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Electronics => Electronics => Topic started by: Joker94 on December 27, 2009, 08:28:36 PM

Title: Calculating maH
Post by: Joker94 on December 27, 2009, 08:28:36 PM

Hi every one

i have to make a battery charger circuit and i need to know how to calculat maH. As the fast charge rate is 550 maH and the charger i have is 740 maH. so i need to find out what resistor i need

thankd alot

Joker94

Title: Re: Calculating maH
Post by: SmAsH on December 27, 2009, 08:36:38 PM

So, the charger you have charges at 740mah and you need to bring that down to 550mah via a resistor?

Title: Re: Calculating maH
Post by: Joker94 on December 27, 2009, 08:39:42 PM

yeah that is my theory, will that work

Regards

Joker94

Title: Re: Calculating maH
Post by: SmAsH on December 27, 2009, 09:01:41 PM

Any particular reason you want to use a resistor?
Why not use a current limiting ic like the lm317?
Also, what voltage is the charger?

Title: Re: Calculating maH
Post by: Joker94 on December 27, 2009, 09:12:22 PM

well i have resistors laying around. The voltage is 10 volts. and the battery is 6v

Regards

Joker94

Title: Re: Calculating maH
Post by: SmAsH on December 27, 2009, 09:15:03 PM

Using my intelligence (lol) im gonna say 50 ohms...

Title: Re: Calculating maH
Post by: waltr on December 28, 2009, 08:44:26 AM

Quote from: Joker94 on December 27, 2009, 08:28:36 PM

Hi every one

i have to make a battery charger circuit and i need to know how to calculat maH. As the fast charge rate is 550 maH and the charger i have is 740 maH. so i need to find out what resistor i need

thankd alot

Joker94

Watch your units!

maH is milliAmp times Hours and is a rating of battery capacity, ie 100mA for 5 hours = 500mAh.
The changer can source a current, just Amps, no hours in the unit.

A constant current source like the LM317 wired correctly (see the LM317 data sheet) works well for most battery changing.
But no one asked, What type of Battery are you changing? NiCad, NiMH, LiPol ? It makes a difference.
 

Title: Re: Calculating maH
Post by: SmAsH on December 28, 2009, 05:22:00 PM

Quote

But no one asked, What type of Battery are you changing? NiCad, NiMH, LiPol ? It makes a difference.

It would be niCad or NiMH.

Title: Re: Calculating maH
Post by: Joker94 on December 28, 2009, 06:34:40 PM

Very, Very sorry guys

it is a 6v NImH
1100mAh
Fast charge rate 550mAh

thanks for your help, i'll throw a LM317 in to my next order.

Joker94

Title: Re: Calculating maH
Post by: SmAsH on December 28, 2009, 06:44:30 PM

Just fyi, im pretty sure dick smith sells them.
If im down there anytime ill pick one up for you :)

Title: Re: Calculating maH
Post by: Joker94 on December 28, 2009, 06:51:52 PM

if they do i'll have a look the nest time i am there, as i am in desperate need of more copper clad board. :)

But thanks for the offer smash

Joker94