Maximum voltage allowed

Hello folks at Sandisk,

Is 5.6V or even 6V safe on the USB input of the Clip+ please (I’m aware of the USB specs being less than this)?

Being able to recharge off a block of 4 NiMH when I’m out and about (week long hiking etc) without having to worry about making sure the batteries were slightly discharged first, would be great.

Cheers

From the AS3525 charger spec sheet:

Charger Supply Voltage (min)4.5 (max)5.5

 So no, 5.6v is out of spec and should be considered unsafe.  Most likely it will work, since USB ports tend to be poorly regulated and these devices take that into account with lots of safety margin, but you risk your player doing so.  You might want to look into putting together a 5v regulator circuit to be safe.

@dihenydd wrote:

Hello folks at Sandisk,

Is 5.6V or even 6V safe on the USB input of the Clip+ please (I’m aware of the USB specs being less than this)?

 

Being able to recharge off a block of 4 NiMH when I’m out and about (week long hiking etc) without having to worry about making sure the batteries were slightly discharged first, would be great.

 

 

Cheers

NiMH batteries are 1.2V each, so you would only get 4.8V from four in series.

Saratoga:

Cheers for the info. It’s kinda interesting given the USB Spec states 4.5V - 5.25V, it worries me that a commercial product goes to 5.5V.

As you say, most USB ports are badly regulated and the player is likely to handle a higher voltage.'m hoping for a Sandisk Official to confirm this. It would be odd for the Li-Pol charging circuit to not have a regulator on it.

Can’t add a regulation circuit without upping the voltage to ~7V (regulators need headroom, and simple zener diode circuits need inline resistors for current limiting. at 350mA charge current (someone claims it to be so) that’s one hell of a drop on just a 1ohm resistor. I’ve considered the internal resistance of the battery pack to act as the resistor, but I have little confidence.

gwk1967:

NiMH sit at 1.4V on full charge and go to 1.2V after about 5-10% use (and fortunately hold that voltage until damned near flat).

So, for the initial use there may well be 5.6V at the output. And, now for the complex bit:

USB Spec

Voltage: 4.5 - 5.25 V

Current:

On intitial attachment a client may only draw 100 mA from the host *, to draw more the client MUST negotiate this with the host first. Provide the host gives the thumbs up the client then may draw up to 500 mA. And, there-in lies the problem.

Assuming an internal resistance of 0.17 ohm ± 0.04 ohm per cell.

Therefore the internal resistance of the battery is 0.52 - 0.84 ohm (again, it’s an assumption but it does give leeway for various brands)

Time: 0 sec

Open Circuit: 5.6 V

100 mA: 5.6 (V) - ( 0.1 (A)  * 0.52 (ohms) ) = 5.548 V (above both USB spec, and that of the previously mentioned mains / USB adapter)

350 mA: 5.6 (V) - ( 0.35 (A) * 0.52 (ohms) ) = 5.418 V (worst case, Fails USB, passes previously mention adapter spec)

350 mA:  5.6 (V) - ( 0.35 (A) * 0.68 (ohms) ) = 5.362 V (still fails USB spec at typical internal resistance)

Time: some point later

350 mA: 4.8 (V) - ( 0.35 (A) * 0.84 (ohms) ) = 4.506 V (Just in spec - assuming the device honours the USB Spec**)

500 mA: 4.8 (V) - ( 0.5 (A) * 0.68(ohms) ) = 4.46 V (Below the USB Spec)

There is generally very little overhead for USB powered Li-* chargers (at least according to Maxim) so under voltage is likely to cause a huge issue.

So, provided the device can accept up to 5.6V and only draws 350 mA (someone has measured it to be this apparently) then it’s all hoopy. There are certainly enough AA / USB adapters on the market that assume this.

I know, I’m being a paranoid penguin!

* The spec has been amended so that if the data lines are shorted (if I’ve remembered this correctly) the device can assume it is connected to a dumb charger and can ignore negotiations, going straight for high current.

** There are some devices which don’t like having as little as 4.5V, so technically shouldn’t hold the USB logo as they aren’t spec compliant.

@dihenydd wrote:

Saratoga:

Cheers for the info. It’s kinda interesting given the USB Spec states 4.5V - 5.25V, it worries me that a commercial product goes to 5.5V.

As you say, most USB ports are badly regulated and the player is likely to handle a higher voltage.'m hoping for a Sandisk Official to confirm this. It would be odd for the Li-Pol charging circuit to not have a regulator on it.

 

 

It is regulated (lipoly chargers have to be regulated) but the maximum voltage is 5.5v.  

dihenydd wrote: 

 

 Can’t add a regulation circuit without upping the voltage to ~7V (regulators need headroom, and simple zener diode circuits need inline resistors for current limiting. at 350mA charge current (someone claims it to be so) that’s one hell of a drop on just a 1ohm resistor. I’ve considered the internal resistance of the battery pack to act as the resistor, but I have little confidence.

 

 

 

Spend $4 and get a good boost regulator.  That way you can discharge the batteries well below 5v and still power the device.  As an extra benefit, you can get away with using fewer NiMH cells to save weight. 

You can probably do cheaper then this one, but the application example they give is up regulating a low voltage battery pack to USB voltage so maybe its worth the few dollars:

 http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1116,P87927 

dihenydd wrote: 

 

USB Spec

Voltage: 4.5 - 5.25 V

Current:

On intitial attachment a client may only draw 100 mA from the host *, to draw more the client MUST negotiate this with the host first. Provide the host gives the thumbs up the client then may draw up to 500 mA. And, there-in lies the problem.

 

 

 

 All the sandisk players I’ve used ignored that part of the spec and charged at full power regardless of what the host negotiated.  This is actually really common.  No one makes 100mA USB ports because they’d be burned up in no time.  Make sure you can supply the full 500mA and some extra to be safe. 

Saratoga:

Cheers for all the info, unfortunately the converter you found only gives ~240 mA if the input is 2.4V so the 2 battery approach is out (unless I’ve misread the datasheet). I had briefly considered using a booster in the past and decided if I were to go down that route I’d probably just buy one (effectively 2 full time jobs, shame I only get paid for one of them, and exceptionally good at throwing soldering irons if used for more than a very short time - muscle spasms, not patience).

A lot of people on the net are creating various packs with differing degrees success using nothing more than 4 AA cells, but if I do screw the unit I wouldn’t feel right trying to send it back under warranty.

Retail Products:

  http://www.portablepowersupplies.co.uk/aausbbattery.htm

is good for the UK (£10.50 inc p&p)

  Varta also create one that is similar and probably available world wide.

A few dollars? What’s one of them? Lets convert that $4.5 to good old sterling… £7.91

I love the USA / UK conversion rate. People wonder why we buy stuff from HK.

Again, cheers for all your help.

It seems to me that a 2 cell approach would be much less efficient than a 4 cell one and that two cells would provide much less power from each cell than a 4 cell approach. it is hard to find test data on this.

If you could get away with using 4 AA cells without any other circuits that would be the most efficient, however, it’s not guaranteed to work.

The Linear Tech part mentioned earlier definitely has a loss in efficiency when working with lower input voltages, it is however designed to work with higher voltages when you want that sort of current.I part designed specifically for 2 - 3.5 V in 5V out should be much more efficient (although probably not when compared to 4.8V on a device designed specifically around that voltage). I would be surprised to see more than 10% difference between the two optimised solutions.

Okay, there are a huge number of assumptions there so the statement is rather risky.

Testing would be simple. Provided I had a 4x and a 2x unit to test. I have a couple of variable supplies which give current supply reading accurate to 1 mA (give or take only a couple mA from my experience). Use the supply in place of the batteries to charge a mp3 player and check the current draw.

Don’t forget that there are plenty of options open in the three-cell posibility.  I’ve seen plenty of products using three AA / AAA size batteries.  This gives you a reduction in size, and better efficiency.  Your charge pump won’t have as much work to do.

µsansa

I am not skilled/knowledgeable in this area, but had a thought anyway… Maha sells a charger (http://www.thomasdistributing.com/shop/maha-mhc9000-advanced-battery-chargerbrfree-deluxe-storage-case-included-p-405.html?SP_id=&osCsid=6dgp3m9tsvht77bonp78maub94) that lets you do a lot with how batteries are charged/discharged, etc.  This might allow you to charge/discharge the NiMH batteries to the level you need.  I have used the charger for about a year now to charge all of the AA/AAA batteries I use (GPS, Cameras, old MP3 player, remotes, computer mice, etc.) and it does a great job, even on crappy batteries (Energizer).  I have found that the Sanyo Eneloop and Maha Imedion are great low discharge batteries, and the Maho PowerEx are great recharable batteries.  All three last well in devices, and recharge to at least 95% (or greater) of the stated battery levels.  Also, the vendor in the above link has been great all the way from pre-order questions to answering support questions.

NOTE:  I have no affiliation with Thomas Distributing other than they have been a great company to work with as a customer!

Eric

Microsansa:

I assume Sandisk aren’t willing to provide the input voltage specs (unless Saratoga was correct with 5.5V), or are just an avid fan and not actually employed by Sandisk?

I’ve not seen any 3 cell packs out there, still I’ve ordered a 2 cell pack and I’m sure it’ll be fine, can’t be any worse than the Clips natural battery life ;).

EricBr:

I too own a Powerex Wizard (Is Maha the USA name for what we UKians call Powerex, or are Maha bad at advertising their name?) great charger, I highly recommend it to any one who doesn’t mind a slight initial outlay for much longer life in cells. This would definitely do the job of performing a quick drain on the cells so they would work well, but I’d be stuck if I was in the back end of nowhere and could only get alkalies. It’s also too much hassle trying to remember to discharge them, and also remembering if I have discharged them.

@dihenydd wrote:

Microsansa:

I assume Sandisk aren’t willing to provide the input voltage specs (unless Saratoga was correct with 5.5V), or are just an avid fan and not actually employed by Sandisk?

 

 Since Sandisk didn’t make the battery charger (they are a flash memory company not an analog IC company), I don’t think they can give you the specs.  However, since they used a stock off the shelf part with a datasheet that says 5.5v, I’m not sure what else you really need. 

But yes, I was thinking of a three cell pack.  The voltage is almost perfect. 

@dihenydd wrote:

 

 

A few dollars? What’s one of them? Lets convert that $4.5 to good old sterling… £7.91

I love the USA / UK conversion rate. People wonder why we buy stuff from HK.

 

 

Again, cheers for all your help.

You have the conversion backwards.  A pound is worth more then a dollar, not less.  $4.50 is worth approximately 2.77 pounds.  

Have you guys looked at the Tekkeon Tekcharge MP1550?

http://www.tekkeon.com/products-tekcharge1550-specs.html

My apologies, I assumed the AS3525 was an external charger (ie sandisk brand mains to USB adapter), well further proof that assuming makes an ass out of me. That is actually the definitive answer I was looking for.

"You have the conversion backwards.  A pound is worth more then a dollar, not less.  $4.50 is worth approximately 2.77 pounds. "

Nope: I got it right, the UK electronics industry has it backwards. When negotiating cost at work we use dollars for bulk buy from a USA supplier / manufacturer, when we buy from firms like Farnell (for low lead time, dev. parts) we get right royally rogered. The price I quoted was Farnell’s (RS would be the same) 1-10 parts, the 10-99 parts cam in at ~£4.50. This country is the same with all electronics and books. A book published in Ireland would be shipped to America and charged at $X and sold in the UK for £X, electronics they normally take the number, add a bit on and then switch the sign to £. The Clip+ is £60 here (okay, £45 on Amazon), it would be regardless of where it’s made.

Hence, why a lot of hobbyists over here just buy straight from Hong Kong. We get stuff at a good price.

The sad bit is, I have a degree in electronics, a job in design electronics, and an interest in electronics. But, due to not having my tongue wedged firmly up managements rear end I’m never allowed to do any actual design work. So, I jump on the chance for hobbies and make a thorough fool of myself on the way do to a distinct lack of experience, and end up giving up.

Most certainly, the power supply requirements of the AustriaMicrosystems device are designed to integrate with the USB standard, as the USB interface is resident in the SOC.

If you have a look at the published AMS datasheets, there are some really cool functionalities available that are not currently used on the Sansa.  There are some capabilities I’d love to use, but these are more logically implemented on a larger player.

For additional information or queries regarding the device, you can contact AustriaMicrosystems.  The 3525 family is but one of many versions.  The current Sansa device has integrated memory.

Bob  :stuck_out_tongue: