Problems With The Power Distribution Block

[Brandon Holley]

At the winter warzone we had all kinds of problems with the block arc-ing and causing our victors to short out. It cost us the quarterfinals there.

[seanl]

the block is not totally useless. it seves a good purpose, it just has a few "bugs". i agree that it could be a bit lighter, but i dont really mind it. the only problem we had with it was that the main ground wire got pulled out by a divetrain person accidentally tugging on it, which was easily fixed with a screwdriver. overall i dont really care about the block. i just hope FIRST fixes the bugs in the block if they are going to implement it in next years game.

For other purposes, the block would be amazing. For example, I plan to buy one for a project I'll be doing in my room. It'll be great for that, as I need breaker panels all over the place. However, on a vibrating, moving, slamming robot with only two breaker panels, it's practically useless.

We never had any problems (yet) with the block. One idea we had to meet the rules was to drill holes straight through the block from wire point to wire point, and run the normal wires through the holes. However, we ended up deciding to just wire the thing up in the required manner.

[Al Skierkiewicz]

Originally Posted by Brandon Holley

At the winter warzone we had all kinds of problems with the block arc-ing and causing our victors to short out. It cost us the quarterfinals there.

At 12 volts these blocks cannot arc. Intermittant wiring will cause heating and intermittant electrical power can cause problems with any electronics. All termination devices at normal robot currents will have these problems including the interface to the battery terminals.
The Rockwell blocks use quasi-parallel clamps to secure the wires. If a wire is not stripped back enough or if the wire is not inserted far enough, the clamp will squeeze/push the wire out of the terminal. If you take a look at the picture (thank you to the Rockwell site) you will see that a wire that is not inserted to the end of the clamp will loosen and fall out. The specification from the Rockwell Catalog for this series (1492-J16) is "Wire Strip Length 0.63 in (16 mm)". The molded-in wire stop correctly positions the wire in the jaws for best termination. Additionally, stranded wire will be forced to change cross section as the clamp pushes down on the wire. This may force teams to check the tightness from time to time. (robot movement will shake wires and make this worse) For these reasons, Loctite is a bad idea on these blocks.
Some folks have suggested the use of ferrules over the wire. Debate is still raging but i have some Panduit samples coming in the next week or so to look over. stand by...

[Danny Diaz]

Originally Posted by Pavan

At Bayou, we checked our wires on and we ended up putting in some Loctite. I was against it, but after a mentor showed me how loose some of the wires were I said anything was better than nothing, and so we gave it a go. Well, none of the wires popped out to my knowledge and the drive team didn't have to tighten them after we put in the Loctite so I was satisfied. It works...but I'll get to do a better electrical inspection come Thursday at Lone Star and be even more sure!

I'll see about getting you a, "But it works on our robot!" sticker. We've had mountains of problems with wires coming loose during the build season, so we've instituted wire tightening/inspection specifically for the block in our pre and post match checklist.

-Danny

[Hieb]

I know that some manufacturers of similar power distribution blocks (not sure about Rockwell--I haven't spent enough time looking) have spring loaded connectors that may be more suitable for our applications. At least that way the vibration wouldn't loosen the screws and let the wires fall out.

[MrForbes]

The spec sheet for the terminal blocks suggests tightening the screws that hold the wires in, to 17 to 35 lb-in torque. That's a lot of torque to apply with a slot screwdriver! Maybe what's needed is to make sure someone with strong hands tightens the connections.

Also double check the wires are stripped the minimum 5/8" length.

Having a checklist to double check the tightness of the screws before competition, is a good idea.

[Al Skierkiewicz]

Originally Posted by Hieb

I know that some manufacturers of similar power distribution blocks (not sure about Rockwell--I haven't spent enough time looking) have spring loaded connectors that may be more suitable for our applications. At least that way the vibration wouldn't loosen the screws and let the wires fall out.

Rockwell also has a line of spring loaded blocks to be used only for solid wire. Never use solid wire on moving devices, they will fatique and fail.

[Alan Anderson]

Originally Posted by Hieb

I know that some manufacturers of similar power distribution blocks (not sure about Rockwell--I haven't spent enough time looking) have spring loaded connectors that may be more suitable for our applications. At least that way the vibration wouldn't loosen the screws and let the wires fall out.

The problem isn't usually with the screws themselves loosening. It's almost always because the stranded copper wire deforms and is no longer held tightly. This can happen not only with the Rockwell parts, but with the 40-amp fuse block as well.

Make tightening the electrical connections part of your standard preventive maintenance and pre-match checks, just like keeping proper chain tension or making sure the pneumatic release valve is closed.

[eugenebrooks]

I am not enamored with the rockwell power distribution block.
The positive end of the block is completely redundant, one can
simply route the positive wire through the max-fuse block to
the panel for smaller fuses and be done with it. We can do
a much lower resistance job for the ground returns with the
ground lug from 2004 than we could ever get from the power
distribution block.

Loctite should not be used on electrical connections, it is not
a conductor. There is no substitute for proper torque on all
of the electrical screws, and proper stress relief for the wires.

The terminal block does need to be tightened to specifications.
If you don't have a suitable torque screwdriver, you can do quite
well with a wrench attached to a hex drive screw driver, and a
small "fishing scale."

We have not had problems with bare wire in the power distribution block,
but if we have to use this distribution block next year we will certainly
use the ferrules.

Eugene

[T3_1565]

All we did was put solder on the wires to stop them from fraying apart, which seemed to be our problem with why they were slipping out. Anyone tried that?

[Al Skierkiewicz]

Originally Posted by T3_1565

All we did was put solder on the wires to stop them from fraying apart, which seemed to be our problem with why they were slipping out. Anyone tried that?

T3,
Tinning wire before insertion into a clamp type terminal should not be used. It prevents the wire strands from compressing inside and providing maximum contact area with the terminal. A tinned, stranded wire will act like a solid wire in most cases, usually making the problem worse and raising the series resistance.