To be deleted...

[nul-points]

Hi nul-points, goo-day mate, hehe.
...
I'll have to give more thought to the step back down idea.
In the meantime, i ventured back to the Rene re-emf charger idea.
So in my case, 2 lithium cells in series charging directly another lithium cell, with transistor and primary of blocking oscillator in line and of course lighting the led bulb off secondary.
I am swapping the single lithium charging cell periodically with one of the input series cells, it seems to be working well so far.
...

Ha, g'day Skywatcher

Ok, no worries - i hadn't heard of Rene's charger, but i've seen (and experimented witb) others which use 2 to charge 1

I decided to stick with the same storage size on both i/p & o/p to make it easier to swap the batteries electrically, but otherwise it's the same idea

I like your idea of creating a lantern, or reading lamp - i'm not expecting to get much more than a pocket-flashlight thing going

All the best, keep us posted
np

[citfta]

Thanks so much for such a simple and worthwhile circuit.  I have mine together and it seems to be working great.  I only had a very small LED so I will be looking for some larger ones to try.  My charge battery is gaining voltage nicely while only drawing 30 ma from the run battery.   Will keep you posted as I learn more.

Thanks again,
Carroll

[nul-points]

Thanks so much for such a simple and worthwhile circuit.  I have mine together and it seems to be working great.  I only had a very small LED so I will be looking for some larger ones to try.  My charge battery is gaining voltage nicely while only drawing 30 ma from the run battery.   Will keep you posted as I learn more.

hi Carroll, pleased to hear you've got a circuit going!  I have a couple of circuits running at the moment - one uses a regular panel-mount type LED, hi-brite, that circuit only draws 10+mA but it's still quite bright to look into the lamp - the other circuit has a board-mount 1 Watt LED and can give brighter illumination at higher currents, so this might be a good LED type for you if you want to draw around 30mA

The current draw can be adjusted with VR1, so you can choose the current to suit the LED - obviously the battery discharge time decreases with increased brightness/current, but we're aiming to extend the usefulness of one 'external' charge by recharging 'internally' somewhat (a few times?)

Since the circuit is recharging one battery whilst discharging the other, our external charges shouldn't need to be more  than either:-

a) 1 battery fully charged, one discharged
b) 2 batteries, each half-charged

all the best with your experiments
np

[SoManyWires]

hi Carroll, pleased to hear you've got a circuit going!  I have a couple of circuits running at the moment - one uses a regular panel-mount type LED, hi-brite, that circuit only draws 10+mA but it's still quite bright to look into the lamp - the other circuit has a board-mount 1 Watt LED and can give brighter illumination at higher currents, so this might be a good LED type for you if you want to draw around 30mA

The current draw can be adjusted with VR1, so you can choose the current to suit the LED - obviously the battery discharge time decreases with increased brightness/current, but we're aiming to extend the usefulness of one 'external' charge by recharging 'internally' somewhat (a few times?)

Since the circuit is recharging one battery whilst discharging the other, our external charges shouldn't need to be more  than either:-

a) 1 battery fully charged, one discharged
b) 2 batteries, each half-charged

all the best with your experiments
np

very nice work there chief!
thankyou for sharing this.

(much applause sound here)

[nul-points]

 
thanks SMW, glad you like


ok - here are some preliminary results to see whether this type of approach is worth investigating more

first, a few general observations about the energy capacity of these NiMH cells used here:

- a fully charged cell can provide its Ah rating starting at an initial voltage of approx 1.4V and finishing at a practical discharged voltage of approx 1.2V
*
- a resting terminal voltage of 1.3V represents approx 50% charge remaining in the cell

- with a resistive load, the total energy supplied by these 750mAh cells, between full charge and discharge would be approx 1.3V x 0.75Ah = 0.98 Wh

you can see from the attached graph that Vb2 started and ended at approx 1.3V - therefore it started and finished with an approx 50% charge - its end voltage (1.31V) was only slightly higher than its initial voltage, so i'm going to ignore it in our energy accounting (although it made a real contribution in extending the runtime of the flashlight)

the 'flashlight' was illuminated at the same setting for 96 hours - the average current draw for the circuit was approx 10mA

cell B1 was connected as input for the first 80 hours of operation, and it discharged to 1.3V - this would normally be the 50% charge point, but we can see that this cell started at approx 1.45V, so it may be that it had supplied a little more than 50% of its expected capacity

by this point, cell B1 had supplied approx 800 mAh, both illuminating the LED and charging cell B2 from 1.3V to 1.35V

After the 80 hour point, cells B1 & B2 were swapped between input & output every 1 or 2 hours, for a further 16 hours

the terminal voltage of cell B1 was recharged back above 1.3V for all of this 16 hour period

so, the outcome of this test was that effectively the length of time before cell B1 terminal voltage fell below 1.3V was extended by at least 16 hours and the total amp-hours supplied to the circuit was 960mAh up to an approx 50% charged point

using an 'area under the curve' calculation, and a dual-slope approximation to the discharge graph, the total energy expended by the flyback flashlight for the duration of the test was approx 1.3Wh - and it only used just over half of the charge in cell B1

when you compare this with the expected total capacity of the cell (ie. a full charge) of approx 1Wh, this approach is definitely worth investigating more!

np