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atoof

battery and HDD

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hi all
i want to make power supply to my Hard  disk from battery to use it as external one
so i did  :)
MY HDD use 12v .75A,5v .8A DC ,i made a circuit using 7805,7812 to get voltage from battery,
i measured the voltage and it was good
after connecting i think its motors tuned on but PC can't see it  :o
it's ok the circuit didn't work,but the surprise was HDD was damaged  :'(
can any one help me ,i want to know why this happened?
and any one suggest another circuit to get power from battery i want to make it.
any one can help me plz reply here or email me my E-mail is atef_m_y@yahoo.com
thanks

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hi indulis,
ok 7812,7805 ,if we said that they can't support this current may they damaged themselves but why HDD damaged?
if you have an answer plz post it :)
if you (or any one who see my question)can suggest another regulator plz do
thanks for your reply
atef

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What is the voltage of the battery when it has a full load and is partially drained? The 7812 needs an input minimum of 14.5V. The output voltage drops if the current is too high or if the input voltage is too low. The HDD crashes with the voltage too low. 

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Hi atoof,

If the HDD is an IDE type the IDE bus needs to have common ground with the motherboard or the two floating grounds can obtain a destructive voltage between them. This means there is no protection against static or some stray voltages. My guess is the IDE controller circuit in the HDD is gone! :(

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hi all
thanks for your reply
my battery was over 18 vDC (3 batteries in series each one 6v DC,4A),and when HDD had been attached battery volt was around 17V
i didn't measure the output of 7805,7812 after attaching (it was only few minutes and everything gone :'()
if HDD crashes when the voltage too low (as audioguru said )i think it was the
problem

but the problem of common ground( as Ante said) between motherboard &battery i think it is not problem becouse IDE bus has 4 pin as ground are connected  to motherboard ,so there is no need for external connection.
anyway i still want to make this circuit and if any one can help me plz do
thanks
    atef

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Hi atef,

The question is; are the four IDE ground pins connected to the negative of the power connector onboard the HDD or not?
On the motherboard they are connected but this does not help if the HDD gets its power from another source.

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hi Ante
the board of HDD that takes power from supply will connect this ground from supply to IDE ground pins itself :)
and then IDE will connect it to ground of PC supply

i checked this the -ve of battery is conncted to PC ground
happy for ur reply
  atef

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Your voltage regulator ICs can't supply enough current to the hard drive to get it spinning quickly. It draws a very high current when its speed is accellerating.

Remember 8-track tape players that drew about 10A to change tracks??

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hi  Audioguru
thanks for your reply
if you can tell me for another regulator that gives me high current plz do :)
by the way you said 8-track tape players that drew about 10A to change tracks of course it is so large but that is tape player but i think HDD takes less current :)
anyway if anyone can tell me something about HDD current at all times of operation plz do
thanks
  atef

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You cannot select another regulator with higher output current until you find out the max current of the HDD.
You could look on the datasheet of most manufacturers' 78xx regulators where they show how to add a power transistor for nearly unlimited output current.

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hi all
thanks for your reply :)
i have a circuit that gives me 12v dc with high current but i want to know your comments plz
i attached it
wait for your comments
atoof


The emitter resistor shouldn't be there. It causes the transistor to current-limit with a current too low.
The base resistor in datasheets is 3.0 ohms.

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HDD needs stable voltage and I think LM317 is not appropriate in supply voltage to your application, esp. you can't guarantee the resistors values are stable.

Where do you buy lousy resistors that change their value?
I use cheap carbon film resistors that don't change, and also pretty cheap metal film resistors that are even better. No problem.

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