DIY Battery Is Alive !!

[johnb2713]

As some of you will know Ive been making my own 14 kWh AC coupled battery storage system. The first switch on was yesterday, the good news is there was no smoke / fire, the bad news is it didnt work. Schoolboy error and couple of changes resulted in the Victron Inverter talking no problem at all to the SEPLOS BMS. I very briefly did a short test charge and a short discharge due to it being dark and raining. The SEPLOS BMS emulates about 10 different main stream battery protocols and even though Victron dont have it on their approved list, it work flawlessley.

Today I have fully charged the battery and it's currently discharging running the tumble drier, washing machine, dishwasher and 2 aircon units for good measure.

The EVE cells look absolutely amazing and showed only a 1 deg C temperature increase whilst charging at 70 amps.
The total cost including the shed and all of the ancilliary bits was £4250, the inverter being a premium product and one capable of 5kW continuous output on battery being about half the total cost. Payback should be around 2 years at the current prices assuming no solar storage which of course there will be.

It looks pretty cool with 4.7 kW load on the system the battery charge only going down on a very shallow slope. For a short time this morning both the Growatt and Victron inverters were running feeding the house with no problems fighting each other which was a worry I had.

So, on Sunday our Christmas dinner, heating and lighting will all be from off peak electricity stored on my battery systems.

Have a great Christmas - J

 

[bladerunnerpv]

Congratulations on your successful project John, , hats off to you and so glad to hear it didn't end up as a complete turkey.

Would be great to see a schematic and hear more about how you did this whenever you have time & inclination

I think I should recommend a final system test though - check you have some cranberry sauce....!

 

[roys]

Very interesting John

 

[johnb2713]

It was a bit of a leap into the unknown and very much outside my experience namely - 2 x grid tied inverters from different manufacturers, a BMS that was not on the approved list which resulted in Victron refusing to discuss any aspect of it (the user group forum was excellent though and a german expert logged into my system and confirmed it should work).

I will do a schematic of it all when I get a minute or two, if anybody wants to have a go at this I'm happy to help.

 

[ProDave]

Please tell me more about the grid tied inverter(s) you are using?

I too am considering a DIY battery storage system, and the brick wall I have hit is finding an grid tied inverter where you can set the output power from it to match your load (so you don't export any) So I am very interested in a technical discussion on how you are doing that please.

 

[roys]

Me too ^^^

 

[Leigh Winspear]

It was a bit of a leap into the unknown and very much outside my experience namely - 2 x grid tied inverters from different manufacturers, a BMS that was not on the approved list which resulted in Victron refusing to discuss any aspect of it (the user group forum was excellent though and a german expert logged into my system and confirmed it should work).

I will do a schematic of it all when I get a minute or two, if anybody wants to have a go at this I'm happy to help.

Sounds brilliant but scary.................what energy supplier or plan do you need to be on if this matters?

 

[johnb2713]

The nuts and bolts of it are really straight forward with three major components - The battery, The BMS and the Inverter.

Batteries
I looked at these for quite a while and it seemed the 'EVE' cells were the ultimate cells to get, there are lots of reviews around on the net, I purchased mine at a very good price from Fogstar. There seemed to be two sizes 100a/h or 280a/h, I went with 280a/h. 16 of them in series, I built them into modules of 4 to make them easier to handle and house etc.
The batteries are all wired in series and connected to the BMS.

BMS
Battery Management System, it protects the batteries from overcharging, over discharging and will balance them too. It does have other features such as short circuit protection, temperature monitoring etc. There is a small signal wire from the BMS to each cell so that it can read the voltages. I did this on my modules with a small 7 pin socket giving me the 5 cell connections and the temperature probe. The main battery leads came out onto Anderson connectors. The BMS output goes to the inverter.

Inverter
My existing inverter is a Growatt SPH6000 Hybrid, originally I was going to use one of these but later found on battery it's output was only 3 kW. More searching and I cam across a Victron Multiplus II GX 48/5000. This unit was designed to be used on boats, large RV's as well as domestic installations. The number of settings in the configuration is scary, there's way more than on the Growatt. That said theres very good support for it with a lot of very knowledgeable people falling over themselves to help, they really are geeks on this subject. A potential nightmare is the communications between BMS and inverter, there are about 15 batteries on the Victron approved list, my BMS was not one of them but I was assured the Seplos unit would talk to it. The inverter can communicate to the monitoring by ethernet or WiFi, the BMS comms is handled by Canbus with a modified network cable. The only other sensor involved is a CT on the meter tail, I was concerned about this because it's 25 metres away. I pulled the CT apart and added 25 metres of screened twisted pair.
All of this was built into a small toolshed at the side of my house (£170 on Amazon) it was a perfect size and half decent quality. Obviously I had a DC isolator, a DC fuse, I also installed a small consumer unit on the 50amp supply to give me local sockets, lighting and an inverter MCB

Configuration
I have set the inverter for 0w export and scheduled charging 00:30 to 04:30 which will be occurring for the first time tonight (I did try another schedule to prove the function). With the export at zero it doesn't try to export at all, it simply stays 3 or 4 watts on the import side, the Growatt inverter happily co-existing. This morning when the sun came out briefly the Victron started to charge the battery with the excess energy (I assume it had seen the grid export via the CT in order to initiate the charger. I'd like to claim to be an expert in this DIY battery but the truth is, it was really simple just a lot of it . The Victron Inverter is an extremely heavy unit, built to last by a very well respected company and I feel it was the secret to the success of my little project.


This is one of the 4 battery modules. You can see the threaded rod keeping the cells in compression and the perspex lid magnetically held down on top of the battery module. The Anderson connector at the front is rated at 175 amps I'll be running a maximum of around 100 amps so a little bit over whats needed. The circular connecter at the side is for the balance lead from the BMS, you can see the thin wires going to each battery terminal, I was slightly concerned about getting short circuits on this wiring and connectors, I added a 500mA wire ended fuse on each wire under the heat shrink at the terminals.


This is what the BMS looks like, I made a trial front panel for the stand before make the final version.


This is the start of the heavy wiring to the BMS, this was the only part I didnt like the design. The negative has to go onto the shunt in the middle, you end up with 4 x heavy cables onto the PCB.



This is my little power shed, the lower door is the battery compartment. The two temperature controllers on the R.H wall look after heating and cooling.


This is the simple inverter monitoring screen that tells the story nicely.

The whole project took weeks of research trying to find the right tools for the job, I believe it paid off really well and was very much worthwhile spending time and money on it.

Key Parts
Victron Multiplus II (Amazon is as good a place as anywhere for this)
Seplos BMS (direct from Seplos in china. They give great support throughout)
EVE Cells (Fogstar UK based and give good prices).

 

[johnb2713]

Sounds brilliant but scary.................what energy supplier or plan do you need to be on if this matters?

I'm on Octopus GO which gives me 4 hours at 7.5p kWh and 20 hrs at 29.2p kWh. By almost maxing out my grid supply (96 amps) I can charge both batteries, both EV's, dishwasher, Washing Machine, sometimes tumble drier and immersion heater all running in that 4 hour period.

 

[ProDave]

Thanks for a fantastic explanation.

What technology are the batteries?

Total cost for all that kit?

I was going to mention the monitoring cables and potential hazard but you thought of that with the in line fuses.

I am thinking of s similar system, but I am not interested in charging from the mains, i literally want it to charge only from the solar PV panels and only discharge through the inverter and only when the house is importing so never to export anything. So not sure your inverter charger is what I want but is is all good stuff.

 

[roys]

Well done John this is the type of mix of clever and practical stuff I like.

 

[johnb2713]

Thanks for a fantastic explanation.

No problem.

What technology are the batteries?

LifeP04

Total cost for all that kit?

Including the shed and all ancilliaries (mini disboard, cooling fans, heaters and temp controllers and the shed £4247.62

I was going to mention the monitoring cables and potential hazard but you thought of that with the in line fuses.

It was a sort of lightbulb moment as I soldered up the small balancing sockets, the though of a short in there. My first thoughts were to let the cable blow which it would have done easily but then wire ended fuses were lee than 1 p each so it seemed to make sense to include them.

I am thinking of s similar system, but I am not interested in charging from the mains, i literally want it to charge only from the solar PV panels and only discharge through the inverter and only when the house is importing so never to export anything. So not sure your inverter charger is what I want but is is all good stuff.

The Multiplus II can do that, simply turn off the mains charger it will then take charge from the solar via the AC when it sees an export taking place and will output from batteries when an import is happening.

 

[johnb2713]

Well done John this is the type of mix of clever and practical stuff I like.

Thank you, it's been a lot of work but very worthwhile and I've learned a lot on the journey.

 

[Ucatchmydrift]

Looks like youve done an amazing job there john, all very professional, neat and tidy, with the added bonus of knowing exactly how everything works as you build it all from scratch, making any future faults far easier to diagnose versus a kit that a company installed for you!

Also a thank you from me as i may not have gone down the diy battery route myself if it was not for you suggesting it a number of months ago

Ive been up and running too now for a few weeks and its an awsome feeling getting all that energy from the grid at cheap rate and using it throughout the day avoiding the expensive bills. (not to mention any free energy from the solar panels, which is often not alot this time of the year!)

(im currently paying about 12.5p kw/h from 12:00- 0700 via edf economy 7, (which is changing to 8.8p kw/h in january!) and octopus have not been taking any new customers for their cheap ev tarrif now for a few months, BUT, apparently, utilita offer an economy 7 tarrif of 10p kw/h, but NO standing charge! (they charge 90p kw/h for the first peak hour used each day instead, but for us, that would be ideal as we obviously will never be using peak priced leccy again! Ha!) - meaning, for me personally that would mean that a maximum bill of £24 a month based on my 8kw daily usage! - and thats with no solar! - so basically free for most of the year, and a max of £24 for a couple/ few months. Not bad.

Going to have to do my own little build thread now lol! (im currently top balancing my second battery bank, giving me the same amount of storage as you- 14.4kw!)

 

[ProDave]

The Multiplus II can do that, simply turn off the mains charger it will then take charge from the solar via the AC when it sees an export taking place and will output from batteries when an import is happening.

It's a little more complicated and a little less standard.

I already have an ordinary 3.68kW simple system of panels and inverter. Most of what that generates is self used, very little gets exported.

I am looking at adding a second set of PV. No point havint that on a simple grid tie inverter, much of the time that would mean generation would then exceed what I can self use.

So what I want from my second system is the PV panels only charge the batteries, no direct connection to the grid. And then the batteries feed a grid tie inverter to power the house mostly in the evenings or other times the main PV is not generating much. The inverter from the second system will need to monitor import / export and only power up the inverter when the house is importing and never allow export.

It is the inverter for that I have not yet found.

 

[johnb2713]

It's a little more complicated and a little less standard.

I already have an ordinary 3.68kW simple system of panels and inverter. Most of what that generates is self used, very little gets exported.

I am looking at adding a second set of PV. No point havint that on a simple grid tie inverter, much of the time that would mean generation would then exceed what I can self use.

Understood.

So what I want from my second system is the PV panels only charge the batteries, no direct connection to the grid. And then the batteries feed a grid tie inverter to power the house mostly in the evenings or other times the main PV is not generating much. The inverter from the second system will need to monitor import / export and only power up the inverter when the house is importing and never allow export.

The Multiplus II does have a remote input that you can use to switch it on and off, maybe thats an option, a timer and relay detecting import start the inverter up.

It is an odd sort problem, I can see their would be difficulties with typical off the shelf systems.

It is the inverter for that I have not yet found.

 

[johnb2713]

Looks like youve done an amazing job there john, all very professional, neat and tidy, with the added bonus of knowing exactly how everything works as you build it all from scratch, making any future faults far easier to diagnose versus a kit that a company installed for you!

Thank you, I am pleased with the end result, my next one will have a bespoke stainless steel enclosure.

Also a thank you from me as i may not have gone down the diy battery route myself if it was not for you suggesting it a number of months ago

Thank God it worked or i'd be responsible for the failure LOL

Ive been up and running too now for a few weeks and its an awsome feeling getting all that energy from the grid at cheap rate and using it throughout the day avoiding the expensive bills. (not to mention any free energy from the solar panels, which is often not alot this time of the year!)

Yup, mine is currently charging from the sun at 1.8 kW, absolute result.

(im currently paying about 12.5p kw/h from 12:00- 0700 via edf economy 7, (which is changing to 8.8p kw/h in january!) and octopus have not been taking any new customers for their cheap ev tarrif now for a few months, BUT, apparently, utilita offer an economy 7 tarrif of 10p kw/h, but NO standing charge! (they charge 90p kw/h for the first peak hour used each day instead, but for us, that would be ideal as we obviously will never be using peak priced leccy again! Ha!) - meaning, for me personally that would mean that a maximum bill of £24 a month based on my 8kw daily usage! - and thats with no solar! - so basically free for most of the year, and a max of £24 for a couple/ few months. Not bad.

I have heard that Octopus arent taking people on for EV tariffs but I'm also told if you ring them up it's no problem. You have to go onto a standard tariff first and then transfer to GO etc.

Going to have to do my own little build thread now lol! (im currently top balancing my second battery bank, giving me the same amount of storage as you- 14.4kw!)

View attachment 14661

Excellent, that looks good, where did you go for the batteries, was it Fogstar?

What BMS / Inverter combination are you using? any comms issues?

J

 

[Jedw]

Good job John. Any DNO obstacles ?
@dave Have a look at the 5th gen Solis hybrid inverters, you can set export to zero so pv charges batteries with anything thats not self use. You will need an energy dump for over generation.

 

[binky]

It's a little more complicated and a little less standard.

I already have an ordinary 3.68kW simple system of panels and inverter. Most of what that generates is self used, very little gets exported.

I am looking at adding a second set of PV. No point havint that on a simple grid tie inverter, much of the time that would mean generation would then exceed what I can self use.

So what I want from my second system is the PV panels only charge the batteries, no direct connection to the grid. And then the batteries feed a grid tie inverter to power the house mostly in the evenings or other times the main PV is not generating much. The inverter from the second system will need to monitor import / export and only power up the inverter when the house is importing and never allow export.

It is the inverter for that I have not yet found.

You're making life over complicated for yourself, just use a grid tied hybrid inverter set for zero export. No need to reinvent the wheel!

 

[shaunuk]

Looks great !

Any figures on how much energy the heater uses for keeping the batteries warm ? I need to do this soon. Also how are you getting on with the 5000kva victron. Do you find you are always pulling annoying extra power from the grid ? With my multiplus II 8000 when it’s on grid and the house pulls more than 6.5kw the additional comes from the grid. When it’s off grid it can make 9.5kw sustained (although complains about overload)