DIY battery + Capacitors, useless or ok?

[SamTexas]

You're welcome. If you do decide to proceed with the capacitor experiment, do come back for a detailed report. I would like to know how it works out.

[spuzzete]

You're welcome. If you do decide to proceed with the capacitor experiment, do come back for a detailed report. I would like to know how it works out.

I just ordered 2 cell-log 8s so I can produce decent data for the tests I am about to set. I am also tempted to order some of those 1F 5.5v capacitors and try to connect them to each 3,6v "block".

Let's see if it's a total bust or not!

[megacycle]

You're welcome. If you do decide to proceed with the capacitor experiment, do come back for a detailed report. I would like to know how it works out.

I just ordered 2 cell-log 8s so I can produce decent data for the tests I am about to set. I am also tempted to order some of those 1F 5.5v capacitors and try to connect them to each 3,6v "block".

Let's see if it's a total bust or not!

Looking forward to that if you do, though do'nt use those 1F 5.5's, they'll be back up type, they wont work at all.
You need the pulse power low/ultra low esr variety. I'm about to purchase mine thru Maxwell's site.
Tectate's on the site are the same price right up to 10F @ 2.7v @ $2,so x2, 5F @ 5.5v $4 x 10 =$40 + shipping.
There's also be the time constant thing, i'm trying to get my head around as my set up is to be multi tier
how much power to deliver into what impedance, for what duration Back emf oh no headache again

cap_balance_5.jpg (27.05 KiB) Viewed 342 times

Fetchter's and co. have been doing some nice mod's on the cell logs @ viewtopic.php?f=14&t=20142, i'm using them and done the jumper mod, not sucking so much now on the 1&2 channels.
Good Luck with it.

[megacycle]

You're welcome. If you do decide to proceed with the capacitor experiment, do come back for a detailed report. I would like to know how it works out.

I just ordered 2 cell-log 8s so I can produce decent data for the tests I am about to set. I am also tempted to order some of those 1F 5.5v capacitors and try to connect them to each 3,6v "block".

Let's see if it's a total bust or not!

Looking forward to that if you do, though do'nt use those 1F 5.5's, they'll be back up type, they wont work at all.
You need the pulse power low/ultra low esr variety. I'm about to purchase mine thru Maxwell's site.
Tectate's on the site are the same price right up to 10F @ 2.7v @ $2,so x2, 5F @ 5.5v $4 x 10 =$40 + shipping.
There's also be the time constant thing, i'm trying to get my head around as my set up is to be multi tier
how much power to deliver into what impedance, for what duration Back emf oh no headache again

cap_balance_5.jpg (27.05 KiB) Viewed 342 times

something like this but it's drawn wrong, as off, in the switching area.

Fetchter's and Co. have been doing some nice mod's on the cell logs @ viewtopic.php?f=14&t=20142, i'm using them and done the jumper mod, not sucking so much now on the 1&2 channels.

Good Luck with it.

[Njay]

If you do that cap experiment remember that the cap bank will pull a huge amount of current the instant you connect it to the battery (all sparky and all), so you'll probably need to pre-charge the bank.

[etriker]

If you are using a 10s laptop cell pack then you can parallel a 11s A123 26650 pack and they will act like caps and keep the current draw lower on the laptop cell pack.

I am using 10s 4p 2600mah laptop cell pack in parallel with a 11 s 3p A123 26650 pack to keep the current draw low on the laptop cell pack.

Allows use of a smaller number of laptop cells.

Going up hills the A123's deliver the amps and down hill the laptop cells recharge the A123 cells.

About 14 ah total. 73 cells total.

A friend is using a 10s 4 p laptop cell pack in parallel with a 11 s 1p A123 pack and also gets good results.

His is an ebike and uses less peak amps than my etrike.

[Tommy L]

If you are using a 10s laptop cell pack then you can parallel a 11s A123 26650 pack and they will act like caps and keep the current draw lower on the laptop cell pack.
I am using 10s 4p 2600mah laptop cell pack in parallel with a 11 s 3p A123 26650 pack to keep the current draw low on the laptop cell pack.
Allows use of a smaller number of laptop cells.
Going up hills the A123's deliver the amps and down hill the laptop cells recharge the A123 cells.
About 14 ah total. 73 cells total.
A friend is using a 10s 4 p laptop cell pack in parallel with a 11 s 1p A123 pack and also gets good results.
His is an ebike and uses less peak amps than my etrike.

This is interesting. What is the voltages of the two packs?
10s V?
11s V?

I'm trying to wrap my head around this.

Tommy L sends...

[etriker]

They are in parallel so the voltages on each pack are the same when sitting with no current draw on the packs.

With a load both packs will sag depending on the load.

The A123's will sag less than the laptop cell pack and deliver more current as the load increases.

Real world ebiking is up and down hills and stop and go for most of us.

The max load on my laptop cell pack does not go very high because the A123 packs hold the voltage up and the laptop cells cannot sag.

The less you sag the laptop cell pack the less you overload it.

[Tommy L]

They are in parallel so the voltages on each pack are the same when sitting with no current draw on the packs.
With a load both packs will sag depending on the load.
The A123's will sag less than the laptop cell pack and deliver more current as the load increases.
Real world ebiking is up and down hills and stop and go for most of us.
The max load on my laptop cell pack does not go very high because the A123 packs hold the voltage up and the laptop cells cannot sag.
The less you sag the laptop cell pack the less you overload it.

May I please have the standalone voltages of each pack....

10S pack voltage?
11S pack voltage?

When you parallel packs, the higher voltage pack will try to discharge into the lower voltage pack continually trying to equalize.
Do you unplug these packs while not in use?
Or do you charge them together so the voltages always remain the same?

Tommy L sends....

[etriker]

They are discharged in parallel and disconnected and each pack balanced charged with a Hyperion charger.

When they are first connected, both fully charged, the laptop cell pack will deliver current to the A123 pack starting at about 7 amps and dropping to 0 amps in about a min or two.

That is with no load.

10 x 3.7v is 37 volts.

11 x 3.3 is 36.3 volts.

The difference in voltages is the key to this working.

Makes a battery pack setup that can deliver high amps but with a duty cycle.

http://www.zena.net/htdocs/FAQ/dutycycle.shtml

[spuzzete]

Looking forward to that if you do, though do'nt use those 1F 5.5's, they'll be back up type, they wont work at all.
You need the pulse power low/ultra low esr variety. I'm about to purchase mine thru Maxwell's site.
Tectate's on the site are the same price right up to 10F @ 2.7v @ $2,so x2, 5F @ 5.5v $4 x 10 =$40 + shipping.
There's also be the time constant thing, i'm trying to get my head around as my set up is to be multi tier
how much power to deliver into what impedance, for what duration Back emf oh no headache again

cap_balance_5.jpg

Fetchter's and co. have been doing some nice mod's on the cell logs @ http://endless-sphere.com/forums/viewto ... 14&t=20142, i'm using them and done the jumper mod, not sucking so much now on the 1&2 channels.
Good Luck with it.

Thank you for the suggestion!

I will update as soon as I will have all I need to begin the tests.

[spuzzete]

That is with no load.

10 x 3.7v is 37 volts.

11 x 3.3 is 36.3 volts.

This is interesting!

What you presented there are the nominal voltages. What are the real voltages of the batteries fully charged?
I charge my li-ion cells to 4.1v each so the pack is about 41v fully charged.

[etriker]

Right. The A123 pack is slighty lower and when first connected with no load the laptop pack will discharge a little and the A123 pack will overcharge a little. Not much because the laptop pack does not have much power to deliver at that voltage and the voltages even out soon.

I take off and ride right after I connect them in parallel so they both start to discharge soon.

Dkangls mapping battery cells posts show the voltages where cells have their power.

You can also map whole packs.

The goal is to use all the cells so not to overload any of them and run them in the range suggested in their data sheets.

Alone an a123 11s 3p pack will not power my trike for long and the 10s 4p laptop pack would be way overloaded by itself.

Together they will push my trike about 40 miles if I help a little.

[liveforphysics]

Just working some energy storage vs voltage drop calcs.

You could add enough super caps to your battery to be equal to the size and weight of your battery, and have less than 10sec of discharge before the caps drop to the voltage your cells would sag to with no caps, making the caps dead-weight until you let off the throttle for 20-30seconds again, then you could get 10seconds of simulating running a less saggy battery again.

Also, this is kinda funny, but good RC LiPo can output higher power per volume and per weight than super caps.

[CamLight]

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

Those are very high internal-resistance caps. Be sure to do the math for their current-supplying capabilities.

[CamLight]

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.

Huh?
Of course caps can be placed in series. It's the only way to use capacitors in an application where the voltage level is higher than the cap's rating. There's absolutely no way I can use a 2.7V-rated 400F supercap along with a 4S LFP motorbike starting pack without the cap blowing up instantly. However, I can take six of those 400F caps, wire them in series, and get a killer 67F-equivalent pack that easily supplies 200A for a couple of seconds.

Do I go down from 400F to 67F when putting them in series? Of course, that's basic electronics for caps in series. But not because caps are supposed to be in only used in parallel. It's the only way to achieve a voltage rating for the thousands of applications out there for 2.7V (in that range) supercaps.

[CamLight]

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.

Using a 5.5V cap connected across each cell is a great idea. Unfortunately, that cap you mentioned will only supply milliamps (if that) at a time. You need a cap that supplies 10's of amps, with a very low ESR (resistance) value to prevent large voltage drops inside the cap. This low ESR requires LOTs of room to achieve and leads to very large supercaps. There's just no way to do it with small caps.

There are some 5.5V caps with moderate ESR that might be able to help your cells a bit. Not as much as another cell or the very-low ESR cap types (typically 2.5V or 2.7V-rated), but perhaps just enough. Or, you could wire two 2.7V low-ESR caps in series across each cell and just take your chances in regard to balancing. With only two caps in series there's a lower chance of them going out of balance.

[CamLight]

Also, this is kinda funny, but good RC LiPo can output higher power per volume and per weight than super caps.

Agreed!
I'm working with a client now doing some preliminary tests using LiPo in an application where we were originally only considering supercaps. There are some definite benefits to both approaches, it's been very interesting!

[liveforphysics]

It's also important to realize the energy storage of caps placed in parallel or series is identical.

Say we have 4 x 2.5v 100F caps. If we stick them all in parallel, we get a 2.5v 400F cap. If we go 2p2s, we get a 5v 100F cap. If we go 4s, we have a 10v 25F cap.

2.5v^2*400F = 2500J
5v^2*100F = 2500J
10v^2*25F = 2500J

No matter how you group them, as many in series or parallel as you like, the energy stored is just the energy storage of a single cap multiplied by the number of caps, the capacitance decreasing as you stack them in series is not a decrease in energy storage.


Caps are great for filtering voltage spikes in either direction. Caps are an awful alternative to a battery for anything involving stead-state current draw.

[megacycle]

Really enjoying this thread, very lively , learning a lot.

Sorry about the double post i'll try and have it deleted,
think it happened as there were two or more of us posting at a time.

Good to have some figures Luke.
If those 3x16V@25F small blocks i mentioned were used that would be around 4000J, yeh then there's losses in those series esr's and even say 3800J is say only 380W of sag fill for those 10 sec you were talking about, and the caps then asking for recharge from a depleting battery anyhow, so hill climbing's no good and at around $400+ for those cap's, those supplementary A123's look good for the solution to your problem.

With the secondary packs that could hold true for a few combinations, that's great news.

[spuzzete]

Also, this is kinda funny, but good RC LiPo can output higher power per volume and per weight than super caps.

Hi liveforphysics,

wouldn't be cheaper and less complicated to use RC LiPo (http://www.hobbyking.com/hobbyking/stor ... _Pack.html) instead of supercaps then? Etriker did it with A123 cells, but I think it's better to use lipo with li-ion, the operating voltages are closer than A123.

I find this discussion extremely interesting, lots of learning for me.

[spuzzete]

Using a 5.5V cap connected across each cell is a great idea. Unfortunately, that cap you mentioned will only supply milliamps (if that) at a time. You need a cap that supplies 10's of amps, with a very low ESR (resistance) value to prevent large voltage drops inside the cap. This low ESR requires LOTs of room to achieve and leads to very large supercaps. There's just no way to do it with small caps.

There are some 5.5V caps with moderate ESR that might be able to help your cells a bit. Not as much as another cell or the very-low ESR cap types (typically 2.5V or 2.7V-rated), but perhaps just enough. Or, you could wire two 2.7V low-ESR caps in series across each cell and just take your chances in regard to balancing. With only two caps in series there's a lower chance of them going out of balance.

Thank you for the heads up on the 5.5V caps! I would have wasted my money!

I think I would wire 2x2.7V supercaps to each cell if I decide to try supercaps.

[etriker]

I stopped testing rc lipo when I found the cells can dead short.

A shorted lipo cell in a pack that is in parallel with another pack could be really bad.

Other than that they might work ok. Or they might get puffy and well, you know !

Anyone want to try and let us know ? I am scared to try that.

I am collecting Makita cells to test in a parallel pack with laptop cells. If they don't need balancing then the whole setup could be charged at once.

The A123 cells I am using are from 2006 recovered from bad Dewalt packs.

6 years old and still going !

Overcharge them, overdischarge them, for being li cells they are hard to kill.

Laptop cell packs make good extender packs for long rides. My laptop cells are also from 2006 recovered from bad hp battery packs.

[megacycle]

The A123 cells I am using are from 2006 recovered from bad Dewalt packs.

6 years old and still going !

Overcharge them, overdischarge them, for being li cells they are hard to kill.

Laptop cell packs make good extender packs for long rides. My laptop cells are also from 2006 recovered from bad hp battery packs.

6 years how many cycles you had, and how are they handling, capacity and C still good

[etriker]

Over 120 on the laptop cells at least. Am using b grade cells for sure that were stacking up so I wanted to do something with them.

The A123 cells are on their 3rd life. They were used in a rc car.

When going on trips of about 12 miles or less the A123 pack alone is fine.

Up to about 40 miles I hook them both together.

The A123 pack has way more cycles than the laptop pack.

There is another goal too and that is to make the pack last because it sure does take a lot of time to test the cells and build one.

Old laptop cells will last longer if you don't get them too warm.

I charge the laptop pack at about 2 amps. Slow. The cells don't get warm.

Same with discharge. Don't sag them too hard and only use about 70% or less.

The A123 cells charge really fast.