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Chris Hobson

Which batteries should I buy (rhetorical question)

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I  am considering BYD  Bbox pro 10 -  http://www.byd.com/energy/bbox.html - 6000 Cycles 10 KWH 

my challenge is to manage 30 Kwh /day with 6 KWp and BYD At least the solar water heater will help somewhat. No permission from Better Half yet to replace the telly  and all lights are already LED  with most of them automated. 

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These Pylontech batteries look pretty decent and priced quite well... What i wanna know is, lets say you only get 1 of these bad boys, that's about 2.2kwh. Now pair that up with a 5kva\4kw Axpert... is my understanding correct when the battery specs says it can deliver 5kw for 1min, so in the 5kva\4kw Axpert, assuming you were to have a load of 4kw, then a single 2.2kwh battery will only give you roughly 1min 20 secs of power before shutting down? 

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Hi, I will not recommend pairing one of these with an Axpert for the following reasons:

- Axpert self consumption from battery is approx 70W (yes even in Bypass mode).  That is a full kWh during a winter night.  So if you set your inverter to switch to Eskom lets say at 50V and you had a slow discharge to that point (no big peaks pushing you to to bypass mode prematurely) your Pylon will have less than 20% charge left going into the evening and will discharge fully due to the Axpert self consumption and the battery will shut down, shutting the system down.

- Axpert 5kW (the new ones is 5kW) can draw 100A constant current which will probably damage the battery if there is only one.  The spec says it can only push that for 15 sec.

From my experience the smallest you can go with Lithium on the Axpert is 3.6kWh so running two Pylons should be fine.

On that calculation of yours.  Theoretically and ignoring losses etc a 2.2kWh battery can deliver 2.2kW for one hour or 5kW for 2.2/5 = 0.44 hrs or 26 minutes.

image.thumb.png.f5ca0877a26134a7191b145c133e5778.png

Edited by Hannes7212
Added image of Pylon spec sheet

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Thanks for the response. Its clear that we should never pair only one of these units with an Axpert, I was looking at 2 initially and later expanding if required. I intend switching to Eskom during the peak evening periods then switching back to batteries after that. 

I'm still toying with the idea of lithium but it does seem to be the way to go from a longer term perspective. We also not sure when super capacitors will be available at a retail level.... So need something for the interim. 

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13 hours ago, Hannes7212 said:

Axpert self consumption from battery is approx 70W

Isn't it closer to 40W or 50W? I mean even that strikes me as a tad high, the Vickies do 35W at no load and less than 5 in passthru. When in passthru, my whole system including the CCGX draws only 6W from the batteries.

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After doing more and more reading on these Pylontech lithiums... a few questions came to mind. 

The Pylontech inverter setup manual that installers use has no mention of the LifePO4 firmware that needs to be installed on the Axpert... It just has the following settings that need to be set: 

image.thumb.png.7edd06b26392c9cbd7cd242b89e3055f.png

2 questions that i have: 

1. Do we need to install the LifePO4 firmware? and if yes, are there any benefits?

2. What float voltage needs to be set?

 

 

 

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1 hour ago, PurePower said:

After doing more and more reading on these Pylontech lithiums... a few questions came to mind. 

The Pylontech inverter setup manual that installers use has no mention of the LifePO4 firmware that needs to be installed on the Axpert... It just has the following settings that need to be set: 

image.thumb.png.7edd06b26392c9cbd7cd242b89e3055f.png

2 questions that i have: 

1. Do we need to install the LifePO4 firmware? and if yes, are there any benefits?

2. What float voltage needs to be set?

 

 

 

The absorb on Axpert is not ajustable in normal firmware. Normally lithium with active balancing need max 1 hour absorb . and with passive balancing absorb is not needed at all 

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5 hours ago, PurePower said:

After doing more and more reading on these Pylontech lithiums... a few questions came to mind. 

The Pylontech inverter setup manual that installers use has no mention of the LifePO4 firmware that needs to be installed on the Axpert... It just has the following settings that need to be set: 

2 questions that i have: 

1. Do we need to install the LifePO4 firmware? and if yes, are there any benefits?

2. What float voltage needs to be set?

 

  1.  The supplier should pre-install the firmware - the warranty is void without it.
  2. Float voltage should also be set to 53.2V. This is not unusual as many of the Lithium PIP users I have been following do the same.

From a Victron discussion board I see that one can parallel 40 units (2000A). The cables running from your busbar will have to be serious. At 1000A (48V) you need to have 500mm2 to keep losses under 1%.

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On 11/4/2017 at 8:48 AM, Hannes7212 said:

 Axpert self consumption from battery is approx 70W (yes even in Bypass mode). 

That seems a bit high.  I measured some time ago my Axpert's quiescent current at 46W. This was in line with AEVA forums reported 50W. I have just run the inverter in bypass mode with no battery charging and the BMV registers about 35W.

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2 hours ago, Chris Hobson said:

That seems a bit high.

Perhaps the newer ones (with TX6 removed) draw a little more? That's a wild guess, as I recall the earlier models had a small SMPS so that it can power itself from a grid connection in case the battery was very low, but this isn't there with the new ones.

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My apologies gents.  I have not measured the latest Axperts and when I calculated this before I now realise I could have been counting one or two other items on the DC side as well.

SO, like a true "I am never hardly ever wrong" type of person my wife claims I am I set off to prove you all wrong and I can report the following:

image.thumb.png.b088810756ab78478d686b37a38be89c.png

But now I must confess that that is two Axperts in parallel drawing a combined 1.593 amps at 51V from my very lonely single Lithium battery (as the other one has been sent in to be repackaged with a real BMS).  So 40W per inverter it is!  Some guys in this forum are just never wrong.  I hate that.

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31 minutes ago, Hannes7212 said:

Some guys in this forum are just never wrong.  I hate that.

You must be referring to Plonky :D.  I have been wrong too but the best solution is to blot it out of your mind and forget it ever happened. It does ones ego no good:D

On a more serious note. If we can challenge one another without ending up feuding then all is good. With solar there are so many grey areas, where things are not right/wrong but rather elegant or less elegant.  There are myriads of examples (don't mix different solar panels - don't have too many battery strings don't add new batteries to old etc). All these rules/advisories come with qualifications or ways of mitigating the negative effects. 

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Well said and totally agree which is why I bother to read, and when I can, contribute.  Very sad to see how people can get all snotty with each other if you don't mind the term on many (particularly international) forums.  Proud to that is not the case on this one.

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11 hours ago, Chris Hobson said:

You must be referring to Plonky

Oh dear... I too have been charged by the wife with wanting to be right just a little bit too much. My defense is that only an idiot is okay with being wrong... but even I can see that's not what she means. Humility is a virtue that is seriously underrated :-)

In this respect, really, I'm plowing with other people's oxen. I've never had my hands on an Axpert. I saw the first 24V 3KVA one the other day (UPS at a tool rental place) and thought "good grief that is small... makes the Multi look like a tank!" :-)

17 minutes ago, Hannes7212 said:

the other one has been sent in to be repackaged with a real BMS

This intrigues me. What was in it and what are you replacing it with? I occasionally speak to one of the guys at that company where you like to source batteries, and he mentioned that they also replace BMSes of another lithium company (which shall also remain nameless)... that is to say, apparently BMS upgrades are a thing :-)

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Hi Plonkster, happy to give you details one on one but would rather not comment publicly.  Suffice to say the "old" bms could never get the balancing of the cells right which is why it always switched off pre-maturely.  The good news is that the cells still test very good (as in as new) 18 months later.  And I did put that battery through a beating so that is very good to see.

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On 11/6/2017 at 4:39 PM, Chris Hobson said:

 

  1.  The supplier should pre-install the firmware - the warranty is void without it.
  2. Float voltage should also be set to 53.2V. This is not unusual as many of the Lithium PIP users I have been following do the same.

From a Victron discussion board I see that one can parallel 40 units (2000A). The cables running from your busbar will have to be serious. At 1000A (48V) you need to have 500mm2 to keep losses under 1%.

Ok great thanks... 

I'm up and running with my Pylontech Batteries, thus far i am impressed. First time i've seen a DOD of 70% on 100ah batteries! And it charges up nicely, by 10:30am in the morning the batteries are full again.

I do feel that the recommended program setting 12 = 48v is a bit high... Axperts do not have dynamic cut off values like Victron does... so during high load, a drop in voltage is normal and it hits 48v so easily and switches to grid... it happens at least 2 or 3 times a day for me.

I don't see why we can't drop this a little, like 47v (47.5v would be ideal, but prog 12 does not allow 0.5v increments) as the Pylontech data sheet allows for a discharge voltage between 45 ~ 54v... @Coulomb , do you think prog 12 can be changed to allow for 0.5v increments?

image.png.afa862650a38fae5cdcb3a0046ba4703.png

 

So if we change prog 12 = 47v, then i would also change prog 29 = 46.5v. So effectively, it will switch to grid and momentarily give you a low battery warning at 47v. Those are my thoughts so far... 

I've also looked at other inverter manufacturer settings and they to seem to set it at 47v. I know the cut off values do not work exactly the same as the Axpert but this is just a thought to stop switching to grid for no real reason, in my opinion. Below are other inverter manufacturer parameters that i have found thus far:

Victron https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom

image.png.8c5a352bea738f0e09de557db75cd888.png     image.png.ebf150652de1e95a7e412d509d99bc7d.png

 

Sofar Solar ME3000SPhttp://www.homeswitch.co.uk/battery-storage-installation-guide

image.png.d0782abdaad612847ea39aa9623d0f24.png

SOLAXhttp://www.nuvisionenergy.co.uk/index.php?route=pavblog/blog&id=101 

These are for the older version of the Pylontech batteries, so i'd take these values with a pinch of salt :) 

image.png.4677870c67e89854ad4977eb93a54e3e.png

 

Any comments?

Edited by PurePower
Added Sofar Solar Settings

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Hi there, I have about 20 or so Lithium based systems in the field (most of them on Axperts) and the batteries I use have CALB cells.  If you have one battery (3.6kWh) on a single Axpert I find that if you set the cut-over to grid at 48V you stand the risk of the BMS turning the battery off at about 46V to protect the cells (I do think that is quite a conservative cut off value).  This only happens if the load on the battery was very low so it drained it slowly to 48V, really getting the most out of it.  If a spike caused it to switch at say, 20% SOC, then no problem.  But if discharged very slowly without spikes to 48V that battery is basically flat.

So, until we can let the Axpert act on SOC and not voltage (there is some development locally on that front), I am forced to leave that cut-over voltage at 50V for small banks and 49V for larger banks (10kWh and up).  And for what it is worth we float those CALB cells at 53.8V and then they charge up nicely to about 90 - 97%.  I dont like pushing them to 100% every day.

Hope that helps.

 

Cheers

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2 hours ago, PurePower said:

Coulomb , do you think prog 12 can be changed to allow for 0.5v increments?

Not really. This setting is compressed to about 4 bits when sent in a CAN bus message to paralleled or 3-phase machines to synchronise settings. So then you'd have to reduce the range, and users would disagree about what values they would want to keep.

I sometimes wish they used half volt steps myself. 

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3 hours ago, PurePower said:

recommended program setting 12 = 48v is a bit high

 

1 hour ago, Hannes7212 said:

if discharged very slowly without spikes to 48V that battery is basically flat.

Same experience with my blue setup. With dynamic cut-off, it will cut out at 52V (or 26V on my much smaller setup) at very low loads (0.005C), but at high loads it only cuts out at 48V (24V here). But then I ran into another problem, I have about a 0.5V drop at full power (it's less than 2%), and this drops be to 25.5V with a 50% SoC and a high load... causing the Multi to go into Sustain mode (which is what it does if it hits the cut-off).

That is to say, 48V really should be low enough and I would not go lower than that. It does seem to me that the PylonTech batteries aren't quite as capable as the Winston- or CALB-based cells and do draw down a bit lower, but as a catch-all 47V really does feel a tad low.

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I am starting to think the Pylontechs can be regarded as the Axpert of the battery world.  The BYD 2.56kW is marginally more expensive but the BYD is also tolerant of greater DOD. The Victron 2.4kWh Lithium units are nearly double the price of the Pylontechs

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Question regarding the Pylontech's: On the solaradvice website it says for a pylontech unit "Not for off grid use" Why would that be?

I also see they have a very specific list of inverters to pair with, before they'll honor the warranty.

 

-G-

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8 minutes ago, gallderhen said:

Question regarding the Pylontech's: On the solaradvice website it says for a pylontech unit "Not for off grid use" Why would that be?

In an off-grid situation you could easily exceed the 25A limit of a single unit. 4 Pylontechs however could supply 100A an under those circumstances I think whether the system is off-grid or not is irrelevant. According to the Victron forum Pylontech are busy testing in off-grid situations.

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1 hour ago, Chris Hobson said:

 

In an off-grid situation you could easily exceed the 25A limit of a single unit. 4 Pylontechs however could supply 100A an under those circumstances I think whether the system is off-grid or not is irrelevant. According to the Victron forum Pylontech are busy testing in off-grid situations.

BYD recommends 3 x 2.5 KWH for a 5 KW solution. my  10 KWH ( 4x 2.5 ) 48 V system regularly reports 140 Amps charge-discharge limits at 30 DEG . 

 

This charge  limit drops rapidly when the temperatures are lower than 12 DEG C 

Discharge current.JPG

Charge current .JPG

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Here is my new bank... those beauties are busy charging up now. I may decide to add another in the new year. Pic taken around 9:30am today.

IMG_20171122_092928.thumb.jpg.db990f68425f2766254ec99f73c16610.jpg

I am also using the ICC software and in addition to the inverter program 12 setting,  i also use both SOC and time to switch to grid. Currently, it switches between 5pm - 9pm to grid (evening peak hours), thereafter its on batteries for the remainder of the day. If a 25% SOC is reached it will switch back to grid. 

image.png.4b8a69703a4ca67bf45926c9c492d8d1.png

Battery trend for today...

image.thumb.png.2735d4727fb9fa0a5606a4ed944890c9.png

You will notice that the battery voltage only touched 48v in the morning...it was actually 48.22v, SOC was around 40%. This most likely happened when i used the kettle. These readings are from the BMV-702 battery monitor. I don't trust the reading from the inverter itself. The inverter would have switched over to grid at that point (at 48.5v) but i'm testing prog 12 = 47v and so far its working for me. The Pylontech batteries also has several protection systems built in as part of its BMS. So if it goes below its min voltage threshold, then it will shutdown to protect itself. 

I am quite happy with the setup at the moment. I could never do this with my previous set of Narada 200ah AGM's. 

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15 hours ago, PurePower said:

These readings are from the BMV-702 battery monitor

Remember to adjust the charge efficiency setting when switching from lead-acid to Lithium. The recommendation I got was to set it to 97%, but I noticed it fills up "early" every day and resets to 100% too often, so I gradually increased mine and it is now sitting at 99% and working well.

You can sort-of see clearly when a LFP battery is full. The charge current just drops way down (under 1 amp) and within a few minutes the chargers will go to float. This is when most batteries balance cells. Some BMSes allow you to look at individual cell voltages and its interesting to watch it. In mine, I can see the voltages in one battery is higher than the other, and that one also feels warmer when you touch it. That's the passive balancing going on... it's bleeding off energy.

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