Battery Parallel connect only

[Mrjmegson]

Hey guys,

I'm looking at these batteries:

https://www.pytesgroup.com/product-detail/&122
They just appear to be Pylontech.

My issue is that they state the connection type to be "parallel".

Does that mean they can only be connected in parallel and not series?

Surely I can connect them either way, why would a battery only allow a parallel connection?

 

[johnb2713]

Hey guys,

I'm looking at these batteries:

https://www.pytesgroup.com/product-detail/&122
They just appear to be Pylontech.

My issue is that they state the connection type to be "parallel".

Does that mean they can only be connected in parallel and not series?

Surely I can connect them either way, why would a battery only allow a parallel connection?

The only thing I can think of is if the battery supply isn't isolated, if negative is earthed, it may not be the case but if it was connecting in series would put a dead short on one battery via the earthed casing. The same would occur in the comms leads too.

I assume you have a high voltage battery connection on your inverter i.e. above 50v?

 

[Mrjmegson]

The inverter is the FOXESS H1 6kw.

You worked out the correct way to connect batteries to it for me.

I've emailed the company and asked the same question, see what they say.

 

[Mrjmegson]

So I've just watched this YouTube video:



About series linking LifePo4 batteries, and he says the issue is having them all at the same state of charge, and says you can't just go by the voltage, you have to individually charge them all to 100% before linking them together, and use a specific li-ion charger to do so.

What are your thoughts?

Not heard back from the manufacturer of the batteries yet.

 

[johnb2713]

I float charged all of mine but, having now connected them to the BMS I wouldn't bother any more, I was sceptical when I did charge them, it really isn't necessary for the packs in series. In parallel, I would get the voltages as near to equal as possible.

 

[Mrjmegson]

So that's the opposite to what he said in that Clip and what I've read. Can you say why you think it's not necessary?

Also, what is float charging?

Are your batteries LifePo4 John?

 

[binky]

I float charged all of mine but, having now connected them to the BMS I wouldn't bother any more, I was sceptical when I did charge them, it really isn't necessary for the packs in series. In parallel, I would get the voltages as near to equal as possible.

As I understand it, that's exactly what the BMS is for, managing the charge on each battery. But I could be wrong about that.

 

[Mrjmegson]

But everyone says they need to start at exactly the same charge as each other.

Sounds like the BMS shuts down charging as soon as 1 gets full, as though it can't control them individually.

 

[binky]

But everyone says they need to start at exactly the same charge as each other.

Sounds like the BMS shuts down charging as soon as 1 gets full, as though it can't control them individually.

People talk shite

BMS, battery management system, if you look at battery stacks they have cat 5 connections so the BMS can monitor the individual batteries. Now, according to some things I've seen, this is not necessary, and possibly weak in it's operation. I've added batteries to existing stacks and they sort themselves out within a day. Simple answer is that you are worried about this, just make sure all the batteries are fully charged. I'll state again I'm no great expert on batteries. I've mostly fitted pylontech with solis or solax inverters, and my comments are based on how they seem to work. Don't overstress it

 

[johnb2713]

As I understand it, that's exactly what the BMS is for, managing the charge on each battery. But I could be wrong about that.

Youre 100% correct Binky but many Youtube 'experts' suggest batteries should be topped off with a very small float charge. It really isnt needed for series connection.

In terms of balancing domestic storage BMS systems are nothing like the ones used in the aero modelling world. My BMS for home storage is capable of 2 amps discharger for batteries of 280A/h, the one used in my modelling hobby can do 6 amps when used with batteries of 12 A/h. The balancing in the storage battery will be slow but then again, they are permanently connected 24/7.

 

[johnb2713]

But everyone says they need to start at exactly the same charge as each other.

Sounds like the BMS shuts down charging as soon as 1 gets full, as though it can't control them individually.

When connecting in parallel as you are, you need to guard against circulating currents. If for example your new battery was fully discharged when connected it to the other 3 that were fully charged, substantial current would flow to the discharged battery. By getting the voltages as near as possible the same that wont occur.
As long as youre not in extremes like above, you should be fine, the BMS should trip battery if currents are excessive.

 

[Mrjmegson]

Hi guys,

Thanks once again for your advice, it's really appreciated, and in this instance, really comforting.

John, I do struggle with this, so sorry, but just to clarify, my inverter is high voltage, and can only charge/discharge at 35A, so I think I need to series link my batteries, not parallel. Is this correct?

 

[johnb2713]

Hi guys,

Thanks once again for your advice, it's really appreciated, and in this instance, really comforting.

John, I do struggle with this, so sorry, but just to clarify, my inverter is high voltage, and can only charge/discharge at 35A, so I think I need to series link my batteries, not parallel. Is this correct?

Hi,

Sorry yes, youre quite right your thread is series linked batteries. This being the case, connect them up and off you go.

How many batteries are you connecting to the system?

 

[Mrjmegson]

That's cool, cheers.

I would assume that the manufacturers will charge all the batteries to a specific percentage before they go out anyway. I would think that different states of charge would only apply to used batteries.

I can't believe how different his video is to what you guys say. Do you think he has shares in a battery charger company?

Initially I'm going to connect 4 batteries to each of the two inverters, then run them for a while, and see how the two arrays charge them, then may alter the ratio at some point. 4.6kw usable in each battery.

 

[Mrjmegson]

Can anyone translate this response I've had from the "supplier" of the batteries I've ordered, I asked, like the title of the thread, why it states in the manual to parallel connect the batteries.

Cheers.


Hi Jason,

Most battery packs for energy storage commonly use 48V, benefit from less electric shock hazard and have a reasonable power rating for house use. It is easier to extend the capacity by parallel connecting more batteries.
In contrast, the high voltage battery with higher electric shock hazard. A high voltage battery bank can extend power by adding more batteries in serial connection and benefit with lower current. Still, a high voltage battery bank will need additional external BMS (battery management system) to balance the batteries, and high DC voltage requires handling by a professional.

Different brand inverters and batteries need compatible communication protocols, which need programming and testing by the factory. Pytes battery can’t be compatible with Fox ESS inverter due to different voltage and protocol.

I recommend changing the FOX inverter to our 6 kW Afore hybrid inverter; it is fully compatible with the Pytes battery, built by the highest industry standards and comes with ten years warranty. Most importantly, we will be able to aggregate your inverter to participate in electricity trading and grid service in the future, which will make additional earnings from the energy storage. Due to your circumstance, we would offer you a 20% special discount on the inverter.

If you have any questions please feel free to contact us.

Warm Regards
George Huang

 

[johnb2713]

I would be asking why an external BMS is needed, surely each battery will have it's own BMS which will look after the individual cells within that battery, why is external needed?
The shock hazard is misleading, of course you are more likely to 'feel' a 100v shock as opposed to 50v BUT the inverter youre connecting to has at very least 240v grid supply on there and potentially more from the solar PV.
Communications is likely to be an issue BUT comms to the inverter is not essential, many systems run free standing. There are many BMS's that have different protocols available for the various inverters, I'm about find out if my SEPLOS BMS will talk to my Victron inverter, Victron dont want to know, SEPLOS have offered to have a group chat with one of their senior technicians who will remote into my system and get it working. Dutch £2,200 inverter with zero help 'v' £180 BMS where they will fall over themselves to help.
There really needs to be an agreed protocol shared amongst all inverter manufacturers and BMS suppliers.

 

[Mrjmegson]

So you'd just say stick with the order and see what happens?

I agree that the BMS will look after the batteries, so no real issue if the inverter can't chat to the batteries for the batteries sake, but what about the inverter sending my excess solar to the batteries to charge them, if I can't chat to them, it won't know they need charging will it?

Sorry, all this is winding me up now, as you say, why isn't there an international standard.

 

[johnb2713]

So you'd just say stick with the order and see what happens?

I agree that the BMS will look after the batteries, so no real issue if the inverter can't chat to the batteries for the batteries sake, but what about the inverter sending my excess solar to the batteries to charge them, if I can't chat to them, it won't know they need charging will it?

Sorry, all this is winding me up now, as you say, why isn't there an international standard.

You have to be a brave man to commit to this with the guaranteed lack of support.

I went through all of this with the battery I'm building BUT it was a very competitive price going the DIY route hence why I'm doing it. There are a few videos around on YouTube with systems running with comms between inverter and BMS.

 

[Mrjmegson]

Sorry John, can you elaborate, what does your last line mean?

Thanks, I hope I am being brave and not stupid. If it works it will be amazing, if not, I have no idea where to go.

 

[johnb2713]

Sorry John, can you elaborate, what does your last line mean?

Thanks, I hope I am being brave and not stupid. If it works it will be amazing, if not, I have no idea where to go.

I wanted a decent size battery to run my house on off peak electricity all day through winter including heat pumps. I looked around and they were all silly money IMHO. Looking at the component parts I could make an AC couple 14kWh battery for less than £4k and this is the road I set out on. Due to inverter supply difficulties (I couldnt get another Growatt SPH 6000 anywhere) I changed to a Victron Multiplus II 5kW inverter, unfortunately this raised the price to just under £5K which I feel is good value considering I have opted for very best of LifeP04 cells (EVE) and top notch equipment.

I spent a considerable time trying to coax information out of Victron their comms protocoal and other data for BMS comms, without success. The forums however did have a wealth of data and Seplos seemed to be the BMS of choice. I contacted Seplos in China, they could not been more helpful. They made a whatsapp group between myself, the tech sales guy I spoke and one their senior techs who assure me it will work and they will talk me through the setup via whatsapp and zoom.

Hopefully by the end of this week I will know if thats true or not, I have a little more work to including mounting all of the gear in shed that I have built for the purpose of housing it all.