simple DC electrical question, I hope

[kcbarnes]

All you need to do is put a dc ammeter in series with the battery and toy to find out the amp/milliamp draw is and then go to ripshack and get an ac to dc converter rated as large or larger than your toy draws.

 

[TWINKLE_TOES]

Gary,

A couple of items in your post caught my eye. The first <font color=blue>10amps reading from lining 4C cells </font color=blue> The second <font color=blue>paying(out the snoot) for Ni-Cads.</font color=blue>
Ten amps short circuit current is pretty high for an alkaline battery. Paying out the snoot for Ni-Cads is a little strange for the toy application which doesn't appear to have a charger. The 10 amp reading and low capacity is consistent with Ni-Cad batteries. Alkaline batteries of the same size will have 3-4 times the capacity of the equivalent size NiCad. Are you perhaps using NiCad batteries as throw away when dead?

<font color=blue>some were nearly 20% off the voltage information </font color=blue> This is not unusual.
Most DC wall transformers are transformer/rectifier/filter capacitor configuration (no voltage regulation in most) and the open circuit (no load) voltage will be up to 40% higher than the voltage at rated current. A 9 volt DC rated wall transformer @ 500mA would read ~ 12.6 V with no load. At a load of 500mA the voltage should be 9 volts. Tell me a little about the toy. I suspect it has a little motor that runs infrequently (200-300ma) something smart that tells the little motor when to run (10's of micro amps) a whistle/bell/light flashes intermittently(a few milliamps). For this kind of operation you should get good life from alkaline cells. Have your hopes been dashed for the simple DC electrical question? Nothing on this board is simple, most, after they log off, go to bed and red line the bible./w3tcompact/icons/wink.gif
Al

 

[RMulkey]

Gary,

Finally I can use something I learnt (sic) in EE school.

Your measurement method is actually measuring the resistance of the meter you are using to make the measurements. Anyway,to get an accurate mesurement of the current the toy is consuming, this measurement method will work:

1) Connect the original batteries using WIRES to the toy power connections.

2) Cut one of the battery wires and insert a LOW resistance resistor (100_Ohm). Measure the resistance of the resistor by itself with your Ohm Meter (before you hook it up).

3) Hook up the toy and start it up.

4) Measure the VOLTAGE drop across the resistor using a your volt Meter.

5) Using the formula: Vdrop=I*R, I=V/R, where
Vdrop= Measured Voltage drop across the resistor (in Volts)
R = the Measured value of the Resistor, (Ohms)
I = the Measured current in the wire. (in Amps, not milli or micro)

6) The key to success is to not use too high a value of resistance that the toy does not run and always use the measured voltage and resistance values. If the toy does not run, lower the resistor value (like 10_Ohms).

Hope this helps,
-Roger