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I've been toying with this idea for years. A few months back I came across a Utube video of a guy in the US (AlexLTDLX) who was drag racing his electric supercharged V8 and doing 9 second passes. I watched most of his videos on the subject and was inspired to try it myself. Link here to his DIY parts list :
We all know that the RX8 is considered one of the best handling cars around but lacks the power of the cars it gets compared to, so I figured this was worth trying.
My goals are different to Alex's though. His videos and website gave me a great starting point but from there I found there is very little info readily available on how to do this.
My biggest challenge was learning about the electrical side of this - I knew next to nothing.
Initial Goals:
1/Looking for the extra 40-50WHP that everyone says the car needs. Hoping for similar power to what the average Greddy setup makes. Was aiming for 3-4psi boost pressure to achieve this. You don't need as much boost to get the same power (more on this later)
2/ Want it to be PRACTICAL so I can just hop in the car and drive - knowing boost is always on tap. So batteries need to last a decent time and they have to recharge as I'm driving.
3/Don't want to have to push too many buttons to get it operational.
4/Don't want to add too much weight to the car.
5/Want the system to be SAFE - not as easy as it sounds with the batteries I'm using.
6/Cost HAS to be less than half what my turbo system costs to implement. Performance will never be as good as what I'm getting from the turbo setup so it's never going to be worth spending as much as that system cost me.
7/ Didn't want to get to point that I need special fuels or intercooling. IE make the most power with the least fuss.
So I set about researching and getting all the components together. Making it all fit in was a major PIA but this is what I came up with:
After some late night tuning the night before, yesterday was my first shakedown test drive.
System performed pretty well, but as expected there is lots to work on.
*The batteries I bought were fairly cheap LIPOs that did what I hoped (IE gave me a start) but are obviously not going to be satisfactory for this task. So I've ordered some more powerful batteries already.
*Performance isn't earth shattering and I haven't taken it past 6000rpm yet . But when batteries were at full charge there is definitely a noticeable bump in power at 3.5psi Boost.
* DC-DC charger I purchased is amazing- but is a little cumbersome to get going at startup.
*Battery/speed controller box is a major PIA to get to - but It needed to be out of the engine bay so I put it behind the front bumper.
*I knew the maf setup was going to be problematic - and .......... it is!
Special thanks to :
ALEXLTDLX for the inspiration to even attempt this
Nathan Toa for the vital info and part I needed to get the ESC working.
Sandie Sullivan for helping with testing.
Wow did you do this already!?! I was planning to make a similar thread considering the potential implementation of e-tech in a DIY manner for the RX8.
Honda just released an e-charged 3 cylinder motorbike which is what got me thinking if they can fit something like that under a gas tank on a motorbike, then under the hood of a car shouldn't be too difficult.
Wow did you do this already!?! I was planning to make a similar thread considering the potential implementation of e-tech in a DIY manner for the RX8.
Was going to start a thread before I built it ...but could hear all the negativity ringing in my ears from the doubters, so decided to wait till I had a least got it to the point where I consider it a viable thing!
As someone who's been using that kind RC parts listed there long before being old enough to drive... messing with lipo batteries in a car is a good way to set it on fire. When those batteries catch fire there is no stopping them. They catch fire from 2 things: mechanical vibrations piercing the insulator sheets and excessive heat(thermal runaway). At least use hard cases to protect them and install individual cell voltage/temp monitors. My "record" for the biggest electric powered thing was a RC heli that used up 150A @ 50V - thing was much like 2 chainsaws tied back to back and flying about.
Pic of my rx8 on the yearly occasion I use it as a literal aircraft carrier.
Beyond that if you really wanna make it worthwhile and not haul 2kg of batteries to your house every time you drive the car you'd better set up battery charging during fuel cut. Of course this would further add to the rats nest that I can imagine is already in place.
I'm here if you need more input on the electronics side. I can see some potential for 20-30hp but I don't see it worthwhile, mainly because of safety concerns and having to take care of some lipo's not to burn my car down, or swell up due to being left charged, or draining too much current. In my RC models batteries rarely last past 30-50 flights(one charge-discharge cycle at a current equal to 10x the stated capacity in amps-hour)
As someone who's been using that kind RC parts listed there long before being old enough to drive... messing with lipo batteries in a car is a good way to set it on fire. When those batteries catch fire there is no stopping them. )
Comments like this are exactly why I decided to 'just do it' - and see what happens rather than listen to all the negativity. Thanks for confirming that for me .
I did read up a lot on Lipo batteries and it scared the crap out of me .... initially. I decided to go ahead anyway because of the w/kg advantages they have.
I also found there was a company in Sweden that already use lipos in a comercially available electric supercharger kit. If they can do it .............it must be possible.
Ever heard of SMC batteries ? ... realistic 250C rated
Some of the measures I've taken to try make the LIPOs safe:
Mounting position is out of the engine bay and in the airstream. So far they are staying nice and cool.
Mounted in a container which is lined with battery insulating foam, ventilated and protected from water intrusion.
Battery Temperature is monitored and charger will stop charging if temp exceeded - plus a warning light.
Set charger to 96% charge instead of 100%
Set ESC to max protection so batteries don't discharge below 3.4 volts per cell
Can turn off the charger but still use supercharger so this enables me to discharge the batteries quickly to a safe storage level on the way home.
Charge rate is only 1C
The battery tech has not improved much in the past 15 years that I've known it. Yes, wh/kg and wh/volume is unbeatable for lipo batteries - that's why they are in RC models. No, you can't beat them under any shape or form. Perhaps supercapacitors but the wh/volume is much worse.
The market's been offering "120C" batteries for ages now, what they don't ever give is the longevity at that discharge rate, internal resistance(for voltage drop computation and power dissipation). In reality the C rating of any lipo battery is inflated by at least a factor of 3. Imagine pulling 120x7 = 840amps out of those batteries you have now... lets do the math again for 350C.... 7000mAh lipo at 350C = 2450 amps ? At 50V that would mean 120000 watts or 120kw or close to the power output of a 4 port renesis....
In a few words what I am trying to say is that what mfgs. of batteries claim has very little to do with what the actual batteries can do. I mean to help you adjust your expectations - I know too well that RC stuff is expensive. And the more you push batteries, the faster they degrade. At first they swell, then their internal resistance skyrockets, and lastly they do a thermal runaway.
Getting over that... after all the variables are known, would it be acceptable that a battery pack lasts for 100-200 boosted pulls before its performace drops too much and you need new batteries? Up to everyone to answer.
This is the average lifespan of such a lipo when used well(30-50 full charge cycles). I've churned too many batteries like this to keep count.
Safety wise there is too much to list in a short post... most important is to keep guard of temperature at all times and to prevent mechanical shock. As said... inside these things there is literally a paper thin insulator in between electrodes. That paper allows for a short, is bent, damaged in anyway, you're in for a barbeque.
Last edited by ciprianrx8; Nov 24, 2024 at 04:18 PM.
Beyond that if you really wanna make it worthwhile and not haul 2kg of batteries to your house every time you drive the car you'd better set up battery charging during fuel cut. Of course this would further add to the rats nest that I can imagine is already in place.
I'm here if you need more input on the electronics side. I can see some potential for 20-30hp but I don't see it worthwhile, mainly because of safety concerns and having to take care of some lipo's not to burn my car down, or swell up due to being left charged, or draining too much current. In my RC models batteries rarely last past 30-50 flights(one charge-discharge cycle at a current equal to 10x the stated capacity in amps-hour)
My first thought after reading is wouldn't finding a suitable full size automotive lithium battery provide enough power to operate the e-charger while also offering long service life?
I'm curious what Honda has developed for their system; I imagine the battery to be HD compared to the industry standard and the charging system must support it in some clever way.
The battery tech has not improved much in the past 15 years that I've known it. Yes, wh/kg and wh/volume is unbeatable for lipo batteries - that's why they are in RC models. No, you can't beat them under any shape or form. Perhaps supercapacitors but the wh/volume is much worse.
The market's been offering "120C" batteries for ages now, what they don't ever give is the longevity at that discharge rate, internal resistance(for voltage drop computation and power dissipation). In reality the C rating of any lipo battery is inflated by at least a factor of 3. Imagine pulling 120x7 = 840amps out of those batteries you have now... lets do the math again for 350C.... 7000mAh lipo at 350C = 2450 amps ? At 50V that would mean 120000 watts or 120kw or close to the power output of a 4 port renesis....
In a few words what I am trying to say is that what mfgs. of batteries claim has very little to do with what the actual batteries can do. I mean to help you adjust your expectations - I know too well that RC stuff is expensive. And the more you push batteries, the faster they degrade. At first they swell, then their internal resistance skyrockets, and lastly they do a thermal runaway.
Getting over that... after all the variables are known, would it be acceptable that a battery pack lasts for 100-200 boosted pulls before its performace drops too much and you need new batteries? Up to everyone to answer.
This is the average lifespan of such a lipo when used well(30-50 full charge cycles). I've churned too many batteries like this to keep count.
Safety wise there is too much to list in a short post... most important is to keep guard of temperature at all times and to prevent mechanical shock. As said... inside these things there is literally a paper thin insulator in between electrodes. That paper allows for a short, is bent, damaged in anyway, you're in for a barbeque.
I'd be tempted to build the batteries with 18650s or similar, provided that I could find a suitable BMS.
I've done it before. Custom packs for a long-range e-bike. Worked very well.
The battery tech has not improved much in the past 15 years that I've known it. Yes, wh/kg and wh/volume is unbeatable for lipo batteries - that's why they are in RC models. No, you can't beat them under any shape or form. Perhaps supercapacitors but the wh/volume is much worse.
The market's been offering "120C" batteries for ages now, what they don't ever give is the longevity at that discharge rate, internal resistance(for voltage drop computation and power dissipation). In reality the C rating of any lipo battery is inflated by at least a factor of 3. Imagine pulling 120x7 = 840amps out of those batteries you have now... lets do the math again for 350C.... 7000mAh lipo at 350C = 2450 amps ? At 50V that would mean 120000 watts or 120kw or close to the power output of a 4 port renesis....
In a few words what I am trying to say is that what mfgs. of batteries claim has very little to do with what the actual batteries can do. I mean to help you adjust your expectations - I know too well that RC stuff is expensive. And the more you push batteries, the faster they degrade. At first they swell, then their internal resistance skyrockets, and lastly they do a thermal runaway.
Getting over that... after all the variables are known, would it be acceptable that a battery pack lasts for 100-200 boosted pulls before its performace drops too much and you need new batteries? Up to everyone to answer.
This is the average lifespan of such a lipo when used well(30-50 full charge cycles). I've churned too many batteries like this to keep count.
Safety wise there is too much to list in a short post... most important is to keep guard of temperature at all times and to prevent mechanical shock. As said... inside these things there is literally a paper thin insulator in between electrodes. That paper allows for a short, is bent, damaged in anyway, you're in for a barbeque.
Thanks .... you are easier to take when you aren't flying off the handle with negativity.
Anyway - the 250C battery I mentioned holds world records for RC speed boat drag racing ..so it's no joke. And yes ...I've seen the you tube vids on ridiculous 'C' ratings and what that mean for the user. I've also come across a guy that specialises in LIPO testing and am basing my next purchase on his results- some excellent info!
As far as battery life goes - no I didn't realise they were so shortlived. I am doing what I can to maximise life based on what the 'experts' on youtube say, but will just have to find out for myself how that goes.
Implementing that would cost more than a proper turbo setup doing x3 the power this setup would ever achieve.
I'm far from an expert on batteries or electrical systems but I am aware that certain utility vehicles and trucks have two batteries capable of running multiple accessories at once for extended periods of time. Would you not be able to A.) rig up a completely independent system dedicated to e-charging and related management or B.) incorporate an extra second battery (with support mods to oem electrical and or charging systems if necessary) to accommodate the extra demand / load?
I feel like option A would have the potential to be very cost effective, especially if one is resourceful. Like something as simple as mounting the second battery in the trunk with a kill switch and running the wiring into the engine bay (there's obviously more to it than that, but I'm speaking in general).
Last edited by Federighi; Nov 24, 2024 at 07:44 PM.
I'm far from an expert on batteries or electrical systems but I am aware that certain utility vehicles and trucks have two batteries capable of running multiple accessories at once for extended periods of time. Would you not be able to A.) rig up a completely independent system dedicated to e-charging and related management or B.) incorporate an extra second battery (with support mods to oem electrical and or charging systems if necessary) to accommodate the extra demand / load?
I feel like option A would have the potential to be very cost effective, especially if one is resourceful. Like something as simple as mounting the second battery in the trunk with a kill switch and running the wiring into the engine bay (there's obviously more to it than that, but I'm speaking in general).
I looked into other battery types and found you need an enormous/heavy/expensive battery to get an output of 150A @ 48v - which is what I need to make this project viable.
Using lipos enabled a 2kg battery mounted very close to the motor which meant minimal losses through the cables to the ESC as well.
Honda just released an e-charged 3 cylinder motorbike which is what got me thinking if they can fit something like that under a gas tank on a motorbike, then under the hood of a car shouldn't be too difficult.
I wouldn't mind betting that a good % of the power for this comes directly from the alternator/charger enabling the use of smaller/more stable batteries. The way I see it every electrical kw produced is capable of making something like 7kw to the wheels.
Initial virtual dyno comparison with the same car (pre- ESC)
N/A ............................blue-red
ESC to 3.5psi max. - yellow-green
Looks like a 30whp gain across the rev range so far
I feel top end will improve by more than 30 once I have better batteries in place.
Will a top tier bloody expensive battery do 120C? Perhaps, maybe once or twice and for 20 seconds, before it inflates like a doughnut and is no longer capable of doing 120C. Is this really what is trying to be achieved here...
WRT longevity... look at your smartphone battery. It's a 1 cell at 3Ah give or take. What's the power usage of your device? Deff no more than 1-2C at peak and 99% of the time it's nearly 0. Your smartphone battery performance degrades in 2-3-4 years of usage, given that it is charged once a day. Keep in mind, this is at 1-2C.... not 100-120C, and the smartphone battery wont ever do more than 2C.
I'd be tempted to build the batteries with 18650s or similar, provided that I could find a suitable BMS. I've done it before. Custom packs for a long-range e-bike. Worked very well.
Those kinds of cells have a much, much lower discharge rate ("C" factor) and are of different chemistry (li-ion). If a top tier lipo has allegedly 120C(more like 60C), then a top performer 18650 has 15C at best! If you were to use those, bulk and weight would skyrocket. They are used in e-bikes because they are cheaper and more mechanically durable(being encased in metal canisters like regular AA batteries). Long range = low power. Not quite what this application needs(high acceleration for a short period of time).
At any rate, moving this setup from a 12S lipo to 18650 would not help; commercially available 18650s are geared for longer use at very small currents(like laptops, flashlights) instead of short massive peaks of power(like you'd want when flooring it and requiring some boost on demand).
Question: is that compressor wheel freespinning when not in boost? How much aerodynamic drag does it add when doing so ?
Last edited by ciprianrx8; Nov 25, 2024 at 03:08 AM.
Question: is that compressor wheel freespinning when not in boost? How much aerodynamic drag does it add when doing so ?
I doubt it spins at all when it's not powered. There is a ton of drag from the e motor. Iv'e done some acceleration logs with the wheel stationary and overlayed those against some logs I did before the install. It doesn't affect performance at all up to about 7000rpm - (haven't actually gone past there yet). At cruise there is no difference. The size of the unit is big enough such that there's hardly any restriction.
So ... I did a pull to the redline with batteries fully charged. Really buzzed with this result - better than I was expecting!
57WHP gain up top !!!!
Red/blue is with eSC and 3.5psi
Green/yellow is N/A before SC fitted
hose kinds of cells have a much, much lower discharge rate ("C" factor) and are of different chemistry (li-ion). If a top tier lipo has allegedly 120C(more like 60C), then a top performer 18650 has 15C at best! If you were to use those, bulk and weight would skyrocket. They are used in e-bikes because they are cheaper and more mechanically durable(being encased in metal canisters like regular AA batteries). Long range = low power. Not quite what this application needs(high acceleration for a short period of time).
At any rate, moving this setup from a 12S lipo to 18650 would not help; commercially available 18650s are geared for longer use at very small currents(like laptops, flashlights) instead of short massive peaks of power(like you'd want when flooring it and requiring some boost on demand).
As long as there are enough cells in parallel it would work, and at these numbers I doubt weight is the major concern. I mean, considering for a Tesla in Plaid mode - and is based on similar cells - it certainly is possible.
For example, these cells Molicel P26A 18650 Battery - High Discharge Rate and Longevity would probably need to be 6P to handle the peak of that motor and controller. A 12S6P pack is doable, would weigh ~9-10lbs, and probably cost around $460 USD (just looked up cells and BMS, would need to add on connectors, wire, heat shrink, etc)... if implemented correctly it would be more reliable and longer lasting than Lipos.
Depending on environment, there might be heat considerations too, regardless of battery chemistry choice. OEM automotive packs incorporate (warming and) cooling solutions.
That extended range e-bike pack I built before was 14S (8 or 9P, I don't recall), and it wasn't too difficult to assemble. Lots of welding nickel strips.
Just food for thought. I'm not about to go build that pack right now myself. I'd be using lipos for PoC purposes too.
Last edited by 3toedSloth; Nov 28, 2024 at 02:55 AM.
Alex is using LTOs for his setup- putting out 35kw ! That's a pretty heavy pack that would have to live in the boot - but that's the way I'd go too if I ever decided to make some big power with it.
A quick search regarding longevity for a LiPo battery, as function of State Of Charge used, indicates its in the same ballpark as Lithium batteries used on electric cars. Here you can see that if you keep away from the extremes and keep it between 20 - 80% SOC, batteries will last a very long time:
LiPo: https://www.researchgate.net/publica...y_A_case_study
I assume there are similarities to how much current you use vs life span, if you avoid the maximum discharge, life will increase exponentially. Looking at my old spreadsheet again, at 8kRPM and 3.5psi, it seems like you need about 10kW to the compressor. That means just shy of 200A on a 48V system. My old electronics rule of thumb say "use no more than 50%", but that may not be valid for this scenario.
Hope you are right re longevity.
10kW sounds a bit high - I was closer to 6 using Matchbot. Compression efficiency is up around 76% on this unit at these flows.
Will be testing Amps tomorrow so will know more.
For proper test, remember to trend voltage as well to be able to calculate true power. I would guess regulator compensates when voltage drop, and current increases to be able to pull required power needed. Whats the efficiency of motor?
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