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Old 03-26-2015, 06:24 PM   #1
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Default Lightweight battery snobs...

Cliffs: this guy has built a couple of replacement car batteries out of surplus Maxwell brand ultracapacitors.




Normally I wouldn't post stuff like this, as the source doesn't appear to be wholly credible (eg: his claim that he's getting these capacitors for $6 seems dubious), but it's an interesting concept for those folks who find LiIon batteries to be far too heavy and/or don't want to risk the possibility of killing one due to over-discharge.


That, and the manufacturer of the capacitors in question actually does product a couple of "battery" modules intended for automotive engine starting:

Maxwell Technologies Engine Starting Module

http://www.maxwell.com/images/docume...00552_EN_1.pdf
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Old 03-27-2015, 10:46 AM   #2
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People in the comments say those caps are $60 a pop. It's hard to take the guy seriously when his reason for doing the conversion is saving 20lb for fuel economy (plus is awful glued together plywood). Also, caps in his engine bay without any kind of battery box? Seems like a great way to start a massive car fire.
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Old 03-27-2015, 01:28 PM   #3
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Erm, I'm pretty sure my LiPo battery weighs less than the plywood he used to hold that pack together.
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Old 03-27-2015, 02:15 PM   #4
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Quote:
Originally Posted by Leafy View Post
Erm, I'm pretty sure my LiPo battery weighs less than the plywood he used to hold that pack together.
This was my thought.
My aluminum battery box weighs more than the battery..

-Ryan
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Old 03-27-2015, 02:23 PM   #5
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The brass terminals that most people put on the motorcycle type batteries to work in cars weigh (~1200g) more than my battery (~1000g).
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Old 03-27-2015, 02:25 PM   #6
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Leafy, what battery do you use.
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Old 03-27-2015, 02:34 PM   #7
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Leafy, what battery do you use.
https://www.hobbyking.com/hobbyking/...dProduct=58820

Between this battery, my volvo electric power steering pump, and the geo tracker alternator (55amp at idle) it will pull this battery down to unsafe voltages in 20 minutes if I hold the power steering pump against the stop as hard as I can (80 amp in this case) while idling. In other words, its fine because I'm sure the pump would have problems in less time than that. Havent run it long enough to need to balance it. Another guy that I race with was running one in his daily driver civic as a test, he left his headlights on while at work one day and killed the battery, like it swole up and wouldnt hold a charge anymore kill, but thats a problem with all lipo batteries.
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Old 03-27-2015, 06:02 PM   #8
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Are you just using that 4S pack with no charge circuit? What prevents the battery from being over charged?

I only ask because I can get 4S lithium batteries through work....just concerned about safety over the course of several hours of running.
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Old 03-27-2015, 06:20 PM   #9
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No circuit, if you're really concerned you can build one, but the alternator's own circuitry works well enough. Motorcycles work the same way or even less sophisticated and they've been using 4s lipo and lifepo4 packs for years.
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Old 03-27-2015, 07:20 PM   #10
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Couldn't you use a simple charging chip to keep the battery from over-charging. Or draining too much?
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Old 03-28-2015, 02:57 AM   #11
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Quote:
Originally Posted by Leafy View Post
No circuit, if you're really concerned you can build one, but the alternator's own circuitry works well enough. Motorcycles work the same way or even less sophisticated and they've been using 4s lipo and lifepo4 packs for years.
Hmmm...Interesting, I guess I've just seen too many batteries puff and get sketchy with our RC cars that makes me a little more apprehensive especially since there is nothing to ensure the cells stay balanced. I think some of my apprehensiveness also comes from my lack of knowledge of how the stock alternators circuit works.

I do have a spare 4S that I use for jumping cars in case of emergencies, but maybe I'll give this a try, but just build a battery enclosure (just to be safe!).
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Old 03-28-2015, 03:01 AM   #12
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I do have a spare 4S that I use for jumping cars in case of emergencies
Tell me more about this. I've been looking for a cheap jump box for a while.
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Old 03-28-2015, 03:24 AM   #13
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Quote:
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Tell me more about this. I've been looking for a cheap jump box for a while.
I just have small gator clips that I put on the 10ga wire that goes to my 4S battery and its cranked over plenty of full sized cars with ease. I will periodically check the charge of the battery and just re-peak it on my charger.

I can take pictures of this tomorrow if you'd like.
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Old 03-28-2015, 03:25 AM   #14
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Pictures, links, instructions, etc would all be awesome.
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Old 03-28-2015, 11:02 AM   #15
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Old 03-28-2015, 11:24 AM   #16
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Quote:
Originally Posted by Leafy View Post
No circuit, if you're really concerned you can build one, but the alternator's own circuitry works well enough. Motorcycles work the same way or even less sophisticated and they've been using 4s lipo and lifepo4 packs for years.
Have any links? Because that sounds real stupid. How are you going to keep the cells balanced when charging with an alternator?
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Old 03-28-2015, 11:26 PM   #17
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It stays balanced pretty well naturally. If you're really concerned you can buy a blinkly balancer for $40 and it'll automatically bleed amperage from any of the cells that over volt as it charges normally. Its not a big deal pretty much all of the LiFePO4 motorcycle batteries do not have internal balance circuits (ballistic, braille, anti-grav, etc), and they're fine I would take it off the car yearly and throw it on the balancer. This is way less traumatic to the battery than being run in an r/c car, it'll pretty much never see any sort of low charge levels. Oh, and dont use a normal LiPO, the voltage is too high it'll over volt the car and then it wont even come close to being fully charged. And LiPOs are the explody hydrogen batteries, LiFePO4 much less so.

Here's what it looks like in the back of the car for more size reference. Maybe I'll come up with something that doesnt involve a zip tie when I have more time in like 3 years. The battery weighs about as much as the tiedown hardware and tray from the stock battery.

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Old 03-29-2015, 01:24 AM   #18
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Is there any reason someone couldn't ditch all the wire to the trunk and just shove that little thing under the hood? If we are talking weight that should add up, plus better cranking volts with less drop?

I don't really agree with running it with no protection circuit though, I don't really know much more than 18650's and discharge rates though.

That wiring looks like the **** in my trunk. I burned the grey rubber positive boot cover. After that I kinda quit messing around with zip ties and all that to hold it down, actually bought factory hold downs.
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Old 03-29-2015, 07:14 PM   #19
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Sure go ahead and move it. This was quick and dirty because my oem battery died. I eventually plan to rewire the car and I'll move the battery then.
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Old 03-29-2015, 08:43 PM   #20
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Perhaps if you guys feel like reading?

12V BoostPack
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