Charge gel cell with car charger?

[Mike Cook]

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.

 

[Mike Cook]

The gel cell is 12v.

 

[[email protected]]

Followups set to sci.electronics.repair .

Can the car charger be used to charge this battery?

Probably. Do you know what the amp-hour capacity is of the battery that
is in there now? A little Googling *1 suggests that the original 12 V
battery might have been six Gates/Hawker/Enersys "Cyclon" 2 V cells in
series; the replacement that one site sells looks suspiciously like the
common or garden 12 V 7 amp-hour "gel cell", plus a couple of brackets
to make it fit. If the battery capacity is around 6 or 7 amp-hours,
then the 0.5 A charger will work OK, as long as you don't mind it taking
12 or more hours for a full charge.

One manufacturer of these batteries *2 says this is how you charge the
12 V, 7 Ah size:

"Limit initial current to 2.1A. Charge until battery voltage (under
charge) reaches 14.4 to 14.7 volts at 68°F (20°C). Hold at 14.4 to 14.7
volts until current drops to under 70mA. Battery is fully charged under
these conditions, and charger should be disconnected or switched to
"float" voltage."

So... the 0.5 A car battery charger should be OK. The charger you have
may not do the automatic float and shutoff - more below.

The voltage output by the car charger will be slightly different than
what a sealed battery needs; this is probably not too important in this
application, but may reduce battery life a little. If you want, you can
get an "official" charger for sealed batteries for $35 or so; *3 has
0.8 A output and will work a little faster. Or, get one of the
automatic car battery maintainers like a Deltran Battery Tender or
Schumacher Battery Companion; these usually have 1.0 to 1.5 A outputs
and will automagically switch to a low-current charge once the battery
is full. These are easy to find at local stores.

He can install a timer to limit charge time if that's something
required.

If the charger doesn't have any kind of automatic shutoff, then this
might not be a bad idea. The million dollar question is "how long is
enough". The answer depends on how discharged the battery is. The
simple answer (for a 7 amp-hour battery) is 7 amp-hours / 0.5 amps =
14 hours. But: the charge won't be 0.5 A for the whole time. It may
start off that way but it will go down as the battery charges up, so
a full charge will take longer.

At a guess, I would get one of those 12 hour spring wound timer switches
(often used with attic fans) from the hardware store, and put it in an
outlet box along with an outlet and a cord. Maybe set it for 2 or 3
hours the first time, then when it shuts off, measure the battery
voltage to find out how full it is. If not full enough, repeat. After
a few runs you will know what to set the timer to initially.

*1 http://www.ereplacementparts.com/ry...battery-trimmer-parts-c-7931_15633_18531.html

*2 http://www.power-sonic.com/images/p...es/ps_psg_series/12volt/PS-1270_11_Feb_21.pdf

*3 http://www.mouser.com/ProductDetail/Power-Sonic/PSC-12800A-C/?qs=XATL/JQ9g1zerdAMdrMzKQ==

Standard disclaimers apply; I don't get money or other consideration
from any companies mentioned.

Matt Roberds

 

[Phil Allison]

"dave"

Phil Allison

They have vents.

** So you have no fucking idea what really happens.




..... Phil

 

[SoothSayer]

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.

 

[SoothSayer]

They have vents.

Which are NOT meant for overcharge relief.

 

[Jamie]

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

 

[[email protected]]

Why is everyone so rude around here?

Why are you here?

 

[SoothSayer]

I didn't say they were. I was speaking to the "bits of battery and acid"
prediction above.

I wasn't saying you said something wrong. I was merely iterating that
those vents are not for charging pressure relief, per se.

 

[SoothSayer]

13.6 Vdc is the float voltage.

No shit, dumbfuck.

Virtually all amateur radio equipment,
most mobile communications equipment and power supplies (for above) are
rated at 13.6 Vdc,

No shit, dumbfuck.

the nominal Voltage of a 6 cell lead acid battery.

But you very likely have no clue as to why.

That is a fact, no matter how rude you become.

It is also a FACT that a battery at 12 Volts is NOT discharged as you
claimed, DORK.

It has nothing to do with rudeness, it has to do with your lack of
accuracy.

Here's another flash, your 1.5 V "AA" NiCads are only putting out 1.2 Vdc.

I don't need a primer from a dipshit who cries like a wimp when he gets
corrected.


And almost everyone knows that rechargeables and alkalines are not at
the same voltage.

AND, asshole, they are NOT "1.5 Volt NiCads". They ARE 1.2 volt
NiCads.

so, I am "rude", but YOU are "stupid".

 

[Phil Allison]

"dave"

** Most do not - eg:

http://cdn-products.austinkayak.com/p_8037_700.jpg

An acquaintance had a 12V gell battery like the one pictured explode
violently while doing just what the OP here is contemplating. He was
sleeping nearby at the time an got one HELL of a scare !!!!

Makers all warn against using unregulated ( ie raw, rectified AC ) chargers
with gell or SLA batteries.

BTW:

Makers also warn against shorting the battery and often quote a max safe
discharge current.

The penalty for ignoring this advice is a dead battery when the deliberate
(weak link ) fuse inside goes open.


..... Phil

 

[SoothSayer]

The old "iron-transformer" chargers were usually impedance limited, so the
off load voltage will be significantly more than nominal (enough to get a
mildly sulphated battery going). In addition a capacitor would charge to the
AC peak so what you read would be even higher still.

Until you load it.

Unloaded, an old xformer/rectifier battery charger always had
significantly higher voltage without a battery on it.

BIG ripple!

But once a battery is charged and even peaked out, that higher voltage
peak can blow the damned things up, so all charging sessions had to be
monitored to keep them from exploding. Then better chargers came out.

Now, I wouldn't be surprised if there wasn't one you could operate or
observe with your iPad. There are Wi-Fi and/or bluetooth handheld meters
now. That would be enough to know when to go shut it off.

 

[SoothSayer]

they always include a safety pressure relief valve.

As

For NORMAL battery utilization. NOT a vent for charging pressure
relief.. The device and or person doing the charging has to keep the
process below any overt gassing level.

 

[[email protected]]

I am here for entertainment, mainly.

Ah Ha!

most of the substantive stuff is
over my head, but the lead-acid battery is on the FCC exams you take for
an advanced license,

Oohhh! I'm impressed. You took a *real* FCC license exam. Did you
pass?

plus I used to maintain a fleet of trucks at a
construction company, where I also serviced 2-way radios and 5 mW
surveyor lasers.

So you know it all. Great!

 

[Phil Allison]

"dave"

they always include a safety pressure relief valve.

** Kindly point this out in the pic I posted - smartarse.

The battery will simply blow apart if overcharged.


.... Phil

 

[Jamie]

---
My request was about having you describe the dynamics of a
light-bulb-in-series-with-a-battery current limiter which, no matter
how loudly or how long you squeal excuses about why you can't, you
can't, of course.

Unlike you, I've done empirical work which has resulted in published
plots of tungsten lamp filament resistances being functions of
voltages across, and currents through the filament.

I'll email you the plots, if you like.

Your admission to being a copycat hardly qualifies you as an
authority, and certainly explains why you "can't be bothered drawing
pictures" of what you can't envision.
---




---
Wow, with your super-quick response, you must really want me to notice
you and have you suck my dick or have me **** you up the ass...

Sorry, Charlie...

One of your fetishes?

Jamie

 

[[email protected]]

I specifically stated that I did not. You may be a good engineer but
you are a shitty reader.

I can't help it if you can't make up your mind.

 

[Jamie]

Well, a lot of us love to watch a circus side show..

Jamie

 

[mike]

---
???

If a you want the current to change linearly with voltage, then a
simple resistor will do the trick so, obviously, you don't understand
how the bulb trick works.
---


---
The words are no problem but it seems, for you, the theory _is_.

Would you like me to explain how the bulb trick works in terms even
you could understand?

I understand how the light bulb works, but I'm very interested in
hearing YOUR explanation.

 

[mike]

When the battery terminal voltage is low and the drop across the
filament is high; the bulb does its best job of current limiting - just
when high charging current would be no bad thing. As the battery
terminal voltage approaches or exceeds the required voltage, the
inherent PTC characteristic of the filament means as it cools its
resistance falls, its much less effective as a current limiter - just
when the (possibly overcharging) battery needs it most.

The bulb as a current limiter is less than ideal for battery charging -
but better than nothing if you don't have a float capable charger to hand.

I didn't bother to dumb it down for JF - you can draw pictures for him
as a homework excercise.

So, you're saying that a light bulb can work very well for current charging
as long as you pick the voltage and the bulb correctly.

Also, a light bulb can work well to limit the maximum charge current
to stay within the limits of the battery and charger, even in the event
of shorted cells or other faults...as long as you pick the voltage
and bulb correctly.

You can do better. You can abuse any charge method.
IMHO, the bang for the buck of a light bulb current limiter is
second to none when properly applied.