6V SLA Dropping resistor for a 5VDC Filament Supply

chrismercurio · 29th January 2012, 06:32 PM

I'm dangerously close to finishing a 71a line stage but my DMM is suspect and giving various inconsistent values and won't measure 1% resistors accurately.

Can someone lend me a hand and tell me the approximate fixed resistor value to lower a 6v SLA to 5V for a 71a .25a filament supply? Even better would be tell me how to apply ohms law or KVL/KCL to the current scenario so that I don't have to ask such a pedestrian question again.

I know I need a new DMM but that is going to have to wait for a few weeks.

Thanks!

astouffer · 29th January 2012, 07:02 PM

Number of volts to be dropped divided by the current.

Although what you really need is a low dropout regulator. Using a resistor will give you no overhead when the battery starts to lose voltage.

chrismercurio · 29th January 2012, 07:08 PM

So....1v/.25a=~4ohms?

DF96 · 29th January 2012, 07:45 PM

Yes, Ohm's law.

29th January 2012, 06:32 PM	#1
chrismercurio diyAudio Member Join Date: Aug 2006 Location: Silicon Valley	6V SLA Dropping resistor for a 5VDC Filament Supply I'm dangerously close to finishing a 71a line stage but my DMM is suspect and giving various inconsistent values and won't measure 1% resistors accurately. Can someone lend me a hand and tell me the approximate fixed resistor value to lower a 6v SLA to 5V for a 71a .25a filament supply? Even better would be tell me how to apply ohms law or KVL/KCL to the current scenario so that I don't have to ask such a pedestrian question again. I know I need a new DMM but that is going to have to wait for a few weeks. Thanks!

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29th January 2012, 07:02 PM	#2
astouffer diyAudio Member Join Date: Jun 2004 Location: Pittsburgh, crumbling wasteland	Number of volts to be dropped divided by the current. Although what you really need is a low dropout regulator. Using a resistor will give you no overhead when the battery starts to lose voltage.

29th January 2012, 07:08 PM	#3
chrismercurio diyAudio Member Join Date: Aug 2006 Location: Silicon Valley	So....1v/.25a=~4ohms?

29th January 2012, 07:45 PM	#4
DF96 diyAudio Member Join Date: May 2007	Yes, Ohm's law.

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