Charging/discharging 6 (or more) Li-Ions at a time?

[donn_]

What's the best way to do this? I have 3 Ultrafire chargers, but it's inconvenient, at best, and takes forever on the larger cells. I want to be able to do at least 6 cells at a time, including Cs and 18650s as well as the smaller cells.

I've been looking at the high-end hobby chargers, but I can't find a source for banks of loose cell holders to connect to them.

Any suggestions appreciated.

 

[donn_]

 

[SilverFox]

Hello Donn,

Check out the Schulze Next 7.36-8. It can charge and balance up to 8 Li-Ion cells, as well as a whole lot more. You still have to provide 12 volts DC to power it, and come up with a way to hold your cells, but it will give you close to 1 hour charging for all of your cells.

Tom

 

[drew2001]

For holding multiple cells and attaching the charger leads, I've used a set of LuxLuthor's magnetic leads and a series of small magnets. Like the ones that Lummi -Orb sells with nano chargers. Use one magnet between cells to make the contact.

 

[donn_]

Hello Donn,

Check out the Schulze Next 7.36-8. It can charge and balance up to 8 Li-Ion cells, as well as a whole lot more. You still have to provide 12 volts DC to power it, and come up with a way to hold your cells, but it will give you close to 1 hour charging for all of your cells.

Tom

Ouch! $459, without a PS or holders?!? I'm afraid that's a bit rich for my needs.

Drew..I've read it isn't good to charge these cells in series.

 

[JimmyM]

I have the Bantam BC-8. It has integrated balance charging for up to 8 Li-Ion/Polymer batteries and it cost something like $250US. You still have to buy a 12V power supply though. They can be had for $20-50.
As far as holding the cells. I built a set of 2 cell holders with the balancing taps integrated into the pairs of single cell holders. I have a switch that selects single or 2 cell charging. To do 6, you'll just need more holders. Digikey has holders as well as many other places. If you can, get solder-tabbed holders instead of wired. The wires that come with those holders are really thin. You want to use something heavier. 18Ga is OK, 14 is better. Heavier than that really isn't necessary.
Series charging of many cells is perfectly acceptable provided that you use a balance charger.

 

[SilverFox]

Hello Donn,

OK, the Schulze combination is a bit expensive... but it is an excellent charger.

A very cheap option requires you to have all the intelligence and has no safety's built in, is to use a power supply. Mastech offers power supplies that allow you to set the voltage and the current you want to charge at. Keep in mind that you are responsible for using the correct settings, and if you don't, you could end up burning your house down.

You can come up with a holder that connects all 6 of your cells in parallel, then charge them, in parallel, to 4.2 volts. If you got one that was capable of 20 amps, you could still charge 6 3200 mAh cells in around an hour, but 20 amp power supplies are more expensive. I believe the smallest unit Mastech offers is a 3 amp one. That unit would be OK for your smaller cells, but it would take around 9 hours to charge 6 3200 cells in parallel.

The problem with charging in series is that the cells get out of balance. With Li-Ion cells, when the voltage gets too high, they rapidly vent with flames. The solution to series charging Li-Ion cells is to use a balancer with them. The balancer equalizes the voltage of each cell, so they all stay balanced. With a balancer, series charging is safe.

You can do a search on the internet for balancers to get an idea on how they work. The Astro Blinky balancer would be a good place to start. I believe they are good for 3 cells in series, but there is a way to hook 2 of them together to balance a 6 cell pack.

Tom

 

[SilverFox]

Hello JimmyM,

You are correct that you can find a power supply for $20, but I don't believe you can get the full use of your charger with a $20 power supply.

The RC chargers are looking for a clean 12 volts for power, like from a 12 volt battery. Power supplies tend to have some ripple in their output voltage. The cheaper power supplies have more ripple than the more expensive ones. The RC chargers can malfunction when run on "dirty" power. This usually results in a premature shut down, but it can also damage the charger. I think it is false economy to invest in an expensive charger and run it off of a sub standard power supply.

It seems that all of the RC chargers will function properly with power supplies that provide < 3 mV voltage ripple, but < 1mV is better.

Also, keep in mind that power supplies often are not capable of providing their maximum output for extended periods of time. The Bantam BC-8 is capable of charging at 7 amps. The Schulze Next 7.36-8 is also capable of charging at 7 amps and Schulze recommends a power supply of about 25 amps to properly power it.

I don't believe you can find a 25 amp power supply with < 3 mV ripple for $20.

Tom

 

[JimmyM]

Hello JimmyM,

You are correct that you can find a power supply for $20, but I don't believe you can get the full use of your charger with a $20 power supply.

The RC chargers are looking for a clean 12 volts for power, like from a 12 volt battery. Power supplies tend to have some ripple in their output voltage. The cheaper power supplies have more ripple than the more expensive ones. The RC chargers can malfunction when run on "dirty" power. This usually results in a premature shut down, but it can also damage the charger. I think it is false economy to invest in an expensive charger and run it off of a sub standard power supply.

It seems that all of the RC chargers will function properly with power supplies that provide < 3 mV voltage ripple, but < 1mV is better.

Also, keep in mind that power supplies often are not capable of providing their maximum output for extended periods of time. The Bantam BC-8 is capable of charging at 7 amps. The Schulze Next 7.36-8 is also capable of charging at 7 amps and Schulze recommends a power supply of about 25 amps to properly power it.

I don't believe you can find a 25 amp power supply with < 3 mV ripple for $20.

Tom

Right you are. I was thinking about what it would take to charge his cells. To get the full use of the charger, then $20 ain't makin' it. I use a 20A supply with my BC-8, but I've never charged over 3A. That was with 10 AH D NiMH cells. I'm in no rush, so I generally slow charge my cells. Especially the Li-Ions.

 

[donn_]

Thanks for all the feedback. It looks like I'm in for some more Google time.

I may have given the impression I need ultra-fast charging times...I don't. I'd just like to improve on the ~6 hours it takes the Ultrafire to charge 2x C cells.

On series charging; one of my lights which uses Li-Ion Cs is Fivemega's FM11, which has a built-in charging circuit with a jack in the side of the body. Should I assume he knows about this cell balancing thing, and built it into the light? I thought about using this light as another charger, but I wouldn't want to blow it up!

 

[JimmyM]

FMs light does not incorporate balance charging. Series charging of 2 cells isn't too bad. Not the safest, but not too bad.
For 6 cells, balance charging is the way to go. Unfortunately, balancers or balance/chargers that do 6+ cells aren't cheap. As a byproduct you get high current capability inherent to most high dollar chargers.

Thanks for all the feedback. It looks like I'm in for some more Google time.

I may have given the impression I need ultra-fast charging times...I don't. I'd just like to improve on the ~6 hours it takes the Ultrafire to charge 2x C cells.

On series charging; one of my lights which uses Li-Ion Cs is Fivemega's FM11, which has a built-in charging circuit with a jack in the side of the body. Should I assume he knows about this cell balancing thing, and built it into the light? I thought about using this light as another charger, but I wouldn't want to blow it up!

 

[donn_]

The more I read, the more confusing this all gets.

I stumbled upon a series of threads involving modifying a 4-slot holder from Voltcraft, and coupling one or two of them with a variety of charger/power supply combinations.

I think I need to find someone with the knowledge and ability to build me a turnkey system for charging multiple LiIon cells properly. Otherwise, I'll just continue to use the Ultrafire chargers until someone comes to market with a better option.

 

[JimmyM]

Something like this doesn't exist in the market place today. A "turnkey" system would have to be defined first.
Would it only charge 6 cells? or would it have to be capable of charging anywhere from 1 to 6 or 8 cells?
As soon as you exceed charging of 4 cells simultaneously, you start talking big money. www.allbattery.com has a 4 cell balancing charger with power supply for $90. It will do 1 to 4 cells. If you want 6 or 8, you're going to need a BC-6 or BC-8 charger. I suppose you could buy 6 or 8 single cell Li-Ion chargers. They're pretty cheap, but there's no true balancing though.
There's no cheap solution that has all the safeties built in.

 

[donn_]

There's no cheap solution that has all the safeties built in.

Why should the charger be the only "cheap" part of my addiction? I already have the cheap chargers, Ultrafire.

AllBattery seems to be down for construction. Do you have the brand name of the 4-cell charger? Does it include battery holder?

 

[JimmyM]

Why should the charger be the only "cheap" part of my addiction? I already have the cheap chargers, Ultrafire.

AllBattery seems to be down for construction. Do you have the brand name of the 4-cell charger? Does it include battery holder?

I don't have the part number, but try this link. http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=1327&HS=1

For charging 18650s I just bought a DSD from Kai or DX for $5 and threw out the guts to use the holder part. For 6 cells you have to get 3 of them, but they'd make a nice battery charging rack.
The Bantam BC-6 or BC-8 are the cheaper Li-Ion chargers that have internal balancing. The Schulze is at least as good (probably better) but costs a LOT more. If you want to invest in a BC-6 or 8 it's no problem to build the plug in charging cradle for your cells.
4 DSDs or other way to hold 8 cells would be pretty simple to implement. You would manually select how many cells and set the charger accordingly. If you set things differently, the my charger throws an error.

 

[donn_]

Yes, the Tenergy charger. It's one of the chargers used in the modded Voltcraft cradle threads. It requires an external PS, as well.

 

[JimmyM]

I guess it's really up to you how to proceed.
If it were me, and I had 6 cells to charge but wanted to charge anywhere from 1 to 6 without building a new charging rig. I would do the following.

Buy a Bantam BC-6, a 20-25A Regulated DC power supply, and 3 DSD chargers.
I'd wire them up on a board with a rotary switch rated at 2.5+ Amps.
Then the "board" can just be connected to the charger and you select how many cells you want to charge, set the charger, and off you go.

I just did some pricing.
Bantam BC-6 $180 or Hyperion EOS 0610i $170
23A power supply $140
Rotary switch = $6
DSD $6/ea

 

[donn_]

Thanks, Jimmy. Now if we can just solve the problem of how to charge Li-Ion C cells, and possibly D's in the future, I may have my solution. I don't think they'd fit in the DSD.

 

[JimmyM]

Setting up a 6 cell charger for Cs or Ds is pretty cheap if you go the non-Voltcraft route. single cell battery holders are cheap and plentiful.

It would involve creating more than one charging board, but the battery holders are pretty cheap and so is the rotary switch.
If I remember correctly, the Voltcraft holder had to be modified to take 18650s. Do that in the future. Once you're in for $300 for the charger and supply, another $30 isn't so bad. Digikey has solderlug single cell holders for less than $1

 

[donn_]

AW's current Li-Ion C is longer than a standard C, and wouldn't fit in a standard C holder. That may be why the Voltcraft was used in the first place, to deal with longer than standard cells. It could probably be made to work in a standard D holder.