Batteries & Chargers

[AtomSoft]

actually a friend was tell me charge pump. How about a MAX711 ? With 2-3 AA batteries

 

[Hero999]

What are you trying to do?

Measure the LED current?

Don't bother, just use ohm's law; you know the LED current formula?

If you really need to know the current then measure the voltage across the 270Ω resistor and calculate it.

 

[AtomSoft]

Hero999 (read above post (like 3 or so up)

 

[ericgibbs]

Im not sure i fully understand. Should it do it like this:

hi atom,
Thats it, just place the 1R in series with the +V lead from the psu.

You can connect the 200mV meter across the 1R only when you to check a current while you are testing,, it leaves the DVM free for other jobs, rather than keeping the meter connected to the psu.

OK.?

Can I make a suggestion,?
Please draw your circuits with the +V rail at the top and the 0V at the bottom,,, I'm getting dizzy having to keep standing on my head...

 

[AtomSoft]

oh so i can use 1 dvm.

This better: (?)
**broken link removed**

 

[ericgibbs]

oh so i can use 1 dvm.

This better: (?)
**broken link removed**

hi atom,
Whats the next step in your project now that you have determined the load.?

'agu' has given some advice on batteries.

BTW, one test I would do, thats if your psu is a variable type.?
Get the full circuit working with say with +5V and slowly reduce the +V and see the lower limits before the circuit hangs up and what happens after that when you slowly increase the +V back to +5V..[monitor the mA's while you do it]

I'm thinking Brown Out detection as you are running on batteries.???

 

[AtomSoft]

you are one smart dude! I even forgot about that feature . I dont have a variable PSU but i will make one later on when i fully wake up lol. I have to get like a 5/10k POT. from RadioShack. I never used brown out so i guess ill have to read up on it.

 

[AtomSoft]

ok just made my variable power supply lol. So small and simple. Rectifier and all. I will try what you said before about testing minimums. Here is it(the psu):

 

[AtomSoft]

Normal 162mA @ 5v

120mA = Barely viewable. V = 4.7v (kinda jumpy since using a pot)
I guess once the hits 120mA needs recharging also @ 16mA the PIC is still running! Cool.

Around 2-3 mA the pic turns off(resets). The only issue is the screen needs plenty of power. 5v @130mA min

 

[ericgibbs]

Normal 162mA @ 5v

120mA = Barely viewable. V = 4.7v (kinda jumpy since using a pot)
I guess once the hits 120mA needs recharging also @ 16mA the PIC is still running! Cool.

Around 2-3 mA the pic turns off(resets). The only issue is the screen needs plenty of power. 5v @130mA min

hi,
Neat looking little psu.

With the measurements you have got it should be possible to work out the best battery for the job.

The problem with LCD backlights is the current required, you could reduce the current a little by increasing the 8R to 10R or 12R, see what B/L intensity you get.

 

[AtomSoft]

Ok ill try it out now. Thanks for helping again.

 

[AtomSoft]

with 8 Ohms im using 136mA and with a 10 Ohm i use 110mA and it still looks good! I dont have a 12 ohm but will try other values including a pot.

 

[ericgibbs]

with 8 Ohms im using 136mA and with a 10 Ohm i use 110mA and it still looks good! I dont have a 12 ohm but will try other values including a pot.

hi,
Whats the voltage measure across the LCD backlight leds, between the junction of the 8R and the LED's to 0V.???? Use +5V as normal for the test.

 

[AtomSoft]

Like this? I measure 3.97V from those points.

 

[ericgibbs]

Like this? I measure 3.97V from those points.

hi,
I think the 1R0 must be a dwg error.? 8R thru 12R.??

Reason for asking was regarding the lower voltage tests you did.
Below about 3.9Vsupply the B/L leds should not be lit, so the current drawn from the psu should be the current only required by the PIC.

 

[AtomSoft]

yep i didnt notice i forgot the "0" lol its a 10 Ohm. Sorry about that. And yes below a voltage i think it was like 3.8v or your 3.9v the BL turns off.

Now what? lol

How can I.... well how would you determine how many and what type of battery to use. and how to charge them?

I have now like 6 NIMH Batteries all at 2500 mAh and 1.2v.

 

[ericgibbs]

yep i didnt notice i forgot the "0" lol its a 10 Ohm. Sorry about that. And yes below a voltage i think it was like 3.8v or your 3.9v the BL turns off.

Now what? lol

How can I.... well how would you determine how many and what type of battery to use. and how to charge them?

I have now like 6 NIMH Batteries all at 2500 mAh and 1.2v.

hi atom,
This link gives discharge curves for NiMH batteries
How long do you want your project to run on a fully charged set of 2.5AHr batteries.?
You now have values for the current required by the project.

https://www.powerstream.com/AA-tests.htm

EDIT: this is a 2.5AHr datasheet.

https://www.powerstream.com/AA-tests.htm

also a pdf.

 

[AtomSoft]

cool thanks i will be sure to look over it when i get back from store.

 

[AtomSoft]

I was looking at pdf and didnt know you can get datasheet on a battery lol i found mines
https://www.electro-tech-online.com/custompdfs/2008/08/nh15-2500.pdf

EDIT:
Also found this which i think tells me how to charge:
https://www.electro-tech-online.com/custompdfs/2008/08/chfm1.pdf

AA @ DC 2.8V, 360mA ± 10%

BTW thats my charger lol. I might as well learn from it lol

 

[AtomSoft]

ii need a thermistor like my buddy krumlink said and monitor so it doesnt reach over 55°C aka 131°F

Also he told me about:
http://www.stefanv.com/electronics/usb_charger.html

Now i was thinking about using this design and instead of usb i would use a 9v wall adapter.