charging batteries

[Trumpkin]

How do you know when your batteries are charged with those plug in the wall things that don't have any indication on them?

[cooldog]

do some caculations to estimate how long it will take.

i don't know the exact caculation but admin mentioned it in the $50 robot when he says how to make a baterry charger

[airman00]

Two things

do you know the milliamp/ hour or amp/hour of your battery. Do you know its voltage


Also, do you have a multimeter?


Measure the voltage and amperage from the adapter and then see how long it would take to charge up the battery. The voltage from the adapter should be  ~  5V higher than the voltage of the battery and the amperage of the adapter should be < 50% of the battery's

[Admin]

calculating it like cooldog said is the most sure way

I usually just plug it in at night and it'll be charged by the time I get home from work the next day. Too lazy to do math . . .

(says he who is doing that as we speak)

You could also use a multimeter and measure the voltage after a day's charge, and know that is the fully charged voltage.

[cooldog]

i found the link to make a battery charger.

http://www.societyofrobots.com/step_by_step_robot_step3A.shtml

just scroll about half way down the page

[Trumpkin]

is there some way I could make a battery monitor circuit  so I cuold see when It's fully charged? I have seen the tutorial on how to make one but it sounds like you need a microcontroller and the batteries

[Admin]

You forgot to search google for battery monitor circuit 

[Trumpkin]

I found this one circuit http://psn.quake.net/eco8/battery_monitor.html but I am not sure if I can change it to meet my needs.  can ayone show me how to make an led light up when my battery gets charged??

[Trumpkin]

airman said that the charger rating should be 5 volts higher than the voltage of the battery but on the tutorial for using a cell phone charger it says it should be the same voltage?

[Trumpkin]

I guess I forgot a couple of thing, airman, the voltage is 6 volts and yes I do have a multimeter, this is the battery I got. http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=495

[airman00]

IF the voltage of the adapter is 6V , the battery will not charge properly

The voltage from the adapter should be  ~  5V higher than the voltage of the battery and the amperage of the adapter should be < 50% of the battery's

Also, use the multimeter to see how much milliamps is coming from the adapter  - it should not be more than 1150 ma  - that is even stretching it

[Trumpkin]

but battery chargers that say they charge 6 volt batteries always have 6 volt output

[airman00]

Charging lead-acid batteries with a power supply

Lead-acid batteries can be charged manually with a commercial power supply featuring voltage regulation and current limiting. Calculate the charge voltage according to the number of cells and desired voltage limit. Charging a 12-volt battery (6 cells) at a cell voltage limit of 2.40V, for example, would require a voltage setting of 14.40V.

The charge current for small lead-acid batteries should be set between 10% and 30% of the rated capacity (30% of a 2Ah battery would be 600mA). Larger batteries, such as those used in the automotive industry, are generally charged at lower current ratings. Cells constructed of a non-antimonial lead grid material allow higher charge currents but have a lower capacity. The cylindrical Cyclone is sealed and can sustain a pressure of up to 3.5 Bar (50 psi). A pressurized cell assists in the recombination of gases.

Observe the battery temperature, voltage and current during charge. Charge only at ambient temperatures and in a ventilated room. Once the battery is fully charged and the current has dropped to 3% of the rated current, the charge is completed. A good car battery will drop to about 40mA when fully charged; a bad battery may not fall below 100mA.

After full charge, remove the battery from the charger. If float charge is needed for operational readiness, lower the charge voltage to about 13.50V (2.25V/cell). Most chargers perform this function automatically. The float charge can be applied for an unlimited time.

a search on google yielded that

[ed1380]

from what I've seen, the voltage on a charge is about 1/3 higher than battery voltage. IE 12v battery charged with 16v charger

cellphones have LION batteries, so they're special

[maverick monk]

actualy most phones have lipo batteries, im currently planning to make a 7.4v li-po battery form 2 3.7v cells from creative labs zen micro

[airman00]

from what I've seen, the voltage on a charge is about 1/3 higher than battery voltage. IE 12v battery charged with 16v charger

cellphones have LION batteries, so they're special

Yep , just like ed1380 put it


In summary of all these posts 
you need a higher voltage to charge the battery

[cooldog]

can't he use a trickel charge were the voltage is the same as the battery

[paulstreats]

you can trickle charge, also i believe that there is a very simple circuit that makes an led light up while the battery is charging, and when the battery reaches the same voltage as the charger, the led goes out. I have one somewhere it is literally just 2 resistors and an led ill try to find it tomorrow, it came from an electric shaver, most of them have this type of facility.

[airman00]

can't he use a trickel charge were the voltage is the same as the battery

Well yeah, but then again its a "trickle" charge - a bit slow for me 
I like it when my batteries charge in two hours!

[HDL_CinC_Dragon]

also i believe that there is a very simple circuit that makes an led light up while the battery is charging, and when the battery reaches the same voltage as the charger, the led goes out. I have one somewhere it is literally just 2 resistors and an led ill try to find it tomorrow, it came from an electric shaver, most of them have this type of facility.

Well all you really have to do is have the ground lead on the LED attached the to the ground lead on the battery charger and then the positive lead from the LED attached the ground lead on the battery. Then hook up the positive leads to eachother. The current will then flow from the charger, through the LED turning it on, into the battery. Thinking of it as pressure, it would go from high pressure to low pressure until they are equaled out. When they are finally equal, the current stops thus theirs nothing to power the LED. because neither is greater than the other... The resistors would probably be to make sure the LED doesnt burn out.

[Admin]

Without seeing the circuit, I suspect it has to do with the .7V drop of the LED.

An LED needs at least .7V to turn on, and when the voltage difference between the charger and the battery goes below .7V, the LED turns off meaning it is fully charged.

[Admin]

You mind find this interesting:
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1666

The MAX712 is specifically designed for battery charging circuits.

It even gives you the full schematic at the bottom.