LFP and Alternator settings

[sailorboy1]

How are people preventing their alternators from overcharging their LFP batteries during a long motor? I assume it is in the regulator programing and not hoping the BMS does it. What settings have you programmed in?

[Networker]

Use the external regulator and tell it to stop when voltage hits 14.4v. I use wakespeed.

[jordanbigel]

What I do is use a SOC% relay. I use a BMV700 which has a customizable relay. You can configure the relay to turn on and off at SOC% set points. In my setup, the relay is wired to the voltage regulator (through an intermediary device - a Victron SolidSwitch104).

When the SOC% drops to 50% the regulator is powered and starts its normal charging cycle. When the SOC% hits 80% the relay cuts power to the regular, stopping all charging. The choice of what trigger point and target point you set (when to stop charging) depends on your own preferences and how you use your boat. And, you have to accept that once you reach that target SOC% you will keep motoring without generating any power at all, running completely off battery power, even though the engine is ticking, until you hit the trigger SOC% and it goes back on.

Also, I wired a LED push-button override conveniently located which bypasses the relay and feeds power to the regulator. This way, if I need my bank at more than 80%, I can press the bypass button (which lights up to indicate it is enabled) and then the regulator will continue to charge as controlled by the regulator's programming, until the override button is released.

[wholybee]

I have an externally regulated alternator, with the charge voltage set very conservatively at 13.8V.

However, I also have enough solar to rarely need the alternator. So, I installed an on-off switch that lives in the off position. So, for long motor trips, the alternator isn't on at all. I highly recommend such a switch, whatever else you do as well.

[fxykty]

Originally Posted by sailorboy1

How are people preventing their alternators from overcharging their LFP batteries during a long motor? I assume it is in the regulator programing and not hoping the BMS does it. What settings have you programmed in?

Any constant voltage charging above around 13.6V will eventually overcharge an LFP battery, so unless your regulator includes a setting for tail current to stop absorption you cannot rely on the external regulator.

The Wakespeed WS500 can be controlled by CAN bus. AFAIK that’s the only external regulator that has that capability. We have Balmar MC-614 regulators and they don’t have any control settings nor external comms. We have them set to bulk 13.8V, absorption 13.7V, float 13.2V. Absorption time is short (0.3h) so on long motors they do sometimes drop into float, but we don’t rely on that.

We don’t hope our BMS will prevent overcharging - we rely on it. We have two automated systems plus manual switches to control alternator charging.
- BMS uses a certain SOC% to stop charging, which triggers a relay to turn off the external alternator. If SOC is out of whack then the BMS uses a certain cell voltage to stop charging, which triggers the same relay to turn off the external alternator. Generally SOC-based stop happens before voltage-based stop
- BMS uses a certain cell voltage to disconnect the charge bus. The stop charge command always takes place first. We’ve not yet had this happen
- Our engine control panel has a switch to turn off the external regulator. Since we have relatively small engines and big alternators we use these switches to give us more propulsion, as well as to manually stop charging

[sailorboy1]

Sounds complex so far

[SoonerSailor]

I tend to be highly involved with my electrical and electronic systems, so my approach is probably rare amongst cruisers.

I'm using a Balmar MC-618 regulator and Balmar 100 A alternator to charge a 420 Ah LiFePO4 bank. The regulator is programmed to limit alternator charging to a maximum of 60 A. Small case alternators can't manage more than that for more than a few tens of minutes before heat issues necessitate reducing output to about 60 A, so I'm not losing much by doing that. In addition, I have wired a switch to the regulator that limits charge rate to 30 A, which I will do if I expect to be motoring a lot - figuring it saves on belt and ultimate alternator life. Another switch is wired to force the regulator into float mode if I wish to keep the SOC somewhere between 50% and 80%. Finally there is a 3 position switch to turn off the external regulator completely and stop charging, or switch over to the Balmar alternator's internal regulator in case of failure of the external regulator. All of these switches are built into an easily accessible switch box next to the MC-618, both of which are outside of the engine room.

Monitoring is done with a Victron BMV-712 and the Victron app via Bluetooth.

Admittedly this is not for everyone, but it suits me well and allows for easy control of LFP bank state of charge.

[sailorboy1]

While I see it as effective to have a manual switch to turn off the alternator, it doesn't seem acceptable to rely on remembering to do it.

[Networker]

Originally Posted by sailorboy1

While I see it as effective to have a manual switch to turn off the alternator, it doesn't seem acceptable to rely on remembering to do it.

Just get a wakespeed, it monitors volts, currents and temp, and stops charging if batteries are full. If batteries need to be filled, it tells regulator to charge. If it’s hot, it backs it off.. It’s dead simple and you can also add a switch to change the field % to something lower than 100% if you want, but so far I’ve found I’ve never used it.

I had the Balmar mc-618 and it worked too, but I had to keep the field manager to 50% to keep the heat down when motoring. But it’s a pain to program as it needed a magnetic pen. The wakespeed can be programmed with an android phone and usb cable.

[SoonerSailor]

Having programmed it, I certainly have no need to keep reprogramming the MC-618. As I said, I’m very happy to be involved with managing the charging the way I do. I only very occasionally take the bank up to full charge, so having a Wakespeed to manage that form me doesn’t feel like a need.

[smac999]

Float at 13.5v. Same as sitting at the dock 360 days a year which most boats do.

No bms I have seen stops charging. (Victron, mastervolt etc) Maybe some of the home made ones do.

[Ballsnall]

Originally Posted by fxykty

We don’t hope our BMS will prevent overcharging - we rely on it.

Then your doing it wrong, program you charge source to not achieve an over voltage situation.

[sailorboy1]

More I think it over the more it seems to me that the only proper way would be to turn off the charging based on a %SOC. But I can see setting the alternator voltage low enough would be a plus as then the alternator is powering the loads instead discharging the batteries. At same time I wonder it that is a case of thinking like lead acid batteries.

I would think by now all this is clearly sorted out. If someone knows a website etc. please let me know. I hopefully have 6 months to 10 years to figure this all out.

[jordanbigel]

Originally Posted by sailorboy1

More I think it over the more it seems to me that the only proper way would be to turn off the charging based on a %SOC. But I can see setting the alternator voltage low enough would be a plus as then the alternator is powering the loads instead discharging the batteries. At same time I wonder it that is a case of thinking like lead acid batteries.

I would think by now all this is clearly sorted out. If someone knows a website etc. please let me know. I hopefully have 6 months to 10 years to figure this all out.

I came to the conclusion after reading dozens of threads like this one, before I switched to LifePo4, that this HAS been clearly sorted out, but, like most things, there are always people who choose a different path for reasons which they feel are compelling. Like the member above (smac99) who says he floats his bank at 13.5 at the dock on shore power - nearly everyone agrees that is bad. And yet, many of the drop-in manufacturers claim this is okay and tell their customers to do exactly that.

Maybe the reason is that they don't care if their batteries last 15 or 20 years because they only offer a 5 year warranty anyway, because even if you float them (keep them FULLY charged over long periods of time - again, something that the consensus DOES say is bad for longevity) they will still last more than 5 years. And maybe for a lot of boaters that is okay. And because they want to sell boaters new batteries, they gloss over the whole BMS disconnect fry your alternator issue, and don't want to confuse their customers by explaining how they should not be floating the batteries but triggering cutoffs based on SOC% - that's not going to sell batteries if they explain all that, because a lot of boaters are not willing to make the adjustments or change out chargers for more capably systems, etc.

For me, I want them to last at least 10 years, hopefully longer. So I go with Best Practices for longevity, keep them out of the "knees" (voltage too low or too high). Bottom line, floating a LifePo4 bank at 100% SOC is always bad for longevity. This is what I have learned over the last 2 years researching this topic - and I am no expert, there are plenty on CF who are, and I tried to learn from them what I could.

My observations and research has convinced me that there is consensus on at least a few key points. 1) don't charge to 100% SOC and leave them there, and 2) don't let your BMS HVA disconnect while the alternator is energized (even if you have an APM/Zap Stop device installed).

[sailorboy1]

Ok so where can I find accepted “best practices”?