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battery works, DC power doesn't?

I've got a piece of electronics on my bench that is normally powered by

3 C batteries, wired in series and thus producing about 4.5 Volts. I wanted to power this device with a bench power supply just so I don't drain the batteries while I'm experimenting with it for hours.

But it won't work with the DC power supply -- it's the weirdest thing. With the batteries, the device (a child's toy) chatters away at full power, but if I disconnect the batteries and wire in the DC PS in their place, it runs veeeeery slowly, if at all.

I feel like it's the 18th century and I'm missing the right amount of "essence" or "ether" or "humours" or something :)

I've checked and double checked the voltage including polarity. I've tried running at depressed voltage (e.g. 3-4V). The power supply should be able to provide far more current than the batteries, and at a low output impedance. I have two power supplies, one a fancy bench model and the other a wall wart, and it does the same thing with both. Only with the magic batteries will it work properly.

Perhaps related, in the device at the + side of the battery back is an orange disc which appears to be a ceramic capacitor wired in SERIES, but I don't see how it could be given that this is a DC device. I've been attaching the DC PS on the battery side of this disc, in order to provide DC power to the circuit just like the batteries. I don't know if this is relevant.

Any ideas?

Reply to
chris-google
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What is the actual voltage from the DC power supply across the + and - battery terminals when you attempt to use the supply and have the toy activated? My guess is that the batteries are putting out more current than the supply is capable of delivering or the gauge of wire you are using is too small. In either case the voltage at the battery terminals should be well under the 4.5V nominal and is likely insufficient for the application. The solution here is a larger capacity supply and/or heavier gauge wire.

Another possibility is that the DC supply you are using may have high AC ripple thereby reducing the effective voltage. In this case you can add a large filter capacitor and see if this improves the performance.

Bob

Reply to
Bob Shuman

I'll second what Bob said, use a meter and make sure the correct voltage is actually making it to the battery terminals on the device.

Another idea, this is unusual but not unheard of: make sure the device only has one (+) and one (-) connection to the batteries. Some things (R/C cars, trucks, etc. commonly) have power connections

*in between* the batteries to effectively provide a bipolar or mutiple-voltage supply.

Eric Law

Reply to
EL

On 5 Apr 2005 10:02:48 -0700, snipped-for-privacy@pobox.com put finger to keyboard and composed:

The disc is probably a "polyswitch" PTC.

formatting link

It provides automatically resettable protection from overloads.

- Franc Zabkar

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Reply to
Franc Zabkar

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