Ah Thank You! I was scared there for a second. Mine is 24V 400mA.

Right. So with the help of tomb and mono I was able to successfully put together the circuit and all is well. All except that there still isn't any bass when I plug it in and listen. I tried first with some Zune buds just to make sure it would work, but then they started to get really warm. Taking them out, I switched to my KSC75s and that is when I discovered the lack of bass. I know tomb mentioned this in an earlier post, but is there any sort of solution? Get a wall wart closer to the projected voltage (I am using 19V and need 13.3)? Add another battery in series?

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That wouldn't cause the problem. No bass can be caused by a number of things, none of which have to do anything with the charger.

Before we go off-topic with this thread on a subject other than the trickle charger - you might post a separate thread for your problem. You might ask - "PIMETA - No Bass?" or something like that.

You'll get more help that way, anyway. I promise I'll try to help.

I have a 12v sealed lead acid battery of the kind that power PowerWheels or emergency lighting in buildings. Can I just use a wall wart at 15v, and hook it, up, trust the current regulation in the wall wart to limit the current, and leave it hooked up for a 'long time'? Car batteries are constantly under like 15v from the alternator, right?

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There is no current regulation in a walwart to trust. It'll supply as much current as physically possible until the battery is destroyed or until it's charged enough that the current flow starts to drop. At which point, the voltage will climb on the now lightly loaded, unregulated walwart until it damages the battery again.

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What exactly is "wall wart at 15V"? Linear, switching or unregulated? The important part of running this unregulated with it's only inherant voltage:current foldback limits is what it's peak VA and unreglated regulation range is. In other words how high the voltage really gets and what current rate results at end of normal charging cycle, and how long you'd really want or need to leave it charging. Occasional, slight overcharging may not degrade the battery lifespan enough to matter but it should not be persistently overcharging itself.

Some devices do use a basic unregulated wart to charge SLA cells, I've a all-in-one jump-starter/tire-inflator/flashlight thingamajig that charges it's *12V* 12Ah battery with an unregulated 12V/500mA wart and it doesn't seem to have harmed it much, it still has reasonable runtime after 3 years but I don't ever leave it plugged in to charge for more than a day at a time. Incidentally I don't recommend one of those all-in-ones for inflating tires, it's so asthmatic it might only get a beach ball inflated before you got tired of waiting.

To get good charge the voltage depends on temp but generally around room temp it is about 2.3V per cell so a 6 cell *12V* battery is around 13.8V. Anything beyond this that the charger provides, and can maintain current while delivering, would just be an ever increasing charge rate which is not a problem in itself unless your wart were quite large, the rate is low enough but once the cell becomes fully charged the problem is this higher voltage causes electrolysis.

To avoid that you want to either unplug the battery when it is done charging - that point determined through measurements of voltage, or select a charging system that limits the fully charged voltage from the wart to a "float" voltage level, which for typical SLA batteries is a a range but the upper part would be your concern, a peak barely above 14.0V. It never hurts to have battery manufacturer datasheet to compare to their recommendations.

If you wanted to be really cheap to get the job done you could try putting a resistor in series on the positive charger lead, such that it drops the current down to a negligable level once the battery is fully charged (again determined through measurements, but maybe somewhere in the dozens-of-ohms value resistor would suffice depending on exactly what this charger wart is, maybe a few hundreds of ohms).

Naturally the sky is the limit for how elaborate you could do it instead, the more conservative answer is of course to develop some circuit based around a charger IC.

Now I have to ask, why are you using a large (compared to most battery packs) SLA battery? It is not going to sound any better than running straight from a typical linear regulated wall wart unless you had some circuit that was particularly susceptible to noise.

Capacity.
Portability (well, transportability).
I got it for free.
I use it for lots of other stuff, like field charging my RC batteries, emergency jumping my toyota, camping.

I have been just taking it home now and again to charge it on my dad's automotive charger, but I'm getting tired of that.

If you really want to try a wall wart I suggest either the resistor in series or choosing a lower capacity wart like 12V & no more than 500mA, or really both of these if not a regulator (maybe an LDO) to limit voltage to 14V. If your peak voltage with present wart isn't much higher you could try a series of diodes to drop the voltage down a tad instead, 14.0V isn't really a target you can aim slightly lower but just a tad over 13.8 should be a minimum unless it is very warm then drop the voltage a few tenths of a volt.

Hi,

I have tried this solution - and designed a PCB for this. If you are interested check this thread.

I thought I would revive this tread with a trickle charger I use.
It has both current limit and voltage limit.
The schematic is from the LM317 data sheet so I don't mind sharing.
Components were chosen from what I had in my "junk box".
The Eagle file is available by request.
 

 

 

Wow - brilliant. As if by magic I had just finished a conversation with a friend about making a portable amp and how he'd go about charging the batteries without removing them... HeadFi, you've done it again!

can we use LM317LZ instead of LM317T?
 
if we can, what's the difference with the LM317? or are they practically the same?

The T version is in a TO-220 package, the LZ version is in a TO-92 package.  Big difference in the amount of heat they can dissipate.
 
If your charging current is low, you can use the LZ version.

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cobaltmute said:

The T version is in a TO-220 package, the LZ version is in a TO-92 package.  Big difference in the amount of heat they can dissipate.
 
If your charging current is low, you can use the LZ version.

Click to expand...

my charger specs are 15V, 500mA. is the LZ gonna be sufficient?

hi again.. say i want to add an LED indicator to indicate whenever the charger is charging the battery. where should i place it?