Double Bubble Battery Banks

[G4RNI]

Although my installer sold me eight HV2600, Fox, when I contacted them about some weird system behaviour, told me the maximum ought to be seven. They suggested eight may give over voltage issues and I can confirm I did get occasional battery over voltage alarms. I also found the battery capacity meter to be wildly inaccurate with the supposed 20kWh capacity of eight batteries plummeting to around 40% (60% or 12kWh claimed to have been used) with a calculated draw of only around 4 to 5kWh (1.5kW for about 3 hours). When charging, at say 2.5kW, the capacity meter would suddenly leap to full (99%) in around 2 hours thus confirming my consumption had indeed been around 4 to 5 kWh and NOT the 12kWh claimed by the capacity meter. Reducing the stack to 7 batteries vastly improved the accuracy of the capacity meter although it was still imperfect. I can therefore concur that 8 batteries, whilst they do work, can result in wildly inaccurate capacity readings AND throw up occasional battery over voltage alarms. Note that my capacity meter NEVER showed 100% with 8 x HV2600 V1.

Being aware of the standing plans for power outages (see your leccy bill for the little square symbol with your rota disconnection letter if that threat seems like BS to you) I decided to expand my system with a second bank of HV2600 and so lashed out on a V2 BMS and seven V2 batteries.

I installed a 500V x 125A four pole, interlocked single throw changeover switch to switch from battery bank A (original V1 batteries) to bank B (the new V2 batteries) then the common on to the new V2 BMS battery input terminals. The "data" leads were fed to a 2 way manual "ethernet" switch to changeover data from battery stack A to B. The "power" leads are Pylontech AWG4 so well over engineered by at least 100% and come with the correct SURLOK connectors ready fitted, being cheaper than I could buy the connectors alone!

To change over I first power down the BMS and throw its battery breaker switch to OFF (right). Next, I throw the data switch from A to B (or vice versa) then throw the four pole power switch from A to B (or vice versa). I then throw the BMS battery breaker to ON, restart the BMS and I'm on the other battery stack. It can take several minutes for the app to respond to the changeover but that's due to its sampling rate of something like 6 x per hour.

I've learned that the capacity meter is then sometimes slightly confused for a while until the chosen battery bank discharges somewhat and recharges. It then reads perfectly! Killing the entire system (PV off, AC off) for a few minutes whilst the BMS is powered down avoids the battery capacity hiccup but I've decided to live with that small irritation as it corrects itself in a while and once recharging begins.

My capacity meter is now as accurate as I could have wished for. 7 batteries have a capacity of 17.92kWh but let's call it 18 for ease of figures. I drew them down to 40% (roughly 11kWh used) then the next day they recharged, taking 11kWh, (according to the Fox app) to reach 100%. Yes! The capacity meter now reads 100% (not 99) and the calculated draw and charge figures all agree.

It appears to me that the new BMS/battery combination is by far more accurate than the V1 with Version C batteries. I'll compare with the older batteries after these new ones, stack B, have had a month or so to "bed in". I also appear to have a minimum of 2 x 16kWh useable battery stacks and feel I no longer need to keep 35 or 40% in reserve for the dreaded power outages they keep promising us.

Min SOC 10%
Min SOC on Grid 17%.

So they system is now:

H1-3.7-E Inverter Hardware Version : -Master : 1.54; Slave : 1.02; Manager : 1.57
15 x 330W panels (6 + 9)
BMS V2
7 x HV2600 V1(C)
7 x HV2600 V2
Necessary changeover switching.
Empty savings account.

I also have 1 x HV2600 V1(C) battery either to flog or keep as a spare. I'm in North East England if anyone's interested in an extra battery.

George
Retired (National Grid Pensioner) Comms & Instrumentation Tech

[Dave Foster]

Interesting approach, thanks for the write up - I always like a big Flash Gordon switch

Your comments about 8 batteries are loosely in-line with my experience, they mostly work although if you're unlucky / depending on the age of the batteries/inverter combination you can see over voltage alarms and top balancing problems because the inverter charger is right at it's limits (450v) when the cell voltages are high.

So just to confirm you've got 2 BMS units - each one dedicated to it's own stack but with no mixing of V1/2 batteries? - do you have any standby charging for the off-line pack?, or is it essentially charge the pack fully then disconnect, switch to the other bank rinse and repeat.

[G4RNI]

No, I use ONE V2 BMS. The big, gnarly switch changes over the BMS DC feed from stack A (V1 bats) to stack B (V2 bats). The disconnected stack is then completely alone (shame) with no connection to anything. The original V1 BMS is kept handy, just in case I ever need to resort to only the original bats should say the V2 BMS throw a wobbler. Simply a case of unplugging the new leads and plugging in the old ones.

George

[JameseHide]

Hello George,

Do you still have a spare battery? is it a version C.

I would like to add another to my H1-3.7 all in one.

Kind Regards,

James.

[Dave Foster]

Hello George,

Do you still have a spare battery? is it a version C.

I would like to add another to my H1-3.7 all in one.

Kind Regards,

James.

Hi James,

the version 1 HV2600 batteries are coming back into stock and you can get the rev D (compatible with rev C) here https://www.tradesparky.com/solarsparky ... re-battery

[Nredshaw]

O very interesting write up would love to know the cost of your big switch method as just brought a second hand cube setup as had that much unreliable issues like you decided to get second batteries, and would have bought these brand new if fox was honest,! About 7 being the maximum as had 5 v1s before as 3x hv2600 for £4800 but can only use 2 x wasnt enough and very expensive for all the hassle,
i would have new 2x cube 4100s for about same price and added more later.
after months of 8 x hv2600s mixed v1-v2 batteries after lots of help from fox they replaced my v2 batteries with v1s so now got 8 v1s and v1 bms again was hoping to have issues melt away but no after lots of balancing etc the cell imbalance is fixed but still same issue you described and now fox gone back to there 7 max advise as like you getting stange low soc issue of 30-38% left then on only 300-400 w base load would drop to 10% and import on 8 but ive gave up and on 7 now and can get more usable energy out of 7 V1 hv2600s than 8 X ! Still bit of stange low soc sometimes but alot more reliable so far ! So im another person with a spare v1 hv2600 pack going up for sale ! Anyone interested in sensible pricing pack let me know in Lincolnshire !

[calum]

Worth checking you have latest firmware for all your battery modules and BMS if you haven't already.

[Nredshaw]

Yes according to fox were upto date as of few week ago . What version you on ?
Inverter h1 5.0 on 1.60 master1.02 slave 1.63 comm
And 8 but 7 in use v1 hv2600s on m 00.01.020 and all 8 s are on 1.00.01.06 on a v1 bms

[calum]

Looks like you're on the latest, clearly the Fox support people have been updating all your gear.

I'm a few versions behind but my system is currently fairly well behaved, so I'm following the "if it ain't broke don't fix it" school of thought