LA-Lithium Battery Transition - An Alternative Solution

[PaulCrawhorn]

Originally Posted by s/v Jedi

I agree with all you write except this part. You don’t explain how the FLA start battery is harmed by a DC-DC converter at a rating at half the alternator rating. The context here is that the alternator has a FLA charge profile, matching the battery chemistry and I read your comment that adding the DC-DC converter harms the FLA battery, which I dispute.

Yes, it does not. The lead starter is really not even "in the path", only relevant for its protection buffer dump load effect if/when the DCDC draw is turned off

[PaulCrawhorn]

CC is a misnomer.

Just means the earlier stages before the CV setpoint is reached.

Yes voltage is varying - climbing - as SoC% is climbing

but current is not at all necessarily "constant".

Obviously the whole point of the current limiting circuitry, is to prevent that amps level from rising above the point where destructively high temperatures are reached.

Ideally you can fine-tune the current setpoint for varying conditions and also have temperature based over-rides for when you get it wrong.

[PaulCrawhorn]

Originally Posted by sailingharry

On the first boat, acceptance took at least 15 minutes to reach and sometimes as much as half an hour. On this boat, it can take over an hour to reach acceptance.

I do not know what you think "reaching acceptance" might mean.

Usually the CAR rating is the maximum C-rate a chemistry draws at low SoC%, Bulk / CC stage.

So FLA is rarely going over say 0.17C at least not for long. AGM might briefly pull 0.7C but usually safe to use 0.5C.

LFP may be at least ten times that, and maintains that as a continuous rate for much longer higher up the SoC% curve, and thus even a small battery need the current limiter device in the circuit, to protect both the alternator circuitry and the LFP cells, since it is not conducive to longevity to charge much faster than 0.4C

The transition from Bulk to Absorption (CC to CV) is that what you meant by "reaching acceptance"?

At a low enough rate with lead, may happen at 95% SoC, at a high rate maybe 70%

With LFP it always happens late enough that for normal cycling, no CV stage is required at all, easier and healthier to minimise it, even "just charge to your V setpoint and Stop"


> initially the alternators are the limiting factor. If I put in 10 times more AGM, or shifted to an even larger lithium, the load on the alternator for the first half hour to hour would be unchanged

This maximum amps limiting is not what alternators do, the DC-DC or external regulator must be there to limit current.


> My disagreement with conventional wisdom is that alternators work very hard in the early stages even with lead. Lithium doesn't suddenly change the alternator from barely doing anything to finally being overloaded.

Again, using C-rate rather than amps helps make this more clear. A 200+A alternator with a 200Ah bank, compared to an 80A alt charging an 800Ah bank will starkly highlight the difference.

[CaptainRivet]

before all this discussions I highly suggest to make a charge calculation (means how many amps do you need that your bank is completely recharged in a day). And as 2nd then define your main charge source (cheapest and easiest is solar If you can fit it.
The rest needs to be just as cheaply adapted as possible to work with your system.

[sailingharry]

Originally Posted by PaulCrawhorn

I do not know what you think "reaching acceptance" might mean.

Usually the CAR rating is the maximum C-rate a chemistry draws at low SoC%, Bulk / CC stage.

So FLA is rarely going over say 0.17C at least not for long. AGM might briefly pull 0.7C but usually safe to use 0.5C.

LFP may be at least ten times that, and maintains that as a continuous rate for much longer higher up the SoC% curve, and thus even a small battery need the current limiter device in the circuit, to protect both the alternator circuitry and the LFP cells, since it is not conducive to longevity to charge much faster than 0.4C

The transition from Bulk to Absorption (CC to CV) is that what you meant by "reaching acceptance"?

At a low enough rate with lead, may happen at 95% SoC, at a high rate maybe 70%

With LFP it always happens late enough that for normal cycling, no CV stage is required at all, easier and healthier to minimise it, even "just charge to your V setpoint and Stop"


> initially the alternators are the limiting factor. If I put in 10 times more AGM, or shifted to an even larger lithium, the load on the alternator for the first half hour to hour would be unchanged

This maximum amps limiting is not what alternators do, the DC-DC or external regulator must be there to limit current.


> My disagreement with conventional wisdom is that alternators work very hard in the early stages even with lead. Lithium doesn't suddenly change the alternator from barely doing anything to finally being overloaded.

Again, using C-rate rather than amps helps make this more clear. A 200+A alternator with a 200Ah bank, compared to an 80A alt charging an 800Ah bank will starkly highlight the difference.

I believe I have mixed acceptance and absorption. Although I will admit I do not know what acceptance is then.

My current AGM bank is 800 Ah. I have two alternators rated for a total of 270A, but at normal cruising RPM rarely see more than 200. Absorption voltage is about 14.7. if I am down 30%, or 250 to 300Ah it will take over an hour to reach 14.7 volts (I usually hit absorption voltage someplace around 85-90% SoC). While the output drops because the regulators throttle back as the alternator temperature increases, the alternators are producing the maximum current for the conditions. In that first hour, the output would not change with an LFP bank.

To put this in C-rates, I start off with about .25, and as the alternators warm up reach something more around 0.12, which then drops more once absorption voltage is reached.

[PaulCrawhorn]

Originally Posted by sailingharry

I believe I have mixed acceptance and absorption. Although I will admit I do not know what acceptance is then.

As I stated, the CAR charge acceptance rate, is the maximum C-rate a given battery/chemistry draws, usually for at least say 10-15 minutes.

> My current AGM bank is 800 Ah.

So likely it can draw 500-600A at low SoC, but maybe only for say 5min, at a half hour might only be 300-400A

Whether or not that is stressful to your charge source without current limiting can be determined through IRL testing.

> I start off with about .25

That is likely not the max CAR for your AGM, but IRL observed behaviour.

Temps take time to rise, ambient is a key factor as is cooling airflow.

The wiring infrastructure may also act as a current limiting resistance, but if so that can get dangerous when LI is substituted for lead.

Even a 100Ah LI bank may draw more than yours, because its CAR is so much higher, internal resistance so much lower.

> While the output drops because the regulators throttle back as the alternator temperature increases, the alternators are producing the maximum current for the conditions

In effect that is your current limiting protection already in place.

So long as the ramp-down curve keeps the alt circuitry below a stressful range.

Different from an explicit current adjustment but can deliver the same desired result.

As stated heat buildup in other locations also needs to be checked, more critical if only using alt heat sensors, rather than explicit current amps adjustable limiting.

[CaptainRivet]

Originally Posted by sailingharry

I believe I have mixed acceptance and absorption. Although I will admit I do not know what acceptance is then.

My current AGM bank is 800 Ah. I have two alternators rated for a total of 270A, but at normal cruising RPM rarely see more than 200. Absorption voltage is about 14.7. if I am down 30%, or 250 to 300Ah it will take over an hour to reach 14.7 volts (I usually hit absorption voltage someplace around 85-90% SoC). While the output drops because the regulators throttle back as the alternator temperature increases, the alternators are producing the maximum current for the conditions. In that first hour, the output would not change with an LFP bank.

To put this in C-rates, I start off with about .25, and as the alternators warm up reach something more around 0.12, which then drops more once absorption voltage is reached.

wrong the output of the alternator will change and will be higher and throttling most probably much faster then with AGM. AGM has a much higher resistance even in bulk then Li limiting the current.
LI Internal resistance is way lower which means your Li will accept more amps and longer which heats up the alternator faster.
What is the throttling temp of the regulator, can you adjust it? Where is the sensor located on the alternator?

What is your main charge source: Means what's gonna charge the Li in 80% of time? If it's not the alternator your current alt setup is fine.
Optimize your main charge source to get out of it as much as possible but long term save.
the rest of the charge sources has to just work with the smallest cost possible as the run a small amount of time overall.

[Melbourne Park]

Originally Posted by s/v Jedi

I agree with all you write except this part. You don’t explain how the FLA start battery is harmed by a DC-DC converter at a rating at half the alternator rating. The context here is that the alternator has a FLA charge profile, matching the battery chemistry and I read your comment that adding the DC-DC converter harms the FLA battery, which I dispute.

I agree with you. My belief is that if the current passes via the VRLA start battery to downstream, such as a DC-DC is connected to the VRLA start battery for current with the DC-DC charging the downstream battery bank, as long as:

1 - The start battery is fully charged
2 - The current passing into the start battery is more than the current being drawn from the start battery
3 - The start battery will not be effected. The current will pass via the power cables.
4 - Hence the VRLA battery will not be effected.

[s/v Jedi]

Originally Posted by Melbourne Park

I agree with you. My belief is that if the current passes via the VRLA start battery to downstream, such as a DC-DC is connected to the VRLA start battery for current with the DC-DC charging the downstream battery bank, as long as:

1 - The start battery is fully charged
2 - The current passing into the start battery is more than the current being drawn from the start battery
3 - The start battery will not be effected. The current will pass via the power cables.
4 - Hence the VRLA battery will not be effected.

The current to the dc-dc converter does not pass through the battery, it goes straight from the alternator to the converter, eliminating any charge/discharge losses.

But yes, the alternator must have ample output for both start battery and converter. I have posted my recommended diagram in it’s own thread to keep threads like this one on topic, but here’s the image (put any comments in the other thread)

[Tetepare]

Originally Posted by s/v Jedi

(put any comments in the other thread)

Link to other thread please? I thought I'd bookmarked it, but nope.

[s/v Jedi]

Originally Posted by Tetepare

Link to other thread please? I thought I'd bookmarked it, but nope.

Yes, I had to go and find it myself

Here it is: https://www.cruisersforum.com/forums...am-268360.html

[Melbourne Park]

Originally Posted by s/v Jedi

The current to the dc-dc converter does not pass through the battery, it goes straight from the alternator to the converter, eliminating any charge/discharge losses.

But yes, the alternator must have ample output for both start battery and converter. I have posted my recommended diagram in it’s own thread to keep threads like this one on topic, but here’s the image (put any comments in the other thread)

Maybe not ... if the DC-DC charger only operates after the start battery is charged, then the alternator would not have to handle a combined charging output.

And when the charge battery is charged, the current would not effect the start battery, even if the DC-DC charger is installed immediately downstream of the start battery.

For myself, I think I will put in more lithium capacity, and initially, just charge them from the marina's AC power outlet. Since I am mostly just operating the auto pilot, a larger capacity should give me maybe 60 hours of auto-pilot. I intend to add some solar, and DC-DC later. So the only hardware I think I will put in at first, is a switch between the house lithium system, a smart shunt with a display and I presume an alarm, and an AC shore powered lithium battery charger.

Later on, I may install a replacement start battery - most probably a hybrid lithium, the hybrid is the installed Maxwell 16 volt super capacitor, along with a 25 AH 12v lithium battery. This combination can output well over 1,000 amps for several seconds and hence crank a diesel motor. Then the connected lithium battery takes a few seconds to charge the super capacitor. When charging, there is a similar load to a lithium battery via its BMS, as the capacitor would already be charged, and also, the capacitor has very little capacity.

[s/v Jedi]

Originally Posted by Melbourne Park

Maybe not ... if the DC-DC charger only operates after the start battery is charged, then the alternator would not have to handle a combined charging output.

And when the charge battery is charged, the current would not effect the start battery, even if the DC-DC charger is installed immediately downstream of the start battery.

Downstream? I compare electric with water streams now and then, but what you describe here defies laws of nature (electricity is not subject to gravity)

The Smart Orion dc-dc converters/chargers are actually smart and can detect a spinning alternator. You want the dc-dc converter to start charging the lfp from alternator power immediately in order to reduce charging time, reduce engine run time and increase engine load. The alternator regulator, with it’s alternator-mounted temperature sensor regulates alternator output to prevent overheating.

LFP does not work well for start batteries; the idea you describe with a lfp battery in parallel with a super capacitor will lead to a short lifespan of the lfp. The reason is that lfp does not like to be fully charged. The reason I use AGM is that it loves to be fully charged

[Melbourne Park]

I could call it down arrow if I was referring to a drawing with arrows.

The hybrid Capacitor Lithium batteries assembled in Australia should last a long time. The reason for that is besides the long life of lithium even if they are held at 95% of their capacity, the final charge level for the lithium depends on its BMS's charge acceptance setting. The starting is also not done by the lithium cells - the power is provided by the capacitor. Then the lithium takes a few seconds to "re-charge" the capacitor. The life hardly matters though, because the capacitor has an incredible cycle life, and the lithium part only holds 25 AH. Its only there to re-power the capacitor, and that takes typically 3 to 5 seconds. Such a package in Australia is often cheaper than a typical AGM starter battery. I expect they'll become common. For one, there light weight is appealing.

[s/v Jedi]

Originally Posted by Melbourne Park

I could call it down arrow if I was referring to a drawing with arrows.

The hybrid Capacitor Lithium batteries assembled in Australia should last a long time. The reason for that is besides the long life of lithium even if they are held at 95% of their capacity, the final charge level for the lithium depends on its BMS's charge acceptance setting. The starting is also not done by the lithium cells - the power is provided by the capacitor. Then the lithium takes a few seconds to "re-charge" the capacitor. The life hardly matters though, because the capacitor has an incredible cycle life, and the lithium part only holds 25 AH. Its only there to re-power the capacitor, and that takes typically 3 to 5 seconds. Such a package in Australia is often cheaper than a typical AGM starter battery. I expect they'll become common. For one, there light weight is appealing.

Got ya!