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power supply probs

bodge

Jun 29, 2010
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i am having problems with powering a MUSTEK pvr 400.
the internal battery gives me 45minites of recording time. if i use the mains power unit (output 5v 2a) i can extend the recording time to 4 hours.
so i thought if i buy a car adaptor and connect it to a 12v battery this would extend the time as well.
i bought a 12v 3a adaptor from maplins and connected it to a 12v 7ah yuasa battery but found that it didnot extend the time at all. before i throw any more money at this can anyone tell me what i am doing wrong. thanks.
 

Resqueline

Jul 31, 2009
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First of all, what is this? Can you provide any links to reviews etc.? Google didn't return much of use to me..
 

bodge

Jun 29, 2010
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sorry i got the model wrong . it is a mustek pvr h140. it is a 40gb media player recorder video and audio.
 

davenn

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Sep 5, 2009
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sorry i got the model wrong . it is a mustek pvr h140. it is a 40gb media player recorder video and audio.

OK so what is written on the unit as far as power requirements are concerned ?

Dave
 

bodge

Jun 29, 2010
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on the input jack it just says 5v. on the label on the back of the unit it says
rating dc 5v - 2a.
in the manual it just says power source -internal rechargeable li ion battery 1000 mah x2 (built in charger through power adaptor).
 

davenn

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on the input jack it just says 5v. on the label on the back of the unit it says
rating dc 5v - 2a.
in the manual it just says power source -internal rechargeable li ion battery 1000 mah x2 (built in charger through power adaptor).

ok... so assuming the 12V 7AH battery you used was fully charged and in good condition
it should have lasted you at least 3 hours.

Maybe the battery is old and no longer holding a full charge it almost has to be the reason

put a multimeter in Volts DC mode across the battery that has been charged then power up the player and watch and see how quickly the voltage drops. That will tell you pretty quickly if the battery you used is a dud.

cheers
Dave
 

bodge

Jun 29, 2010
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ok davenn will try that tonight brit time and see. i am asuming that if i did away with the 12v to 5v converter and plugged a 6v battery to a 5v input that would be very bad. i just wondered if the converter was taking some of the power from the 12v battery before passing on the 5v to the unit.
 

bodge

Jun 29, 2010
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ok , so 12v battery stays at 11.97v for over 30 mins until unit switches off. output is constant 5v but pvr still only records for 25-30 mins. it is almost like the unit sees that it is not connected to the mains charger and fails to charge the internal battery with the external battery 5v. the converter that i am using is a 12v auto regulated supply that will output a variety of voltages from 2.5 to 9v. does regulated have any bearing on the problem.
 

ChosunOne

Jun 20, 2010
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Boge, I do a lot of work with the 12v, 7Ah sealed lead-acid battery. Fully charged I expect it to read anywhere from 13 to 13.5 VDC open-circuit voltage. A light load might drop it to 12.5-->12.8 V, a moderate load down to maybe 12.2-->12.3; and it takes a heavy load indeed to start out at less than 12.0 volts.

If your Li-ion 1000mAh battery runs it 45 minutes, that's not a load heavy enough to draw the voltage of a the lead-acid battery down that far until many hours later. Either you aren't charging the battery or, as davenn said, it's old and just not holding a charge.

Hope you got it at a good price.
 

davenn

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ok , so 12v battery stays at 11.97v for over 30 mins until unit switches off. output is constant 5v but pvr still only records for 25-30 mins. it is almost like the unit sees that it is not connected to the mains charger and fails to charge the internal battery with the external battery 5v. the converter that i am using is a 12v auto regulated supply that will output a variety of voltages from 2.5 to 9v. does regulated have any bearing on the problem.

ok mate....
not knowing the specifics of the 12V - 5V regulator you are using its efficiencyfor me is an unknown factor. There will be some losses in it but if it was a reasonable one I would expect those to be relatively low.
is there anything written on it ?
how complex a circuit is it ?

is you really wanted to to prove that that regulator is ok, you could build up a quickly assembled 12V to 5V reg with a LM338 adjustable regulator. Use the TO3 metal cased one it can go to 5Amps

here's a quick circuit ... adj the trimpot to get 5V out before connecting your media player
you will find it in the datasheet for the LM338 online :)

cheers
Dave

grrrrr I cant remember how to embed images :(
 

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bodge

Jun 29, 2010
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thanks a lot for all of your help people. thanks dave. i will go and lie down in a darkened room and build the circuit in the near future. i am rather disapointed with the response from MUSTEK but perhaps i need to learn another language??
it now appears that the mains adapter is charging the internal battery at a greater rate than the external battery can. this enables the unit to continue to operate for a long period. i will check the amps used by both power supplies whilst unit is switched on, maybe the 12v - 5v converter is suppling a smaller amp output than it says on the tin.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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My guess is that the external power is used only to charge the internal battery and the charge rate is less than the drain on that battery when it is playing.

It sounds weird, but I have a USB device that works in the same unfortunate way. In my case external power extends the operating life of the unit, but it only extends it to about an hour. After that I have to let it charge a bit (while sitting idle) before I can use it again.

Frustrating.

Your option might be to create a power supply which bypasses the battery. A lot depends on how easily you can lay your hands on a circuit diagram or figure it out.
 

bodge

Jun 29, 2010
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i think you have hit the nail on the head steve. if i sort it out then i will post a answer. i may have to just replace the internal battery with a larger external one but the internal one has three wires i am guessing that they are + - and charge+ but dont want to mess with it at present. will do in the future if i cannot sort it any other way. thanks for your help.
 

(*steve*)

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Three wires are normally +, - and a temperature sensor (a thermistor).
 
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