Question about Voltage used to charge batteries
#1
Junior Member
Thread Starter
Join Date: Sep 2008
Location: Bucharest, ROMANIA
Posts: 14
Likes: 0
Received 0 Likes
on
0 Posts
Question about Voltage used to charge batteries
Hello,
I don't fully understand the following. What does voltage play in the charging of lipo batts.
So for example if I have a theoretical 6V 10amp charger and I want to charge a 2cell 7.4V 5000Mah lipo that supports 2C charging, I could charge it at 2C since my charger does 10A but what about voltage. Must I charge it a 7.4V ? Will I break it if I don't give it 7.4V or will it just charge slower ?
And i've seen that some higher end chargers support even 30V, but this is useless without an expensive power source rated to output that much voltage. That charger would probably need somewhere around 900W powersource (30Vx30A) if it has 30A capability and you want to use them all.
Thanks,
Mike
I don't fully understand the following. What does voltage play in the charging of lipo batts.
So for example if I have a theoretical 6V 10amp charger and I want to charge a 2cell 7.4V 5000Mah lipo that supports 2C charging, I could charge it at 2C since my charger does 10A but what about voltage. Must I charge it a 7.4V ? Will I break it if I don't give it 7.4V or will it just charge slower ?
And i've seen that some higher end chargers support even 30V, but this is useless without an expensive power source rated to output that much voltage. That charger would probably need somewhere around 900W powersource (30Vx30A) if it has 30A capability and you want to use them all.
Thanks,
Mike
#2
Senior Member
My Feedback: (325)
Join Date: Mar 2003
Location: LaGrange, OH
Posts: 14,857
Likes: 0
Received 0 Likes
on
0 Posts
RE: Question about Voltage used to charge batteries
The voltage follows the battery's voltage plus whatever it takes to do the set current until the CV stage. Then it stays at 4.2 per cell and ramps current down to maintain the 4.2 volts.
#3
My Feedback: (5)
RE: Question about Voltage used to charge batteries
Most chargers operate with a voltage source between 10 to 18 volts DC. I'm sure there are others that operate at lower or higher voltages too.
If your charger can operate on 6 volts dc and that is the input power source you have available then it will take a longer time to charge a 7.2volt lipo pack than if you were using a 12 volt dc input source.
If your charger can operate on 6 volts dc and that is the input power source you have available then it will take a longer time to charge a 7.2volt lipo pack than if you were using a 12 volt dc input source.
#5
Junior Member
Thread Starter
Join Date: Sep 2008
Location: Bucharest, ROMANIA
Posts: 14
Likes: 0
Received 0 Likes
on
0 Posts
RE: Question about Voltage used to charge batteries
Hey guiys thanks for the posts. I was just trying to figure out what would happen to a battery if I charge it below its voltage and why would it charge slower at a lower voltage if I still give it 1C or even more charge.
#6
Join Date: Jul 2010
Location: Aberdeen, UNITED KINGDOM
Posts: 1,009
Likes: 0
Received 0 Likes
on
0 Posts
RE: Question about Voltage used to charge batteries
It will not charge if the voltage does not mach. In your example your chargers max poer is 6vx10amps= 60watts.
If you tried to charge a 7.4 lipo the charger would have to increase the voltage so 60watts/7.4= (about) 8amps. So you only have 8amps (not 10) because some of the energy is going in to boosting the voltage.
It gets worse if you try to charge a 11.1volt because now 60watts/11.1= (about) 5amps. So you can only charge at max rate of 5amps.
In reality this is even less becuase some energy is wasted during the conversion as heat. Usuful equation;
Watts= Volts x amps
If you tried to charge a 7.4 lipo the charger would have to increase the voltage so 60watts/7.4= (about) 8amps. So you only have 8amps (not 10) because some of the energy is going in to boosting the voltage.
It gets worse if you try to charge a 11.1volt because now 60watts/11.1= (about) 5amps. So you can only charge at max rate of 5amps.
In reality this is even less becuase some energy is wasted during the conversion as heat. Usuful equation;
Watts= Volts x amps
#7
My Feedback: (5)
RE: Question about Voltage used to charge batteries
ORIGINAL: Gogu
Hey guiys thanks for the posts. I was just trying to figure out what would happen to a battery if I charge it below its voltage and why would it charge slower at a lower voltage if I still give it 1C or even more charge.
Hey guiys thanks for the posts. I was just trying to figure out what would happen to a battery if I charge it below its voltage and why would it charge slower at a lower voltage if I still give it 1C or even more charge.
What kind of a charger are you using ?
#8
Join Date: Oct 2010
Location: newcastle, UNITED KINGDOM
Posts: 658
Likes: 0
Received 1 Like
on
1 Post
RE: Question about Voltage used to charge batteries
I'm confused.
A 2s 5000mah needs 42W at 1C, at 2C it requires 84W.
A 6V 10A charger has 60W
This is where i'm confused, Why does the input voltage need to be the same or higher than the output voltage, If the power is already higher, or have i missed something somewhere.
A 2s 5000mah needs 42W at 1C, at 2C it requires 84W.
A 6V 10A charger has 60W
This is where i'm confused, Why does the input voltage need to be the same or higher than the output voltage, If the power is already higher, or have i missed something somewhere.
#9
Join Date: Jul 2010
Location: Aberdeen, UNITED KINGDOM
Posts: 1,009
Likes: 0
Received 0 Likes
on
0 Posts
RE: Question about Voltage used to charge batteries
A 2cell (7.4) 5000mah (5amp) needs 37watts to be charged at 1c.
The input voltage needs to be higher than the output voltage otherwise the charger will use some of its amp allocation to increase the output voltage. So if the input voltage is lower than the required output voltage you will not be able to charge at the charger's maximum amp out put....
The input voltage needs to be higher than the output voltage otherwise the charger will use some of its amp allocation to increase the output voltage. So if the input voltage is lower than the required output voltage you will not be able to charge at the charger's maximum amp out put....
#10
Junior Member
Thread Starter
Join Date: Sep 2008
Location: Bucharest, ROMANIA
Posts: 14
Likes: 0
Received 0 Likes
on
0 Posts
RE: Question about Voltage used to charge batteries
Thanks that was what I was trying to find out. Though I'm not sure of there is a charger such as this that can put out a voltage beyond its factory spec.
#12
RE: Question about Voltage used to charge batteries
There is confusion here because the OP still has not fully defined wht he means by a "theoretical 6V 10amp charger ". If, in fact, he is saying his charge will only put out 6 volts then he won't be able to charge a 7.4V battery at all and could destroy the charger. As he correctly infers, a battery is charged by current, not voltage. However, the voltage output has to be at least the maximum voltage the battery can go to or he will wind up very quickly discharging the battery. And if a LiPo he will probably destroy it.
If you have ever put a voltmeter on a battery as you charge it you would see that the battery and the charger are at the same voltage. And if you measured the current you would see it going from the charger to the battery. Most battery chargers control the current outout and let the voltage float to the battery level. TO A POINT. If the maximum output of the charger is less than the battery you would see the current flow back to the charger and that would not be a good thing at all.
So, quite simply, if your "theoretical" charge is really only a 6V charge DON"T try to charge your 7.4V battery.
If you have ever put a voltmeter on a battery as you charge it you would see that the battery and the charger are at the same voltage. And if you measured the current you would see it going from the charger to the battery. Most battery chargers control the current outout and let the voltage float to the battery level. TO A POINT. If the maximum output of the charger is less than the battery you would see the current flow back to the charger and that would not be a good thing at all.
So, quite simply, if your "theoretical" charge is really only a 6V charge DON"T try to charge your 7.4V battery.
#13
Senior Member
My Feedback: (325)
Join Date: Mar 2003
Location: LaGrange, OH
Posts: 14,857
Likes: 0
Received 0 Likes
on
0 Posts
RE: Question about Voltage used to charge batteries
ORIGINAL: Gogu
Hey guiys thanks for the posts. I was just trying to figure out what would happen to a battery if I charge it below its voltage and why would it charge slower at a lower voltage if I still give it 1C or even more charge.
Hey guiys thanks for the posts. I was just trying to figure out what would happen to a battery if I charge it below its voltage and why would it charge slower at a lower voltage if I still give it 1C or even more charge.
#14
Junior Member
Thread Starter
Join Date: Sep 2008
Location: Bucharest, ROMANIA
Posts: 14
Likes: 0
Received 0 Likes
on
0 Posts
RE: Question about Voltage used to charge batteries
SO,
It seems I haven't understood anything.
What I'm trying to understand reading about Lipo batteries is what would happen If I would charge a 2S 7.4V pack (well actually 8.4V when fully charged) at a lower voltage and would this be possible. As Rgburrill states probably not. It seems that I would damage both the charger and the battery and that current would flow backwards since the difference in potential is not high enough to overwhelm that of the battery.
But then Goldenduff said the following:
So what am I getting from this is that a 6V 10A charger would actually be able to charge this 7.4V pack by increasing its nominal voltage to 7.4V but sacrificing amps in the process. So I would not be able to charge it at 1C but maybe 0.6C.
Also I'm not sure I understand what you guys mean from input and output voltages. I assume input means the voltage that is fed into a charger from a powersource (like a car battery) or directly from the wall outlet. output voltage would be what the charger is actually capable of delivering to the battery ?
So to understand what Goldenduff is saying it would seem that the wall outlet would need to supply a higher voltage to the charger than what it is capable of delivering to the battery else it will need to increase its voltage to output the necessary amount needed to charge a pack ?
It seems I haven't understood anything.
What I'm trying to understand reading about Lipo batteries is what would happen If I would charge a 2S 7.4V pack (well actually 8.4V when fully charged) at a lower voltage and would this be possible. As Rgburrill states probably not. It seems that I would damage both the charger and the battery and that current would flow backwards since the difference in potential is not high enough to overwhelm that of the battery.
But then Goldenduff said the following:
ORIGINAL: Goldenduff
A 2cell (7.4) 5000mah (5amp) needs 37watts to be charged at 1c.
The input voltage needs to be higher than the output voltage otherwise the charger will use some of its amp allocation to increase the output voltage. So if the input voltage is lower than the required output voltage you will not be able to charge at the charger's maximum amp out put....
A 2cell (7.4) 5000mah (5amp) needs 37watts to be charged at 1c.
The input voltage needs to be higher than the output voltage otherwise the charger will use some of its amp allocation to increase the output voltage. So if the input voltage is lower than the required output voltage you will not be able to charge at the charger's maximum amp out put....
Also I'm not sure I understand what you guys mean from input and output voltages. I assume input means the voltage that is fed into a charger from a powersource (like a car battery) or directly from the wall outlet. output voltage would be what the charger is actually capable of delivering to the battery ?
So to understand what Goldenduff is saying it would seem that the wall outlet would need to supply a higher voltage to the charger than what it is capable of delivering to the battery else it will need to increase its voltage to output the necessary amount needed to charge a pack ?
#16
Senior Member
My Feedback: (325)
Join Date: Mar 2003
Location: LaGrange, OH
Posts: 14,857
Likes: 0
Received 0 Likes
on
0 Posts
RE: Question about Voltage used to charge batteries
Yes, two different voltages. Some chargers are able to boost the output voltage to a value much higher than the input , but some are not and actually need a higher input than output in order for the charge to go the right way. Most all chargers have a very specific range of input voltage AND output voltage. Going outside that range many times results in an error.
In every case the total power (minus loss) must be equal between input and output wattage. Let's use your example (which is pretty uncommon because most chargers use 12 volts input) of 6 volts and 10 amps = 60 watts if the charger can do it. You'll be able to do a 50-60 watt job on the output side. For a 2s pack that is about 60 watts / 8.4 volts = about 7 amps MAX if your charger can do it. You should be able to charge your 2sx5.0 ah pack at about 7 amps max.
In every case the total power (minus loss) must be equal between input and output wattage. Let's use your example (which is pretty uncommon because most chargers use 12 volts input) of 6 volts and 10 amps = 60 watts if the charger can do it. You'll be able to do a 50-60 watt job on the output side. For a 2s pack that is about 60 watts / 8.4 volts = about 7 amps MAX if your charger can do it. You should be able to charge your 2sx5.0 ah pack at about 7 amps max.
#18
Junior Member
Thread Starter
Join Date: Sep 2008
Location: Bucharest, ROMANIA
Posts: 14
Likes: 0
Received 0 Likes
on
0 Posts
RE: Question about Voltage used to charge batteries
ORIGINAL: guver
Yes, two different voltages. Some chargers are able to boost the output voltage to a value much higher than the input , but some are not and actually need a higher input than output in order for the charge to go the right way. Most all chargers have a very specific range of input voltage AND output voltage. Going outside that range many times results in an error.
In every case the total power (minus loss) must be equal between input and output wattage. Let's use your example (which is pretty uncommon because most chargers use 12 volts input) of 6 volts and 10 amps = 60 watts if the charger can do it. You'll be able to do a 50-60 watt job on the output side. For a 2s pack that is about 60 watts / 8.4 volts = about 7 amps MAX if your charger can do it. You should be able to charge your 2sx5.0 ah pack at about 7 amps max.
Yes, two different voltages. Some chargers are able to boost the output voltage to a value much higher than the input , but some are not and actually need a higher input than output in order for the charge to go the right way. Most all chargers have a very specific range of input voltage AND output voltage. Going outside that range many times results in an error.
In every case the total power (minus loss) must be equal between input and output wattage. Let's use your example (which is pretty uncommon because most chargers use 12 volts input) of 6 volts and 10 amps = 60 watts if the charger can do it. You'll be able to do a 50-60 watt job on the output side. For a 2s pack that is about 60 watts / 8.4 volts = about 7 amps MAX if your charger can do it. You should be able to charge your 2sx5.0 ah pack at about 7 amps max.
#20
Senior Member
My Feedback: (325)
Join Date: Mar 2003
Location: LaGrange, OH
Posts: 14,857
Likes: 0
Received 0 Likes
on
0 Posts
RE: Question about Voltage used to charge batteries
ORIGINAL: Gogu
Yes that is if my charger could change its voltage from 6v to the 8.4v needed to charge a 2s lipo. It would then even be able to charge a 3s pack at about 4.7A right ?
ORIGINAL: guver
Yes, two different voltages. Some chargers are able to boost the output voltage to a value much higher than the input , but some are not and actually need a higher input than output in order for the charge to go the right way. Most all chargers have a very specific range of input voltage AND output voltage. Going outside that range many times results in an error.
In every case the total power (minus loss) must be equal between input and output wattage. Let's use your example (which is pretty uncommon because most chargers use 12 volts input) of 6 volts and 10 amps = 60 watts if the charger can do it. You'll be able to do a 50-60 watt job on the output side. For a 2s pack that is about 60 watts / 8.4 volts = about 7 amps MAX if your charger can do it. You should be able to charge your 2sx5.0 ah pack at about 7 amps max.
Yes, two different voltages. Some chargers are able to boost the output voltage to a value much higher than the input , but some are not and actually need a higher input than output in order for the charge to go the right way. Most all chargers have a very specific range of input voltage AND output voltage. Going outside that range many times results in an error.
In every case the total power (minus loss) must be equal between input and output wattage. Let's use your example (which is pretty uncommon because most chargers use 12 volts input) of 6 volts and 10 amps = 60 watts if the charger can do it. You'll be able to do a 50-60 watt job on the output side. For a 2s pack that is about 60 watts / 8.4 volts = about 7 amps MAX if your charger can do it. You should be able to charge your 2sx5.0 ah pack at about 7 amps max.