-- THE SINGLE CELL CHARGER POST --

Put here ALL your find about SINGLE CELL CHARGER LiFe/LiPo

It is clear that one of the best way to charge lipo and LiFe cells is to charge each 1s using a single charger CC-CV to (3.6V or 4.2V)

It could be an adjustable switching power supple you found at digiket, newark..etc

the adaptor case type charger (like the 2A for life at 10$..)

The goal of this thread is to rassemble all that exist for that single cell charging application.

Let's begin

Doc

http://www.voltphreaks.com/

Tony at VP is who i got my 18 x 2 amp LiFe chargers from, i have not yet fully tested them to my own liking, but i know of at least one member here who is using them so far.. :wink:

OK. Here's my 20 single-cell chargers from batteryspace:
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1231

charging my 20s15p pack of lithium 18650s from all-battery:


As most of us know, for lithium, single cell chargers automatically rebalance every cell in the pack with every charge without any extra battery management circuitry.

Here's my 10-cell setup of the 2A VoltPhreak single cell LiFe chargers:



I use this setup to charge these 10s4p packs:




I ended up with powerstrips that had the connectors pretty close together so I had to cutoff the round "wings" on each charger with a Dremel, in order to get them to fit side-by-side with the narrow powerstrip. It was worth the effort, as this setup works great. I'm finally getting my packs fully charged. the problem with RC-type balancers like the TP-210V, or the AF "Blinky", is that they take a long time to balance a pack that has cells that are more than .2V out-of-balance, and if you are trying to charge the pack at the same time, it will take even longer. I had a few packs that haven't been balanced in awhile, and they had cells that were as low as 3.42V and some that were 3.72V, fresh off the charger. I connected these to the balancer and it took hours to get the cells down to where all were at around the same as the lowest (3.42V...). I then had to recharge the pack.

I had another unbalanced pack that had the same sort of cell variances so I hooked it up to the single-cell chargers and all were charged up to about 3.7V in no time. I really like this single cell charger approach, but I just wish this could be scaled up to a higher charge rate. Bob Mcree suggested to me that slightly modified versions of these 5V/8A supplies might be used as individual cell chargers: http://www.weirdstuff.com/cgi-bin/item/22063. I'm thinking of ordering a few, for testing, and then pester the heck out of Bob until he helps me figure out how to change the voltage limit to 3.7V.

-- Gary

GGoodrum said:

Here's my 10-cell setup of the 2A VoltPhreak single cell LiFe chargers:-- Gary

Click to expand...

So let me get this straight, you are charging 4 cells at once that are connected in parallel with each of these single cell chargers?

Edit: If so, I suppose you could parallel 5 cells to each charger and it would just be slower, yet still balance, since they are all tied together?

First of all, the chargers you used from Batteryspace are not the same as these, from VoltPhreaks, which are specifically for LiFe-type cells. Yours, I believe, have a cutoff of 4.2V and are rated for 1.5A. These are rated for 2A and have a CC/CV cutoff of about 3.7V. Also, they do, in fact, have the proper constant current (CC) and then constant voltage (CV) charging profile that is required to best charge the cells. The cutoff voltage for LiFePO4-based cells is lower than what is required for Li-Co and Li-Mn chemistries, which need 4.2V.

Also, the LEDs/lights on these LiFe chargers are actually 3-colored. When a discharged pack is first connected, the charger goes into the CC mode, and the LED is red. When the voltage rises to the cutoff voltage, the charger switches to the CV mode, and the LED turns yellow. When the current drops to about 200 mA, the charger stops, and the LED turns green. Yesterday, after a quick test ride which used 1.440 Ah, it took less than an hour for all 10 LEDs to turn green, which is about right.

In your case, I think the failures you saw were probably related to you trying to cram them into the neck of your custom scooter frame. As you have pointed out, xyster has used 20 of the same units you apparently fried, for over a year, and they work fine for him.

BTW, one thing you should be aware of is that the power tool companies, like DeWalt and Milwaukee overstate the voltage for their tool packs, for marketing purposes. Most Li-Co cells have charge voltages of 4.2V and "nominal" voltages of around 3.7V per cell. After being connected to a load, even a light one, for about 10 seconds, the cell voltage will drop to a "resting" voltage around 3.7V. Many "older" Li-Ion cells have charge voltages of 4.1V and rated nominal voltages of 3.6V. When the eMolis first came out, we found that in our RC applications, the nominal voltage was about 3.5-3.6V. So if you use 3.6V nominal, your 14s6p setup's "rated"voltage is really more like 50-51V, not the 56V that Milwaukee would have you beilieve. For you to get to 60V, you would really to use 16 or 17 in series, not 15. DeWalt does the same thing. The max charge rate for a123 cells is about 3.7V, but the nominal voltage is more like 3.3V per cell. DeWalt, however, rates their 10-cell tool packs as 36V.

As for the "practicality" of using these 2A chargers with big setups, most days I could care less if it takes two hours or 10, to complete the charging process. If I am in a hurry, however, I have several other SLA and RC chargers, with much higher max charging rates. I have a Zivan NG1 SLA charger, for instance, that will go to 18A and several RC chargers that have a max of 10A. These can be used to get the packs to about the 80-85% level fairly quick, and then I can use the individual cell chargers for the final "topping off" and balancing.

-- Gary

EMF said:

GGoodrum said:

Here's my 10-cell setup of the 2A VoltPhreak single cell LiFe chargers:-- Gary

Click to expand...

So let me get this straight, you are charging 4 cells at once that are connected in parallel with each of these single cell chargers?

Edit: If so, I suppose you could parallel 5 cells to each charger and it would just be slower, yet still balance, since they are all tied together?

Click to expand...

Yes, that is right. You can put any number of cells in parallel and they will self-balance to where each end up with the same voltage level. Using the tried and true water analogy, think of having four or five identically-sized buckets of water, all with varying water levels. If these buckets were then all connected together with hoses (at the bottom...), their levels would all equalize to the same level.

So yes, it will take longer, the more cells you have in parallel, but at the end they will all be perfectly balanced.

-- Gary

xter uses these chargers with great success, but his 33ah packs take about 12 hours to charge. That's not bad for such big batteries.

Click to expand...

The one time I ran my pack down all the way during testing, it took 30 hours to recharge. I think that 12 hours was probably referring to recharging overnight between ~20% and 80% capacity.

Normally, I use 20-30% of my pack's capacity to ride 20 miles, running the cells down to ~3.85 volts from ~4.0 volts.

Charging from 3.85v back up to 4.0v takes about 4 hours. This works out to about 10ah/4hours = 2.5 amps. Charging slows dramatically as the cells' voltage rises above 4.0 volts. Temperature seems to make a difference, and there's a lot of variability between the chargers -- so I have to pull some off before others.

A four hour charge time to get a 20 mile ride is pretty good, IMO.

GGoodrum said:

EMF said:

GGoodrum said:

Here's my 10-cell setup of the 2A VoltPhreak single cell LiFe chargers:-- Gary

Click to expand...

So let me get this straight, you are charging 4 cells at once that are connected in parallel with each of these single cell chargers?

Edit: If so, I suppose you could parallel 5 cells to each charger and it would just be slower, yet still balance, since they are all tied together?

Click to expand...

Yes, that is right. You can put any number of cells in parallel and they will self-balance to where each end up with the same voltage level. Using the tried and true water analogy, think of having four or five identically-sized buckets of water, all with varying water levels. If these buckets were hen all connected together with hoses (at the bottom...), their levels would all equalize to the same level.

So yes, it will take longer, the more cells you have in parallel, but at the end they will all be perfectly balanced.

-- Gary

Click to expand...

Hate to distract you from the A123 thread, but got it, thanks. So, you just have to make sure you are not also capable of a series circuit at the same time? In other words, have your discharge arrangement wiring disconnected ( switched off ) at the time of charging - then remove your charger from the parallel arrangement prior to discharging ( switch on to the controller )?

xyster said:

Normally, I use 20-30% of my pack's capacity to ride 20 miles, running the cells down to ~3.85 volts from ~4.0 volts.

<<SNIP>>
A four hour charge time to get a 20 mile ride is pretty good, IMO.

Click to expand...

I would be happy if I could set up a pack that I could carry my charger(s) and plug it in at work, since I am stuck there for at least 4 hours before lunch. Maybe if I break up my Dewalts the right way, this could be done with single chargers. I can even have a charger that I leave at work.

All I would need with a pack like the one you mention above, is a bib to catch my drool. :wink: Do you find that more cells helps to reduce voltage drop at a given amperage?

EMF said:

Hate to distract you from the A123 thread, but got it, thanks. So, you just have to make sure you are not also capable of a series circuit at the same time? In other words, have your discharge arrangement wiring disconnected ( switched off ) at the time of charging - then remove your charger from the parallel arrangement prior to discharging ( switch on to the controller )?

Click to expand...

No disconnection of anything is required. Each charger is completly isolated from the others, so it doesn't hurt to basically wire them in series, just like the pack. The - side of the 2nd charger is connected to the + side of the first, and the - side of the nth charger is connected to the + side of the nth-1 charger. For 10 chargers it takes 11 wires. One each for the - of the 1st cell, one for the + of the 10th cell and nine more for all the junctions between all the rest.

That the one thing I like about this setup, I don't have to unplug the packs from the bike. I just plug the chargerwiring harness into the Packs balancer plugs. No muss, no fuss.

-- Gary

Also, they do, in fact, have the proper constant current (CC) and then constant voltage (CV) charging profile that is required to best charge the cells. The cutoff voltage

Click to expand...

I'm sure they have that charging profile built into them. I'm just trying to say that when you use them on bigger packs, they gradually raise the voltage, and they're not able to use that profile. I think yours works so well because you're using 4 cells (I was using 6) and your chargers are a bit more powerful than mine.

However, I assure you xters chargers don't just push the voltage up to 4.2v and hold it there. I'll beleive that when I see it.

I agree that power tool companies overstate voltage. 12v SLAs charge to 13v, so a 48v pack starts at 52v. So my 56v pack should be called a 52v pack.

Beagle123 said:

I'm sure they have that charging profile built into them. I'm just trying to say that when you use them on bigger packs, they gradually raise the voltage, and they're not able to use that profile. I think yours works so well because you're using 4 cells (I was using 6) and your chargers are a bit more powerful than mine.

However, I assure you xters chargers don't just push the voltage up to 4.2v and hold it there. I'll beleive that when I see it.

I agree that power tool companies overstate voltage. 12v SLAs charge to 13v, so a 48v pack starts at 52v. So my 56v pack should be called a 52v pack.

Click to expand...

The profile doesn't change if you use more or less cells in parallel, it just takes longer with more cells. I also have a 20s6p pack on another bike that I use this same setup, and it works just as well.

-- Gary

GGoodrum said:

Each charger is completly isolated from the others, so it doesn't hurt to basically wire them in series, just like the pack. The - side of the 2nd charger is connected to the + side of the first, and the - side of the nth charger is connected to the + side of the nth-1 charger. For 10 chargers it takes 11 wires. One each for the - of the 1st cell, one for the + of the 10th cell and nine more for all the junctions between all the rest.

-- Gary

Click to expand...

Took a while for this to sink into my thick head. Hopefully, I understand. Is this what you are saying?

EMF said:

xyster said:

Normally, I use 20-30% of my pack's capacity to ride 20 miles, running the cells down to ~3.85 volts from ~4.0 volts.

<<SNIP>>
A four hour charge time to get a 20 mile ride is pretty good, IMO.

Click to expand...

All I would need with a pack like the one you mention above, is a bib to catch my drool. :wink: Do you find that more cells helps to reduce voltage drop at a given amperage?

Click to expand...

Yes. The cells are only good for a continuous 1C. Trying to suck 35 amps from a single 2.2ah cell would not be advisable ; from 12 is doable, from 15 makes a fine pack that only sags 6 volts out of 80 volts under full, 35 amp load.

xyster said:

Yes. The cells are only good for a continuous 1C. Trying to suck 35 amps from a single 2.2ah cell would not be advisable ; from 12 is doable, from 15 makes a fine pack that only sags 6 volts out of 80 volts under full, 35 amp load.

Click to expand...

Thanks for the info, I wondered about that.

Any of you could be interested about a buy group for the LiFe single cell??

.. maybe we could get a better price... they are 9.98$ for 5+.. but for something like 50 or 100 chargers... it could be interesting... think about 12 or 15 chargers for 110$.....i hope...

Hey guys, I've just wrote to Tony from VoltPhreaks to get some info about a buy group.. or some possiblility to get the BMS/charger they use for their 12V battery. Check out what i got: :wink:

Hello,

We are many enthousiast about high performance electric bike from a forum and we would like to create a buy group for the Single cell LiFePO4 charger and we would like to know if we could get a better price than 9.98$ if we would liike to buy for something like 50 to 100 units.

We have multiple A123 cells pack made from dewalt pack and we generally have pack of between 33V and 108v... the single cell charger is the best method for us to recharge our pack and to ensure they are balanced well. Maybe you could have some pcb circuit board charger for charge 12V(13.2v) that you use for the 12V battery that you could sell to us too. We would appreciate to have some info about that.

Thanks


THE ANSWER FROM TONY

Hi Stephane,

We can work on a better price, but we'd need at least 100 units. For 100 units, we can go $8.60. The chargers work because they are isolated, allowing you to charge multiple cells in a pack simultaneously without disconnecting the cells in the pack from each other. We've considered putting four together to charge a 12V pack, though but haven't made anything like that at the moment.

Do you guys have a web page, I'd love to check out the bikes!

- Tony



Not bad at all ! 100 unit for 8.60$ ...

Simply think about a 10s 2A PERFECTLY balanced and protected cell charger for 86$ !!

1.5h to charger perfectly...

I may want to go in on some if you guys get enough people together. I'm surprised us ES users don't put out more of these group buy feelers.

I would take ten of course, once Gary makes his boards with the cross balancing wire ports available - or at least figures he will make them available for sure on his website. This makes creating packs so much easier, safer and they are a nice size/weight when completed.

PS- Good letter and a good idea! 8)

EMF said:

I would take ten of course, once Gary makes his boards with the cross balancing wire ports available - or at least figures he will make them available for sure on his website. This makes creating packs so much easier, safer and they are a nice size/weight when completed.

PS- Good letter and a good idea! 8)

Click to expand...

The a123 kits will be available tomorrow.

Put me down for about 10 more, Doc.

GGoodrum said:

EMF said:

I would take ten of course, once Gary makes his boards with the cross balancing wire ports available - or at least figures he will make them available for sure on his website. This makes creating packs so much easier, safer and they are a nice size/weight when completed.

PS- Good letter and a good idea! 8)

Click to expand...

The a123 kits will be available tomorrow.

Put me down for about 10 more, Doc.

Click to expand...

Do the kits allow the battery charger to be plugged into the bms ports of the a123 cells?

edit scratch that....


39wh/klm i'd need roughly 30k for a single charge at 72v at the speeds i'm after - so i'd need 1170w of capacity on a single charge.

that means 1170 / 72v = 16.25 ah minimum to do the distance

16.25/2.3 = 7.06 cells in parallel (lets be safe and make it 8)

how long would it take to charge an 8p setup of these? (at 240v 2a)? i'm guessing its going to be 8 x 1.5 hours (for a single cell) ignoring inefficiencies etc...
sadly thats just too long for the size of the pack i'm after :S (16.25ah) the only way around that would be to use 40 chargers... and i'm not willing to do that (charge in pairs).

sadly this is just too slow for my purposes...

Gary,

I am interested in the single cell charger solution as well.

Next time you charge one of your 10s4p packs with these charges, could I get you to measure the voltage of each of the 10 parallel strings and report the voltage of each.

example
1. 3.70V
2. 3.69V
etc
10. 3.73V

I would like to know how much variation there is in the final voltages.

Thanks
Greg

I tested a few last night and got 3.85v peak before the light went green. fyi.

The open circuit voltage is 3.750 on 2 of the chargers i tested so far.

For the large AH packs, i think a large regulated power supply is the way to go.. I'll be charging 48v 25ah !!!!!