hi Jeanna & crowclaw
thanks for your kind comments - appreciated!
i'll try & answer some of the points you raise:
> could you have missed capturing more?
i agree - there's a lot more going on in spikes than we usually see with our test equipment - and i suspect that this is exactly where all the interesting stuff is happening!!
i took a variety of scope 'snapshots' throughout the different tests i did with battery charging, to see what how my test circuit was operating with batteries compared to the usual resistive load - it looked pretty much the same (apart from the fixed voltage offset on the output caused by the output battery itself, of course!)
due to the nature of the energy conversion of around 4000 Watt-seconds total at only 160mW per second, each test took many hours (as you can see from the graphs) - so there was only so much data i could usefully capture with my 'scope in datalogging mode
> I wonder what would happen if you were to charge 4 batteries? Would they charge as high as the 2AAA and in the same amount of time
i suspect not - i ran a test with two batteries in one of the two paths (ie direct pulse charge) and the same output energy as the single battery in that path just got divided between the two batteries
> What if you were to reverse your set-up? Would your NiMH AAA be able to produce high enough spikes to charge your NiMH 8.4v cell?
unfortunately not - my test circuit is not a voltage-booster like the JT - the output voltage on the switched-charge circuit is always lower
> Another q is about the difference it would make if you were to recharge these in parallel?
Do you suppose the spikes could be caught better in a parallel arrangement?
well, the output batteries were 'in parallel' across the circuit - but each was receiving separate 'packets' of charge - so i guess you mean to have the output batteries exactly side-by-side (+ to +, - to -)
i did try this but, as i realised afterwards, this was never going to work:
different batteries have slightly different characteristics and the battery which charges slower 'drags' any parallel batteries down to its terminal voltage - it 'holds back' other batteries from charging at their own individual rates
however, on the JT, since the secondary produces an AC waveform, you can connect two batteries in parallel across the secondary output - you have to connect them in opposite polarity, each with its own separate charging diode:
| JT secondary o/p |
> I am getting higher and more frequent voltage spikes from my jtc's than he gets from his SG wheel, so I should be able to recharge a lot of batteries... right?
i'd be interested to hear if you can get solid quanties of Joules (Watt-seconds) by using just large & more frequent spikes - the evidence i saw from the results i showed above was that the total area under the spikes (the power content) was what gave the actual charge in that test, no matter how many or their magnitude
having said that, i have a long-running test going at the moment to see if i can 'self-trickle-charge' an AAA NiMH driving its own VERY low-power circuit which pulses 3 LEDs in parallel and feeds the output current & flyback current back into the same AAA
the circuit SHOULD just discharge the battery (and will slowly discharge a cap) but i'm hoping that there might be some low-level charging action on the battery just from the spikes - the drain is probably a fraction of a micro-amp though, so it's going to take a looong time to find out if the battery is discharging! (been running a few weeks now, i think, at 1.260V!)
> Did you find the switching frequency important to the timed rate of charge
good question - since each test took many hours (followed by many more to recharge the input battery afterwards!) i didn't try altering the pulse rate very often!
i agree it's an important test to try - i'm interested to hear how you get on
i did try 8.4v to 8.4v recharging on my test circuit but (as i mentioned in answering one of Jeanna's qs above) the output voltage wasn't really sufficient and very little charge got transferred
> my 8.4 volt battery will charge from approx 0.99v (fully discharged) to 10 volts in approx 3 mins. But I still have to log discharge rates before we get to excited...
i agree - one thing i found was that the output battery rises to its final charged voltage very quickly but this doesn't give an indication of the charge it has taken
the batteries would stay at that voltage for hours whilst they received all their charge from the input
only the discharge test at the end showed just how much charge they could deliver back!
sorry - bit of a marathon reply!!!
all the best in your investigations - keep it rolling!