Simviation Forums

Hi Guys

I have recently finished building an R/C plane. The battery packs I use are homemade from five 1.2volt, 300mAH Ni-Cd cells connected in serise. The cells sugest that the should be charged at 30mA for 14 hours. So to charge the pack I should use a 30mA charger for 14 hours at 6volts (I thinks thats how I should do it).

But the problem is I dont have a 30mA charger I have a 650mA charger, I know I can use this it just won't take as long, however charging at this amperage isn't good for the cells. So is there a way to lower the amps? will a resistor work if so what omes does it need to be?

Please help guys I don't want to damage the cells.

Thanks MAtt

Go to where you bought the plane kit. They should have ready-made sets of batteries and chargers that can charge in an hour or less. Or try http://www.towerhobbies.com

tacitblue i would got to the shop but the whole plane is homemade useing straws and toothpics and other stuff. the only stuff i bouth was the receiver and transmitter [img]http://www.simviation.com/yabbuploads/electric%blue1[/img]  [img]http://www.simviation.com/yabbuploads/electric%blue3[/img]

actully all I need is a transformer that converts 230volts ac (standard uk) to dc 6volts and less thand 70ma any one know where i can get one??????? Please help me!

Don't quote me but I'm sure you could do this by using a resistor in the circuit. It's been a while since I messed around with battery packs.

PS. I remember an old friend of mine used an ordinary car headlight bulb in the circuit.

You should be able to find a universal AC adapter on which you can select the output voltage. I don't know if you have a store chain called RadioShack over there, but here they are all over, and they carry that sort of thing.

no we don't have radio shack here and those universal transmormers give out way to many amps

Providing that the output voltage of your charger is REGULATED to supply the correct voltage to charge the battery at the proper rate, the fact that it quotes a high amperage merely means that it can supply that current if required!
The battery will only draw sufficient current to overcome the internal resistance of the battery.
It will draw more current as required at the start of the charge, when the battery voltage is low, and this current will drop as the battery voltage reaches it correct value at the end of the charge.
At the end of the charge when the battery reaches its correct final voltage, the current automatically will fall to nearly zero.

Note that a car battery charger automatically charges at a high amperage at the start of the charge, when the battery voltage is low, and this falls over time as the battery reaches its correct voltage.

The "charge rate" depends upon the charger VOLTAGE setting. The higher the charger output voltage, the more current that is drawn, the quicker the charge.
It is a good idea to ensure that either the charger has a number of output voltage settings, (to vary the charge rate), or use a charger with a fixed, REGULATED, output voltage, ( for safe battery protection).

Paul...slowly blowing a fuse with excessive typing... ... ... ...LOL...!

As an example, think of your computer power pack, the fact that it quotes 500Watt, (Volts X Amps), merely means that it is CAPABLE of supplying that amount of power...IF REQUIRED...most of the time it doesnt...!!
LOL...!

fozzer are you sure thats right? well i'll try it and measure the current next time and can get an ameter (mine broke the other day)

fozzer are you sure thats right? well i'll try it and measure the current next time and can get an ammeter (mine broke the other day)

Hi Littleport....!
I had another think about your problem last night....in bed, got up early this morning...!
So...
Remember that the re-chargeable batteries you are using are 1.5 Volt batteries, therefore you only need four of them connected in series, to equal 6 Volts...!
This means that you can use an ordinary, (plug into the mains), battery charger as used to re-charge digital camera batteries.
My charger is manufactured by "Hahnel", holds four seperate 1.5 Volt, re-chargeable batteries and plugs into the 13 amp mains socket...!

Pop into your local camera/digital camera shop and have a look at the various battery chargers.
They are designed to do exactly what you require, without causing any damage to the batteries...!

Always remember that re-chargeable batteries can be dangerous because of the large amount of power which they contain, about 2 amps/2,000mA...(they get very hot!).

Cheers....!

Paul.

....don't forget...Camera shop... ...!

fozzer the batteries are 1.2 volts so you need five connected together also they are solderd together and then heatshrink put on the outside

Hi Littleport...!

...so I gather you have permanantly soldered 5 batteries together in series, and therefore must charge them together as one group...?

MMMmmmm.... ...!

The batteries must be a bit special to equal 1.2 Volts, the normal single cell battery is 1.5 Volts!

...still can't figure out why you can't use four 1.5 Volt batteries in series, and use a commercial battery charger..?

...post a photograph of the battery assembly, and its container...

Cheers Mate...!

Paul.

For the record, Paul is right- the batteries will only draw as many amps/Milliamps as they need, and no more.

For the record, Paul is right- the batteries will only draw as many amps/Milliamps as they need, and no more.

Quite right, Tacit, me ol' fruit... ...!

Also the charge rate depends upon the charger "on-load" output voltage.
The output voltage of the charger has to be greater than the battery voltage, to enable the battery to be charged.

Connect the charger to the batteries and apply a voltmeter, (DC Volts, watch the polarity!), to the opposite ends of the battery assembly.....The voltage should be slightly higher than the normal combined voltage of the battery pack, (in series).
So it should be greater than 6 volts...(say...7 - 8 Volts, or maybe slightly more?), on load.

Cheers...!

Paul.

The batteries must be a bit special to equal 1.2 Volts, the normal single cell battery is 1.5 Volts!

Not sure about the latest NiMH but rechargeable NiCad batteries are lower voltage than the corresponding dry cells. 1.2v is quite normal for rechargeable cells. The early Futaba radio transmiitters used 7 x 1.5 dry cells. When rechargeable NiCads became popular you had to add an eighth cell (making 8 x 1.2v) to get the correct voltage. It's also common practice to charge the cells as a pack rather than separately. Most radio control equipment uses packs of 4 or 8 rechargeable cells. Electric powered models also run on rechargeable battery packs, or they did in my day.