Open Source Electric Supercharger

[AN]

Originally Posted by neutron256

http://www.ebay.com/itm/Maxwell-1500...item461a649e50

That's a very good option ... I did not look at these smaller ultra caps ... looks like they can carry a lot of juice ... some quick calculations :

if all 12 wired in series we will have a system good for:

Max Voltage : 27v X 12 = 32.4V
Total Capacitance: 125 Farad
Total energy saved @ 28.5 V : (C/2) x V^2 = 50.7 KJ.

Keep in mind this is about 40% of the power stored the Phantom setup. Thats a lot of Jouls .. most importantly immediately available .. unlike the lead-acid batteries.

If used in conjunction with 4X 10Ah batteries (which are very compact) .... it would be more than enough for even very demanding motors.

I need to look up if this has been done elsewhere for any other energy demand.

[AN]

could be a really silly idea .. but can we use an EDF motor as a co-axial compressor ...

e.g. http://www.hobbyking.com/hobbyking/s...Rotating_.html

There are a lot more powerful ones too ...

[neutron256]

Originally Posted by AN

could be a really silly idea .. but can we use an EDF motor as a co-axial compressor ...

e.g. http://www.hobbyking.com/hobbyking/s...Rotating_.html

There are a lot more powerful ones too ...

Check out around Page 18 of this thread. Someone did a long writeup about an idea for using a co-axial compressor with two motors spinning counter rotating wheels. I don't think it's a design I would try but the writeup is pretty detailed and I certainly learned a lot about co-axial compressors.

[rusty959]

Originally Posted by AN

Actually no .. since it will be in parallel to the battery , its voltage will not drop a whole lot more than the battery ... as immediately charges itself from the battery. Those combo will not discharge quicker than the battery alone. The cap only increases the systems ability to provide high spikes in current demand ... which the 1.5 pack shows is a bottleneck for the Pb-Acid batteries for this scenario.



We can find some caps that surge at 30V. Even if we have to put 2 caps in series ... the capacitance halves but energy storage doubles ... given twice the voltage ... we do not have to go huge on caps in the first go around ... I think 2x of the most compact caps with 10+ F in parallel should do the trick ... again .. not for primary energy delivery but to ease the most extreme loads on the battery pack. What implication will it have on the motor controller ... I am not sure ...

Please note in my theoretical statement I never mentioned nor implied that there was a battery in parallel. I only mentioned capacitance. I wasn't trying to say that 60F is useless completely.

Also, calculating energy is mostly worthless in this situation, especially with the way brushless motors work. With any direct drive setup we currently have, the RPM is critical, and we are maxing these motors out. Max motor speed is directly related to Voltage, so if you spec a motor that hits max rpm at that 28.5V and then the voltage drops to 22V, you all of the sudden lose thousands of RPM which is a significant loss, especially when engine RPM is typically climbing at the same time.

Now, as soon as a system comes along that doesn't need to max out motor RPM (such as a centrifugal supercharger based setup) the charging systems will be less important and wont require such a focus at keeping absolute best voltages. But at that point I would probably just run a 12v based setup, as then you could just throw in a nice 12V battery and call it a day. (although it is harder to find a ESC that can handle the current needed for a 12v setup, depending on your goals)

[neutron256]

Good to see all the discussion around this. It's getting me fired up to start working on this again. I can't wait for my SeaDoo supercharger to get here so I can start tearing it apart and adapting it. It will still be a direct drive but the compressor is engineered to work a slower RPMs so this might be a great solution.

Ideally I want to design a compressor setup that could be built in their basement by someone with a drill press and other basic tools. However for this SeaDoo setup I will use whatever tools and experience I have at my disposal to get a solid working prototype. Then I can go back and try and simplify the build process.

While I wait for parts to arrive I've been thinking of a better cleaner charging system. I need to take some measurements, but I think there is enough room to create a 24v system that integrates all three batteries along with the MinnKota charger in the stock battery location. It would be great to have this be boxed into one solid unit that that just swaps out with the stock battery.

I just got my new puppy yesterday which is sucking up most of my time, but if I can get her to take some naps today I will see if I can model the battery/charger concept tumbling around in my head.

[neutron256]

So I got my SeaDoo supercharger compressor today. Here it is next to a T3/t4 compressor wheel to give you an idea what a major difference in size there is. I'm hoping this will be a good fit for a larger motor with lower max RPMs.

The larger size of the wheel also gives me more options for coupling it to the motor shaft.



Edit: For some reason my dog absolutely hates the sound of me routing the shaft in the compressor housing.

[neutron256]

The SeaDoo compressor wheel diameter is 128mm vs. 70mm on the T3/T4 wheel. That's 82% greater speed at the outer edge at the if spun at the same RPM.

[AN]

Sweet .. I hope it works ... So you will be coupling it with Turnigy Aquastar T20 ? Will you wire it Y or Delta ? What RPM do you expect this setup to run ... also .. any maps for this seadoo compressor ?

[neutron256]

Originally Posted by AN

Sweet .. I hope it works ... So you will be coupling it with Turnigy Aquastar T20 ? Will you wire it Y or Delta ? What RPM do you expect this setup to run ... also .. any maps for this seadoo compressor ?

The documentation doesn't make it clear but the AquaStar T20 is limited to 23V in Delta configuration. So I'll be running it in a Y configuration that in theory will give me about 20K rpm.

I also have my eye on another motor that would run a little faster about 24K rpm. http://www.hobbyking.com/hobbyking/s...m_Fan_5kw.html


Edit: I haven't been able to find any compressor maps but from what I gather in the 1.8L engine running at 8500 RPM it's designed for it will produce about 14psi. Figuring the gear ration that is a compressor speed of about 45K RPM.

If anyone can find a compressor map for this it would be very helpful, even though you really don't know until you test it. The engine is actually built by Rotax.

[rusty959]

Just throwing this out there... and don't come running to me if you try it and something blows up... but your two battery setup will be pretty close to 23V under load once you factor in all the resistance. (this can be seen in the phantom setup) Considering the short duty cycle you will be using, it might be fine still. I don't recall what ESC you are using, but the bigger problem might be getting the extra current through it.

[neutron256]

Originally Posted by rusty959

Just throwing this out there... and don't come running to me if you try it and something blows up... but your two battery setup will be pretty close to 23V under load once you factor in all the resistance. (this can be seen in the phantom setup) Considering the short duty cycle you will be using, it might be fine still. I don't recall what ESC you are using, but the bigger problem might be getting the extra current through it.

I've considered that, and might try it depending on what sort of results I get. The thing is if it were just running a 23V motor at 24V maybe no big deal, but it's really running it at as high as 28V and I don't think the motor would hold up long to that.

I'd be more likely to run a 36V (42V peak) system with the AquaStart in a 'Y' configuration. That would do around 30K RPM and a lot more torque to actually spin it at that speed. The problem with that is that for my purposes 36V makes for a very large unwieldy system.

[neutron256]

Building this compressor design may be easier then I was expecting. I ordered a collet style prop adapter. It's almost perfect. The only real problem is that the nut is right hand thread so I would need to make sure it doesn't loosen with use. Maybe a castle nut and lock wire or cotter pin.

With this one I would also need to make a custom washer to make sure the wheel is centered on the shaft. I'm looking for a version with an M10 thread that will fit the 10mm hole.

I've even got an idea for mounting the motor that should be pretty simple, but I need to fully disassemble the compressor firts which requires some speciality tools which I just ordered.

[AN]

Thats great to hear that the coupling is easier on the new compressor. Btw .. have you seen this motor ? 7000W , 35000rpm. Little pricey but part of the money can be recuperated by selling the edf assembly.

http://www.hobbyking.com/hobbyking/s...watt_12s_.html

[neutron256]

Originally Posted by AN

Thats great to hear that the coupling is easier on the new compressor. Btw .. have you seen this motor ? 7000W , 35000rpm. Little pricey but part of the money can be recuperated by selling the edf assembly.

http://www.hobbyking.com/hobbyking/s...watt_12s_.html

Holycow that thing is a real beast. But at only 700kv you're depending on pretty high voltage, plus it's an outrunner motor which might not be bad, I just don't personally have much experience with them.