lithium and agm batteries: a warning !

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   This looks like a right setup ( the one with 3 DCDCs and all charges to service), one only has to worry about shutting off the alternator if service Li bank gets overcharged and BMS wants to turn off all charging sources, I think smart alternators are capable doing it.

Edited by marsella - 04 July 2025 at 15:07

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marsella Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 21 June 2022 Location: Antigua Jolly H Status: Offline Points: 592	Post Options Post Reply Quote marsella Report Post Thanks(0) Quote Reply Posted: 04 July 2025 at 15:02
	This looks like a right setup ( the one with 3 DCDCs and all charges to service), one only has to worry about shutting off the alternator if service Li bank gets overcharged and BMS wants to turn off all charging sources, I think smart alternators are capable doing it. Edited by marsella - 04 July 2025 at 15:07

Arcadia Members Profile Send Private Message Find Members Posts Add to Buddy List Admiral Joined: 27 November 2017 Location: Sag Harbor, USA Status: Offline Points: 1112	Post Options Post Reply Quote Arcadia Report Post Thanks(0) Quote Reply Posted: 04 July 2025 at 15:31
	I don’t think there is any real danger with that issue. A multi battery lithium bank will gradually decrease current to zero with each battery shutting off at slightly different times. Any alternator would be able to deal with this. It’s an abrupt disconnect of current that will cause the kind of spike that could damage diodes. Also keep in mind that even with the lithiums at zero charge current, you will still likely have house and navigation loads providing a certain load current as well as the dc to dc chargers.
	Leon / ARCADIA 2018 Hanse 588 Sag Harbor, NY

32mike Members Profile Send Private Message Find Members Posts Add to Buddy List Commadore Joined: 26 March 2020 Location: FLorida, US Status: Offline Points: 453	Post Options Post Reply Quote 32mike Report Post Thanks(0) Quote Reply Posted: 04 July 2025 at 16:29
	I have been studying this for a future upgrade to lithium. Here’s what I’m seeing from my research: I have a generator, so these are in consideration of that. Without one, you may go in another direction. Option 1 (easiest and cheaper of the two) Alternator from engine is connected to AGM start battery. DC to DC charger (30-50 amp limited) is connected to house bank. Original battery combiner is removed. In this setup, the DC to DC limits the house bank from over drawing the alternator and thus keeps it from overheating. The DC to DC also only operates when the engine is running so that the house bank can’t drain it down to zero. The alternator is protected from a BMS shutdown by virtue of also being connected to the AGM start battery which dampens the shock. The drawback is that my 125 amp alternator is not being used to its full capability in charging the house bank while running. My generator capability backs that up when needed. Also, this eliminates the charging of the AGM start battery on shore or generator power because the DC to DC is one way to the house bank. This limitation can be overcome with a small battery charger which is wired to the shore/generator only output from the inverter/charger. Alternately, you could just wire one solar panel to the start battery only to keep it topped off. I have been told that using the small trickle charger output of the inverter/charger would not be advisable in this setup because when the DC to DC is running, there is a circular current path with that trickle charger - still a little fuzzy on that. This trickle charger is fine to use with the standard all AGM setup but is unnecessary because of the battery combiner which does the trick. Option 2. (More complicated and more expensive but probably the best setup) Remove the battery combiner. Upgrade to a bigger alternator or keep the same one and install an alternator regulator like a Wakespeed, Sterling or the new Arco Zeus (this one is designed to be used with the bigger alternator for faster charging at idle engine speeds). In this installation, the alternator charges the house bank and the alternator is kept from overheating by the regulator and you can use the full capability of the alternator for charging the bigger house bank directly. A DC to DC is then used to charge the AGM start battery. The alternator is protected from a BMS shutdown by the BMS itself which shuts off the alternator. All the batteries get charged anytime with either shore, gen or engine running. I don’t run AC’s off of the batteries, so that’s not a problem for me. My bow thruster AGM is charged from a small DC to DC off of the house bank which would just stay that way. From what I have learned, the biggest problem with just keeping the battery combiner and not using a DC to DC between the alternator and lithium bank is that the large lithium house bank can easily overwhelm the alternator because of its very high charge capability. In essence, it can take everything the alternator can give which will cause an over temp and destroy the alternator. Disclaimer: I am not a marine electrician or even an expert, only an internet researcher (yikes!)
	Mike S/V Dulces Sueños 458 #087 Tampa, FL

32mike Members Profile Send Private Message Find Members Posts Add to Buddy List Commadore Joined: 26 March 2020 Location: FLorida, US Status: Offline Points: 453	Post Options Post Reply Quote 32mike Report Post Thanks(0) Quote Reply Posted: 04 July 2025 at 16:46
	Pierro, Take a look at the MasterVolt ChargeMate. If you have this installed instead of the battery combiner, it will prevent the house bank from draining the AGM start battery. The drawback is that you won’t have charging of the AGM start battery unless the engine is running. You could solve that by installing a small battery charger which runs off of the short/gen only output of your inverter charger.
	Mike S/V Dulces Sueños 458 #087 Tampa, FL

marsella Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 21 June 2022 Location: Antigua Jolly H Status: Offline Points: 592	Post Options Post Reply Quote marsella Report Post Thanks(0) Quote Reply Posted: 04 July 2025 at 17:24
	Mike - option 2 we are talking about. BTW our Valeo 125A alternator can be upgraded with Balmar regulator kit, 1h work to install and there is youtube video showing the steps

Arcadia Members Profile Send Private Message Find Members Posts Add to Buddy List Admiral Joined: 27 November 2017 Location: Sag Harbor, USA Status: Offline Points: 1112	Post Options Post Reply Quote Arcadia Report Post Thanks(0) Quote Reply Posted: 04 July 2025 at 18:03
	Some alternators can deliver more current than they are capable of dissipating. This gives a high output number on paper but not in practice. Balmar is in this category as evidenced by the unusually small cases vs claimed output level. This why they recommend dialing down the charge level with their regulator. I’ve burned up a few in the past with previous boats. I’ve upgraded the Volvo D3 140 amp on mu 588 to a drop in 180 amp unit which can happily deliver full output without overheating. It’s all a matter of how the windings are done internally as well as designing the field current so as not to exceed the heat dissipation capacity. With this set up, I can charge directly to my lithium bank with full output. Edited by Arcadia - 04 July 2025 at 18:17
	Leon / ARCADIA 2018 Hanse 588 Sag Harbor, NY

32mike Members Profile Send Private Message Find Members Posts Add to Buddy List Commadore Joined: 26 March 2020 Location: FLorida, US Status: Offline Points: 453	Post Options Post Reply Quote 32mike Report Post Thanks(0) Quote Reply Posted: 04 July 2025 at 18:47
	Marcella, “ This looks like a right setup ( the one with 3 DCDCs and all charges to service), one only has to worry about shutting off the alternator if service Li bank gets overcharged and BMS wants to turn off all charging sources, I think smart alternators are capable doing it.” This is what I understand is the weak spot in this setup. From what I’ve read, if the BMS shuts off charging while the alternator is charging, it could disable the alternator. By connecting the alternator to the AGM and then to the house bank through a DC to DC, the AGM absorbs the shock(?) of the lithiums shutting off the in-current. Questions for you - how is your alternator hooked up now? Have you added the Balmar alternator regulator or just thinking about adding it? Do you still have the combiner?
	Mike S/V Dulces Sueños 458 #087 Tampa, FL

marsella Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 21 June 2022 Location: Antigua Jolly H Status: Offline Points: 592	Post Options Post Reply Quote marsella Report Post Thanks(0) Quote Reply Posted: 04 July 2025 at 19:31
	My current setup is our original alternator but with a replaced regulator from Balmar that is programmed for Li profile. I also have a Victron battery combiner, which replaces the original combiner from Hanse. The only difference is that the victron conbiner can disconnect if BMS tells it to do so. The downside I see that engine battery is charged by Li profile but I think is not a big deal since AGMs can be abused. In the setup which we talk here the alternator and all other charging sources are directly connected to service bank.For alternator one can lower the voltage of the combiner as Arcadia said (not sure if I can reprogram the victron combiner for this) or just remove the combiner. At the same time DCDC charger is inserted to charge engine battery same as DCDC chargers do for thrusters. I think its a nicer setup which alllows proper charging profiles for all components. I have to think more if there is any downside going that way but its easy to hook everything this way, just need to buy another DCDC from Victron.

Pzucchel Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 13 March 2020 Location: floating Status: Offline Points: 659	Post Options Post Reply Quote Pzucchel Report Post Thanks(0) Quote Reply Posted: 06 July 2025 at 09:09
	as usual , Leon is right. I think there is a battery combiner, called in the schematics batterie combiner 8K1, that should disconnect the engine battery from the service bus in certain conditions first trivial question: where is it ? second trivial question: what model is it and how it works? what's the impact of replacing lead batteries with lithium: will it still work? this could change my analysis. let's assume it works correctly: the lithium bank went down in voltage , the starter battery was disconnected from the bus...and my battery is "tired", e.g. subject to sulfation because I don't float it (my settings are for lithium). then it didn't have the crank capacity that it has when the two buses are connected...thanks to the lithium! now I also understand why Leon insists on moving the alternator to the service battery. the battery combiner may separate the alternator from the service battery, making recharging the service battery when the service battery goes down impossible with the engine. still , in my boat solar panels and generator will charge it. in practice, what does it mean to move the alternator onto the service battery: deploy 200A cables from the engine room to the service battery? Edited by Pzucchel - 06 July 2025 at 09:25
	Hanse588#55

marsella Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 21 June 2022 Location: Antigua Jolly H Status: Offline Points: 592	Post Options Post Reply Quote marsella Report Post Thanks(0) Quote Reply Posted: 06 July 2025 at 10:01
	The combiner is very close to positive busbar of the service bank on 458 so I think its similar on all boats. And you dont need to add any cables, the cables from the alternator to the service bank are there already. You either remove the combiner or lower its voltage which Im actually not sure is possible but Leon said so. Would love to hear how exactly it can be modified.



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