The LDSA serves two main purposes for LiFePO4 "Drop-In" batteries.
#1 Provides a path to the lead acid "starting / reserve" bank for alternator current so the lead acid battery can act as a buffer in a BMS disconnect.
#2 It keeps a lead acid battery on the distribution bus so long as the engine switch is still in the ON position. This is what we call the stay-alive function and allows the vessel to still remain running/powered should the LiFePO4 battery disconnect itself from the vessel.
Note: See wiring diagram in the images.
A LiFePO4 drop in battery has an internal sealed BMS which can disconnect the battery from the vessel for multiple reasons such as; high temp, low temp, cell voltage spread, BMS PCB temp, over-current, bank high voltage, low bank voltage, cell high voltage or cell low voltage just to name but a few. A lead acid battery cannot do this. Unfortunately, LiFePO4 drop-in batteries offer no warning of a pending BMS disconnect to the vessel operator. A communication/warning systems for these batteries is actually part of ABYC TE-13 yet not too many actually comply with this. The reason why this is part of ABYC TE-13 is because bad things can happen if the BMS disconnects the battery from the vessel. Navigation equipment can be lost, power can be lost and a load dump can cause a massive voltage transient that can damage not only an alternator but also your on-board electronics. While the Sterling Power APD will work to clamp the transient, it can only do that. The LDSA is designed to work directly with the Sterling Power Alternator Protection device and keep the vessel powered via the start/reserve lead acid bank. The LDSA sits between the LiFePO4 bank and the lead acid start /reserve bank and is only energized when the engine is running thus isolating the lead acid and LiFePO4 banks when the batteries are discharging.
We worked for many months with our US solenoid manufacturer running all the scenarios such as windlasses off the start bank and charging on LiFePO4 etc. etc.. This is the 150A model and it is hermetically sealed for marine use. Because this is to be used with LiFePO4 the contacts were designed to handle inrush currents of up to 750A, 295A for 30 seconds and 395A for 45 seconds and 150A of continuous current. A 220A LDSA solenoid is still in the works. The 220A version will work even with high amp bow thrusters and large 200A+/- alternators. The LDSA has allowed CMI to come up with one of the easiest, & least expensive ways to install a LiFePO4 drop-in battery bank and to protect against BMS loads dumps and 12V power dropping out, all at less than $50.00.
With the LDSA solenoid you can charge your LiFePO4 directly, which is best for optimal charging performance. This allows you to take advantage of the high acceptance rates of LiFePO4 so long as your alternator can handle the load and not over-heat itself. We advise using an externally regulated alternator with a performance voltage regulator such as a Wakespeed WS500 or Balmar MC-614. Your regulator should have the ability to limit alternator current and have alternator temp sensing, when charging LiFePO4.