No .... will just have to see how it holds up.

Another good reason for not going too overboard on boost.

 

Seems like the biggest impediment is that you can’t really have enough electricity storage and regeneration (charging from alternator) to replenish batteries for 100% use or even close. I saw in a review that basically with a system kit like TORQAMP you get 4 minutes of operation for every 40 minutes of downtime to allow battery to cool down and recharge. Compared to turbocharging (exhaust energy harvesting) and supercharging (belt driven) electric turbocharging is the worst (and significantly so) parasitic demand (even if not in real-time). Rather than going with an electric turbo it seems a supercharger would be a superior choice to achieve about the same effect compared to an electric turbo or better yet just hybridize the two to minimize the use of the electric turbo. I can see the benefit of either supercharging or electric turbocharging vs exhaust turbocharging because there would be little back pressure (provided high flow or no cat) putting less stress on the engine. Although it would seem turbocharging is favored because it yields the least parasitic losses thus best HP increases per psi of boost. Anyways, supplementing with an electric turbocharging can eliminate turbo lag - some car manufacturers are doing just that.

 

I think what I have is better than that but essentially you are correct.
What most people don't think about however, is that with a turbo or SC you are NEVER on boost 100% of the time. So lets look at different scenarios and alalyse where this concept could work:

Roadcourse Track car ; Lets just say you are on boost for 50% of the time - so even with a better charger and much bigger batteries than what I currently have you will be struggling to make it last more than about 10 mins. Most races and track day sessions are timed for around 20mins. So ..... No

Autocross: Only lasts a minute and there are long waits between runs - ample time to allow a recharge. So ...Yes

Street car driven around town: Usually this involves sporadic short periods into boost intermingled with longer periods of cruising/recharging. So ...Yes.

Twisty road weapon: My longest runs doing this usually are no more than 20mins but the time on boost is dramatically less than a race track. From my logs I estimate it's less than 10% of the time. This is my aim for the car and I'd say it falls short currently. But with some improvements a definite ...maybe!

Long drives with occasional boosting : Depending on how much you are hammering it and for how long ..............YES

Drag racing ... A definite YES

Cruise/drag sessions here in NZ like : madmikes summerbash/chrome/rotary REunion ETC. These are not race meetings but it's where you can cruise around the track and have the occasional roll race with whoever is nearby at the right part of the track ............ YES

Roll Racing ..... One 10 second roll race followed by a sedate lap around the track with some wait time before the next 10 second race. ..........YES

Not much there that can't be done - even with my current very limited setup.
Although my current setup isn't going to win many drag/roll races I've really only scratched the surface of what's possible. There's no reason I couldn't have a 'high boost' setting just for these activities.

 

Brettus -

Maybe I missed it in the message chain, but have you considered or investigated higher output alternator options. I don’t think an alternator would get you to the point of sustaining turbo demand separate of battery storage, but it could change that operation/recharge duty cycle from 10% to maybe 15-20%. Of course that will be a larger parasitic load if it’s just a dumb (no electronic smarts) alternator/charging circuit.

I would believe ECU mapping should be much easier with an electric turbo vs exhaust driven because you can more predictably control the boost either by pedal engagement, on/off switch, etc.

 

Yes ....a larger alternator doesn't help with the components I currently have but a higher voltage one definitely would. The charger can handle 11-50V input . Have been looking at 24v 60-80A alternators, with which I could double the charge wattage. A lot of learning for me on how to integrate one seamlessly though.

 

I must admit this is looking like a more attractive option to explore for someone who just wants to do a modest 3-4psi of boost with minimal modifications or having to build a new engine with lower compression rotors. I’m curious to see where this goes. It seems like a relatively low cost option to get maybe +50HP with pretty minimal mechanical work. The TORQAMP Lite system can be had for a little over $2K and produces 5.8psi max. My question for them is if that can be limited but I would imagine it can be. From what I understand you really can’t boost an NA rotary more than 5psi without flirting with disaster……

 

I looked at the Torqamp, but when I saw that's it's maximum flow was only a little over half of what a Renesis can flow N/A , I knew it would be useless at the top end. Would be really handy to know how they are doing their battery management etc though!

 

That’s good to know. I couldn’t find that information, but I didn’t look too hard yet. So basically the TORQAMP is going to work like a supercharging and kill high RPM power/torque…

As I understand the system has an integrated charging/discharging controller that will turn off battery charging when you turn on boost with either a switch, ECU PWM, etc. and allow power to turbo. It has some heat management provisions as well to disable turbo compressor when battery packs get too hot. It has an integrated charging controller which will tap 500W off standard alternator and step up regulate from 12V to 48V battery. All these things aren’t too complicated from an electrical standpoint. Although that’s coming from an electrical engineer…. TORQAMP probably has all this integrated on a circuit card but one could probably find these components off the shelf and integrate them together.

Have you provided a link to the turbo you are using and what is the max flow rate needed by Renesis at 8500RPM (1.3L x 8500RPM / 60sec/min = 185L/s)?

 

I don't know that TA would kill top end .... but it certainly wouldn't make any boost past about 5000rpms. You would get a decent bump in torque from 3-4000rpms - more than I'm seeing with my setup. But two TA units in parallel would barely do what mine is doing at the top end.

My background is Mechanical Engineering - building circuit boards to do all that is beyond me.

A (good) Renesis flows 220g/s at 8500. The TA falls on it's face at 140g/s. The unit I'm using is capable of flowing approx. 700g/s at 2.0 PR.

 

In certain instances I think it's appropriate to mention how well a high compression / low boost engine performs in terms of response and available off boost power. The Renesis is perfect for the e-charger project (imo) where only a few psi are needed to make modest gains that will arguably fill in some of the performance gap people may think is lacking. Some of the most enjoyable / fun cars feature a high revving engine paired with a small turbo and that's not a coincidence. ymmv.

And wow 700g/s is a lot of air. Can't wait for more updates.

 

Agreed. I think the lack of EMAP means it should be relatively safe at these boost levels even though peak IAT is into the 50s C .
I have noticed however, that power does drop off as ambient temp goes up and heat soak comes into play. I think some water/meth cooling will be beneficial to extract the most power from it. A very different scenario to my turbo setup though, as that already does have a very efficient IC.

 

Some eturbo sounds

 

Crystal meth should take the experience to the next level Since the compressor is not spinning as fast as a turbo, maybe it would work reliable to spray before SC? If memory serves me right, there are some benefits doing that.

 

Might be worth trying for sure! Have been pondering where the best place to have it would be , might have to do some sperimentin'.

 

Friends(reliable) experience on an old turbo Kawasaki was 0.7Bar before knock without, 1.2Bar with. Simple washer fluid spray in front of compressor, that together gave usable atomization.

One idea to reduce stress of water impact on blades may be to direct the spray close to center of wheel, where speed of the blades are lower, then let the blades sling it out. Must be tested as you say.

 

Xmas came early for Bluey.
Hope these will do the business!

 

You are doing gods work here, wishing you all the success so I can selfishly try this later on the cheap

 

Looking back through your implementation, I notice you have the compressor before the MAF sensor. How does this affect measured air flow. I assume it is still used and you are tuning the factory ECM? I don’t have experience boosting an RX-8 but from what I’ve read convention states to put the compressor after the MAF. Can you educate me on this?

 

Where I have it is a terrible place to have it and I would discourage anyone from trying it. I did it , essentially, because I wanted IAT information and was being lazy. I was only able to tune it like this with some 'trickery' and it's fine as is ...for now.

 

That’s good to know. The implementation looks the easiest, so I understand why you would do it that way. I assume your goal is to ultimately come up with a robust and stable solution that the rest of us could hopefully duplicate . Which means the final implementation will look a lot different.

 

The risk with the batteries is not something I'd like to be encouraging others into. May well invest in a safer, larger, heavier, more powerful battery pack in the future and dial up the boost. Not sure if it's something that others would be interested in though.

 

With regard to batteries overheating or longevity/charge/discharge cycles? It’s possible to put temperature sensors on the batteries and disable the system powering compressor in response if overheating is a concern. Ultimately this type of system should have switching between charging or discharging batteries, but not do both at the same time. Essentially when no boost, recharge batteries. When boosted disconnect batteries from alternator and only discharge into compressor. Also I would assume you locate batteries in trunk to avoid engine heat and provide safety to driver. Even if you go with higher capacity, “safer” batteries, you are going to need provisions to monitor and protect against overheating. Then secondarily you want to protect battery life too by knowing when to stop discharging the batteries and disable the compressor…

The TorqAmp system compressor doesn’t provide enough flow like you said but the electronics are pretty robust from a requirements/safety standpoint. I considered what if you used two of their compressors in parallel…. That gets more expensive but at 2 x 140g/s that should still give you at least 3-4psi at 8500RPM. You’d still want a bypass valve for when compressors off. You do start paying up closer to an exhaust driven turbo setup though…

The real question is can you do your own system for cheaper that is better suited to the Renesis. One turbo instead of two has appeal for simplicity sake. But I think doing your own electronics gets a lot more complicated and you really need to come up with a set of requirements to cover all the contingencies that may arise in this type of system. I’m tempted to sketch up a block diagram of what all the electronics need to ultimately be and just throw on this forum posting.

 

1/I do have a temp. sensor and charging is disabled if set temp. is reached.
2/Think about what is happening to all the charging energy while the batteries are being discharged. I'm no EE but I'd bet it's ALL going to the compressor and none is going to the batteries. I'm thinking electric energy is going to take the path of least resistance - just like compressed air. Correct me if I'm wrong here!
3/The ESC has a low voltage safety which prevents compressor starting if it voltage gets low.
4/New batteries are rated for 5C charging and I'm only charging at 1C.
5/Batteries are stored in the front bumper, so lots of ambient air flow over the batt. box.

So between these measures (along with full balance charging) I believe I have battery safety covered and it's fine to leave the charger going all the time while the engine is running. I have the old batteries out now and there is no sign of any issues.
BUT and it's a big but ..... there's still a risk with these LIPOs.


Really don't like the idea of buying two TA compressors + two controllers etc. The cost is too high relative to the alternatives and the complexity doubles both electrically and mechanically.

 

The biggest problem with LIPOs is going to be heat…

#1 - you also need to disable discharging too when overheated. That’s actually going to cause much more battery heating due to higher current than charging.

#2 - Yes you are right if you have alternator running with both compressor and battery connected current will flow from alternator and battery into both compressor assuming the battery has sufficient charge. The reason to disconnect alternator from battery is so that the battery and only the battery provides energy to the compressor. This eliminates the load of the compressor on the alternator and thus on the engine, robbing some power of course. Maybe you don’t care about losing that HP which in that case keeping the alternator connected to your battery and compressor all the time.

Are you charging the batteries through a regulator from the alternator and then running the compressor from the batteries?

#3, #4 - sound good.

#5 - Sounds like a huge fire risk in the event of a crash with batteries in front bumper…

 

1/Not really........... when the low voltage safety is triggered they no longer get discharged and if they are hot they don't get charged either. In reality this is what happens and the batteries don't get too hot. This is my observation so far anyway, by the time the batteries are getting hot - they are discharged.
2/ Every watt of electrical power is worth approximately 7 watts of engine power. Plus, I'm only charging at 450ish watts which is 5/8ths of f'all to an engine producing 200 odd KW. Not even worth thinking about when you consider that it helps the batteries keep up and extends your boosted drive time.
The batteries are charged by a 12vDC to 48vDC balance charger that is connected directly to the car battery.
5/ Maybe - they are behind the crash bar which helps.