Icebreak
Flashlight Enthusiast
I have an old Radio Shack multi-battery charger. Can I use it for charging NiMHs ?
Thanks
Thanks
NiCad NiMH charging
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Icebreak
Flashlight Enthusiast
Thanks lemlux. Even though I know nothing about NiMHs, that is what I suspected. This thing is 15 years old. Don't think NiMHs were around then. It has 4 double slots and 2 single slots. On the back it shows the output as DC 1.3V/2.6V/7.8V 150mA.
You can always do the timer method.... but it will possibly be dangerous. If you are charging batteries of capacity 1500 mah and above, then this shouldn't be a problem. Batteries nowadays are design to be able to "handle" overcharging currents of 1/10 of their capacity indefinitely with no leakage, explosion. Just divide (battery capcity x 1.2) with current used during charging (in this case 150mah) to get number of hours needed.
Using this method, you won't get a fully charged battery if it's drained down completely but you can be sure that you won't overcharge it either.
If you have some method of discharging the battery to below 1v per cell, then you muplitply the battery capacity with 1.5 instead of 1.2 so that you get (battery capacity x 1.5) divide by 150 ma = hours that battery should be in charger.
Hope that the above is not too confusing. And I don't provide any claims that the above information will work well for you. It's just one of the ways to re-use what you have left from the past ten years...
Any errors in the above information will be corrected by our kind senior members here.
Using this method, you won't get a fully charged battery if it's drained down completely but you can be sure that you won't overcharge it either.
If you have some method of discharging the battery to below 1v per cell, then you muplitply the battery capacity with 1.5 instead of 1.2 so that you get (battery capacity x 1.5) divide by 150 ma = hours that battery should be in charger.
Hope that the above is not too confusing. And I don't provide any claims that the above information will work well for you. It's just one of the ways to re-use what you have left from the past ten years...
Any errors in the above information will be corrected by our kind senior members here.
Icebreak
Flashlight Enthusiast
Nerd-
Your skills my be lost on me.
I haven't bought the NiMHs yet, but to see if I have your calculation down I'll use this example. The battery has a capacity of 1.25 volts.
(1.25v x 1.2) / 150ma = 0.01
What does that tell me?
How does the residual charge affect the calculation?
Should I just bite the bullet and get the correct charger?
Thanks
Your skills my be lost on me.
I haven't bought the NiMHs yet, but to see if I have your calculation down I'll use this example. The battery has a capacity of 1.25 volts.
(1.25v x 1.2) / 150ma = 0.01
What does that tell me?
How does the residual charge affect the calculation?
Should I just bite the bullet and get the correct charger?
Thanks
Jonathan
Enlightened
Batteries are classified by a number of measurements, things like internal resistance, how the internal resistance changes with temperature, mass, volume, etc. But for most work, two numbers give you a good way of approximating what you need to know.
These are 'nominal voltage' and 'nominal capacity'. Voltage is measured in volts, and capacity is measured in ampere-hours. A very rough approximation is that voltage is like the pressure in a tank, and capacity is like the volume of the tank.
Now, since an ampere is simply 'so many electrons moving past a point per second', an 'ampere-hour' is really just another way of saying 'so many electrons', and the ampere-hour capacity of a battery is a way of describing how many electrons that battery can push through a load. An ampere hour is simply the number of electrons that would move if a current of 1 ampere were to flow for 1 hour. You calculate the value by multiplying the current times the time; 1 amp for 1 hour or 10 amps for 6 minutes or 10 milliamps for 100 hours are all 1 ampere-hour worth of electrons.
A _very_ important way in which a battery is different from the analogy of a 'tank of electrons' is that the total number of electrons in the battery stays constant both during charge and discharge. The battery will push the electrons through an external load, from the negative terminal, but they always return to the battery, at the positive terminal. During the trip the electrons are going from a high energy state to a low energy state, and giving up that _energy_ to the load, but the total number of electrons stays the same.
If you wish to recharge the battery, then you have to connect an external device (the charger) that pushes the electrons in the opposite direction, from the positive terminal back to the negative terminal. To recharge the battery, you need to push the same quantity of electons back as the battery pushed through the load. Thus you need the charger to move the same number of amp-hours through the battery as the battery moved through the load.
If the battery is fully discharged, then you know roughly how many amp-hours have moved through the load, since this is just the battery capacity. So you want to run that many ampere-hours through the battery to recharge it. Say the battery capacity were 1 ampere hour (which is the same as 1000 milli-ampere hours), and the battery is fully discharged. Well, you could run a current of 1 amp for 1 hour, or 100mA for 10 hours, or 5 amps for 12 minutes in order to push the proper number of electrons around, but there are a few other factors to consider.
One is that batteries can only really accept charge at a maximum rate, usually the 'C' rate, meaning the rate that would charge the battery in about an hour.
Two is that there is always some inefficiency; to fully charge a battery, you usually have to move something like 1.2x the theoretical charge.
Three is detection of end of charge. Once a battery is fully charged, any additional current flow goes into electrolyzing the water in the battery into hydrogen and oxygen, which will cause the battery to heat up or explode. In general, you can't charge a battery at the 'C' rate unless you have some mechanism for detecting when the battery is fully charged.
If you charge at a low enough rate, then any overcharge that occurs overcharge will do only minimal damage to the battery, and will not cause an explosive failure. For most NiCd batteries, this is the C/10 rate, for most NiMh this is a somewhat slower rate (in that some capacity damage will occur), but you can _safely_ charge at the C/10 rate.
So a _simple_ charging scheme is to take the nominal battery capacity (in ampere hours), and divide by 10 hours, to get a nominal charging current in amperes. You then supply this current to the battery for 12-15 hours (theoretical 10 hours, plus extra for inefficiency).
Now, the charger that you have is rated at 150mA. Take the capacity of the battery (in milli-amp hours), divide by 150, to get the theoretical time for a full charge (in hours), and then multiply by 1.2 to deal with charging efficiency. This should give you a ballpark number for how long your batteries should be in your charger.
-Jon
These are 'nominal voltage' and 'nominal capacity'. Voltage is measured in volts, and capacity is measured in ampere-hours. A very rough approximation is that voltage is like the pressure in a tank, and capacity is like the volume of the tank.
Now, since an ampere is simply 'so many electrons moving past a point per second', an 'ampere-hour' is really just another way of saying 'so many electrons', and the ampere-hour capacity of a battery is a way of describing how many electrons that battery can push through a load. An ampere hour is simply the number of electrons that would move if a current of 1 ampere were to flow for 1 hour. You calculate the value by multiplying the current times the time; 1 amp for 1 hour or 10 amps for 6 minutes or 10 milliamps for 100 hours are all 1 ampere-hour worth of electrons.
A _very_ important way in which a battery is different from the analogy of a 'tank of electrons' is that the total number of electrons in the battery stays constant both during charge and discharge. The battery will push the electrons through an external load, from the negative terminal, but they always return to the battery, at the positive terminal. During the trip the electrons are going from a high energy state to a low energy state, and giving up that _energy_ to the load, but the total number of electrons stays the same.
If you wish to recharge the battery, then you have to connect an external device (the charger) that pushes the electrons in the opposite direction, from the positive terminal back to the negative terminal. To recharge the battery, you need to push the same quantity of electons back as the battery pushed through the load. Thus you need the charger to move the same number of amp-hours through the battery as the battery moved through the load.
If the battery is fully discharged, then you know roughly how many amp-hours have moved through the load, since this is just the battery capacity. So you want to run that many ampere-hours through the battery to recharge it. Say the battery capacity were 1 ampere hour (which is the same as 1000 milli-ampere hours), and the battery is fully discharged. Well, you could run a current of 1 amp for 1 hour, or 100mA for 10 hours, or 5 amps for 12 minutes in order to push the proper number of electrons around, but there are a few other factors to consider.
One is that batteries can only really accept charge at a maximum rate, usually the 'C' rate, meaning the rate that would charge the battery in about an hour.
Two is that there is always some inefficiency; to fully charge a battery, you usually have to move something like 1.2x the theoretical charge.
Three is detection of end of charge. Once a battery is fully charged, any additional current flow goes into electrolyzing the water in the battery into hydrogen and oxygen, which will cause the battery to heat up or explode. In general, you can't charge a battery at the 'C' rate unless you have some mechanism for detecting when the battery is fully charged.
If you charge at a low enough rate, then any overcharge that occurs overcharge will do only minimal damage to the battery, and will not cause an explosive failure. For most NiCd batteries, this is the C/10 rate, for most NiMh this is a somewhat slower rate (in that some capacity damage will occur), but you can _safely_ charge at the C/10 rate.
So a _simple_ charging scheme is to take the nominal battery capacity (in ampere hours), and divide by 10 hours, to get a nominal charging current in amperes. You then supply this current to the battery for 12-15 hours (theoretical 10 hours, plus extra for inefficiency).
Now, the charger that you have is rated at 150mA. Take the capacity of the battery (in milli-amp hours), divide by 150, to get the theoretical time for a full charge (in hours), and then multiply by 1.2 to deal with charging efficiency. This should give you a ballpark number for how long your batteries should be in your charger.
-Jon
Jon:
Would you please talk about how the 1.2 efficiency factor varies with battery chemistry and "0.X" in charge rate of 0.X/C. In the old days of the 1980's NiCad charger instructions typically suggested charge times consistent with a 1.5 effieciency factor.
Would you please talk about how the 1.2 efficiency factor varies with battery chemistry and "0.X" in charge rate of 0.X/C. In the old days of the 1980's NiCad charger instructions typically suggested charge times consistent with a 1.5 effieciency factor.
Jonathan
Enlightened
Alas, I don't know enough to talk about the details of the efficiency factor. I know that it is referred to as 'coulombic efficiency', because the unit of charge is the ampere-second or coulomb. If you look at the datasheet for a particular battery, you will see charging instructions, and they will often suggest a recommended charge time at a recommended charge current, which should tell you the expected coulombic efficiency.
In general for slow charging, I just monitor temperature. When you apply charging current to a cell, the first thing that happens is you reverse the chemical reactions that produce the electrical output, meaning that you charge the cell. But as the cell gets charged up, you start seeing electrolysis of water, producing hydrogen and oxygen. The cells are sealed with a bit of catalyst, which combines the hydrogen and oxygen, returning the water, but producing heat. You will find that once the cells are fully charged, they will start heating up.
I prefer to use fast charge systems that detect end of charge by measuring voltage, current, and temperature. But if you are limited to slow charging, simply stopping when the cells get pretty warm is a reasonable (if not ideal) approach.
-Jon
In general for slow charging, I just monitor temperature. When you apply charging current to a cell, the first thing that happens is you reverse the chemical reactions that produce the electrical output, meaning that you charge the cell. But as the cell gets charged up, you start seeing electrolysis of water, producing hydrogen and oxygen. The cells are sealed with a bit of catalyst, which combines the hydrogen and oxygen, returning the water, but producing heat. You will find that once the cells are fully charged, they will start heating up.
I prefer to use fast charge systems that detect end of charge by measuring voltage, current, and temperature. But if you are limited to slow charging, simply stopping when the cells get pretty warm is a reasonable (if not ideal) approach.
-Jon
carbonsparky
Enlightened
I would suggest throwing out the old Radio Shack charger and getting one of the newer generation smart chargers. I used to use one of those things to charge AA bats for toy RC cars that my son and I had. It would take all night to charge and the cells would get off balanced (some not charged completely). I have a Ray-o-vac PS4 1 hour charger now and can not dream of a reason to look for the old radio shack charger except for charging some weird sized battery. I am using NiMh's for almost all my high battery usage gadgets and am very happy with the results.
Icebreak
Flashlight Enthusiast
Nerd-
Yes, I see. I can use a multi-meter. That makes the old charger possibly useable for NiMHs.
Thank you.
Jonathan-
So, since I was using 'nominal voltage' and not 'nominal capacity' Nerd's calculation never had a chance.
I've had EEs explain electricity using the water/pipe diameter/pressure analogy with good effect. Your explanation of electron flow in a battery was a fine piece. If it is not currently, it should be used in textbooks for first year EEs. I can almost see the electrons circulating, delivering their energy and returning home to their tank. I can almost see that upon delivery of their energy to the circuitry of a flashlight and it's emission device (whether it in be incan. or LED) cause a beam of kaotic photons to be projected.
One thing you'll surely disagree with but have actually confirmed for a layman like myself is this: Electricity, batteries and flashlights are majic.
I have a great respect for folks like yourself that such an understanding of EE and language use that you can explain concepts so clearly to folks like me that have little knowledge of EE. I really appreciate your efforts.
Thanks again.
Carbonspanky-
Right. In the late 80's I lived in a suburb (for some reason the name escapes me) of Dallas that was adjacent to Mesquite. I don't follow rodeo but one of largest is in Mesquite which most folks don't know is very urban. I digress. Close to the rodeo was an indoor RC car track with a dirt, a carpet and an asphalt track. I raced in the lowest division, Tamiya. I learned to use a multi-meter to monitor the charging of my RC car's six cell battery. I watched the other guys reading their meters and at a point they had determined was before the battery was about to be fully charged; they would spray freon based electric motor cleaner on the battery pack to cool it down and supposedly optimize it's charge. I don't know if they were right about this theory, but I did it too. I used this R/S charger to charge the AAs for the controller. It was a ton of fun. Some of those boys (southern for guys) would show up in $3,000.00 automobiles carrying $3,000.00 RC cars!
The understanding I have gained here, is that this charger's RG LED indicators where designed for NiCads and would likely be inaccurate for NiMHs. I will bite the bullet and get the proper charger for NiMHs. I will keep the old charger even if for nothing more than to remember some very good times.
Thanks for your help.
Yes, I see. I can use a multi-meter. That makes the old charger possibly useable for NiMHs.
Thank you.
Jonathan-
So, since I was using 'nominal voltage' and not 'nominal capacity' Nerd's calculation never had a chance.
I've had EEs explain electricity using the water/pipe diameter/pressure analogy with good effect. Your explanation of electron flow in a battery was a fine piece. If it is not currently, it should be used in textbooks for first year EEs. I can almost see the electrons circulating, delivering their energy and returning home to their tank. I can almost see that upon delivery of their energy to the circuitry of a flashlight and it's emission device (whether it in be incan. or LED) cause a beam of kaotic photons to be projected.
One thing you'll surely disagree with but have actually confirmed for a layman like myself is this: Electricity, batteries and flashlights are majic.
I have a great respect for folks like yourself that such an understanding of EE and language use that you can explain concepts so clearly to folks like me that have little knowledge of EE. I really appreciate your efforts.
Thanks again.
Carbonspanky-
Right. In the late 80's I lived in a suburb (for some reason the name escapes me) of Dallas that was adjacent to Mesquite. I don't follow rodeo but one of largest is in Mesquite which most folks don't know is very urban. I digress. Close to the rodeo was an indoor RC car track with a dirt, a carpet and an asphalt track. I raced in the lowest division, Tamiya. I learned to use a multi-meter to monitor the charging of my RC car's six cell battery. I watched the other guys reading their meters and at a point they had determined was before the battery was about to be fully charged; they would spray freon based electric motor cleaner on the battery pack to cool it down and supposedly optimize it's charge. I don't know if they were right about this theory, but I did it too. I used this R/S charger to charge the AAs for the controller. It was a ton of fun. Some of those boys (southern for guys) would show up in $3,000.00 automobiles carrying $3,000.00 RC cars!
The understanding I have gained here, is that this charger's RG LED indicators where designed for NiCads and would likely be inaccurate for NiMHs. I will bite the bullet and get the proper charger for NiMHs. I will keep the old charger even if for nothing more than to remember some very good times.
Thanks for your help.
I have unconfirm reports of the rayovac charger damaging batteries. It is said that with every charge, the capacity of the battery is lowered by a bit. And that happens with the very first charge.
If you are to buy a new charger, may I recommend you the Maha 401FS 100 min cool charger
http://www.mahaenergy.com/products/PowerEx/Digicams/mhc401fs.htm
It can condition your battery and charge it at the same time. The only draw back is the price ($50).
I personally used the 204F 3 hour charger. It's not bad and for a price of $25 for the charger only, it's reasonable.
http://www.mahaenergy.com/products/PowerEx/ce/mhc204f.htm
Another good charger is the Lightning Pack 4000N by RipVan. It's suppose to charge 4 AA 1600mah batteries in 100 mins. And it's plug can take any voltage from 100-220
http://www.ripvan100.com/products_recharger.htm
Hope tat I have been of assistance. It's always a pleasure to help.
If you are to buy a new charger, may I recommend you the Maha 401FS 100 min cool charger
http://www.mahaenergy.com/products/PowerEx/Digicams/mhc401fs.htm
It can condition your battery and charge it at the same time. The only draw back is the price ($50).
I personally used the 204F 3 hour charger. It's not bad and for a price of $25 for the charger only, it's reasonable.
http://www.mahaenergy.com/products/PowerEx/ce/mhc204f.htm
Another good charger is the Lightning Pack 4000N by RipVan. It's suppose to charge 4 AA 1600mah batteries in 100 mins. And it's plug can take any voltage from 100-220
http://www.ripvan100.com/products_recharger.htm
Hope tat I have been of assistance. It's always a pleasure to help.
Icebreak
Flashlight Enthusiast
Thanks! This saves me weeks of searching.
