We're connecting two 24 volt Tesla batteries to 2 LG panels to have some off-grid power. Do we need a BP 220 for each battery or will one do for both?
asked
How Many BPs Do I Need?
As @Justin Cook already wrote:
Please don't use lithium batteries without a properly designed BMS system with cut-off protection (shunt-trip or relay) so you have a double protection.
As you write you're a novice in this area, please make sure someone is -very- knowledgeable to do this project for you. Or use a supported and proven safe alternative.
Tesla battery modules are great, but they need proper handling, because otherwise they can be great danger! they will burn / explode violently when overcharged for example. And overcharging can happen without exceeding total pack voltage limits (when a module is out of balance).
The BMS system has to monitor all cell-groups and has to be able to disconnect the modules when charging / discharging goes beyond safe limits for whatever reasons.
There are a couple of good BMS options available, but all are for experienced users and require deep electrical and software knowledge. (therefore we cannot recommend BMS x or y)
Yes, I do know this, am aware of the dangers, want to set it up properly, am proceeding with caution. We'd like to be pointed toward the best BMS options. I am working with a very experienced electrician.
I respect these strong positions from Victron regarding the benefits of a BMS but I would appreciate some supporting data. Maybe take some real world examples to derive some conclusions based upon probability analysis?
All batteries introduce risk including ones with on board BMS. so what is the quantifiable difference? I"m really curious
2 (in words: two) LG Panels means a (in words: one) small MPPT will be enough. If you provide specs or model of the LG panels, I can tell you which one.
Here's what we have so far:
Two Tesla Battery Modules 24V 250Ah 5.2 kWh 444 Panasonic 18650 Cells
MPP SOLAR Hybrid 2400w Pure Sine Wave Power Inverter with mppt Solar Charger 80A DC 24V AC Output 110V 120V with 60A Utility Charger 50HZ or 60HZ
Two of these panels: LG340n1c-v5 340w neon n2 60 cell
Nominal Maximum Power: 340 Watts
MPP Voltage: 34.50 Volts
MPP Current: 9.86 Amps
Open Circuit Voltage: 41.10 Volts
Short Circuit Voltage: 10.53 Volts
Module Efficiency: 19.80%
You're saying we don't need external battery protection other than what the Inverter provides....?
We're running the off-grid system to a 24 volt freezer and would like to make a charging station and some nominal lighting.
I'm very new to this (don't understand electricity at all!). I'm working with an older, retired electrician who is quite skilled but this is a new application for him. Any direction very appreciated!
@BonnieLinden, are you asking about the BP (BatteryProtect) or the MPPT (solar charge controller)? A BatteryProtect is unidirectional in operation only, so it would be connected to a DC load side only, and would not be relevant to your PV panels.
Hi Justin, I'm asking about the BP and wondering if each of these batteries needs its own BatteryProtect.
Two Tesla Battery Modules 24V 250Ah 5.2 kWh 444 Panasonic 18650 Cells
Aren't the batteries being protected from too much possible current from the solar panels? Doesn't the DC come from the panels?
We have two of these panels: LG340n1c-v5 340w neon n2 60 cell
Nominal Maximum Power: 340 Watts
MPP Voltage: 34.50 Volts
MPP Current: 9.86 Amps
Open Circuit Voltage: 41.10 Volts
Short Circuit Voltage: 10.53 Volts
Module Efficiency: 19.80%
We have this charge controller: MPP SOLAR Hybrid 2400w Pure Sine Wave Power Inverter with mppt Solar Charger 80A DC 24V AC Output 110V 120V with 60A Utility Charger 50HZ or 60HZ
Sorry, I'm a total novice, don't understand electricity at all. But I'm willing to learn! The installation is at my house so I should understand it as well as possible. Your elucidations welcome.
@BonnieLinden, no worries! Although I only deal with Victron solar charge controllers and cannot comment on the charge controller you list, so long as the controller is functioning properly it should be providing your batteries with the proper DC voltage; you should not require a BatteryProtect on the DC charging line unless your controller is significantly malfunctioning, in which case there are other issues entirely; furthermore whatever BMS (Battery Management System) you have configured to control and protect your batteries should also be online to cut out in case of high voltage being delivered from your controller. If you don't have a BMS connected to the Teslas you should stop and research what a BMS is, what it does, and why you absolutely positively must have one to protect not only your batteries but also all the equipment connected to them.
You can technically use a BatteryProtect as a high-voltage cutout inline with your charge controller if you like (the BP would be connected in reverse of the common connection, in this case with your battery connected to the "out" and the charge controller connected to the "in") but you will most likely want the Smart BatteryProtect so that you can manually set the high voltage cutout point rather than being limited to the default cutout ranges offered by the regular BatteryProtect. Whether you would need two or not depends on how many DC charge lines your controller has; if it has one charge line that connects to a single battery, with your batteries then connected in parallel, then you only need one BP; if your controller has two charge lines, one for each battery, then you'd want 2 BPs, one for each line. Given that your controller only offers 80A charge rate, however, you don't need the 220; the 100A BPs would be fine for that.
All that being said: Please fully understand your system before you start purchasing equipment! Make sure that you have fuses or breakers on all lines, make sure that all cables are sized appropriately to their lengths and current being carried, and please make sure that you have a properly-configured BMS. Given that you're using used Tesla cells and you'll only be able to purchase an off-brand external BMS for them, I can pretty much only wish you luck on that... the use of uncontrolled used lithium cells is not supported by Victron, not supported for the usage or connection of Victron equipment, and very much leaves you on your own when it comes to technical support for your equipment, unfortunately.
