rechargeable batteries and rate of charging
IamSmooth, Mon May 18 2015, 05:04PMI have some lead and lithium rechargeable batteries. I even made a solar charger for one of my 6v lead batteries. The solar panel puts out a maximum voltage and the charger cuts out when the battery voltage exceeds a set point.
Can I speed up the charging rate *safely* if I start at a higher voltage, forcing more amps into the battery as long as I cut out at the set voltage? Is there a maximum rate one can pump charge into a battery? Is it a heating issue? I'm guessing there is some issue, otherwise there would be rapid chargers.
Re: rechargeable batteries and rate of charging
Electroholic, Mon May 18 2015, 06:26PM
Basic charger use the CCCV approach. First, a constant current stage to put in the bulk of the energy, and the a constant voltage stage(soak phase) to top it off, as well allowing the individual cells to self balance(for some chemistry).
Depending on the design of the batteries, there is a maximum rate that it can be charge/discharged, which is the C-rate.
As for solar panel, max volt occurs at zero current draw, and vice versa. And maximum power point for silicon solar cells is at around 80%OCV.
Electroholic, Mon May 18 2015, 06:26PM
Basic charger use the CCCV approach. First, a constant current stage to put in the bulk of the energy, and the a constant voltage stage(soak phase) to top it off, as well allowing the individual cells to self balance(for some chemistry).
Depending on the design of the batteries, there is a maximum rate that it can be charge/discharged, which is the C-rate.
As for solar panel, max volt occurs at zero current draw, and vice versa. And maximum power point for silicon solar cells is at around 80%OCV.
Re: rechargeable batteries and rate of charging
dexter, Mon May 18 2015, 09:09PM
the output of a solar panel varies alot depending on how much light falls on it
rechargeable batteries don't like overvoltage. For lead-acid overvoltage means gas production - damaging the battery and overcgarge also damage the battery
to overcome the above issues you'll need a solar charge controller between panel and battery (e-bay is full of them)
best option (maximum efficiency) is to use a buck converter and a simplified charge controller aka MPPT solar charge controller (e-bay is full of fakes )
dexter, Mon May 18 2015, 09:09PM
the output of a solar panel varies alot depending on how much light falls on it
rechargeable batteries don't like overvoltage. For lead-acid overvoltage means gas production - damaging the battery and overcgarge also damage the battery
to overcome the above issues you'll need a solar charge controller between panel and battery (e-bay is full of them)
best option (maximum efficiency) is to use a buck converter and a simplified charge controller aka MPPT solar charge controller (e-bay is full of fakes )
Re: rechargeable batteries and rate of charging
IamSmooth, Mon May 18 2015, 10:05PM
I think my me ntioning the solar confused the issue. I am not concerned with the solar project. That is long done.
I am talking about building a 120vac powered charger for a LiPo battery. Is there a way to build a fast charger that is safe? Right now I have a LiPo pack for a phantom and the charger takes a few hours. Is there a way to speed this up by increasing the initial current?
IamSmooth, Mon May 18 2015, 10:05PM
I think my me ntioning the solar confused the issue. I am not concerned with the solar project. That is long done.
I am talking about building a 120vac powered charger for a LiPo battery. Is there a way to build a fast charger that is safe? Right now I have a LiPo pack for a phantom and the charger takes a few hours. Is there a way to speed this up by increasing the initial current?
Re: rechargeable batteries and rate of charging
Electroholic, Tue May 19 2015, 10:37AM
The way to speed it up IS by increasing current. Problem is you need to find the datasheet of your lipo cells. or else, stick to C/3 charge.
Electroholic, Tue May 19 2015, 10:37AM
The way to speed it up IS by increasing current. Problem is you need to find the datasheet of your lipo cells. or else, stick to C/3 charge.
Re: rechargeable batteries and rate of charging
Bjørn, Tue May 19 2015, 11:07AM
Lifetime will suffer at higher currents so at some point it might be more economic to buy a spare battery instead. Quadcopters tend to get wrecked or lost long before the battery is worn out so maybe not relevant in this case.
Bjørn, Tue May 19 2015, 11:07AM
Lifetime will suffer at higher currents so at some point it might be more economic to buy a spare battery instead. Quadcopters tend to get wrecked or lost long before the battery is worn out so maybe not relevant in this case.
Re: rechargeable batteries and rate of charging
hen918, Tue May 19 2015, 05:24PM
Yhea, lipos are tricky things, they have a reputation for exploding and burning down your house if you don't treat them right. I've never had a problem, and have over 1kwh of lipos, but I've always been careful and never charged anything more than 1C (the battery capacity in Ah, in amps, so that a full charge at 1C should take an hour to complete). NEVER exceed the manufactures specification.
hen918, Tue May 19 2015, 05:24PM
Yhea, lipos are tricky things, they have a reputation for exploding and burning down your house if you don't treat them right. I've never had a problem, and have over 1kwh of lipos, but I've always been careful and never charged anything more than 1C (the battery capacity in Ah, in amps, so that a full charge at 1C should take an hour to complete). NEVER exceed the manufactures specification.
Re: rechargeable batteries and rate of charging
Dr. Slack, Tue May 19 2015, 06:03PM
LiPos have a two-stage charge process. The first, where the terminal voltage stays below 4.2v, can be done very fast, and delivers 75% to 80% of rated capacity. The second, where the current must drop to lower values to maintain 4.2v, can take an hour, topping the capacity off to 100%. Obviously the second stage cannot be rushed. Some commercial fast chargers simply omit the second top-off stage.
You can increase the recharge cycle life at the expense of capacity by using a lower threshold voltage than 4.2v. You can kill them real fast by exceeding 4.2v. If you deliver a constant current of 1C for one hour, the chances are you will shag them, as the terminal voltage is likely to rise above 4.2v towards the end of the charge, even on an initially fully discharged battery.
Dr. Slack, Tue May 19 2015, 06:03PM
LiPos have a two-stage charge process. The first, where the terminal voltage stays below 4.2v, can be done very fast, and delivers 75% to 80% of rated capacity. The second, where the current must drop to lower values to maintain 4.2v, can take an hour, topping the capacity off to 100%. Obviously the second stage cannot be rushed. Some commercial fast chargers simply omit the second top-off stage.
You can increase the recharge cycle life at the expense of capacity by using a lower threshold voltage than 4.2v. You can kill them real fast by exceeding 4.2v. If you deliver a constant current of 1C for one hour, the chances are you will shag them, as the terminal voltage is likely to rise above 4.2v towards the end of the charge, even on an initially fully discharged battery.
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