• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

14.8v LiPo Battery Pack Charger?

Status
Not open for further replies.

InfiniteInsight

New Member
I'm trying to determine if this battery charger would charge this 14.8v Lithium Polymer 4000 mAH battery pack.

I'm just confused..I don't know what to look for to identify if it will properly work or not. As I am trying to learn if you answer me would you kindly tell me the steps and logic you used to determine if it would work or not?
 

audioguru

Well-Known Member
Most Helpful Member
It is dangerous to charge a Li-Po battery with the charger accidently set to charge a different type of battery. It will happen with this multi-purpose charger then the Li-Po battery will probably catch on fire.

Why use a cheap Chinese no-name-brand charger? Instead of the proper plugs it uses alligator clips.
Why not use a good quality name-brand charger that is designed to charge only your type and brand of battery?
 

InfiniteInsight

New Member
I think the alligator clips are meant to clip onto a car battery so you can charge your RC plane or hellicopter out on the field.

Honestly I am just trying to be budget friendly, but if it turns out that I can't find a proper cheap charger, then oh well I can't find one.

what sort of things should I look for to identify the proper charger? Will any that says 14.8v capable be enough or do I have to be concerned with the capacity of each battery, which is 4000mAH (I think?)
 
Last edited:

Chippie

Member
Nooooo....You should use a charger designed to charge lipo batteries.......at the specified voltage... 4S...


The current rating of the charger needs to match the capacity of the battery pack...less than the C rating is ok but takes longer...Higher than than the C rating is bad for the battery...
 

bountyhunter

Well-Known Member
A Li battery charger MUST MUST MUST be a voltage regulated charger. In other words, the output voltage has to regulate to a very precise value and not overshoot which is typically 4.200V/cell. It also needs to have built in current limiting to prevent over heating the battery.

Cheap chargers do not regulate the final voltage.

The specs on the first one listed in the OP look right, I have never tried it but it might work:

LiPo
Voltage level : 3.7V / cell
Max. charge voltage : 4.2V / cell
Allowable fast charge current : 1C or less
Discharge voltage cut off level : 3.0V / cell or higher
 
Last edited:

audioguru

Well-Known Member
Most Helpful Member
Your 14.8V lithium battery has 4 cells. Each cell must be balanced to be the same voltage as thre other cells while it charges. The charger is supposed to measure the voltage of each cell and adjust the charging so that the voltages are balanced.

Since each cell is fully charged at 4.2V and you have 4 of them then the battery is fully charged at 16.8V which is too high to use a car for charging it unless you make a voltage stepup circuit.
 
Last edited:

InfiniteInsight

New Member
How did you determine it has 4 cells? I thought a cell was an individual battery, and it looks to have several more than 4..???

What about This charger? A cursory google search yielded that (I know its still ebay) but I didn't find much else in the way of chargers on the first search page other than the alligator clip chargers.

Gotta run to work now, will look for more on google there.
 

Chippie

Member
How did you determine it has 4 cells? I thought a cell was an individual battery, and it looks to have several more than 4..???

What about This charger?
I use lipo batteries in my model aircraft and have done so for several years, I think permits me to speak with a degree authority on the subject...

Lipo battery packs are usually made up from cells connected in series.
Each cell has a nominal voltage of 3.7v. Ergo, 14.8 volts would equate to a 4S pack...

(A 4S pack is that... a pack made from 4 cells connected in series)

You really need a charger that can charge at the C rate of your pack else you are going to be waiting a long time....That is, your pack has a capacity of 4000mah, the C rate for charging would therefore be 4 amps. The pack would be recharged in around an hour at that current, the lower the charging current the longer it will take to recharge the battery.
(this is not strictly true, if the battery is not discharged to the safe 3v/cell maximum dishcarge limit....)

Look for modelling related lpo chargers of the balnce charge variety. They are more suitable as they can balance the pack while charging. Balancing is important to maintain the cell voltage. Charging a pack with widely differing cell voltage could lead to the pack becoming overcharged and result in catching fire. There's planty of documented information about charging/overcharging and over discharging on the various R/C related model forums.

Hope this helps...
 

InfiniteInsight

New Member
Chippie, Thank you very much! Your explanation was very informative and it totally explained those mystery acronyms in the name of the pack. (4s Standign for 4 cells in a series makes perfect sense now!)

Though, what exactly does the C in C rate stand for? Current rate or something??

Since you fly RC, are you able to tell me what the alligator clips are for those chargers?

I'm actually going to be using this battery pack to power a bike light that I am going to *TRY* to build. lol wish me luck.
 

Chippie

Member
The C figure is a function of the battery pack's capacity....

Example: If the pack has a capacity of 3000mah then the charge rate would be 1C or 3 amps using a constant current charger...Now the charging regime for lipos is CCCV which is constant current until the pack reaches a predefined voltage(this setting is down to the charger circuitry) then the charger switches to constant voltage mode until the endpoint of 4.2v/cell is reached, during this time of course the charge current is always decreasing...as the battery voltage reaches the 'fully charged' value.

Discharge rates vary with packs...Some you will see are rated for 15C, 20C and 30C. There maybe other values but these are the most popular...

This mean that for a 3000mah pack rated for 20C discharge, the max current you can pull from the pack would be 3000*20 or 60 amps!.
When using lipo packs, it is wise to use some sort of low voltage detection circuitry to cut the power to the load to prevent over discharging the pack. This voltage is usually set to aroind 3.0v/cell as a maximum..dont go below this or you may find the pack be irreversibly damaged...Some chargers axctually detect the pack voltage before commencing the charge cycle, if the voltage is too low they wont charge!!

Hope this explanation helps to clear away some of the mystery....my choice of words may not be the best..
Looks like the 'A' clips are for connecting to any type of connector furnished on a pack
 
Last edited:

InfiniteInsight

New Member
Oh..hm, looks like I've got to figure out how to make low voltage detection circuitry. Wonder if theres a way that I can have the lights dim rather than cut out and a low power indicator LED flash or something. Having the lights just turn off while riding is dangerous.

My lecture kit from sparkfun arrives tomorrow. I can't wait :D I've got a lot to learn before I can make this bike light though.

Though I am still curious about the C, when you read "C" what is the word that you say for it? like v stands for Volts, and in math b stands for slope, what is C? Current?
 

InfiniteInsight

New Member
thank you audio for the clarification :)

I'm definitely glad I found this place. Hope I can make a home out of it and eventually help other people out as you all are helping me.
 

InfiniteInsight

New Member
I've now got my eye on this charger. Its used by hobbycity themselves to balance cells. That seems like a good sign to me. Its 4s capable too.

Though it doesn't say 14.8v though, its higer than that. Am I being hard headed and not realizing that the pack charger I am looking for absolutely must say it works with 14.8v?
 

audioguru

Well-Known Member
Most Helpful Member
Read my post #6 again: "Since each cell is fully charged at 4.2V and you have 4 of them then the battery is fully charged at 16.8V".
The charger from HobbyKing charges a 4S battery to 16.8V which is what you want. It also balances the cells.
 

Ubergeek63

Well-Known Member
A Li battery charger MUST MUST MUST be a voltage regulated charger. In other words, the output voltage has to regulate to a very precise value and not overshoot which is typically 4.200V/cell. It also needs to have built in current limiting to prevent over heating the battery.
That is not entirely true.

To get the fastest charge on these cells the better circuits use IR compensation circuitry to optimize charge time. On a 4.2V cell you can peak a bit higher if you compensate for internal cell resistance. The "cell" still only sees 4.2V while the cell's internal resistance might be dropping 0.3V or more.

Dan
 

InfiniteInsight

New Member
Read my post #6 again: "Since each cell is fully charged at 4.2V and you have 4 of them then the battery is fully charged at 16.8V".
The charger from HobbyKing charges a 4S battery to 16.8V which is what you want. It also balances the cells.
re-reading it. Okay..so why does the battery not actually say 16.8v?

is it something like that it takes 16.8v to charge but outputs 14.8v only?


Thank you for your patience..I literally am starting from ground zero here.

I'm kinda curious about the c rating of this charger. to google i go!
 

audioguru

Well-Known Member
Most Helpful Member
re-reading it. Okay..so why does the battery not actually say 16.8v?
Because the ad is made by salesmen who are not engineers.
A lithium battery cell is 3.2V when dead and is 4.2V when fully charged. So its average voltage is 3.7V. 4 cells x 3.7V= 14.8V.

is it something like that it takes 16.8V to charge but outputs 14.8v only?
Almost.
Its voltage slowly drops as it discharges. It will be 4 cells x 3.2V= 12.8V when it is dead and its protection circuit should disconnect its load.

My electric model airplane shuts off the motor when the battery cells drop to 3.3V each. Then the receiver and servos still have enough power for me to safely land the plane.

If a lithium cell is less than 3V then it is ruined and it might catch on fire if it is charged. The charger should sense a voltage that is too low and reduce the charging current.

Go to www.batteryuniversity.com .
 
Last edited:

weglobal

New Member
Hi
I need a help to design a battery charger from solar panel , I have a 6V 2.2W solar panel which I am connecting to a 3.6V NIMH 2500mAh battery, I want to use a MOSFET as switch so I will be monitoring the bat voltage , when rich 4.5V the MOSFET will be turned OFF , the reason also that I am using the MOSFET is to not have too much losses and also for power of thr battery not to come back to the solar once the MOSFET is OFF and solar voltage is lower than the Battery.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top