Yes, I have ANOTHER question about NiMh charging..
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Re: Yes, I have ANOTHER question about NiMh chargi
C/10 refers to the charging current, not the voltage. Use whatever voltage you want as long as it's higher (give a few volts margin) than the cells you want to charge, with a series resistor to control the current. Your 4 cell pack is 5 volts. So if you have a 9 volt power supply, your resistor has to drop 4 volts. From Ohms law, R=E/I = 4 volts / 0.18 A = 22 ohms. Note that the resistor has to dissipate 4 * 0.18 watts of heat or about 0.8 watts. A 1 watt resistor can handle that if you keep it cool. You're better off using a 2 watt or 5 watt resistor to have a little more thermal capacity.
C/10 refers to the charging current, not the voltage. Use whatever voltage you want as long as it's higher (give a few volts margin) than the cells you want to charge, with a series resistor to control the current. Your 4 cell pack is 5 volts. So if you have a 9 volt power supply, your resistor has to drop 4 volts. From Ohms law, R=E/I = 4 volts / 0.18 A = 22 ohms. Note that the resistor has to dissipate 4 * 0.18 watts of heat or about 0.8 watts. A 1 watt resistor can handle that if you keep it cool. You're better off using a 2 watt or 5 watt resistor to have a little more thermal capacity.
FreeBSDboy
Newly Enlightened
Re: Yes, I have ANOTHER question about NiMh chargi
That's a simple take on it. You neglect the internal resistences of the batteries, which will vary with temperature, which will vary with charge. You can approximate a C/10 rate with the resistor method, but the only way to hold exactly a c/10 rate is with some circuit that senses the current and adjusts the voltage acordingly. You can build a simple current source based on an lm317 with about $10 worth of radioshack components.
That's a simple take on it. You neglect the internal resistences of the batteries, which will vary with temperature, which will vary with charge. You can approximate a C/10 rate with the resistor method, but the only way to hold exactly a c/10 rate is with some circuit that senses the current and adjusts the voltage acordingly. You can build a simple current source based on an lm317 with about $10 worth of radioshack components.
Re: Yes, I have ANOTHER question about NiMh chargi
I know the C/10 is current...that's why I'm asking about voltage. /ubbthreads/images/graemlins/grin.gif So if I was to charge these batteries at 180mah @ 6 volts for about 10 hours would that be good?
I know the C/10 is current...that's why I'm asking about voltage. /ubbthreads/images/graemlins/grin.gif So if I was to charge these batteries at 180mah @ 6 volts for about 10 hours would that be good?
Illuminated
Enlightened
Re: Yes, I have ANOTHER question about NiMh chargi
Zmoz,
I'm an advocate of using the constant-current configuration of the LM317 because it's so simple to set up.
National Semiconductor has datasheets and appnotes available on their site for this and other devices, and it will tell you exactly how to calculate the resistor value needed for the current you want. Just remember that you need a little more voltage from the power supply than the fully charged voltage of your batteries in series, if using this circuit.
Have fun!
John
PS - there's a simple way to add a few components to that circuit that will light a red LED whenever the batteries are connected to the charger. Not a "charge" indicator, but a "charging" indicator.
Zmoz,
I'm an advocate of using the constant-current configuration of the LM317 because it's so simple to set up.
National Semiconductor has datasheets and appnotes available on their site for this and other devices, and it will tell you exactly how to calculate the resistor value needed for the current you want. Just remember that you need a little more voltage from the power supply than the fully charged voltage of your batteries in series, if using this circuit.
Have fun!
John
PS - there's a simple way to add a few components to that circuit that will light a red LED whenever the batteries are connected to the charger. Not a "charge" indicator, but a "charging" indicator.
Re: Yes, I have ANOTHER question about NiMh chargi
I'm sure it would be great, however, my soldering and electronic circuit skills are about as good as my dog's. /ubbthreads/images/graemlins/grin.gif Let's say I have a 180mah 6v power adapter. (I don't, but lets pretend) If I hook that up to the 4 batteries in series for 10 hours...would they be charged?
I'm sure it would be great, however, my soldering and electronic circuit skills are about as good as my dog's. /ubbthreads/images/graemlins/grin.gif Let's say I have a 180mah 6v power adapter. (I don't, but lets pretend) If I hook that up to the 4 batteries in series for 10 hours...would they be charged?
Illuminated
Enlightened
Re: Yes, I have ANOTHER question about NiMh chargi
Zmoz,
As purely my guess? Probably would be charged. Would I consider doing it that way? Only in a real emergency and if there was no other option. Why? Because $17 bought be decent smart charger *and* 4 1800mAh AA's at WalMart.
Help me try to help you out here - by answering a few questions so I know where you're coming from - OK?
1) Can you solder two bare wires or resistor leads together?
2) Are you wanting to charge your 4AA's with what you already have as opposed to spending money on a charger?
Truth is I'm not smart enough to answer your specific question about what the voltage should be to charge 4AA's in series at 180mA rate. Too many things can (will) change the rate during the charge process.
The battery manufacturers recommend other charging methods for a reason, and I gotta go with them on this one.
If you can solder a *little* better than you say (better than your dog) and can do things like strip off 1/8" of insulation from wire ends, use electrical tape to prevent electrical shorts between connections, etc., then I'm sure we can coach you through building a charger using just 3 parts:
A 7.2VDC/300mA or higher wall-wart, an LM317T voltage regulator (looks like a big transistor), and (1) resistor (6.8-ohm, 1/2 watt - if memory serves). That's it. (3) parts.
It will charge 4AA's in series with constant current at about 183 mA, and will take up to about 10 hours if the batts were really down.
Of course, you would also need to connect 2 wires to the batteries...
Like I said, tell us more about what you want to do, and we'll try to help, OK?
John
Zmoz,
As purely my guess? Probably would be charged. Would I consider doing it that way? Only in a real emergency and if there was no other option. Why? Because $17 bought be decent smart charger *and* 4 1800mAh AA's at WalMart.
Help me try to help you out here - by answering a few questions so I know where you're coming from - OK?
1) Can you solder two bare wires or resistor leads together?
2) Are you wanting to charge your 4AA's with what you already have as opposed to spending money on a charger?
Truth is I'm not smart enough to answer your specific question about what the voltage should be to charge 4AA's in series at 180mA rate. Too many things can (will) change the rate during the charge process.
The battery manufacturers recommend other charging methods for a reason, and I gotta go with them on this one.
If you can solder a *little* better than you say (better than your dog) and can do things like strip off 1/8" of insulation from wire ends, use electrical tape to prevent electrical shorts between connections, etc., then I'm sure we can coach you through building a charger using just 3 parts:
A 7.2VDC/300mA or higher wall-wart, an LM317T voltage regulator (looks like a big transistor), and (1) resistor (6.8-ohm, 1/2 watt - if memory serves). That's it. (3) parts.
It will charge 4AA's in series with constant current at about 183 mA, and will take up to about 10 hours if the batts were really down.
Of course, you would also need to connect 2 wires to the batteries...
Like I said, tell us more about what you want to do, and we'll try to help, OK?
John
Re: Yes, I have ANOTHER question about NiMh chargi
Well...maybe I could handle 3 parts. /ubbthreads/images/graemlins/grin.gif Soldering wires is about the only thing I can solder. The reason I want to do this is because the batteries are going to be placed permanently inside of a modified mag. If anyone knows of a smart charger that will do 4 in series that I could hack apart that would work great...but I don't think they make anything like that.
Well...maybe I could handle 3 parts. /ubbthreads/images/graemlins/grin.gif Soldering wires is about the only thing I can solder. The reason I want to do this is because the batteries are going to be placed permanently inside of a modified mag. If anyone knows of a smart charger that will do 4 in series that I could hack apart that would work great...but I don't think they make anything like that.
FreeBSDboy
Newly Enlightened
Re: Yes, I have ANOTHER question about NiMh chargi
you could also build the circuit on a small proto-board for testing. No soldering required.
you could also build the circuit on a small proto-board for testing. No soldering required.
Re: Yes, I have ANOTHER question about NiMh chargi
You have to know what you're doing to fast charge batteries. Among other things your circuit should monitor the cell temperature and adjust charging current accordingly. There are charging chips whose application notes say how to do that, but you're probably better off building a slow charger. Just find a 7.5 volt or 9 volt DC 200 mA "wall wart" transformer (make sure it's DC!!) and put a resistor in series. The resistor value should be (V-5)/0.18 where V is the transformer output voltage. This is conceptually very simple; most of the work will be in drilling and mounting the connector neatly and soldering the wires etc.
Why do you want to do this? Why not just buy yourself a nice rechargeable light like an Ultrastinger?
You have to know what you're doing to fast charge batteries. Among other things your circuit should monitor the cell temperature and adjust charging current accordingly. There are charging chips whose application notes say how to do that, but you're probably better off building a slow charger. Just find a 7.5 volt or 9 volt DC 200 mA "wall wart" transformer (make sure it's DC!!) and put a resistor in series. The resistor value should be (V-5)/0.18 where V is the transformer output voltage. This is conceptually very simple; most of the work will be in drilling and mounting the connector neatly and soldering the wires etc.
Why do you want to do this? Why not just buy yourself a nice rechargeable light like an Ultrastinger?
Re: Yes, I have ANOTHER question about NiMh chargi
Zmoz, if you want a simple option that requires some human brains with each use, plug the wall wart into a timer with all the "activate" pins taken out and one "deactivate" pin left in. Adjust the timer for up to ten hours before turning off the charger, less if you're only topping-up the batteries. Granted there is some risk, but this involves the least construction.
Zmoz, if you want a simple option that requires some human brains with each use, plug the wall wart into a timer with all the "activate" pins taken out and one "deactivate" pin left in. Adjust the timer for up to ten hours before turning off the charger, less if you're only topping-up the batteries. Granted there is some risk, but this involves the least construction.
Illuminated
Enlightened
Re: Yes, I have ANOTHER question about NiMh chargi
Zmoz,
Tomorrow I'll try to post a very simple circuit sketch to build your constant current charger for your Mag. I know you could handle this if you try-and you'll be proud of yourself afterwards /ubbthreads/images/graemlins/thumbsup.gif
I'm working lots lately - but I'll help you as much as I can, OK?
Be cool - John
Zmoz,
Tomorrow I'll try to post a very simple circuit sketch to build your constant current charger for your Mag. I know you could handle this if you try-and you'll be proud of yourself afterwards /ubbthreads/images/graemlins/thumbsup.gif
I'm working lots lately - but I'll help you as much as I can, OK?
Be cool - John
obeck
Newly Enlightened
[ QUOTE ]
zmoz said:
So are you guys getting tired of my questions yet? /ubbthreads/images/graemlins/grin.gif I'll be a little more direct with this one. I want to charge 4 1800mah NiMh batteries in series at C/10. What voltage does that need to be?
[/ QUOTE ]
I have an old Ace R/C dual metered vari-charger. This thing will take up to 10 cells in series and charge them at a constant current. this is actually a very cool charger but it is dated.... only charges up to 200maH. I usually keep things like my Black&Decker screwdriver battery and a string of D cells on a C/20 or C/30 charge.... forever.
So, it as someone pointed out, it takes whatever voltage is necessary to charge at a certain rate, and the rate depends on the battery resistance, type, etc....
zmoz said:
So are you guys getting tired of my questions yet? /ubbthreads/images/graemlins/grin.gif I'll be a little more direct with this one. I want to charge 4 1800mah NiMh batteries in series at C/10. What voltage does that need to be?
[/ QUOTE ]
I have an old Ace R/C dual metered vari-charger. This thing will take up to 10 cells in series and charge them at a constant current. this is actually a very cool charger but it is dated.... only charges up to 200maH. I usually keep things like my Black&Decker screwdriver battery and a string of D cells on a C/20 or C/30 charge.... forever.
So, it as someone pointed out, it takes whatever voltage is necessary to charge at a certain rate, and the rate depends on the battery resistance, type, etc....
Illuminated
Enlightened
Zmoz,
Here's the simple circuit I described previously -
Note that the LM317t in the sketch is shown as viewed from the front, with the metal tab on the rear.
Just make certain of the polarity of the power wires from the wallwart to the circuit, and to the plug/jack battery connections, or you'll damage your batteries at the very least.
I would advise you to locate the circuit closer to the wallwart (or other DC supply) as opposed to near the end of the cord/plug.
You can connect the wires/components directly to each other, but you must make sure that there can be no accidental shorts.
You can even use that plastic tool handle dip stuff to completely coat and insulate the components/wires permanently. That's probably the simplest way I can think of to make the circuit reliable without using a circuit board or mounting everything in some sort of enclosure. Don't use silicone RTV because it can cause corrosion.
The metal tab of the LM317t must not be allowed to touch any other connections or it'll cause problems. You could, however, attach a small piece of copper or aluminum to it for a heat sink before coating everything. I don't expect it to get hot, but it might get somewhat warm.
Hope this helps - John
[EDIT] BTW, this will charge 4 "dead" 1800mAh NiMH AA's in series in about 10 hours - less if their only partially drained. I would not recommend leaving them on the charger continuously, as 184 mA is not considered a "trickle" charge rate for AA NiMH.
Here's the simple circuit I described previously -
Note that the LM317t in the sketch is shown as viewed from the front, with the metal tab on the rear.
Just make certain of the polarity of the power wires from the wallwart to the circuit, and to the plug/jack battery connections, or you'll damage your batteries at the very least.
I would advise you to locate the circuit closer to the wallwart (or other DC supply) as opposed to near the end of the cord/plug.
You can connect the wires/components directly to each other, but you must make sure that there can be no accidental shorts.
You can even use that plastic tool handle dip stuff to completely coat and insulate the components/wires permanently. That's probably the simplest way I can think of to make the circuit reliable without using a circuit board or mounting everything in some sort of enclosure. Don't use silicone RTV because it can cause corrosion.
The metal tab of the LM317t must not be allowed to touch any other connections or it'll cause problems. You could, however, attach a small piece of copper or aluminum to it for a heat sink before coating everything. I don't expect it to get hot, but it might get somewhat warm.
Hope this helps - John
[EDIT] BTW, this will charge 4 "dead" 1800mAh NiMH AA's in series in about 10 hours - less if their only partially drained. I would not recommend leaving them on the charger continuously, as 184 mA is not considered a "trickle" charge rate for AA NiMH.
