Using rechargeable AA on BOE BOT?

basicstampede

I think the manual says to NOT use the rechargeable AA batteries for BOE BOT.

Would it damage the servo motor?· Why?

allanlane5

The problem is, a rechargeable AA battery puts out 1.2 volts when fully charged, while an Alkaline battery puts out 1.5 volts. Thus, 4 x 1.5 volt batteries is 6 volts -- which works. 4x 1.2 volt batteries is 4.8 volts. The 'low-dropout regulator' the BOE uses needs a few tenths of a volt to regulate.

Bottom line -- rechargeables will cause the BS2 to 'brown-out' reset even though they're still almost fully charged.

Now, if you could figure out some neat way to put in a FIFTH rechargeable battery, 5 x 1.2 == 6 volts, and that would work great.

basicstampede

Thanks. So the problem is the BS2 browning out, not burning servo motor. Thanks for the explanation.

Zoot

This topic has come up many times -- some users pick up an extra single or double AA holder and wire it in series with the existing 4AA holder on the Boe-bot. This lets you use 5-6 1.2V rechargeables.

That said, I've been using 4 NiMh rechargeables on my Boe-bot, and I do not get brownouts -- the servos are not quite as quick, and running time is only about 45 minutes, but it seems to work (for me at least). But allanlane5 is right -- it's not really ideal voltage. What's probably happening is the Stamp is running OK at 4.6 volts or so, and since I don't have any other true TTL circuitry on the 'bot, I can get away with it, but it's not ideal.

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When the going gets weird, the weird turn pro. -- HST

basicstampede

OK. What about if I use 9V battery? Any concern for servo damage? Stamp should not complain, right?

Zoot

Do NOT let 9v go to the servos. If you want to use 9v in then set the jumper in between the servo headers on the BOE to "Vdd" rather than "Vin". When the jumper is in the "Vin" position, battery power goes directly to servos. This is appropriate for battery voltage of 6v or less. When the jumper is in the "Vdd" position, the servos will be supplied from the BOE's onboard 5v regulator.

The Stamp (as hooked up on the BOE) has it's own onboard 5v regulator, 9v is fine there.

That said, a 9v battery may not last all that long if it's running servos....

Remember that most servos like a voltage of < 7.2 v max, with 5v-6v probably being ideal for the best trade-off between speed and longevity of the servo.

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When the going gets weird, the weird turn pro. -- HST

jonduncan

I use rechargable energizer 250 mah they work fine