# battery charging.

Discussion in 'General Electronics Chat' started by pudhiyavan, Apr 29, 2009.

1. ### pudhiyavan Thread Starter New Member

Nov 25, 2008
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my apologies for posting such a stupid query here

i have attached one of the lead acid battery charger from AC found in web ,
my query is , instead of AC input if i have to use a solar panel (12v , 1.6 amp), can i just remove the AC charging part and use it for charging the 12V lead acid battery (9ah 6 cell)?

will it work

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2. ### t_n_k AAC Fanatic!

Mar 6, 2009
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In principle it would work but you'll need a voltage source greater than 12V DC to charge the 12V lead acid battery.

3. ### pudhiyavan Thread Starter New Member

Nov 25, 2008
8
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thanks dear t_n_k . the power source is from 18W panel. i guess the power could 14+v usually , could it be okay?

4. ### bertus Administrator

Apr 5, 2008
19,168
3,836
Hello,

Put a diode in series with the solar panel.
In that way the battery can not deliver current back to the solar panel.

Greetings,
Bertus

5. ### pudhiyavan Thread Starter New Member

Nov 25, 2008
8
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thanks Bertus, so can i use IN5402 as it is?

6. ### jvjtech Member

Jan 26, 2008
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Ref: www.batteryuniversity.com: 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.

You will lose about 0.7V across a diode. There are two diode drops in the 1N5402 so you will lose 1.4 V. You should have at least about 14.4 + 1.4 or 15.8 V at the source. For the ac source 12 Vac (rms) gives about 17 V(peak). Regards. JJ

7. ### pudhiyavan Thread Starter New Member

Nov 25, 2008
8
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thanks jj

with the help of multimeter when i was observing the peak voltage it shows 15v+ and the minimum voltage it shows is 11v, so i guess the source serves the needed supply, can you please clarify me on the following queries?, do i need to use the 4 (1N5402 )diodes? also do i need to use 1watt resisters or 1/2 watt or 1/4 watts?, sorry for being so dumb...

8. ### agnivina New Member

May 11, 2009
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I went through various post on the forum and learned that battery charging current should be "1/10th" of its "Ah" rating. However I didn't got any information about time required for charging. I mean how can I calculate time required for charging various batteries?

Is there any standard formula to measure required charging time?
Say If I have battery 12V-2.5Ah, and charging current say 250mA (1/10th) how much time will be required to get battery fully charged?

Thanks.

Apr 5, 2008
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10. ### David Bridgen Senior Member

Feb 10, 2005
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An interesting and observant question.

I had to learn the care and feeding of lead-acid batteries in order to pass one of the examinations to get a "ticket" as R.O. in the Merchant Navy.

A lead-acid battery should be charged from a constant voltage source. The actual voltage will depend to some extent on the ambient temperature and in the interests of accuracy the manufacturer's figures should always be consulted.

A fully charged lead-acid cell will measure 2.2 volts immediately after being charged and disconnected from the charger, dropping to 2V soon after current is drawn from it.

Some manufacturers say that the source voltage should be 13.8 for a 12V battery. Others may give different figures.

The point being, though, is that if, say, a discharged 2V cell is charged from a 2.2V source, the initial current will be fairly high and will slowly reduce as the cell's terminal voltage increases. Once it reaches 2.2 the current will drop to zero or very close to it.
The charger may be left connected indefinitley without cause for concern - as long as it is of the correct voltage.

Nicads are a different kettle of fish.

I learnt the care and feeding of those while working for a defence company whose military radios used them.

They should be charged from a constant current source.
The well known one tenth of the ampere-hour rating figure is widely used.
e.g. 250mA for a 2.5Ah battery as you correctly say.

Duse to losses in the charging process, much (most?) as heat, they need to be charged for 1.4 times the discharge time. In other words, for 14 hours, not 10.

There are other crafty methods for charging them much more quickly. Some of them, I believe, rely on temperature measurement.

Another method is by carefully monitoring the battery's or cells' terminal voltage/s.
Perhaps surprisingly, a Nicad cell's terminal voltage falls very slightly as it reaches full charge. The detection of this voltage drop signals the fully charged conditiion and the current is switched off.

All very well, but, we were always told, in respect of lead-acid batteries, that a long slow charge is much better than a short fast one. I see no reason why that shouldn't apply to Nicads or any other type.

11. ### agnivina New Member

May 11, 2009
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Thanks Bertus & David, I'll go through those links

12. ### bobbyrae Active Member

May 14, 2009
42
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I see some pretty good comments here. The important thing to note is that there is a charging voltage, and then after becoming fully charged you should apply a maintenance (or float) voltage. The charge voltage will be 14.4 - 14.6 depending on battery type and temperature. Maintenance voltage is around 13.3v.

If you try to charge with a lower voltage you won't get a full charge and if you go over the charge voltage you will lose electrolyte due to boiling. So 18 volts is a really bad idea; it will cook your batteries!

I have a Schumaker car battery charger and it has automatic charging, while being a bit crude, it does taper off when nearing full charge and finally shuts off completely at the end. And if you see my post about identifying resistors, you will see the control board from that charger. I am trying to decipher that circuit to see just how they do it!