24V Light on Power Distribution Board

[joachimbean]

We're having trouble with our Power Distribution Board, the 24V light is not coming on. Everything else is working fine (5V, 12V, etc.).

Does anyone know what the issue could be?

[Team#2057-Vegas]

if you have another from past years or just an extra i'd just switch em out. thats the only thing I can tell you.

[joachimbean]

We don't have any extra ones currently (we're a rookie team), but we might be able to find another one we can use.

[Joe Ross]

Was the light ever on in the past? Does it turn back on if you remove all connections to the 24v supply? If it's the latter, it indicates a short in your wiring.

When you measure the voltage with the DMM, what do you read?

[joachimbean]

Yup, it was all working and powering the cRIO as of a few days ago.

[Matt Krass]

Sounds like there may be a short, I'd go ahead and disconnect everything from the 24V power and see if it comes on. Check it with the meter too, just in case the LED is just flaking out.

I don't know for sure, but since there is some kind of reasonably sophisticated power supply in there to boost the 12V to 24V, I'd hope it has some kind of short circuit protection, and is just shutting down.

[joachimbean]

Nope, disconnected everything from the 24V port, and there's still no light. I also checked with the meter, and there's no power. Should the circuit breakers be configured in any way, or should we just leave them the way they're currently connected?

[WizenedEE]

I'd suggest pulling everything off (except the in power, obviously), including circuit breakers and wires going off to other things and check again. Make sure you're using your meter from all the way on one side of the connector to all the way on the other side (there are two 24V and two GNDs on each connector)

Also, there's a connector that fits on top of the 24V output that you screw the wires into; try taking that off.

[Trent B]

Have you tried a new battery too. Despite being a regulated 24v things can get a little funny with lower battery voltages.

[Al Skierkiewicz]

joachimbean,
The 24 volt power supply will operate down to about 4.5 volts on the battery. If you haven't charged the battery, it is possible for the battery to fall to less than 4.5 volts when you try and power the robot. However, there is always the possibility that one of your batteries has been wired backwards. It happens all the time at the beginning of the season. Check all batteries with your voltmeter to be sure. The battery connector is marked with a + and - as well as the PD. Measure the voltage right at the input to the PD to be sure you have the correct polarity and a battery that is well above 4.5 volts.

[Matt Krass]

joachimbean,
The 24 volt power supply will operate down to about 4.5 volts on the battery. If you haven't charged the battery, it is possible for the battery to fall to less than 4.5 volts when you try and power the robot. However, there is always the possibility that one of your batteries has been wired backwards. It happens all the time at the beginning of the season. Check all batteries with your voltmeter to be sure. The battery connector is marked with a + and - as well as the PD. Measure the voltage right at the input to the PD to be sure you have the correct polarity and a battery that is well above 4.5 volts.

Is the PD protected against reverse polarity?
Also, he said the 5V and 12V outputs were working, which would imply that he currently has the correct polarity, but if the board isn't protected a reverse wired battery may have damaged something.

Do we know exactly what boost converter they use for the 24V rail? I'm curious what its datasheet says about reverse polarity.

EDIT:
I realized after I asked all the schematics are on the FIRST website here: http://usfirst.org/roboticsprograms/frc/content.aspx?id=16337

The boost converter is based on the LM3478 chip, and I pulled its datasheet up from NI. I admit I only skimmed it, but it doesn't seem to have any reverse polarity protection, nor does the PD board seem to have. It does have built in short circuit protection, so a short shouldn't have hurt it, but there is a 15A fuse in line with it inside the PD board. If you shorted it, I'm not sure if that fuse would go before the SCP in the LM3478 would kick in, so it's possible that blew I suppose. I guess this is a viable possibility if you guys can't find any batteries wired in reverse.

EDIT2:
I actually think that it's not a fuse but a self resetting internal 15A circuit breaker. I should probably not try to read schematics when half asleep....

[joachimbean]

Yup, all batteries seem to be wired correctly (and getting a reading of 13.5V on the meter). I don't really know what to do at this point.

[EricVanWyk]

You will most likely need to buy a new PD.

Please disconnect the battery and anything from the 24V. Measure the resistance between the positive lug (where the battery is usually connected) and the positive 24V output. If there is a high resistance, the fuse has been blown.

One way the fuse can be blown is if the 24V positive output is shorted to the negative return for a motor or the battery (shorting to its own negative return does not cause this). This can happen if your chassis is not isolated. Please check to make sure that the chassis of your robot is completely isolated from the electronics - and then make sure it is still true when stuff is getting jostled around.


The boost converter is based on the LM3478 chip, and I pulled its datasheet up from NI. I admit I only skimmed it, but it doesn't seem to have any reverse polarity protection, nor does the PD board seem to have.


Matt -

Q12 on page 6 provides reverse polarity protection to the 3 regulated power supplies on the PD.

[Garten Haeska]

We had a similar problem, and it turns out it was a short, every other port worked, and the only one that didnt was the 24v for the crio.

[Matt Krass]

You will most likely need to buy a new PD.

Please disconnect the battery and anything from the 24V. Measure the resistance between the positive lug (where the battery is usually connected) and the positive 24V output. If there is a high resistance, the fuse has been blown.

One way the fuse can be blown is if the 24V positive output is shorted to the negative return for a motor or the battery (shorting to its own negative return does not cause this). This can happen if your chassis is not isolated. Please check to make sure that the chassis of your robot is completely isolated from the electronics - and then make sure it is still true when stuff is getting jostled around.



Matt -

Q12 on page 6 provides reverse polarity protection to the 3 regulated power supplies on the PD.

Ah, I didn't see that. Clever design.

Unfortunately, it seems that the symptoms point towards a short permanently taking out the fuse. I suppose opening the PD up to replace the fuse would constitute a non-competition legal modification?

[joachimbean]

How would we get a replacement? I can't find one anywhere.

[WizenedEE]

How would we get a replacement? I can't find one anywhere.

Andymark sells the Power Distribution Boards, along with a bunch of other FIRST stuff.

[Al Skierkiewicz]

joachim,
Check with First. You may have been given a defective unit in your KOP. It happens...

[Astarties]

Ah, I didn't see that. Clever design.

Unfortunately, it seems that the symptoms point towards a short permanently taking out the fuse. I suppose opening the PD up to replace the fuse would constitute a non-competition legal modification?

Well, if you really can't find anything else that may be causing the problem, you could open up the PD board and see if it's the fuse. If it is, fix the problem, and go on testing your bot. Then, between ship day and competition, order a new PD board and replace the now "modified" one at competition.

[Bob Steele]

Ah, I didn't see that. Clever design.

Unfortunately, it seems that the symptoms point towards a short permanently taking out the fuse. I suppose opening the PD up to replace the fuse would constitute a non-competition legal modification?

I would find it hard to believe that replacing a fuse... no matter how you do it... with another fuse of the same type... would be considered a modification... it would be a repair...not a modification...

Now, I am not sure if it would help but if that is all you did I can't see that as illegal...it might void the warranty on your PD (if there is one...) but illegal modification? I don't think so..

If you replace parts with like parts that would be a repair... no where in the robot rules does it say you cannot repair a piece of your KOP.

Remember though... repairs would need to be done with the same part (fuse, etc.)

Of course, the ability to make a repair would be dependent on your level of expertise. It would always be at your own risk so if a team doesn't really know what they are doing... (not saying you are that team..) best to not attempt it.

[Racer26]

@Bob Steele: Historically speaking, "repaired" control system components (ie. Victors that blew the FETs and subsequently had them replaced) have not been allowed on competition robots.

[Bob Steele]

We are not speaking historically...
I was referring to this year's rules applied with a modicum of common sense.

Blown Victors were rarely repaired with the same components that they came with. But show me the rule that disallows doing this...

Just show me the rule..

i find it difficult to tell a team to spend another $180 for a PD board if it could be fixed by putting in a replacement fuse.

If that is the case, can we replace the fuse on a blown SPIKE? I I know it is on the outside and would appear to be easily replaceable... but what real difference is this?

i always hated having to send my old IFI controller boards down to IFI to have a blade connector replaced if I wanted to use it again..(in competition) ...

respectfully
R

[Al Skierkiewicz]

Bob,
<R55> The control system is designed to allow wireless control of the ROBOTS. The Driver Station
software, FirstTouch I/O module, cRIO-FRC, speed controllers, relay modules, radio, and
batteries shall not be tampered with, modified, or adjusted in any way (tampering includes
drilling, cutting, machining, gluing, rewiring, disassembling, etc.), with the following
exceptions:

The PD is considered to be part of the control system and therefore is included in this ruling.

[Bob Steele]

Thanks Al
I knew I could count on you...

Given your position... I will have to concede the point...

Given this interpretation... NOTHING can be changed on the robot that has anything to do with control...

I still find it hard to see that a repair is a modification...

but I will concede the issue to a greater power.

[Matt Krass]

I would find it hard to believe that replacing a fuse... no matter how you do it... with another fuse of the same type... would be considered a modification... it would be a repair...not a modification...

Now, I am not sure if it would help but if that is all you did I can't see that as illegal...it might void the warranty on your PD (if there is one...) but illegal modification? I don't think so..

If you replace parts with like parts that would be a repair... no where in the robot rules does it say you cannot repair a piece of your KOP.

Remember though... repairs would need to be done with the same part (fuse, etc.)

Of course, the ability to make a repair would be dependent on your level of expertise. It would always be at your own risk so if a team doesn't really know what they are doing... (not saying you are that team..) best to not attempt it.

While I do agree with you in principle (I feel the same way about repairing bricked Jaguars with JTAG) I can understand where FIRST is coming from. If you openly allow teams to crack open the PD board and replace a fuse, you run the risk of any number of catastrophes, if the teams replace the fuse with one that is too high a rating, or worse, short it with some solder (I've seen students try this, the modern version of the penny trick) you could have a dangerous situation at a competition where no one expects the integrated safety device to be ineffective. Anything that must be opened up in any non-trivial way (read: using tools) is automatically more cumbersome for inspectors to verify at a competition, and thus should not be allowed, in the interest of safety and finishing inspections in a reasonable time.

[Bob Steele]

How would we get a replacement? I can't find one anywhere.

http://www.andymark.com/ProductDetails.asp?ProductCode=am-0265

Unfortunately
Out of stock...

email me if you really need one...I have a spare.
If you don't mind replacing it later..

[Joe Ross]

http://www.andymark.com/ProductDetails.asp?ProductCode=am-0265

Unfortunately
Out of stock...


The 2011 version is still in stock. http://www.andymark.com/ProductDetails.asp?ProductCode=am-0865

[Matt Krass]

The 2011 version is still in stock. http://www.andymark.com/ProductDetails.asp?ProductCode=am-0865

Is there any functional difference? Just for my own curiosity I'm wondering, I was under the impression that it was the same thing but from a different manufacturer, but I have no evidence to support that.

[Joe Ross]

Is there any functional difference? Just for my own curiosity I'm wondering, I was under the impression that it was the same thing but from a different manufacturer, but I have no evidence to support that.

The 2009 version did not have the blown breaker detection circuit. The 2010 and 2011 versions do. I don't know of any other differences. I'm not sure whether the Andymark 265 is the 2009 or 2010 version.

[Al Skierkiewicz]

Bob,
I think Matt has explained it pretty well but even I would like to be able to make repairs. It is what I do for a living. However, I have spent a great deal of my life fixing other people mistakes so I know how bad some of those fixes can be. I can tell you that the supposals Matt outlined only scratch the surface of what I have seen. The rule did not come from me but I do support it for these reasons.

[joachimbean]

Sent in for a replacement, and it should be all taken care of now once it comes. Thanks for all of your help!

[linuxboy]

On the point of the reverse polarity I know that someone already verified it with at datasheet but the board that came with the KOP this year has reverse polarity protection, I can verify this because I made that mistake earlier and nothing got fried.