The Metr has to be powered from a 5V source. The easiest is to find a buck converter that can take your battery pack voltage and step it down to 5V reliably. This will keep the Metr running continuously. Please keep in mind that this will also keep ground connected through the metr to your ESC, (as ground is required for CAN connection) so always be sure (if you disconnect power for the ESC from the battery to charge) that the ground is first to be plugged in, last to be unplugged. Positive should be last to plug in, first to unplug. Otherwise you’re charging your ESC capacitors through the tiny wires for the Metr and they might pop. (Ask me how I know)
Just so I understand, you mean a portable power bank like for recharging a phone but installed in the enclosure? You’d need some way to recharge this power bank, so in theory it could work but in practice it would probably be just as complicated to try and work out power bank recharging
IMO the way to do it is get a small buck converter module that can run off the board’s main pack voltage. Attach this to BMS output so the Metr can’t drain the main battery below a safe level
I’ll look into the buck converter. How do I makes sure that ground is always first to go in? Is that a specific plug or do I just modify something?
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Correct- a portable power-bank like for a phone. I was thinking that I’d either add a charging port to the controller box or ideally I was hoping it would be possible to charge the battery from a 5v pin off the vesc. Looks like the buck converter is the way to go.
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This would need to be a high-side BMS, and those are very hard to come by. Almost any off-the-shelf BMS is gonna fry something if it ever cuts the load.
Most BMS don’t cut the red wire, they cut the black wire.
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Yeah I only thought of that after posting, good catch. The Metr CAN uses 2-wire comms with no shared ground, it doesn’t mention being opto isolated or anything so it’s safer to assume it isn’t, and also to assume you’re right and it’s unsafe
Disclaimer: speculation below, do not take this as advice
I think the only way a low side switching BMS would mess up a buck and/or Metr would be if there was an unintended path to ground that keeps them half alive when the BMS disconnects, or keeps the buck going long enough to burn out this unexpected ground trace. It would be through the ESC (UART ground, or an unintended ground path through the CANH/CANL) and also would require that none of the units have polarity protection on ground. From what I remember nfets blocking reverse ground are fairly easy polarity protection but I think diodes on the positive rail are more common.
Doesn’t seem like a good idea to find out the hard way though
Hopefully everything ready now!
Metr App: v4.20.14
Metr Pro FW: v5.57
Metr LTE FW: v5.16
The latest app and firmware should allow for continuous tracking as long as Metr LTE + GPS is powered.
- Power Metr LTE with external 5V, not CAN bus
- Connect only CANH and CANL from Metr LTE to CAN bus
- GPS module must be connected to Metr LTE
- If you swap GPS module from Metr Pro CAN, please be very careful and check cable / pinout. Only latest revision of Metr Pro CAN + SD come with symmetric GPS cable, same as Metr LTE. Please remove the cable from the GPS module and use the cable that came with Metr LTE!
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The Metr Pro does not also need to be powered by external 5v to work? That’s interesting, I thought it was dependent.
Also can the Metr Pro w/ SD retrieve GPS data from the LTE in this configuration?
No, Metr Pro does not need to be powered all the time. Only initially to establish connection with Metr LTE / app.
Yes, Metr Pro + SD can retrieve GPS data from the Metr LTE in this configuration.
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Only 0.0.55 versions to go boys, then we can pack it all in
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I already have my METR Pro (with LTE and GPS) hooked up to a DC-DC always-on. Is it OK to keep it powered this way for continuous tracking or do I need to change the way things are powered?
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It’s OK! Have you tried with latest Metr LTE firmware update? It should work.
I have updated firmware and it’s been reliable ever since. Thanks for all your work!
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Hi i have metr pro. Is there any way to buy metr lte or something similar for tracking?
thnx
Forgive my typical cluelessness. Can you elaborate, are you expressing an opinion? I’m asking honestly, I’m not being snarky. I use metr, but my board is in the shop because I try to kill it
It’s not an opinion. Metr was discontinued but if you read about those products they have much the same functionality and from some of the same people. It could be viewed as next-gen metr. 
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Thanks
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We still have some Metr LTE’s left. Will add them to our shop! https://shop.voyagesystems.eu
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