posted on November 03, 2011 02:00
Project Miatabusa Part 11
Shorai Lithium Iron Battery (and Lots of Plumbing)
by Dave Coleman
Odds are pretty good this is the first Miata in history to have its battery relocated from the trunk to the engine bay. The reasons for this mod are pretty simple. The Hayabusa swap is taking so much weight off the nose of the car, the Miatabusa will actually be tail heavy! Suddenly, the simple ballast-shifting technique of battery relocation needs to go the other way.
But what battery to use? Lithium Ion batteries are the obvious choice, since their incredible energy density would make for an amazingly light battery, but there are two problems. First, Lithium Ion race batteries are comically expensive. Though prices are dropping, in the past year I've seen Lithium Ion race batteries that cost more than this whole Miata bodyshell. The second problem is their instability. Most of my experience with Lithium Ion batteries is from cheap chinese RC Lithium Polymer (LiPo) plane batteries, and these little beasts are notorious for their tendency to burst into flames if charged or discharged improperly.
Enter the Shorai Lithium Iron Phosphate (LiFePo4) batteries. Lithium Iron Phosphate is a relatively stable member of the Lithium Ion family. They're stable in the face of heat, and they won't ignite when shorted or overcharged. They're slightly less energy dense than those Chinese LiPo batteries, but they're still dramatically more dense than a lead-acid battery.
Shorai doesn't technically make any automotive batteries, but they have a full line of motorcycle batteries. I can't think of any reason why Motorcycle battery won't work in a car, and certainly not one powered by a motorcycle engine and charged by a motorcycle alternator. Shorai's direct replacement battery for the Hayabusa (theoretically all we would need to start a Hayabusa engine) weighs only 1.7 pounds!
LiFePo4 batteries have fundamentally different discharge characteristics from lead-acid which makes capacity comparisons a little tricky. Voltage drops less with load than lead acid batteries do, and they maintain high voltage through more of their discharge than lead-acid batteries (check out the chart on the right, a 12V Shorai battery is a dead battery), which means they can still start an engine deeper into their discharge than a Lead Acid battery.
Since the ability to start the engine is really what matters, Shorai concocted a "lead equivalent" amp-hour (PBeq AHr) rating that essentially compares the relative starter turning ability of their batteries to comparable lead-acid batteries. A Shorai battery with a 14 PBeq amp-hour rating doesn't actually have 14 AHr of capacity, but it will start an engine just as well as a 14 amp-hour lead-acid battery can.
Let me just point out that batteries combine two of my least favorite subjects: chemistry and electricity, so I'm just going to take Shorai's word for it on this rating.
Using their "lead equivalent" amp-hour rating, the 1.7-pound Hayabusa battery has a 14 Ah capacity. The 13-pound Odyssey PC680 sealed lead-acid battery I've used in Project Silvia and Project Frankenmiata is 13 Ah and has no problem starting an SR20 or a B6 engine, so this supports my theory that this 1.7 pound battery should be plenty for the Miatabusa. Most impressive, the Shorai Hayabusa battery costs about $150. That's a remarkable price per pound saved if that battery can, indeed, start a car. Still, I didn't get one...
I was so obsessed with this little space, tucked between the gussets on the Miata's shock tower, that I really wanted a battery that fit it perfectly. The Hayabusa-sized Shorai battery would fit easily in this space, but would rattle around loosely. Their much bigger (4 pounds), 24 A-Hr (lead equivalent) Honda Gold Wing battery fit this space like it was designed to go there!
The Shorai batteries only come in three sizes, but each one ships in a box full of adhesive-backed foam so you can make their sometimes-too-small battery fit perfectly in your motorcycle's battery hole. This obviously would have solved my perfect-fit obsession, but in reality, my big battery choice had more to do with the extra cranking capacity. Extra capacity seems like a good idea for two reasons. First, I expect to be running close to the limit of the Hayabusa's charging capacity, what with all the extra headlights and taillights of a car, so some reserve battery capacity seems smart. Also, there's likely to be troubleshooting somewhere in this car's future, and nothing makes troubleshooting more frustrating than a weak battery.
Shorai's dizzying array of battery sizes and capacities can be really hard to sort through until you stumble onto this hidden page with all the specs and dimensions in one easy place.
Thursday, November 03, 2011 1:03 AM
That header looks eerily similar to one I built for our FSAE car a few years back... it should sound pretty nice compared to the stock Hayabusa manifold!
Cool to see someone else using a Shorai battery. I've been using one in my '79 Civic for a few months now and it dropped about 50lbs off the nose of the car!
Thursday, November 03, 2011 4:11 AM
Tell the parts store you need hoses for a Morgan or something they can't find in a computer. Then they'll usually let you in.
Are you at all worried about the exhaust being so close to the upper rad hose? Looks a little tight. That battery looks nice, I'll have to get one for my 240 when the old one goes. Oh and how did the finished intake come out? Or is that still not done?
Thursday, November 03, 2011 4:28 AM
I know that connecting the engine block to the firewall instead of to the stock location saved some weight, but it might not be a good enough connection. Take it from MotoIQ's resident electrical geek--if you start having some really, really weird electrical problems, it might be a bad ground, and you might need to add some additional ground straps.
Thursday, November 03, 2011 6:05 AM
@Dusty Duster. I agree. A 'Hyper Ground' system running to that stock location wouldn't be a bad Idea.
One near the alternator, one to the cylinder head and one to the starter with some 10 or 8 ga car audio wire. (I tend to go over kill)
Thursday, November 03, 2011 6:21 AM
I have a similar ground setup in my 240SX and I have no grounding problems. I DO have wiring issues related to a 20 year old car that was wired by a gorilla, but I don't have grounding problems.
Thursday, November 03, 2011 6:55 AM
@beaters: How do you know they aren't grounding-related? Ground problems manifest themselves in various weird ways.
Thursday, November 03, 2011 7:23 AM
Full Spectrum Power is another option for LiFePo cells. Not as many options as Shorai, but they're tiny, ultra light, and excellent for custom applications.
Thursday, November 03, 2011 7:56 AM
Did Dave really just buy a new battery AND a fancy charger? The hose setup is much more Dave than the battery solution. But I guess a car of this high caliber needs some "fancy" on it.
Thursday, November 03, 2011 8:41 AM
Wait until you see the exhaust system! It's gonna be a totally schizophrenic mix of expensive race bits and shit I found under a table.
Thursday, November 03, 2011 9:59 AM
I'm with beaters on the concern for the upper radiator soaking up a LOT of heat that the header is going to put off. Dave, have you thought about wrapping it in some Kapton tape to help resist some heat soak, while giving it that race car look?
Oh, and definitely looking forward to that schizophrenic mix of exhaust!
Thursday, November 03, 2011 10:37 AM
I'm not worried about the heat impact on the water inside, but I'm quite worried about overheating the rubber and causing a hose failure. Similar issue with the plastic radiator fan. Solutions are in the works...
Thursday, November 03, 2011 11:11 AM
Not sure why the comments about electrical path is incorrect in this setup. Hell, if all sensors, lights, and systems grounded through a dedicated ground wire back to the controlling device, you would not need a ground strap from the engine to the chassis at all.
Also, just so people are clear, Kapton tape is different than gold leaf tape or gold sheet. Kapton has high heat resistance, but it is different than gold sheet. At least from my experience i have never seen kapton tape used as a heat shield in an engine bay. Usually we just use it to protect wires when you are doing heat shrink and to hold service loops together, or applied smartly inside of a controller or logger.
But if anyone wants to enlighten me on why the path above does not seem right for a grounding setup, that would be good.
Thursday, November 03, 2011 12:14 PM
Mark is correct Kapton tape is very heat resistant but not reflective in the slightest. They may make a gold foil version I'm unaware of but all the Kapton tape we use is simply heat and chemical resistant
Thursday, November 03, 2011 1:11 PM
It's nice to know I'm not the only one that uses dry-cleaning twist ties in my projects. They practically give them out for free by the box-load.
Thursday, November 03, 2011 1:59 PM
Dry cleaning twist ties? I'm not sure where you're seeing those, but I'm damn sure I don't own anything that needs dry cleaning!
Thursday, November 03, 2011 2:07 PM
Dave - I've always loved how you throw ingenuity at problems, rather than just dollars! I forgot to mention this earlier but when you were talking about worries for voltage draw, I kept thinking, "Won't it be nice when LEDs are readily available and affordable for automotive use?".
Mark and Skullworks - I had mentioned the Kapton because after seeing it here on the ACS Mustang feature, I've seen it more and more on production type race cars. I know they were using it to help prevent heat soak but I can't speak directly to its heat resistant versus reflective attributes.
Thursday, November 03, 2011 2:07 PM
Dave, have you looked at a Unicoil for shortening the hoses to your oil coooler? http://www.gates-unicoil.com/
Thursday, November 03, 2011 2:13 PM
Scary number of connections on the water side.
Thursday, November 03, 2011 2:49 PM
Yea, Sean, lots of connections, but they're all seriously barbed, and they're all in plain sight, so leaks are easy to spot. I get more worried when I see water lines going to turbos and stuff like that, since they're usually hidden away in dark corners where stuff is so hot that leaks evaporate without leaving a trace.
Bruce, LEDs are planned for the taillights, and HIDs for the headlights. That should easily get me within the charging capacity of the Hayabusa alternator.
squirrelgripper (heh) I don't think tightening the bend radius of the cooler lines would save much length, and it would put more stress on the cooler and mounts. Not worth the effort.
Thursday, November 03, 2011 3:32 PM
The nice thing about LiFePO4 is that they don't vent with fire like many of the other types of lithium ion chemistry when they're abused. Kinda nice.
Thursday, November 03, 2011 4:45 PM
What sort of lifetime warranty do they have on the lithium batteries. Some variants of rechargable lithium chemistry can loose as much as 50% of their capacity over 12months if left fully charged and warm (all lithium I believe suffers from this to some degree). This is exactly the scenario in an engine bay.
I'm also not a big fan of aftermarket ground kits. Electrically they actually don't stack up and essentially 'fix' an actual ground problem by luck (enough wires spraying around will remedy the actual ground link issue)
Thursday, November 03, 2011 5:51 PM
@Dusty: My SR20 swap was wired with electrical tape and wire nuts. Believe me, it's not grounding. I just bought an entire S13 harness that's been uncut, over the Spring or Summer that'll go in and I'll post the before and after pics in the forum. You'll see what I mean.
What amazes me about the project more than anything is how easily some of this stuff is fitting. Like the battery slot, the wiring (which really didn't seem too bad), and some of the other odds and ends. Obviously fabricating a lot of stuff makes it look easy, but the parts that fit where no fab was required is pretty sweet.
Thursday, November 03, 2011 9:11 PM
Are we talking a real HID with a clean, sharp cutoff or a cheap conversion kit?
I have one of the cheap H4 conversions on my motorcycle, and while I know the cutoff might not be as good as stock, plenty of motorcyclists run around with hi beams on the whole time, so I don't feel but so guilty. Hell, the system on my bike can't even charge itself below 2k RPM, much less all the electricals on a car.
Thursday, November 03, 2011 11:10 PM
rhocken, Shorai has a 2-year warrantee, but it doesn't apply for cars (unless they're motorcycle powered), since they haven't explicitly tested with automotive charging systems.
Friday, November 04, 2011 3:30 AM
that's a really neat battery. but that aside i had come to expect more from this project. I'm counting 6 hoses and 4 different kind of hose clamps in the cooling system. it just looks thrown together.
I've made all kinds of crazy swaps and i've spent hours back there in the hose section of the auto parts store. i'm convinced there's a better fitting hose there. and if there isn't, a fabricated metal hose in the middle of two rubber connections that do fit properly would be much cleaner.
also, that welded together barb looks like a failure waiting to happen. if not the barb, the fact that you have all this weight hanging in mid-air with no supporting brackets will cause issues over time. especially since the hoses look stressed to reach their positions. things like the 2nd picture on the fifth page make it obvious that that hose does not actually fit. it was stretched into that position.
and why, with all the custom fabrication on this car it could have been handled much better. a custom thermostat housing on the lower hose would have allowed you to use one hose, an L shaped hose that you just cut to length. and the top would have been a bit more complicated, but a new piece that bolts to the block would have made the coolant come out forwards and then a short length of thin-wall tubing with a bend in it that could be bolted to the engine with a nice bracket would just make everything much more polished.
also, since these motors get swapped into car projects all the time. I'm sure someone makes parts that you could use without having to make anything yourself.
Friday, November 04, 2011 4:39 AM
Der Bruce - I tried to explain, what i thought, was Kapton and Gold Foil - http://www.motoiq.com/forum/aff/12/aft/1041/afv/topic.aspx back a few months ago.
I am completely open to if I am wrong, but I have only ever seen kapton used as Kapton tape and not in the instances i see gold foil.
In fact, as referenced in the post on the forum, the only times i see gold kapton in the google search is for motoiq. In my personal opinion, i think it is being mistaken for gold foil.
Friday, November 04, 2011 4:41 AM
Friday, November 04, 2011 4:44 AM
Shorai does not provide a warranty if used with Automotive charging systems? Did you check out Braille? They are very sharp and have been providing batteries for hardcore motorsports with alternators and various charging systems. Just a thought. Otherwise, this will be one cool project when we all hear that stratospheric redline!
Friday, November 04, 2011 4:56 AM
Kapton (polyamide) is just the substrate, the gold foil is what reflects the heat. I've used Kapton tape for years in high temp applications, but it's transparent amber because there is no reflective foil applied to it. It doesn't matter though as long as we know what people are referring to.
Friday, November 04, 2011 6:24 AM
Mark, The closest Braille battery I could find is the ML9C. Same 4 pounds, will fit in the same space, etc. Braille has a Lithium Amp Hour rating, which is conceptually similar to Shorai's Lead-Equivalent Amp Hour rating, but I have no idea if they're using the same formula. I believe the chemistry is slightly different anyway. So, assuming they're both accurate ratings, the Braille ML9C is 36 Lithium Amp Hour capacity, while the Shorai LFX24 is a 24 Lead-Equivalent Amp Hour capacity. (And I have experience getting away with 13 Amp Hours in the past.) Braille has a 1-year warrantee that is technically void on a street car. Shorai has a 2-year, pro-rated warrantee that is technically void in any car. Braille is $950. Shorai is $250.
Friday, November 04, 2011 6:25 AM
Oh, and Mark, you had a post that just said "copy" which I took to be a mistake, so I deleted it (I have so much power!) If you actually meant something by that post, go ahead and re-post, but be more clear.
Friday, November 04, 2011 6:32 AM
Marc (Why the hell are marK and marC posting back to back!?),
Never make the mistake of expecting a particular level or type of execution on this project! Not only am I wildly unpredictable, but this car is being built in spare time by 3 very different people, and the car keeps moving around from place to place, so the resources at hand keep changing. If it were in Tim's hands, there would be perfect aluminum aluminum coolant pipes. In my hands, it gets what can be done quickly in an evening in my 1-car garage. Consider yourself lucky, last time Alex was in charge of part of this car, we built stuff with condoms.
Friday, November 04, 2011 6:38 AM
Oh, and MarC, the second photo on the 5th page is a little misleading. That's the donor Ford Ranger hose in its original form. Once the last bend is trimmed off it and its spliced with the other two hoses, All the hoses sit naturally with no stress, and there is a support bracket under the first splice making sure the hose doesn't droop into the header.
Friday, November 04, 2011 7:35 AM
# HybridAndy Delete
Friday, November 04, 2011 7:36 AM
Just because I had to know.
Hose 21947 is from a '05 - '11 Ford Ranger
Hose 20568 will fit everything from a '95 Nissan pickup to a '58 Chrysler Imperial and a '63 MG 1100 (versatile damn hose)
Friday, November 04, 2011 7:38 AM
@HybridAndy and others if you have a particularly long link you can either paste HTML in the comment box or you can simply brake it as I did with the return on your keyboard that will kepp the link from running off the page. Your original comment is posted below. Good discussion!
Monday, November 07, 2011 12:48 AM
i got some questions/comment, they are not meant to be harsh, i am french and it i do have some trouble finding the right words.
About that battery, i was always told that the AH rating was the "capacity" of the battery, meaning a 14AH battery can store twice as much energy as a 7AH one. It has no relation to the max power it can deliver at a time. This is the max intensity rating, often noted Amax . With lipo, it is also noted as multiples of "C", but i dont quite know this one.
Anyway what matters for the starter motor is the Intensity max, not the capacity. The AH rating is used to know how many times you will be able to try starting the engine before the battery is depleted.
Considering the hoses, you might want to inquire hose makers. I have a silicon hose maker near my home, and he will make any hose i can design in a CAD file, provided i buy at least 4 of them. It will be much better than connecting a bunch of hoses like you have, and i am quite sure you could find people that can do it too.
Monday, November 07, 2011 1:19 AM
Crousti, Ah is the capacity of the battery. for something like this, you can get away with a tiny battery. I've used a 7Ah ATV battery before to start a car. basically if you had to try to start the car more than two times you had to bring out the jumper cables, but you were otherwise just fine.
it's a cheap way to save weight. it got me down to a 5lb battery. it looks like these get you down even further. my only concern is that max charge current.
Tuesday, November 08, 2011 10:25 AM
actually i think #21947 fits a 1998 saturn sl1.
Tuesday, November 08, 2011 6:43 PM
Battery capacity is all about how many times you can crank it if the engine is hard to start, whether you can start with a partially discharged battery, and how long the car can operate while the charging system is underperforming. As Marc says, in perfect conditions, you can start with far less battery, but to cover realistic problems like weak batteries, hard to start engines, or nasty weather, you need more capacity.
Monday, November 14, 2011 2:31 AM
I just found this site today and am impressed with your project. I have a miata right hand drive in standard form so am very interested in yours. I wonder if you considered putting the battery in the boot. The weight of the bike battery cant make that much difference. i own a a motorbike and started off life as a motorbike mechanic so wonder....
Monday, November 14, 2011 6:00 AM
You're right, the weight of the Shorai battery has almost no impact on weight distribution now that its so light. Partially, I had decided to move it forward before I found Shorai, but also the factory battery cables weigh 3 pounds, and I'm enough of a weight weenie that I get excited over saving 3 pounds...
Tuesday, November 15, 2011 2:40 AM
Dave thanks that makes sense. It will be nice to know how much the car weighs when completed and how it handles or how you handle the loss of weight distribution. I have wondered about the other parts of the car. My boot and doors are very heavy where as the bonnet is very light on the miata. Is it worth replacing some of these to compensate for weight and handling.
Tuesday, November 15, 2011 5:24 PM
It's good that you went oversize on the battery. Thing about lithium batteries (at least the motorcycle lithium batteries I've experienced) is that they don't produce full power until they get a little heat in them. Now, they produce their own heat, so that's neat. But if you get a battery that is "just right" it will crank too slowly to fire it for a crank or two, then the battery gets warm and finally spins it fast enough to start it. But then it might be flooded. By the time the engine is clear, the battery is cold again. Rinse, repeat until the battery is drained. I was the guy jumpstarting my bike at Thunderhill every morning.
I bought a "right-sized" battery for my 500cc single bike and it was totally inadequate. I put it in my 250cc single bike and it's just right. Just sharing my experience :)
Tuesday, November 15, 2011 8:25 PM
What king of ambient temps were you experiencing this?
Tuesday, November 15, 2011 8:47 PM
I dunno, what temperature was it at Arse Freeze 09? Chilly. It was usable in the summer but got marginal in anything past long sleeve weather.
Sunday, October 28, 2012 8:03 PM
I have been running the Braile Lithium ion 3.7 pound battery in my Mini (with B16B honda power, for over 2 years so far with no problems of any kind, including some freezing weather starts, and as many as 20 to 40 starts in a day of Autocrossing. the car has all the full lighting of a 60s highway car. I never had a battery charger on it from day one, and the stock Honda 70 amp Alt keeps it up. Had I known of another lithium battery being available, and for as cheap as the one you are using, I would certainly not have paid 950$ plus tax for mine, (mine does have a nice Carbon Fiber case though ;-)