[Eric_Oz_S2]

[quote name='flash' timestamp='1392991921' post='155337']carbon is not that much lighter than fiberglass. it's usually thinner, due to the rigidity of the fabric not requiring as many layers, which is why it can be lighter, but it still uses the same kind of resin. so, depending on how thick it is, it can actually weigh the same. it also makes a huge difference if you pin the hood, or use hinges, which require metal to be buried in the hood to attach the hardware. a hinged hood only saves a few pounds..[/quote]



There is a prototype carbon hood that has just been done for the 944 here in australia - 1kg top half, less than 2kg for the bottom. That's a hell of a saving.

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[flash]

top half? bottom half? ok - i'm confused



and we are way off topic now - this thread is about batteries. please start a different thread about hoods and such. it would go in the wings and things area

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[Eric_Oz_S2]

Top and bottom of the hood are moulded separately and glued together.



To keep this post in the "on topic" - Battery arrived today.

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[Eric_Oz_S2]

Installed with DIY bracket mount. Basically drilled holes for 2 threaded rods held with lock nuts through tray, used 10mm aluminium tube around rods with aluminium hold down clamp.

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[flash]

we don't have that tray here.

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[Eric_Oz_S2]

Yes, I know that.

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[flash]

lol - i thought this was the other battery thread

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[ds968]

I replaced my Mercedes's battery yesterday. It's a "maintenance free" type and I have no idea what's in those but while lifting it up I thought - holy crap this thing is heavy ! So I checked out the weight : 68.8 lbs ! And we think our 968 batteries are too heavy !



And it's priced on a per lb basis apparently, because it's $ 295 , before tax. That's just to add insult to injury ( from lifting up the battery lol ) , there are no cheaper alternatives , the car's computer throws a fit if you try to sneak a different battery in there. Ugh.

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[PorscheG96]

[quote name='Cloud9...68' timestamp='1392820672' post='155265']

Lithium ion batteries have significantly more energy density than conventional lead acid, and there are a few of them available for the aftermarket, but their prices haven't dropped much (kind of like carbon fiber). So that would be your best option for a lightweight battery, if you can afford it - last I checked, they were in the $1000 range.

[/quote]

I recently picked up a 3 lb Battery Tender with 26-35 Ah for a couple hundred $:



http://www.amazon.co...+tender+battery



I'm just waiting for the m6 SAE battery posts in order to charge and install it for AX this weekend so I can report back on how that goes...it's the first super lightweight battery I've found for under $1k and I'm pretty excited <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" />



How many Ah is your small lead acid battery? I'd guess less than this Lithium Iron Phosphate one, but of course much less expensive. The standard battery is 80 Ah.

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[flash]

i think you will have a problem there. besides only having 480 CCA, which is a bit low for this car, the max charge rate is 10 amps. our alternator puts out 115amps.



having seen what happens to lithium batteries when they get hot (which is what happens under an overcharge), i can't say i'd be comfortable with that.

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[PorscheG96]

[quote name='flash' timestamp='1403710347' post='158983']

i think you will have a problem there. besides only having 480 CCA, which is a bit low for this car, the max charge rate is 10 amps. our alternator puts out 115amps.



having seen what happens to lithium batteries when they get hot (which is what happens under an overcharge), i can't say i'd be comfortable with that.

[/quote]

It doesn't mean that 115 amps is going to charging the battery - the voltage regulator will only send what it needs. I won't link to the forbidden forum, but a Boxster owner there has been using the even smaller 2lb Battery Tender with 280 CCA and 120 A stock alternator with no problem so I thought I'd try it. <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" />

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[flash]

do what you want, but when they get overheated, they explode, and in no timid manner either. we did a LOT of tests on these when working on the MX.



on the 968, i have seen 60 amps coming out of the alternator to the battery more than once. when i was first messing with the stereo, i would run the battery down. when i fired it up, it cranked out 90 for a few minutes before it dropped down. i think it takes 12 to run the engine. add any accessories and it takes more. maybe the boxster takes less, or maybe it's right on the edge, and he just hasn't seen a problem yet. i sure wouldn't want to be experimenting with that. if it blows, it will take out everything in your engine bay.



if you are determined to run that battery, put it in a blast enclosure, similar to a scatter shield. of course, then you defeat the purpose of the light battery to a degree.

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[Cloud9...68]

So wouldn't switching to a smaller alternator, which will as a side benefit further reduce weight, be advisable with a Li-ion battery?

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[flash]

lol - sure - know of a 9 amp alternator?



seriously though, if there is some way to ensure that the alternator never puts more than 10 amps to the battery, it should be safe. other than that, it's a roll of the dice. the voltage regulator will control the voltage, but has limited ability to control the amperage. it just isn't all that critical in cars, and the designers feel that it is better to err on the side of caution and have a bit more going in than less.



i would definitely measure the output under the intended conditions.

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[PorscheG96]

I think you guys are confusing Lithium Ion batteries and Lithium Iron Phosphate, like the Battery Tender, Volt Phreaks, etc. LiFePO is far more stable and safer than Lithium Ion batteries used in consumer electronics. People have also used Volt Phreaks without any problems and they don't even list max charge rate on any of their products; otherwise the specs for power and capacity are very similar except incredibly high price!



http://www.voltphreaks.com/technologylfp.php



Also, if you read the description then it FEATURES a max charge rate of 10 amps, so there's probably current regulation at the battery that won't allow higher current than that, for safety. If you're drawing more than 10 amps then it probably cannot recharge to keep up. The only warnings that come with the battery are for voltage in excess of 14v, not too high amperage.

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[flash]

no confusion here. lithium is an alkali metal, and by that very nature, highly combustible. this is exactly whey they are not currently being allowed in mass produced cars. different casings have to be developed and crash tested. the current casing design results in explosions. once they sort that out, the superior storage capabilities of the batteries will be able to be exploited.



again, do what you want, but i'm sure not going to be the guinea pig on that one.

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[PorscheG96]

I just finished a prototype mount for the 3 lb Battery Tender, installed it and completed cold start tests as well as a 30 min test drive...so far, I couldn't be happier! It cranks just like the standard 35.5 lb battery when engine is cold and I could feel the lightness and ease of turn-in at the front of the car, even during normal driving. It's subtle, but it's there and I'm excited to autocross with it tomorrow.



I just cut a base out of aluminum sheet and adhered padding that was included with the Battery Tender to fit snugly underneath the outer battery tray lip and is secured using the stock stud / nut fastener. A quick temporary solution was 8" bungie cords hooked onto small angle brackets with M5 hardware to the aluminum base. It took 20 min to fab from scratch so I'm happy and it sits very snug in the battery compartment! <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" />



Here's a link to some photos and first start video: http://s206.photobuc...ry/LW%20battery



I'm thinking about putting together a plug-and-play kit with the highest capacity [3.75 lb] Battery Tender battery, M6 to SAE battery terminals [these come separately from the battery] and a carbon mount with toothed plastic strap that fastens to the car securely with factory hardware. Would there be any takers for this once I've done more testing with this battery?

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[flash]

as somebody who has developed a lot of products, and gone through the Q&A process in development, i applaud the enthusiasm, but let me offer some sage advice.



how about we get some real data first? there are enough half-baked things out there (not saying this one is). if this works out it would be cool, but if it doesn't, it could be a big black eye.



i'm doing some homework on lithium batteries to determine its volatility in real world applications. initial information is not promising, but we'll see. it technically "works" but appears to have some very real issues. personally, it's not something i would like to get sued over, and waivers don't hold up in court. as a product developer, you would be assuming the risks, not the user. cover your butt.



in the meantime, how about some load tests, with measured loads and charge rates, as well as some temperature readings under full charge? also, some real information, and not advertised claims, on storage capacity would be important for anybody considering this.



keep up the work and let us all know when you have enough information to make it easy for somebody to pull the trigger on.

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[Bulti]

Lol, what's the alarm going off? Fire?

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[Cloud9...68]

What I'd be most interested in is how many starts your battery car perform on a hot day. The reason is that the fans, which keep running after you turn off the engine, draw about 12 amps, so the battery that I bought, shown here:



http://www.etx15l.com/



can perform at most five starts on a hot day here in Austin. In other words, if I have the battery fully charged, and drive the car until it's fully warmed up, go into a store, and come out and start it again, I can repeat this process at most five times before the battery dies. This isn't a huge problem for the way I use the car, but whatever battery I would buy to eventually replace mine would have to perform at least this well. Also, the lower temperature limit for its ability to start the car is about 35 degrees F. But with only 220 cold cranking amps, this isn't surprising. This is actually more of a limiter, because it would prevent me from going to the track on a cool (not even really cold) day.



Please keep us posted as to how your battery performs, especially how many starts it can do on a hot (if there is such a thing in the Bay Area!) day. But don't leave yourself stranded!



Flash, I'm confused as to your concerns over the safety of lithium ion batteries. I know they have a tendency to do nasty things like explode and catch fire, but they're been used for a few years now in Chevy Volts, Nissan Leafs (Leaves...?), and Teslas. Yes, there have been a few well-publicized problems, but overall, they seem to be performing pretty well. But I also know these cars have pretty elaborate cooling systems built into their battery packs. Are you concerned that aftermarket lithium-based batteries, without benefit of the protective systems the car manufacturers build into their cars, going to be less safe?

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