2

Author Topic: Nimh batteries  (Read 839 times)

0 Members and 1 Guest are viewing this topic.

Offline tipipliouTopic starter

  • Full Member
  • ***
  • Posts: 48
  • Helpful? 0
Nimh batteries
« on: October 13, 2010, 07:23:23 AM »
hi
when we need  a 5V power supply  for an electronic device( Micrcontrolller or any kind of circuit that doesn't need much power ),

knowing that NIMH batteries voltage fluctuate when discharging,is it prefereble to use a 4.8v Nimh Battery directly or should I regulate a   9v battery   to 5 v?


Offline Conscripted

  • Robot Overlord
  • ****
  • Posts: 291
  • Helpful? 10
Re: Nimh batteries
« Reply #1 on: October 13, 2010, 07:31:05 AM »
ALL batteries are going to have a power level that fluctuates. When dealing with microcontrollers it's a good idea to use a voltage regulator. This will give you a stable source of power for the microcontroller. You don't have to run 9V though. Depending on what type of regulator you use a 6V or a 7.2V battery pack will work. 9v batteries have a horrible battery life.

If you can provide more information about your project and budget we can provide more specific advise.

Conscripted

Offline tipipliouTopic starter

  • Full Member
  • ***
  • Posts: 48
  • Helpful? 0
Re: Nimh batteries
« Reply #2 on: October 13, 2010, 09:11:04 AM »
ok
thanks a lot
just one thing,when using a battery without a regulator,what's the worse that could happen?

sorry for english mistakes

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: Nimh batteries
« Reply #3 on: October 13, 2010, 12:46:02 PM »
Hi,

just one thing,when using a battery without a regulator,what's the worse that could happen?
The worst that could happen is a too high voltage, but if you make sure it ain't too high from a fresh battery, you're OK.

You call it a fluctuating voltage, but that would mean that it went both up and down and since a battery voltage only goes down, it would be better to call it a descending voltage (or something like that).

If the current draw is low, you could use a zener diode and a resistor to regulate down without a dropout voltage worth mentioning.

Square 9V batteries (PP3/"transistor batteries") have around 100..150mAh (some 9V batteries are built from 6 AAAA (4xA) cells). Alkaline AA-size cells are more than 2000mAh.
So, 9V x 150mAh = 1.35Wh
and 1.5V*2Ah = 3Wh

The AA, which costs around a fourth of a 9V battery has got more than double the power available and with 6 cells you get 9V @ 18Wh.

A 4 cell NiMH will be up to 5.8V right out of the charger and is flat at somewhere between 3.6V and 4.4V (depending on current draw [4.4V at a low current draw] and specifications).
So, it starts at a voltage that could harm a controller and only have part of it's discharge time in a useable range.

Much better to use 6 cells (5.4/6.6V flat and up to 8.7V newly charged) to make sure it will always be higher than needed and then use either a zener regulator or an LDO regulator.

The ultimate best regulator for a battery supply is a SEPIC switcher, as it allows the battery voltage to be higher or lower than the output.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline tipipliouTopic starter

  • Full Member
  • ***
  • Posts: 48
  • Helpful? 0
Re: Nimh batteries
« Reply #4 on: October 14, 2010, 04:44:38 AM »
ok ,I see 
thanks a lot for your answers

 


Get Your Ad Here