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grounding together different battery types — Parallax Forums

grounding together different battery types

AnnoyingAnnoying Posts: 50
edited 2010-05-24 22:35 in General Discussion
I am using a 6 V battery pack consisting of AA Ni-MH rechargeable batteries to power a servo and a rechargeable 9 V battery for the Basic Stamp. I have the grounds from these separate supplies soldered together (someone·told me to do this a·while ago)·and I was wondering if this is bad? If you are supposed to do this, I do not understand why. My 9 V battery loses charge and heats up, drops to 6.3 volts after a few minutes and I don't know if the connected grounds might be the problem. I have tried multiple fully charged 9 V batteries so I know the fault is not with the batteries themselves. I measured the resistance between the 5 V regulated voltage from the BS2 and ground, and it was 8 kohm--is this normal? why should there be a resistance here?
Thanks!

Comments

  • W9GFOW9GFO Posts: 4,010
    edited 2010-05-24 20:36
    In the case of a servo and a Basic Stamp like you have the Basic Stamp will send a signal to the servo using whatever power supply the Stamp is hooked up to. That signal needs to complete a circuit by going to ground somewhere. The only option it has is to use the same ground that the servo is using - which is also the same ground that the servo's power supply is using.

    So yes, you must have the grounds hooked together. They don't have to actually be hooked to each other but they must both connect to ground.

    If your 9 volt is being used up so quickly I would check your wiring to be sure that the servo is drawing from your 6 volt pack and not the 5v regulated output.

    Yes, there should be resistance as measured from the regulator to ground. Otherwise it would be a short circuit.

    Rich H

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    The Simple Servo Tester, a kit from Gadget Gangster.
  • W9GFOW9GFO Posts: 4,010
    edited 2010-05-24 22:35
    I missed the part about your 9 volt being of the rechargeable variety. They are typically only 7.2 volts, have high internal resistance (more of a voltage drop under load) and low capacity. I have not had very good experiences with them. They seem to go bad quickly. I would try a regular alkaline 9 volt battery just to see the difference.

    Rich H

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    The Simple Servo Tester, a kit from Gadget Gangster.
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