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New USB LiPo charger
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New USB LiPo charger

by jdumond3 on Wed Jun 30, 2010 2:21 pm

Saw the new LiPo charger,thought it was interesting.

I've got two questions though questions though:

Can a load draw power from the system (Charger/Battery/USB) while the LiPo charger is plugged into USB?

The blog post says
“Keep the battery connected to the charger and pass power through the additional JST connector using the included cable!”

This means it can draw power from the battery while the USB is not connected, right?
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Re: New USB LiPo charger

by rickrump on Wed Jun 30, 2010 4:54 pm

I have a similar question. Would it be safe to use this as a (nearly) full time USB power source for a LiPo powered device - e.g. wireless phone. I frequently have many conference calls a day using my wireless phone in my home office. My phone often starts complaining of a low battery part way through a call. If I hacked a charging jack on the phone, could I plug this charger in parallel with the battery and leave the battery in the circuit? Unfortunately the (not so smart) circuitry in the phone hangs up the line when you put the phone in the charging base.

Rick
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Re: New USB LiPo charger

by adafruit on Wed Jun 30, 2010 6:27 pm

Any non-timered charger (such as this one) can work with the lipo loaded or unloaded 'indefinitely' - the charger will stop once the voltage reaches 4.2v and start again when the voltage drops. This should only be done with batteries that have protection circuitry (just in case).

Of course, the battery wont charge as fast and once it is completley charged, without an extra mosfet and diode you may see the battery charge and discharge constantly instead of being 'smart' and having the USB only provide power instead of the battery.

We will try to do an experiment to see precisely what happens when our battery is fully charged and then used under load while plugged in - whether it cycles or not
:)
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Re: New USB LiPo charger

by adafruit on Wed Jun 30, 2010 6:29 pm

rickrump wrote:I have a similar question. Would it be safe to use this as a (nearly) full time USB power source for a LiPo powered device - e.g. wireless phone. I frequently have many conference calls a day using my wireless phone in my home office. My phone often starts complaining of a low battery part way through a call. If I hacked a charging jack on the phone, could I plug this charger in parallel with the battery and leave the battery in the circuit? Unfortunately the (not so smart) circuitry in the phone hangs up the line when you put the phone in the charging base.
Rick


Make sure that you are connecting DIRECTLY to the battery! depends a bit on the phone of course, and make sure its a 3.7/4.2v liion cell
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Re: New USB LiPo charger

by jdumond3 on Wed Jun 30, 2010 9:03 pm

Good news.

So as I understand it, when a load circuit is attached to the LiPo charger along with a battery below 4.2 V, both the battery and the circuit will draw from the charger. When the battery is fully charged the charger may or may not (pending results of your experiments) provide power.

Few more questions:
Will the load circuit see a constant 4.2 V throughout the charging process described above process?

Can the charger be used as a 4.2V power supply for a circuit if no battery is attached? Or is it more of a current source?

How does one calculate charging time for a LiPo. Would a 1100mAh battery being charged with 110 mA take 10 hours to charge?

I'd love to see a video of your experiments if its not too much trouble. Maybe at the next Ask an Engineer.

Thanks for your help! My purchase will be in shortly. :D
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Re: New USB LiPo charger

by adafruit on Wed Jun 30, 2010 9:24 pm

1. No! The voltage on the cell ranges from 3.7-4.2V!
2. This will not work at all, there must be a battery
3. Yes
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Re: New USB LiPo charger

by jdumond3 on Wed Jun 30, 2010 10:04 pm

aah ok.

Will the voltage decrease have an adverse effect on say a ATmega328 running on an internal oscillator driving nothing but LEDs. I understand LEDs will dim, I'm mostly concerned about the performance of the uC.
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Re: New USB LiPo charger

by adafruit on Wed Jun 30, 2010 10:09 pm

you should use a voltage regulator (say 3.3v) to get yourself a clean supply - this is always suggested. otherwise there will be fluctuations that can affect frequency and performance. Get one with a 400mV or less dropout
Regulators, they are Awesome!
http://www.ladyada.net/wiki/partselector/vreg
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Re: New USB LiPo charger

by jdumond3 on Wed Jun 30, 2010 10:31 pm

Will do! Thanks for your help. You guys are awesome!
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Re: New USB LiPo charger

by midwinter on Thu Jul 01, 2010 11:56 am

Hi there,

Just a quick question -- It looks like this has a charge circuit with overvoltage protection (and thermal protection?) from the MCP73833, but it doesn't look like there's a protector (like a DS2764) for (amoung other things) discharge protection to protect against undervoltaging and overcurrent draw. I remember from when I was playing with LiPolys a year or two ago that it's supposed to be potentially very dangerous to draw too much current or drain a LiPoly below a certain voltage threshold, after which there (if I remember correctly) is a chance that the battery will explode upon recharge. That being said, I've noticed the datasheet mentions "preconditioning" deeply depleated batteries with trickle charges until they get to a certain threshold, before fast charging them. Is it the case that this charger is likely only suitable for LiPoly batteries that have integrated undervoltage and overcurrent protection, or where the application can *guarantee* that these conditions never occur, or does the MCP73833 handle everything (from a safety standpoint), including these undervoltage/overcurrent conditions?
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Re: New USB LiPo charger

by adafruit on Thu Jul 01, 2010 12:21 pm

good question. the mcp is designed to work even with 'unprotected' lipolys. it will do its best to not overcharge batteries and precondition. There is NO WAY for a charger to protect against overcurrent draw (battery short) or under-voltage!!!
The lipoly that we sell -itself- has a protection circuit. its underneath the orangey kapton tape. It provides overcurrent, over&under voltage protection. We always suggest having two layers of charging protection - one on the battery and one on the charger. these batteries also are tested to not be volatile on overcharging or use. Check the datasheet for the safety tests performed.

While you may be able to use the charger with unprotected cells, its a really bad idea. we would never suggest or sell unprotected lithium cells.
The cells' protection circuit, likewise, does mean you can go out of your way to 'abuse' the batteries. Yes it has a PTC but that doesnt mean you should be shorting them for fun. There is overvoltage protection but you should still only use a proper charger.

Like most lipos, the batteries we sell do not have thermistors built in. This is why we suggest charging at 1/2C or less - 500mA. Thats still plenty fast and wont heat up the cell. The charger does support having a thermistor but you would have to solder it in and remove the 10K SMT resistor.
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Re: New USB LiPo charger

by midwinter on Thu Jul 01, 2010 1:48 pm

Thanks for the response. I ask because I would typically have to use two devices on my boards (the charger, and the protector), and was curious if they'd come out with a single IC for it all. The microchip parts are also a lot easier to source in small quantities than the parts I am using.

One neat thing about some protectors (like the DS2764) is that you have access to a lot of extra functionality, including some statistics (like battery voltage, current draw) over I2C, as well as soft power. It's a really neat device to use on embedded systems, although they might have something even better out this year.

I read your blog almost every day, to see all the neat things you folks are up to. As someone just about to finish their PhD, I'm sometimes lured by the starving-artist-esque romanticism (not that i'm saying you're starving! :) ) around having your own open source hardware business, and wonder what it would be like to go that route. It seems sort of like academia in that you get to develop what you'd like to, but also outwardly productive in that you get to see your results a lot quicker and get to help folks learn and create and build and make. Also, I'd love to just be able to give the designs away -- I'm going through the patent process for my startup, and it's just so very crazy and costly. I think what I'm trying to say is, very well done, it's great to see all the new products and designs, and all the fantastic good they do at helping folks be creative learners and students of science.
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Re: New USB LiPo charger

by STrRedWolf on Mon Jul 05, 2010 12:38 am

Two questions:

First, can this charger handle the 6 Amp LiPo battery available at SparkFun? It's URL is: http://www.sparkfun.com/commerce/produc ... ts_id=8484

Second, are there any plans to integrate this plus a LiPo battery with the Mintyboost? There's an instructable on it, but I think a cleaner one-board design could be worth more (and require carrying of Altoids mints instead of gum).

I got too many gum tins...
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Re: New USB LiPo charger

by adafruit on Mon Jul 05, 2010 1:13 pm

that will work fine, might want to bump up the charge rate by soldering in a new R4 (see the schematic for new values you may want to pick) for like 500mA so it doesnt take a week to charge

we have a nimh rechargable mintyboost in beta testing, while we like lipos - they're best used by people who are more experienced with electronics. nimh's are much safer and common :)
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Re: New USB LiPo charger

by adafruit on Fri Aug 27, 2010 9:46 pm

hey mpechner! sorry we accidentally hit the delete button when its right next to "reply" :( but we say your post about removing r4

if you can do that, go for it. if its not easy for you to do, just calculate what the parallel resistance is and make sure thats what you want. so figure out what resistor in parallel with 10K is equal to 2K (probably like 2.5 or 3K)
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