# For you brilliant electronic wizards.....a question



## jboydjr (Jul 8, 2007)

Is it possible to charge a battery while that battery is being discharged (running a torch, for example)? I think some of you probably know where I am going with this. If it would be possible, then would it extend the runtime of the battery that is being discharged and charged concurrently, and would it be a significant increase in runtime? 

Jim


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## bfg9000 (Jul 8, 2007)

Can you use your car headlights while the car is running?

So long as the charger can supply the needed current the battery would not drain at all, and "runtime" should depend on how much gas you have or the local electric utility...


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## jboydjr (Jul 8, 2007)

Well, my reason for asking is that I have an idea for a device that could be marketable, but the good problem is that the charge would be quite low (I think).


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## bfg9000 (Jul 8, 2007)

Well if what you have in mind is a battery-based emergency charger like the Energizer Energi To Go, you could probably just add up the watt-hour capacities of both batteries (subtracting for conversion inefficiencies).

With a mains AC or automotive based charger it only makes sense to make the charger of sufficient capacity.


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## monkeyboy (Jul 8, 2007)

I wonder if memory effect would be a problem with nickel batteries.


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## matrixshaman (Jul 8, 2007)

Sounds like a solar charger idea? I had a cell phone with a solar battery - just leave in the sun and it kept charged without plugging it in unless I did a lot of talking. If that's the plan I'm doubting it will get much interest. I've got a Big Lots light that has solar cells built in and it's big and squarish so while unique it will likely only be useful in a situation where there is no electricity.


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## jboydjr (Jul 9, 2007)

Well Matrixshaman, you have come close. My idea was to build a lantern that focused it's beam on photovolectric (sp?) cells, that would trickle it's output back to the power source. You would still have the ambient light, thus accomplishing what a lantern is supposed to do, but the reflective material would be the charging material. Now, go make a million, but remember me when you are in that mansion.


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## modamag (Jul 9, 2007)

Remember the "Second Law of Thermodynamics"
It's better to just reduce the output of the LED :"D


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## jboydjr (Jul 9, 2007)

I really want to let you all know how much I appreciate the fact that you very tactfully gave me the answers to my questions using humor and without embarrassing me. You all are really a class act. Thanks again for responding. I guess I knew it would have been done a long time ago by better minds than mine if it were possible.

Sincerely,

Jim


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## Cornkid (Jul 10, 2007)

Now, if you managed to somehow use the excess heat and convert it to a current (however small it may be), then you might be in business...


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## jboydjr (Jul 10, 2007)

Well, I thought of that, too, but was sort of convinced that I couldn't generate a significant amount of energy from the photo-v's. What I was thinking was that, since heat rises, if I could generate enough heat, it could turn a small fan, connected to a very efficient motor, thusly capturing just about all of the heat and light energy I could between the two. ???


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## IMSabbel (Jul 22, 2007)

No, that would be extremely inefficient.

The most sensible solution would be a thermoelectric element between the led-base and the heatsink.
Those have efficiencies in the order of 5%.

Otoh, it would be perfectly possible that the decrease in efficiency due to the increase in temperature due to the decrease in thermal conductivity could outweight the gain by this element.


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## matrixshaman (Jul 25, 2007)

I've got a little music box that plays a Beatles tune when light hits the solar cells on top. It doesn't take much Sun light to get it going but even my brightest LED lights don't do much for it (including a Cree that's likely 180+ Lumens). An incandescent will get it going but it takes a strong one to really move it. So I don't believe the concept will be very effecient. Solar chargers take a lot of light to produce a little current over considerable time. It's a good idea but solar cells are currently far from being effecient enough to work well in this way. There's no harm in thinking along these lines and I commend anyone who is trying for ways to get more energy from what we have. I've researched alternative energy for many years and I see the biggest block to achieving any alternate designs as people who can't accept new ideas as being workable. Many people feel if it hasn't already been thought of and built then it must not be possible. That IMO is very wrong. I think we have yet much more to discover than we have already discovered.


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## Eugene (Aug 5, 2007)

monkeyboy said:


> I wonder if memory effect would be a problem with nickel batteries.



Nickel what, NIcad or NiMH? You sound like that outdated battery university page which lumps both nicad and nimh into one nickel category and gives bad information since they are different.


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## Eugene (Aug 5, 2007)

jboydjr said:


> Is it possible to charge a battery while that battery is being discharged (running a torch, for example)? I think some of you probably know where I am going with this. If it would be possible, then would it extend the runtime of the battery that is being discharged and charged concurrently, and would it be a significant increase in runtime?
> 
> Jim



There are several Maxim IC's which can be used like this. They have a few app notes on chargers which charge and run the load at the same time. One of these days I'm going to order a few and mess with them.


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## TorchBoy (Aug 8, 2007)

jboydjr said:


> Well, I thought of that, too, but was sort of convinced that I couldn't generate a significant amount of energy from the photo-v's. What I was thinking was that, since heat rises, if I could generate enough heat, it could turn a small fan, connected to a very efficient motor, thusly capturing just about all of the heat and light energy I could between the two. ???


My gut feeling is that the fan would provide more energy than the photovoltaic panels (which from memory are maybe 15% efficient at best, much less normally). But on the subject of fans and gut feelings, if you plugged a hose into... oh, never mind.

Going back to your original post, my solar powered watch is using the battery faster than it's charging when I do something power-hungry with it, but the solar panel is still helping a little.


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