SparkFun Forums

[newbiebot]

Hi,
I have various PCBs on my robot each doing a function (I'm planning to design 1, as a mother board but still couldn't find time). When I connect them to the battery, I always see sparkles. Some questions:

1. Why we have sparkles there? (one PCB is my DIY Arduino, has a 7805 to step-down to +5, and the battery is 12v @ 7amp (acid) and I see those sparkles when connecting it, wondering about over-current in first second?)
2. What if we have this scenario:
a. suppose I have PCB-A and PCB-B which must have a ground connection
b. the A consumes +3v but B consumes +5v, and GND already is connected between them
c. I use alligators to connect both of them to the batter
d. once, starting to connect them to the battery I first connect + from the B and (say, by mistake) - from A
result: will 5v pass via A and is there possibility to hurt A? If so, what to do to avoid possibility of such a scenario please?

Thank you.

[Ross Robotics]

Hi,
I have various PCBs on my robot each doing a function (I'm planning to design 1, as a mother board but still couldn't find time). When I connect them to the battery, I always see sparkles. Some questions:

1. Why we have sparkles there? (one PCB is my DIY Arduino, has a 7805 to step-down to +5, and the battery is 12v @ 7amp (acid) and I see those sparkles when connecting it, wondering about over-current in first second?)

Do you have on-off switch? If you don't you need one. If you do, then there is some current leaking somehwere. The sparks happen when something is drawing current from the battery when connecting it.

2. What if we have this scenario:
a. suppose I have PCB-A and PCB-B which must have a ground connection
b. the A consumes +3v but B consumes +5v, and GND already is connected between them
c. I use alligators to connect both of them to the batter
d. once, starting to connect them to the battery I first connect + from the B and (say, by mistake) - from A
result: will 5v pass via A and is there possibility to hurt A? If so, what to do to avoid possibility of such a scenario please?

No, it shouldn't but I don't see any details on what you have connect or specs on those boards. A ground is just a reference for positive.

Thank you.[/quote]

[newbiebot]

Thank you for answer.

1. Could you please help me understand: how the on-off switch helps so that those sparks won't happen? I mean, what is electrical event happening underground, it is a mystery for me still.

2. I have motor controller board and micro controller board which as you mentioned, for reference have GND connected. I'm just looking for harmful effects that could cause by this GND reference connection. So as I understand, in "shorting" scenario a GND reference connection never could have a role right? Or you have any example case (for this configuration of motor controller and MCU board)?

[Ross Robotics]

Thank you for answer.

1. Could you please help me understand: how the on-off switch helps so that those sparks won't happen? I mean, what is electrical event happening underground, it is a mystery for me still.

Electricity only flows if you a power source and something that consumes that power. So since you are connecting a battery to something that immediately wants that power, you get sparks. Putting a switch in and having it in the off position, when you connect the battery, you won't get sparks since nothing is wanting power until you turn the switch on.

2. I have motor controller board and micro controller board which as you mentioned, for reference have GND connected. I'm just looking for harmful effects that could cause by this GND reference connection. So as I understand, in "shorting" scenario a GND reference connection never could have a role right? Or you have any example case (for this configuration of motor controller and MCU board)?

No, the GND reference won't cause any problems. Those boards should have caps and and other components to protect itself from spikes.

[newbiebot]

Thanks for details,

One new question comes:
Then adding switch will anyway let in sparks, if the only reason for sparks is the device immediately taking power in, right?

[Ross Robotics]

Correct. The sparks will create spikes on the positive rail, but those boards should have decoupling caps that should take care of it.

[newbiebot]

Thank you very much! I'd go learning more on decoupling caps now!