Our team has 3 out of 4 not working VRM’s.
We’re trying to find the cause of this, what could be the reason for the burnt/not working VRM’s?
Maybe you are connecting things to the, that draw too much current?
Let us know exactly how you are using the VRM. What do you connect to it?
How have you determined that they’re broken?
What was connected when they allegedly died?
What wiring practices are you employing to stop short circuits at the connectors?
What was happening with the robot’s electrical system when they died?
Do you disconnect your main breaker before changing batteries?
Y’all got any more of them details?
While not disconnecting the battery SB connector under load is certainly a good idea and generally a best practice, I am not sure if it any less electrically Noisey than the breaker switch. It not like there is a lot of load on it.
We have found the VRM very reliable. But we are very careful with the electrical. With the little information given, I would start with looking for shorts and making sure you are not trying to draw too much current. Talking directly to CTRE customer service would be useful too.
Have they been connected with the input voltage reversed? Have the outputs been connected to the 12 V from the PDP?
My understanding is that the VRM has two switching regulators in it, one to make the stable 12 V output and one to make the 5 V output. These circuits typically have very good self-protection features and usually can survive a short circuit.
If 3 in a row have died, check the input wiring from the PDP, both ends.
I can concur from experience. We accidentally had a pinched wire coming off of the VRM in 2016 and it was able to take it perfectly.
You got a bunch of responses.
We’d like to hear back from you.
We’re connecting only the radio to the VRM, nothing else
So does it work now?
It is most likely that an incorrect connection was made to the 12 V supply on the PDP. Unfortunately, if what you have now is working, the evidence of an incorrect connection will have been destroyed.
In the future, have a second, detailed oriented person check EVERY wire against the wiring diagram before applying power.
We checked the connections, they are okay, the burnt VRM’s are not working no matter what, our other VRM is working fine so we assume that they probably drew too much current.
As stated before, all of the chips used in designs like this are designed to protect the circuit from output short circuits without sustaining permanent damage. All the ones I have worked with could withstand having a constant short applied across the output and will start working properly once the short is removed. It is virtually impossible for a chip manufacturer to sell one that cannot do this now.
It is more likely that the dead ones were connected with the input wires reversed or the 12V input was connected to the outputs. That is why I suggested that in the future, have a second, detailed oriented person check EVERY wire against the wiring diagram before applying power. This is standard operating procedure in a manufacturing environment.
For a definitive answer, you can contact CTRE and ask if they will perform a failure analysis on the dead ones if you send them back to them. Since they are the developers of this product, they are likely to have seen examples of many different failure modes. They might even be able to repair them for a reasonable fee :). Sorry, I just noticed that you are in Israel so the cost of the shipping might make it impractical to ship the dead ones around.
We’ll make sure to check the connections before applying power.
Thanks everyone!
Please save those burned-out VRMs in a safe place, and bring them to the US if you guys go to champs.
Give them to CTRE for autopsy.
You really should find out what caused their death, so you can learn what not to do.
We’ll make sure to do that, thank you!
beanie,
What you describe is generally related to the wiring going to the radio. Be sure that everything is fully insulated and the wiring is not pinched under a mechanical part of the robot. The wire that is supplied with the radio has very thin insulation and it is common to be pinched together under a mechanical part. The best method to check the cable is to squeeze the wire between your fingers and slide them from one end to the other. Any part of the cable that feels rough or has indents was likely damaged at one point. Replace when you can, it will fail you when you need the most.
i’d be in the FLL tournament in Haifa at the 31st.
i can drop at your workshop and get a glimpse of the wiring and the dead VRM’s if your team likes (your mentor’s should have my contact info, or if not they can get it from FIRST Israel)
Another set of questions :
Are you using a barrel connector to connect to the radio, if so was it bought in Israel or the one that comes in the KOP?
did you made sure that you do not have any metal shreds (גרדים) on your electrics ?
could you upload photos of your setup?
Make sure that your Fuse in the PDP is the right ones in Amperage (it should protect your VRM’s from frying, which apparently it does not), those fuse are standard automotive fuses and can be purchased in any gas station in Israel for 10-15ILS a pack (DO NOT replace them with any other style fuse)
if you need any local help, feel free to contact me (or any other Israeli orange-hat)