Charging lithium with alternator and B2B charger

[Ivanvet]

Hi all,
In my path to learning about lithium systems I’ve been reading the issues involved with charging with the engine alternator, and I have a question about it. One of the options I found in the marinehowto website, is connecting the alternator to the start battery (likely not lithium), and then using a DC battery to battery (B2B) charger to charge the house bank (lithium).



If I understood this correctly, the reason for this option is to protect the alternator when the BMS shuts charging once the batteries reach their voltage (very nicely explained int the article).https://marinehowto.com/understandin...ttery-charger/

Since the biggest B2B (from sterling) allows only 60 Amps, you can connect more than one of these chargers in parallel to increase the current to the house battery bank.

My question is regarding how to choose the ideal/max alternator size in a hypothetical system wired in this fashion:
- Let’s say that you have a 12V 600 Ah lithium battery bank (2x300Ah Victron in parallel) with a continuous charging rate of <300Ah (<150Ah per battery, from their website).
-Ideally you could wire as many chargers, in parallel as you need to allow for 300Ah. That would require 5 chargers, which is crazy, but let’s go with it because that’s not the point of the question.

Would the start battery size limit the alternator that you can add to this system? If you can put the biggest alternator that you can fit based on space and engine HP, let’s say one of the Balmar large case alternators that can output 200-300Ah, and you have a starter battery that is only 100Ah, would that be a problem?

Thanks!

[john61ct]

No.

The alternator VR will only put current out to match the demand "pulled".

Say your Starters were out of the loop completely, charged off the House circuit otherwise.

Even a cheap little 20Ah lead battery could function as the buffer for alt output against spikes / surges / load dump issues, and as the attachment point for the Sterling array's input.

[john61ct]

However, rather than using the B2B's, it would make more sense to convert the alternator(s) to external VRs that allow for user-custom setpoint adjustment and can limit the current as needed instead.

Check out

Wakespeed WS500 and APS AP500, very similar progeny from Al Thomason's FOSS project "Smart Alternator Regulator" SAR / Very Smart Regulator VSR project.

Balmar MC-614

MGDC Mark Grasser DC Solutions

Ample Power?

[Ivanvet]

Great. Really appreciated!

[Ivanvet]

Originally Posted by john61ct

However, rather than using the B2B's, it would make more sense to convert the alternator(s) to external VRs that allow for user-custom setpoint adjustment and can limit the current as needed instead.

Check out

Wakespeed WS500 and APS AP500, very similar progeny from Al Thomason's FOSS project "Smart Alternator Regulator" SAR / Very Smart Regulator VSR project.

Balmar MC-614

MGDC Mark Grasser DC Solutions

Ample Power?

In this case, do you mean connecting the alternator to the house battery (lithium) and using the VR (i.e., Balmar MC-614) to limit current? Wouldn't the alternator be still 'exposed' to spikes if the battery BMS shuts off?

[john61ct]

Personally I advise caution about allowing the BMS charge control.

Make sure the implementation is failsafe, so there are multiple OVP and OCP in place, and ideally each component's failure mode is safe, resulting in charge termination.

That usually means buying quality user-adjustable charge sources appropriate for your desired charge profiles

and letting the BMS just act as a final-layer protective backup, for when the normal charge regulation fails.

[john61ct]

Originally Posted by Ivanvet

In this case, do you mean connecting the alternator to the house battery (lithium) and using the VR (i.e., Balmar MC-614) to limit current? Wouldn't the alternator be still 'exposed' to spikes if the battery BMS shuts off?

All significant charge sources should ideally be routed directly to House, as a default design principle.

The paralleled lead battery "upstream" of the charge buss contactors isolating the House bank, remains on the alt-side circuit to buffer its output after they open.

This could be the Starter batt(s)0, but not necessarily, as I said a cheap sacrificial batt can be dedicated for this, just replace it routinely every few years.

There are also fancy "alternator protection" gadgets including from Sterling, but I think a solution in search of a problem.

[Ivanvet]

Yes, that makes sense. Not that I'm putting things together yet, just understanding the concept, but based on the mentioned above, I was hoping to connect the alternator to the start battery and using the B2B to charge the house bank (this would protect the alternator from spikes), and in addition, use the external regulator to protect the alternator with temperature regulation AND to limit current to the batteries. Then, wiring the positive from te B2B to the HVC relay to so charging shuts off once the batteries reach the SOC stablished.

[Ivanvet]

Originally Posted by john61ct

There are also fancy "alternator protection" gadgets including from Sterling, but I think a solution in search of a problem.

I imagine you are talking about the linearisation device https://sterling-power.com/products/...-70f-ald-17500

I saw it but I need to read about it a little bit more.

[john61ct]

If you are going for a high-end installed system like Victron, get solid reco's for a good dealer that's had extensive experience with all the systems discussed here.

The Wakespeed / APS lines are very recent so support is thinner.

Bruce @ OceanPlanet is a good starting point stateside, and can likely refer you to someone more local to you if needed.

I'm sure others can chime in with their own suggestions too.

[Ivanvet]

Originally Posted by john61ct

If you are going for a high-end installed system like Victron, get solid reco's for a good dealer that's had extensive experience with all the systems discussed here.

The Wakespeed / APS lines are very recent so support is thinner.

Bruce @ OceanPlanet is a good starting point stateside, and can likely refer you to someone more local to you if needed.

I'm sure others can chime in with their own suggestions too.

Absolutely. There is no way I'll design/install a system like this on my own. I just want to understand how things are wired, specially with new technologies. Thanks for your contribution!

[john61ct]

Originally Posted by Ivanvet

Yes, that makes sense. Not that I'm putting things together yet, just understanding the concept, but based on the mentioned above, I was hoping to connect the alternator to the start battery and using the B2B to charge the house bank (this would protect the alternator from spikes), and in addition, use the external regulator to protect the alternator with temperature regulation AND to limit current to the batteries. Then, wiring the positive from te B2B to the HVC relay to so charging shuts off once the batteries reach the SOC stablished.

The B2B is an expensive redundancy if you already regulate the alt output properly.

No alt spike issues long as the lead buffer remains connected.

As stated the BMS/HVC can just be standby protection, only used if the charge source fails.

You will likely have multiple other charge sources, select good ones and let them handle the primary. charging regulation

[john61ct]

You could use the B2Bs instead of fancy VR, in which case can use to filter inputs from any old chargers, solar etc.

But the VR approach gives finer granularity of current limit control.

The Sterling BBW series goes higher amps 120A?

and with the added remote offers the same user-custom setpoint adjustability as the BB series. Noisier fan though, designed for outside use.

But going for 5x 60A would give 10 steps in your current levels in 30A increments, more than enough.

PS the B2Bs are optimistically rated just like alts, do not actually output 60A. Will also derate themselves in overtemp conditions.

[Maine Sail]

Originally Posted by Ivanvet

Would the start battery size limit the alternator that you can add to this system?

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

Originally Posted by Ivanvet

If you can put the biggest alternator that you can fit based on space and engine HP, let’s say one of the Balmar large case alternators that can output 200-300Ah, and you have a starter battery that is only 100Ah, would that be a problem?

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.

A B2B is best used when someone does not want to upgrade the alternator, and to charge drop-in LFP batteries. In this case the alternator should be at least 40% larger, in output rating, than the B2B charger.

[Ivanvet]

Originally Posted by Maine Sail

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.

A B2B is best used when someone does not want to upgrade the alternator, and to charge drop-in LFP batteries. In this case the alternator should be at least 40% larger, in output rating, than the B2B charger.

That makes sense. I was just reading about the APD. In the future, since I will redesign the system from scratch I will most likely upgrade the alternator and connect it directly to the house bank with the appropriate regulator and the APD.

Thanks for your input.

I.