New Power Distribution/ Fuse Pannel Problem

[mole]

Hey everyone, im from team 772 in Canada,

we have our robot fully wired and then we were testing the voltage from each port to make sure that power was flowing properly; but when we remove a fuse the voltage that is measured between the main (input from battery) and the terminal output is 12V. This is concerning because this defeats the purpose of a fuse being placed on the board. If it is a faulty board, we would like to know asap.

Thanks for the help

Team 772

[Vikesrock]

Originally Posted by mole

Hey everyone, im from team 772 in Canada,

we have our robot fully wired and then we were testing the voltage from each port to make sure that power was flowing properly; but when we remove a fuse the voltage that is measured between the main (input from battery) and the terminal output is 12V. This is concerning because this defeats the purpose of a fuse being placed on the board. If it is a faulty board, we would like to know asap.

Thanks for the help

Team 772

You may need to describe the measurement you are taking in more detail to get a certain answer.

If you are measuring from the Positive battery terminal the voltage difference is 12V. It may show as +12 or -12 depending on your meter and which lead you put where. In this case the terminal output is ~12V below the battery terminal.

If you were measuring from the Negative terminal of the battery it is possible that your PD board is faulty. I would double check that the fuse you removed corresponds to the terminal you are measuring and then contact FIRST to see about getting it repaired/replaced.

[mole]

Perhaps I can clairfy.

The battery voltage is 12 volts from the mains, going into the PD board. When you put the fuse in, the output from the terminal is 12 volts. However, when the fuse is removed, the output is STILL 12 volts.

It sounds to me like the board may indeed be faulty, as the output should be ZERO (I would think) after the fuse is removed. Otherwise, what is the purpose of a fuse if current/voltage is still allowed to pass through.

[Vikesrock]

Originally Posted by mole

Perhaps I can clairfy.

The battery voltage is 12 volts from the mains, going into the PD board. When you put the fuse in, the output from the terminal is 12 volts. However, when the fuse is removed, the output is STILL 12 volts.

It sounds to me like the board may indeed be faulty, as the output should be ZERO (I would think) after the fuse is removed. Otherwise, what is the purpose of a fuse if current/voltage is still allowed to pass through.

As Eric posted above you there is an internal connection between the battery input and the terminal outputs that bypasses the fuse through about 100kOhms of resistance.

This means that with no load, no current flows through that 100kOhms and you see the battery voltage at the output terminal even with no fuse in place. If a load is attached a very small amount of current will flow through this 100kOhms and the load and the 12V will be dropped across the 100kOhms (assuming the load resistance is << 100kOhms)

PS. Anyone can create an account on the FIRST Forums. Click the "Register" button and fill out the forms.

[DonRotolo]

Originally Posted by mole

However, when the fuse is removed, the output is STILL 12 volts.

Repeat that measurement with a load on the output terminal (any 12 volt load, like an automotive light bulb or small motor, or perhaps a 1k Ohm resistor). You will see the voltage is (nearly) zero with any load.

The proper measurement is from the output terminal to the panel's negative terminal.

[MrForbes]

Is there a load connected to the power panel when you are measuring it? or did you disconnect the wires?

I would expect to see a 12v potential across the fuse holder if the load and battery are connected, and the fuse is removed.

[EricVanWyk]

Mole -

The appropriate place for this post is http://forums.usfirst.org/forumdisplay.php?f=1004 , formerly http://forums.usfirst.org/forumdisplay.php?f=745 . Please post / search these forums first - it makes it much easier for us tech support folk to monitor things.

There is ~100kOhms between the battery input shank and the output WAGO terminals. When any load is applied, this voltage will vanish. This is an artifact of the (currently defunct) blown breaker indicator circuit. It will not affect normal operation of a robot.

I could have sworn I updated section 3.2.5 to indicate this, but it must not have made it in the most recent revision. Thanks for the catch!

Long story short, your board is good to go.

[mole]

Where do we find the login information for the FIRST Fourms. I thought this infomation was avaliable under TIMS, however, it dosn't appear to be there (anymore).