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Old 14-01-2022, 00:09   #16
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

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Thanks all - the dilemma of which way to pass alternator charging in a split lithium / AGM setup has haunted my drop-in Lithium upgrade plans for a long time, and from web searching it's pretty clear there is no 'right' way, and no industry standard or consensus.

Option 1 (alternator to Lithium, and then DCDC to start battery) gets complicated with regulator upgrades/alternator diode concerns/questionable protection modules/no BMS access/coordination (dropins)/etc. In this setup, DCDC would keep AGM start batteries topped up all the time. Lithiums are charged by all 'primary' charging methods (solar, shore power, alternator).

Option 2 (alternator to AGM start battery, and then DCDC to Lithium bank) seems like inefficient pass through of alternator to charge lithiums, with question of how to keep AGMs 'topped up' when engine not running. Complications of having competing DCDC chargers in opposite directions (if I try to top up AGMS back from Lithiums)/heat from DCDC charger running full blast when engine on/etc.

My setup goal is to make it as 'hands off' as possible, and so far Option 2 seems like right direction, possibly with a supplemental small amp shore power charger to keep my AGM start batteries topped up if needed.

Maybe two DCDC chargers (from AGM start battery to Lithiums) in parallel to get as much current over to the LFP bank if I needed it in a pinch.
I am going the DCDC route but am also splitting my solar power so a lesser amount feeds the AGM's and the rest goes to the Lithium (part via MPPT and part via solar input on DCDC charger). Since I seldom use shore power and therefore currently my AGM's seldom get an extended float charge am thinking of adding in a small charger to allow for periodic manually switched float charging from the Lithium.

The DCDC chargers I have bought (Renogy) require a 12v trigger feed to start charging so am adding in VSR's so that they will feed the Lithium bank regardless of where the charge is coming from (solar, wind gen or alternators).

Also looked at Nordkyn VRC-200 as an alternative to DCDC but that only solved part of the equation for me.

TwT
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Old 14-01-2022, 01:12   #17
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

Connecting your charge sources to the loads that need it most is the most electrically efficient. However the big proviso is what is the bms disconnect strategy and can your alternator survive.

If you donít or canít upgrade your alternator then you only have option 2.
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Old 14-01-2022, 02:02   #18
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

Direct alternator charging used in a traditional split charge system with a VSR will only achieve around an 80-90% charge state. VSR,diode,fet separator simply allow charge to pass directly from the alternator to the auxiliary battery whereas Battery-To-Battery chargers take the alternator output and boost or reduce it to provide a stable voltage output according to a multi-stage charging profile. This provides a 100% re-charge for your leisure battery in a controlled way and typically achieves it faster than with direct alternator charging.

Tomorrow i buy any BMS,DC-DC charger who limit charging lifepo4 exact to 80% SOC and buy additional 20% bigger lifepo4 battery(if need)

why.
ANY Simple lifepo4,lipoly, lithium battery who charged to 80% and no discharged under 20% you extended life minimum 100%
In Rimac battery lab have proof. also for some reason all lifepo4 battery after 3000-4000 cycle must cell exchange polarity. cell before be - must exchange position to +.

Idealy for lifepo4 on boat id diode battery seperator vith 0,5V drop

Idealy for winter lifepo4 discharge battery to 50-70% and disconnect from charging and discharging
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Old 14-01-2022, 02:10   #19
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

Using a DC-to-DC charger is the only reliable solution if you intend to re-charge a second battery in a modern engine that has an ECU-controlled 'smart' alternator (generally Euro 5/6 compliant car engines and some big engine in motor yacht,and soon all new engine in marine in EU). These have a highly variable voltage output that is often too low to provide a charge or (in the case of regenerative braking systems in mobile home van) so high that it can damage some battery types. Due to this highly variable voltage VSRs are not suitable for use with 'smart' alternators.
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Old 14-01-2022, 02:29   #20
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

usually, i don't touch inside the alternator, starter (only make/build holder with sometime with lathe guy) Because we have a pro specialist for this,and time is money. I simple call phone. Alternator engine xx don't work,battery lifepo4 .he send me new alternator i remove and resend him broken. for a couple days i have repaired alternator with sticker lead battery only or lifepo4 engine xx. and return in magazine next time only take this alternator and exschange
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Old 14-01-2022, 04:44   #21
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

I have a 170a alternator connected to a 1200AH Lithium Bank as I want as much charging capacity as possible. I have a Dc-DC charger going to a starter battery, but at 30a. If I had the alternator connected to that, the house bank would never charge.
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Old 14-01-2022, 06:28   #22
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

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If both of your banks are 12V and the starter battery is only used for startingÖ and the starting battery is AGM, then I donít think you need a DC-DC converter for charging it. I believe the self discharge rate for AGM is 3% per month so even when you donít run the engine for a year, it will still start. You probably also have an emergency switch to start from your house bank.

I have that Orion because my house bank is 24V and I still have large 12V loads during sailing (electric winches).

My Victron SmartSolar controllers have an output relay that can be programmed to switch on when solar power is detected. The Orion DC-DC converters have an input that you can connect to that to enable/disable them based on solar production.

For the alternator you donít need this as the Orions have a very good alternator detection algorithm. I also think the voltage level detection works pretty good and that is how I currently trigger.

Just make sure you get the smart versions of this gear.

I attached a diagram of our DC.
I have been hoping for a thread like this. We have a comparably small system that is currently all AGM. 1 start and 2 house. I would like to convert the house to LiFePO4 but keep the AGM start. We have an external regulated 140 amp alternator and 350 Watts of solar coming through a single MPPT controller. I don't think DC to DC from the start to the house is best. Didn't know that you could go the other way. That is quite the schematic you have. How did you produce it?
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Old 14-01-2022, 06:30   #23
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

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Old 14-01-2022, 09:35   #24
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

You normally want your start batteries to be charged up first so that you can always start your engine. If you use a smart charge system (Merlin, Victron, Sterling etc), as soon as the start battery is full, usually within 5~10 minutes of starting the engine, a relay is closed and the charge is shared with the house batteries. Certainly Merli's Smartbank system is designed to work withe LFP batteries and I'm pretty sure the others do also. As someone else said, your start battery will be the least expensive to replace by several magnitudes, so if the system is set for LFP batteries, and you accept the reduced lifespan on the start battery, you should be fine.
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Old 24-01-2022, 08:09   #25
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

Hi,

I would never use option 1 as it could end up killing your alternator when the BMS disconnects the battery during charging unless you have an alternator protector.


Option 2 is the typical standard approach. Also have the alternator connected directly to a FLA battery for protection unless you have an alternator protector.


Option 3: If you previously installed an ARC for combining battery banks then use it in place of the DC-DC charger but use a switch to control the ACR ground. This allows for full alternator charging where as DC-DC chargers are greatly limited (i.e. 30A for Victron). See my blog describing how to use a simple push-pull switch and a smart (arduino) switch for controlling the ACR. https://svjohannarose.blogspot.com/2...m-w-solar.html




Quote:
Originally Posted by jc1409 View Post
Two scenarios:


1. Alternator connected to Lithium house bank, with DC-DC charger used to charge the start batteries


2. Alternator connected to start batteries, with DC-DC charger used to charge Lithium house bank


Assuming proper setups, charge configurations, sufficient wiring, and all other things being 'equal', which is better?
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Old 24-01-2022, 08:15   #26
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

Quote:
Originally Posted by jc1409 View Post
Two scenarios:


1. Alternator connected to Lithium house bank, with DC-DC charger used to charge the start batteries


2. Alternator connected to start batteries, with DC-DC charger used to charge Lithium house bank


Assuming proper setups, charge configurations, sufficient wiring, and all other things being 'equal', which is better?
The question depends on your systems competency and your desire to " get things right "

From a systems design point of view, The devices requiring the greatest recharge ability should be directly connected to the devices producing such a charge . This is electrically the most efficient and reliable .

However because many Lithiums systems have integrated BMS system that do emergency HVC cutoffs , you have a alternator under load disconnect issue , so from a system perspective you need to build in alternator protection or remote alternator shutdown. ( you may also need a regulating device to step down your alternator output to prevent overloading the alternator )

But, for some reason people , while spending thousands on Litiums and support systems , shy away from replacing the alternator controller/regulator or installing and alternator protection device

Hence the " workaround " and that's it is to leave a FLA in the circuit and even worse then charge the Litiums via DC DC convertors , a solution that's arguably more expensive then fitting an alternator protector , more unreliable and less efficient

My advice, invest in fixing the problem , the crappy car regulator on your alternator

Note as I said before there's no evidence that an attached FLA will protect an alternator or connected electronics if a full load disconnect occurs anyway
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Old 24-01-2022, 08:21   #27
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

I have a catamaran and opted for option 1. The starboard engine starts off the house battery and the port engine has a separate FLA battery for start. The idea is if house is dead, I can still start the port engine and then starboard engine. The alternators were converted to external regulation and are limited to 100A charging each to preserve belts and alternators. The port start battery is charged with a 30A victron DC-DC charger. It all works well but option 2 would have less invasive work (original alternators, no new regulators) but would have less charging capacity from the alternators to the house (at least for what I looked at). I also was concerned about high amp DC-DC charging with low RPMs loading up the alternators, I didn't see enough control on the DC-DC chargers that I looked at to make me happy.
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Old 24-01-2022, 08:36   #28
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

I think this will help protect the alternator from an abrupt cut off from the BMS.

https://www.sterling-power-usa.com/a...iondevice.aspx
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Old 24-01-2022, 08:45   #29
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

It should be also pointed out that, as has been mentioned, a system properly setup should never trigger an HVC event in normal operation , hence one could simply make a call that the chance of alternator damage might be a tradeoff worth taking . Personally I would just upgrade the alternator regulator as car engine regulators are NOT designed to charge batteries as their primary objective whereas a boat ones have that objective
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Old 24-01-2022, 08:51   #30
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Re: Two scenarios: Alternator to LFP House Bank or Alternator to Starter battery?

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Originally Posted by jc1409 View Post
Thanks all - the dilemma of which way to pass alternator charging in a split lithium / AGM setup has haunted my drop-in Lithium upgrade plans for a long time, and from web searching it's pretty clear there is no 'right' way, and no industry standard or consensus.



Option 1 (alternator to Lithium, and then DCDC to start battery) gets complicated with regulator upgrades/alternator diode concerns/questionable protection modules/no BMS access/coordination (dropins)/etc. In this setup, DCDC would keep AGM start batteries topped up all the time. Lithiums are charged by all 'primary' charging methods (solar, shore power, alternator).



Option 2 (alternator to AGM start battery, and then DCDC to Lithium bank) seems like inefficient pass through of alternator to charge lithiums, with question of how to keep AGMs 'topped up' when engine not running. Complications of having competing DCDC chargers in opposite directions (if I try to top up AGMS back from Lithiums)/heat from DCDC charger running full blast when engine on/etc.





My setup goal is to make it as 'hands off' as possible, and so far Option 2 seems like right direction, possibly with a supplemental small amp shore power charger to keep my AGM start batteries topped up if needed.



Maybe two DCDC chargers (from AGM start battery to Lithiums) in parallel to get as much current over to the LFP bank if I needed it in a pinch.
Just add a MPPT to just the start batteries theyíre rarely depleted to a point that a small array wouldnít restore and maintain them. So DC to DC charger with your current alternator terminated to the start battery and an MPPT takes over maintenance duty when anchored for extended periods. Regardless If you have the room solar is going to be your primary power source anyway and compared to the alternator far more efficient at restoring the house bank/Maintaining the start battery.

Iíll also add a real world observation that your concern regarding efficiency isnít founded unless youíre going to use your alternator as a primary charging source and or your motoring very short distances. On a typical passage that would utilize the engine your run time is dictated by the weather and the distance and would likely exceed the time required to restore the houseBank with a small 30amp DC/DC charger.

Plus this eliminates the possibility of a BMS disconnect taking out your alternator. Also eliminates the possibility of overheating your alternator along with any need for external regulation or reprogramming.
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