Super capacitors to replace the battery

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jfunk
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Super capacitors to replace the battery

Post by jfunk » Thu Jun 23, 2016 9:50 am

This is purely just a bit of fun at this stage and I know it is not a practical solution yet.
I plan on replacing the heavy lead acid battery with light weight super capacitors as it may be a cheap way to shave off 15-20kgs but not sure how well it will work in the RX8 yet so I will start off small and cheap before going the whole hog

SO..

Good points of capacitors
Light weight
High current output
Low internal resistance so they don't get too hot

Bad points
They lose voltage over time so not good if you don't use the car regularly
Smaller capacity so if your car does not start first time it may be game over

I have seen people online start a car with 360 farads @ 12V but 3000f seems to be a more practical long term solution for a daily driver. If this works it would probably be good for track days where you just need to get it fired up and running but keep the weight down

As an experriment I am going to try firing up the car with a bank of 500 farad capacitors at rated up to 16V

I picked up the capacitors and the protection board for £47 and have started to make a case for them from acrylic not wanting to throw too much money at it until I have proved whether it is likely to work as a 3000f unit would cost around £200 in parts. This 500f bank weights around 850g including the case

Image

Image


This is very much a suck it an see experiment and according to my calculation it is border line whether 500f it will be enough to fire up the car but either way it will be interesting
If any one has any tips or ideas on the subject please let me know
Last edited by jfunk on Sat Dec 17, 2016 6:22 pm, edited 1 time in total.

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Re: Super capacitors to replace the battery

Post by PeteH » Thu Jun 23, 2016 10:56 am

Cool idea!

I'm sure you know this already, but a typical lead acid car battery contains around 1million to 1.5million Joules. Your 500f capacitor bundle can hold about 64 thousand Joules, so you only have about 4% of the energy of a lead acid battery. As you say, you could get sufficient current, but you'd have to hope it fires first time! The second issue will be that current. How are you going to get up to 200A off that board without melting it all? The third thing is that Lithium Ion batteries are now quite common, and also weight less than 1kg, but hold around 200thousand Joules, so there may already be a better "solution" to this one.

Having said that, it's a great idea, and I'll be fascinated to see how you get on. Good luck.
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Re: Super capacitors to replace the battery

Post by Nerdstrike » Thu Jun 23, 2016 11:14 am

There was a time when a farad capacitor was the size of a beer keg. Impressive miniaturisation.
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jfunk (Thu Jun 23, 2016 11:56 am)

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Re: Super capacitors to replace the battery

Post by jfunk » Thu Jun 23, 2016 11:56 am

PeteH wrote:Cool idea!

I'm sure you know this already, but a typical lead acid car battery contains around 1million to 1.5million Joules. Your 500f capacitor bundle can hold about 64 thousand Joules, so you only have about 4% of the energy of a lead acid battery. As you say, you could get sufficient current, but you'd have to hope it fires first time! The second issue will be that current. How are you going to get up to 200A off that board without melting it all? The third thing is that Lithium Ion batteries are now quite common, and also weight less than 1kg, but hold around 200thousand Joules, so there may already be a better "solution" to this one.

Having said that, it's a great idea, and I'll be fascinated to see how you get on. Good luck.
Yes - you are preaching to the choir :)
I looked up the spec for the protection board and it claimed to have no upper limit for current draw but I know that can not be the case, The traces on the PCB are pretty thick but may vaporise as soon as I turn the key - I will have a fire extinguisher on standby and try to video it as either way it will be interesting. As the capacitors are not too expensive, if that happens I may hard wire them and give it another go.
I know LiFePO4 cells would probably be a much more practical solution until graphine caps better and cheaper but if this works it will be a cheaper alternative.
This it just a bit of fun and I will probably end up using the caps in some other electronic projects after this experiment

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Re: Super capacitors to replace the battery

Post by Nerdstrike » Thu Jun 23, 2016 1:02 pm


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Re: Super capacitors to replace the battery

Post by joney » Thu Jun 23, 2016 9:05 pm

Love PhotonicInduction. I've seen people do a kind of hybrid with a lipo and super caps so you get the best of both worlds
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Re: Super capacitors to replace the battery

Post by jfunk » Sun Jun 26, 2016 6:35 pm

Well... I have been doing a bit more head scratching, testing and tweaking while it continually rains outside. As Nerdstrike mentioned the board was potentially a weak point but looking at the way the balancing circuit worked I noticed you could add bridges in between the caps without bypassing it to get the best of both worlds so I added a bit of heavy gauge silver wire I had knocking around.

Image

Unfortunately wile doing a bit of proper research I realized I had messed up :oops: I had not had to run caps in series before - with standard caps you just find one with the voltage range you need but super caps can only take 2.7V ish so you have to run multiple ones in series to get up to a higher voltage. What I had forgotten is that the capacitance goes down with each one added so this pack of 6 500f caps has an effective capacitance of 83.3f and it is highly unlikely it would be able to turn over my 2kw starter for long enough to fire up. I would have to use 3000f 2.7v caps to get 500f @ 16.2v.

So - looks like these will be used for something else and I will have to save some pennies to get bigger caps to have another go
Last edited by jfunk on Sat Dec 17, 2016 6:24 pm, edited 1 time in total.

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Re: Super capacitors to replace the battery

Post by Sonic KaBoomii » Tue Jun 28, 2016 1:09 am

This looks like a great way to test the notoriously weak ignition system.

Hope you get some data on the battery life before the engine eats itself :o
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Re: Super capacitors to replace the battery

Post by TomJ » Tue Jun 28, 2016 7:49 am

I must admit, doesn't it make sense to try this on something ordinary first before running the flooding risk on the RX? Super effort though.

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Re: Super capacitors to replace the battery

Post by PeteH » Tue Jun 28, 2016 11:38 am

I could be wrong here, but isn't the flooding risk caused by slow cranking? The motor is very rich during cranking, so if a nearly dead battery causes it to spin too slowly to fire then it floods. The one thing the capacitors would do is spin the engine quickly (just not for very long). So I would imagine capacitors might actually help prevent flooding, since you will get a few seconds of very fast cranking for it to try to catch, then nothing.....
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Re: Super capacitors to replace the battery

Post by TomJ » Tue Jun 28, 2016 12:16 pm

No idea Pete. I may be doing the 2+2=5 sum again.

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Re: Super capacitors to replace the battery

Post by SeriousSam » Tue Jun 28, 2016 5:25 pm

The cranking speed would be governed by the voltage across the starter motor terminals and the starter motor itself, and the torque of the starter motor is governed by the current that the supply can deliver - up to the maximum that the starter will draw. Supercaps should be able to deliver the maximum voltage and current consistently, but would discharge extremely quickly, as opposed to a battery which discharges more slowly, but can deliver lower voltages and currents when partially charged or in poor health - hence lower cranking speed.

Basically supercaps would give the best possible cranking speed from your starter motor for a few seconds, but it's a one-shot deal, because if it doesn't fire first time the caps will be fully discharged. That wouldn't necessarily help to prevent flooding, since flooding is caused by turning off the engine when it's still running rich and cold. I'm not sure whether a faster starter and new battery resolves the flooding risk on its own, I suspect the Renesis is just more susceptible to flooding. It may clear it on the first shot if you're lucky, but the only way to find out would be to flood your engine then try to start it on caps. I won't be running that test!
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Re: Super capacitors to replace the battery

Post by zippyonline » Tue Jun 28, 2016 7:31 pm

TomJ wrote: the 2+2=5 sum again.
If you've rounded from one decimal point back to no decimals, that could be correct :thumright:

2.4 + 2.4 = 4.8

Rounded to 0 decimal places, that's 2+2=5 :P
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Re: Super capacitors to replace the battery

Post by Sonic KaBoomii » Wed Jun 29, 2016 12:33 pm

You could start the car off a portable jump-starter pack if you were worried about cranking amps / flooding

It's the long-term effects on the ignition system I'd be worried about.
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Re: Super capacitors to replace the battery

Post by jfunk » Thu Jun 30, 2016 12:01 pm

I was thinking of getting the engine warmed up before the 1st test to help eliminate the flooding risk - I know it takes a couple of extra revolutions to start when hot but may be safer for the first test. I have put in an order for some 3000f caps from china so when they arrive I will give it a pop and see what happens.
I reckon adding one of these packs in parallel with the battery would help with cars that have stating issues as it would give your starter motor a lot more current to play with initially. The starter would initially draw a lot of current to deliver all the torque needed to spin up the flywheel and then it would taper off - one of these small packs would fill in the extra current the battery cold not supply and stop too much voltage sag.

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Re: Super capacitors to replace the battery

Post by jfunk » Sat Dec 17, 2016 6:19 pm

So .. After a lot of playing, I don't think capacitors are quite there yet. Too much self discharge to make them practical at the moment - time for phase 2

I got my hands of some 30Ah LiFePo4 pouch calls with a 400A discharge rate - these seem like a good candidate for a super light battery. I am starting work on a casing from them as they will need to be held under pressure to stop them from bulging and will probably need to make something to balance the charge but they are looking super promising. I may run them in parallel with super caps to take some of the strain during start up.

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Re: Super capacitors to replace the battery

Post by warpc0il » Sat Dec 17, 2016 7:41 pm

Hi jfunk

Could you please update your profile with your location
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Not that I normally bother about that sort of thing, but I'd like to know which way to look when watching out for the mushroom cloud... :xmaswink:
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Re: Super capacitors to replace the battery

Post by Phil Bate » Sun Dec 18, 2016 12:07 am

I'm not sure keeping the cells compressed is a good idea. The recent case of exploding Samsung Galaxy Notes was apparently partly due to a lack of expansion room built into the chassis. As the cells swelled the pressure imparted on them by some components caused them to short internally and burn uncontrollably.
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Re: Super capacitors to replace the battery

Post by joney » Sun Dec 18, 2016 12:25 am

I fly quad copters powered by lipo battery's and can say that if a cell puffs it generally means it's fopard and you should get ride quick. What phil said is very try most cells will swell a little but it's when they puff and have no room then you get boom
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Re: Super capacitors to replace the battery

Post by jfunk » Sun Dec 18, 2016 8:25 am

LOL - Don't worry these are not Li-ion or Lipo. They are Lithium iron phosphate. Much less explody than Lipo. They have a really low internal resistance and are deemed safe for automotive use. That said. I will ware my asbestos pants while testing
https://en.wikipedia.org/wiki/Lithium_iron_phosphate

I did just find this vid of some Chinese testes - I am not sure their health and safety regulations are as stringent as ours
[youtube]https://www.youtube.com/watch?v=aQs7L5LmEss[/youtube]

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Re: Super capacitors to replace the battery

Post by warpc0il » Sun Dec 18, 2016 3:38 pm

jfunk wrote:I did just find this vid of some Chinese testes...
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Re: Super capacitors to replace the battery

Post by warpc0il » Sun Dec 18, 2016 11:44 pm

Just watched that vid and, while it might have helped doing those first testing outside in sub-zero temperatures, those guys must still have balls of steel.
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jfunk (Mon Dec 19, 2016 3:08 pm)
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Re: Super capacitors to replace the battery

Post by Shagrington » Mon Dec 19, 2016 2:56 am

Much like the village blacksmith at the ball of Kerrymuir, but his were made of brass. :beer:
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