Another Charging Question

[u_couple]

Looking for some help once again guys

I was wondering if I could charge 2 batteries (in series) using one of these USB chargers ? I plan on stripping the board from the inside of this charger, and using it in a box mod I am planning. I know it will charge one battery OK, but am unsure about two.

Here is a link to the charger I am talking about
http://www.qualitychinagoods.com/xtar-charger-14650176701865018700-battery-p-1785.html

thanks in advance guys

 

[deach]

What kind of batteries? If you're talking about two 3.7 volt batteries in series NO....that says it's rated at 5 volts. It "Might" do 2 in parallel but I'm certainly not recommending that. If you need to charge two Li Ion batts, I'd say get the right charger. YMMV
Regards,
Deach

 

[CraigHB]

You can't charge series packs with a USB charger because there isn't enough voltage. A single Li-Ion charger requires 4.5V minimum which is available from a USB port since USB is 5V. A pack charger requires a 9V supply for two cells and higher for more cells.

You don't need to tear apart a charger to get the charging circuitry you need. You can get modules like this and this.

 

[deach]

don't need to tear apart a charger to get the charging circuitry you need. You can get modules like this and this.

Thanks for the links....good ones!

 

[u_couple]

Thanks guys, much appreciated.

 

[slimest]

You can get modules like this and this.

Actually you can't use these modules without a special additional schematic. These things are not easy to use if you use them for a batteries in series. Don't do it if you don't completely understand what you are doing.

 

[u_couple]

Don't do it if you don't completely understand what you are doing.

I hear you there buddy, I`m just gonna use a single 18650.

 

[CraigHB]

The only way to charge a series pack with USB is to incorporate circuitry that pulls the cells out of series and into an isolated configuration. Each cell is then connected to a dedicated USB charger. You need two USB chargers, but you can run them from one USB connector. You don't want to switch the cells to parallel and use a single USB charger because you can get high equalization currents. Cells in parallel need to be permanently connected.

I don't' think it's worth the trouble to incorporate USB charging for a series pack. If you really don't want to remove the cells to charge, you can install a DC connector to connect a 2 wire pack charger to the cells or install a 3 wire connector to connect a balancing charger to the cells.

 

[Str8V8ping]

Iv personally will never charge in series . No need to add any extra danger when using liion cells. Stacking cells is already a added risk factor but built in charging of stacked cells is just too much of a risk.

 

[slimest]

Str8V8ping, batteries in series are not dangerous. Absolutely. If there are a problems with them, this is not connection method And charging in series is not dangerous: have you got a laptop? Another thing - who and how makes it.
I read the latest news, but it seems like "New iPhones explode"...

 

[Str8V8ping]

Str8V8ping, batteries in series are not dangerous. Absolutely. If there are a problems with them, this is not connection method
I read the latest news, but it seems like "New iPhones explode"...

Where are you getting this info from . I have been using Li-ions for a long time over at CPF and stacking Liions is never really recommended not that we dont do it but charging stacked li-ions can be dangerous. One cell will drain or charge faster then the other.

 

[slimest]

stacking Liions is never really recommended not that we dont do it but charging stacked li-ions can be dangerous. One cell will drain or charge faster then the other.
LiIon batteries are used and charged in series everywhere if you use and charge them correctly, using balancer. The same exists in your laptop. Is it dangerous?

 

[u_couple]

I also seen a mod on another forum where someone used a "smart charger" to charge two 18650's in series, it wasn't USB, more like a cell phone charger, maybe this could be worth thinking about

 

[MadmanMacguyver]

Actually I have an advanced mod design that charges batts in series...it requires the proper circuitry to do it safely and there IS a miniscule inherent risk but no more than a laptop batt pack...

As for batts in series becoming unbalanced str8 I am about to post a thread in another month(testing my theory) that will blow that out of the water(PM Me if ya want a hint)(Note that invitation is for str8 not 50 other people to flood my inbox...others will not be answered...)

but my mod has not had any issues w the batts having any detectable differential in voltage of course I have also managed a few other Boons w my current config... but all that will come later...

To get back to the OP...forget charging w USB if you intend to do large MAH batts its simply inefficient...there are much better chargers out there...also you should look at CC/CV charging algorithm chargers...these cheap Chinese Brute force chargers are dangerous...I'm sure it will come out in the news some time from now that the poor guy in Florida threw his batts in a mod after the came off a cheap Chinese charger w no CC/CV and the batts were older and could not handle being pushed to 4.2 anymore...boom....a good CC/CV setup will stop before the batts go over what they can take...

 

[CraigHB]

Unlike NiMH, NiCad, and lead-acid cells, Li-Ions are not pushed outside normal operating range when charging. For any other type of battery, that's not the case. A Li-Ion comes off the charger at the terminal voltage of the charger which is within the cells normal operating range.

There are two primary fault modes for a Li-Ion charger. It can either go over the cell's 4.2V operating limit (for a 3.7V nominal cell) or go over the cell's maximum tolerable current which depends on the size the cell itself. There are secondary safety points like cell temperature, but they generally are not monitored with an inexpensive charger.

If there's an issue with a Li-Ion charger on the market, it would be due to one of those two primary faults. Li-Ions do not become intolerant to their terminal voltage with wear. They simply lose capacity and don't run as long on a charge.

The main issue with using USB on larger cells is not due to the cells themselves, but the limits on current you see with USB ports. A USB charging port has a higher current limit so you can get around that issue when limited to that type of port. Another issue is the connector. The mini-B type connectors have lower current ratings than the regular A and B connectors. There's also the voltage drop across the cable itself. It can render a charger unable to charge a cell at its programmed rate.

There's another potential issue with high rates involving the charger itself. Heat can be a big problem. For example, if the you are using a 1A rate and the battery requires 3.5V at its current state of charge, there's a 1.5V difference between supply and output for the charger. Most USB chargers use a linear type of regulation so one would need to dissipate 1.5W for that example. That's quite a lot for a small chip. The charger controllers I use go into thermal regulation mode when they get too hot which drops down the charging rate quite a bit. Heat sinking is a major concern for those chips.

 

[jimbalny]

The only way to charge a series pack with USB is to incorporate circuitry that pulls the cells out of series and into an isolated configuration. Each cell is then connected to a dedicated USB charger. You need two USB chargers, but you can run them from one USB connector. You don't want to switch the cells to parallel and use a single USB charger because you can get high equalization currents. Cells in parallel need to be permanently connected.

I don't' think it's worth the trouble to incorporate USB charging for a series pack. If you really don't want to remove the cells to charge, you can install a DC connector to connect a 2 wire pack charger to the cells or install a 3 wire connector to connect a balancing charger to the cells.

Then how does the darwin incorporate USB charging of two series lithium polymer cells? I've seen pictures of its internals where both battery leads connect to the pcb. Is it possible using a step down regulator for the vaping part and a boost converter for the usb charging part?

Maybe with this chip Battery Management - Battery Charge Management - BQ24100 - TI.com

 

[ninjaguy]

TI has a decent paper on cell imbalance and their cell balancing solutions.http://www.ti.com/lit/an/slyt322/slyt322.pdf. As it was suggested earlier the best solution would probably be to have a high current 12V source for charging. A USB port just wouldn't cut it at the capacities you are looking at. You already have two batteries to charge. They will charge a lot faster if you are not using USB.

 

[jimbalny]

TI has a decent paper on cell imbalance and their cell balancing solutions.http://www.ti.com/lit/an/slyt322/slyt322.pdf. As it was suggested earlier the best solution would probably be to have a high current 12V source for charging. A USB port just wouldn't cut it at the capacities you are looking at. You already have two batteries to charge. They will charge a lot faster if you are not using USB.

Not looking to charge my batteries fast, just looking to keep em topped off while in work van, at home on my powered usb hub, and possibly with a usb wall wart while staying at hotels and whatnot. So unfortunately something I'd need to lug around with me isn't a very good solution in my case. And I'd prefer a step down regulator due to the wide output ranges and high efficiency/output current.

 

[CraigHB]

Then how does the darwin incorporate USB charging of two series lithium polymer cells?

I don't know for sure since I don't own a Darwin, but I believe the cells are connected in parallel and the device uses a boost regulator. I've read something to that effect on the forum here before. There's good reason to use two cells in parallel. It may be needed for the additional drain capability a booster requires.

It's possible to incorporate USB charging in a series cell mod, but as convoluted as it is to do that, I doubt it would be something you'd find in a production unit. It's a more expensive solution and production costs for consumer goods are always a priority. Also, if the Darwin was using a buck regulator (which I don't think it is), it would be capable of an output higher than the 12 point something Watts it's limited to.

 

[MadmanMacguyver]

I have seen the inside of a darwin...and unless they have changed it is a single lipo or LiFe cell Boost mod...simple to charge but limited in output...

and I don't suggest charging at the wrong rate is an issue w cells becoming imbalanced when in a series batt mod...its the discharge above the rated specs which we do all the time...most of the cells used in mods are (truth be told) rated for .5 to 2 amp at most... I am currently testing a VV mod design w internal charging using series batt config...I am having NO issues w the cells becoming unbalanced...but I am using a system I came up with and it won't work w usb USB is simply to weak an input ...but it does connect directly to an A/C outlet...hence no need for a wall wort and another device...

srry if I caused confusion on the charge/discharge ratings comment but the OP seemed to be addressing an Issue I have been working to solve...I just wasn't going the same direction to solve it...why should ya need to carry 2 devices to charge the batts in the mod when ya only need one...I have solved that issue...

as for stacking li-ions being dangerous...Not if its done properly...it is done all the time...look at cell phones,power tools etc...and I have seen more issues w cell phones going critical than I have anything else... and they are one LiPo in a plastic housing...well most of em anyway...seems they are switching to LiFe in some cases now...