I am awaiting a new lithium bank to arrive and as I do so i’m planning out what needs to be done to setup my charging for the bank.
I am going to be using the argofet to that my main engine alternator will plug into to charge both my house lithium bank as well as the start battery.
I have a DC generator(small kubota with a 175a alternator) that also charges my house bank.
I am thinking that I should be able to use the 200A 2 bank argofet and run both my alternator charge sources to this argofet to distribute out the charge to the house/start battery? Why would i need to run 2 of them? Am i wrong?
@jordand If you draw more current through a FET than its rating it will blow up. FET is a Field Effect Transistor and it is just a componet rated to a certain level. If you push it too hard it will fail. An MPPT is a complex device that is quite smart so it has the ability to not exceed its rating. I don’t understand how one ArgoFET can handle two charge sources but I would caution just connecting an alternator to the Lithium House bank. The reason is the internal resisitance of a lithium battery is such that a lot of current can flow to charge it and the normal alternator of a car for instance can overheat and burn up. That is why an external regulator on the alternator is a good idea as that will have a temperature sensor that can be bolted to the body of the alternator to derate the current if the body temperature gets too high.
I would suggest having the house bank being charged by the alternators with external regulators and use a DC-DC charger to keep the starter battery topped up. I wouldnt use the argoFET at all.
Thank you. Everyone i’ve talked to has said “I dont really know, we just install the bigger one usually as its only a small cost more”.
Running 2 alternators to it was just going to be using a power post to bridge both alternators then a single connections to the input on the ArgoFET.
Having read/talked to more people, i have realized that the ArgoFET at the upper bound actually drops voltage more than anticipated(0.1v), not the end of the world, but not something i personally like so the FET is not going to be the ideal solution.
Both of my alternators are externally regulated(balmar 614 and a 618) so running them to handle charging the lithium isn’t a problem for me.
I also have a cerbo gx + smart shunts and a bunch of other victron gear onboard, I pulled the trigger on a 9amp DC-DC charger for the start battery so this will keep the battery topped up while alternator sources will go direct to the lithium bank.
I will be adding NC relay’s into the field wire on each of the regulators which will be connected to the cerbo GX that will cut the field when the SOC of the lithium is at 95% full. The regulators will be programmed so they should never hit the HVCO that I will set in the JK BMS’s. In theory if the cerbo fails to open the NC relay’s when SOC hits 95%, then the regulator programmed settings will be the failsafe at preventing over voltage and a BMS shutdown event so the alternators in theory will be protected.
@jordand it sounds like a good setup. Some lithium batteries with internal BMS have a “protection” facility so that when the battery reaches 100% full they disconnect and sit in a “protection float” mode.
Please consider that if you stop charging slightly earlier than 100% maybe the battery cell voltages may not equalise sufficiently and over time may not track as they should. I do not know this for sure but I would caution against not allowing the batteries to fully charge.
Both Balmar external regulators have temperature sensor inputs. I you use the Balmar external temperature sensors, from memory when they reach 100 degrees C, they reduce the alternator excitation current by 50% allowing the alternator to cool down a bit.
I understand your concern that the batteries can open circuit and cause some concern to the alternators but at that stage they have reduced charging current to practically zero, so the alternators are not fully excited, and you still have the load of the vessel (and the DC-DC charger) on the alternator output. It is quite different to having a high charge current from the alternator and instantly open circuiting the output of the alternator. I dont think the alternators will be damaged by the open circuiting of the batteries by the BMS for that reason.
I would simply let the batteries charge to 100%, allow them to protect themselves if that happens, use the DC-DC charger for the start battery and live happily ever after.
I would use the Smartshunt as the “Battery Monitor” and not use DVCC if you are not quite 100% sure how the batteries will react or the BMS will report. One of the issues with using the Smartshunt as the Battery Monitor if you only intend to let the batteries reach 95% charge is the Smartshunt will never “Sync” to 100% and that will allow the reading of SOC to drift over time so eventually it will be very inaccurate. The reason is the Smartshunt measures the terminal voltage of the battery, measures the current and deems the battery 100% full when the battery voltage is as specified (Charged Voltage) and charge current is low (Tail Current). At that stage the SOC is reset to 100% so that is the datum point for that charge cycle. If the tail current never gets to a low value that reset will never happen and the SOC will drift from reality depending upon settings of battery efficiency and Peukert value.
Another reason for using the Smartshunt as the battery monitor is the battery BMS will report its internal voltage but when it goes into “Protect Float” mode it disconnects from the actual terminals of the battery. You could have 14 volts on the terminals but have the BMS telling you the terminal voltage is 13.3v. That could be very confusing unless you are aware of the situation.