Wiring BCU for a lifepo4

[solaar]

Can anyone help explain how to wire this up? I'm pretty confused by the diagram. It looks like I have to connect the pos and neg wires from the BCU ppak and from the charger in a "T". If this is so, then how do you do that?

Thanks, and sorry if this is dead obvious I'm new to all this.

[Sunking]

Not sure how to tell you to wire it because you have the detailed diagram showing you exactly how to wire it up. Connect the BCU power directly to the battery Term Post. There is no T, just poor illustrations. Connect the Loop wires to the Vampire Board Loop, and the Relay Control wire to the Battery Relay.

What Vampire Balance Boards are you using?

Your BCU has 5 wires.

2 wires used for Power that connect directly to the battery term post after the fuse. This makes sure your battery will be completely destroyed if it operates and you do not catch it in time. The BCU keeps taking power from the batteries after the charger and load are disconnected from Low Voltage Disconnect. On the flip side the BCU will disconnect the charger and load if the voltage goes to high so it does not destroy the battery


2 wires for the Control Loop. 1 wire goes to Vampire Board 1, and the other to Vampire Board 4. The Vampire Boards are Daisy Chained together to complete the Loop. Each Vampire Board has a set of Relay Contacts that open and close. When Closed passes the signal to the next Board, which pases the signal to the next Board which passes signal to the next board and the last board passes the signal back to the BCU to form a Closed Loop. If for any reason one of the Vampire Board triggers opens the Loop, and your battery and charger are disconnected as shown.

1 the last Single wire is the control signal to the Battery Disconnect Relay. If the all Relays are Closed, then your battery is connected to your charger and load. If any Relay opens for any reason, your battery will be disconnected from your charger and load.

So attach your Vampire Boards to each cell, it take one Vampire Board for each cell. Looks like you have 4S configuration means you need 4 Vampire Boards. Each Vampire Board has two wires. You daisy chain the 4 Vampire Boards in a Series fashion. That will leave you two wire that are not connected. One on cell 1, and cell 4. That is what you connect to the BCU. Be sure to test it with a Ohm Meter. You should read a short circuit for normal operation. If not fix it. Because if it is open circuit is the signal to disconnect your battery

Easy Peazy. Make it even easier. You do not need it if you are using it to power an Inverter. Your Inverter should have a Low Voltage Disconnect that triggers at 11 volts which is 1 volt Higher than your BCU will operate. You can charge it anywhere from 13.6 to 14.2 volts. Keep in mind those Vampire Boards used to protect your cells are the number one cause of failures and fire. They earned their nickname Vampire Boards. The industry calls them various names like Balance Boards or Bleeder Boards, in your case they are called BMS Modules in your drawing. . Simple device, they turn on when cell voltages reach 3.6 volts or so, and apply a Load to the battery to Bleed it or Discharge. The problem is when they fail, they do not disconnect and Bleed your battery to Death like a Vampire. If you are lucky it just destroys the cells and you get to replace them. Otherwise you have to repair the fire damage first before you replace them.

To charge a lithium on solar, all you need is a very simple charge controller that you can set the voltage to 14.2 volts. That is the Industry Standard voltage for LiFeP04 solar charge controllers. If the panel wattage is 140 watts or less Genasun makes Charge controllers for Lithium Batteries as well as lead acid batteries. The Lithium units are less expensive than Lead Acid as they are much simpler with only one function, 14.2 volts no matter what else you want. Just make sure you order the right part number. Lithium has 3 part codes one each for LTO (12.5 volts), LFP (14.2 volts), and LCO (16.7 volts). Additionally you can use any standard charge controller if you can dumb it down and set it to 14.2 volts For most Programmable models you set Bulk = Absorb = Float = 14.2 volts. That turns it from a Smart 3-Stage Charger for Lead Acid to a Dumb 14.2 volt lithium battery charger.

[karrak]

2 wires used for Power that connect directly to the battery term post after the fuse. This makes sure your battery will be completely destroyed if it operates and you do not catch it in time. The BCU keeps taking power from the batteries after the charger and load are disconnected from Low Voltage Disconnect. On the flip side the BCU will disconnect the charger and load if the voltage goes to high so it does not destroy the battery.

This is not correct. In the event that any of the cell voltages gets too low (<2.6V) or the overall battery voltage gets below 11.9V (average 2.975V/cell) the BCU will disconnect the load from the battery. If you had a 60A load on your 60Ah battery when this fault occurred your battery could be damaged within minutes. If the BCU disconnects the battery, the load on your battery will go from 60A to the power drawn by the BCU and BMS modules (<0.020A). At this current it will take days or even longer before the battery is damaged by the current draw from the safety circuitry. It would be better to have two separate relays, one to disconnect the solar panels from the charge controller if any cell voltage gets too high and one to disconnect the load if the voltage gets too low. IMO and industry standard practice would say that it is better to have some protection rather than none.

Easy Peazy. Make it even easier. You do not need it if you are using it to power an Inverter. Your Inverter should have a Low Voltage Disconnect that triggers at 11 volts which is 1 volt Higher than your BCU will operate. You can charge it anywhere from 13.6 to 14.2 volts. Keep in mind those Vampire Boards used to protect your cells are the number one cause of failures and fire. They earned their nickname Vampire Boards. The industry calls them various names like Balance Boards or Bleeder Boards, in your case they are called BMS Modules in your drawing. . Simple device, they turn on when cell voltages reach 3.6 volts or so, and apply a Load to the battery to Bleed it or Discharge. The problem is when they fail, they do not disconnect and Bleed your battery to Death like a Vampire. If you are lucky it just destroys the cells and you get to replace them. Otherwise you have to repair the fire damage first before you replace them.

The BCU disconnects the load at 11.9 volts, not 10 volts as Sunking has stated. At 11.9V you will still have >10% of charge left in your battery.

As for failing, there are a number of people using these devices from this manufacturer in Australia. I haven't heard of any failures. I agree with Sunking that if they do fail they could damage your battery if you didn't find the failure in time. The BCU will give you some warning, but not much by disconnecting the battery if one of the cells is discharged by a faulty BMS board.

To charge a lithium on solar, all you need is a very simple charge controller that you can set the voltage to 14.2 volts. That is the Industry Standard voltage for LiFeP04 solar charge controllers. If the panel wattage is 140 watts or less Genasun makes Charge controllers for Lithium Batteries as well as lead acid batteries. The Lithium units are less expensive than Lead Acid as they are much simpler with only one function, 14.2 volts no matter what else you want. Just make sure you order the right part number. Lithium has 3 part codes one each for LTO (12.5 volts), LFP (14.2 volts), and LCO (16.7 volts). Additionally you can use any standard charge controller if you can dumb it down and set it to 14.2 volts For most Programmable models you set Bulk = Absorb = Float = 14.2 volts. That turns it from a Smart 3-Stage Charger for Lead Acid to a Dumb 14.2 volt lithium battery charger.

Charging and floating an 12V LFP battery at 14.2V (3.55V/cell) will reduce its lifespan and could damage it if there is no BMS system installed. A charge voltage of 3.55V/Cell is equivalent to an SOC (State of Charge, how full the battery is) of >99.8% (see my post https://www.solarpaneltalk.com/forum...679#post320679 for more details). With the BMS you have you will need to charge to at least 14.2V to make sure the battery stays in balance. For longer lifespan while still charging to nearly 100% a charge voltage of 13.8V (3.45V/Cell) is preferable. A float voltage of 13.4V (3.35V/cell) will keep your battery close to 100% full while the sun is shining.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger https://github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller

[solaar]

Thanks Sunking.

The battery I bought from a company called EV Power with the BMS system already in place (not sure what type) and an outlet for communication with the BCU. The BCU came already wired as shown in the picture.

What I really need clarification on is attaching my solar charger (Victron programmable type) and appliances to the system.

Do I attach the positive cable from my solar charger to one of the "Load" connection points on the relay, and then attach the negative wire from the charger directly to the negative terminal on the battery?

And likewise, for a cigarette lighter connection to power a 12V appliance: connect the positive to the "Load" relay and the negative to the battery?

Then, will I also need another wire running from the positive terminal on the battery (after a fuse), to one of the "Battery" connection points on the relay?

[karrak]

The battery and BMS is manufactured by EVPower in Western Australia. Sounds like you are in Australia as well.

Your wiring description is correct.

Cigarette lighter connectors are not known for their reliability, Anderson connectors or something similar are a better alternative.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller