Regulating charging

[Rubberjohnny]

Yet another busy weekend making up a Magnum clone with a twist. Instead of using L-ion I have utilised a triple (in series) pack of 1000mAh re-chargeable NiMh 1.2 volt AAA that fit snugly allongside each other in a 23mm internal diameter tube to give 3.6 volts at the atomiser.The aim of using these batteries is the ability to re-charge in situ via a standard DC power socket and a mains driven transformer.
The finished mod is a joy to use with both excellent vapour production and long battery life.Now for the question to the more technically advanced modders;

1) My understanding is that one can trickle charge NiMh batteries without the need of any protection/cut off circuit and there will be no damage/fire risk as long as the feed current does not exceed 10% of the battery capacity.Since I am using 3 in series am I correct in thinking 300mAh would be a safe level at say 6volts off a mains transformer?This would indicate a re charge from exhausted of some 10 hours.
I have such a transformer (ex cordless phone) which certainly does the job,the batteries geting slightly warm to the touch as they take current.However since I have no means to tell how low the battery pack is prior to overnight top up they could well end up fully charged and still being fed from the transformer.

2) Should I consider (if practical/available) some sort of control circuitry to shut of charge once the battery pack is fully charged even at this low re charge rate or is it perfectly o/k if the charge continues at 10% of capacity?

3) If 2 above is practical I could obviosly charge at higher (say 500mAh) rate thereby reducing re charge time.

 

[RayJ1]

Charging at 300mah is more than fine for three AAA nimh's. However....that's really not a trickle charge. You might overcharge if left on overnight. You really will have no way of knowing where your batteries are w/o using a peak detection charger. I run 4AAA nimh's in my mod in series and use a dedicated peak detection charger that will charge 4 nimh batteries in series. I looked high and low for a low cost peak detection charger for 3 AAA's but could not find one that was relatively inexpensive. Rechargeable nimh's really do need a decent peak detection charger to keep there mah capacity and there ability to deliver it. I charge my 4AAA nimh's at 1.0 amp and there fine.

 

[Rubberjohnny]

Many thanks for your advice. I will try to hunt down a suitable charger.
I am still puzled as to how why so many household items (battery hand vac, cordless phone, electric screwdriver) that utilise various numbers of NiMh re-chargeables do so without seeming to have any charge regulation.I have examples of all the above and they all seem to re-charge directly off there supplied mains transformers.The vac and cordless phone are both permanantly connected to their working transformers.

 

[RayJ1]

Many of those devices are trickle chargers charging at a rate of 50mah's or less. With a fully depleted 3pak of AAA's nimh at 1000mah's would take forever to recharge at 50mah's. Many of the above devices you mentioned are only used for afew minutes and thrown back on the charger. The batteries in those devices also degrade pretty quickly. Lot's of people have had expereince with home cordless phone batteries losing there capacity pretty quickly because there always on the trickle charge and overcharged. NIMH's do like to be fully discharged and then charged at a higher rate to full charge. My peak detection charger charges at 1amp to full charge when the voltage drops, and then goes to trickle charge.

 

[kender]

Your having no problems with 4 NiMH batteries? There was a long thread on here saying that 4 NiMH batteries would burnout the atomizer on the first try. Never tried it but could not figure out why NiMH as compaired to li-ion would burnout the atomizer.

 

[Rubberjohnny]

That is why I run triple set ups giving 3.6v at the atomiser. I have built several 4 cell mods (4.8v NiMh) and experienced repeated atomiser failure,in one case with immiediate loss of 3 atomisers one after another.I do wonder if a small resister in the circuit would smooth out the initial burst of power that seems to do the damage.However I find using any voltage (L-ion or NiMh) over 3.6/3.7v tends to give much more burnt and off flavours so have given up on making higher voltage mods and am continuing the quest to design a "Magnum" type mod that does not require battery removal to re-charge.If only I could source a 3.6v peak detection charger at a reasonable cost the job would be done!!
Thank you RayJ1 for your valuable guidance.

 

[cosican]

That is why I run triple set ups giving 3.6v at the atomiser. I have built several 4 cell mods (4.8v NiMh) and experienced repeated atomiser failure,in one case with immiediate loss of 3 atomisers one after another.I do wonder if a small resister in the circuit would smooth out the initial burst of power that seems to do the damage.However I find using any voltage (L-ion or NiMh) over 3.6/3.7v tends to give much more burnt and off flavours so have given up on making higher voltage mods and am continuing the quest to design a "Magnum" type mod that does not require battery removal to re-charge.If only I could source a 3.6v peak detection charger at a reasonable cost the job would be done!!
Thank you RayJ1 for your valuable guidance.

RJ morning I am not a modder, however, I have become a large mod buyer and user!! I read your post of losing 3 atz in a row, I just lost
5, all back to back, ( yes, I probably should have stopped at, hello)
but I needed to see what up. Is there ANY specific reason for that type of failure, Can batteries be overcharged?? Can a lay person, like me
do anything to somebodies else's mod to correct??

 

[Rubberjohnny]

Hello Cosican. I assume (dangerous I know) the "blow out " occur simply because the atomiser is designed to run at 3.7volts or thereabout. Since the atomiser is only a simple nichrome wire coil (not unlike the tungsten coil in a light bulb) it will burn out if subjected to higher voltages than it's design parameters.However there will be some degree of latitude for higher voltages.I had bad atomiser failure experience at all voltages around or exceeding 5volts. However many other modders run as high as 6volts seemingly without major problems.Certainly you have to be right on the ball keeping the atomiser wet if you run higher voltages since a dry atomiser is a sure fire failure.I do not consider higher voltages much if any advantage over and above a high capacity L-ion or NiMh battery pack running 3.7/3.6volts respectivly.High capacity 3.7/3.6v will produce plenty of vapour with minimal risk of burnt/off smells (Acrolein??).
As far as your existing mod is concerned maybe the inclusion of a simple resistor would take the edge off the initial damaging burst of power?I am sure more advanced modder's than I will guide you allong the right path.

 

[RayJ1]

Your having no problems with 4 NiMH batteries? There was a long thread on here saying that 4 NiMH batteries would burnout the atomizer on the first try. Never tried it but could not figure out why NiMH as compaired to li-ion would burnout the atomizer.

When I first take the 4AAA nimh's off the charger they register 5.5 volts. After about 20 or so hits...the voltage drops down to about 5volts and stays there. With a voltmeter attached the voltage drop upon taking a drag is about .5 volts. I have been using the same atomizer for the past three weeks with this mod, and it seems to be holding up quite well so far. I have been using only juice from e-smokey treats so I don't know if other juices could be causing premature coil failure. My atomizer is pretty clean! The atomizer I'm using is one from the NJOY PRO(not the penstyle). Perhaps I have been lucky with the atomizer, but I am pretty careful to keep the atomizer stoked! I don't run it dry, and when I hit the "on" button it's only for three to four seconds. I also draw a little air in while pushing the button down, and draw a little air after the button is released. This action may be keeping the atomizer cooler after being heated.

 

[RayJ1]

RJ morning I am not a modder, however, I have become a large mod buyer and user!! I read your post of losing 3 atz in a row, I just lost
5, all back to back, ( yes, I probably should have stopped at, hello)
but I needed to see what up. Is there ANY specific reason for that type of failure, Can batteries be overcharged?? Can a lay person, like me
do anything to somebodies else's mod to correct??

I know you directed this at RJ, but one way to reduce voltage to the atomizer running at higher voltage is to use an 1N4001 power diode. They have them at Radio Shack for about $1.00 for two. Each power diode wired in series will drop voltage by.35 volts. Two in series will drop voltage by .70 volts. I tried that mod and measured the voltage drop, and it works.

 

[RayJ1]

That is why I run triple set ups giving 3.6v at the atomiser. I have built several 4 cell mods (4.8v NiMh) and experienced repeated atomiser failure,in one case with immiediate loss of 3 atomisers one after another.I do wonder if a small resister in the circuit would smooth out the initial burst of power that seems to do the damage.However I find using any voltage (L-ion or NiMh) over 3.6/3.7v tends to give much more burnt and off flavours so have given up on making higher voltage mods and am continuing the quest to design a "Magnum" type mod that does not require battery removal to re-charge.If only I could source a 3.6v peak detection charger at a reasonable cost the job would be done!!
Thank you RayJ1 for your valuable guidance.

My pleasure to help!

 

[RayJ1]

If I had to guess on atomizer failure with higher voltages...it would probably point to a few things.

1) running the atomizer dry.

2) higher voltage with some atomizers on the market coupled with a smaller diameter coil wire than other atomizers. Don't know that thats the case ...just guessing.

3)Poor solder connections of the coil. Maybe the person making my atomizer did a better job...who knows.