Fast charging solar batteries at night

...Ghost...

I have a serious problem!

I'm addicted to solar and load shifting and I can't get enough. I blame all of you on here! 😋

I need a little nudge here, as I am planning the next steps.

My setup is currently 5kW Solis Hybrid with 5kW of solar and 15kWh LFP DIY storage (another 15 purchased for August), smart meter standard day/night EI tariff.

For those with larger than 15kWh storage and 3-4 hour super cheap night rate, how do you do it?

My hybrid inverter will only charge my battery at 5kW. So I can fully charge it in 3 hours, but when I add another battery, most likely another 2 batteries to bring me to 40kWh (usable), the inverter won't cut the mustard. My batteries will all be connected via bus bar. Reason I am looking at 40kWh, is my house uses this on average per day, divided over the year. The solar now supplements this, as does the load shifting with the 15kWh battery but winter is always coming.

I'm still new at this, but my thoughts are to either:

a. Add a dumb solis inverter and slave it out the master. Not sure how this would be wired to the batteries, but would allow faster charge AND discharge if I wanted to.

b. Increase the inverter size to allow for faster charge/discharge, but I would still be limited by the 3 hour window realistically and would rather keep my existing inverter for now.

c. Add a timed battery charger and connect to the bus bars. I think this is the most feasible option to get additional juice into the batteries, even if I am not able to fill from empty to full.

If I go with option c, I have some spare ways in the CU, so could safely throw at least 3kW (12.5A) at the batteries, couldn't I?

If I have 2 batteries and my inverter is throwing 5kW, they are sharing the load, so only charging at 2.5kW (or 10A) each. Now that I am looking at the numbers written down, I could probably just hook up a couple of 10A chargers on timers and let them feed the the batteries via the bus bars. It seems a bit too simple, so what am I missing here?

What way do you have yours connected lads?

I would love to add as much juice in as short a time as possible, as I am considering moving to the pinergy 5c 3 hour smart EV tariff. It would mean plugging the EVs in every night to keep them topped up, but I could live with that if I get my rate down that low and run the house off batteries the rest of the time. I would only ever draw from the grid when the house load is high, like when the electric shower is on, or I really need to top-up an EV during the day.

I'd be interested to know what battery chargers you use, or recommend, either connected to the CU directly, or from a 13A domestic plug. Thanks all in advance for your input on this and other questions I asked elsewhere.

jasgrif11

Option C: Rectifier will allow you add another 3kW charge at night. Wire batteries in parallel
https://www.aliexpress.com/item/1005003755306962.html?spm=a2g0o.order_list.order_list_main.26.1d341802Ro7fws

Option B: There are larger inverters (8kW), but NC6 only permits 25A export.

...Ghost...

https://www.boards.ie/discussion/comment/122330415#Comment_122330415

Thanks for that. I had been looking at a victron one, but it's pricey and doesn't add as much as what you've linked judging by a quick look at the specs.

SD_DRACULA

There is only king in power and price: https://www.deyeinverter.com/product/hybrid-inverter-1/sun12-14-16ksg01lp1-1216kw-single-phase-3-mppt-hybrid-inverter.html This would be my second choice but only available in the US which is annoying:

https://signaturesolar.com/eg4-chargeverter-gc-48v-100a-battery-charger-5120w-output-240-120v-input/

...Ghost...

https://www.boards.ie/discussion/comment/122331159#Comment_122331159

The EG4 would be a nice to have, but as you say…only available in the US. I don't know when next i'll be state-side, but might bring one back when I am.

SD_DRACULA

https://www.boards.ie/discussion/comment/122332072#Comment_122332072

You can easily order it with anpost address pal or whatever is called but I assumed some customs will have to be paid.

...Ghost...

I want to go with 35mm^2 or 50mm^2 cable and parallel the batteries for now. I'll add a bus bar between the first battery and the breaker to connect an AC charger later. I have no problem finding 35 or 50mm^2 cable and lugs, but I can't seem to find the connector to go into the Solis inverter.

The existing cable is 25mm^2 which is fine until I add another load for charging. I can see 35mm^2 Seplos Mason plug connectors, but I don't know if these are the same connections to go into the Solis inverter. If I am running the juice from the batteries through the cables pretty much 24/7, it probably makes sense to go with the bigger cable to help keep it cool/safe.

Any pointers?

These are the connectors I am talking about for the mason kit, but I don't know if these are the same connection the inverter takes.

Seen these ones on Ebay which are probably more what is needed? Again, not sure if compatible.

SD_DRACULA

https://www.boards.ie/discussion/comment/122337275#Comment_122337275

They are not the same plug, you need to unplug the Solis end and measure the internal diameter of the "round" plug inside, it will be something like 6 or 8mm and then buy the correct one but I am about 99% sure it cannot take anything bigger than a 25mm2 cable on the solis side as I did this same research a while back.

My dyness batteries came with 35mm2 cable and surlok plugs and it would not fit into the solis, too big.

Also no point in doing it since the solis can't pull more than 100a anyway so 25mm2 is fine

...Ghost...

https://www.boards.ie/discussion/comment/122337576#Comment_122337576

If upgrading the cable going into the solis, I expect that both the male end which connects to the cable AND the female end on the Solis would need to be changed out.

Here is where my concern is.

1. I connect the batteries in parallel with 35mm^2 cable right up to the 125A DC breaker.
2. I connect from the breaker to the inverter the 25mm^2 cable that came with the Solis.
3. I connect a bus bar between the DC breaker and the 1st battery and connect an AC-DC charger to that in order to charge the batteries more quickly during the night.

When charging the batteries at 5kW from the inverter and also using a 2kW AC-DC charger, wouldn't that cause excessive heat on the 25mm^2 portion of the line between the breaker and the inverter? Or maybe there would be no excess heat on the smaller cable, because the batteries are drawing the power toward them and away from the 25mm^2 line?

Man, I hate electronics!! I over-engineer the problems or questions out of my design.

A drawing aid:

graememk

https://www.boards.ie/discussion/comment/122338450#Comment_122338450

The most the leads to the solis will see is 100 amps. And it's protected by the 125 amp MCB.

Fuses and MCBs protect cables not devices.

Id want a fuse of some sort on the charger too.

It's not electronics, it's electrics 😉

SD_DRACULA

https://www.boards.ie/discussion/comment/122338450#Comment_122338450

Not a chance of overheating, sure every battery will only be able to send a max of 33a and then at the joining point will still be 100a.

If you know you're not updating the inverter in the future I wouldn't even bother with 35mm2 cable for the batteries, use 25mm2.

And yeah what @graememk said, you could add a fused switched disconnect instead of the DC breaker (assuming each battery has its own breaker in it)

...Ghost...

Thanks lads. Feeling a lot better about what I am doing now.

https://www.boards.ie/discussion/comment/122338888#Comment_122338888

Grand, so for the medium term, the 25mm^2 will do the job. I don't think I will put a breaker between each battery as originally planned, but I will have the one shown in the diagram.

I hadn't thought of it, but yeah, I would have put a fuse, or breaker between the bus bar and the charger. A switched fuse might make most sense there?

Electrics 😁

https://www.boards.ie/discussion/comment/122339168#Comment_122339168

I don't see myself upgrading the inverter anytime soon. I will be adding more panels and with that, I will be adding another inverter to my system. I'm thinking a dumb inverter to keep it simple.

I'd really love to be able to lift the ability for the solar/batteries to fill larger draws from the house. I was observing earlier that between the batteries and the solar, the max the house could take via the inverter was the 5kW. 3kW from the solar and 2kW from the battery with the other 2 coming from the grid. Would have been nice to see 4kW coming from the battery instead.

Maybe having the second system as an independent system would solve this? A dumb 5kW solis with no batteries feeding into my shed CU which will connect to the main CU?

Are you connecting your new roof panels to your existing inverter, or going for a separate unit?

Anyway, I better get back out there and finish the second cabinet frame while the weather holds off.

oaklands

On my 5kW Sunsynk the max current is 109A (Discharge) & 88A (Charge). The 35mm2 cables get noticeably warm but not 'hot'. See image below.

Remember the current will depend on the voltage level at any time. The numbers above assume the current measurement is accurate. (I did calibrate the voltage on the BMS & simple calculation suggests the current numbers above are OK-ish)

If adding an additional 2kW Ac charger, then add 40% to the numbers current numbers above, which will get you over the 125A breaker!!!. (actually circa 125A for charging only which is too close for a 125A breaker/fuse)

@SD_DRACULA Note that 33A to/from each battery is correct unless one or two are offline when the current will be 50A or 100A. So need to design for full 110A on a 5kW LifePo4 system (or ~125A on a 5+2kW system)

...Ghost...

https://www.boards.ie/discussion/comment/122339370#Comment_122339370

The numbers I was getting when doing the sums were based on 48V. So, (5kW @ 48V = ~105A) + (2kW @ 48V = ~42A) = ~150A. If I were to use a 1000W AC-DC charger, the sums put me at the ~125A max.

I was sure I must be wrong and I still think I am doing something wrong with the math, because it seems nuts that adding a relatively small DC charger would max out the 125A breaker. And if my math is correct and the Amperage is going to be as high as 125A - 150A, then should I be looking to upgrade the cables and breaker if I want to add a charger?

What about this breaker?

https://www.amazon.co.uk/Heschen-Circuit-Breaker-HSM1PV-250-Photovoltaic/dp/B0C7VC2DF4/ref%3Dci_mcx_mr_mp_m_d_sccl_3_14/262-8104047-6343767?pd_rd_w=oSFhQ&content-id=amzn1.sym.f7bedd75-e78c-4f36-bec2-2c45c51ef5c3:amzn1.symc.15cbde64-36a4-47c6-b315-5d1a0d7227bc&pf_rd_p=f7bedd75-e78c-4f36-bec2-2c45c51ef5c3&pf_rd_r=EEX8F2GN37G6HH976S1W&pd_rd_wg=QHmwo&pd_rd_r=66544186-59a5-432c-9db1-0c678fc36a63&pd_rd_i=B0C7VC2DF4&psc=1

graememk

https://www.boards.ie/discussion/comment/122340234#Comment_122340234

People are getting mixed up.

As per your drawing you were connecting your charger on the battery side of the MCB. That's fine.

Then I suggested adding another MCB on the cables of the charger.

It's to protect the cables.

...Ghost...

I ran out of battery twice in the past week because of poor weather. I finally got the second battery installed this evening. I used a hoist to get both batteries onto wall cabinets I built for them. The battery packs are connected in series. B1 was at 50% and B2 was at 30%. The inverter showed a total of 40%, so it looks like comms are good.

I'll know soon enough if I need a third battery, but I am hoping these 2 do the job. ~26kWh useable. I can take 20kWh during the 2am-6am Energia cheap rate without changing my setup. Car charges at same time at 7kW.

Until my supply is upgraded, I won't be drawing anything more, so a third battery would be pointless right now anyway, as I wouldn't be able to charge it most nights.

Here they are. Cabinets will have fronts on them before the cold weather hits.

flatty

Does anyone forsee any problems down the line with home insurance and batteries?

graememk

Id be worried more about the dodgy chargers, and li ion phone batteries/ scooters/ etc rather than the LFP batteries in the solar storage batteries

The batteries used in solar systems are LFP or LiFePO4 (same thing but different ways of writing it)

Battery tests from gwl

https://youtu.be/Qzt9RZ0FQyM?si=-2xyLsT3uEM7iWwD

paddy236

https://www.boards.ie/discussion/comment/122339370#Comment_122339370

I'm also seeing a charge current of 88A with my Sunsynk 5kW, even though the datasheet says 120A. I have the BMS set to 120A.

What is limiting it to 88A charge current?

graememk

Likely the AC grid input current.

What is your grid voltage? Your prob pulling the 22 amps but if the grid voltage is 220 instead of 230-240v which would reduce the power a bit.

oaklands

https://www.boards.ie/discussion/comment/122583739#Comment_122583739

I presume you are talking about charging from Grid @ 5kW…..its the overall charge/discharge kW power which is the actual limit not just the individual current or voltage limits.
I would assume that you might get better charging if coming from Solar (@ max solar or a combination of Solar + Grid))

P=V*I

That threw me initially too.

So if you had a very low battery pack voltage of just over 40V then you could see the ~ 120A.

SD_DRACULA

Precisely, my 8kw sunsynk was doing the same, it is rated 200a charge/discharge, from grid it would max out at 140a which was 8kw AC but from panels it could go up to 200a just fine.

paddy236

Yes, looks like i'm maxed out at ~5000W.

on_the_roots

Is it ok to simply connect a "dumb" charger like this (no way to schedule charging time directly on the charger, only via timed switch) in parallel with the inverter?

I have Energia 2~6am EV plan. Can I simply set the time switch of the charger to start 2am and stop at 6am? What could go wrong if the inverter stops charging say at 5am (100% SOC) and the additional charger continues on until 6am?

...Ghost...

https://www.boards.ie/discussion/comment/122897173#Comment_122897173

Good question. With the inverter connected to the BMS of the battery, the BMS can tell the inverter when the pack is full and the charging will stop. With a dumb charger, I am not sure what would happen, because it is already on the battery side of the inverter.

There is nothing to tell the dumb charger to stop feeding power to the circuit as far as I can tell. I'm guessing here, but maybe as the batteries reach a high SOC, the power reduces in the same way a small AA/AAA battery charger works. As the voltage of the pack gets closer to the rated voltage of the charger, the "pressure" from the battery increases and less power flows into the pack and eventually they equalise, stopping the flow completely.

Anyone else?

graememk

https://www.boards.ie/discussion/comment/122911706#Comment_122911706

Yep thats how it works. (And how the inverter works) They don't vary the voltage, they output the charge voltage and the battery pulls it down to its voltage.

The BMS will cut the connection to the battery if a cell goes out of spec. Not graceful (not demure 😂) but will protect the battery.

Voltage of the charger is important too. 56v would be a safe one, but will drop off as the battery fills past 56 v and the inverter does the sole charging.

Technically you could run the inverter from the charger.. (say if power was out and you had a generator)

on_the_roots

Thanks guys. That's what I thought initially, as long as there is voltage difference between the battery and the additional charger the current will flow until they match and it stops.

My idea is to just give a boost on the charging and stop at some point before both batteries reach 100% SOC, leaving the final stretch to the inverter only. I'm thinking on one of those Emmerson chargers @54V to help lifting the SOC to 80~90%, then it stops and leave the rest to the inverter alone. I'm expecting to be able to pull the entire 32kWh for both batteries + the absorption phase within 4h cheap rate window. (my inverter is a 5kw Solis).

graememk

54v is too low, that's only 3.75 per cell, when under charge. And at that point the separate charger will be delivering 0 current

As you push more power into a battery the battery voltage will rise accordingly, (take away that charge and the voltage would quickly drop back down)

on_the_roots

https://www.boards.ie/discussion/comment/122912719#Comment_122912719

But 54V is 3.375V per cell (16x), isn't it around ~80% SOC?

I just want something to stop feeding current at most 95% SOC. Then a smart switch will turn off the additional charger and the inverter finishes the charging.

graememk

https://www.boards.ie/discussion/comment/122912900#Comment_122912900

with LFP unless full or empty, you cant really get the SOC from voltage. Especially not if under charge or discharge.

Here's mine charging last night from about 40% SOC (actually 45, as i know its currently 5% out)
More or less straight away it goes above 54V, Pushing around 130-140 amps. until near the end of charge, where the current drops back. As the voltage of the pack gets closer to the charger voltage it will slow, and then stop if the battery passes it.
What is your charge voltage currently? id go maybe 0.5 -1v below it. Then you dont have to have automation to stop the charge.

...Ghost...

https://www.boards.ie/discussion/comment/122912900#Comment_122912900

I went with the 57V Emerson. Not installed yet. There is no reason to dial down the voltage by getting a lower rated charger, as this will b done automatically with a 56 or 57V Emerson. The over voltage on the BMS is 57.6V, so why go lower than 57V?

Also you won't be charging 32kWh, as you will have a 15% buffer, right? That's 5kWh less, so you have 27kWh available. Over 4 hours, he inverter will charge the batteries by 20kWh. There then remains 5kWh (15%) you can't access and 7kWh (21%) of useable buffer. So, why your SOC is 36% or higher at 2am, your batteries will fully charge. How much energy do you use outside of the 4 hour window?

Based on your pack size:

100%=32kWh

10%=3.2kWh

15%=4.8kWh

1%=0.32kwh

3%= 0.96kWh (1kWh)

on_the_roots

@graememk

Interesting. I didn't find a way to see the charging voltage remotely, but I believe this is 58V as it peaks at this value just before reaching 100% SOC.

@...Ghost...
I allowed the inverter to discharge the battery until 6% SOC. So the buffer here would be something around 2kWh max?

This inverter charges @~4.75kw, not 5.

Also, looking at the charging curves it takes about 20min between 99% to 100% with a very low charging current (is this the absorption phase?).

Considering I have to start the charging at 2:05am (stupid inverter drifts the clock forward overtime) I have to pull up to ~30kWh in roughly 3,5 hours in a cloudy and very cold day.

...Ghost...

https://www.boards.ie/discussion/comment/122913231#Comment_122913231

I'm conservative and keep 15% buffer with forced charge at 10%. Considering dropping those by 5 points each, keeping safe because of potential cliff dives or temperature drops which could damage a very low SOC battery. If you are using 30kWh regularly from the pack daily, you might want another battery.

I have 48kWh with 40kWh useable. I tend to use around 20kWh, so I have a big reserve which I have used a few times. The dumb charger will let me dump some power to the grid ad hour or two before the cheap rate and then I will get up to 30kWh between the inverter and charger over 4 hours. Benefits of exporting for extra credit, and my pack will be better cycled from low to high.

We suck another 25ish from the grid to the EVs most nights too.

graememk

https://www.boards.ie/discussion/comment/122913231#Comment_122913231

Can never remember what way around is float and absorption.

But what your seeing with the battery slowing it's charge at the end is the voltage difference between the battery and inverter getting smaller and smaller.

The closer the two voltages are, the less current flows.

I don't have a seplos, so I can't say what setting influences the requested charge voltage

on_the_roots

https://www.boards.ie/discussion/comment/122913307#Comment_122913307

I'm aware of the risks with discharging below 10% SOC. This is not every day it discharges to 6% and this is only until I get my 2nd battery (hopefully this month). With 2x batteries I can raise it to 10/15% as it will be very rare to discharge this much.

Sounds like we have a similar project in mind with a second charger. I will see how it goes before ordering an Emmerson rectifier.

mjatkey

https://www.boards.ie/discussion/comment/122913464#Comment_122913464

I found this on DIY solar, not sure how accurate it is, not sure what they mean by current bridge is best way for SOC?

graememk

https://www.boards.ie/discussion/comment/122914123#Comment_122914123

I assume it's a current shunt.

You measure power in/power out. That's how the BMS do it. And that's also why a good 100% is critical. It's a form of dead reckoning.

300ah pack, you count 150 ah out, your at 50% you count 100ah back in your at 83%.

There will always be drift due to losses/self discharge, and that's why a semi regular 100% is needed.

Your chatting about a tenth of a volt according to that chart between 40 and 80% and that when the battery is at rest too, not under active charge.