end power would require a supercharger. Once the turbocharger takes over, then the supercharger is no longer needed, so an electric supercharger can be shutoff completely. Yousuf Khan And a 1 liter vehicle is going to have a battery capable of |
system capable of replentishing said battery?
I'm still sceptical.
At best.
#20
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"VanguardLH" <V (AT) nguard (DOT) LH> wrote in message news:h9ftsr$t3j$1 (AT) news (DOT) albasani.net... JD wrote: It would still take WAY more electricity than the car's electrical system can deliver. Guess that depends on how many amps your alternator can put out, how much is consumed during driving (after startup), and the difference left over for reserve (usable to other devices). I doubt that the load by this pre-booster is large or sustained. Just a short burst (surge) of boost is all that is needed to compensate for turbo lag. It doesn't matter. There are electrical losses no matter how you size it up and the reason they don't generally build electric superchargers is for that very reason. Power is not free; to make it, requires gas. Even if it could, the electrical losses would limit how much boost could be provided at any range. All the blower has to do is pressurize the exhaust from the fan. Doesn't take much horsepower to run an electrical motor even at 70K RPM. I do doubt that it provides as much boost as the turbocharger. It just provides SOME boost before the turbo kicks in (i.e., to eliminate the turbo lag). That's why I said you need to look at their chart and then create a NEW chart that shows the *differential* between the boost afforded from the start of the curve to when the turbo takes over. That differential shows the pre-boost isn't that high. If you look at their chart, their pre-boost unit only provides half the boost and only over a small 500 RPM range (between 1000 to 1500 RPM). If you do a bit of math, to get even 10 PSI (to overcome just the vacuum of the engine) takes a BIG electric motor. A direct-drive supercharger would be FAR more efficient in combination with the turbo. But is still dependent on engine RPM whereas there is no RPM dependency for an electrically controlled supercharger. |
Quote:
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An engine idling at 600 RPM will generate far more boost than a small electric motor. In addition, the electric supercharger would draw enough power that even at idle, the car would be a considerable gas hog just to get to ambient pressure. You would be better to size a direct-drive supercharger and a wastegate for the application. |
Not to mention if you did not disable the alternator when boost was
called for, it would draw so much power from the engine you would have
a severe stumble just from the power consumption of the alternator.
I'm still not buying.
Quote:
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Turbochargers have a definite lag before there is enough exhaust flow to spin its fan fast enough to pressurize its output. Supercharger boost (for dynamic compressor types) are dependent on the engine RPM. This VTES pre-boost supercharger isn't to add more horsepower but simply move the curve of when it is available. I doubt it works. There are serious limitations to electric motors for such applications. I don't think the point of the experiment was to create a monster horsepower car but to eliminate the turbo lag. Nowadays the throttle response for turbochargers is nearly the same to mechanically powered superchargers. Both still have lag. The VTES description says it is a compressor type supercharger so there would also be lag if it were dependent on the engine RPM; however, since it is electrically controlled, it can be made to provide boost faster than for the increase in engine RPM. Having this pre-booster handle the low RPM range also means a larger turbocharger (with more lag) could be put into the car to provide even more horsepower. That is assuming it has the power to do that; which it won't. A typical electric motor would lose 10% over direct-drive drive and the size of the motor would be a limiting factor. A direct-drive supercharger requires a belt or chain. An electric supercharger of that size would require a huge motor and monstrous cables to conduct the electricity. Its all about conservation of energy and you can't beat the physics yet. "The supercharger¢s speed can increase from zero up to 70,000rpm in less than 1/3 of a second. That's great. Gor how many cubic feet of air per minute? To charge a 2.5 lire engine just to ambient, would require a fan to move more than 600 cubic feet per minute of air. That is a lot of air. So how much lag is there with a compression-type supercharger? How much does the RPM have to come up before there is effectual pressurization? An electrical supercharger doesn't have lag but might not be able to handle as large a load for sustained periods - but then it doesn't look like this was a standalone solution, either. With your turbocharged car and mashing down on the accelerator, how long before you feel that rush of power kicks in? With your supercharged car, how long after mashing the accelerator before you get a significant increase in horsepower? Does a mechanically-driven supercharger based on the engine's RPM not have any lag? The article says they are using a 25kW electrical motor at 12V. There's no way they're going to get over 2000 amps from the alternator. I doubt their motor is consuming 25kW but is instead simply designed to operate at that current load for a sustained period because it makes for a motor that can handle a large surge current. It's a peak (or spike) rating, not a sustained rating. It might be that, yes, this motor can take a high surge current for quick spin-up but it cannot be sustained. Maybe it's only designed to handle the pre-boost load for a couple of seconds (until when the turbo is expected to kick in). With that short blurb of a "news" article, there are just too many variables in implementation that are unknown. More info is definitely needed. There is no way that any cable in any car (except hybrids and electric cars) can handle 25KW, and most 25 KW motors are several hundred pounds. |
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