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Breaktru Forum  |  eCigarette Forum  |  Battery  |  Topic: USB Charging 2 Li-Po Batteries.
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Author Topic: USB Charging 2 Li-Po Batteries.  (Read 33015 times)

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Online Breaktru

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USB Charging 2 Li-Po Batteries.
« on: February 20, 2012, 12:46:30 PM »
Running two Series Li-Po batteries for powering an OKR-T/6 or any other regulator that requires 2 series 3.7v batteries and charging them in parallel w/ a USB single charger circuit Takes about 4 ½ hrs @ 500mA. Not much different than the charge time for two 18650 on a standard Li-Ion charger.
 The circuit will place the Li-Po's in series (8.4v) when the 3PDT. switch is in the UP position and the Li-Po's will be in parallel with the 3PDT switch is in the DOWN position which also places the USB charger on line.
The 3PDT toggle switch rating should be 3A or better.



The charger has a "Smart" chip MCP73831/2 which Pre-Conditions the batteries.

From the datasheet:
The MCP73831/2 employ a constant-current/constant voltage
charge algorithm with selectable preconditioning
and charge termination. The constant voltage
regulation is fixed with four available options: 4.20V,
4.35V, 4.40V or 4.50V, to accommodate new, emerging
battery charging requirements. The constant current
value is set with one external resistor. The MCP73831/
2 devices limit the charge current based on die temperature
during high power or high ambient conditions.
This thermal regulation optimizes the charge cycle time
while maintaining device reliability.
« Last Edit: October 12, 2013, 12:59:30 PM by Breaktru »

Offline CraigHB

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Re: USB Charging 2 Li-Po Batteries.
« Reply #1 on: February 20, 2012, 03:22:41 PM »
I was wondering if anyone was going to attempt this.

I've though about it a bit.  I was thinking in terms of a MOSFET array to automatically switch the cells back and forth in as required.  There's a couple issues with that.  One is the controller needs to be powered full time and the other is dealing with the potential for high equalization currents when the cells are switched to parallel.  It can be hazardous for a LiPo.  I read about a guy who blew one up when connecting cells in parallel for charging.  LiPos have very low internal resistance and it only takes a small differential for a lot of current to flow.  Maybe a PTC fuse or two USB chargers could be employed for protection against that. 

As far as your approach, I'd get rid of the diode and replace it with another pole on the switch or a MOSFET.  Diodes are lossy and Zeners are even more so.  Keep in mind the forward drop on a Zener is pretty much the same as a standard diode if not a little higher.

Add a PTC fuse between the cells on the parallel connection to protect them from high equalization currents.  Or, rather than connecting the cells in parallel, use an isolated USB charger controller on each cell.

Online Breaktru

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Re: USB Charging 2 Li-Po Batteries.
« Reply #2 on: February 20, 2012, 04:35:30 PM »
Very good Craig and thank you very much.
I was trying to use the single USB charger I already had and would like to install it inside the mod (small package).

Good advise about another fuse between the batteries. How about on the "+" of the second battery.
Can I leave the Zener for blocking voltage below 6.2v in addition to the extra pole on the switch?
Lossy meaning voltage drop? This Zener (1N5341BTPMSCT-ND) has a 1.2v@1amp, does that mean it will drop 1.2v?

I will have to use a 3.P.D.T. switch

Offline CraigHB

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Re: USB Charging 2 Li-Po Batteries.
« Reply #3 on: February 20, 2012, 05:52:40 PM »
Welcome.

A design like this kind of burns brain cells to think about so I haven't actually fleshed out a circuit like you have.  As far as I've thought about it, you should be able to stick a fuse between the positive terminal and switch on one of the cells to keep them from swapping too much current.  You could probably just put it in line with the positive terminal on one cell and the switch.  It could do double duty in protecting from high equalization currents as well as a backup for protection against atomizer shorts.  Basically, just relocate the fuse already shown between the cells.

Forward voltage of 1.2V at 1A is pretty high.  With a 1A supply current you're looking at power consumption of 7.4W (based on nominal battery voltage).  You'll be losing 1.2W at the diode.  That's a 16% loss in efficiency which is large.  Get rid of the diode and use a MOSFET slaved to the switch or another pole on the switch.

Offline Dasen22

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Re: USB Charging 2 Li-Po Batteries.
« Reply #4 on: March 10, 2012, 09:29:03 PM »
I like the idea of Parallel charging. Nice way to do it. Looks like it would work.  :thumbsup:
I believe this would remedy the balancing of two unequal cells.  :Thinking:

Offline Squance

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Re: USB Charging 2 Li-Po Batteries.
« Reply #5 on: March 11, 2012, 06:07:50 PM »
I'm going to attempt this circuit for my mod. Where did you get the 3PDT switch?
And what USB charger circuit are you using?

Online Breaktru

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Re: USB Charging 2 Li-Po Batteries.
« Reply #6 on: March 11, 2012, 06:12:12 PM »

Offline steamEngine

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Re: USB Charging 2 Li-Po Batteries.
« Reply #7 on: March 23, 2012, 08:44:10 PM »
Haven't seen anyone mention this type of setup.. good one breaktru

Offline Madmanmacguyver

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Re: USB Charging 2 Li-Po Batteries.
« Reply #8 on: March 28, 2012, 07:24:01 AM »
lol Breaktru it would be you that would try that circuit...I've seen it toyed aroud w elsewhere but noone actually did it...bet it takes forever to charge...

Online Breaktru

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Re: USB Charging 2 Li-Po Batteries.
« Reply #9 on: March 28, 2012, 07:45:01 AM »
I would imagine it would take awhile to charge. Have it wired up in a new mod. Haven't completed it as yet. Spring is here and have lots of outside chores to do. Been refurbishing my Bar-B-Que. Did a MacGyver on the Dip pan. Wasn't going to spring for $85 bucks for a new one so a piece of sheet aluminum, shears, hammer & dolly for shaping it did the trick. You would think an $700 B-B-Q would last forever. Had to spring for another $250 for new parts.

Online Breaktru

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Re: USB Charging 2 Li-Po Batteries.
« Reply #10 on: April 01, 2012, 03:28:40 PM »
PTC over-current protection / reset-able fuse.

What happens when you use a 4a or 6a trip rated PTC on a circuit board. The weakest link would be the trace on the board.
The Traces for higher current on a PCB require wider traces as mentioned:
0.010" 0.3 Amps
0.015" 0.4 Amps
0.020" 0.7 Amps
0.025" 1.0 Amps
0.050" 2.0 Amps
0.100" 4.0 Amps
0.150" 6.0 Amps


However it is not always practical to use a wide enough trace when using a 6a trip rated PTC. 0.150 is a very wide width and would require a lot of realestate.

I try to use a backplane for all my ground/neg connections and a frontplane for my positive connections distributing the higher current paths.
Even with this said, there is always a weak point as I discovered the hard way. I blew opened a narrow point in the trace when I first connected my batteries. A heavier jumper wire fixed that.

Online Breaktru

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Re: USB Charging 2 Li-Po Batteries.
« Reply #11 on: April 01, 2012, 08:08:11 PM »
Completed the charging circuit as shown in the Original Post with 2x 20c Li-Po batteries and put the half charged batteries on charge. After two hours the charger red LED extinguished and I measured 4.19v on each cell. So far so good.  :thumbsup:

update:
Found this in the comments for the USB Charger @ sparkfun:

Customer:
This is a single-cell charger, so it won’t work on batteries in parallel.

Sparkfun tech:
Sure it will. In fact, our larger 3.7V LiPo batteries are just multiple cells in parallel and it charges them quite well. The maximum USB current is indeed 500mA, but that only means it takes longer (our largest 3.7V LiPo, at 6Ah, takes 12h to charge).

The only gotcha is that you’ll want all the batteries you have in parallel to be fairly closely matched. They should be the same capacity, and preferably the same age. If they’re mismatched, the charger will get false indication of full charge and won’t charge the entire stack properly.
« Last Edit: April 14, 2012, 06:30:06 PM by Breaktru Admin »

Offline CraigHB

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Re: USB Charging 2 Li-Po Batteries.
« Reply #12 on: April 01, 2012, 09:27:57 PM »
Bitchen, always nice when that happens.

BTW, I've burned a few circuit traces in my time. 

Offline elzakivis

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Re: USB Charging 2 Li-Po Batteries.
« Reply #13 on: May 29, 2012, 12:05:44 PM »
 :thankyou: breaktru.
I copied your design and I must say it works quite well.
Nice to have a regulator running series batteries and able to charge them in parallel  ;cheers;

Offline Dznutz

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Re: USB Charging 2 Li-Po Batteries.
« Reply #14 on: October 02, 2012, 12:02:48 AM »
So say I wanted to run a 2400 mah 3.7 mod with 2 1200 mah batts in parallel the spark fun charger would charge them no problem? 

Online Breaktru

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Re: USB Charging 2 Li-Po Batteries.
« Reply #15 on: October 02, 2012, 09:42:39 AM »
So say I wanted to run a 2400 mah 3.7 mod with 2 1200 mah batts in parallel the spark fun charger would charge them no problem? 

Read Reply #11 in case you missed it

Offline Madmanmacguyver

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Re: USB Charging 2 Li-Po Batteries.
« Reply #16 on: October 22, 2012, 01:05:23 AM »
so you have had it together for awhile...do the batts stay balanced...?
read PM for additional...(new Idea not speaking of in public yet)...and don't spam me w questions yet guys if the Idea works well I'll post a new internal charging full range mod in a few mo...maybe just in time for an xmas mod for some...

Online Breaktru

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Re: USB Charging 2 Li-Po Batteries.
« Reply #17 on: October 22, 2012, 10:06:57 AM »
so you have had it together for awhile...do the batts stay balanced...?
read PM for additional...(new Idea not speaking of in public yet)...and don't spam me w questions yet guys if the Idea works well I'll post a new internal charging full range mod in a few mo...maybe just in time for an xmas mod for some...

Putting the switch in Parallel mode for a few minutes seem to be balancing the batteries okay and do it before putting it on charge. Haven't had any issues.

I'll look over your PM as soon as I have my second cup of coffee.....

Offline ADozer

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Re: USB Charging 2 Li-Po Batteries.
« Reply #18 on: January 01, 2014, 09:14:05 PM »
Been lurking around and reading for about a day. I must say I love this forum. I'm currently working on putting together a schematic and parts list for my first box mod.

I wanted to incorporate this switch, but as a 3P3T with the center being completely off. Needless to say I'm a complete newbie to switches that are more complicated than a momentary or a simple on-off toggle. So I would appreciate any guidance on how to substitute a switch like that into the above schematic.

Thank you in advance.

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Re: USB Charging 2 Li-Po Batteries.
« Reply #19 on: January 02, 2014, 11:09:32 AM »
I think I have it down. Can someone look it over and let me know?
Check it thoroughly before attempting to connect the batteries.
I used a 3P3T slide switch. Link here --> G-368S-0000
Up is series/vape mode, Center is OFF and Down is Charge in parallel

Offline ADozer

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Re: USB Charging 2 Li-Po Batteries.
« Reply #20 on: January 02, 2014, 06:06:59 PM »
Thank you very much. I like this idea more than a separate on/off switch honestly. Unless that approach would be safer to implement along with the first schematic.

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Re: USB Charging 2 Li-Po Batteries.
« Reply #21 on: January 10, 2014, 11:16:00 PM »
Yet another question from a noob. If this were hooked up to a okr-t/10, wouldn't the contact current rating have to be 10a to support the max output capabilities of the okr-t/10?

edit: Nevermind, data sheet on the converter states maximum input current is 4.53amps, I'm still guessing I'd want a contact current rating of at least that right?
« Last Edit: January 10, 2014, 11:25:06 PM by ADozer »

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Re: USB Charging 2 Li-Po Batteries.
« Reply #22 on: January 11, 2014, 07:55:01 AM »
The switch is rated 3A @ 125V which equates to 375W. You will be using 8.4v at the most. So the switch should be able to handle 44.64A at 8.4v

The above is more of a guess than an exact calculation. You would have to find the datasheet with the Load Limit Curve chart which I can't find for that switch.
« Last Edit: January 11, 2014, 10:13:37 AM by Breaktru »

Offline ADozer

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Re: USB Charging 2 Li-Po Batteries.
« Reply #23 on: January 11, 2014, 10:42:50 AM »
Ahhhh... so it all comes back to watts! Thank you.

Offline CraigHB

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Re: USB Charging 2 Li-Po Batteries.
« Reply #24 on: January 11, 2014, 02:45:17 PM »
Ratings for DC switches typically come down to power.  However, as Breaktru pointed out, switches do not handle power in a linear fashion.  The ratings are provided in terms of a single point with a voltage and amperage.  You can multiply the two for a pseudo power rating.  However, keep in mind that it's going to change an amount based on applied voltage.  There's a point where the switch hits a current limit regardless of applied voltage.  Unfortunately, absolute maximum currents are not provided for DC switches.  It's pretty much a guess.

Switches for AC applications are typically rated in VA which is a power rating.  Those are normally intended for a particular voltage like 110AC or 220AC so they're more constrained in that way.  Even the industrial ones used for voltages in the kV are rated in VA, but they're still constrained by a voltage rating.

It's a pretty safe assumption that a switch rated for 3A and 125V can handle 6 Amps and 8 Volts.

Offline kurtus

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Re: USB Charging 2 Li-Po Batteries.
« Reply #25 on: January 22, 2014, 10:23:40 AM »
This is just what I was looking for, sure beats installing 2 usb boards. Thanks for pointing this out to me Squance:)

Is is possible to just break the + to - connection of the series batts then have each battery individually wired from the usb board effectivly parallel charging while breaking the series connection with a spst switch? Not too sure if this senerio would create a short in series having the parallel connections still hooked up through the usb board while in series to run a vmax chip.

Offline CraigHB

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Re: USB Charging 2 Li-Po Batteries.
« Reply #26 on: January 22, 2014, 04:21:31 PM »
You need to switch the batts from series to parallel to charge both cells with a USB charger.  That's the function of the drawing in the OP.  However, you can not leave the charger connected when engaging the + to - connection on the cells.  It would create a short circuit.  This is why the multi-pole switch in the OP is required.  Using one or two USB charging boards makes no difference.

There's number or ways to charge two series cells without reconfiguring them.

Use a virtual ground with two USB charger boards.  In that case, you need two separate USB power supplies.

Use a boost converter on the 5V USB input and raise it to 9V which would allow the use of two boards with a virtual ground requiring only one external connection.

Use two boards with a virtual ground and a 9V power supply requiring a different connector type (typically a barrel connector).

Use a balance charger with a charging header externally accessible.

Offline kurtus

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Re: USB Charging 2 Li-Po Batteries.
« Reply #27 on: January 22, 2014, 11:20:26 PM »
Thx Craig, my brain was going nuts trying to visualize if this would cause a short. As much as I have a number of balance chargers for my RC hobby I think it would be too much of a pain to mod it redering it only useful to me. I think i'll stick to the schematic and play safe ;cheers;

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Re: USB Charging 2 Li-Po Batteries.
« Reply #28 on: January 23, 2014, 03:50:28 PM »
The first three things I mentioned are too convoluted.  Really the best and only way to charge series cells without reconfiguration is to use a balance charger with a charging connector built into the mod.  Other than that, a series-parallel switch with a USB charger is the next best option.

One big disadvantage with reconfiguring the cells is you can't charge and vape at the same time.  Though it would be possible to devise a solid state switch array that automatically reconfigures the cells, but again, you're getting into a design that's too convoluted. 

The advantage of a balance charger connection is you save a bunch of space by removing the requirement to build charging electronics into the mod and you can charge and vape at the same time.  Of course, all of this is only a concern when using non-removable cells.  My feeling is that built-in charging with removable cells is rather redundant, though people do it anyway.

Offline forever23

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Re: USB Charging 2 Li-Po Batteries.
« Reply #29 on: May 23, 2014, 12:41:40 PM »
Not sure if it is mentioned but does anyone know what fuses are used in line on both batteries. I see an F1 and F2. Thanks in advance.

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Re: USB Charging 2 Li-Po Batteries.
« Reply #30 on: May 23, 2014, 04:28:27 PM »
Not sure if it is mentioned but does anyone know what fuses are used in line on both batteries. I see an F1 and F2. Thanks in advance.

10A PTC for each battery (2 PTC fuses total) or 2 x 5A in parallel for each battery (4 PTC fuses total)

Offline forever23

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Re: USB Charging 2 Li-Po Batteries.
« Reply #31 on: May 27, 2014, 06:12:44 PM »
So I have never messed with a PTC fuse before. Now when you say 10a are you talking about the    Voltage - Max     Current - Max        Current - Hold (Ih) (Max)        Current - Trip (It)   

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Re: USB Charging 2 Li-Po Batteries.
« Reply #32 on: May 27, 2014, 06:43:08 PM »
HOLD current

Offline forever23

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Re: USB Charging 2 Li-Po Batteries.
« Reply #33 on: May 27, 2014, 06:46:35 PM »
I really appreciate the help. This is the last step I needed in my PTR08100W NES mod. Once I get all the parts I'll post the build if youd like.

Offline eddie8111

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Re: USB Charging 2 Li-Po Batteries.
« Reply #34 on: June 02, 2014, 05:38:10 AM »
iv followed this:
http://www.e-cigarette-forum.com/forum/battery-mods/538730-arlo-dual-18650-dna20-30-step-step-how.html

by mamu and iv altered it for duel lipo 20c running a dna30d in a very small box would i need 1 of these switches to charge in parralel if so i may need to change my box as there aint any room for a grain of rice in there now lol

Offline michamer

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Re: USB Charging 2 Li-Po Batteries.
« Reply #35 on: June 02, 2014, 08:05:15 AM »
iv followed this:
http://www.e-cigarette-forum.com/forum/battery-mods/538730-arlo-dual-18650-dna20-30-step-step-how.html

by mamu and iv altered it for duel lipo 20c running a dna30d in a very small box would i need 1 of these switches to charge in parralel if so i may need to change my box as there aint any room for a grain of rice in there now lol

Charging and running two batteries in parallel would not require any switching. This topic is for running two batteries in series and charging them in parallel.

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Re: USB Charging 2 Li-Po Batteries.
« Reply #36 on: June 02, 2014, 08:12:04 AM »
So mine ar fine to charge in parralel then yes

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Re: USB Charging 2 Li-Po Batteries.
« Reply #37 on: June 02, 2014, 06:58:46 PM »
There are no additional concerns in using a USB charger for parallel batteries, but there are concerns in general with parallel batteries.

To use removable parallel cells safely you must have some kind of protection for charge mismatch which includes the possibility of a battery inserted backwards.  Large equalization currents can occur between cells if they are not charged to the same level.  Depending on the cells, it may not be that much of a mismatch required to cause hazardous currents.

If using parallel removable cells, you pretty much have to fuse each cell individually to protect from these potential issues.  For non-removable cells it's not an issue since the cells act as one once permanently connected.  Also it's not an issue for protected cells since the protection acts as a fuse does.

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Re: USB Charging 2 Li-Po Batteries.
« Reply #38 on: June 03, 2014, 06:29:24 PM »
Fully charged over night but when got down to about half charge on dna 30d it says weak battery??

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Re: USB Charging 2 Li-Po Batteries.
« Reply #39 on: January 04, 2016, 02:06:11 PM »
What if i use a relays?

Offline bestkeptsecret

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Re: USB Charging 2 Li-Po Batteries.
« Reply #40 on: June 10, 2018, 08:38:25 AM »
Hi Everyone.

Just signed up to the forum on recommendation from another.

This is exactly what I've been looking for......Almost

has anyone come across a similar chip that is capable of managing a charge current of up to 8A?





Offline elzakivis

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Re: USB Charging 2 Li-Po Batteries.
« Reply #41 on: June 10, 2018, 02:17:14 PM »
Hi Everyone.

Just signed up to the forum on recommendation from another.

This is exactly what I've been looking for......Almost

has anyone come across a similar chip that is capable of managing a charge current of up to 8A?

Welcome to the forum.

Charging batteries at 8A? or a regulator capable of outputting 8A?

Offline bestkeptsecret

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Re: USB Charging 2 Li-Po Batteries.
« Reply #42 on: June 10, 2018, 03:29:28 PM »
Welcome to the forum.

Charging batteries at 8A? or a regulator capable of outputting 8A?

Thanks for the welcome.

And definitely a 8A charging circuit yes. I'm looking at putting a setup together that would take 4 26650's or 4 21700's in parallel. Ideally I'd want to be able to switch between 4 and 8 and 2 so I could have each cell drawing 2, 1 or 0.5A



Offline elzakivis

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Re: USB Charging 2 Li-Po Batteries.
« Reply #43 on: June 11, 2018, 02:07:03 PM »
Sorry BKS, I don't know of any 8A charger. Maybe one of the members could help.

Offline charming

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Re: USB Charging 2 Li-Po Batteries.
« Reply #44 on: June 12, 2018, 02:22:26 PM »
Sorry bro, don't know

Breaktru Forum  |  eCigarette Forum  |  Battery  |  Topic: USB Charging 2 Li-Po Batteries.
 

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