Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: cooldog on February 01, 2008, 09:31:51 AM

Title: power switching circut
Post by: cooldog on February 01, 2008, 09:31:51 AM
i was thinking is there a circut that will monitor the voltage from a solar panel and when it drops below a certain voltage it switches to battery's. then when the voltage from the solar panel gets back to the required voltage it switches back
Title: Re: power switching circut
Post by: Trumpkin on February 01, 2008, 09:37:22 AM
I think a switching regulator will do that.
Title: Re: power switching circut
Post by: paulstreats on February 01, 2008, 09:55:55 AM
you need an under voltage monitor. The come in a 3pin package, power & gnd & out. When voltage drops below a certain level the out pin can switch on or off . They cost about $0.30 from microchip
Title: Re: power switching circut
Post by: cooldog on February 01, 2008, 10:02:25 AM
do you need to program them for a certain volatge
Title: Re: power switching circut
Post by: paulstreats on February 01, 2008, 10:03:23 AM
no, you buy them with predefined threshholds
Title: Re: power switching circut
Post by: cooldog on February 01, 2008, 10:19:13 AM
i can't find any that will work at 5v
Title: Re: power switching circut
Post by: gmatkins on February 01, 2008, 12:25:59 PM
This is a pretty common problem in BEAM robotics. The typical solution is to use a voltage trigger like this little fellow...

http://www.solarbotics.com/products/1381/
Title: Re: power switching circut
Post by: ed1380 on February 01, 2008, 04:53:37 PM
go to some sites that give samples. it should be under power management
Title: Re: power switching circut
Post by: cooldog on February 01, 2008, 05:00:14 PM
while were on the topic of power manajment does anyone know where i can sample a 5V Linear Regulator
Title: Re: power switching circut
Post by: paulstreats on February 01, 2008, 05:57:26 PM
sample them from microchip, you could also sample the voltage detectors from there (they go up to 4.63v detection)
Title: Re: power switching circut
Post by: cooldog on February 01, 2008, 06:09:19 PM
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en010606

is this the right size that admin used in the $50 robot
Title: Re: power switching circut
Post by: paulstreats on February 01, 2008, 06:25:10 PM
That one only outputs 300ma, try to get one that outputs 1000
Title: Re: power switching circut
Post by: cooldog on February 01, 2008, 06:35:53 PM
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en021857

this better
Title: Re: power switching circut
Post by: SmAsH on February 01, 2008, 06:54:28 PM
yes..
Title: Re: power switching circut
Post by: paulstreats on February 01, 2008, 06:57:09 PM
try this
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en531455 (http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en531455)

get
MCP1826S-5002E/AB

in the TO-220 package.

And Smash, that one is a 6 lead design - that is the first thing that makes me think it is nothing like the 3 lead version in the $50 robot

Title: Re: power switching circut
Post by: Rebelgium on February 02, 2008, 07:57:38 AM
keep in mind that when your solar panel voltage is for example 6V, and your circuit will decide it's high enough to switch your load to it, then your solar voltage will drop (because of the current you draw from it) , your circuit will decide the voltage is too low, and it will swithc your load back on the battery. Because the load is not on the solar panel anymore, the solar voltage will rise to 6V again, and your circuit will decide it's high enough again.
etc.

this will cause the the system to swithc between the two sources again and again... not good.