I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
toy electric car (the kind that a kid can ride). The previous battery
didn't hold a charge when I bought the car.

One reference from batteryuniversity.com mentioned something about
2.50V per cell for SLA batteries. I'm assuming my battery has 3
cells. Another website mentions use of an L200 voltage regulating
chip (http://www.myra-simon.com/bike/charger.html).

I've got a 6VDC (nominal) wall wart that puts out just over 9V open-
circuit.

How should I charge it?

Thanks,

Michael

On Mar 9, 8:17=A0pm, mrdarr...@gmail.com wrote:
> I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
> toy electric car (the kind that a kid can ride). =A0The previous
battery
> didn't hold a charge when I bought the car.
>
> One reference from batteryuniversity.com mentioned something about
> 2.50V per cell for SLA batteries. =A0I'm assuming my battery has 3
> cells. =A0Another website mentions use of an L200 voltage regulating
> chip (http://www.myra-simon.com/bike/charger.html).
>
> I've got a 6VDC (nominal) wall wart that puts out just over 9V
open-
> circuit.
>
> How should I charge it?
>
> Thanks,
>
> Michael

What became of the charger that came with the car that showed you the
original battery is now bad?

GG

On Mar 9, 9:42 pm, stratu...@yahoo.com wrote:
> On Mar 9, 8:17 pm, mrdarr...@gmail.com wrote:
> > I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
> > toy electric car (the kind that a kid can ride). The previous
> battery
> > didn't hold a charge when I bought the car.
> >
> > One reference from batteryuniversity.com mentioned something about
> > 2.50V per cell for SLA batteries. I'm assuming my battery has 3
> > cells. Another website mentions use of an L200 voltage regulating
> > chip (http://www.myra-simon.com/bike/charger.html).
> >
> > I've got a 6VDC (nominal) wall wart that puts out just over 9V
> open-
> > circuit.
> >
> > How should I charge it?
> >
> > Thanks,
> >
> > Michael
>
> What became of the charger that came with the car that showed you the
> original battery is now bad?
>
> GG


Charger wasn't available. Got the car for $5 from a Thrift Store,
intending to utilize the motor assembly only. Turns out the rest of
the car was in pretty good condition, and the tiny 6V 4A-h battery
worked for maybe a month, then no longer held a charge.

I suppose I could run to Wal-Mart and buy a $30 charger for their
Power Rangers line, but that would not be nearly as satisfying as a
DIY solution... plus, I'm not sure if their charger is tied to the 4Ah
battery or not.

MD

On Sun, 9 Mar 2008 21:17:03 -0700 (PDT), mrdarrett@gmail.com wrote:

>I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
>toy electric car (the kind that a kid can ride). The previous battery
>didn't hold a charge when I bought the car.
>
>One reference from batteryuniversity.com mentioned something about
>2.50V per cell for SLA batteries. I'm assuming my battery has 3
>cells. Another website mentions use of an L200 voltage regulating
>chip (http://www.myra-simon.com/bike/charger.html).
>
>I've got a 6VDC (nominal) wall wart that puts out just over 9V open-
>circuit.
>
>How should I charge it?

My preferred solution to SLA charging is to use the TI/Unitrode UC3906. If
you're not into building your own PCB then ready-to-assemble kits are available.

http://www.altronics.com.au/index.asp?a ... m&id=K1685

They do ship internationally if you can't find a souce for a similar kit nearer
to you.

mrdarrett@gmail.com wrote:
> I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
> toy electric car (the kind that a kid can ride). The previous battery
> didn't hold a charge when I bought the car.
>
> One reference from batteryuniversity.com mentioned something about
> 2.50V per cell for SLA batteries. I'm assuming my battery has 3
> cells. Another website mentions use of an L200 voltage regulating
> chip (http://www.myra-simon.com/bike/charger.html).
>
> I've got a 6VDC (nominal) wall wart that puts out just over 9V open-
> circuit.
>
> How should I charge it?

Per the manufacturer's recommendations.
But that's not what you wanted to hear,
so read below.

>
> Thanks,
>
> Michael

Here is a way you can charge it:
Build a float charger. Set the float voltage to 7 volts.
Use a 9 or 12 volt DC wall wart (not your 6v wall wart)
The schematic is on the first page of the datasheet
http://cache.national.com/ds/LM/LM317.pdf?

There are better ways to charge your battery, but this
way won't cook it and is simple to build.

If you can't build, buy a charger recommended for
that battery.

Ed

<mrdarrett@gmail.com> wrote in message
news:a8841939-ddff-4175-8be7-476b6a198445@s13g2000prd.googlegroups.com...
>I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
> toy electric car (the kind that a kid can ride). The previous battery
> didn't hold a charge when I bought the car.
>
> One reference from batteryuniversity.com mentioned something about
> 2.50V per cell for SLA batteries. I'm assuming my battery has 3
> cells. Another website mentions use of an L200 voltage regulating
> chip (http://www.myra-simon.com/bike/charger.html).
>
> I've got a 6VDC (nominal) wall wart that puts out just over 9V open-
> circuit.
>
> How should I charge it?
>
> Thanks,
>
> Michael


You can probably use your 6VDC wall wart. Unless it is a really hefty wart,
it'll probably droop considerably when subjected to the battery. It may
actually fail if the battery is discharged, since they often have internal
fuses to prevent fires. So, use a 4.7 ohm 1W resistor in series with it just
in case. If the resistor gets too hot to touch (which it won't) while
charging, post again with specs for the wart.

Regards,
Bob Monsen

On Mar 10, 6:07 am, "Bob Monsen" <rcmon...@gmail.com> wrote:
> <mrdarr...@gmail.com> wrote in message
>
> news:a8841939-ddff-4175-8be7-476b6a198445@s13g2000prd.googlegroups.com...
>
>
>
> >I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
> > toy electric car (the kind that a kid can ride). The previous battery
> > didn't hold a charge when I bought the car.
>
> > One reference from batteryuniversity.com mentioned something about
> > 2.50V per cell for SLA batteries. I'm assuming my battery has 3
> > cells. Another website mentions use of an L200 voltage regulating
> > chip (http://www.myra-simon.com/bike/charger.html).
>
> > I've got a 6VDC (nominal) wall wart that puts out just over 9V open-
> > circuit.
>
> > How should I charge it?
>
> > Thanks,
>
> > Michael
>
> You can probably use your 6VDC wall wart. Unless it is a really hefty wart,
> it'll probably droop considerably when subjected to the battery. It may
> actually fail if the battery is discharged, since they often have internal
> fuses to prevent fires. So, use a 4.7 ohm 1W resistor in series with it just
> in case. If the resistor gets too hot to touch (which it won't) while
> charging, post again with specs for the wart.
>
> Regards,
> Bob Monsen

Bad idea, Michael the OP has stated that it produces 9V off load.
The current drawn by the battery drops as it charges.
If left plugged in past the full charge point the bettery will receive
excessive voltage. Leaving the battery plugged in for a week
will result in a dead battery.

Around there the DIY superstores sell very cheap flashlights
with lead acid batterys and unregulated chargers. They are
notorious for the batterys failing.

Bob

On Mar 10, 12:50 am, Bob <b...@mailinator.com> wrote:
> On Mar 10, 6:07 am, "Bob Monsen" <rcmon...@gmail.com> wrote:
>
>
>
> > <mrdarr...@gmail.com> wrote in message
>
> >news:a8841939-ddff-4175-8be7-476b6a198445@s13g2000prd.googlegroups.com...
>
> > >I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
> > > toy electric car (the kind that a kid can ride). The previous battery
> > > didn't hold a charge when I bought the car.
>
> > > One reference from batteryuniversity.com mentioned something about
> > > 2.50V per cell for SLA batteries. I'm assuming my battery has 3
> > > cells. Another website mentions use of an L200 voltage regulating
> > > chip (http://www.myra-simon.com/bike/charger.html).
>
> > > I've got a 6VDC (nominal) wall wart that puts out just over 9V open-
> > > circuit.
>
> > > How should I charge it?
>
> > > Thanks,
>
> > > Michael
>
> > You can probably use your 6VDC wall wart. Unless it is a really hefty wart,
> > it'll probably droop considerably when subjected to the battery. It may
> > actually fail if the battery is discharged, since they often have internal
> > fuses to prevent fires. So, use a 4.7 ohm 1W resistor in series with it just
> > in case. If the resistor gets too hot to touch (which it won't) while
> > charging, post again with specs for the wart.
>
> > Regards,
> > Bob Monsen
>
> Bad idea, Michael the OP has stated that it produces 9V off load.
> The current drawn by the battery drops as it charges.
> If left plugged in past the full charge point the bettery will receive
> excessive voltage. Leaving the battery plugged in for a week
> will result in a dead battery.
>
> Around there the DIY superstores sell very cheap flashlights
> with lead acid batterys and unregulated chargers. They are
> notorious for the batterys failing.
>
> Bob


Yep, 9V off load; once loaded, voltage dropped to about 6.42V @
177mA. I monitored the voltage every half-hour or so until voltage
rose to 6.77V 6 hrs later, then cut the juice (it was bedtime
anyway). I was just trying to figure out the point where I should
stop charging.

I'll study the other responses and see what I can do.

Thanks,

MD

On Mar 9, 10:55 pm, ehsjr <eh...@bellatlantic.net> wrote:
> mrdarr...@gmail.com wrote:
> > I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
> > toy electric car (the kind that a kid can ride). The previous battery
> > didn't hold a charge when I bought the car.
>
> > One reference from batteryuniversity.com mentioned something about
> > 2.50V per cell for SLA batteries. I'm assuming my battery has 3
> > cells. Another website mentions use of an L200 voltage regulating
> > chip (http://www.myra-simon.com/bike/charger.html).
>
> > I've got a 6VDC (nominal) wall wart that puts out just over 9V open-
> > circuit.
>
> > How should I charge it?
>
> Per the manufacturer's recommendations.
> But that's not what you wanted to hear,
> so read below.
>
>
> > Thanks,
>
> > Michael
>
> Here is a way you can charge it:
> Build a float charger. Set the float voltage to 7 volts.
> Use a 9 or 12 volt DC wall wart (not your 6v wall wart)
> The schematic is on the first page of the datasheethttp://cache.national.com/ds/LM/LM317.pdf?
>
> There are better ways to charge your battery, but this
> way won't cook it and is simple to build.
>
> If you can't build, buy a charger recommended for
> that battery.
>
> Ed


Thanks! Looks simpler than the L200.

Just wondering, where did you get the value of 7.00V? Should I apply
a brief charge at 7.50V to get maximum capacity?

"At 2.37V, most lead-acid batteries start to gas, causing loss of
electrolyte and possible temperature increases. The exceptions are
small sealed lead acid batteries (SLA), which can be charged to 2.50V/
cell without adverse side effect." http://www.batteryuniversity.com/partone-13.htm

MD

"Bob" <bob9@mailinator.com> wrote in message
news:1dc6c3ed-94e3-4b00-aaf0-f1338f75f79e@m44g2000hsc.googlegroups.com...
> On Mar 10, 6:07 am, "Bob Monsen" <rcmon...@gmail.com> wrote:
>> <mrdarr...@gmail.com> wrote in message
>>
>> news:a8841939-ddff-4175-8be7-476b6a198445@s13g2000prd.googlegroups.com...
>>
>>
>>
>> >I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
>> > toy electric car (the kind that a kid can ride). The previous battery
>> > didn't hold a charge when I bought the car.
>>
>> > One reference from batteryuniversity.com mentioned something about
>> > 2.50V per cell for SLA batteries. I'm assuming my battery has 3
>> > cells. Another website mentions use of an L200 voltage regulating
>> > chip (http://www.myra-simon.com/bike/charger.html).
>>
>> > I've got a 6VDC (nominal) wall wart that puts out just over 9V open-
>> > circuit.
>>
>> > How should I charge it?
>>
>> > Thanks,
>>
>> > Michael
>>
>> You can probably use your 6VDC wall wart. Unless it is a really hefty
>> wart,
>> it'll probably droop considerably when subjected to the battery. It may
>> actually fail if the battery is discharged, since they often have
>> internal
>> fuses to prevent fires. So, use a 4.7 ohm 1W resistor in series with it
>> just
>> in case. If the resistor gets too hot to touch (which it won't) while
>> charging, post again with specs for the wart.
>>
>> Regards,
>> Bob Monsen
>
> Bad idea, Michael the OP has stated that it produces 9V off load.
> The current drawn by the battery drops as it charges.

Do you know how much the current drops?

> If left plugged in past the full charge point the bettery will receive
> excessive voltage. Leaving the battery plugged in for a week
> will result in a dead battery.

There is such a thing as overdesign. For example, it is possible to use a
kit, a charger chip, or a discrete circuit like this one:

8 - 12 V input
------o-----o------------o-----o------.
| | | | |
| | | | .-.
| | | | | | 1.38 Ohm 1W
| | | | | |
| >| |< | '-'
| |-----o--| >| |
.-. /| | |\ |----o
4.7k | | | | | /| |
| | | '----o | |
'-' o------------)-----o---||-+ N-MOSFET
| | | ||->
| | | ||-+
| | | |
| | | 10k |
| |/ \| ___ |
o---| |--o-|___|-o--------.
| |> <| | |
| | | | |
| '-----o------' .-. ---
| | | | 22k -
z 5.1V .-. | | --- 6V SLA
A | | 1k '-' -
| | | | |
| '-' | |
| | | |
-----o-----------o-----------o----------------'
GND

All PNP 2N3906. All NPN 2N3904

Constant current at 500mA until battery reaches 7.5V

(created by AACircuit v1.28.6 beta 04/19/05 http://www.tech-chat.de)

(I've included an LTSpice of it, for those interested.)

However, I suspect that would be overkill for the poor guy.

>
> Around there the DIY superstores sell very cheap flashlights
> with lead acid batterys and unregulated chargers. They are
> notorious for the batterys failing.
>

I think they specify that you should take the battery off the charger after
it is charged.

> Bob

Regards,
Bob Monsen

Here is the circuit in LTSpice format:

Version 4
SHEET 1 880 680
WIRE -112 16 -336 16
WIRE 48 16 -112 16
WIRE 208 16 48 16
WIRE 336 16 208 16
WIRE 336 32 336 16
WIRE -112 48 -112 16
WIRE 48 48 48 16
WIRE 208 64 208 16
WIRE -32 96 -48 96
WIRE -16 96 -32 96
WIRE -336 112 -336 16
WIRE 336 112 272 112
WIRE -32 160 -32 96
WIRE 48 160 48 144
WIRE 48 160 -32 160
WIRE 336 160 336 112
WIRE -112 176 -112 144
WIRE 208 176 208 160
WIRE 208 176 -112 176
WIRE 288 176 208 176
WIRE -112 224 -112 176
WIRE 48 224 48 160
WIRE -176 272 -224 272
WIRE 128 272 112 272
WIRE 144 272 128 272
WIRE 336 272 336 256
WIRE 336 272 224 272
WIRE -336 288 -336 192
WIRE 128 304 128 272
WIRE 336 304 336 272
WIRE -224 336 -224 272
WIRE -112 336 -112 320
WIRE -32 336 -112 336
WIRE 48 336 48 320
WIRE 48 336 -32 336
WIRE 336 336 336 304
WIRE -32 352 -32 336
WIRE -336 448 -336 288
WIRE -224 448 -224 416
WIRE -224 448 -336 448
WIRE -32 448 -32 432
WIRE -32 448 -224 448
WIRE 128 448 128 384
WIRE 128 448 -32 448
WIRE 336 448 336 400
WIRE 336 448 128 448
FLAG -336 288 0
FLAG 336 304 a
SYMBOL voltage -336 96 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 9V
SYMBOL pnp 272 160 R180
SYMATTR InstName Q2
SYMATTR Value 2N3906
SYMBOL res 320 16 R0
SYMATTR InstName R1
SYMATTR Value 1.38
SYMATTR SpiceLine pwr=1
SYMBOL pnp -48 144 R180
SYMATTR InstName Q3
SYMATTR Value 2N3906
SYMBOL pnp -16 144 M180
SYMATTR InstName Q4
SYMATTR Value 2N3906
SYMBOL npn -176 224 R0
SYMATTR InstName Q5
SYMATTR Value 2N3904
SYMBOL npn 112 224 M0
SYMATTR InstName Q6
SYMATTR Value 2N3904
SYMBOL res 240 256 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R2
SYMATTR Value 10k
SYMBOL res 144 400 R180
WINDOW 0 36 76 Left 0
WINDOW 3 36 40 Left 0
SYMATTR InstName R3
SYMATTR Value 22k
SYMBOL res -48 336 R0
SYMATTR InstName R4
SYMATTR Value 1k
SYMBOL cap 320 336 R0
SYMATTR InstName C1
SYMATTR Value 1
SYMBOL voltage -224 320 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 5.1
SYMBOL pmos 288 256 M180
SYMATTR InstName M1
SYMATTR Value FDS4953
TEXT 408 280 Left 0 !.ic V(a) = 6
TEXT -370 458 Left 0 !.tran 10

On Mar 10, 9:57 am, "Bob Monsen" <rcmon...@gmail.com> wrote:
> "Bob" <b...@mailinator.com> wrote in message
>
> news:1dc6c3ed-94e3-4b00-aaf0-f1338f75f79e@m44g2000hsc.googlegroups.com...
>
>
>
> > On Mar 10, 6:07 am, "Bob Monsen" <rcmon...@gmail.com> wrote:
> >> <mrdarr...@gmail.com> wrote in message
>
> >>news:a8841939-ddff-4175-8be7-476b6a198445@s13g2000prd.googlegroups.com...
>
> >> >I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
> >> > toy electric car (the kind that a kid can ride). The previous battery
> >> > didn't hold a charge when I bought the car.
>
> >> > One reference from batteryuniversity.com mentioned something about
> >> > 2.50V per cell for SLA batteries. I'm assuming my battery has 3
> >> > cells. Another website mentions use of an L200 voltage regulating
> >> > chip (http://www.myra-simon.com/bike/charger.html).
>
> >> > I've got a 6VDC (nominal) wall wart that puts out just over 9V open-
> >> > circuit.
>
> >> > How should I charge it?
>
> >> > Thanks,
>
> >> > Michael
>
> >> You can probably use your 6VDC wall wart. Unless it is a really hefty
> >> wart,
> >> it'll probably droop considerably when subjected to the battery. It may
> >> actually fail if the battery is discharged, since they often have
> >> internal
> >> fuses to prevent fires. So, use a 4.7 ohm 1W resistor in series with it
> >> just
> >> in case. If the resistor gets too hot to touch (which it won't) while
> >> charging, post again with specs for the wart.
>
> >> Regards,
> >> Bob Monsen
>
> > Bad idea, Michael the OP has stated that it produces 9V off load.
> > The current drawn by the battery drops as it charges.
>
> Do you know how much the current drops?


Current dropped from 177 mA @6.42V to 140mA @ 6.63V about 90 minutes
later. After that I just took voltage measurements only.

What will happen if I charge with my (underpowered?) wall-wart, just
watching until voltage reaches 7.5V? I'm in no particular hurry, and
can monitor the voltage every hour if necessary, at least for now.
I'm guessing the reason for the 500mA is for a faster charge? Or is
this necessary for the health of the SLA?

Thanks for the circuit,

MD


>
> > If left plugged in past the full charge point the bettery will receive
> > excessive voltage. Leaving the battery plugged in for a week
> > will result in a dead battery.
>
> There is such a thing as overdesign. For example, it is possible to use a
> kit, a charger chip, or a discrete circuit like this one:
>
> 8 - 12 V input
> ------o-----o------------o-----o------.
> | | | | |
> | | | | .-.
> | | | | | | 1.38 Ohm 1W
> | | | | | |
> | >| |< | '-'
> | |-----o--| >| |
> .-. /| | |\ |----o
> 4.7k | | | | | /| |
> | | | '----o | |
> '-' o------------)-----o---||-+ N-MOSFET
> | | | ||->
> | | | ||-+
> | | | |
> | | | 10k |
> | |/ \| ___ |
> o---| |--o-|___|-o--------.
> | |> <| | |
> | | | | |
> | '-----o------' .-. ---
> | | | | 22k -
> z 5.1V .-. | | --- 6V SLA
> A | | 1k '-' -
> | | | | |
> | '-' | |
> | | | |
> -----o-----------o-----------o----------------'
> GND
>
> All PNP 2N3906. All NPN 2N3904
>
> Constant current at 500mA until battery reaches 7.5V
>
> (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)
>
> (I've included an LTSpice of it, for those interested.)
>
> However, I suspect that would be overkill for the poor guy.
>
>
>
> > Around there the DIY superstores sell very cheap flashlights
> > with lead acid batterys and unregulated chargers. They are
> > notorious for the batterys failing.
>
> I think they specify that you should take the battery off the charger after
> it is charged.
>
> > Bob
>
> Regards,
> Bob Monsen
>
> Here is the circuit in LTSpice format:
>
> Version 4
> SHEET 1 880 680
> WIRE -112 16 -336 16
> WIRE 48 16 -112 16
> WIRE 208 16 48 16
> WIRE 336 16 208 16
> WIRE 336 32 336 16
> WIRE -112 48 -112 16
> WIRE 48 48 48 16
> WIRE 208 64 208 16
> WIRE -32 96 -48 96
> WIRE -16 96 -32 96
> WIRE -336 112 -336 16
> WIRE 336 112 272 112
> WIRE -32 160 -32 96
> WIRE 48 160 48 144
> WIRE 48 160 -32 160
> WIRE 336 160 336 112
> WIRE -112 176 -112 144
> WIRE 208 176 208 160
> WIRE 208 176 -112 176
> WIRE 288 176 208 176
> WIRE -112 224 -112 176
> WIRE 48 224 48 160
> WIRE -176 272 -224 272
> WIRE 128 272 112 272
> WIRE 144 272 128 272
> WIRE 336 272 336 256
> WIRE 336 272 224 272
> WIRE -336 288 -336 192
> WIRE 128 304 128 272
> WIRE 336 304 336 272
> WIRE -224 336 -224 272
> WIRE -112 336 -112 320
> WIRE -32 336 -112 336
> WIRE 48 336 48 320
> WIRE 48 336 -32 336
> WIRE 336 336 336 304
> WIRE -32 352 -32 336
> WIRE -336 448 -336 288
> WIRE -224 448 -224 416
> WIRE -224 448 -336 448
> WIRE -32 448 -32 432
> WIRE -32 448 -224 448
> WIRE 128 448 128 384
> WIRE 128 448 -32 448
> WIRE 336 448 336 400
> WIRE 336 448 128 448
> FLAG -336 288 0
> FLAG 336 304 a
> SYMBOL voltage -336 96 R0
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V1
> SYMATTR Value 9V
> SYMBOL pnp 272 160 R180
> SYMATTR InstName Q2
> SYMATTR Value 2N3906
> SYMBOL res 320 16 R0
> SYMATTR InstName R1
> SYMATTR Value 1.38
> SYMATTR SpiceLine pwr=1
> SYMBOL pnp -48 144 R180
> SYMATTR InstName Q3
> SYMATTR Value 2N3906
> SYMBOL pnp -16 144 M180
> SYMATTR InstName Q4
> SYMATTR Value 2N3906
> SYMBOL npn -176 224 R0
> SYMATTR InstName Q5
> SYMATTR Value 2N3904
> SYMBOL npn 112 224 M0
> SYMATTR InstName Q6
> SYMATTR Value 2N3904
> SYMBOL res 240 256 R90
> WINDOW 0 0 56 VBottom 0
> WINDOW 3 32 56 VTop 0
> SYMATTR InstName R2
> SYMATTR Value 10k
> SYMBOL res 144 400 R180
> WINDOW 0 36 76 Left 0
> WINDOW 3 36 40 Left 0
> SYMATTR InstName R3
> SYMATTR Value 22k
> SYMBOL res -48 336 R0
> SYMATTR InstName R4
> SYMATTR Value 1k
> SYMBOL cap 320 336 R0
> SYMATTR InstName C1
> SYMATTR Value 1
> SYMBOL voltage -224 320 R0
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> SYMATTR InstName V2
> SYMATTR Value 5.1
> SYMBOL pmos 288 256 M180
> SYMATTR InstName M1
> SYMATTR Value FDS4953
> TEXT 408 280 Left 0 !.ic V(a) = 6
> TEXT -370 458 Left 0 !.tran 10

On Mar 10, 10:04=A0am, mrdarr...@gmail.com wrote:
> On Mar 10, 9:57 am, "Bob Monsen" <rcmon...@gmail.com> wrote:
>
>
>
>
>
> > "Bob" <b...@mailinator.com> wrote in message
>
> >news:1dc6c3ed-94e3-4b00-aaf0-f1338f75f79e@m44g2000hsc.googlegroups.com...=

>
> > > On Mar 10, 6:07 am, "Bob Monsen" <rcmon...@gmail.com> wrote:
> > >> <mrdarr...@gmail.com> wrote in message
>
> > >>news:a8841939-ddff-4175-8be7-476b6a198445@s13g2000prd.googlegroups.com=
....
>
> > >> >I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
> > >> > toy electric car (the kind that a kid can ride). =A0The previous ba=
ttery
> > >> > didn't hold a charge when I bought the car.
>
> > >> > One reference from batteryuniversity.com mentioned something about
> > >> > 2.50V per cell for SLA batteries. =A0I'm assuming my battery has 3
> > >> > cells. =A0Another website mentions use of an L200 voltage regulatin=
g
> > >> > chip (http://www.myra-simon.com/bike/charger.html).
>
> > >> > I've got a 6VDC (nominal) wall wart that puts out just over 9V open=
-
> > >> > circuit.
>
> > >> > How should I charge it?
>
> > >> > Thanks,
>
> > >> > Michael
>
> > >> You can probably use your 6VDC wall wart. Unless it is a really hefty=

> > >> wart,
> > >> it'll probably droop considerably when subjected to the battery. It m=
ay
> > >> actually fail if the battery is discharged, since they often have
> > >> internal
> > >> fuses to prevent fires. So, use a 4.7 ohm 1W resistor in series with =
it
> > >> just
> > >> in case. If the resistor gets too hot to touch (which it won't) while=

> > >> charging, post again with specs for the wart.
>
> > >> Regards,
> > >> =A0Bob Monsen
>
> > > Bad idea, Michael the OP has stated that it produces 9V off load.
> > > The current drawn by the battery drops as it charges.
>
> > Do you know how much the current drops?
>
> Current dropped from 177 mA @6.42V to 140mA @ 6.63V about 90 minutes
> later. =A0After that I just took voltage measurements only.
>
> What will happen if I charge with my (underpowered?) wall-wart, just
> watching until voltage reaches 7.5V? =A0I'm in no particular hurry, and
> can monitor the voltage every hour if necessary, at least for now.
> I'm guessing the reason for the 500mA is for a faster charge? =A0Or is
> this necessary for the health of the SLA?
>
> Thanks for the circuit,
>
> MD
>
You seem to know what you're doing, monitoring the voltage and
current.
SLA's have a charging protocol that goes in three stages: bulk,
absorption and float. If the battery has discharged a substantial
amount of its capacity and you put it on to charge it will pull a lot
of current and draw down the voltage of the charger. It pulls down
the voltage of the charger either because the charger has a designed-
in current limit or because of the charger's output impedance -- for
example, your wall wart can only put out a certain amount of current
(it has an output impedance). All good and well, it means your
transfomer is small enough not to boil the battery right off the bat!
(Some manufacturers recommend initial charging current limit for small
SLA's around .3 C, or 1.8 amps for your battery).
Then as the battery takes on bulk charge, the voltage rises. With a
properly regulated charger, this plateau will be somewhere around 2.4
to 2.5 volts. For an SLA, 2.5 is not too high. This is the
"absorption" stage. The charger holds the voltage steady at the
setpoint. Gradually, the current drawn by the battery begins to
decline. When it reaches about .03 C (180 mA), the battery is
considered charged and a "smart charger" will drop the voltage to
float, about 2.2 or 2.3 volts per cell.
Your wall wart won't behave is such a precise and predictable way, but
it will work fine to charge your battery as long as you monitor it.
Such an unregulated charger only poses a danger to your battery if you
leave it on indefinitely, because the batttery will take on so much
charge that it will draw negligible current, causing your charger to
approach its open-circuit voltage, which is too high for the battery.
Just disconnect before it happens.

mrdarrett@gmail.com wrote:
> On Mar 9, 10:55 pm, ehsjr <eh...@bellatlantic.net> wrote:
>
>>mrdarr...@gmail.com wrote:
>>
>>>I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
>>>toy electric car (the kind that a kid can ride). The previous battery
>>>didn't hold a charge when I bought the car.
>>
>>>One reference from batteryuniversity.com mentioned something about
>>>2.50V per cell for SLA batteries. I'm assuming my battery has 3
>>>cells. Another website mentions use of an L200 voltage regulating
>>>chip (http://www.myra-simon.com/bike/charger.html).
>>
>>>I've got a 6VDC (nominal) wall wart that puts out just over 9V open-
>>>circuit.
>>
>>>How should I charge it?
>>
>>Per the manufacturer's recommendations.
>>But that's not what you wanted to hear,
>>so read below.
>>
>>
>>
>>>Thanks,
>>
>>>Michael
>>
>>Here is a way you can charge it:
>>Build a float charger. Set the float voltage to 7 volts.
>>Use a 9 or 12 volt DC wall wart (not your 6v wall wart)
>>The schematic is on the first page of the datasheethttp://cache.national.com/ds/LM/LM317.pdf?
>>
>>There are better ways to charge your battery, but this
>>way won't cook it and is simple to build.
>>
>>If you can't build, buy a charger recommended for
>>that battery.
>>
>>Ed
>
>
>
> Thanks! Looks simpler than the L200.
>
> Just wondering, where did you get the value of 7.00V?

From the same place you got the quote below! They
give a range and I used 7.00, which is within the range.
But read on for a little more detail. The smiley is because
we've (posters on the newsgroups) have been searching for
years for the answer I warn you (below) not to look for.

> Should I apply
> a brief charge at 7.50V to get maximum capacity?
>
> "At 2.37V, most lead-acid batteries start to gas, causing loss of
> electrolyte and possible temperature increases. The exceptions are
> small sealed lead acid batteries (SLA), which can be charged to 2.50V/
> cell without adverse side effect." http://www.batteryuniversity.com/partone-13.htm
>

Yes. But read the whole thing.
"Correct settings of the voltage limits are critical and range
from 2.30V to 2.45V. Setting the voltage limit is a compromise."

If you look above the part you quoted, you will see a table
showing advantages/disadvantages. The 7 volt figure was
chosen for maximum service life.

According to the site, you can apply a 7.5 volt charge for
2 hours, once every 6 months, provided the temperature is
below 86F during the 2 hours, AIRC.

Now here is a warning: "they" (meaning many folks who write
about batteries) _seem_ to play fast and loose with the numbers
and the recommendations. You will find small differences in what
is said, depending on where you read. There is no *exact* level
or procedure that is 100% applicable. As the battery university
says, any level (within the general parameters) is a compromize.
The way the battery is used, how deeply and rapidly discharged,
how rapidly charged and the charging procedure, and the ambient
temperature all play a part in it. Obviously, the battery
chemistry, construction and number of cells also play a part in
it. So the warning is, don't expect to find a one size fits all,
perfect answer to how to charge batteries.

You can spend a lot (relatively) and buy a 3 stage charger or
you can build something real simple, or go somewhere in between.

Ed

> MD
>

On Mar 9, 11:17 pm, mrdarr...@gmail.com wrote:
> I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
> toy electric car (the kind that a kid can ride). The previous battery
> didn't hold a charge when I bought the car.
>
> One reference from batteryuniversity.com mentioned something about
> 2.50V per cell for SLA batteries. I'm assuming my battery has 3
> cells. Another website mentions use of an L200 voltage regulating
> chip (http://www.myra-simon.com/bike/charger.html).
>
> I've got a 6VDC (nominal) wall wart that puts out just over 9V open-
> circuit.
>
> How should I charge it?
>
> Thanks,
>
> Michael

I've got a lot of 6V SLAs. I charge them on the cheapest 6V/12V
motorcycle battery charger that I could find at the local auto parts
store. Cost was about $15 each & charge at a rate of about 1A/hr. I
just hook 'em up overnight & they're ready in the morning. I've been
doing this for many years & never had any problem.

JM

On Sun, 09 Mar 2008 21:17:03 -0700, mrdarrett wrote:

> I bought a 6V, 6Ah battery from Home Depot to power my 3-year-old's
> toy electric car (the kind that a kid can ride). The previous battery
> didn't hold a charge when I bought the car.
>
> One reference from batteryuniversity.com mentioned something about
> 2.50V per cell for SLA batteries. I'm assuming my battery has 3
> cells. Another website mentions use of an L200 voltage regulating
> chip (http://www.myra-simon.com/bike/charger.html).
>
> I've got a 6VDC (nominal) wall wart that puts out just over 9V open-
> circuit.
>
> How should I charge it?

Put a voltmeter on it, and connect the wall wart directly to the
battery || voltmeter. Sit and watch it. When it reaches ~7.2 volts,
disconnect the wall wart, let the battery cool, check the
voltage, and if it's 6.6V or more, you're good to go.

Good Luck!
Rich