Solar PV battery options

unkel

Deagol wrote: »

This is just my slightly educated guess as to why they don't like 16x2!

A BMS can only reliably read the voltage of individual cells, so if they are in parallel the reading gets dodgy. That's why for 32 cells you can have 2 times a 16S1P battery in parallel with both packs having their own BMS or you can have a single 16S2P pack, but this is not recommended

Better of course would just be to get cells of double the capacity, so you could still have your 16S1P pack with just the one BMS. But cells like that can be expensive or even non-existent

Personally with CALB cells I'd go with the 16 * 200Ah. I ordered mine last month to replace my current setup of 16 * 90Ah that I installed last year. Who knows I might upgrade again in a year or two to 16 * 500Ah depending on how much they then cost, how much my current batteries are then still worth, etc.

DrPhilG

unkel wrote: »

That's why for 32 cells you can have 2 times a 16S1P battery in parallel with both packs having their own BMS or you can have a single 16S2P pack, but this is not recommended

If using this scenario, can both packs still connect to the one inverter, in the same way that I currently have 2 PylonTech?

Again the downside though being that the inverter (and me) have to guess the SOC.

championc

Two separate strings can be paralleled. Each string would have it's own BMS and the output of each joined into the Solis. The positive side would also be similarly paralleled.

And think about the marine switch knobs for isolation of one string from another. Ensure all MCB's are 2 Pole for disconnection of both the positive and negative legs

It could be that I could have got a combo Canbus and BT if I ordered both st the same time, but it sounded like something internal in the unit I bought made it impossible to go Canbus after the unit was shipped.

graememk

As for 3 strings of 16 on one Inverter,

I'm not sure what's the max AH setting, maybe

But that's 30kwh, it would take 10 hours to charge that at 3kw. - only ever get that on the best of summer days. - and that is what's not used by the house.

Then what do you do with it? Discharge when on night rate?

DrPhilG

Some light reading/viewing for me, and anyone else who might be interested...

DALY Official Store wrote:

Daly Smart BMS Tutorial Video https://www.youtube.com/channel/UCENHUfQQqPXwQwH6mMAAvMA

1. Daly Smart BMS Touch screen Connection Tutorial https://www.youtube.com/watch?v=uVzdiTusfK4

2. Daly Smart BMS SOC light board Connection Tutorial https://www.youtube.com/watch?v=SxJWjg5Geic&t=96s

3. Daly Smart BMS PC screen Connection Tutorial https://www.youtube.com/watch?v=lIDImJAK5F0

4. Daly Smart BMS CANBUS Connection Tutorial https://www.youtube.com/watch?v=nZnDJsilcr4

5. Daly Smart BMS Bluetooth APP Connection Tutorial https://www.youtube.com/watch?v=xnHunhNvrTg&t=6s

6 Daly Smart BMS UART、RS485 Connection Tutorial https://www.youtube.com/watch?v=iwdChhE1NIY

DrPhilG

graememk wrote: »

Then what do you do with it? Discharge when on night rate?

Maybe so, yeah. If I filled the battery on August first, then I could quite possibly not draw a tap from the grid the rest of the month. August 1st at sundown, I'd start discharging. Would probably be down to about 20kWh by the start of generation on the 2nd so would be full again by the evening and repeat.

The only thing that would take the battery down to empty would be either a crap days generation, or charging the car overnight.

You're right though, it's probably overkill and I doubt if I'll go above 20kWh but just curious on the theory.

DrPhilG

championc wrote: »

Two separate strings can be paralleled. Each string would have it's own BMS and the output of each joined into the Solis. The positive side would also be similarly paralleled.

Thanks, I think that's probably the cleaner option. Increased bms costs but they're not that expensive so not a big deal. When you say the output of each joined into the Solis, is that possible? 2 separate canbus inputs? Or do they merge first?

championc wrote: »

And think about the marine switch knobs for isolation of one string from another. Ensure all MCB's are 2 Pole for disconnection of both the positive and negative legs

I will do, once installation looms I'll make up a list of the bits and pieces needed and I'll have my spark help out with the connections.

championc wrote: »

It could be that I could have got a combo Canbus and BT if I ordered both st the same time, but it sounded like something internal in the unit I bought made it impossible to go Canbus after the unit was shipped.

Cool, thanks. I thought perhaps they were just telling me what I wanted to hear but 3 different suppliers on 2 different products have now said that it's possible so hopefully they're right.

graememk

DrPhilG wrote: »

Thanks, I think that's probably the cleaner option. Increased bms costs but they're not that expensive so not a big deal. When you say the output of each joined into the Solis, is that possible? 2 separate canbus inputs? Or do they merge first?

Its the power thats joined together. - no idea on the canbus though

Both strings should track with each other so really you'd only be needing to connect 1, as the inverter should be cutting off before the bms has to.

championc

You're right - not sure how two BMS's would "talk to the Solis (or any other for that matter). Pylontech have theirs daisy chained.

I apologize as I have mislead you. It was RS485 I was looking for with BT rather than Canbus.

The reason being that we can set the Sofar ME3000 into a passive (dumb) mode and then control it over RS485 using Node-Red. I figured that if I could read the SOC from the BMS by RS485, I could then tell the ME3000 what I wanted it to do. This is all to do with charging to certain levels using night rate particularly during the winter. For instance, I only charged to 40% on Monday night and the excellent day yesterday got them up to 100% from there. The previous two days I charged to 100%, due to the crap forecast on those days.

DrPhilG

Just got a message back from the OYE store, who I had been asking about BMS solutions also.

They're recommending the previous suggestion from both graememk and championc. They just sent this drawing, presumably just scribbled up by the sales guy lol.

[IMG][/img]

DrPhilG

Just got a message back from the OYE store, who I had been asking about BMS solutions also.

They're recommending the previous suggestion from both graememk and championc. They just sent this drawing, presumably just scribbled up by the sales guy lol.

graememk

Hah, 16s2p like we said. At least it's clarified now!

DrPhilG

graememk wrote: »

Hah, 16s2p like we said. At least it's clarified now!

Yeah the guys at Solis just said the same too.

They don't officially support home build batteries of course but they said that (a) a canbus connection from the BMS will allow the Solis to read SOC etc and (b) they also recommended 16s2p.

Deagol

graememk wrote: »

Hah, 16s2p like we said. At least it's clarified now!

Just don't drop a spanner across any terminals

Seriously though, i'd wonder what the failure rate is on a cell? Having so many makes me concerned about the reliability. Would it make sense to buy a couple of spare cells?

championc

Deagol wrote: »

Just don't drop a spanner across any terminals

Seriously though, i'd wonder what the failure rate is on a cell? Having so many makes me concerned about the reliability. Would it make sense to buy a couple of spare cells?

Worst case, we drop back to 15s, which is what's in the Pylontechs

Deagol

championc wrote: »

Worst case, we drop back to 15s, which is what's in the Pylontechs

True. Though identifying the knackered cell would be fun

graememk

Deagol wrote: »

True. Though identifying the knackered cell would be fun

Not too difficult, the likes of the heyo or daly, it will flag it/see it on the app. It would be the lowest cell,

That or a multimeter and find the low cell when its discharged.

championc

Tradnuts wrote: »

I bought a phase tester last week!

Seriously, buy yourself a digital multimeter. A preferably one which has a clamp which can wrap around live wires to measure AMPs, and therefore one which can measure DC Amps as well as AC Amps

I would highly recommend the UNI-T model UT210D

unkel

DrPhilG wrote: »

Just got a message back from the OYE store, who I had been asking about BMS solutions also.

They're recommending the previous suggestion from both graememk and championc. They just sent this drawing, presumably just scribbled up by the sales guy lol.

Eh yeah, that is the one thing I wouldn't do and I explained why. Either go single pack 16S1P or two packs of 16S1P in parallel each with their own BMS

Deagol

unkel wrote: »

Eh yeah, that is the one thing I wouldn't do and I explained why. Either go single pack 16S1P or two packs of 16S1P in parallel each with their own BMS

I know a guy who does battery packs for UPS on offshore platforms - these are seriously big Lead Acid systems but I assume the same principles apply. If I can get contact with him I'll ask about best practice. I know from talking to him before though he said it's important to put diodes between each cell to stop back flow of current caused by impedance imbalances.

The Continental Op

Deagol wrote: »

I know a guy who does battery packs for UPS on offshore platforms - these are seriously big Lead Acid systems but I assume the same principles apply. If I can get contact with him I'll ask about best practice. I know from talking to him before though he said it's important to put diodes between each cell to stop back flow of current caused by impedance imbalances.

Do the loses across the diodes have an effect of the voltage?

Deagol

The Continental Op wrote: »

Do the loses across the diodes have an effect of the voltage?

Assuming you're using Schottky diodes, there would be some power loss I would think - though what it would be I'm not sure. I would think ~1% but without knowing the numbers I can't calculate it.

The Continental Op

Deagol wrote: »

Assuming you're using Schottky diodes, there would be some power loss I would think - though what it would be I'm not sure. I would think ~1% but without knowing the numbers I can't calculate it.

But a calculation you'd need to make or your batteries could be over charged?

Deagol

The Continental Op wrote: »

But a calculation you'd need to make or your batteries could be over charged?

Not sure what you are talking about. Can't do the calculation without knowing the specifications / values of the parts in question. Since I don't have either it's kind of impossible.

The Continental Op

Deagol wrote: »

Not sure what you are talking about. Can't do the calculation without knowing the specifications / values of the parts in question. Since I don't have either it's kind of impossible.

What I am asking is that with diodes in the circuit is your controller measuring slightly lower voltages than the batteries are actually producing and as a result apply more charge or are the diodes only in the balancing part of the circuit so the full voltage is seen by the controller.

Deagol

The Continental Op wrote: »

What I am asking is that with diodes in the circuit is your controller measuring slightly lower voltages than the batteries are actually producing and as a result apply more charge or are the diodes only in the balancing part of the circuit so the full voltage is seen by the controller.

I guess as there's always a v drop across a diode there must be some effect but honestly no clue about how that works in this situation. As I said, this information came from a guy I know from working offshore - he's a specialist UPS bloke and I was just a bit fascinated about the huge battery pack I was standing next to on a rig and asked some questions. I've been trying to get hold of him but no answer yet.

DrPhilG

So this is the BMS I'm going for, haven't missed anything have I?




Getting the 100a version with Bluetooth and CAN connections.

championc

That's spot on. Just get them to confirm the thermal cutoff capability. Will Prowse reported that it didn't work on one he got in one of his videos. That was partially what put me towards HEYO, although I never tested it with the HEYO yet, as I managed to then buy a tubular Heater which is on a shelf below the battery string.

DrPhilG

championc wrote: »

That's spot on. Just get them to confirm the thermal cutoff capability.

Will do.

What is the thermal cutoff capability? The temperature that the bms will make the battery stop charging?

graememk

DrPhilG wrote: »

Will do.

What is the thermal cutoff capability? The temperature that the bms will make the battery stop charging?

Yep