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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 [email protected]
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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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 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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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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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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