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Charging batteries

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.

Reply to
Alan
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"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.....

Reply to
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

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Reply to
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.

Reply to
Robert Baer

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

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Reply to
mike

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