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DIY LifePo4 - Multiple banks without comms?


smurfdbn
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A lot of BMS's (eg Smart ANT and Daly) expressly prohibit parallel connection. Find out what BMS you are using, and confirm if it is approved or not.

I have no idea why most do not allow it - probably due to limits when one BMS opens but not the other.  If this is the case, then it should be possible, if you set the total charge/discharge currents lower than each individual BMS.

 

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1 hour ago, Louisvdw said:

Charge both to full charge separately and then add them in parallel

That seems sensible, thanks

49 minutes ago, JustinSchoeman said:

Find out what BMS you are using, and confirm if it is approved or not.

Using a Daly for now

There's been a few members posts where chaps have run 2p16s.  The one setup (jaqkar) appears have a single BMS for the bank.  Gerlach's setup has 2 banks with a Smart BMS for each bank (looks like ANT), could not tell if there was comms with Inverter (don't think so?) 

1 hour ago, JustinSchoeman said:

probably due to limits when one BMS opens but not the other

Can see that might be a problem

1 hour ago, JustinSchoeman said:

if you set the total charge/discharge currents lower than each individual BMS.

Definitely

Thanks for your thoughts
 

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2 hours ago, smurfdbn said:

Hi All

Have a DIY LifePo4 bank with a Daly BMS  - no comms, connected to Multiplus II with ESS.  Would love to add a 2nd bank.

Is this doable without comms or does one have to have BMS with comms for multiple strings?

Thank you

Absolutely. I have a Narada that blew its BMS with a lightning strike last year, replaced it with a "Daly without comms". All still running fine. I am running 4 of them, first to busbars and then to inverter.

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On 2020/10/05 at 2:07 PM, smurfdbn said:

Hi All

Have a DIY LifePo4 bank with a Daly BMS  - no comms, connected to Multiplus II with ESS.  Would love to add a 2nd bank.

Is this doable without comms or does one have to have BMS with comms for multiple strings?

Thank you

Hi Smurf

Are you planning to increase your output(kW)?

If not, why don't you just parallel the cells? You can then just use the same BMS...

Ian

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Hi Ian

10 hours ago, Ian said:

If not, why don't you just parallel the cells? You can then just use the same BMS..

It's certainly an option - downside is that if there is any issue with the bank and BMS shuts down, we could be in the dark...

Planning on at least 3 banks and i'd be more at ease with each bank having it's own BMS.  While it does add to the cost per kWh, overall cost is still streaks ahead of units like Pylontech etc.

Will require some fiddling but I enjoy fiddling 🙂  

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  • 3 weeks later...

@Sc00bs Hi, from all the reading on various forums and BMS literature, yes, the general "rule" is No, parallel setup is not supported.

I jumped down the rabbit hole a few weeks ago and am running 2 x 48v DIY banks in parallel on a Multiplus II 48/5000.

Early days and has taken a bit of tinkering with charge voltages and ESS settings etc but so far, the setup is behaving just fine.

There are a few other guys on this forum that are quite happily running parallel DIY setups with a "dumb" BMS

For now, i'm one of them 😀

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@smurfdbn I am building a LiFePO4 battery with 16 of 2 cells from @Bain Viljoenin parallel. Got them from @Mike who resides in our village.

@Ian said In an earlier post that he did that and also put blocks of 3 cells in parallel for a neighbour. Perhaps he would be so kind and post his experience thus far for us to learn. As I understand it, parallel cells will self balance over time and the ANT BMS which I have should balance the pairs of cells. Multiple batteries, each with their own BMS have the problem of keeping the batteries in balance. If they are not, one or more with lower voltage may cause the ones with higher voltage to overcharge and then self-protect by disconnecting. There is after all no electronics keeping the banks in balance so no real difference to parallel cells. If a block of parallel cells have too low a voltage, it will cause some others to reach overcharge voltage and the ANT will detect that and also stop charging. 

Seems to me the parallel cell option may be preferable on balance. Will Prowse also has a video about it on YouTube. 

 

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@ebrsa Good luck with your build... 

Here is an interesting discussion on this - for me, the take-away is not to push the bank/s to their limits on charge/discharge to keep the BMS happy, hence the lower charge volts setup as I and others have done.  On discharge, I have my inverter max power set to 1.5Kw so should mostly never draw more than 30A so even if 1 BMS does shutdown, I should never stress a single bank.  My config is set to use down to 20% SOC - getting 10KWh which i'm more than happy with.

diysolarforum.com/threads/ant-bms-in-parallel-configuration.11317/
 

Edited by smurfdbn
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12 hours ago, smurfdbn said:

@Sc00bs Hi, from all the reading on various forums and BMS literature, yes, the general "rule" is No, parallel setup is not supported.

I jumped down the rabbit hole a few weeks ago and am running 2 x 48v DIY banks in parallel on a Multiplus II 48/5000.

Early days and has taken a bit of tinkering with charge voltages and ESS settings etc but so far, the setup is behaving just fine.

There are a few other guys on this forum that are quite happily running parallel DIY setups with a "dumb" BMS

For now, i'm one of them 😀

So, this is my understanding, please note that I am no expert on this and would like to hear from anyone that knows more about it than I do. It is obviously not an option to have batteries of different chemistries connected in parallel due to different operating voltages. 

From what I understand, the state of charge of the battery packs running in parallel will always be the same as long as they are connected together and the amperage supplied will be in proportion to their capacities.

The way it was explained to me was to think of it as having a number of water tanks of the same height (voltages) but with different diameters (capacities) connected in parallel. The water levels between the tanks will always be the same and when you draw water out of them they will both drop their levels at the same rate or fill up at the same rate. 

There are obviously a lot of complications that happen as the batteries are being independently managed by BMS's

So If you have a 10kw and a 5kw pack in parallel, the 10kw will contribute at twice the amperage as the 5kw. 

You will be limited to the BMS with the lowest supply amperage in proportion to it's capacity

So, in my example if both the 10kw and 5kw banks are able to supply  100A, the 5kw will only be able to supply 50A as the 10Kw will be supplying 100A, so max amperage for the paralleled banks will be 150A. If you go over that the BMS on the 10KW pack will disconnect as it is supplying more than 100A and the power requirement will switch to the 5kw causing it also to disconnect.

There are all sorts of complications that can happen as a result of having your packs go out of sync and being at different states of charge and then trying to reconnect resulting in uncontrolled current flows 

Have been thinking about it though and think I can understand why the manufacturers would not be keen to have packs not designed to run together in parallel doing so.

I think that as long as you understand the Amperage limitations it should not be a problem as long at the voltage settings of the BMS's is the same and the battery chemistries are the same. Only hurdle to overcome would be making sure that the pack voltages are the same when they are connected in parrallel.

 

JohnB

 

 

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@smurfdbn Thanks for your good wishes with my build and the link you posted.

From what I have read, it seems that as long as you keep upper and lower voltage battery settings below and above the respective disconnect settings, your system should mostly work just fine. So will parallel cells with a single BMS I would expect. Time will tell but not much difference between the two systems and most of the time by far things seem to work just fine. 

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