Wire VRM by another VRM

Technical Electrical
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1

Is it legal and possible to power VRM out of another VRM?

2

I dont think there’s anything that prohibits it, but also heavily asking why you are considering this, just doesn’t seem practical given you can also wire them in parallel rather than series

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3

It’s a good idea, we just wanted a shorter cable

4

According to R621 you can have up to 3 VRMs, however at no point in the game manual do they say what the VRM power supply should be like, but the circuit in series can increase the current that the last one will receive which is something you should be careful about. avoid problems with power outages.

5

I wouldn’t do this. You’re likely to overload the first VRM in the chain and end up without either of them.

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6

It’s not a good idea.

  • This would mean the second VRM is only able to provide as much power as it can pull from the first VRM. (Actually less due to efficiency losses.) The VRM “2A” ports are only rated for 1.5A continuous (2A peak) so if you connect your second VRM to the 12V/2A output of the first one, you can only pull a total of about 1.5A out of all its ports.
  • Daisy chaining is inefficient - if each converter is say 90% efficient, then you’re losing 10% of your input power at each stage in the chain. This offsets any gain you might have from the shorter cable.
  • There’s no reason to do it. This year, you don’t need a VRM (or RPM) to power your radio. You can use a VRM as a generic DC-DC converter, but at that point it’s a custom circuit - you can power both off of a single PDH/PDP circuit, with a splice (a 3 position Wago 221 is also a nice way to do this).
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7

Why do you think it is a good idea?

Which wires become shorter?

Presumably, the total distance from your load to the PDP/PDH is unchanged and instead of two longer pair of wires (PDP/PDH to VRM to load) you now have three pairs of shorter wires (PDP/PDH to VRM1 to VRM2 to load). In addition to the extra inefficiency of the second VRM, you have added 4 extra connection points, each an opportunity for a failure.

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8

Thanks to everyone for the responses, we appreciate it a lot, have a good one, we will still probably do it :stuck_out_tongue_winking_eye:

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9

You can still get shorter wires w/o putting 2 VRMs in series by doing something like this (assuming this is legal, I don’t feel like checking the rules lol)

image
image850Ă—405 102 KB

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10

This does not seem to violate the main text of R618 as such, but might not comply with the blue box (“appropriately spliced”). If one of the VRMs is powering the radio, then R617 seems to exclude this under options A and B (fused channels), but not C (PDP 2.0). Obviously this picture violates R624 (wire colour), but black lines would have been impossible to see.

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11

Just remember: when it backfires, we want an update on how spectacularly it backfires, so we can then use those pictures as examples of “why this is a bad idea”.

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12

:laughing: I was kidding but all the hate really makes me want to do it lol

13

What people are giving you is not hate. It is the accumulation of a lot of (sometimes bitter) experience.

You free to do what you want. There is nothing in the Game Manual requiring that your robot functions correctly when it is placed on the field.

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14

Are you just wanting shorter wires connected to one another through some means? That has a lot of solutions on its own.

You could use WAGO connectors to easily extend a length of wire without haing to cut a new one (although beware, if they’re not tight and taughtness on the wire will pull them free – WAGO connectors are really best on practice bots and then you can finialize your connections with andersons or by just cutting a longer wire for teh final bot).

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15

@uriGoldstein What is it you’re trying to power from the 2nd VRM?

Thinking about this more:

  • You’re using the 12V 2A (really 1.5A) output of the first VRM to power the second one.
  • So if your loads are 12V, there’s no point in using the 12V outputs of the 2nd VRM vs. simply splitting the 12V output of the first one to power the loads; thus
  • The only conceivable reason to do this is to get a little bit more regulated 5V power, at which point
  • You’d be far better off just putting a dedicated 5V regulator on the robot - it will be a lot smaller, simpler, cheaper, and less trouble prone.
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