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Mixing Pylontech US Batteries


martynw
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Hey,

Hope everybody is keeping safe during the current Covid-19 crisis!

Does anybody have any experience of running a mix of different Pylontech batteries?

I've got a Sofar Solar ME3000SP connected to SIX Pylontech US2000 batteries as follows:
 
2 x US2000B from 07/02/2017
2 x US2000 Plus from 28/02/2018
2 x US2000 from 04/06/2019
 
They are connected to the ME3000SP  via RS485 and one of the latest manufactured US2000 is the master.

The ME3000SP is supposed to automatically configure itself to the Pylontechs and it sets the following:

Battery Capacity: 200Ah

Discharge Depth: 80%

Over Voltage Protection: 54.0V

Max Charge Current: 65A

Max Charge Voltage: 53.2V

Max Discharge Current: 65A

Min Discharge Voltage: 47.0V

 

Based on other posts most of these seem correct, although the Battery Capacity is wrong - I can't change this in the settings, although I can override the other parameters if I want to, but I think the Ah is cosmetic only anyway as I don't think it's used anywhere.

 

In general the system is working well, but I want to ensure that it's set up optimally.

As well as the data I can retrieve from the ME3000SP I also have the Pylontechs being queried every minute via the console port so I get a pretty good overview of how the system is performing. In particular I've noticed that the amps remaining / % remaining in each pack can vary throughout a discharge cycle by quite a bit. 

Often the ME3000SP stops the discharge cycle a bit too early as it seems to use the lowest % remaining figure to govern when the Discharge Depth has been met, so for example yesterday it stopped the discharge cycle at 20% but only one of the packs was showing 20%, the others still had a few % more (ranging from say 21% to 25%).

Interestingly the newer US2000 and US2000 Plus always seem to track fairly closely together and the older US2000B usually always seem to have more left when the discharge cycle stops (sometimes I've seen these still sat at 28% for example). What sometimes happens then is that the packs seem to balance amongst themselves, i.e. the ones with > 20% discharge and the others charge.  Sometimes (but not always) this even gets to the point where e.g. all the packs then have ~ 22% in them and the ME3000SP will continue a discharge cycle for a few more minutes.

On a charge cycle they always seem to balance OK based on the data from the console, all cells seem to reach target voltages and all packs hit maximum amps / % remaining (they all show that "bump" in their graphs at the top end).

 

Shouldn't the Pylontech BMS manage the packs a bit better?  I'd have thought during the discharge cycle it would report a % remaining based on some sort of average across all the packs, as opposed to the lowest value?

From my research so far the BMS is also supposed to be able to sleep individual packs when they reach their own discharge depth and the other packs should carry on? That's my understnading from https://midsummerwholesale.co.uk/pdfs/pylontech-intercompatibility-guide.pdf although that in itself is a bit confusing as it mentions that the older US2000B packs only "sleep" when the SOC is <= 0%? As I understand it at 0% it would be dead and a pack should never be discharged that low?

My other thought is to increase the Discharge Depth setting a bit in the ME3000SP.  Since the four newer modules should go to 90% anyway then perhaps that would allow the two older packs to discharge closer to their 80% DOD target?  My only concern there though is that if for some reason the SOC on the older packs somehow became lower the ME3000SP would then allow them to go too far, although in fairness I've never actually seen that in any of the data I've collected so far - they always seem to be higher than the newer packs.

 

Thanks for any thoughts,

 

Martyn

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2 hours ago, martynw said:

Battery Capacity: 200Ah

Should be 300Ah

Discharge Depth: 80%

Over Voltage Protection: 54.0V

Max Charge Current: 65A

This should be 150A (25amp ber battery) 

Max Charge Voltage: 53.2V

Same as above. 

Max Discharge Current: 65A

Min Discharge Voltage: 47.0V

 

Based on other posts most of these seem correct, although the Battery Capacity is wrong

 

 

2 hours ago, martynw said:

(they all show that "bump" in their graphs at the top end).

Pretty normal for Pylontechs. 

 

2 hours ago, martynw said:

Since the four newer modules should go to 90% anyway then perhaps that would allow the two older packs to discharge closer to their 80% DOD target?

Just read the warranty, If i remember correctly it mentions a 70 or 80% minimum discharge. After that they might reject a claim...

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From what I've been able to gather by comparing what the ME3000SP reports via its own RS485 interface and the console data (or RS485 data) direct from the Pylontech battery packs, the ME3000SP is using the lowest percentage remaining reported from each of the battery packs to determine when to stop discharging.

If I look at the CANBUS data direct from the battery packs, this is using a much simpler protocol which provides an averaged percentage remaining for ALL the battery packs.

So for example at the moment the ME3000SP is reporting 35% remaining, which matches the lowest reading from a single battery pack (via the console on the battery packs), whereas the CANBUS is reporting an average of 41%.  

I asked Sofar Solar technical support about this and they claimed that there's no difference in connecting to Pylontechs using RS485 or CANBUS but I'm not sure that I believe this now.  My guess is that when connected by RS485 they're trying to do their own calculations based on each individual pack reporting to determine when to stop discharging. Could be that they're not even processing all the packs, which might be why the capacity is only showing at 200AH.

Based on that I think I will switch the ME3000SP to connect to the Pylontechs using CANBUS instead as to me it looks like this is presenting a simpler data set for the ME3000SP to use - difficult to see how it can go wrong if it only has one averaged SOC to deal with!

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On 2020/04/30 at 4:05 PM, Jaco de Jongh said:

Just read the warranty, If i remember correctly it mentions a 70 or 80% minimum discharge. After that they might reject a claim...

What exactly do you mean here? Should the batteries be discharged by a minimum of 80%?

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