diy solar

diy solar

Which Daly BMS for 48V EVE system?

HighVolt

New Member
Joined
Oct 20, 2020
Messages
21
Just purchased 16X 280A EVE cells from Xuba for my first off-grid system. I am going with a MPP all in one unit, 5Kw inverter and 4Kw of panels. The panels are second hand and I have confirmed max historical output on the inverter of 4,6Kw. By my calculations maximum continuous charge/discharge for the BMS in my application is 100A @ 48V. I am planning to keep the batteries in the 10-80 DOD range in order to try to extend their useful life.

Looking at the Daly BMS the limiting factor seems to be the discharge rating. The smallest BMS that will support the 100A discharge from the inverter is the 200A common port unit. Is this correct? -> aliexpress link. I'm aware the EVE pack can support a 1C / 280A discharge rate, but given the 300A BMS is twice the cost, is there a good reason to purchase it for this application?

Also, my location does not have internet access. Would I get any advantage from the Daly SMART BMS? I would be quite happy with a no frills unit, that keeps the cost down. The MPP will provide an operator's panel and I envisage only using the BMS connected to my phone for any troubleshooting. If it were possible to log to a small Raspberry Pi I might do that, but not sure. I'm reading people are having issues with the SMART BMS.

Cheers
Richard
 
Last edited:
The Daly or other MosFet based BMS' are ok with a qualifier. When they state 200A Capacity for discharge, that is the absolute limit of capacity. The usual recommendation is, that if you know you will need 100A going through a BMS, then get 150A, if you want 200A then get 250-300A model. Having that elbow room means you won't push the FETS to death.

Typically FET based also only does 50% of the rating for charging. So a 100A BMS will max out at 50A Charge rate, this can be an issue with a large capacity bank. These cells can also take up to 1C Charge rate but it's recommended to not exceed .5C (140A) The more amperage behind the charge the faster they will charge and top off BUT they WILL diverge at the top side... IT IS NOT UNUSUAL for the cells to deviate by 1mv per AH so with 280AH cells you can see 280mv differential. LFP will NEVER sit at 3.65V per cell, even if you charge it till the cells are only taking 0.1A, stop charging and within an hour or two they'll settle between 3.5V to 3.6V each, this is normal.

The other common BMS type uses Relays/Contactors and therefore do not suffer such limits as the Relay is what handles the amperage being passed through it. Contactors can be had up to 1,000A. These do tend to cost more than the FET based BMS and you do have to buy the Relay/Contactors but the payback in performance & capabilities makes it worthwhile. I should note that EV's use Relay/Contactor based BMS' for load handling & reliability.

Basic BMS info:
- There are Dumb BMS'
which just do their job, they are preprogrammed and the end user has no access to anything within (settings etc). These are preset with values for the specific chemistry you are using.
- There are Interactive "Smart BMS" which can be accessed by Wifi or BlueTooth or ? These can be configured & tweaked for personal preferences like cut-off points and such. Some offer logging that can be retrieved / accessed. Some have CanBUS or ModBUS others just RS232 output for logs.
- Smart BMS with advanced features: Similar to above BUT with Balancing Capabilities, this adds to the cost and "can be of benefit" if the correct type is selected for the application. The two Basic Balancing are Passive or Active.
-- Passive Balancing is a simple method in which the HIgh Voltage cells in the pack get discharged by the BMS to balance with the lowest voltage within the pack. This is a long slow & tedious process where the BMS burns off the extra voltage which results in heating of the BMS as well, due to the process. (Not much use on cells above 100AH as this is very slow) Also the cheapest form of Balancing Function.
-- Active Balancing actually takes Voltage from High Cells and transfers it to the Low Volt cells within the pack. These can range from 1A to 10A capacity and is more suitable for Large Capacity cells. This ADDS Cost due to the extra requirements for the electronics but can result in improved battery pack performance (IF DONE RIGHT) it is tricky and varies with BMS type & Model.

General Info & Links.

I use Chargery BMS8T-300 with DCC (Solid State Contactors) (I'm 24V) but have Passive Balancing OFF because I am running large cells (280AH & 175AH) and instead using QNBBM 8S Active Balancer for each pack.

SUGGESTED READING !
BU-803a: Cell Matching and Balancing – Battery University
Pre-Balancing Cells | Orion Li-Ion Battery Management System
Li-Ion BMS - White Paper - Dissipative vs. nondissipative balancing (a.k.a.: Passive vs. Active balancing)


Hope it helps, good luck.
Steve

PS: Remember, these 280AH are Grade-A COMMODITY Cells. They are NOT Matched & Batched as equal cells (that can cost up to $50 per cell to get done). They are Grade-A "Manufacturer Specs" and comply with that classification. See the first TWO Links in the suggested readings. That means they will have slightly variable IR (Internal REsistances) at different voltages (most notably at the top & bottom of their voltage range). Remember the Divergence I mentioned.

You may want to watch this as well, Will covers some issues that people raise and it's best to put the nonsense to bed right off the batt.
 
Thanks Steve, That is really helpful. It seems like there is a lot of information on 12V and 24V packs, but I was struggling to put it all together with 48V. I was put off the Chargery because some of the videos were not that complimentary. I will do some more research before I decide exactly what to do. I have a month or two waiting for the cells it seems.

Cheers
Richard
 
Here is a link to the Daly Official Store on Aliexpress. You want to be looking at a 16S BMS for 48V.

They offer a basic and a smart BMS (the basic is the one people here have the most experience with), further broken down by common port or separate port (separate port means the BMS controls charging and discharging separately, common port means the BMS controls them together)
 
You might want to consider a Heltec BMS. Comparable price to Daly. I bought an 8S, 300A BMS for the 24V 280AH battery pack I am building. I am pretty impressed by the cable connection compared to my 150A Daly 7S BMS.


I will find out if it works as well as it looks. Reports from other uses have been positive.
 
Last edited:
  • Like
Reactions: Dzl
F.Y.I.

If you are using an inverter/charger then you want a common port BMS. Otherwise you will not be able to automatically recharge the battery if it drops below the low voltage disconnect threshold. Most people get a common port BMS because of this (it is what I use).

Separate port BMS also tend to greatly reduce the maximum charge current you are able to use compared to the same BMS in common port mode.

-Edit-

Now I am uncertain about this.

The Daly 7S BMS I am using is a common port version, but internally it is has a separate disconnect circuit for the charge and discharge functions, they are just internally connected to a single wire.

This means if the discharge disconnect trips at low voltage, the charge connection is still made. Question I have is how does this play when you combine a solar charger? I guess I need to set my inverter low voltage disconnect high enough that the BMS disconnect never triggers or else I might end up having to hook up an external battery to bring the BMS back to life (I have read about people having to do this).

Seems no matter how much you learn, you always end up feeling like a dummy. This stuff is complicated.
 
Last edited:
The Daly or other MosFet based BMS' are ok with a qualifier. When they state 200A Capacity for discharge, that is the absolute limit of capacity. The usual recommendation is, that if you know you will need 100A going through a BMS, then get 150A, if you want 200A then get 250-300A model. Having that elbow room means you won't push the FETS to death.

Typically FET based also only does 50% of the rating for charging. So a 100A BMS will max out at 50A Charge rate, this can be an issue with a large capacity bank. These cells can also take up to 1C Charge rate but it's recommended to not exceed .5C (140A) The more amperage behind the charge the faster they will charge and top off BUT they WILL diverge at the top side... IT IS NOT UNUSUAL for the cells to deviate by 1mv per AH so with 280AH cells you can see 280mv differential. LFP will NEVER sit at 3.65V per cell, even if you charge it till the cells are only taking 0.1A, stop charging and within an hour or two they'll settle between 3.5V to 3.6V each, this is normal.

The other common BMS type uses Relays/Contactors and therefore do not suffer such limits as the Relay is what handles the amperage being passed through it. Contactors can be had up to 1,000A. These do tend to cost more than the FET based BMS and you do have to buy the Relay/Contactors but the payback in performance & capabilities makes it worthwhile. I should note that EV's use Relay/Contactor based BMS' for load handling & reliability.

Basic BMS info:
- There are Dumb BMS'
which just do their job, they are preprogrammed and the end user has no access to anything within (settings etc). These are preset with values for the specific chemistry you are using.
- There are Interactive "Smart BMS" which can be accessed by Wifi or BlueTooth or ? These can be configured & tweaked for personal preferences like cut-off points and such. Some offer logging that can be retrieved / accessed. Some have CanBUS or ModBUS others just RS232 output for logs.
- Smart BMS with advanced features: Similar to above BUT with Balancing Capabilities, this adds to the cost and "can be of benefit" if the correct type is selected for the application. The two Basic Balancing are Passive or Active.
-- Passive Balancing is a simple method in which the HIgh Voltage cells in the pack get discharged by the BMS to balance with the lowest voltage within the pack. This is a long slow & tedious process where the BMS burns off the extra voltage which results in heating of the BMS as well, due to the process. (Not much use on cells above 100AH as this is very slow) Also the cheapest form of Balancing Function.
-- Active Balancing actually takes Voltage from High Cells and transfers it to the Low Volt cells within the pack. These can range from 1A to 10A capacity and is more suitable for Large Capacity cells. This ADDS Cost due to the extra requirements for the electronics but can result in improved battery pack performance (IF DONE RIGHT) it is tricky and varies with BMS type & Model.

General Info & Links.

I use Chargery BMS8T-300 with DCC (Solid State Contactors) (I'm 24V) but have Passive Balancing OFF because I am running large cells (280AH & 175AH) and instead using QNBBM 8S Active Balancer for each pack.

SUGGESTED READING !
BU-803a: Cell Matching and Balancing – Battery University
Pre-Balancing Cells | Orion Li-Ion Battery Management System
Li-Ion BMS - White Paper - Dissipative vs. nondissipative balancing (a.k.a.: Passive vs. Active balancing)


Hope it helps, good luck.
Steve

PS: Remember, these 280AH are Grade-A COMMODITY Cells. They are NOT Matched & Batched as equal cells (that can cost up to $50 per cell to get done). They are Grade-A "Manufacturer Specs" and comply with that classification. See the first TWO Links in the suggested readings. That means they will have slightly variable IR (Internal REsistances) at different voltages (most notably at the top & bottom of their voltage range). Remember the Divergence I mentioned.

You may want to watch this as well, Will covers some issues that people raise and it's best to put the nonsense to bed right off the batt.
Did you compare the Heltec Active cell balancers? The 5A version of the Heltec is 1/4 the cost of the QNBBM so right off the bat that makes me wary of the Heltec. What factors drove the decision in favor of the QNBBM for you?

 
F.Y.I.

If you are using an inverter/charger then you want a common port BMS. Otherwise you will not be able to automatically recharge the battery if it drops below the low voltage disconnect threshold. Most people get a common port BMS because of this (it is what I use).

Separate port BMS also tend to greatly reduce the maximum charge current you are able to use compared to the same BMS in common port mode.

-Edit-

Now I am uncertain about this.

The Daly 7S BMS I am using is a common port version, but internally it is has a separate disconnect circuit for the charge and discharge functions, they are just internally connected to a single wire.

This means if the discharge disconnect trips at low voltage, the charge connection is still made. Question I have is how does this play when you combine a solar charger? I guess I need to set my inverter low voltage disconnect high enough that the BMS disconnect never triggers or else I might end up having to hook up an external battery to bring the BMS back to life (I have read about people having to do this).

Seems no matter how much you learn, you always end up feeling like a dummy. This stuff is complicated.

If I understand what you are describing, I believe what you are talking about here (Functionality of a separate port BMS, but wired like a common port BMS) is what @FilterGuy refers to as a "hybrid port" BMS. I think this is the best term to date, as it would be incorrect to call it common port (since it has the capabilities of a separate port BMS), and slightly incorrect to call it separate port (since it doesn't actually have separate ports).
 
Did you compare the Heltec Active cell balancers? The 5A version of the Heltec is 1/4 the cost of the QNBBM so right off the bat that makes me wary of the Heltec. What factors drove the decision in favor of the QNBBM for you?

To put it simply, it's a different mode / type of active than the Heltec. I was also more inclined when I saw them working in conjunction with Chargery BMS', you might say, that added a wee bit of encouragement as well. So far, I am quite pleased with the results, presently doing some thrashing on the bank for the next few days. Today for example did 100A Charging on the bank as part of that thrashing. Gave the Samlex a workout LOL.
 
Back
Top