DC-DC charger - which direction for Lithium batteries?

[SOLAR SUPPORT]

Using an advanced regulator that controls the charge load from outside by canceling the regulator inside the alternator is offered as the simplest and most economical solution. However, I would like to remind you that the average temperature in the engine chamber is 60 °C. Even when the alternator is operating at half capacity, it tries to get rid of the higher heat generated within itself. Add to this the vibration caused by the engine, the oxidation caused by the high humidity of the marine environment. Your precision regulator will surely be a key one day.

The only reason for connecting the LA engine battery between the dc-dc charger and the alternator is to prevent excessive high voltage accidents caused by the alternator, which occurs as a result of the HVCutoff trigger of the LFP battery. However, the drawbacks of connecting batteries of different chemistry are known.

It is possible to use the factory alternator with a dc-dc charger or to use a modified alternator for Li-LFP charging with an external regulating regulator. It's up to you to decide how to use it. My suggestion is that if there is sufficient solar energy, which is safe to charge your LFP bank then this source should be used before commissioning the alternator when you start the engine. The alternator should not be used as a primary charging source for LFP bank unless it is necessary.

[SV Confianza]

Originally Posted by Pete7

My LFP battery manufacturer won't offer a warranty for batteries directly connected to an alternator.
Pete

What LFP manufacturer is that? I've not heard of such a thing. All the setups that I've seen so far in the wild have the alternators charging the LFP bank.

[Ballsnall]

Originally Posted by mait

So quick and efficient charge from alternator is pretty important.

If that is your goal then the stock alt just won't cut it, probably good for 30A continuous.
You will need to invest in a high output alt & external regulator with temp control. To drive this add a serpentine belt system to cope with high output alt, possibly additional cooling as well. Given this significant investment you would do well to incorporate battery disconnect protection or a high end system where the BMS control's the alt.

Now this high output alternator will put substantially more drain on your 29hp engine so you might like to add alternator control at the helm if you want full power for maneuvering.

If you want to go the full Monty, there is a lot to consider to do it right.

[mait]

Originally Posted by Ballsnall

If that is your goal then the stock alt just won't cut it, probably good for 30A continuous.

That's somewhat less than I was hoping for from a 75A alternator.

Let's say I want to keep the stock alternator (75A). And we assume it is not capable to put out more that 30A continuos.
Then it makes no sense to modify the stock alternator for external Balmar regulator and connect it to LifePo.

The same result (30A to LifePo4 bank) can be achieved without modifying the alternator. Just connect it to charge the LA start battery and via Orion DC-DC to LifePo4 house bank.

Now if the stock 75A alternator could supply more than 40A continuos that would be a game changer.

Sorry to hijack the thread...

[goboatingnow]

Originally Posted by Ballsnall

If that is your goal then the stock alt just won't cut it, probably good for 30A continuous.
You will need to invest in a high output alt & external regulator with temp control. To drive this add a serpentine belt system to cope with high output alt, possibly additional cooling as well. Given this significant investment you would do well to incorporate battery disconnect protection or a high end system where the BMS control's the alt.

Now this high output alternator will put substantially more drain on your 29hp engine so you might like to add alternator control at the helm if you want full power for maneuvering.

If you want to go the full Monty, there is a lot to consider to do it right.

I have a 70A stock alternator charging my 240 AH VRSLA bank, it’s a very useful source of recharging. So with a comparable Li bank, I see no reason to not use the same alternator to do the job with the Li

A balmar MC618 runs at around $340 , a victron 30A dc dc runs at $250. , ( the Renology 40A is a bit cheaper ) the alternator can do about 35-40A without new belts or any additional cooling.

So the net difference is quite small and there are other gains including better charging profiles in the alternator and better protection for the alternator. Even if you have SLA a good upgrade to the alternator regulator is a good idea anyway

Then I can use a cheap small 10A dc dc to charge from lithium to SLA.

To me this is the better engineering solution , has little additional cost and delivers quantifiable gains.

I certainly don’t need a 40 A capable system charging a small SLA battery. That’s nonsensical in my opinion

The other thing is your alternator puts out what it can ( controlled via a suitable regulator ) consistent with heat buildup. This is identical whether SLA or Li is connected. The dc dc system doesn’t get an ounce more power from the alternator.

[Ballsnall]

Originally Posted by goboatingnow

I have a 70A stock alternator charging my 240 AH VRSLA bank, it’s a very useful source of recharging.

All well and good for your situation but mait's goal was
quick and efficient charge from alternator which can not be achieved with the stock alternator.

[goboatingnow]

Originally Posted by mait

That's somewhat less than I was hoping for from a 75A alternator.

Let's say I want to keep the stock alternator (75A). And we assume it is not capable to put out more that 30A continuos.
Then it makes no sense to modify the stock alternator for external Balmar regulator and connect it to LifePo.

The same result (30A to LifePo4 bank) can be achieved without modifying the alternator. Just connect it to charge the LA start battery and via Orion DC-DC to LifePo4 house bank.

Now if the stock 75A alternator could supply more than 40A continuos that would be a game changer.

Sorry to hijack the thread...

Extracting more then about 60% from a alternator isn’t easy. Cooling is a huge issue. This has nothing to do with Li or lead acid

[goboatingnow]

Originally Posted by Ballsnall

All well and good for your situation but mait's goal was
quick and efficient charge from alternator which can not be achieved with the stock alternator.

But it’s no different irrespective of battery connected. You cant extract 100% plated power from a typical small case alternator. The best is 50-60 % and that needs a good external alternator regulator anyway.

[Ballsnall]

Originally Posted by mait

Now if the stock 75A alternator could supply more than 40A continuos that would be a game changer.

You may be able to get close to 40A continuous at high revs but I think you will need add significant cooling to achieve that.

[mait]

Originally Posted by Ballsnall

All well and good for your situation but mait's goal was
quick and efficient charge from alternator which can not be achieved with the stock alternator.

Well, I should have worded it better

Like - "as quick and efficient as possible without changing the stock alternator."

[Ballsnall]

Originally Posted by goboatingnow

But it’s no different irrespective of battery connected. You cant extract 100% plated power from a typical small case alternator. The best is 50-60 % and that needs a good external alternator regulator anyway.

I absolutely agree. But if in someone's situation they don't need additional alternator charging over a stock alternator/regulator then the additional costs are hard to justify.

[Ballsnall]

Originally Posted by mait

Well, I should have worded it better

Like - "as quick and efficient as possible without changing the stock alternator."

Your correct, if you want to get the max out of your stock alt for lfp charging then your advice it spot on

[mait]

I think for me the way to go is (simplified):
1. modify the stock alternator to use Balmar MC618
2. charge from stock 75A alternator via BalmarMC618 directly to house LifePo4 bank
3. use Sterling Alternator protecting device just in case
4. charge lead acid start battery via DC-DC charger from LiFePo4 house bank

5. If output from 75A stock alternator does not meet the needs, it is easy to replace it with Balmar higher output alternator (and pulleys / belts) because the system is already designed and wired to accept it.

[goboatingnow]

Originally Posted by mait

I think for me the way to go is (simplified):
1. modify the stock alternator to use Balmar MC618
2. charge from stock 75A alternator via BalmarMC618 directly to house LifePo4 bank
3. use Sterling Alternator protecting device just in case
4. charge lead acid start battery via DC-DC charger from LiFePo4 house bank

5. If output from 75A stock alternator does not meet the needs, it is easy to replace it with Balmar higher output alternator (and pulleys / belts) because the system is already designed and wired to accept it.

Yes this in my view is the best compromise. It maximises your potential charge sources and directs them all at the Li bank.

You shouldn’t need the APD as you have control via the Balmar. But sure it’s cheap bit of insurance

[CaptainRivet]

Originally Posted by goboatingnow

There is much debate about this and the jury is out . ISO new lithium spec for boats specifically forbids paralleling different chemistries and many Li suppliers do not reccomend it . ABYC are more circumspect about paralleling

There are issues where the SLA is highly discharged and can be subject the li to large currents or vice versa.

Secondly the charge source profiles optimised for lithium are not great choices for SLA.

So the answers is if they are the same voltage it’s possible and safe and in fact one boat tech website actually designed a “combiner controller “ that uses voltage

My view is it’s unwise to do so. It’s not “ safety first “

My second view is that charge sources should be optimised for the bank that’s needs then the most. Inevitably that means the Li domestic bank in most cases.

However this means dedicated alternator controllers and people spending $$$$$ on Li seem to have mental block about the alternator and won’t upgrade its regulator to suit lithium.

Hence we get the “ tail wagging the dog “ with DC DC from starter to lithium battery purely because the alternator remains “ stock” and can’t be controlled by the BMS.

To me this is a silly approach as it’s optimising a system based on a failure to act ( the alt controller) rather then a good design decision

Given the very mediocre changing a starter battery needs the obvious and proper method is a DC Dc from the lithium to the starter. All charge sources optimised for lithium charging . The DCDC is then set up optimised to charge the SLA. The two banks never get connected.

if your alternator is setup for lithium, there is no need for another chemistry...just get an Li starter bat or even make the house big enough and let the BMS based on SOC switch of the other loads and have one big Li Bank for all or make 2 separate banks LI.

2nd why you don't want to upgrade your alternator is simple.
complexity and costs, if you look at all the cases upgrading one alternator on a Volvo D1 or D2 installed and trouble free runing is 2000-3000 Euro total and nearly all have a lot of troubles till that runs. means 4-6k for two...only the mounting kit for a 2nd alternator is 2k....
the standard one on your engine, in my case 2 are like new and can deliver each 60A of their 115A rating. Motorsailing with 1 engine so 60A longthermed works fine=2 Victron 30A DC DC charger and I keep my 300AH hybrid starter/deep as starter and backup in case of Li shutdown. mounted in 3h working and total costs are 500Euro.

and eg 2 wakespeed to control both stock alternators are 1600 but not worth it as mostly 1 engine runs and the short time 2 are running its not worth the money.

the whole alternator stuff is actually over the top and no sufficient solution for the 80-120 Stock alternators.
And the big case alternators are totally overpriced, there are cheap out there (eg schoolbus ones) but there there are no mounting brackets available.
Why no one till now copied the volvo bracket for the D1 and D2 for a 2nd alternator that's about 2k, copy it with a CNC Maschine and sell for 300 (and have 250Euro profit). As sailors we don't have a Maschine shop and the resources to copy that and you need to buy one to do so.