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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.
It sounds like you have all the bases covered. I guess I don’t understand the concern on your part about the batteries. If thermal protections are covered then it’s just the economics of longevity and whether battery life is prohibitive. There’s been good feedback on keeping batteries between 20 and 80% to maximize life and slow charging obviously. I still would be hesitant to put batteries in front even with the benefit of air cooling, but it seems like something you’ve thought about at least. I still would probably opt to put them in the trunk.
Thanks for responding to my concerns. I am still interested to see what you end up with. I thought about this myself some and the biggest issue to me is just fitment and potential custom parts. Would you envision needing a bypass valve and if so do you have an aftermarket product in mind of would you have to get something fabricated? Likewise with the MAF housing/tube. If you were to get parts fabricated to make this fit I might be interested in going in on to reduce unit prices. Perhaps other members might be too.
Re the batteries : I'm doing my best to mitigate the risk and am comfortable with experimenting. Wouldn't want to encourage others to do the same.
Bypass: have not seen the need for one ... yet.
Awesome work! This is definitely a cool way to add some extra punch to a drag racer or autocross car that really benefits from 10-60 seconds of extra power.
Originally Posted by Brettus
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!
The RX-8 seems to attract a certain type of know-it-all that can be an absolute nightmare to deal with. Kudos for continuing to push through and innovate in this space!
I think the biggest upside would be if it put your operating point in a more efficient zone, you'd end up with lower IATs, especially since it's non-intercooled.
So a ceiling of about 25psi of boost? Are there any desirable tradeoffs with going with a compressor with a lower boost/flow ceiling?
Very minimal IMO : the efficiency difference would be 1-2% max., maybe less weight and slightly better spool. That's all assuming there was one available - good luck finding something suitable.
What I like about this this one is the low resistance to flow - I can run the engine without the eSC running and there is no noticeable reduction in power.
One burning question I have with supercharging is - is the Renesis more tolerant of higher boost levels at lower RPM without significantly compromising engine life? On one hand my logic seems as if the heating would be lower at lower RPM provided you aren’t running AFR too lean or maybe slightly richer although the combustion/exhaust pressures would still be higher just at a lower frequency. From what I understand belt driven superchargers over stressed engine bearings.
Last edited by schm1347; Dec 30, 2024 at 11:43 PM.
One burning question I have with supercharging is - is the Renesis more tolerant of higher boost levels at lower RPM without significantly compromising engine life? On one hand my logic seems as if the heating would be lower at lower RPM provided you aren’t running AFR too lean or maybe slightly richer although the combustion/exhaust pressures would still be higher just at a lower frequency. From what I understand belt driven superchargers over stressed engine bearings.
More tolerant than ???
My turbo setup sees 10psi by 3100rpm - engine is perfectly happy there. Never seen accelerated bearing wear in any of the turbo engines I've pulled down.
More tolerant than ???
My turbo setup sees 10psi by 3100rpm - engine is perfectly happy there. Never seen accelerated bearing wear in any of the turbo engines I've pulled down.
More tolerant of higher boost at 3000 vs 8500. But you answered my question…
The good news is that the new batteries are installed and tested. The bad news ............. they made a difference of about 0.2 psi, so barely noticeable. Will do a VD when temp comes down below 20C to confirm.
Next move is to go up one pulley size (14 to 15T) which my calcs tell me should raise boost a further 0.75psi to around 4.5PSI. Won't dyno it till I have that pulley in place. The aim is 250-260whp range with the current setup.
3rd gear ...........4 psi from 3000-6000 then dropping to 3.5psi 6500 and up.
Managed a 3rd gear log tonight. Looks like midrange is very strong now plus peak is a little higher.
Looks pretty good. I would be happy with those numbers. So battery current is no longer the limiting factor? Is it now the DC motor driving the compressor?
Looks pretty good. I would be happy with those numbers. So battery current is no longer the limiting factor? Is it now the DC motor driving the compressor?
I need to get someone to watch the boost gauge for me - just looking at that log makes me think it's dropping off at the top end.
Toothed belt is driving the compressor.
I need to get someone to watch the boost gauge for me - just looking at that log makes me think it's dropping off at the top end.
Toothed belt is driving the compressor.
That makes sense…is the belt showing signs of slip wear on the teeth or stretching? I suppose there is no (easy) way to directly mate a motor to the compressor drive to eliminate the belt. Seems like unless you do that you running into the same limitations as an engine belt driven supercharger.
That makes sense…is the belt showing signs of slip wear on the teeth or stretching? I suppose there is no (easy) way to directly mate a motor to the compressor drive to eliminate the belt. Seems like unless you do that you running into the same limitations as an engine belt driven supercharger.
Haven't touched the belt since the install - no signs of wear or loss of tension. I mounted it like I did for packaging and the ability to change ratio with ease.
Direct mounts have been done but require some engineering. Not sure what limitations you think will be caused by the drive - seems to me the biggest limitations are batteries/charging.
Haven't touched the belt since the install - no signs of wear or loss of tension. I mounted it like I did for packaging and the ability to change ratio with ease.
Direct mounts have been done but require some engineering. Not sure what limitations you think will be caused by the drive - seems to me the biggest limitations are batteries/charging.
If you have more batteries in parallel then you should be able to increase the current output (e.g. double batteries in parallel will double current output). What about your wire gauge and length? Your resistance? Vmotor = I*Rmotor = Vbatt - I*Rwire (roughly…battery will have source resistance, but more batteries in parallel should reduce).
10 AWG: Copper wire has a resistance of about 1 ohm per 1,000 feet
20 AWG: Copper wire has a resistance of about 10 ohms per 1,000 feet
30 AWG: Copper wire has a resistance of about 100 ohms per 1,000 feet
I would look at both the max current output per battery as well as wire resistance. Instead of doing just two batteries, try four. And then consider if wiring is limitation on current flow as well. Beyond the motor current that’s your domain …
If you have more batteries in parallel then you should be able to increase the current output (e.g. double batteries in parallel will double current output). What about your wire gauge and length? Your resistance? Vmotor = I*Rmotor = Vbatt - I*Rwire (roughly…battery will have source resistance, but more batteries in parallel should reduce).
10 AWG: Copper wire has a resistance of about 1 ohm per 1,000 feet
20 AWG: Copper wire has a resistance of about 10 ohms per 1,000 feet
30 AWG: Copper wire has a resistance of about 100 ohms per 1,000 feet
I would look at both the max current output per battery as well as wire resistance. Instead of doing just two batteries, try four. And then consider if wiring is limitation on current flow as well. Beyond the motor current that’s your domain …
Right now it's all working ok at this boost level and I don't have the space to do much to improve it.
My challenge comes when/if I try to increase the boost significantly. At that point I need to abandon the LIPOs and everything I've done wiring wise so far, and go boot mounted with a heavier/more powerful battery pack etc.
Golf cart batteries would probably work well for this application. About 50lbs, 120A continuous current with 350A peak. 3kWH capacity so you can run a 5kW turbo for 36min continuous. These batteries are driving electric motors. Of course this goes in the trunk. Build your own solar panel spoiler to charge them :p
Golf cart batteries would probably work well for this application. About 50lbs, 120A continuous current with 350A peak. 3kWH capacity so you can run a 5kW turbo for 36min continuous. These batteries are driving electric motors. Of course this goes in the trunk. Build your own solar panel spoiler to charge them :p
That would handle what my (5lb) LIPOs are currently doing (albeit for much longer). But If I went to say 6-7PSI we'd be looking at over 300A for 50% duty. Based on the above ----- I doubt it would handle the job.
The LTOs I'm looking at ...would ...with ease.
That would handle what my (5lb) LIPOs are currently doing (albeit for much longer). But If I went to say 6-7PSI we'd be looking at over 300A for 50% duty. Based on the above ----- I doubt it would handle the job.
The LTOs I'm looking at ...would ...with ease.
Are there reasonably priced LTO battery packs around? I did look and had a hard time finding battery packs for reasonable price, but maybe you can enlighten me.
It’s great to build your own stuff as he did in the video, but it’s a lot of time and access to proper tools to make it happen. That’s great if you are a single guy with nothing but free time outside of work. Building battery packs seems like one of the lowest return/impact items to focus your time and attention on. Time is a valuable resource too…
I also question whether LTO is actually superior to LiFePO4 other than from a safety standpoint (and yes strong arguments can be made for the sake of safety). Energy density is significantly less for LTO. Yes you can get more current per per that energy, but what about current per weight and capacity? Again, enough cells in parallel of any battery technology will give you the current you want and LiFePO4 is cheaper (even lead acid batteries will do the job but they are horridly heavy). I haven’t done a careful comparative study but it seems like when I look at the specs of the LTO battery packs vs LiFePO4 that they are comparable for current discharge capabilities with similar internal resistances in the tens of mOhm. Maybe there’s bias in that assessment, because LTO is a much smaller market share with less options (there’s a reason for that and it has to do with low energy density). The other thing is too, if you build your own battery packs you probably aren’t going to adhere to the margin of safety with BMS max current draws as a manufacturer of a battery pack would and then are you going to get the expected life? So when you build up a bunch of LTO batteries together with your own BMS is that really apples to apples?
Maybe my assessment is wrong and I don’t have the complete picture… Again, I applaud your efforts and think what you are trying to do is really neat. And it’s something I’m really considering doing myself as well down the road.
That lifepo4 battery you linked is 25kg and it definitely wouldn't supply 300-350A (they rate it at that for only 1 second! )
The LTOs are rated at 520A continuous and would weigh 17kg(ish) but with approx. half the total energy (26Ah vs 60).
That's a slam dunk for the LTOs ... IMO
20 of these would cost me around $600US. But then there is the BMS to consider.
You make some good points. I already spent a ton of time researching/thinking/experimenting etc to get to where I am now. Luckily, I do have the time and enjoy the journey. So If I need to learn about making my own batteries to take the next step - maybe that's what I'll do.
That lifepo4 battery you linked is 25kg and it definitely wouldn't supply 300-350A (they rate it at that for only 1 second! )
The LTOs are rated at 520A continuous and would weigh 17kg(ish) but with approx. half the total energy (26Ah vs 60).
That's a slam dunk for the LTOs ... IMO
20 of these would cost me around $600US. But then there is the BMS to consider.
You make some good points. I already spent a ton of time researching/thinking/experimenting etc to get to where I am now. Luckily, I do have the time and enjoy the journey. So If I need to learn about making my own batteries to take the next step - maybe that's what I'll do.
Can you make me some? Lol. You do make a good point about LiFePO4 battery weighing 55lbs and only sourcing 120A. It’d be interesting to understand better the constraints, which I admit I don’t (lifecycles, heating, internal wiring limitations?), because you can get LiFePO4 batteries with less capacity to crank a starter too but that is more pulse energy.
I wonder Alex needed to go through all the work of machining battery thermal bus bar plates. I’ve gotta believe you could buy battery terminal crimpable connectors and connect together with low gauge copper wire…. That would be a lot faster and less custom.
Another question is understanding the heating aspect of bunching batteries together in a plastic insulated pelican case. Granted that’s how batteries are provided for the benefit of packaging but at the expense of cooling. From a thermal standpoint placing the batteries in a flat chassis with body of that metal chassis in contact with negative/housing of battery (keep positive terminal insulated) and bolted into the car frame would provide superior heat dissipation. Something to think about regardless of battery technology.
The Lishens do come with connectors (plus you can get plastic holders for them cheap). Not sure why Alex made his own - maybe the supplied ones weren't meaty enough....
The Lishens do come with connectors (plus you can get plastic holders for them cheap). Not sure why Alex made his own - maybe the supplied ones weren't meaty enough....
Hmmm…yeah. That’s exactly what I would expect…. Then it should be pretty straightforward to build up. I would just leave them open air in trunk. Maybe put a plastic or foam cover over contacts for safety. If I used these i don’t think I’d put in a case.
Did Alex say 2.4V operating? So 20 batteries in series for 48V then.
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