Open vs Closed Loop w/Sol-Ark 15k

[karamazov]

Just ordered 32 EVE 304Ah cells for my whole-home system I am working on. I've done a considerable amount of research into battery construction and BMS, but I still can't figure out what the best solution for my situation would be as far as constructing this battery bank. I want to be able to supply 200A continuous from the battery bank.

So my understanding is there's basically two ways to set up a battery bank: closed loop and open loop; closed loop means the inverter is communicating with the battery bank, and open loop means it is not. Closed loop it seems tends to be a lot more complicated.

As stated in the title, I have a SolArk 15k inverter on order which will be AC coupled to my utility connection. I contacted SolArks technical support to ask about this, and they told me the only 'officially' supported BMS for DIY batteries is the Orion series. Seplos (saw this in another thread) says that they can emulate the CAN message protocol for a few different battery manufacturers (such as Pylontech, which SolArk has a configuration for), so that also may be an option.

The other option I was looking at was to parallel two Overkill 16s BMS as opposed to building a single 16s2p bank.

So at this point I'm left with a few questions that my research hasn't really answered:

- In this scenario what (if any) would be the tangible benefits of closed loop over open loop?
- If I go the closed loop route, with say the Orion, what other components (if any) would/should I include in my battery build?
- In general, aside from a BMS what components are generally recommended for a good build (disconnect switches, monitoring shunts, etc.)?

Appreciate any insight that y'all can provide me.

 

[BentleyJ]

- In this scenario what (if any) would be the tangible benefits of closed loop over open loop?

1) Having access to the BMS data on the inverter display or inverter app. without having to use a separate app to view BMS data or change the set up. At this early point in development, its very likely that even with closed loop communication you would still need to use a separate BMS app for some of the features.
2) Being able to use the SoC readings from the BMS as control values for charging start/stop points or gen auto start Etc. This would be limited by the accuracy of the BMS SoC values and how well it stays calibrated.

- In general, aside from a BMS what components are generally recommended for a good build (disconnect switches, monitoring shunts, etc.)?

A higher accuracy shunt is always desirable but what brand, if any, would be compatible with closed loop communication?

Others on the Forum have been down this road and in the end gave up on closed loop communication because it was too unreliable.

Closing Thought: This is actually an interesting subject and I've thought about and struggled with it quite a bit. CAN data from a ZEVA BMS is not compatible with the proprietary Schneider XANBUS and even if it was the SoC data from the BMS is not accurate enough to make it useful since it cannot read anything below approx. 150mA. For applications with a lot of standby time the error is quite significant.
IMHO, I believe this subject is one of the biggest disappointments of the DIY solar equipment industry in general. For example, a post earlier today mentioned the NMEA2000 CAN Bus standard used by the Marine industry to ensure communication compatibility between equipment even among various brands. Why does something like this not exist for our sector?

 

[Jason.Blier]

I have a Sol-Ark 15K and 4 banks of 280Ah cells. I am using it in open loop - even the BMS units are not aware of each other. After a few charge/discharge cycles, the Sol-Ark internal shunt is within 1-2% of the BMS SOC readings.
The inverter limits are set within the BMS limits and it's been working really well thus far.

I look at all the comms and tend to think that it's just another thing to go wrong, complicate the system, and/or mess things up when it glitches.

If a battery pack fails, the other 3 take the load. I can run on 2 of the packs without issue. If 3 of the packs fail, the 4th will go into over current or low SOC at some point and shut down. The Inverter will then sense there is no battery present and act accordingly (grid passthrough and shutdown).

- J

 

[Tiger Tom]

I have a Sol-Ark 15K and 4 banks of 280Ah cells. I am using it in open loop - even the BMS units are not aware of each other. After a few charge/discharge cycles, the Sol-Ark internal shunt is within 1-2% of the BMS SOC readings.
The inverter limits are set within the BMS limits and it's been working really well thus far.

I look at all the comms and tend to think that it's just another thing to go wrong, complicate the system, and/or mess things up when it glitches.

If a battery pack fails, the other 3 take the load. I can run on 2 of the packs without issue. If 3 of the packs fail, the 4th will go into over current or low SOC at some point and shut down. The Inverter will then sense there is no battery present and act accordingly (grid passthrough and shutdown).

- J

What BMS are you using.
I am building a 4 16s strings 304ah battery system with 2 SolArk15Ks.

 

[Jason.Blier]

What BMS are you using.
I am building a 4 16s strings 304ah battery system with 2 SolArk15Ks.

I am using JBD 7s-20s 200A unit. Common port with contactor (instead of FETs). If I choose, I can have them report their status to Solar-Assistant - from there, the S-A software can send commands to the Sol-Ark if needed.

 

[On_The_Road]

I am using JBD 7s-20s 200A unit. Common port with contactor (instead of FETs). If I choose, I can have them report their status to Solar-Assistant - from there, the S-A software can send commands to the Sol-Ark if needed.

Where did you source those BMSs with the contactors?

 

[Jason.Blier]

Where did you source those BMSs with the contactors?

I bought them through Amy Zheng from Docan. You can also buy them direct from JBD if you want,.

 

[On_The_Road]

Awesome, thank you - awesome Sol-Ark and diy battery install btw. I couldn't tell from the pictures what did you use to tie the battery outputs together before sending it into the SolArk?

We're researching a battery only grid tied system using diy batteries like you've done to take advantage of a tou plan.

 

[Quattrohead]

Contactor type bms do not share well, great for a single high capacity battery but not for paralleling multiple batteries.

 

[On_The_Road]

Contactor type bms do not share well, great for a single high capacity battery but not for paralleling multiple batteries.

What type of problems are typical?

 

[Jason.Blier]

Awesome, thank you - awesome Sol-Ark and diy battery install btw. I couldn't tell from the pictures what did you use to tie the battery outputs together before sending it into the SolArk?

We're researching a battery only grid tied system using diy batteries like you've done to take advantage of a tou plan.

I used a 4x1/0 - 2x4/0 distribution block each for the pos and neg. So 4x 1/0 feeds from the batteries combine to 2x 4/0 feeds to the sol-ark.

 

[Jason.Blier]

Contactor type bms do not share well, great for a single high capacity battery but not for paralleling multiple batteries.

I’ve never heard that. I have 4 banks in parallel. Each contactor can take thousands of Amps without welding itself and still shut off. All my BMS units play together nicely. Also, if the BMS does decide to shut down one of the battery packs, the contactor opens which physically disconnects the battery.

 

[On_The_Road]

I used a 4x1/0 - 2x4/0 distribution block each for the pos and neg. So 4x 1/0 feeds from the batteries combine to 2x 4/0 feeds to the sol-ark.

Where did you source that grey thing for your balance leads and bms leads? I found a few of your pictures....any more available? Thanks!

 

[Quattrohead]

They will not turn on the contactor because they have no load, until the "regular" batteries are almost dead, then they kick on and try to dump 100A+ into the other batteries.
I replaced both contactor BMS with regular MOSFET type and now all 6 batteries are in perfect alignment both charge and dis-charge.

 

[Jason.Blier]

They will not turn on the contactor because they have no load, until the "regular" batteries are almost dead, then they kick on and try to dump 100A+ into the other batteries.
I replaced both contactor BMS with regular MOSFET type and now all 6 batteries are in perfect alignment both charge and dis-charge.

So, Im not sure what you are saying. I have 4 batteries, all with contactors, all in parallel. Running continuously for a year now. The contactors dont shut off right away when there is no load - they have to have no load for over 8 hours continuously before they shut down - you can also set them to never turn off unless there is a alarm event.

 

[Jason.Blier]

Where did you source that grey thing for your balance leads and bms leads? I found a few of your pictures....any more available? Thanks!

Those grey terminals are just DIN rail Terminal blocks - used widely with industrial/PLC. You can pick them up on Amazon, Newark, Mouser, Gescan, etc - various electronics outlets.

 

[BentleyJ]

Contactor type bms do not share well, great for a single high capacity battery but not for paralleling multiple batteries.

This DuraKool has a copper bus bar with 2 holes, seems like it would be perfect for combining 2 batteries maybe even 4 with 2 lugs per hole.

DSC60

An automotive LVDC contactor with a rated load of 600A 60VDC. SPST-NO with optional auxiliary contact. Bi-stable latching is also an option. Busbar power terminals. UL Recognised.

www.durakool.com

 

[Quattrohead]

you can also set them to never turn off unless there is a alarm event.

What setting is this, would solve my problems !!!

Supplementary note:
Continuous standing for 65000s (settable) will automatically disconnect the relay and reduce the standby power consumption of BMS. A large charge discharge current will be identified through the pre charge discharge circuit, and then close the relay.

Is this the FET ctrl setting that makes the relay click continuously if set to 0s....I found this and changed to 10s and it has been working, except it turns off when other batteries are charging/dis-charging.

 

[Jason.Blier]

What setting is this, would solve my problems !!!

You are really jogging my memory

I think one of the settings is in the alarms settings - and it’s the restart state. You set it to always restart unless it’s a short circuit.

The other setting is sleep mode - can’t remember where it is in the app, but you disable it or set it on a long timer.

I’ll have to fire up the pc app and find it for you.