Voltage of the TTOG

We are making an off-grid gateway station with a bunch of other devices which are all 24V. The TTOG seems to require 55V, or at least this is the voltage provided by the PoE brick. Anybody tried to run their TTOG on 24V? What is the minimum voltage they require?

Cheers,
Fred

One would wonder that if it would run on 24V, why would a 55V adapter be supplied.

PoE typically runs at 48VDC to compensate for the losses in the cabling.

If you are running off-grid, just don’t use the PoE brick, then you won’t have to generate mains voltage to power the brick to provide lots-a-volts to lose down the end of a relatively short cable which will then buck it down to 24VDC.

But it may be worth stringing them all together to see if you can get some perpetual motion gig going …

As @descartes said, to compensate for cable losses if long network cables are used.

We definitely want to avoid inverting to mains and then back to DC. But I would also like to avoid going from 12 to 24V and 55V, especially knowing that the 55V is actually likely to be taken down to much lower voltages in the box.

I was wondering if it would work if powered at 24V (on a short cable). I guess we’ll have to try.

@Jeff-UK, who just loves a TTOG(a) party, can advise but I sort of doubt that the universe has been running such a beast on a bizarre chain of voltage conversions.

Maybe the docs can elucidate what the normal non-PoE voltage power supply provides?

The only mention of voltages I have seen are that of the mains power brick, which is why I was asking here, hoping someone would know. I guess we’ll have to produce 24V and 55V…

Or hold your horse long enough to let other volunteers that I’ve paged reply …

Patience!

Sadly no direct hand on experience with the TTOG - never received my review unit (was due just as Covid hit) - but question is what have you tested? It does no harm to try other (lower) voltages to see what happens. I believe this will be set for nominal 802.3af PoE which sets nominal 48V - (spec 44-57V) - no doubt 55V on PSU allows for cable losses in worst case. Spec is set for longest ENet cable runs with supply current draw from 10-350mA (15.4W spec) so on shorter runs with lower loss the source feed can of course be set lower. I have seen other systems use a 24V PoE (Ubiquiti being the stand out name in network kit that I recall), and rather than follow the standard for my stand alone solar rigs I often go down the path of passive PoE at nominal 12V or 24V…as stated the trick is to test how the systems PSU and brown out circuits will respond… one of my favourite early GWs was the Laird RG186 and in tests I found though nominal power (to main socket vs PoE connection) set with their PSU at 12V it worked reliably to well below 8V with nicely behaved brown out action… so Passive PoE splitters allowed Ethenet + Power over singe cable with power delivered through main barrel conector vs direct to ethernet socket. Have noted similar good behaviour on others where taking direct to ENet port such as the RAK 7249 where supply could go well below 10V and still function :slight_smile: As noted only way to find out is to test and to then allow a small headroom depending on cable length (I allow 1.5V on short cable runs, 2.5V on medium and 5V on full length, with no operational reliability issues see in the field so far. WRT TTOG specifically I know Al @eggfriedrice and the Connected Things/Sensational Systems team up in Edinburgh sell/support this unit and can perhaps chip in with advice and experience on that specific unit?

Agree - can only type so fast! :slight_smile: No doubt saw me replying :wink:

OK, peaked my interest enough to look at the docs - Browan etc off the Xmas card list for being silly, like the way they hide the USB serial adapter for the TTIG.

I’d have to have one to poke about to see how the power is laid out on the inside - it may even have a separate board to do the PoE conversion (like they do with the RPi (rip)).

Scrub that, found these pictures: The Things Outdoor Gateway Teardown, the PoE is on the board.

I’d sell the one you’ve got and buy something that you can power easily - like a TTIG.

@Jeff-uk may not know about TTOG’s but he does know how to power a gateway with sunshine.

One other little wrinkle is the TTOG DS calls out 803.af and that is also in Installation Notes but I did see that at one point they (Browan) recommend PoE Switch (Network kit) and cabling be rated as 802.3at - the more recent/higher powered (25.5W) version - though unsure if this is typo or just overkill? In many cases installing in legacy cabling .3at may not be an option and I think TTOG should be ok (its only an SX1301/1257 system + LTE at the end of the day :wink: ). The supplied Borowan PSU @nominal 55V/0.6A/0.8A is over spec’d just in case :slight_smile:

Why do you want run on 24V? Is that the only voltage you have available (no AC or anything else)?

What about using a buck regulator?

Thanks all for your input. Here are some additional points.

We are off grid so no mains. In fact we currently have an inverter and use the default power bricks and this is horrendously inefficient (and generates a lot of heat that also needs to be dissipated). So we want to go direct 12V to whatever voltage is needed.

Indeed we have Ubiquiti equipment as part of the same system, which requires 24V. We also need 12V (direct from the battery) and 5V (for micro controllers). I was just trying to avoid yet another DC-DC converter to try to be more efficient.

So far I have not tried to directly inject power from a DC source so have not tried anything else than the 55V from the power brick. Unfortunately I don’t have easy access to the TTOG at the moment to do tests (it’s out on a tower on top of a hill).

So I might just bite the bullet, get another DC-DC converter and hope the battery/solar panel capacity will be good enough (won’t be worse than going 12V to AC back to DC).

Could you elaborate on this a bit ? There is a USB serial adapter for TTIG ?

Yes, the DIY way is to crack the case open and solder on some header pins. But one of the TTI team mentioned that there was an adapter you could put in to the USB socket that wired up the serial to the USB.

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We finally did some testing, and it starts working (in the lab, no RX/TX tested) at about 36V. At 48V, current consumption peaks at about 0.1A.