Chris, See red Below,
Steve,
My charger can accept a contact input from a BMS. Based on this input the charger will either stop charging, or go to some configurable float value. I'm wondering how you are setup.
Chris,
My charger, a BRUSA, is one of the best out there. However it's now being used as a "dumb" charger fully controlled by the BMS. In other words on/off signals only with slow ramp down when the batteries are full. LiFePo4's don't like trickle charging (defined as a low charging when the batteries are full or at their set point %.) I'm assuming that the Configurable float value you mention is also when the charger is off. Though the BRUSA is fully programable, unlike many chargers that may be factory set, there is a built in program for the LiFePo4's.
Also, I often need to supplement my battery bank with charger output with the genset running during times that it's not possible to make headway under sail.
This one is a little tricky.. My Genset is rectified to an adjustable output to as high as 160V. So in other words I can adjust the output to maintain the output AMPS to maximize the charge to the batteries. I could have had this done through automation but decided that I didn't want to deal with the complexity of the system (somewhat complex anyway) and I had heard of some horror stories of the genset trying to start when no one was aboard there boats. Not a good thing…
So my BMS has alarms for both Over State of Charge and Low State Of Charge as well as a signal (an owner defined set point) to start the charger (Used only with shore power). At the Dock, if the bank is below the FULL charge state the charger is in gauged automatically and charges to the owner defined full state (in my case 98%) If I'm out under power and I see the bank is down to say 50% I manually start the Genset and charge. The BMS will shut down (this is defined as putting the genset into idle mode, no charging but still running at a lower RPM) and I then shut off the genset by key. Since the max charge is 98% that is where the Genset goes to idle and I know I can shut the genset down completely after a cool down period.
In your case you probably start he genset, the charger get's the signal from the BMS to charge when at a low state of charge and then the BMS shuts the charger off. You then shut the genset off. While charging you probably here your genset sag a bit.
Does the battery bank have to drop to a certain SOC before the BMS will tell the charger to start providing current again?
YES, See above OP for under shore power since I assume your charger is used with the genset as well and you just start the 120V output from the genset to go to the charger. The BMS should keep the charger output from the batteries until the SOC is below it's set point then switch the charger on.
I'm assuming the pack voltage would drop enough as soon as the drive is engaged triggering the charger to start.
I'm not sure I understand this one. "As soon as the drive (motor?) is engaged triggering the charger to start" would mean that the charge setpoint is too close to the Fully Charged State possibly causing a short cycle condition to occur. If you mean ACTIVATE as in ready to start charging once the lower value, say 50% SOC, is reached than yes the charger would be in a "ready" mode. Your batteries shouldn't have that much sag or the setpoint that close to trigger the charger.
If I go LiFePo4 I'd probably have 2 banks with 2 BMS with the 2 banks able to be tied together, or be run separately. I'm guessing I would just series, or parallel contact outputs (depending on contact state) as one input to my charger.
This one Chris is over my head (2 separate banks) and I will defer to maybe James for an answer. Off the top of my head I'd say that the contacts and the BMS (2) probably would be fighting each other and through the system into a tissy…80)
How are you monitoring your state of charge of the pack?
Hope that helped,
Steve in Solomons MD
Lagoon 410 S2E
Posted by: "Steve Dolan" <sdolan@scannersllc.com>
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