Our CTRE VRM has malfunctioned and only the 5V rail is functioning. Are there any methods to resolve this problem, and if repairing the VRM is not an option, are there any alternative ways to power a radio that requires 12V/2A power?
2020-R47: The Wireless Bridge (Radio) power must be supplied directly by the 12V 2A output of a CTR Electronics Voltage Regulator Module (VRM) (P/N: am-2857, 217-4245) and must be the only load connected to those terminals.
As to repairing it, I suspect CTRE’s support will provide a better answer.
The first thing I would do is to turn it upside down and shake it. Sometimes metal shavings can get inside and cause trouble. After that, as @krf said, contact support.
Speaking of which…
If you’re wanting to power the radio in the meantime… Bear in mind that NONE of these methods are going to be FRC-legal, but will likely keep you running.
- 2A breaker/fuse in the PDB. (PDB supplies 12V, you just need it supplied at a very low amperage)
- Specifically break R47’s blue-boxed prohibition on active PoE Injectors and use one anyways.
- Buy a second (and possibly third) VRM. FRC-legal, incidentally–there’s no particular rule saying that you can’t have 2 on your robot, and most teams make it a habit to have a full spare control system if they can afford it. FIRST Choice credits may be able to get you a couple…if there’s any in there.
- Get… creative. (Please don’t. We don’t want you to set your robot on fire.)
“PDB supplies 12 V” is a bit misleading. The PDB will supply the battery voltage, which might vary from 9ish volts to like 13.8. I don’t know what the radio’s voltage specs are; that range might be permissible, or it might not.
Definitely do not do this. If the radio could take that wide of a voltage range (likely not given its source as a consumer access point) then that would be the FRC recommended configuration. Even if plugging in a 13v battery doesn’t make it become an expensive and hard to replace paperweight, it will reboot as soon as the motors start moving.
However, the VRM is just a handful of buck/boost and buck converters in a pretty case. You can pick up a buck boost converter like these ones: https://www.amazon.com/dp/B00LOG4XC0/ref=cm_sw_r_cp_apa_fabc_eWV6FbSNCWSZQ?_encoding=UTF8&psc=1 for fairly cheap. Make sure you adjust it to the proper voltage before you plug the radio in, but if you didn’t know that you needed to do that you might just want to buy another VRM and skip the custom electronics period.
We’ve decided to use an active injector, more specifically the TP-Link TL-POE150S. This is just for a mock game, so it shouldn’t be a problem!
Can you give us some suggestions as to how to wire the injector up to a 12V battery?
Thanks a lot!
Normally I’d say to go through the VRM…
As you can probably tell from the previous responses, I’m not an electrical expert, so I’ll have to defer to those folks. (Though I will ask a really obvious question for those concerned about the voltage range: Why is the PoE injector 18-24V, yet it gets 12V/2A from the VRM same as the normal plug, and the radio still works like normal?)
No proof, but I’ll bet money the voltage range is a wee bit more forgiving than we suspect.
I also suspect the radio isn’t guaranteed to work below 12V which a battery routinely goes.
The specs for the OM5P-AC aren’t terribly precise, but it does say it works over a 12V-24V range with 1A power supplies. The big issue with plugging it directly into the PDP is not the high end of the voltage, but the low end (battery voltage can have short drops to 6-8V under severe conditions) and electrical noise conducted from motors. The VRM helps with both those aspects (stable regulated voltage, and noise suppression). For non-competition use powering off of a separate 12V battery should work.
That requires 48 VDC input. So you will need a boost regulator that can generate 48 V from the 12 V battery.
You want something like this: https://www.digikey.com/en/products/detail/pololu-corporation/2577/10451159 (or a new VRM). Do try shaking the one you have upside down first though.
Shaking the VRM didn’t work. The output still didn’t function, and the 12V indicator LED didn’t turn on either.
The part I linked will work – it’s $15 plus shipping and the time it takes to arrive. Not all that much different than ordering a new VRM, but some savings. You can also order it here (I don’t think it makes a difference, but be sure to pick the 12V version if you use this link). You could also use a separate battery, if you need something you can buy locally. Or, another team may have a spare VRM they can loan you.
Hooking this up is pretty easy. You can use the PDP connections where the VRM plugged in, or one of the smaller regular PDP outputs. There’s an enable connection that you just ignore. And there’s the output, where the radio will connect. Pay attention to the polarity (+/-).
Do this, and then the input wires go to the PDP and the output wires to the radio. Make sure nothing metal can touch it when mounted, and you probably want to allow for air circulation.
I see that you’re pretty far from the shipper for this part – you could probably find something closer to home but you have to pay careful attention to the specifications. You want at 12V, 1A DCDC converter that takes an input voltage from a low voltage (8 or 9V, but lower is better if you can find it) to at least 15V.