DIY battery + Capacitors, useless or ok?

[Tommy L]

Is your pack 24ah or 2.4ah? Somethings not quite right.... \\m//

My pack is 24Ah (twenty-four). As I wrote before it's made out of 120 Li-Ion (li-co) 18650 cells recovered from "dead" laptop batteries.

What's wrong?

Without knowing the exact specs of the 18650 cells, I'd only be guessing at this point. The guess would be that the pack you built
is not capable of sustaining 30amps. 33amps x 36v is 1200 watts. If you have built a 24ah pack, then it's not capable of sustaining a
1.375C. Possible weak or dead cells, bad connections(cold solder joints). I would think that a healthy 24ah/36v pack should/would be able to
sustain 1.375C without an issue. When you have a solid pack, you will not be looking at Caps.

Tommy L sends... \\m//

[spuzzete]

Without knowing the exact specs of the 18650 cells, I'd only be guessing at this point. The guess would be that the pack you built
is not capable of sustaining 30amps. 33amps x 36v is 1200 watts. If you have built a 24ah pack, then it's not capable of sustaining a
1.375C. Possible weak or dead cells, bad connections(cold solder joints). I would think that a healthy 24ah/36v pack should/would be able to
sustain 1.375C without an issue. When you have a solid pack, you will not be looking at Caps.

Tommy L sends... \\m//

From what I gather from people that use the same cells it's pretty common for this pack to have "voltage sag" this way (discussion here viewtopic.php?f=3&t=26383) . These are not high discharge cells. Thing is when I pull 30 amps and the motor is already moving the voltage doesn't sag so much (3.2v alarm is not triggered).
The longest trip I had with this pack is 27km and the voltage under load looked still good (above 35v). Tomorrow if the weather is good I will go for a 40km+ trip, let's see.

[ProDigit]

I would just buy any 48V battery pack, preferably the regular Li Ion batteries, and plug that one in parallel with your current pack.
That way not the battery alone, but also the extension battery will provide the amps.
I personally would choose the cheapest Li Ion battery, because too much risk in destroying, stealing, breaking, accidents etc.
But even if not, 48V@10A provides you with an additional 480W sustained power, and it extends your range somewhat!

Although a capacitor might be really good to catch voltage fluxuations and spikes, it won't be able to catch the cranking amps the motor demands in the beginning.
Large capacitors are expensive, but perhaps a capacitor meant for industrial purposes (like the ones rated for 3000V, bout the size of a hot dog) would do the job.

[CamLight]

Although a capacitor might be really good to catch voltage fluxuations and spikes, it won't be able to catch the cranking amps the motor demands in the beginning.

Actually, ultra-capacitors (super-capacitors) are incredibly good at supplying hundreds to thousands of amps for even several seconds without problems. I have a 6S ultra-cap string (using 400F caps) here that can easily start a 1000CC motorbike.

Yup, these things are big.
Yup, they're expensive too.

[CamLight]

Hi,

thank you for posting the formula! So based on your calculation I would need about 1F for 0.5 seconds with the data you used.

So I should expect to "see/feel" some changes using a 5F supercapacitor.

I am thinking to use the cell-log8 to have a log and see the behaviour of the bat with and without capacitors. For now I will not use supercaps, I will just try with all the free stuff I can get.

Any suggestion about accurate logger(s)?

A supercap string with an effective capacitance of 1F would be the absolute minimum I'd recommend trying out. A 5F (effective) string would be better.

Assuming 2.7V supercaps running at 2.5V max, you'd need 17 caps in series to cover a fully charged 10S pack.
And since the capacitance is reduced when you connect caps in series, you'll need a string of seventeen 20F supercaps to get a 1F string that will handle 42V without problems. Better to have a string of seventeen approx. 100F supercaps though (effectively 5F).

Caps in series formula:
Ceff = 1 / (1/C + 1/C + 1/C ....etc.)
Where Ceff= effective capacitance of the cap string and C is the capacitance of each cap.

Be sure that the ESR (internal resistance) of each cap is very low because putting seventeen in series will severely limit the cap string's effectiveness otherwise. A few passes at some Ohm's Law equations will let you know how much the voltage will drop for any particular caps you find.

[Edit] Almost forgot....
You'll need to balance the string of supercaps since they typically operate quite close to their maximum rated voltage. You can do that with a 250 ohm resistor across each supercap, allowing 10mA of balancing current to flow. Unless you charge each cap individually before assembling the string, it will take a few days on the charger/power supply to balance the caps. And, there will be a continuous 10mA flow from the battery pack through these resistors as long as the cap string is connected to the pack. You can disconnect the cap string and allow it to discharge but it will draw a huge surge from your pack when you connect it again.

Just a few of the reasons why supercaps are only good for a very few, specific applications.
They can be a lot of fun to play with but a new battery pack would be a lot less expensive.

[megacycle]

3 of these @ 8F X 48v would give that bike a serious kick in the ass. I'm thinking 150A or so they could deliver,
not much sag then, own built in balancing too
Shame they're $135 each pretty small @ about 100 x 50 x 50mm, 500+ group buy give them a price $5 each .
http://www.tecategroup.com/store/index. ... ts_id=1225.

Supercaps are coming down in price, they're be one hanging off every heavy duty lipo set up soon.
Thet will have to do until they bring out these in a year or two.
http://www.technologyreview.com/article/40220/

[ProDigit]

Just one question,

We all know capacitors can blow.
What happens if they do? Will it short circuit, or will it disconnect? (usually when they blow,is when one of the anode plates touches a cathode plate, and it blows.

If you ask me, the higher the voltage handling, the better the cap, as it will probably last longer on lower voltages.
Instead of finding on that operates on 36/48/96V or even 110V, wouldn't it be better to have one that operates at 1kV or so?

Too high values aren't good neither, as their leakage may be larger (eg: 5V leakage on a 5kv capacitor, may be insignificant for those 5kV operations, but if it's operating at only 20V, 5V is a lot).

[ProDigit]

3 of these @ 8F X 48v would give that bike a serious kick in the ass. I'm thinking 150A or so they could deliver,
not much sag then, own built in balancing too
Shame they're $135 each pretty small @ about 100 x 50 x 50mm, 500+ group buy give them a price $5 each .
http://www.tecategroup.com/store/index. ... ts_id=1225.

Supercaps are coming down in price, they're be one hanging off every heavy duty lipo set up soon.
Thet will have to do until they bring out these in a year or two.
http://www.technologyreview.com/article/40220/

Why not simply solder 2 lower powered ones in parallel, to get the same rating if that's cheaper?

Also,the cap you linked to has an operating voltage of 16V, you must go higher than your max voltage (that is, in case the battery is fully charged, and the motor is regenerative breaking (think 60V +)


I think audio capacitors might be really nice!
Capacitors used in audio amplifiers (especially for high power car amplifiers), are reasonably priced.
They usually handle upto about 60V, though I can't tell from the amazon specs.

This one would look quite cool to mount under the bike, especially because it has a blue led built in (10Farad, ~$65):
http://www.amazon.com/Boss-CAP10-10-Far ... =de_a_smtd

[Tommy L]

I would just buy any 48V battery pack, preferably the regular Li Ion batteries,

I had to kick in here..... you say: "Regular Li Ion Batteries".

Read this..
A battery is a transducer that converts chemical energy into electrical energy and vice versa. It
contains an anode, a cathode, and an electrolyte. The anode, in the case of a lithium battery, is the source
of lithium ions. The cathode is the sink for the lithium ions and is chosen to optimize a number of
parameters, discussed below. The electrolyte provides for the separation of ionic transport and electronic
transport, and in a perfect battery the lithium ion transport number will be unity in the electrolyte. The
cell potential is determined by the difference between the chemical potential of the lithium in the anode and
cathode, ¢G ) -EF.

My question is: what is the regular cathode material to be a regular Li Ion cell?

CoO2 (cobalt oxide)
Mn2O4 (manganese oxide)
NiO2 (nickel oxide)
FePO4 (ferrous phosphate, also know as Iron phosphate)

So the combined chemistry gives the cell a certain potential.
What concerns me here is that we are all trying to help each other, so I'm trying to point out that there is
no such thing as a Regular Li Ion Cell or Battery Pack for someone to purchase. Each chemistry has
pro's and con's and care/maintenance to have longevity and safety.

What one to pick and how much you need is almost always based on what you are trying to achieve and being able
to understand it's limitations and safety requirements once you choose a Li chemistry. \\m//

Tommy L sends.....\\m//

[ProDigit]

with a 'regular' Li battery I mean Li-Ion, which is currently the standard of Li batteries (soon to be replaced by lifepo4); but also one of the cheapest batteries, as lifepo4 can be quite expensive.

They are used in electric bikes, are extremely lightweight (more so than liFePo4), and handle good current flow.
Whatever power generated by the motor through regenerative breaking (if applicable) can be shared and absorbed over both batteries.

any battery has the same properties as a capacitor, in that it can charge and discharge like a capacitor, only a little slower, but handles much more capacity.

I know there are lots of Li-type of batteries out there, the best would be LiCd, because of it's superior power handling, and peak draw, but it's considered unstable, and can catch fire. But just any battery you can get your hands on, like the ones they sell in BMSbattery.com

For the purpose of just having more torq when accelerating, that depends on the motor. The motor can only handle a certain amount of power, and there's no use going above that. However, if your battery only delivers 15 sustained amps, and 30 peak (@48V that is 1440W); but you're equipped with a 700W motor that can handle a peak draw of 2kW, you will benefit more from installing a second battery than a capacitor.

For instance:
An electric bike does not have much storage space,
This battery is only 66mm X 168mm X 158mm, just about as large as a 2 large capacitors.
http://www.bmsbattery.com/48v/166-48v-1 ... -pack.html

It handles power fluxuations well too
It gives more than enough power to the motor to max out the motor's powerhandling, when plugged in parallel with the stock battery
Any voltage spike will be shared over the two batteries, meaning spikes will be halved, current draw (cca) will be significantly reduced
On top of that, it gives you longer mileage,something a capacitor does not do.

[ProDigit]

Interesting news article concerning research of super capacitors:
http://www.technologyreview.com/article/40220/

[spuzzete]

Assuming 2.7V supercaps running at 2.5V max, you'd need 17 caps in series to cover a fully charged 10S pack.
And since the capacitance is reduced when you connect caps in series, you'll need a string of seventeen 20F supercaps to get a 1F string that will handle 42V without problems. Better to have a string of seventeen approx. 100F supercaps though (effectively 5F).

Will it be better or worse if I will connect a 1F 5.5v cap ( http://www.ebay.ca/itm/1F-1-Farad-10000 ... 27c21b24d5#ht_1628wt_952) to each one of the 3.6v cells?

Using supercapacitors and having to balance them separately sounds like a pain.

[dogman]

Well, I sure blew my comment a few pages back. Somehow I got the idea he'd used 18650 A123 cells.

But now I'm positive he's got a battery problem. Caps might be fun, but if your average discharge rate over a long period is high enough, even using caps, the cells are getting beat like a dog that peed on moms rug. Those cells will just have to work hard to refill those caps, and nothing will be gained untill the battery improves.


It's a battery problem. $$ will fix it. http://www.hobbyking.com/hobbyking/stor ... _20C_.html

BTW, if you get the voltages to match, you could just paralell the lipo with your existing battery, Just like a cap, but it would work better, actually lowering the c rate on your laptop cells.

8582(3).jpg (61.31 KiB) Viewed 140 times

[spuzzete]

It's a battery problem. $$ will fix it. http://www.hobbyking.com/hobbyking/stor ... _20C_.html

Well, I know I can spend a bunch of $$ and get what I want. But that's not my point. I want to build things recycling stuff, it's not fun just buying everything and putting it together.
For me it's a learning experience.

[SamTexas]

Ignore dogman's comment. You don't have a problem with your battery. The voltage sag your seeing is normal. This type of cell is designed for laptops, typical discharge rate is 0.5C. You can 1) increase your battery capacity or 2) add more cells in series to compensate for voltage sag.

[ProDigit]

Ignore dogman's comment. You don't have a problem with your battery. The voltage sag your seeing is normal. This type of cell is designed for laptops, typical discharge rate is 0.5C. You can 1) increase your battery capacity or 2) add more cells in series to compensate for voltage sag.

Putting batteries in series is not recommended, lest you destroy the controller or other electric gear on the bike, unless the voltage of the battery you put in series is really low. Like for instance, buy 2x LiFePo4 cells, make sure you solder enough in parallel that they have a larger Ah rating than your internal battery, put them in parallel with each other, then the bundle of batteries, put that in series with the internal battery.
It won't act like a very good buffer, but the voltage increase should give you tiny bits more torq, and some buffering should be done by the batteries.
Your mileage should increase insignificantly but it's there...

Either way I'd not recommend this configuration anyway; too hard with charging them and stuff...

[dogman]

Well, I still think caps won't make those laptop batteries perform. They can do what they do, no more.

So ignore the spend $$ comment. I understand not wanting to do it that way. So paralell in enough freebie batteries to get the amps you want. You will just murder that pack if you keep pulling 32 amps spikes.

[megacycle]

3 of these @ 8F X 48v would give that bike a serious kick in the ass. I'm thinking 150A or so they could deliver,
not much sag then, own built in balancing too
Shame they're $135 each pretty small @ about 100 x 50 x 50mm, 500+ group buy give them a price $5 each .
http://www.tecategroup.com/store/index. ... ts_id=1225.

Supercaps are coming down in price, they're be one hanging off every heavy duty lipo set up soon.
Thet will have to do until they bring out these in a year or two.
http://www.technologyreview.com/article/40220/

Why not simply solder 2 lower powered ones in parallel, to get the same rating if that's cheaper?

Also,the cap you linked to has an operating voltage of 16V, you must go higher than your max voltage (that is, in case the battery is fully charged, and the motor is regenerative breaking (think 60V +)

I think audio capacitors might be really nice!
Capacitors used in audio amplifiers (especially for high power car amplifiers), are reasonably priced.
They usually handle upto about 60V, though I can't tell from the amazon specs.

This one would look quite cool to mount under the bike, especially because it has a blue led built in (10Farad, ~$65):
http://www.amazon.com/Boss-CAP10-10-Far ... =de_a_smtd

That's why specified 3 in series at a high F to give that value for his 36V pack, also they're rated to go a decent amount over, 55v probably wouldnt hurt, also got to get those caps made to deliver pulse power, the 1F dual layers of the ebay would be back up type rated at like ohms of ESR to deliver like mA over say minutes ,not Asecs.

Generally supercaps i've sourced have a standard voltage similar to lipo of 2.5=2.7V, 5.5v for dual layer.
The audio caps what's thier V fating & ESR, what's they're pulse power they could be good,if the specs are there

[liveforphysics]

with a 'regular' Li battery I mean Li-Ion, which is currently the standard of Li batteries (soon to be replaced by lifepo4); but also one of the cheapest batteries, as lifepo4 can be quite expensive.

Umm... wow. If you're completely clueless, it's better to post less and read more.

[Tommy L]

with a 'regular' Li battery I mean Li-Ion, which is currently the standard of Li batteries (soon to be replaced by lifepo4); but also one of the cheapest batteries, as lifepo4 can be quite expensive.

Umm... wow. If you're completely clueless, it's better to post less and read more.

AMEN!

Tommy L sends.... \\m//

[SamTexas]

You will just murder that pack if you keep pulling 32 amps spikes.

Once again, ignore dogman's comment. The 32A spikes you have while accelerating is PERFECTLY ok with your 24Ah battery. This 32A spike only happens once every few minutes (if you do a lot of start stop riding) and each spike only lasts 1 seconds or so. What you want is to maintain around 0.5C (12A) or less while you're cruising, and slow down (or pedal assist really hard) on long uphill.

with a 'regular' Li battery I mean Li-Ion, which is currently the standard of Li batteries (soon to be replaced by lifepo4); but also one of the cheapest batteries, as lifepo4 can be quite expensive.

Umm... wow. If you're completely clueless, it's better to post less and read more.

The above is just one of many.

[megacycle]

Assuming 2.7V supercaps running at 2.5V max, you'd need 17 caps in series to cover a fully charged 10S pack.
And since the capacitance is reduced when you connect caps in series, you'll need a string of seventeen 20F supercaps to get a 1F string that will handle 42V without problems. Better to have a string of seventeen approx. 100F supercaps though (effectively 5F).

Will it be better or worse if I will connect a 1F 5.5v cap ( http://www.ebay.ca/itm/1F-1-Farad-10000 ... 27c21b24d5#ht_1628wt_952) to each one of the 3.6v cells?

Using supercapacitors and having to balance them separately sounds like a pain.

Beckup power lol, reckon your on to something there though, go to cell level, Eureeka matey thanks for that, that's similar to the set up for a prototype cap balancer i'm trying out. It might be a double and i did'nt realise it.
The supercap balancer (floating cap type) set up i'm knocking together takes charge and shuffles it, but if they are idle they are still across the cells, if they balance the cells then they are balanced themselves and they're pulse power's there for the ev grin, totally complementary as they're supposed to be, beaut.
These are the one's was hoping to use, 2 in series should give the time constant i need, though how does this relate to scratching my head again .
http://www.tecategroup.com/store/index. ... ucts_id=95

[spuzzete]

Hi everyone,

thank you for your contribution(s) to the discussion. I haven't read all the recent comments, I will do it later.

I went for a bike ride today and I got some data. The trip was 47.7 km (#5 in the table below). I pedalled very little to help the motor uphill or at few traffic lights to get out of the way asap. I stopped only to check where I was (I am new to this place) and for about 15 minutes to a friend's house at half distance.All the time I could I was full throttle.I am quite satisfied with the performance. Again the cells go below 3.2v only when the motor is not moving. I guess If I can set the controller to put only 20A from still it will probably solve the problem.

Rides Data

Fullscreen capture 5262012 42446 PM.bmp.jpg (118.29 KiB) Viewed 128 times

Est range is calculated on 80% DOD.

I tracked the trip with a gps application (strava) on my phone, and I have a nice graph of the ride:

Tracking

Fullscreen capture 5262012 42609 PM.bmp.jpg (72.55 KiB) Viewed 128 times

[ProDigit]

That's why specified 3 in series at a high F to give that value for his 36V pack, also they're rated to go a decent amount over, 55v probably wouldnt hurt, also got to get those caps made to deliver pulse power, the 1F dual layers of the ebay would be back up type rated at like ohms of ESR to deliver like mA over say minutes ,not Asecs.

Generally supercaps i've sourced have a standard voltage similar to lipo of 2.5=2.7V, 5.5v for dual layer.
The audio caps what's thier V fating & ESR, what's they're pulse power they could be good,if the specs are there

You can not solder caps in series, they won't function. THey'll function just like the weakest capacitor in the chain at best, at worst they will function just like an interrupted wire.

[ProDigit]

with a 'regular' Li battery I mean Li-Ion, which is currently the standard of Li batteries (soon to be replaced by lifepo4); but also one of the cheapest batteries, as lifepo4 can be quite expensive.

Umm... wow. If you're completely clueless, it's better to post less and read more.

Post less I would agree, read more, unfortunately there aren't that many posts concerning the issues I'm dealing with.
Clueless, not at all!
Tell me what I wrote is incorrect, unless I made a spelling mistake, or said 'series' instead of 'parallel' somewhere (which makes a big difference in real life, but when it's late at night, i tend not to proof read my posts too much...


And TommyL, it seems you're very close to being one of those forum jerks who only tend to bitch at people when they differ in opinion about something, or disagree with you, or talk about things you don't know pipsqueak about!
I mean, it's not nice to treat people like this if they honestly want to help out other people. And unless you can point out my error, please refrain from bashing other forum members, it makes you very unpopular.