1. Home
  2. Electronics Design
  3. Battery power supply with a low battery indicator

Battery power supply with a low battery indicator

Hi all

I'm trying to make a power supply for an autonomous robot. I think about using NiMH batteries. Do you think it is a good choice ?

I'll separate batteries for logical circuitry supply (5V) and motors supply (12V), in order to avoid perturbations. So I need 2 regulators : the LM7805 for the 5V supply and the MC78T12 for the 12V supply. One of my problems is that I don't know exactly yet how much current the motors will need. The MC78TXX seem to be good, because they accept a 5A peak output current. Do you think the quescient current is an important matter ? Because it is quite high on this regulator.

Another of my problems is I would like an indicator to see when the battery is low. My first idea is a simple comparator. But can't see how to do this. Could you help me ?

Just another question: if I put a led to see the indicator, would it be an unnecessary current consumption ?

Thank you for your help, and sorry for the mistakes I can make, I'm french..

Reply to
pauline3
Loading thread data ...

schrieb im Newsbeitrag news: snipped-for-privacy@v45g2000cwv.googlegroups.com... | Hi all | | I'm trying to make a power supply for an autonomous robot. I think | about using NiMH batteries. Do you think it is a good choice ? | | I'll separate batteries for logical circuitry supply (5V) and motors | supply (12V), in order to avoid perturbations. | So I need 2 regulators : the LM7805 for the 5V supply and the MC78T12 | for the 12V supply. | One of my problems is that I don't know exactly yet how much current | the motors will need. The MC78TXX seem to be good, because they accept | a 5A peak output current. Do you think the quescient current is an | important matter ? Because it is quite high on this regulator. | | Another of my problems is I would like an indicator to see when the | battery is low. My first idea is a simple comparator. But can't see how | to do this. Could you help me ? | | Just another question: if I put a led to see the indicator, would it be | an unnecessary current consumption ?

Learn what a switched moded power supply is. Then replace the MC78T12 with such a thing. 5A is pretty much! You will need a large cooling area. If you use a microcontroller, then control the motor directly with PWM. For a

12V motor you need a battery voltage of at least 18V. LiIon is ligther. Cheaper is lead battery. NiMH is reasonable.

Google Comparator. The LED will light with current between 5mA and 25mA. Compare it to the motors this is just nothing.

- Henry

--

formatting link

Reply to
Henry Kiefer 

--
It\'s OK.
Reply to
John Fields

Bon jour madame'

Alkalines bateries have more capacity than Nimh for same form factor, however ni mh are recahrgable.

I do not like the idea of using 7805xx series of linear egulator as you waste so much heating power. for exmaple 12 volts regulated to 5 leave 7 across the 7805. this 7 volts times the ciruit current will be a higher poer than the 5 volts (you need) at th same curent. so you are getting robbed in power and for battery this is bad.

try a simple 2575 simple switcher here if you delivr 5 volts at 1 amp (5 watts) your waste will be < 1watts with the 7805 (at 1 a) your watse would have been 7 watts!

Good luck and have fun. start early with building and measuring as electronics really never works the first time, and you learn so much by watching how things dont work as expected. Make sure you evaluate and observe each part, resitors can act "funny" or be improperly markd and capacitors are especially tricky when it comes to releasing the stored energy the intenral series resistance is often a limitng factor.

Ciao,

Marc

Reply to
LVMarc

Hi Pauline,

Check this report at

formatting link

Srinivas EMITT Solutions

snipped-for-privacy@free.fr wrote:

Reply to
nsreddy

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.