DIY 48v 16S1P UK Based Time of Use Inverter/Charger System Query

[bazza2000]

Hi, I'm new to the forum so please go easy.

I've spent a few months going through various YouTube channels, from Will, to Andy (Off Grid Garage) and more recently the Digital Mermaid. All excellent channels and have given me lots of information.

What I find difficult is that there isn't a lot of UK based channels, I know we don't get a lot of sun, but recently wholesale energy prices have rocketed causing a lot of energy providers to fold so there is potentially more interest in what I'm trying to do which is, build an initial grid tied system with a DIY 15kwh battery using some of the EVE 3.2v 280Ah cells in a 16S1P configuration, with the potential to expand the system out to 30kwh (16S2P) in the future.

Solar is not really an option for me as we have a funky roof configuration which doesn't give me a great deal of roof real estate to mount panels, so my only option is to use Off Peak Charging using my current supplier (Octopus Energy) my tariff gives me 4hrs of low cost power between 00:30 and 04:30.

I therefore need a charger which can initially charge at 3.75kw (15kwh / 4hrs) but when I upgrade to the 30kwh battery it will need to charge at 7.5kw (30kwh / 4hrs). I know these figures arn't exact as I'll probably only be doing an 80% DoD, but you get the idea. The selection of BMS will also need to cater for the charge/discharge figures.

What I'm looking for is a Grid Tied inverter/charger (if possible, without any PV) which can handle these charge figures which is available in the UK. I've searched around a lot and not found anything other than the expensive Victron Quattros which get anywhere near. My max AC load would be around 5kw peak, with average usage of around 1 to 1.5kw throughout the day. (I'm a heavy user ). Happy to take any advice or pick apart my solution. I'm also looking for other people in the UK who are either interested, or have already done something similar.
Cheers.

 

[DJSmiley]

But what is your daily use?
You're now assuming you will completely discharge the cells during the day, requiring you to charge them from 0 to 100% during offpeak.

I don't think that's likely. Check what your average consumption is which you have to charge on a daily base.

Also, you can opt for charging outside the off-peak periods in case if needed. I don't know the price difference between on and offpeak, but it still might be cheaper charging incidently onpeak if needed, and charge off-peak in general, still will save on the bills.

Charging at those high rates is going to be hard and/or pricey. The majority of the 16S BMSses is restricted to 100A, thus approx 5kW max.
If you're willing to charge higher with the 16S2P, you're going to need 2 packs, with each a seperate BMS (so you can charge/discharge up to 200A combined).

A Victron Quattro is going to be expensive. For this specific application it might be cheaper to go for a regular inverter to power the loads, and a seperate charger.
You can schedule that charger to start charging during offpeak, or when a minimum SOC is reached. Requires some DIY.

Another option might be using something like a Growatt or MPP Solar inverter. Configure it to run from batteries only, use grid only when SOC is eg <30%, and add a second high-power charger to the cells directly, and schedule that charger to only power on on off-peak times.

A nice charger would be a Mean Well DBR-3200-48. That one provides charging at 55A, which is, at a bost voltage of 56V, about 3kW of power.
So during off-peak you can feed 12kWh into the batteries. Since you're not going (/wanting) to pull the 280Ah string to 0% SOC, i'm quite sure that would be more than enough to keep them topped up during off-peak times.

They do have some nice features for DIY. They do have a remote on/off so you can hookup anything to enable/discharge. If your supplier has different tariffs, you even can build your own Arduino/rPI/ESP to charge based on tariff rates. Or just simply use NTP timesync to enable/disable charging during offpeak.

Its preferred to use a remote on/off. Using a swiched outlet can, but I don't like that. You're drawing high amps: 3kW of charging is about 13A continously. Using a regular time clock.. that's not going to last long. They usually are rated for 10-16A, but if you pull that continously, they are fried pretty fast.
Also you probably have to hardwire the powersupply, if i remember correctly, most UK sockets are both switched and 10A max... And the same applies for them: Running high amps continously isn't going to be any good.

Another benefit of those Mean Wells is they allow current sharing. You can hook up to 3 in parallel to charge at even higher rates (assuming your grid can handle that).
So if you're adding more storage to your bank, you can add chargers if you want to keep them up-to-charge in the 4hour window. (Off course your usage has to be that high also, there is no need to charge at higher amps if a single supply can keep up for the daily demand during those 4 hours)


If you're really into DIY, have some electronics knowledge and want to spend pennys instead of 4digit pounds..
Grab an old powersupply on Ebay or Gumtree, configure it to 56V, and use a shunt to enable/disable it.
As long as it has CC (constant current) limiting, any powersupply can work as a charger. Due to lack of charge profile, you need to manually stop charging to prevent overcharging, but you can do that with eg the relay port of a Smartshunt, or interface a shunt with RS485 or similar to a rPI/Arduino/whatever.

I do have for example 4 massive powersupplies, got them for free. Used to be 3 in parallel, each one provides 2800W... they were part of the powersupply of a big-ass router
If youre lucky, you can find something similar, occasionally they become available on the used market for cheap.

https://static6.arrow.com/aropdfconversion/3f13518885dec5edc2fa108f0818aba92ffdd560/apcms28powerrack.pdf

for the DIY route:
- find a powersupply with 48V output, preferable up to 56-58V
- find a pinout how to power it up as stand-alone (google, lots of them are already figured out by others), or figure out yourself
- Check if it has current limiting (charge an empty battery bank, check with a DC clamp meter the current if you can't find a datasheet)

A nice one to look for might be an Eltek one. I do see them on Ebay: 15GBP for a 48V / 3000W / 62A unit.
Even without too much info, might be worth to give it a try if you have some electronics experiences.
They seem to have current limiting ( https://www.eltek.com/globalassets/...ectifiers-ds---24111x.105.ds3---1---7---1.pdf ) and for 15GBP it looks like a bargain to me.
you only need to make your own disconnect - stop charging when full since it's just a single voltage PSU.

Batrium even seems to have it supported in the past (ok, legacy, but still). googling around those Elteks seem to be nice units for various projects! They even sell board kits to use it for your own projects without having to mess with specific connectors

Batrium

support.batrium.com

Eltek Valere FlatPack2 48/2000 241115.100 Thai Modification, voltaje output mod

Eltek Valere FlatPack2 48/2000 241115.100 Thai Modification, voltaje output mod

www.ea1ddo.es

https://www.ebay.co.uk/itm/193562474340 (note for the 3kW you need to use the appropiate wires/connectors, and this listing is PCB-only)

Edit: i had a look into Octopus Energy.
Seems they also have a product Agile. That one allows dynamic pricings.
They do have an API. So you can interface with them to make your charging even cheaper.. Using the default rates if your SOC is really low, and use the low tarifs to enable your charger in all other cases. That might be cheaper than the off-peak rates for a regular subscription...
( https://octopus.energy/ifttt/ )
I don't know the prices for the regular offpeak, but it *might* be a lot cheaper to use this dynamic pricing.. if you can charge from 0.30-4.30 at eg 9p/kWh, and the pricing for the next day at 13.00-16.00 is only 4p (due to excess solar availabilty on the grid) it will be even cheaper to do so, and skip that specific night

 

[bazza2000]

Thanks for the comprehensive response. I'm still digesting all of the info, but in the mean time I thought I'd reply with some details you queried.
My current daily usage is ~30kwh.
At present my charges are locked in with Octopus Go:
Off Peak (00:30 - 04:30) - 5p/kwh
Peak - 14.63p/kwh
Come March 2022, which is the end of my current agreement, the current assumption is the following:
Off Peak - 5p/kwh
Peak - 25.87p/kwh (~76% increase)
In relation to the Arduino/rPI/ESP options, I currently run Home Assistant and have a number of different options already integrated around the house, so this could definitely be an option.
Thanks again, I'll have a better look at the links and the options when I get home from work later on.

 

[bazza2000]

Had a bit more time to digest and really like the idea of a separate Inverter/Charger setup. Need to do more research on the "Mean Well DBR-3200-48" but looks like its flexible enough on the surface. I could use my current home assistant solution to control the remote on/off which both removes a lot of the costs of systems which have extensive software options to perform all of this and also gives me the added flexibility of not being restricted to just the options available in the respective inverter software.
I've had a quick look at Growatt and MPP Solar inverters, but can't seem to find one with the SOC option you mentioned, do you have a specific model in mind?

 

[DJSmiley]

Not sure if you can read the SOC from these inverters directly.

However, you can add a Victron BMV (battery monitor) / Smartshunt between the battery and the inverter. That registers all flows in and from the battery and provides you with a SOC indication.
With an USB cable you can connect to the VEDirect bus, and make something to integrate it in your HA.
( see eg https://community.home-assistant.io/t/victron-energy-vedirect-bluetooth/20726/42 )

That allows you to not only read SOC, but also voltages from your batteries and current usage/charging.

You can for example configure your HA to enable charging from grid
- If SOC = <20%, then charge to 30%, any time and send message 'dude, this is going to be expensive....'
- If time = off-peak enable charger till SOC = 90% or off-peak = ending

That 3200 Meanwell is expensive, but you can charge 220Ah in the off-peak hours. You might be good to go with the smaller 1600W version, but it depends on your daily use.

As said: Those Eltek's are much cheaper. And with the HA you can use them as well. They are no chargers (don't stop when full) but that can be managed by HA..... A single one does about 60A, thus 240Ah during off-peak
If you connect 2, that would be double (But it does require sufficient grid capacity to feed them)

The Eleks also seem to have a remote on/of which you can use with a relay (or maybe optocoupler) to enable/disable them.
( See https://dta0yqvfnusiq.cloudfront.net/conle38747825/2018/07/Flatpack2-HE-Front-End-5b44b5d5e3926.pdf )

SHORT_PIN: The short pin is used to disable the rectifier if it is not fully seated in the slot. It is must be tied to OUTPUTin the shelf backplane in order for the rectifier to provide proper output voltage. The pin must be terminated.

Unfortunately, shipping is too expensive for me, otherwise I would have ordered a few, for 15GBP it seems a bargain. ( https://www.ebay.co.uk/itm/393534025226 )
Maybe they are still available next year, if covid doesn't f*ckup things anymore I'm planning on visiting the UK with my campervan.


As for the inverter: I'm looking into the MPP Solar's. They seem very affordable and also do have MPPT trackers. If you can, install solar panels. Even if they can't cover your usage, it still helps.. I don't know about the UK, but here in NL, the electricity price is only a small portion of the final bill. Total price/kWh = 'bare' kWh + all various taxes (which is about 0,15 eur/kWh). So even with a variable contract and a price of only 1ct/kWh I still have to pay 0,16 ct.

In the summer, solar panels will help. Might limit the amount of kWh you have to charge offpeak, but it might also cover for any AC usage.. So even a few panels might still be something to consider (Note: Many of those all-in-ones require a higher voltage on their MPPT, so you probably going to need 4 panels in series or so, or go with a seperate charge controller)

 

[edcoopered]

I'm building a UK grid only system in January when my cells my arrive (16 x 230ah), plan is Seplos BMS with Sofar ME3000SP inverter/charger, might add a second Sofar later if I'm often demanding over its 3kW rating.