Battery charger ??

Hi All,

A few months back I bought a really nice hand held spotlight and last night it crapped out on me. I put it on charge and this morning it was still dea d so I opened it up. A small 2.3AH, 6-volt sealed battery and a wall-wart c harger with the prongs facing out of the back. A bit of a visual surprise.

A bit of poking around and the wal-wart (6vdc 300ma) is a done for. I have a 7vdc 700ma wall wart that I am hoping I can use. The original had no char ging controller, the output went straight to the battery. I am hoping I can do the same with the 7vdc.

No load output was 11vdc. Clipping to the battery it drops to 8.4vdc and as I watched, about every 20-seconds the voltage would drop 0.01v. Not sure w hy but then I am a **Mechanical** Engineer. {grin}

Nothing got hot after 5-minutes, with the charger removed, the battery was already holding 5.4vdc, so I am guessing that is still OK.

The questions.

1: Should I have a resistor as a current limiter? If so what value and wattage ? 2: Is it OK to just let the 7vdc supply just feed into the battery? Providing of course I unplug it after a reasonable amount of time? 3: Will the battery and charger find a balance at somewhere around 7v when the battery is fully charged?

This is a really good light when it was working and I am reluctant to spend anther 60-bucks when it is only a charging problem.

Useful suggestions?

Thanks

Reply to
Dave, I can't do that
Loading thread data ...

On Saturday, August 31, 2013 10:43:06 PM UTC-4, Dave, I can't do that wrote :

ht it crapped out on me. I put it on charge and this morning it was still d ead so I opened it up. A small 2.3AH, 6-volt sealed battery and a wall-wart charger with the prongs facing out of the back. A bit of a visual surprise .

e a 7vdc 700ma wall wart that I am hoping I can use. The original had no ch arging controller, the output went straight to the battery. I am hoping I c an do the same with the 7vdc.

as I watched, about every 20-seconds the voltage would drop 0.01v. Not sure why but then I am a **Mechanical** Engineer. {grin}

s already holding 5.4vdc, so I am guessing that is still OK.

ge?

g of course I unplug it after a reasonable amount of time?

he battery is fully charged?

nd anther 60-bucks when it is only a charging problem.

In answer to your specific queries, please note:

  1. If the battery capacity rating is 'X' AH, the maximum charging current must be X/10.0
  2. The 7 Volt DC should be fine. There has to be a potential difference for the current to flow from the charger to the battery. Also note that a sealed lead acid battery is a rugged device and a bit of overcharging would not damage it, provided the charging current is controlled (please see 1.0 above)
  3. When the battery is fully charged, it will not draw any current from the charger. All of the above hold for sealed lead acid cells as they are inherently rugged. Other batteries as Li-ion are very delicate.
Reply to
dakupoto
  1. If the battery capacity rating is 'X' AH, the maximum charging current must be X/10.0
  2. The 7 Volt DC should be fine. There has to be a potential difference for the current to flow from the charger to the battery. Also note that a sealed lead acid battery is a rugged device and a bit of overcharging would not damage it, provided the charging current is controlled (please see 1.0 above)
  3. When the battery is fully charged, it will not draw any current from the charger.

** Fraid it will and rather too much in this case.

A DC supply ( like the OP has) and a battery charger are very different things.

All of the above hold for sealed lead acid cells as they are inherently rugged.

** They explode if overcharged.

The 8.4 volts reported by the OP when the battery is on charge is way too high.

His 2.3AH battery is probably stuffed as well as the charger.

... Phil

Reply to
Phil Allison

I agree. SLAs are more readily damaged by overcharging because the resultant gassing may be vented to the environment and water cannot be added to restore the electrolyte as in a flooded lead-acid battery. It may survive a short time of overcharging at C/10 or longer at about C/100, but it is best to end the charge when the battery is full and wait several months before recharging. And they can remain fairly well charged over a 6 month to one year period.

Some useful information:

formatting link
formatting link

formatting link
formatting link
formatting link

Lead acid batteries have a normal voltage of 2.2 to 2.3 volts per cell fully charged, and 2.4 to 2.5 volts per cell maximum when charging. So the 6V battery should never see more than 7.2 to 7.5 volts under charge. 1.67 volts per cell is the lowest it should ever be before damage occurs, so 5 volts is essentially dead. There is also a temperature coefficient and internal series resistance which can affect the voltage when charging and discharging.

Here is a thread where I asked for and found much information on charging SLA batteries. I plan to make a BMS for 12V SLAs so multiple batteries may be safely charged in series:

formatting link

Paul

Reply to
P E Schoen

-------- ------- | Wall +|---Vin| LM317 |Vout---+ | Wart | ------- | | 7V | Adj [R1] | 700 mA | | | | | +-----------+---[+BATT-]---+ | | | | -|-------------------------------------+ --------

The above is a simple "overnight" current limited charger. For your battery to charge at about C/10 you want to limit the current to about 230 mA. R1 computes to ~ 5.45 ohms at about 1.25 watts. Make R1 by putting a 10 ohm and a 12 ohm resistor in parallel - use 1 watt resistors. Use a heatsink on the LM317.

Ed

Reply to
ehsjr

7V isn't enough to charge a "6v" sealed lead-acid battery. you want to charge to avout 7.2 volts

That helps.

The battery sounds a bit sick.

Typically you want to limit the charge voltage instead.

yes, but determineing the correct time to disconnect it could be tricky

yes, but the battery will then start to heat up,

you could try one of these:

formatting link

--
?? 100% natural 

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
Reply to
Jasen Betts

Thanks to those helpful replies and one not-so-helpful. :)

Being a little lazy, the charger in Jasen's post seems the best option, although it will not be from that crackhead-laden auction site. Once burned...

Ehsjr's little ASCII art makes sense if I can find the parts here. If I have to buy parts to build, I may as well buy the charger, but thanks so much for the other good replies.

@Phil, it is fine to show us/me how clever you are, but I am asking for help and your post did nothing in that vein. Dare I point out the closing line in my OP, "Useful suggestions," which you failed to read obviously. :)

Reply to
Dave, I can't do that

"Dave, I can't do that"

** Fuck you.

** Hey, we got a live one here folks...

** Hey - fuckhead.

I did NOT post ANY reply to YOU !!

I was correcting the nonsense posted by another trolling idiot here.

Pearls before swine, in your case.

... Phil

Reply to
Phil Allison

Ahhh, phil, what a nice man.

OK, back to the charger and the helpful replies. Bought a charger from Amazon for $3.50-shipped. After a 10-hour charge, the battery is just fine and holding charge well.

Thanks to all who responded, including you phil and I hope your anger clears up soon. I am left to muse if you would be so aggressive if we were standing toe to toe. My guess is not.

Reply to
Dave, I can't do that

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.