Absolute MAX Voltage for BOE-Bot
Robert Hodgen
Posts: 8
I know that on the BOE it says 9-6VDC, but I was wondering what the absolute maximum voltage I could supply the BOE-Bot before it fried. I would like to know so I can find another battery pack for a project I'm working on. There are some high capicity RC car batties out there (7.2V 2000mAH and another pack at 9.6V with 1600mAH). I also noticed that the BOE-Bot seems to reset when the voltage drops, exactly what point does it do that at? Would a 9.6V battery fry the BOE and BS2?
Comments
·· Your question depends on how the servos are powered.· If the servos are powered from Vdd, you can safely run 12V into the on-board regulator.· If the servos are being powered from Vin, you shouldn't exceed the 6 volts that the battery pack supplies, as it will wear out and/or damage·the servos.
·· As for brownout, that happens at around 4.3 volts.· But the stamp may not come back until 4.6 volts is reached.· This can happen more frequently if you're using rechargeable batteries (Not recommended) because they run at a lower voltage than alkaline batteries.··As for your 9.6V battery pack, use the BOE on-board voltage regulator and you should be fine.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
I have it set to Vdd with a 9V powering it, but the BOE-Bot will burn through a brand new 9V in 30min (with the servos running ~ 90% of the time). Could there be something wrong with the voltage regulator on my BOE?
I have the 2 servos that came with the BOE-Bot, the piezo-speaker that came with the BOE-Bot (but it only sound for a sec. when it resets) the Ping))), and 2 red LEDs (that came with the BOE-Bot with 220ohm resistor). Does reprogramming the BOE-Bot (I do about every min for fine tuning the program) take a lot of power from the 9V on the BOE-Bot? I can’t think of any other explanation for this excessive power draw.
Thanks,
Robert
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Jon Williams
Applications Engineer, Parallax
Dallas, TX· USA
That's why the BOEBot from Parallax uses 4 AA batteries to power its two running servos -- they last longer than a 9-volt would.
What Jon is saying is that if you power your servo's directly from Vin at 9-volts (bypassing the regulator, in other words) then they tend to melt. Max voltage for a servo is about 7.5 volts -- really they expect 5 volts to 6 volts as their 'normal' operating range.
·· Based on replies, as well as your original post, let's make sure we're on the same wavelength...Are you using the 9.6V pack you specified above, or a standard 9 Volt transistor battery?·· The 9V transistor battery will have insufficient current to power a BOE-Bot for any length of time, however the 9.6V R/C Battery Pack you were asking about should.
·· Now 2 factors can affect the performance of your batteries...One, how they're charged and discharged...And this includes charging them with the wrong type of charger (For example NiMH batteries in a NiCd charger).· the second factor is heat (Probably not a factor here).
·· Which battery are you having the problem with?· You've already established that you're using Vdd to poewr the servos.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
No, there is no way that should happen (unless you're using 30 servos). But perhaps you've now replaced a 9-volt transistor battery with the 9.6 volt RC car battery, so you have longer life now.
When you say your regulator generates +/- 7 volts, is it REALLY generating -7 volts? I would assume not, since that's 14 volts total peak to peak, which is hard to get out of a 9-volt battery. So I assume then that your regulator gives you 7-volts from a 9.6 volt source. And the 7-volts then drives your servos.
If all that is true, then you are overdriving your servo's slightly -- that's assuming the servos are rated 5 volts to 6 volts. The 7 volt overdrive shouldn't damage any of the electronics in the servo -- but it may reduce the life of the electric motor inside the servo. Only you can decide if this is a problem.
If the servo's are in fact designed for use with 7.2 volt RC car batteries, then you are doing no damage at all, and in fact have quite a clever implementation.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
He's going to be disappating power anyway -- it actually makes more sense to disappate (2-volts * <Servo_Current> + 4-volts * BS2_current) than to disappate 4-volts * (BS2 + Servo_Current).
Since the Servo_Current is MUCH more than the BS2, his approach makes lots of sense -- basically wastes half the power of the 5-volt regulator by itself.
·· The idea was to try and eliminate an unknown (The extra regulator) from the circuit to see what effect it has.· Yes he gets more voltage to the servos currently, but 7 volts is more than they are normally rated at anyway.· No harm in simply trying it to see how quickly the batteries fade in the suggested configuration.· With what's happening, they could even fade quicker for all we know.· He needs to isolate the problem.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
So, what do you say Robert? The RC battery doesn't die as fast, surely?
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Chris Savage
Parallax Tech Support
csavage@parallax.com
I was using a regular 9V battery like you could find anywere. The application I'm using the BOE-Bot for requires the servos to constantly move one way or another (chaning really fast).
I switch to the 9.6V RC car battery and it hasn't quit on me yet (I'v been using it for 2 days off and on). Another reason why I went with my voltage regulator was I originally built it for use with a RC car battery, I just had to get it into the BOE (I think it was easier using my regulator than having to mess around with the battery leads).
·· So what you're saying is that the battery that was being depleted was a regular 9V battery?· Well most of us at Tech Support got the impression the 9.6V R/C Battery was dying prematurely.· Okay, we now see the light.
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Chris Savage
Parallax Tech Support
csavage@parallax.com