Smart phone charging.

[sureshot]

Looking for some advice on SLA batterys used for charging.
What i am looking to build is a portable smart phone charger with long life between charging the SLA.
So its a 12 volt SLA 7.5 Ah dropped down with a linear voltage regulator.
My question is can an SLA battery be discharged between charges, or is this bad for the batterys condition and working life of the unit.
Any help apprecited.

 

[BobK]

You should use a switching regulator. A linear regulator from 12V to 5V will waste 60% of the power, whereas a switching regulator can waste as little as 10%.

I am not sure what your are asking about discharging the battery. If you mean to purposely discharge it, I don't see why.

Bob

 

[(*steve*)]

So its a 12 volt SLA 7.5 Ah dropped down with a linear voltage regulator.

You're not asking, but if you use a switchmode regulator then your battery will last twice as long.

My question is can an SLA battery be discharged between charges, or is this bad for the batterys condition and working life of the unit.

If you can't discharge a battery then it;'s not a lot of use is it?

The question is "how far can you discharge it?" For a 12V Lead Acid battery, discharging below 10.5V is not to be advised. And if it ever gets down to 10.5V it should not be left that way for long. (Actually a reference I have here suggests 100% discharge is 11.7V!)

 

[sureshot]

Thanks for the info fellas, you both answered my questions, the switching regulator is more efficient way to go and don't discharge below 11.70 volts, with this in mind i should be able to construct a portable high efficient charger.

Thanks again for your help much appreciated.