I'd like to make one battery box for the bot I'm working on, that will simultaneously supply 3V, 6V, 9V, and 12V. The first version of this box will get its juice from eight D cells.What I don't understand is: how can I wire this up so that it has terminals at those four different voltages, but no matter how loads are applied to them in any combination, the eight batteries drain evenly? (I want to avoid the situation where I need to change different batteries at different times, just because that would be a nuisance.)My guess is that to do this, I need to wire all eight D-cells in series, and then from this 12V supply, hang three DC-DC voltage converters in parallel for the 3V, 6V, and 9V outputs. (And the 12V output goes directly out.) Does this make you experienced roboticists recoil in horror for some reason? Is there a more elegant solution?Thanks,- Joe

The 3 DC-DC converters approach is the best way to get the batteries to drain evenly. As for recoiling in horror, it depends on what you are going to hang on the different outputs. If motors are on any of them, it would make me pretty nervous. Motors are electrically noisy and can have really high transient loads. The transient loads can cause voltage dips that cause problems for the other regulators. The high frequency noise will go right through switching regulators and cause trouble, especially with logic. With good filtering and good luck, you can do this but be prepared to spend some time messing with it.Proper grounding design will also be needed. Remember that as much current and voltage drop occurs on the ground path as the +V paths. Star or single-point grounding with the common point as close to the battery negative or bulk filtering capacitors as possible will help.Good Luck,Bob

That's not hard to do. You can buy "Battery Eliminator Circuits",or BECs, from any of the R/C hobbyist suppliers. They take in a noisy7 to 20VDC and output a clean 5VDC. Here are some commercial units: regulator with big heat sink for $9, switching regulatorfor $47. Choose based on how important battery life is in yourapplication. How much current do you need? John Nagle

battery box supplying 4 different voltages?

Apr 20, 2007 21 Replies

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John Nagle 19 years ago

That's not hard to do. You can buy "Battery Eliminator Circuits", or BECs, from any of the R/C hobbyist suppliers. They take in a noisy

7 to 20VDC and output a clean 5VDC.

Here are some commercial units:

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Linear regulator with big heat sink for $9, switching regulator for $47. Choose based on how important battery life is in your application.

How much current do you need?

John Nagle

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Jon Hylands 19 years ago

The only issue with 9 volt batteries is they have a pathetically small capacity - typically on the order of 150 mAh.

For $15 you can buy a nice switching regulator that is a plug-in replacement for a 7805...

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Later, Jon

-------------------------------------------------------------- Jon Hylands snipped-for-privacy@huv.com

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Project: Micro Raptor (Small Biped Velociraptor Robot)

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