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Mini^3 Problem

post #1 of 10
6/13/10 at 9:43pm
Thread Starter 

Hi,

 

I've just finished building a Mini^3 and I think I have a big problem with the charging circuit - when connected to my wallwart, the mini^3 builds up a whole lot of heat. I opened it up and connected it again and have traced the heat to U2 (voltage regulator) - it got so hot that it started to deform the battery! The red led and everything else functions ok, and there were no problems with heat until the Mini^3 was plugged in for charging. Any help much appreciated...

 

Cheers,

 

Lipponz

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post #2 of 10
6/13/10 at 9:57pm

Double check all parts in that circuit, make sure you didn't mess up the current limiting resistor or shorted something.

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post #3 of 10
6/13/10 at 10:10pm
Thread Starter 

No R8 (and R7 - but that for the LED right?) are measuring correctly. Do you think it could it be a problem with a diode? How do you check? This is my first DIY project so I'm a bit of a noob:)

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post #4 of 10
6/14/10 at 12:25am

R8 sets the current for charging

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post #5 of 10
6/14/10 at 3:24am

What voltage is the PSU you're using?

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post #6 of 10
6/14/10 at 2:35pm
Thread Starter 

It's 18.02 volt measured with DMM, center positive...

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post #7 of 10
6/14/10 at 3:00pm

Measure the charge current and voltage as outlined in the Mini3 "initial setup" page......

 

 

 

Quote:
 
  1. Set your multimeter to measure DC mA (for a manual ranging meter, set to 200mA range). On most meters, the red probe lead must be connected to a different jack on the meter to measure current.
  2. Connect the red probe to the positive battery contact and the black probe to the negative battery contact.
  3. Connect the AC-DC adapter output plug to Mini³'s DC jack. The charge LED should illuminate.
  4. If the R8 resistor is the default value (75Ω), then the the meter should read approximately 16mA. If you used a different R8 value, then you should read the current that you set the charging system to. See the Parts list section for details.
  5. Switch the meter to measure DC V (for a manual ranging meter, set to 20V range). Reconnect the red probe lead on the meter to the proper jack for voltage measurement if necessary.
  6. Connect the red probe to the positive battery contact and the black probe to the negative battery contact.
  7. With the AC-DC adapter still connected, you should read about 12V DC.
  8. Disconnect the AC-DC adapter. If your measurements are OK, then you are done.
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post #8 of 10
6/14/10 at 9:59pm
Thread Starter 

I don't think my DMM can measure current - it's a Amprobe PM53A. I've been emailing Ti and we seem to think it could be a damaged voltage regulator (U2). I have a wallwart with removable plugs - I accidentally connected it to the Mini^3 with the polarity reversed which may have damaged U2, and is now causing it to run extremely hot. I've already removed it and have to wait about a week for a replacement...Do you agree that this could be the problem?

 

I'll post again if that doesn't fix it.

 

Thanks everyone for your help so far!

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post #9 of 10
6/15/10 at 1:00pm

You could probably measure the voltage across R8 and use Ohm's law to calculate the current (I = V / R). For 16mA, you should see ~1.2Vdc across R8.

 

Connecting power sources with the polarity reversed generally does bad things, and you should have mentioned this in your first post.

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post #10 of 10
6/15/10 at 5:04pm

I would suggest ordering a new C2 while you are at it....

(tantalum capacitors tend to behave "strangely" when the polarity has been ignored)

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