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need help with a circuit

im trying to make a circuit with 2 voltage sources and one resistor.
the voltage sources simultaneously change constantly from 2 to 6 volts (really slowly, its not an AC source)
and my goal is that when the overall voltage goes above 10 volts, one voltage source will be disconnected and only one voltage source will feed the resistor. ive been trying to make something with transistors and inverters but nothing helps, anyone can help?
dragonuv

Posts: 235
Joined: Tue Dec 04, 2007 1:22 pm

Re: need help with a circuit

This is going to be trouble without some sort of "smart" electronics.
My reasoning;
a.) no source goes to 10 Volts.
b.) both sources are variable.
c.) no source is "master" (the go-to source when the total Voltage reaches 10 Volts).

Your circuit will have to monitor the voltage of both sources and choose the higher voltage while monitoring the total voltage to decide when to eliminate the lower-voltage source. It will have to be able to decide when to return to using both sources and allow for "historisious" to eliminate osculating between the both/one states of operation. (can't get spell-check to correct "hisrorisious" :)

You could do this with a micro controller, but it would be a bunch of additional hardware (power load) and require a larger and more complex enclosure. I don't know what plans you have for this, so I can only guess this will be a semi-fixed location with something like a solar array and battery pack.

Another solution considering the solar thing might be to put two battery packs in the thing and when one is charged, switch your solar panel to the discharged pack. Alternating between the "full" pack and the running pack as the cells recharge. Keep the solar panel out of the load circuit and use it only for charging the discharged battery pack. A "fall-back" could be added to switch the load to the partially-charged pack should there be no input from the solar array and the "on-line" pack become discharged.

I imagine the switching system for this could be non-computerized, using voltage comparators and diodes, with relay switching.

This is not as you hoped, a "solution" to your problem, only a re-work of what you might have already thought of. :)

Phil
phil.drummond

Posts: 125
Joined: Sun Feb 08, 2009 4:57 pm

Re: need help with a circuit

I will guess there is a better approach. As I recall these are 2 solar panels? So you don't want to go above 10V? If that is all true, and the current is not large, I would just throw a linear regulator on it and call it a day.

zener

Posts: 4567
Joined: Sat Feb 21, 2009 2:38 am

Re: need help with a circuit

phil.drummond wrote:Your circuit will have to monitor the voltage of both sources and choose the higher voltage while monitoring the total voltage to decide when to eliminate the lower-voltage source.

how could the microcontroller eliminate the charging of one battery?

phil.drummond wrote:so I can only guess this will be a semi-fixed location with something like a solar array and battery pack.

you sure got that right, but instead of a battery pack its a large 12v battery (i had to say 12v instead of 10v)

phil.drummond wrote:Another solution considering the solar thing might be to put two battery packs in the thing and when one is charged, switch your solar panel to the discharged pack. Alternating between the "full" pack and the running pack as the cells recharge. Keep the solar panel out of the load circuit and use it only for charging the discharged battery pack. A "fall-back" could be added to switch the load to the partially-charged pack should there be no input from the solar array and the "on-line" pack become discharged.

I imagine the switching system for this could be non-computerized, using voltage comparators and diodes, with relay switching.

can this method or other similar one be implemented to a charging system with 1 large battery instead of battery packs?
and it sure can be no computerized, but if there is a relay, doesnt it mean that i have always have to be there and alternate between charging?

and thanks very much zener, i will look in wikipedia or something how the linear regulator works.
dragonuv

Posts: 235
Joined: Tue Dec 04, 2007 1:22 pm