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Universal Power Adapter with a Boe-Bot?? — Parallax Forums

Universal Power Adapter with a Boe-Bot??

PorkinsPorkins Posts: 3
edited 2010-02-15 19:04 in Robotics
I have an old Radioshack (Archer) universal power adapter that I use a lot. Can I use it with the Boe-Bot board? I got it last year, so it is the newer version with the BS2 and the included USB adapter. What would the proper setting be? 6V? Should the tip be negative? I don't want to fry my board. Thanks!

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2010-02-12 18:36
    Any setting from 6V to 9V should work. 6V or 7.5V would be best. The tip must be positive or it won't work. If you connect it backwards, the BOE regulator may save things, but no guarantees. The main question for you is "what's the current capacity of the power adapter?" If your BoeBot draws too much current, the power adapter won't work. Servos can draw up to 1A each when under high mechanical load. Under light load, we're talking about maybe 0.25A each. The BOE itself will draw much less. Parallax recommends a 7.5V 1A adapter.
  • ScopeScope Posts: 417
    edited 2010-02-12 19:45
    Welcome Porkins!

    Tell us about yourself & your 'bots.
  • PorkinsPorkins Posts: 3
    edited 2010-02-15 18:47
    It is actually 300mAh. So I can use it, but I might need a 1A version once I start using the servos.

    I also had a general question I thought of while pondering power and batteries. I know you can connect batteries in parallel to maintain the same voltage while increasing capacity. So 4 AA batteries connected in parallel yields 1.5V, and should last as long as if you were using a single AA until discharged·and change it out 3 more times. Can I take a bunch of AA's that are mostly discharged, and hook them up in parallel to squeeze more power out of them. I often have to recycle batteries that still have juice in them, but not enough for whatever device they were powering. It would be nice to connect a bunch of the almost dead ones in parallel to power a breadboard project or 2. I always prefer less waste. And rechargeable batteries seem to always be a big no-no for projects like these. I don't really no why either...
  • Mike GreenMike Green Posts: 23,101
    edited 2010-02-15 19:04
    The problem with connecting batteries in parallel when they're not in an identical state (or nearly identical) is that the battery voltage drops as the battery discharges and the "better" batteries with a higher voltage will tend to discharge through the "weaker" batteries with a lower voltage until they're all equally discharged. You can get around this by connecting a diode in series with each battery to prevent one battery from discharging through another, but the diodes take a voltage drop of around 0.7V which doesn't help much if your battery voltage is only 1.5V at best. A better way to get the most from your batteries would be to put them in series to get a 12V to 15V output voltage and use a switching (buck) regulator to get the 5V or 3.3V regulated voltage that you want. You could check the individual cells from time to time and replace them as their voltage drops below 1V.
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