going from LiPo battery to wall power?

I'm trying to run a tablet I have that runs on a 3.7v battery off of the wall directly without a battery. Reason is my sister broke the charging cable, and thus I decided to convert it to an android TV of some sort. I got a buck converter and I set it to 3.7v but the tablet doesn't turn on! it flashes on for a second and then turns off. I tried using different amp measurements, but all that did was keep the screen on a few fractions of a second more before it turns off again

0 Former Member over 10 years ago in reply to shabaz

I found this information:

Module Spec: non-isolated step-down (BUCK)
Rectification: non-synchronous rectification
Input voltage: 4V-35V
Output voltage: 1.23V-30V
Output Current: 3A (max)
Conversion efficiency: 92% (the highest)
Switching frequency: 150KHz
Output ripple: 30mV (max)
Load Regulation: ± 0.5%
Voltage Regulation: ± 2.5%
Operating Temperature: -40 ℃ to +85 ℃
The peripheral dimensions: 48 * 23 * 14 (L * W * H) (mm)
Notes: Default output is 20V from factory setting.

LM2596 Power Module

it seems like the 12v input is ok, so I'll try that in a bit. However, I'm curios; does the switching frequency have anything to do with this?
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0 shabaz over 10 years ago in reply to Former Member

Ehab Charek wrote:

I do have, however, a few good 12v power supplies. Is it safe to use those instead?

Unfortunately I don't know, you'd need to check with the vendor of your DC-DC converter.
I'm all out of ideas I'm afraid!
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0 Former Member over 10 years ago in reply to shabaz

I've added the capacitor to the circuit as mentioned by John as of yesterday. Which, according to you, means that it could either be the power supply, or the buck converter. I am, in fact, using a converter I got from ebay. I am also using a power supply I got from a flea market, as I don't have another one with 6-7 volts of output. I do have, however, a few good 12v power supplies. Is it safe to use those instead?

Mark, as for your suggestion, the button works with no issues when the tablet is running off the battery.
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0 mcb1 over 10 years ago in reply to Former Member

According to this site
http://www.pipomall.com/index.php?main_page=faq_info&faqs_id=112

Is it possibly the open/close button causing the issue.?

Mark
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0 shabaz over 10 years ago in reply to Former Member

According to your earlier post you're connecting your power supply to the terminals where the battery connects. And you just have a 2-pin battery.
In that case, the issue is likely to be your power supply/DC-DC converter. If it is a cheap e-bay one then it may not be able to supply sufficient current, or may need the capacitor as mentioned by John.
If these tips don't help, you probably need to investigate further and supply more detail.
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0 Former Member over 10 years ago in reply to shabaz

it works perfecty fine when running off the battery
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0 shabaz over 10 years ago in reply to Former Member

Are you sure the tablet actually works? Perhaps there is a fault causing it to immediately power off.
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0 jw0752 over 10 years ago in reply to jw0752

Sorry I mistyped - I meant to say I have never personally tried to circumvent an integrated battery so I am not the best person to be answering this question.
John
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0 Former Member over 10 years ago in reply to mcb1

thanks for the reply!
the tablet is a chinese one made by a company called PIPO. And the model is the Pipo M9. here's the battery for that tablet:
Original 3.7V 7800mAh Rechargeable Lithium Battery For PIPO M9 Tablet - US$37.26
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0 shabaz over 10 years ago in reply to jw0752

Hi John,

I think this is a likely issue. There are often three or more connections, one being a thermistor in the battery pack. With that absent, the power management IC won't start up the device.
Tablets have fairly big batteries so there may be a third connection somewhere. We need to know the tablet model. According to youtube teardowns, even supermarket-branded tablets can have more than two connections to the battery pack.
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