DIY battery + Capacitors, useless or ok?

[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 133 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 120 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 120 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.

[megacycle]

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...

I see the magic smoke in what he's saying Luke.
What's the pro's opinion on the supercap thing for improving sag in low C packs are supercaps complementary or a waste of time here.

[Tommy L]

Based on your 36v/24ah pack that apparently is rated at 0.5c you are probably drawing 1.5c at your Max Speed.
Also, you are trying to pull more watts or constant high watts if there is heavy head winds or hills while at max speed.

Sam Texas was saying to peak the pack at 1.5c on occasion is fine but if you are maintaining 47kph and/or headwinds/hills
the pack would have a shortened life. If the packs internal resistance is high, the cells will heat up. Heat is nearly always
a killer.

I like the Nikola Tesla approach...."Experiment - Observe - Take notes"
This style of learning is priceless!

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

[megacycle]

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.

imagesCAM1CZ27.jpg (6.63 KiB) Viewed 118 times

Electricity 101 you can put caps in series.

[ProDigit]

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.

imagesCAM1CZ27.jpg

Electricity 101 you can put caps in series.

Well, just try it out if you don't believe me. Capacitors should be placed in parallel:
http://lmgtfy.com/?q=solder+capacitors+ ... +or+series

http://www.electronics2000.co.uk/calc/s ... ulator.php
Capacitor calculator shows a DECREASE in capacity when soldering in series; they will function,but just less good than when you'd just take the most powerful capacitor and connect it by itself.

[spuzzete]

Sam Texas was saying to peak the pack at 1.5c on occasion is fine but if you are maintaining 47kph and/or headwinds/hills
the pack would have a shortened life. If the packs internal resistance is high, the cells will heat up. Heat is nearly always
a killer.

I like the Nikola Tesla approach...."Experiment - Observe - Take notes"
This style of learning is priceless!

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

I think you missed the graph I posted. You can clearly see that 47Kph is downhill. My bike has a 36v 500w geared motor. Top speed on the flat (no pedalling) is 32kph If I want to go more I go downhill or I pedal. I am fine with that. Also typical power draw on the flat and no pedalling is between 300-500w depending on wind/slight uphill or downhill.

I may not be an expert in electronic but I can count.

Peace.

[Tommy L]

I think you missed the graph I posted. You can clearly see that 47Kph is downhill. My bike has a 36v 500w geared motor. Top speed on the flat (no pedalling) is 32kph If I want to go more I go downhill or I pedal. I am fine with that. Also typical power draw on the flat and no pedalling is between 300-500w depending on wind/slight uphill or downhill.

I may not be an expert in electronic but I can count.

Peace.

Fair enough, it looks like you have it under control.

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

[Tommy L]

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!

oh my, if you read any of my posts you will see that I genuinely try to help others here. And we help without using profanity.

Did you read this from my earlier post? It does clarify many things to a new poster here. I'm merely trying to assist "SPUZZET".

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.

[SamTexas]

Fullscreen capture 5262012 42609 PM.bmp.jpg (72.55 KiB) Viewed 340 times

If that's how you ride, you don't have a single thing to be concerned about your battery.

Looking at your final resting voltage and the number of Wh already used, I suspect you have overestimated the true capacity of your pack by 20% to 30%. I think your pack actual, usable capacity is 18 to 20Ah. By actual, usable I mean resting voltage of 3.30V per cell.

[megacycle]

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.

imagesCAM1CZ27.jpg

Electricity 101 you can put caps in series.

Well, just try it out if you don't believe me. Capacitors should be placed in parallel:
http://lmgtfy.com/?q=solder+capacitors+ ... +or+series

http://www.electronics2000.co.uk/calc/s ... ulator.php
Capacitor calculator shows a DECREASE in capacity when soldering in series; they will function,but just less good than when you'd just take the most powerful capacitor and connect it by itself.

Most tecs like me do calcs like these in their heads and i'm nowhere near as knowlegable as a lot of the guru's, i would'nt even be a Howard Wolowitz, but i've got a good grasp on what you can do with most caps just like other passives as long as you know the specs.
caps in series 1/sum of reciprocals, caps in parallel sum, capacity same, Yawn, want to refresh me on dv/dt.

[spuzzete]

If that's how you ride, you don't have a single thing to be concerned about your battery.

Looking at your final resting voltage and the number of Wh already used, I suspect you have overestimated the true capacity of your pack by 20% to 30%. I think your pack actual, usable capacity is 18 to 20Ah. By actual, usable I mean resting voltage of 3.30V per cell.

Thank you SamTexas!

I may have overestimated the real capacity of the pack of course, and maybe I made a mistake in my calculation assuming the pack would be 100% efficient. As there is always a loss in heat somewhere, I guess you're right. Still not bad for those used cells. I am amazed I could ride almost 50 km with no problems!

This last ride I did try to go the fastest I could on purpose to see the limit of the pack. I was almost expecting a cell failure on my way back home but this confirms that I tested those cells properly before putting them together.