Charging batteries

[Alan]

Hi all, I have got a few different battery types that all need charging.

There are different voltages ranging from 3.5 up to 9 volts, they are used
to drive small electric ride on toys and similar usage.

They are all sealed dry batteries.

My question is this, do I need to buy a special multi voltage , variable
amperage charger OR can I use a Walwart type power supply that allows me to
lower and raise the voltage from 12 all the way down to 3 volts.... but the
amps remain the same.

I understand about trickle charging batteries as I worked as a mechanic for
a few years but my knowledge is limited.

Lastly is there a fundamental difference between trickle charging and
Walwart style charging?

I am just worried that I will roast all the batteries and end up having to
buy them all again.

Regards Alan

PS I would like a set up using crocodile clips rather than a plug in affair,
as all the batteries are different shapes.

 

[Robert Baer]

Hi all, I have got a few different battery types that all need charging.

There are different voltages ranging from 3.5 up to 9 volts, they are used
to drive small electric ride on toys and similar usage.

They are all sealed dry batteries.

My question is this, do I need to buy a special multi voltage , variable
amperage charger OR can I use a Walwart type power supply that allows me to
lower and raise the voltage from 12 all the way down to 3 volts.... but the
amps remain the same.

I understand about trickle charging batteries as I worked as a mechanic for
a few years but my knowledge is limited.

Lastly is there a fundamental difference between trickle charging and
Walwart style charging?

I am just worried that I will roast all the batteries and end up having to
buy them all again.

Regards Alan

PS I would like a set up using crocodile clips rather than a plug in affair,
as all the batteries are different shapes.

"Dry" batteries is a term normally used for the origonal carbon-zinc
batteries, and are *NOT* rechargeable.
And alkaline batteries are also *NOT* rechargeable (except for the
Renewal(TM) type).
I do not think that crocodile clips will fit.....

 

[mike]

Hi all, I have got a few different battery types that all need charging.

There are different voltages ranging from 3.5 up to 9 volts, they are used
to drive small electric ride on toys and similar usage.

They are all sealed dry batteries.

My question is this, do I need to buy a special multi voltage , variable
amperage charger OR can I use a Walwart type power supply that allows me to
lower and raise the voltage from 12 all the way down to 3 volts.... but the
amps remain the same.

I understand about trickle charging batteries as I worked as a mechanic for
a few years but my knowledge is limited.

Lastly is there a fundamental difference between trickle charging and
Walwart style charging?

I am just worried that I will roast all the batteries and end up having to
buy them all again.

Regards Alan

PS I would like a set up using crocodile clips rather than a plug in affair,
as all the batteries are different shapes.

Need to know a LOT more about the batteries.
If they're nicad or nimh, you can probably get away with charging at
C/10. Use a high voltage supply in series with an appropriate light
bulb. Select the light bulb for approximately what you need.
Won't be perfect, but works.
mike

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[Robert Baer]

Need to know a LOT more about the batteries.
If they're nicad or nimh, you can probably get away with charging at
C/10. Use a high voltage supply in series with an appropriate light
bulb. Select the light bulb for approximately what you need.
Won't be perfect, but works.
mike

NOT a good idea: 1) too much voltage can cause over-charging and
might cause damage, and 2) light bulbs have a fairly low resistance,
which could result in too much current.
The open-circuit voltage of the supply used for charging should be
set to the highest voltage that the particular cell chemistry supports:
NiCd runs from 1.20V to 1.35V; Li-ion runs from 4.1V to 4.2V; NiMh is
about 1.2V.
Either pick a resistor for C/10 rate based on "discharged" cell
voltage near 80 percent of charged rating, or make a "constant current"
limiter with a JFET and resistor.
BEST, is to use a charger made for the cells; they are made to
optimize charging time and protectionof the cells.

 

[mike]

NOT a good idea: 1) too much voltage can cause over-charging and might
cause damage, and 2) light bulbs have a fairly low resistance, which
could result in too much current.

What you say is partially correct. You can certainly choose a voltage
and light bulb that overcharges the batteries. The objective is NOT to
do that.
A light bulb makes a perfectly good positive TC resistor and a current
source that is rather invariant over a reasonable voltage range,
depending on the source voltage and bulb selection. If you select the
voltage and light bulb correctly, it works just fine. It's plenty good
for battery charging at approximately C/10 for nicads and NiMH.
I am partial to #382 bulbs because they're small. YOu get 35ma give or
take charging current. Parallel as many as you need.

DO NOT GUESS. MEASURE THE CHARGE CURRENT.

If you have wildly varying charge current requiremets, you can put the
bulbs inside the device and the external voltage source.
mike

The open-circuit voltage of the supply used for charging should be set
to the highest voltage that the particular cell chemistry supports: NiCd
runs from 1.20V to 1.35V; Li-ion runs from 4.1V to 4.2V; NiMh is about
1.2V.
Either pick a resistor for C/10 rate based on "discharged" cell
voltage near 80 percent of charged rating, or make a "constant current"
limiter with a JFET and resistor.
BEST, is to use a charger made for the cells; they are made to
optimize charging time and protectionof the cells.

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