Charging 14.4v nimh pack
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Bullzeyebill
Flashaholic
What are specs for the battery pack? What type of cells, brand, AA's no doubt. Is there a charging jack for the pack. Etc. Pictures?
Bill
Mr Happy
Flashlight Enthusiast
You're going to need 17-18 V to fully charge a pack of 12 cells. Whether you have that much voltage depends on how accurate the voltage regulation of the adapter is...
VidPro
Flashlight Enthusiast
measure the actual voltage max on it, might work out good, if its a linear loose regulated power source, take forever to fully top it off, and it must be DC output, even if the input is ac. might work for a while at least to get you started.
if its switching supply or fully voltage regulated it would never get enough voltage.
if you put money into a meter instead of more power things, you find power things all over the house that can work
test them at both ends for the current flow, you want the current at the charged end to be below the overcharge rate for the battery , just dont fast overcharge anything with them.the right linear loose regulated power supply is IMO a good choice for a dumb slow ending charge for balancing out a series set of ni-?? things, because it can be faster at first then slow down as needed.
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Tried it last night, unloaded voltage is only 15.35 volts. Definately did not charge the battery very much. Ran my mag623 for about 6 seconds. Has anyone had a bad experience with the cheap smart chargers? The guy at the hobby store wanted to sell me a $160 charger because apparently the cheap ones blow up batteries. but i really dont want to spend that much
Mr Happy
Flashlight Enthusiast
If you want to charge the pack economically you will need to go with a slow timed charge. For a 1500 mAh capacity pack you will want to charge at 150 mA for 12-16 hours, or until the pack voltage stops rising. For instance, try using a 24 V DC supply wired in series with a 6 V 150 mA bulb for current limiting. The bulb will be over driven for a while when the pack is empty and first put on charge but it should survive it.
I can't tell you about cheap smart chargers but maybe others can.
45/70
Flashlight Enthusiast
I run a 30V bench supply, sorta like Mr H suggested. Normally, I set the pack up (both 12x2/3A and 13x2/3A) charging @ 750mA, and when the pack first starts to get warm, I either stop there, or crank the PS down to 100mA for a half hour or so. You have to keep track of what's going on very closely and not let the pack get too warm! 
Then, about every 5 charge/discharges, I go for 150mA for 14-16hrs to balance the cells.
Dave
Then, about every 5 charge/discharges, I go for 150mA for 14-16hrs to balance the cells.Dave
VidPro
Flashlight Enthusiast
if you have a voltage controlled bench supply, potenitally you can set an exacting voltage for the pack peak, and charge it sorta like a li-ion.
Where the current is higher at the first of charge, and as it reaches the voltage you have set exactally, it Automagically slows down to below the spec overcharge level to finish up and top and balance.
(because the voltage differential between the 2 items becomes less there is less flow of current)
you just have to get it in the zone for the exact rack of cells.
its so simple , yet so workable, because as the cells are mostly charged and most chemicals are converted over to charged, the rate lowers, yet it still can go quickly when the voltage is low, and most of the chemicals are not charged, and without it ending up being forgotten (accidentally by the human) and then ruined from overcharge.
course then you can toss in a current control too to keep anything from going crasy. its manuel but done correctally it is premium, fully automagic and can exist on the charge for any ammount of time. Done wrong and you have a mess on the bench and have to get the fire extingusher out
it is actually easier to do that with the sloppily regulated linear transformer thing because they ALSO will put out less power as the voltage reaches thier max, because of the way they are converting the ac over and its sine wave stuff.
Where the current is higher at the first of charge, and as it reaches the voltage you have set exactally, it Automagically slows down to below the spec overcharge level to finish up and top and balance.
(because the voltage differential between the 2 items becomes less there is less flow of current)
you just have to get it in the zone for the exact rack of cells.
its so simple , yet so workable, because as the cells are mostly charged and most chemicals are converted over to charged, the rate lowers, yet it still can go quickly when the voltage is low, and most of the chemicals are not charged, and without it ending up being forgotten (accidentally by the human) and then ruined from overcharge.
course then you can toss in a current control too to keep anything from going crasy. its manuel but done correctally it is premium, fully automagic and can exist on the charge for any ammount of time. Done wrong and you have a mess on the bench and have to get the fire extingusher out
it is actually easier to do that with the sloppily regulated linear transformer thing because they ALSO will put out less power as the voltage reaches thier max, because of the way they are converting the ac over and its sine wave stuff.
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45/70
Flashlight Enthusiast
I've done it that way, it's a safer approach (you don't have to watch things so closely), but it's a bit slower. I may look into it again though.
Dave
VidPro
Flashlight Enthusiast
only if you know the exact voltage point where it reduces to < 0.1c at the end of charge. if you dont know where it peaks at, then you put it on 0.1c and do the safe slow charge. (when in series like this without other termination methods)
if you are doing a 1c AT the end of charge, then poof your battery is finished
you preferably want it to finish at the < .1c rate at end of charge, so overcharge doesnt hurt it much.must control the voltage, if you dont know where to put the voltage, then you must control the current.
then after you see what happens
, or get to the end of charge location, then you can play with creating your own voltage charging alogrythm.
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Ok, so to figure out the voltage it needs, charge at .1c for the first time. Then remove battery from power supply and the battery voltage then will be the peak voltage it requires. Or should i let it sit for an hour before i measure it?
VidPro
Flashlight Enthusiast
one way is to:
leave it on the power supply, after a full charge, then lower/raise the voltage on the power supply till the voltage differential (between the 2) makes a current of about 0.05c, stabelised . remember if it is LEFT on the charger like this or forgotten it must be below a safe overcharge rate for the ni-?? cells.
then discharge the thing (by using it or whatever), then go back to the power supply and put it on it with that set voltage (set BEFORE putting the battery on) then watch what happens.
if everything is going as planned, when it reaches the end of charge , and the battery is higher voltage, it will slow down and finish with the 0.05c again.
bat - charge
/ / -- max voltage / / 
/ / / / :green: / /
at the first of charge the voltage differential is high:green: / /
and the charge will work hard to pull the battery up :green: / /
to that voltage / / / / bat - charge
- - <--- max voltage - - - - - - - - when the battery is closer to the voltage - - the differential between the two is lower - - and the current flow will automagically drop - - - - i am getting close to being able to draw that, some day, someday.
actually i do just guess the voltage, but then i have a fire extinguisher
and i dont leave the house while charging, and i have failed guessing before, but i got better at it.Notes: C meaning a fraction of the total capacity, not Amps or Ma.
never "overcharge" a ni-?? cell above the 0.1C
this is not about li-ion , there is NO safe overcharge rate for li-ion, voltage for those must be set to below max spec for the cell (4.2v for li-co) and they cannot be balanced in series like ni-??
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45/70
Flashlight Enthusiast
Vid, that's got to be one of the finest pictographs I've ever seen.
Really!
Dave
Really!
Dave
Capo_au
Newly Enlightened
With a bit of fiddling you could always have a go at making your own constant current charger. Downside is its a slow charger (around 12-14 hours) but on the up side its very simple to make.
VidPro
Flashlight Enthusiast
yes much slower, but i think of it more like this
when 90% of the chemicals are ready to be switched up to charged i can go 90% fast
when 10% of the chemicals are left to charge, i want it to go 10% fast
when its all charged up, i want it to go very slow, so potentially it can just stay there for days.
it is almost the reverse of what you need in a v-drop termination method, v-drop has to be fast at the end to cause the drop to see to terminate.
if you need a quick charge from it, it gets to 60-80% fast, depending on your max current, if you forget you put it there
its still ready to go when you get around to it.
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Mr Happy
Flashlight Enthusiast
Yeah, CC/CV charging would be perfect for NiMH except that the voltage is different for every battery and you don't know what it is beforehand. I have these crappy 2700 mAh cells that won't go above 1.43 V during charging, and I have eneloops that get to 1.52 V and above.
If you want to build a charger that will charge any battery you give it, you have a problem. If you know exactly what battery you want to charge and you can measure its peak voltage beforehand, then its great.
If you want to build a charger that will charge any battery you give it, you have a problem. If you know exactly what battery you want to charge and you can measure its peak voltage beforehand, then its great.
