Charging lithium with alternator and B2B charger

[CatNewBee]

First you should think about, what is your goal.

Is it to have a vehicle always ready to start and move or is it a full house bank.

I consider the unit of engine, starter, starter battery and alternator as a system necessary to make me move when needed, so my priority is an always properly charged start battery and not a charged house battery.

Therefore it is for me a no-go to put the start battery second and charge the house directly by the alternator.

Regarding BMS over voltage protection, it will usually never happen, that the OVP disconnects the battery from a stock alternator, simply because the internal regulators are set to about 14.2V for flooded lead acid start batteries and the OVP is set to 14.5... 14.6V on self programmed BMS, and on drop in batteries at 15V way above what the generator would deliver.

A B2B charger is another beast, that is meant to push more Amps in the second battery by step up conversion, adding more load on the alternator than a ACR connected second battery (small AGM house bank eg in a RV). This usually adds significant load on a alternator and leads to a delayed charge of the start battery.

There is a misconception, that a B2B charger would protect a alternator if the battery disconnects under load. In fact, the B2B charger may break on a sudden disconnect of the load. It needs to be switched off gracefully.

If you want a Balmer super alternator, fit it as second unit and leave the original for the start battery, if you want the b2b thing, use it only occasionally when really needed and turn it off in regular motoring to allow a propper recharge and maintenance of your start battery.

[Maine Sail]

Originally Posted by CatNewBee

A B2B charger is another beast, that is meant to push more Amps in the second battery by step up conversion, adding more load on the alternator than a ACR connected second battery (small AGM house bank eg in a RV). This usually adds significant load on a alternator and leads to a delayed charge of the start battery.

If programmed and sized correctly it won't delay charging the start battery.

Originally Posted by CatNewBee

There is a misconception, that a B2B charger would protect a alternator if the battery disconnects under load. In fact, the B2B charger may break on a sudden disconnect of the load. It needs to be switched off gracefully.

The Sterling B2B's (green stripe models) have been specifically designed to handle a load dump. We've tested it on our alternator test bench and not been able to damage one when open circuiting it at full output. That said, we typically still advise an alternator protection device as a back up insurance plan. Feeding the alt to the start battery first, then charging the LFP bank with the B2B. is what minimizes the voltage transient as the alt is always seeing the lead acid battery. With a BMS designed for marine type use obviously cutting the regulator B+ is preferred, but drop-in type LFP batteries don't offer this type of BMS...

[roland stockham]

It depends why you want to go to lithium. If you have high electrical demands such as electric cook stove or A/C running from batteries you need to look at high output charging probably at least 1500w and ideally something above C3 for the bank. Doing this with a single 12v alternator is not easy. You may want to look at twin 24v alternates probably large frame ones designed for buses that are designed to give this sort of power continuously without overheating. You would then look at a B2B charger to charge the start batt which would also be your ballast load. Standard 12v marine alternators are derived mostly from car tech and not for this sort of duty.

Alternatively a direct drive DC generator running of the engine auxiliary drive if you have one.

Remember to check the permissible side and power loading on the engine crank shaft pulley, 200a @ 12v requires more than 2.5hp + cooling pump and seawater pump loads. This could be above the recommended speck for a small engine.

If you are looking at lithium to avoid the problems with sulfation due to partial state of charge life is a lot simpler and you could use a conventional L/A wiring setup but with the controllers set for lithium. As others have said though you need to be a lot more conscious of fail safes and protecting the batteries. Going this route looses the fast charge advantages and most single alternators cannot go much above 100a continuously without overheating and you get into all sorts of complications like remote diodes and forced air cooling. Lots of threads here mention people having to shut alternator output down because of overheating.

[Ivanvet]

Originally Posted by CatNewBee

First you should think about, what is your goal.

Is it to have a vehicle always ready to start and move or is it a full house bank.

The goal is to have the vehicle ready to start and move, AND have a full house bank
Kidding aside, in my case, I have a single engine without a generator, and I don't want to add one. So, although having a vehicle ready to start and move is important, it is as important (for me) to charge the batteries as much/fast as I can, in a safely manner.

Originally Posted by roland stockham

It depends why you want to go to lithium. If you have high electrical demands ...

Yes, it all depends on everbody's goals, that's clear, but the post was just to understand how can be done.

[witzgall]

DC-DC charging from the house to start is a well proven plan, you can put his output devices directly to the house. A simple combiner switch can be added for backup if needed. IN your scenario, there is no real benefit to charging the house bank first. Get the Amps where you want them.

Balmar makes the Digital Duo charge for this type of installation. Small and light, simple for your needs. You can make the start batt a different chemistry. Disclaimer - I work for Balmar.

Chris

Originally Posted by Ivanvet

The goal is to have the vehicle ready to start and move, AND have a full house bank
Kidding aside, in my case, I have a single engine without a generator, and I don't want to add one. So, although having a vehicle ready to start and move is important, it is as important (for me) to charge the batteries as much/fast as I can, in a safely manner.



Yes, it all depends on everbody's goals, that's clear, but the post was just to understand how can be done.

[Nightsky]

Originally Posted by Maine Sail

No, but there are better methods to yield better charging performance.




No, but you would be better off to wire a performance alternator and regulator direct to the LFP bank. If the BMS has an HVC charge disconnect you simply use the relay to interrupt the Balmar regulators red power wire.

If the BMS has no way to warn of an impending BMS shut down, such as most "drop-in" LFP batteries, you can add a Sterling Power Alternator Protection Device and also concurrently use a low volt drop FET based isolator to keep a lead acid start battery always connected to the alternator on one side of the isolator.

Rod, could you diagram out how to use the battery isolator in your above example? I have purchased an alternator and sterling APD from you recently and would also strongly consider the FET isolator.
Joe

[eMarineSystems]

An alternative solution would be to change out the alternator on the engine to a large output model, directly charged LiIon house battery bank directly with the appropriate regulator algorithm for the lithium-ion (very important point). Then use a battery to battery charge connecting from the house battery bank to the starter battery(s). Starter battery requires very little energy to recharge where is the house battery bank is very hungry for energy. And yes be sure to add a transient suppressor across the lithium-ion bank should it inadvertently shut down due to a BMS problem. We always recommend the one from Sterling as it is an active device and accurately clamps at 16.5 V.

Keep in mind there is many different ways to solve your problem ours is only one suggestion and you might find an alternative that better fits your situation.


Good luck...happy holidays.

[john61ct]

Originally Posted by witzgall

Digital Duo charge

Quick Q Chris.

I see the current limit is 30A, in my case that's a great feature, double that of an Echo-charger.

First, the scenario: say the output target bank is a very large LFP bank.

Assume the Digital Duo's voltage output is just right, and the BMS takes the bank offline from the Digital Duo at the right end-charge point, so no overcharge worries.

All wiring is heavy gauge, and the LFP bank is at 50% DoD, so it's trying to pull as many amps as possible through the Digital Duo from the input-side charge source(s).

Now, imagine there's a big motor running WOT, powering multiple high-output alternators.

Finally, my question Q1:

Is there a point at which the input circuit has "too high" a current rate available, that might cause the Digital Duo's current-limiting circuitry to get overly stressed / overheated, causing reduced reliability or lifespan?

________
Q2: is it OK to stack two Digital Duo's in parallel to get 60A throughput?

Thanks in advance. . .

[john61ct]

All the above assumes the Digital Duo is indeed current limiting.

If just current **limited**, so that a fuse is required to prevent it getting damaged from overcurrent, then please point that out, and consider my questions moot.

[smac999]

Originally Posted by CatNewBee

There is a misconception, that a B2B charger would protect a alternator if the battery disconnects under load. In fact, the B2B charger may break on a sudden disconnect of the load. It needs to be switched off gracefully.

It will. Because the alternator will never disconnect from the start battery. Which it is connected too.

The b2b could have issues I supposed if it’s load was shut off. But the b2b failing is not the same as the alt failing.

[smac999]

Originally Posted by john61ct

Quick Q Chris.

I see the current limit is 30A, in my case that's a great feature, double that of an Echo-charger.

First, the scenario: say the output target bank is a very large LFP bank.

Assume the Digital Duo's voltage output is just right, and the BMS takes the bank offline from the Digital Duo at the right end-charge point, so no overcharge worries.

All wiring is heavy gauge, and the LFP bank is at 50% DoD, so it's trying to pull as many amps as possible through the Digital Duo from the input-side charge source(s).

Now, imagine there's a big motor running WOT, powering multiple high-output alternators.

Finally, my question Q1:

Is there a point at which the input circuit has "too high" a current rate available, that might cause the Digital Duo's current-limiting circuitry to get overly stressed / overheated, causing reduced reliability or lifespan?

________
Q2: is it OK to stack two Digital Duo's in parallel to get 60A throughput?

Thanks in advance. . .

The duo shuts itself off if the load is over 30a. And will check back later. Ie ie you run a windlass off the engine bank. the duo will shut off charge from house bank. . And then hopefully start charging again once the windlass is not draining. So it’s can’t actully self regulate itself at 30a

Where as the echo charger will just chug along at 15a.

Victron has a new 30a b2b out this month. Bluetooth programable. Curious to try it.

[john61ct]

Originally Posted by smac999

The duo shuts itself off if the load is over 30a. And will check back later. Ie ie you run a windlass off the engine bank. the duo will shut off charge from house bank. . And then hopefully start charging again once the windlass is not draining.

Aha, yes current protection, not limiting.

Hiccup type, as opposed to latching.

Thanks much.


> Victron has a new 30a b2b out this month. Bluetooth programable

Yes, a proper DCDC **charger** should always be capable of true continuous current limiting.

And user-custom voltage adjustment is always a Good Thing.

[tanglewood]

Originally Posted by smac999

The duo shuts itself off if the load is over 30a. And will check back later. Ie ie you run a windlass off the engine bank. the duo will shut off charge from house bank. . And then hopefully start charging again once the windlass is not draining. So it’s can’t actully self regulate itself at 30a

Where as the echo charger will just chug along at 15a.

To me this is a fatal flaw in the duo's design, and especially problematic if charging an LFP system.


As SMAC999 says, it shuts down when overloaded, then tries again later. The problem is that if the battery being charged by the Duo has no other charge source, it will never become charged. The duo will keep trying, but the battery is low enough to accept more than 30A, so the duo kicks off, and the cycle repeats. I know a number of people who have been screwed by this when a battery had been drawn down below a certain level, and the duo can never get it recharged.


Throw in an LFP bank that will always accept more than 30A, and you are totally forked.