BMS opinions
- Thread starter Jgb3
- Start date
Your electric bill likely reports kWh/month. Since "eventually I want to run the whole house," you should get a scale of that in keep it on the horizon. Otherwise, everything you invest now will likely need to be replaced in the future.
ePowerBank
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For what it's worth, in addition to the monthly bill method, I also installed a product called "Sense" which not only shows the overall usage, but also identifies specific items and the usages etc.
Another easy method I found was looking at meter from day to day.
In my case of understanding my overnight kWh usage, I just checked meter in the evening before bed, then next morning.
I checked in dead-of--winter with a foot of snow so heater running was my worst case.
I read somewhere online that average US home consumes roughly 30kWh a day. And a third of that was basically agreed with my overnight meter read, or 9kWh.
While overall power is one consideration, I'm sure you're also considering peak (or spike) cases. That's where I liked having the Sense to have a baseline idea of power usage.
Another easy method I found was looking at meter from day to day.
In my case of understanding my overnight kWh usage, I just checked meter in the evening before bed, then next morning.
I checked in dead-of--winter with a foot of snow so heater running was my worst case.
I read somewhere online that average US home consumes roughly 30kWh a day. And a third of that was basically agreed with my overnight meter read, or 9kWh.
While overall power is one consideration, I'm sure you're also considering peak (or spike) cases. That's where I liked having the Sense to have a baseline idea of power usage.
ePowerBank
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I'm new to all this and yet to have built a battery and or the back-up system I'm working on.
I believe that some do say that the Daly Smart has had issues though - maybe you can find first hand testimony either way?
Once you start going over 4kw or 5kw of power, the amps (4800/48=100A) I think put you at the limit of a simple BMS setup -- as I understand.
I believe that some do say that the Daly Smart has had issues though - maybe you can find first hand testimony either way?
Once you start going over 4kw or 5kw of power, the amps (4800/48=100A) I think put you at the limit of a simple BMS setup -- as I understand.
This is what the biggest one from Daly says but It’s hard to find reliable reviews. Not sure I would even need something that big I ordered 32 280ah cells to make 2 48v batteries and want to double it in 6 months to a year
Average monthly use is 2884 kWh right now but I’m living with 5 people
podilamaya
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- Mar 17, 2021
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I'm planning to order the same BMS for my 48v 620ah battery. My max usage is 200A,
Our average monthly consumption is 1583kWh (all electrical appliance house)
Last edited:
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
Let's simplify this as you're getting caught with Minutia that will take you astray.
48V/280AH/14.3kWh per battery pack
Max Discharge Capability is 280A for One Hour. 1C
Burst Rates Vary but they can be between 3C-5C for Momentary Burst Delivery (varies by manufacturer & cell Grades, NOT recommended for use)
Max Charge Capability is 140A for Two Hours.
Ending Amp Value = 14A (for charging purposes as 0.05C is the recommended EndAmps for LFP)
Solar Systems using Central Inverters are not recommended to be used above 250A Draw from Battery Banks.
12V*250A=3000W, 24V*250A=6,000W, 48V*250A=12,000W Surge Draw above.
Battery Packs in Parallel should ALL be capable of acting as a StandAlone as the "Last Man Standing" as other packs may cutoff for Hi/Lo Voltage or out of Temp Range. Essential every battery in the bank must be able to take the full Charging Capacity that is available as well as being able to deliver all of the potential demand as well. This is partly the Fault Tolerance & Fall Back safeties we need in place with more complex systems.
*Adding packs to a Paralleled Bank *
LFP is great because you can always add packs in parallel down the road. This makes systems Scalable, unlike the old FLA days where battery aging was a constant issue. It is HIGHLY SUGGESTED to keep the different battery packs close in AH capacity, generally the less difference between packs the smoother charging & discharging will be while maintaining battery bank performance. If packs are too far apart, the Lower AH packs will affect the larger packs as they reach the lower 15% & upper 10% of the voltage ranges. 50AH difference is NOT significant and likely would not even notice, but beyond 100AH difference, things WILL be very apparent at the edges of the Voltage Curve.
FET Based BMS' MUST BE DERATED !
The advertised 250A or 300A IS the extreme edge limit of capability. This is a well learned lesson by MANY ! Always derate by at least 20%. Therefore you will want a BMS that has 20% or more "capability" than you will actually use. Do note that NO High Performance Systems such as EV's Grid Storage Systems and such DO NOT USE FET BASED BMS' ! They all use Relay/Contactors as the controls to turn on/off power going through the systems, as this is more reliable & dependable and teh individual relays can be specd to handle whatever load design there is. Remember that Relays go up to 1000A & High Voltages, they are independent of the BMS as such.
Relay/Contactor controlling BMS' are slightly more complex but they do have increased reliability, especially with high performance & high demand systems.
BMS for 48V/280AH.
As systems should be limited to not exceed 250A draw from batteries, all inverters can handle a Surge above & beyond the normal provision. High Frequency Inverters can typically handle 2X Surge, While Low Frequency Inverters can typically handle 3X Surge. This is typically Momentary and to support motor starts such as a fridge, AC, Well Pump etc.
A 300A FET Based BMS would comfortably support 250A and allow for surge capacity.
Relay/Contactor based would be the same.
Remember that while the system can support 250A, that will NOT be your constant draw, it will be lower, that is unless you have some crazy electric gear that sucks up juice like a Hot Water Tank or old Electric Stove... FYI, Conservation is far cheaper than generation & storage. LOOK at your appliances and get rid of Grandma's fridge you inherited.
Case in Point Example. My system is built to handle 300A and can certainly do it. Thrash Tests have proven it all out. Right now as I sit here writing this, I am drawing 6.4A from my 24V bank, that would be 3.2A if I was 48V. That is running my 47" LED Screen, HP DeskElite i7, Hughes Sat Modem, Router, 2 lights and a few wallwart type items. THAT also includes the Inverters 18W requirement.
Coffer Maker goes on, that 50A off my 24V system for 6 minutes (thermal Carafe no warmer)
Panasonic 1200W Inverter Nukelator = 74A draw on High Power.
GrundFos SQ-5 SoftStart 120VAC deep well pump, 260' deep, set to cutoff at 52PSI. Starts at 550W, ramps by 150W increments till it reaches 52PSI at 1100W. Inverter barely blinks.
Good for Solar & You.
- On Demand Hot Water heater ! would you keep your car idling in the driveway all day & night just because you "might" want to go for a drive ? That is what the Hot Water tank is, 15 minutes of every hour it is heating water for "in case you want it".
- Induction Electric Cook Stove, energy efficient, fast and good for solar.
- Energy Start 5 rated Fridge & Freezer, use low kWh per year. (Mine uses 247kWh in 12 months)
- Coffee Makers with Thermal (thermos) Carafe and No Warmer !
the rest is more obvious but just to give some ideas, where to save and cut losses & wasted energy.
Hope it helps, Good Luck
Steve.
PS, grab stuff from my Signature, the LFP assembly guide, LFP Voltage chart & "Calibrating your system" especially important.
48V/280AH/14.3kWh per battery pack
Max Discharge Capability is 280A for One Hour. 1C
Burst Rates Vary but they can be between 3C-5C for Momentary Burst Delivery (varies by manufacturer & cell Grades, NOT recommended for use)
Max Charge Capability is 140A for Two Hours.
Ending Amp Value = 14A (for charging purposes as 0.05C is the recommended EndAmps for LFP)
Solar Systems using Central Inverters are not recommended to be used above 250A Draw from Battery Banks.
12V*250A=3000W, 24V*250A=6,000W, 48V*250A=12,000W Surge Draw above.
Battery Packs in Parallel should ALL be capable of acting as a StandAlone as the "Last Man Standing" as other packs may cutoff for Hi/Lo Voltage or out of Temp Range. Essential every battery in the bank must be able to take the full Charging Capacity that is available as well as being able to deliver all of the potential demand as well. This is partly the Fault Tolerance & Fall Back safeties we need in place with more complex systems.
*Adding packs to a Paralleled Bank *
LFP is great because you can always add packs in parallel down the road. This makes systems Scalable, unlike the old FLA days where battery aging was a constant issue. It is HIGHLY SUGGESTED to keep the different battery packs close in AH capacity, generally the less difference between packs the smoother charging & discharging will be while maintaining battery bank performance. If packs are too far apart, the Lower AH packs will affect the larger packs as they reach the lower 15% & upper 10% of the voltage ranges. 50AH difference is NOT significant and likely would not even notice, but beyond 100AH difference, things WILL be very apparent at the edges of the Voltage Curve.
FET Based BMS' MUST BE DERATED !
The advertised 250A or 300A IS the extreme edge limit of capability. This is a well learned lesson by MANY ! Always derate by at least 20%. Therefore you will want a BMS that has 20% or more "capability" than you will actually use. Do note that NO High Performance Systems such as EV's Grid Storage Systems and such DO NOT USE FET BASED BMS' ! They all use Relay/Contactors as the controls to turn on/off power going through the systems, as this is more reliable & dependable and teh individual relays can be specd to handle whatever load design there is. Remember that Relays go up to 1000A & High Voltages, they are independent of the BMS as such.
Relay/Contactor controlling BMS' are slightly more complex but they do have increased reliability, especially with high performance & high demand systems.
BMS for 48V/280AH.
As systems should be limited to not exceed 250A draw from batteries, all inverters can handle a Surge above & beyond the normal provision. High Frequency Inverters can typically handle 2X Surge, While Low Frequency Inverters can typically handle 3X Surge. This is typically Momentary and to support motor starts such as a fridge, AC, Well Pump etc.
A 300A FET Based BMS would comfortably support 250A and allow for surge capacity.
Relay/Contactor based would be the same.
Remember that while the system can support 250A, that will NOT be your constant draw, it will be lower, that is unless you have some crazy electric gear that sucks up juice like a Hot Water Tank or old Electric Stove... FYI, Conservation is far cheaper than generation & storage. LOOK at your appliances and get rid of Grandma's fridge you inherited.
Case in Point Example. My system is built to handle 300A and can certainly do it. Thrash Tests have proven it all out. Right now as I sit here writing this, I am drawing 6.4A from my 24V bank, that would be 3.2A if I was 48V. That is running my 47" LED Screen, HP DeskElite i7, Hughes Sat Modem, Router, 2 lights and a few wallwart type items. THAT also includes the Inverters 18W requirement.
Coffer Maker goes on, that 50A off my 24V system for 6 minutes (thermal Carafe no warmer)
Panasonic 1200W Inverter Nukelator = 74A draw on High Power.
GrundFos SQ-5 SoftStart 120VAC deep well pump, 260' deep, set to cutoff at 52PSI. Starts at 550W, ramps by 150W increments till it reaches 52PSI at 1100W. Inverter barely blinks.
Good for Solar & You.
- On Demand Hot Water heater ! would you keep your car idling in the driveway all day & night just because you "might" want to go for a drive ? That is what the Hot Water tank is, 15 minutes of every hour it is heating water for "in case you want it".
- Induction Electric Cook Stove, energy efficient, fast and good for solar.
- Energy Start 5 rated Fridge & Freezer, use low kWh per year. (Mine uses 247kWh in 12 months)
- Coffee Makers with Thermal (thermos) Carafe and No Warmer !
the rest is more obvious but just to give some ideas, where to save and cut losses & wasted energy.
Hope it helps, Good Luck
Steve.
PS, grab stuff from my Signature, the LFP assembly guide, LFP Voltage chart & "Calibrating your system" especially important.
Thanks that helps a lot
podilamaya
New Member
- Joined
- Mar 17, 2021
- Messages
- 50
sorry for the noob question,
How the Relay/Contactor based BMS controls the charging and discharging current rate. My understanding is that kind of BMS out of the current path and relay/contractor is just a binary switch (on or off)
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
The BMS controls 1 or 2 relays to control powerflow from the battery cells typically to a common DC Bus. The power, therefore, is not pushed through a bunch of FETs and completely bypasses the "fine electronics" and leaves the heavy lifting to the relays.
These usually can support either Common Port or Separate Port configurations. Separate Port does require the use of 2 Relays/Contactors.
These usually can support either Common Port or Separate Port configurations. Separate Port does require the use of 2 Relays/Contactors.
