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Charge gel cell with car charger?

Started by Mike Cook February 24, 2013
On Sun, 24 Feb 2013 05:17:53 -0800, dave <ricketzz@earthlink.net> wrote:

>On 02/24/2013 05:14 AM, Phil Allison wrote: >> "dave" >>> >>> You answered your own question. As long as the battery doesn't heat up on >>> a big charge you're probably OK. >> >> >> ** SLA or "gel cells" are prone to gassing when overcharged. >> >> The pressure builds up inside until something gives - then you have bits >> of battery and acid all over the place. >> >> Voltage & current limited charging is the only safe and sensible way. >> >> >> >> ... Phil >> >> > >They have vents.
Which are NOT meant for overcharge relief.
Mike Cook wrote:
> A friend has a battery powered Ryobi lawn trimmer ("weed whacker") which > doesn't work. The 12vdc wall wart puts out only ~ 12.4v. > > I charged the lead-acid gel cell using a car charger. The charge rate > (selectable) was 0.5A. Afterward the trimmer seemed to work as new. > > Can the car charger be used to charge this battery? He can install a timer to > limit charge time if that's something required. > > Thanks. >
THe OEM charger most likely is unfiltered. Put a cap on the output but do not connect it to the battery and then do a voltage check. If you see a jump in voltage then this means the battery is on its last leg and you really shouldn't push it. A good test for this condition is to fully charge it with your auto charger and disconnect it and test the voltage a day later or few hours later to note the discharge. It is possible the charger is bad but I am going with a bad battery. You can always get a weak battery to appear good with an extra current source but the charge will dwindle. Jamie
Do not connect a capasitor. Firstly, you would need a FARAD- ranged unit, n=
ot in  microFarad range, as the battery is very low-impedance load. Secondl=
y, the charger's no-load voltage with capasitor can be much over 15 volts.=
=20

In typical chargers there is usually only a full-wave bridge rectifier in t=
ransformer's secondary circuit (and often an inaccurate AC current meter), =
so current comes in peaks; you should have an RMS current meter to get corr=
ect readings. Voltage is best checked without charger, as mentioned. If no-=
load voltage is over 13.8 volts (typical floating charge value), the lead-a=
cid battery is probably fully charged. - EePee.
On Sun, 24 Feb 2013 00:06:18 -0800, Mike Cook wrote:

> A friend has a battery powered Ryobi lawn trimmer ("weed whacker") which > doesn't work. The 12vdc wall wart puts out only ~ 12.4v. > > I charged the lead-acid gel cell using a car charger. The charge rate > (selectable) was 0.5A. Afterward the trimmer seemed to work as new. > > Can the car charger be used to charge this battery? He can install a > timer to limit charge time if that's something required. > > Thanks.
Go to a boat shop, feed store, hardware store, whatever, and get a float charger. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
Mike Cook wrote:
> > A friend has a battery powered Ryobi lawn trimmer ("weed whacker") which > doesn't work. The 12vdc wall wart puts out only ~ 12.4v.
In or out of circuit? If the thing doesn't have any filter caps, the out of circuit reading will be low.
> I charged the lead-acid gel cell using a car charger. The charge rate > (selectable) was 0.5A. Afterward the trimmer seemed to work as new. > > Can the car charger be used to charge this battery? He can install a timer to > limit charge time if that's something required. > > Thanks.
dave wrote:
> > On 02/24/2013 05:14 AM, Phil Allison wrote: > > "dave" > >> > >> You answered your own question. As long as the battery doesn't heat up on > >> a big charge you're probably OK. > > > > > > ** SLA or "gel cells" are prone to gassing when overcharged. > > > > The pressure builds up inside until something gives - then you have bits > > of battery and acid all over the place. > > > > Voltage & current limited charging is the only safe and sensible way. > > > > > > > > ... Phil > > > > > > They have vents.
They are damaged long before they can vent.
Jamie wrote:
> > Mike Cook wrote: > > A friend has a battery powered Ryobi lawn trimmer ("weed whacker") which > > doesn't work. The 12vdc wall wart puts out only ~ 12.4v. > > > > I charged the lead-acid gel cell using a car charger. The charge rate > > (selectable) was 0.5A. Afterward the trimmer seemed to work as new. > > > > Can the car charger be used to charge this battery? He can install a timer to > > limit charge time if that's something required. > > > > Thanks. > > > > THe OEM charger most likely is unfiltered. Put a cap on the output but > do not connect it to the battery and then do a voltage check.
More bad bad advice from Maynard Philbrook, as usual. Does the voltage across the battery go up when the charger is connected?
> If you see a jump in voltage then this means the battery is on its > last leg and you really shouldn't push it.
Bullshit, as always. The connector for the charger may be bad, especially if it disconnects the battery from the tool while on charge. I've seen connects melted, or the solder overheat 7 the wires fall off poor designs.
> A good test for this condition is to fully charge it with your auto > charger and disconnect it and test the voltage a day later or few hours > later to note the discharge. > > It is possible the charger is bad but I am going with a > bad battery. You can always get a weak battery to appear good with an > extra current source but the charge will dwindle.
You're long overdue for replacement. :(
On Mon, 25 Feb 2013 07:56:18 +1000, Tim Wescott <tim@seemywebsite.please>  
wrote:

> On Sun, 24 Feb 2013 00:06:18 -0800, Mike Cook wrote: > >> A friend has a battery powered Ryobi lawn trimmer ("weed whacker") which >> doesn't work. The 12vdc wall wart puts out only ~ 12.4v. >> >> I charged the lead-acid gel cell using a car charger. The charge rate >> (selectable) was 0.5A. Afterward the trimmer seemed to work as new. >> >> Can the car charger be used to charge this battery? He can install a >> timer to limit charge time if that's something required. >> >> Thanks. > > Go to a boat shop, feed store, hardware store, whatever, and get a float > charger. > > >
Get a gel-cell float charger. The recommended terminal charging voltage for a gel-cell is slightly lower than for a standard lead acid.
On 02/24/2013 05:37 AM, SoothSayer wrote:
> On Sun, 24 Feb 2013 05:17:53 -0800, dave <ricketzz@earthlink.net> wrote: > >> On 02/24/2013 05:14 AM, Phil Allison wrote: >>> "dave" >>>> >>>> You answered your own question. As long as the battery doesn't heat up on >>>> a big charge you're probably OK. >>> >>> >>> ** SLA or "gel cells" are prone to gassing when overcharged. >>> >>> The pressure builds up inside until something gives - then you have bits >>> of battery and acid all over the place. >>> >>> Voltage & current limited charging is the only safe and sensible way. >>> >>> >>> >>> ... Phil >>> >>> >> >> They have vents. > > Which are NOT meant for overcharge relief. >
I didn't say they were. I was speaking to the "bits of battery and acid" prediction above.
On 02/24/2013 05:35 AM, SoothSayer wrote:
> On Sun, 24 Feb 2013 05:12:28 -0800, dave <ricketzz@earthlink.net> wrote: > >> On 02/24/2013 12:30 AM, Mike Cook wrote: >>> The gel cell is 12v. >>> >> >> Most lead acid batteries are ca. 13.6 Vdc > > No most 12 volt car battery chargers operate at 13.6 VDC. That is the > CHARGE Voltage, not the voltage the battery ends up carrying. In order > to charge a battery, one must apply a higher voltage than the battery > operates at. > >> If your car battery ever got >> down to 12 Vdc the car would have trouble starting. > > You're an idiot. A car battery or 12V gel cell that reads 12volts IS > fully charged and will put out its declared rate. > >> Lead acid cells are >> about 2.22 Vdc. > > You're an idiot. Perhaps you should provide a wiki citation or such. > Right now you appear as a joke. > > > > Cross posting fucking retards. >
13.6 Vdc is the float voltage. Virtually all amateur radio equipment, most mobile communications equipment and power supplies (for above) are rated at 13.6 Vdc, the nominal Voltage of a 6 cell lead acid battery. That is a fact, no matter how rude you become. Here's another flash, your 1.5 V "AA" NiCads are only putting out 1.2 Vdc.