Best way to charge a 12s lithium bank?

[off.the.grid]

Got some networking gear I need to operate, just a basic router and a couple or power over ethernet devices over solar.
Power demands will be fairly low.
12watts max, but averages less than 5 or 6 watts most of the time.
I have a small mppt charge board that charges a 2P6S battery bank of 21700 cells off a 50w solar panel.
Problem is that I want to use power over ethernet which the device only operates on a 48V supply.
I could configure the battery bank to 12S and get 50V and use a step down converter to 48V, although that presents an issue if the battery drops below 48V, so might need a boost/buck converter instead?
Any other suggestions that might work better in this application?
Biggest issue is I can't find a charge controller that will charge a 12S bank either.
I'm looking at using a boost converter board off ebay that should give me the 48V, from 25V but don't know how efficient it will be.

 

[Crowz]

Ive never gone up in voltage on my installs its always been stepping down voltage for things. Up converting will of course always be less efficient but you would have to get the specs off what you are wanting to go with to know how bad it will be.

 

[off.the.grid]

Ive never gone up in voltage on my installs its always been stepping down voltage for things. Up converting will of course always be less efficient but you would have to get the specs off what you are wanting to go with to know how bad it will be.

If the step up converters work OK I may just stick with it.
The power draw is not even 0.2A, but there will be some losses.
If anyone can point me to a good step up converter, that would be a great help. I dont know if any PoE injectors run off a 12v supply and step up themselves.

 

[Supervstech]

12s? What cells?
12x 3.2V LFP would be 38.4V average, with a peak of 43.8
12x 3.7V NMC would be 44.4 with a HARD peak of 50.4

Since you are needing a steady voltage output, you would need a boost buck converter capable of producing the correct voltage over a range of voltages.

 

[SeaGal]

I'm looking at using a boost converter board off ebay that should give me the 48V, from 25V but don't know how efficient it will be

A boost would sound a much simpler solution than messing with battery configurations etc. Efficiency should be better than 90% for the buck-boost, so IMHO not significant compared to other losses. If you go down that route make sure you get a well engineered one - some cheap ones don't have sufficient heatsinks for the power ratings they claim, will overheat and then fail.

Another option, depending on your topology would be to just run a separate power line alongside your CAT5/6 cable to the equipment and power it as it's native voltage, rather than using PoE?

 

[off.the.grid]

12s? What cells?
12x 3.2V LFP would be 38.4V average, with a peak of 43.8
12x 3.7V NMC would be 44.4 with a HARD peak of 50.4

Since you are needing a steady voltage output, you would need a boost buck converter capable of producing the correct voltage over a range of voltages.

21700 cells, at full charge they are about 4.2V each, but your right it would go down to about 38v give or take when the battery is almost discharged.
But I believe to extend battery life it's best to charge them to 4v per cell which would give you a 24V bank.

A boost would sound a much simpler solution than messing with battery configurations etc. Efficiency should be better than 90% for the buck-boost, so IMHO not significant compared to other losses. If you go down that route make sure you get a well engineered one - some cheap ones don't have sufficient heatsinks for the power ratings they claim, will overheat and then fail.

Another option, depending on your topology would be to just run a separate power line alongside your CAT5/6 cable to the equipment and power it as it's native voltage, rather than using PoE?

If I can find a decent buck boost converter, I would go with that.
This is about all I can find.

https://www.aliexpress.com/item/4000360679063.html

I also would like to run a camera off one of these units at some point.
Yes they run off 12V and turns out that they come with a 12V supply even though they are advertised as PoE cameras.
What's interesting is it won't work off 12V PoE as I've already tested it, not even 36V will work on the PoE yet its running off a 12V supply.
Probably will be less efficient if it's stepping down the power again inside the Camera, but PoE gives more flexibility. Also means I don't need to run another cable alongside for power.

 

[SeaGal]

IIRC PoE needs 44V minimum. The higher voltage is used to reduce the current in order to mitigate the resistance of network cable, which obviously wasn't designed to carry much power. At the other end, the PoE device will use a buck to reduce back to the 12V or whatever voltage it needs.

The link doesn't show due to being in a different country, but there should be plenty of buck-boost converters out there. From quite professional ones from the likes of Vctron, down to cheap and nasty ones from ebay... Here's an example from Amazon - no idea about the quality of this one, just and example - as I mentioned above go for one that is rated at more power than you need with a decent heatsink.

https://amazon.co.uk/Module-200W-Converter-Charger-Module-Aluminum/dp/B07Y4YHW82

 

[zanydroid]

Is the target device fully PoE compliant? PoE spec covers a range of voltages, it is not exactly 48v. The range should be covered in the Wikipedia article / other easy to find documentation.

Personally I would do 12V to 48V buck boost into a PoE switch that takes 48V directly, there are a few on Amazon, lower power ones though. High power ones usually have integrated AC power supply.

Powering a router or modem via POE is rare and risky due to the elevated chance of ground loops/other voltage offset issues through all the extra copper cable hanging off it. Honestly I prefer to power anything like that over an isolated supply. Cameras and APs, ie devices at the leaf of the topology with no other connections, are more trouble free.

 

[off.the.grid]

IIRC PoE needs 44V minimum. The higher voltage is used to reduce the current in order to mitigate the resistance of network cable, which obviously wasn't designed to carry much power. At the other end, the PoE device will use a buck to reduce back to the 12V or whatever voltage it needs.

The link doesn't show due to being in a different country, but there should be plenty of buck-boost converters out there. From quite professional ones from the likes of Vctron, down to cheap and nasty ones from ebay... Here's an example from Amazon - no idea about the quality of this one, just and example - as I mentioned above go for one that is rated at more power than you need with a decent heatsink.

https://amazon.co.uk/Module-200W-Converter-Charger-Module-Aluminum/dp/B07Y4YHW82

Thanks I will look at that

Is the target device fully PoE compliant? PoE spec covers a range of voltages, it is not exactly 48v. The range should be covered in the Wikipedia article / other easy to find documentation.

Personally I would do 12V to 48V buck boost into a PoE switch that takes 48V directly, there are a few on Amazon, lower power ones though. High power ones usually have integrated AC power supply.

Powering a router or modem via POE is rare and risky due to the elevated chance of ground loops/other voltage offset issues through all the extra copper cable hanging off it. Honestly I prefer to power anything like that over an isolated supply. Cameras and APs, ie devices at the leaf of the topology with no other connections, are more trouble free.

That's right, the specs cover a range of voltages, initially it was 12v iirc and the camera runs on a 12v supply.
I was hoping that I may have gotten the camera to run on 12v through the injector because of this
I'm not running the router on PoE, but I will be running a unifi access point from it.

Specs say IEEE 802.3af / 48V Active on the camera which is rated at 15w. I know the camera actually uses less than half of this when I measured it.

 

[zanydroid]

That's right, the specs cover a range of voltages, initially it was 12v iirc and the camera runs on a 12v supply.
I was hoping that I may have gotten the camera to run on 12v through the injector because of this
I'm not running the router on PoE, but I will be running a unifi access point from it.

I'm not aware of a recent 802.3 standard that is not 48V nominal. 12v and 24v are proprietary. I was referring to that fact that it's 48V nominal but probably give or take 4V

No risk to fry unify access point off PoE, it's a normal use case.

Specs say IEEE 802.3af / 48V Active on the camera which is rated at 15w. I know the camera actually uses less than half of this when I measured it.

The camera will also request a power level as part of the active handshake with the power source. Depending on how good the power source is, it is supposed to allocate power reservation and configure eFuse accordingly. Of course it could also just ACK the request and not do any of that

 

[off.the.grid]

Ok, that's interesting because I've seen a number of PoE injectors that run on various voltages.
I see there are also PoE injector designed for this use case, probably less efficient, but its the only real way I see of doing it unless I use a higher voltage battery.

 

[zanydroid]

Unless the PoE injector has a boost conversion to 48V then it's non 802.3 PoE compliant.

Just get a buck boost converter, there should be tons able to boost to 48V for a single port like this way overkill one: link

If you want to boost to 48V and support a multi-port switch, that is where it gets hard but I don't think that is your case.

To be frank I'm not sure why you consider this super difficult. I can kind of see that it's hard to find a 100% turnkey ready to go plug & play solution, but you can buy a metal box to glue one of those buck-boost converters into and solve this?

 

[off.the.grid]

Unless the PoE injector has a boost conversion to 48V then it's non 802.3 PoE compliant.

Just get a buck boost converter, there should be tons able to boost to 48V for a single port like this way overkill one: link

If you want to boost to 48V and support a multi-port switch, that is where it gets hard but I don't think that is your case.

To be frank I'm not sure why you consider this super difficult. I can kind of see that it's hard to find a 100% turnkey ready to go plug & play solution, but you can buy a metal box to glue one of those buck-boost converters into and solve this?

I've found a PoE switch that has a boost converter built in and provides 48V.
But yeah not overly difficult to find a boost converter, but here in New Zealand there is not much available and have had to order stuff from overseas. I've tried one unit that I think I shared the link to earlier and they blew up on me as soon as I tweaked it to 48V.
They started drawing a ton of current and got hot instantly despite the only load being my multimeter.

 

[zanydroid]

Oops, didn't notice your location. Yeah, sucks to be on an island.

Maybe ask around on some maker forum for what to order from AliExpress. There should be some fine ones. It's probably a lot less annoying than trying to order cells. Just have to wait a while for them to show up. It's possible that there are enthusiasts in NZ that have ordered like a dozen off AliExpress (might as well when it's that cheap/that long to wait) and are willing to share.

One issue with 48V is that a lot of components are only rated to 30V so that's one way a bad design could blow up right away. And you have probably noticed that there is less choice for 48V than 24V.

 

[SeaGal]

Yeah, sucks to be on an island

Not all islands are the same ??

 

[zanydroid]

Not all islands are the same ??

You have a road/rail link to the mainland and don't get accidentally left off of maps, so doesn't really count.

 

[off.the.grid]

Oops, didn't notice your location. Yeah, sucks to be on an island.

Maybe ask around on some maker forum for what to order from AliExpress. There should be some fine ones. It's probably a lot less annoying than trying to order cells. Just have to wait a while for them to show up. It's possible that there are enthusiasts in NZ that have ordered like a dozen off AliExpress (might as well when it's that cheap/that long to wait) and are willing to share.

One issue with 48V is that a lot of components are only rated to 30V so that's one way a bad design could blow up right away. And you have probably noticed that there is less choice for 48V than 24V.

The reason for the 48V standard on PoE is for the losses over the twisted pair cable I think.
That's the only thing that I need 48V for.

It would give me more flexibility going forward however and it's super simple to add a buck converter to step down to any voltage I need.
Are there any open source MPPT controllers out there that might be able to customize to suit?
I'm tempted to build something that can suit my needs, as it stands, I can only find one MPPT board from China that charges the 6S bank I've been using, doesn't seem to put out the advertised 2A output either, but the specs of the chip suggest it can do 4A, but I only need 2A.

 

[zanydroid]

Are there any open source MPPT controllers out there that might be able to customize to suit?

Not sure what the MPPT comes into play. There is a decently written up MPPT design on instructables, I don't remember its customization capabilities. I think it's a buck-only MPPT. Seemed cool and educational.

Victron or MidNite should be programmable to whatever you need.

Note that there is a way to stack a DC-DC optimizer on top of your panels to make your own boost-capable MPPT in two stages. But with 6S bank you won't need that.

 

[off.the.grid]

Ideally a buck charger would be more efficient?
I'm currently putting 18V into a 25V bank, so this controller is a boost unit. Not 100% happy with its output, but its all I can find for now.
If I went to a 48V bank, I would need ideally two panels at least 25V each and put them in series and feed through a buck controller.
I've looked at the units on instructables and your right I'm pretty sure it's buck only.

 

[zanydroid]

Ideally a buck charger would be more efficient?
I'm currently putting 18V into a 25V bank, so this controller is a boost unit. Not 100% happy with its output, but its all I can find for now.
If I went to a 48V bank, I would need ideally two panels at least 25V each and put them in series and feed through a buck controller.
I've looked at the units on instructables and your right I'm pretty sure it's buck only.

Yeah…

There are some buck boost MPPT SCCs on Amazon, main application seems to be charging eMobility stuff like bikes and scooters, which are all higher voltage than a typical single panel.

48V is in the range of voltages those batteries are set up for.