# AC/DC hybrid?



## Qer (May 7, 2008)

valerun said:


> Being AC and therefore more efficient


What's really amazing is that some AC-systems are more efficient than others, so by over simplifying things at this level it's possible to do a circular reasoning that will eventually prove that AC systems will generate more power than you provide from the pack, thus reaching an efficiency way above 100%. 

Or to be more serious; your statement might be true depending on what systems you compare. An AC-motor is often more efficient than a DC-motor, but an AC-inverter is, on the other hand, often less efficient than a DC-controller so the total efficiency of the system means that the AC-motor has to be so much better so it also compensates for the inverters lesser efficiency.

The efficiency of a motor is also depending on RPM, power, current and probably a few other factors as well, so there's a lot of things to be considered. A motor that runs outside it's optimum range will drop in efficiency which means that if you compare a system that run close to it's optimum parameters it is likely to be more efficient than one that doesn't (given a certain vehicle and other environmental factors), regardless of if they're AC or DC.

Also, even if you might improve efficiency by selecting a special motor and controller/inverter it's just one component in the whole efficiency puzzle. Other factors are transmission, brakes, tires, air resistance, batteries etc.

I'm not saying there isn't AC-systems that are more efficient than DC-systems, but what I say is that the assumption that this is some kind of generic rule is flawed and that in reality the difference might not be quite as noticeable that you're sometimes lead to believe and that other factors might be of greater importance than AC or DC.

Another thing to consider is that doing an AC/DC-hybrid like you're considering might hurt efficiency since it'll add weight and also a bit of more friction (two motors that spin). Also, making the vehicle more aero dynamic, replacing the lubricants in the transmission, going for tires with less friction or getting a battery pack with lower internal resistance (thus less losses) are other things to achieve better over all efficiency which might be better solutions for you.


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## major (Apr 4, 2008)

valerun said:


> What do you guys think?


Bad idea  In my opinion 



> Has anyone done it before?


Not to my knowledge.



> Any links / pointers?


If you think that highly of the AC, drop the DC and get yourself a suitable AC drive 

Regards,

major


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## steven4601 (Nov 11, 2010)

AC50 is not designed for 360VDC.

Why not step things up a little? A tritium wavesculptor 200 (165kva), an EVE M3AC60 should give you 90kW (300nm upto 3500rpm) (possibly even 120kW )
Should be fun. Hope it will be in my Z3


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## dimitri (May 16, 2008)

So, in a quest for more efficiency you want to add 150lb to the car? 

You can't use 340V pack for AC50, so now you also need DC-DC conversion or a separate pack for AC50...

all in all, might as well spring for high power AC system and dump the hybrid idea...


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## valerun (Nov 12, 2010)

Qer said:


> the assumption that this is some kind of generic rule is flawed and that in reality the difference might not be quite as noticeable that you're sometimes lead to believe and that other factors might be of greater importance than AC or DC.
> 
> Another thing to consider is that doing an AC/DC-hybrid like you're considering might hurt efficiency since it'll add weight and also a bit of more friction (two motors that spin).


these are very good points. take weight, for example. AC50+controller is ~150lbs. This is ~20 100AH cells, or ~6kWhrs or 20 miles of range - or 25% on top of the, say, 80-cell pack. Too bad I top out at 100 cells with Soliton1 - this actually limits my ability to upgrade for range by adding cells. As I will most likely be using 11HV, I already have to have at least 90 cells to use the full torque band... Not much room left...


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## valerun (Nov 12, 2010)

major said:


> If you think that highly of the AC, drop the DC and get yourself a suitable AC drive


 Thanks Jeff. suitable AC drive tends to cost more than the whole DC conversion... As we are trying to come up with the conversion services that could have a chance in the marketplace at scale, this is a no-go.


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## Bowser330 (Jun 15, 2008)

valerun said:


> these are very good points. take weight, for example. AC50+controller is ~150lbs. This is ~20 100AH cells, or ~6kWhrs or 20 miles of range - or 25% on top of the, say, 80-cell pack. Too bad I top out at 100 cells with Soliton1 - this actually limits my ability to upgrade for range by adding cells. As I will most likely be using 11HV, I already have to have at least 90 cells to use the full torque band... Not much room left...


What about bumping up to the CALB 130AH cells?


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## valerun (Nov 12, 2010)

Bowser330 said:


> What about bumping up to the CALB 130AH cells?


Yea. But where will the 90 100AH cells go then (my current pack)? ;-)


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## Bowser330 (Jun 15, 2008)

valerun said:


> Yea. But where will the 90 100AH cells go then (my current pack)? ;-)


Im sure you could unload them to another DIY'er for close to what you purchased them for....


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