Power Distribution Block Grounding

[Karma]

We are planning on using 6 40AMP CIM motors, but the problem is that according to the wiring diagram we should be grounding the CIMs in the power distribution block. Also according to the wiring diagram (and common practice) we can only use the 4 ports that are on the opposite side of the battery port. Since we need to ground those 6 CIMs and our breaker panel I was wondering if we could use the other 7 ports on the power distribution block to ground with.
I wasn't able to post on the Q&A because I didn't have our teams account password. Feel free to post this on the Q&A if you can. Thanks for any help.

[Daniel367]

I think you can use the disto for a grounding post. thats what i did on my team's bot. Why would they have you ground everything direct when it is most likely that you will have more than 4 items to ground?

thats my two cents,
-Dan

[Mike Betts]

Originally Posted by Karma

We are planning on using 6 40AMP CIM motors, but the problem is that according to the wiring diagram we should be grounding the CIMs in the power distribution block. Also according to the wiring diagram (and common practice) we can only use the 4 ports that are on the opposite side of the battery port. Since we need to ground those 6 CIMs and our breaker panel I was wondering if we could use the other 7 ports on the power distribution block to ground with.
I wasn't able to post on the Q&A because I didn't have our teams account password. Feel free to post this on the Q&A if you can. Thanks for any help.

Karma,

There should be no problem in using all 7 positions on the block. Also, you should find that the block accepts 6AWG wire. Connecting 2 (or 3) 10 or 12 AWG wires into one "port" should not be a problem.

Regards,

Mike

[eugenebrooks]

Originally Posted by Mike Betts

Karma,

There should be no problem in using all 7 positions on the block. Also, you should find that the block accepts 6AWG wire. Connecting 2 (or 3) 10 or 12 AWG wires into one "port" should not be a problem.

Regards,

Mike

From the battery power terminal strip documentation:

Maximum Wire Size and Max Quantity Allowed per 1492-J16xx Terminal

1 - #6 or
1 - #8 or
2 - #10 or
3 - #12 or
4 - #14 or
4 - #16

Don't mess up, the technical inspectors will no doubt be checking.

Also, you want to arrange the wiring to minimize the amount
of current that a given leg of the "jumper" will be carrying.

Have fun,
Eugene

[Ryank]

Originally Posted by eugenebrooks

From the battery power terminal strip documentation:

Maximum Wire Size and Max Quantity Allowed per 1492-J16xx Terminal

1 - #6 or
1 - #8 or
2 - #10 or
3 - #12 or
4 - #14 or
4 - #16

Don't mess up, the technical inspectors will no doubt be checking.

Also, you want to arrange the wiring to minimize the amount
of current that a given leg of the "jumper" will be carrying.

Have fun,
Eugene

Can you still do this or have the rules changed? We have also been wanting to consolidate out victor returns without using both sides of the block.

[DonRotolo]

That's not a rule, it's the manufacturer's recommendation (which, I have to mention, really really should be followed. Not doing so is poor engineering practice, and you might get dinged at inspection for it).

Don

[Bleak]

Originally Posted by Mike Betts

Karma,

There should be no problem in using all 7 positions on the block. Also, you should find that the block accepts 6AWG wire. Connecting 2 (or 3) 10 or 12 AWG wires into one "port" should not be a problem.

would it not be easier to wire the negatives from the victors to the excess negative terminals on the smaller fuse box.. its still creates the same circuit and the fuse block only has 6 positive terminals so why not put them to use

[ebarker]

Originally Posted by Bleak

would it not be easier to wire the negatives from the victors to the excess negative terminals on the smaller fuse box.. its still creates the same circuit and the fuse block only has 6 positive terminals so why not put them to use

Watch out. Wire the motor +/- leads directly to the victor output terminals. Do not wire it any other way.

You have to understand how the victors work. It can apply progressively variable voltage to the motor for forward speed, or reverse the terminals progressively for reverse speed.

It is the reversal that will get you in a bucket of troubles if you try to move the 'ground' off the victor onto a block.

[Al Skierkiewicz]

Originally Posted by Bleak

would it not be easier to wire the negatives from the victors to the excess negative terminals on the smaller fuse box.. its still creates the same circuit and the fuse block only has 6 positive terminals so why not put them to use

Although the Q&A has allowed it, I do not recommend this method for high current loads. The critical component in your robot is the RC, when it fails everything fails. The RC has a critical dropout voltage of 8 volts. When the input to the RC drops below that voltage, the RC goes into standby and disables all outputs during the brownout. When you sum currents in a wire the voltage drop across the wire increases. Even if you are using #6 AWG, a 1 foot long piece will drop 0.1 volts for every 200 amps. If you are running 4 Chalupa motor drive and they all stall (because you drove into the player station) that is 4 x 133 amps=532 amps. Add that to the series resistance of the battery and all of the main wiring and you now have a condition where the RC will drop out. By taking the high current returns back to the Distro block you have eliminated a few precious tenths of a volt that might keep you running continuous.

[DonRotolo]

Originally Posted by Karma

We are planning on using 6 40AMP CIM motors, but the problem is that according to the wiring diagram we should be grounding the CIMs in the power distribution block.

Actually, you are connecting the fuse panel to the block, not the victors or the motors...

I hope that you are not going to use six of the same motor, because

<R45> Items specifically permitted on 2007 FRC ROBOTS include:
<snip> One or two additional 2-1/2” CIM motors (part #FR801-001) in addition to those provided in the Kit Of Parts. This means that up to four, and no more, 2-1/2” CIM motors can be used on the ROBOT.

One additional 3” CIM “Minibike” motor (part #FR801-005). This means that up to two, and no more, 3” CIM “Minibike” motors can be used on the ROBOT.
<snip>

Now, four of one kind and two of the other would be just fine.

You would need two of the golden "Maxi" fuse panels in the case of 2 + 4 big motors.


There should be no concerns with using the SEVEN total available connection points on each part (red/black) of the power distribution block. Although one often sees installations where the inputs are on one side and the outputs on the other, that all changes when you install and use the yellow bus bar jumpers - that is exactly what they are made for!

Also, remember that in this case the term "grounding" is incorrect - when your motors are running in reverse, the black wire has a positive polarity. Victors reverse!

Don

[Al Skierkiewicz]

Originally Posted by Don Rotolo

Actually, you are connecting the fuse panel to the block, not the victors or the motors...

Don

Don,
I think he is planning on using the black terminals on the distro block for the negative returns from the high current Victors per the updated electrical drawing and Tips and Guidelines. This is the preferred method for the high current returns.
As Mike and Gene have pointed out, once the jumper is in place, terminals on both sides of the block may be used for these connections.
Has anybody been able to find any data on max current spec for the jumper? I have searched a few manufacturers and have found no spec for this critical part.

[Mike Betts]

Originally Posted by Al Skierkiewicz

... Has anybody been able to find any data on max current spec for the jumper? I have searched a few manufacturers and have found no spec for this critical part.

Al,

The max allowable current is 85A (reference 1492-J16).

Note also that the nominal acceptable torque for screw terminals is 3 N*m.

Mike

[MrForbes]

85A is the current rating for the whole block system, might we assume the jumper is the weakest link?

[Al Skierkiewicz]

I have done everything but back engineer the jumper. I am guessing that the jumper can handle far less the 200-300 amp intermittant current demands. I would like to hear from teams that are practicing as to the temp of the jumpers on their robot. Please PM me with details as they come about.

[Nitroxextreme]

Im not sure on the legality of this (actually tryin to find the answer myself)....
Couldnt you just run a ground from the distribution block to a smaller circuit board...the circuit boards have plenty of extra ground points on them.

This would also cut down on the size of the power distribution block.