REGISTER | LOGIN
Home    Bloggers    Blogs    Article Archives    Messages    About Us   
Tw  |  Fb  |  In  |  Rss
Analog Angle

When Vendor Numbers Defy Ohm’s Law

Bill Schweber
steve.taranovich
steve.taranovich
11/2/2018 1:04:23 PM
User Rank
Blogger
Re: Something missing
Here are two battery images to support Bill's reply to "Something missing"

Battery #1

Battery 1

Battery #2

Battery 2

50%
50%
Bill_Jaffa
Bill_Jaffa
11/2/2018 7:08:37 AM
User Rank
Blogger
Re: Something missing
I now have the specs on the battery: 3.65 V, 6040 mAh, 22.646 Wh (given with such precision to 5 significant figures!). Measures approx 2.75 x 1.75 x 0.9 inches (70 x 44 x 22 mm) and is in a very custom size/shape enclosure, has mini-USB port for charging via external cable, a mechanical release tab, and 5 small contact bumps. I assume two of the contacts are for internal AC charging input, two are for internal DC out. no idea what the third is-- unless the battery is really a dual unit with bipolar outputs. But that's speculation. Again, it is not my brand new $200 unit soI can't play with it too much, plus I can't risk damaging it either

50%
50%
Bill_Jaffa
Bill_Jaffa
10/31/2018 12:02:10 PM
User Rank
Blogger
Re: Something missing
Good points--yes, I used the worst-case scenario of zero V at the battery, which is how I like to start this kind of analysis. As for your other suggestions: they are also good, but it is not my unit,I can't risk damaging it, and I always like to keep in mind the guideline that "no good deed goes unpunished" -- so I will step away from helping my friend unless I have a clear-cut answer from someone who has figured out the situation and has a solution that has been tried and verified.

50%
50%
HRConsult
HRConsult
10/31/2018 11:26:57 AM
User Rank
Newbie
Something missing
Just a thought: The 50 watt resistor is probably bigger than the unit.

I am missing the part of your analysis where you include the battery voltage in your current calculations. Your analysis starts with the absolute worst case of the entire 25 volts appearing across the 25 ohm resistor. Giving the battery credit for something other than zero volts would immediately decrease the worst case dissipation.

My guess is that the internal charging circuit has lots of control over the conditions applied to the battery, especially the charging current, and that current would be largely independent of the applied voltage. The clue here is that the device is supposed to work ok with the same 25 ohm resistor and the input voltage ranging between 8 and 24 voilts.

I think I would investigate the device a bit with my multimeter. First, I would check the battery voltage. Then I would use an external power supply with current limiting and check the charging current, even going so far as to discharge the battery and measuring the current under that condition. Once I had that information, I would be in a position to determine the right components for the external charging supply.

50%
50%
Pesky Varmint
Pesky Varmint
10/26/2018 11:04:51 AM
User Rank
Newbie
Maybe a 100uF motor starting capacitor?
This from Jerry Steele (aka Pesky Varmint)

 

They are a little on the large side but not worse than a 50 watt resistor.

And, no heat to worry about.

50%
50%
AubreyKagan
AubreyKagan
10/26/2018 10:46:56 AM
User Rank
Newbie
Class 2 transformer
Bill

 

I don't know if this is going to colour your investigations- all transformers used for household purposes like the transformer for the bell are rathed as a "Class 2". What this means is that the transformer is maximum 100VA and maximum 30VAC and is current limited either through the resistance of the winding or by a fuse so as to be "safe". The stadard is  UL 5085-3, There is a bit about them here.n

 

When we qualified a product for Class 2 through UL, "safe" mean that the object with the output in short cicuit would not get hot enough to set fire to anything. Our test involved placing a musln cloth over the device and leaving it in the fualt conditon for 3 days and then checking for charring on the muslin cloth. (3 days seems a bit of an overkill if the device has turned off when overloaded and there is no heating at all)

50%
50%
More Blogs from Analog Angle
Medical devices from wearable to big machines embody leading-edge technologies, but they also must meet an enormous menu of safety, power, and EMC standards that have major effects on design innovation, flexibility, and time to market.
It’s hard to find viable, simple, tangible demonstrations of STEM-related concepts, but an old-fashioned Received Signal-Strength Indictor (RSSI) and TV provided one.
Like Silicon, single-atom sheets of Carbon, known as Graphene, can be the base material for diverse innovations across multiple disciplines and applications.
Basic, all-analog circuitry can be probed and teach STEM students more than about engineering than just keyboard-based coding
flash poll
educational resources
 
follow Planet Analog on Twitter
Planet Analog Twitter Feed
like us on facebook
our partners
Planet Analog
About Us     Contact Us     Help     Register     Twitter     Facebook     RSS