Just double checking my planned LifePo4 set up

[Boatguy30]

1500 watts seems out of whack with 600 amp hour battery bank. I'm no expert for sure but just curious on that ratio.

[witzgall]

DO NOT put a relay on the field wire with the intention of using it to cut field when you want the alternator to turn off. Doing so will spike the voltage, and will likely damage the diodes in the alternator, damage the regulator, or both. with the balmar MC-614, 624 or ARS-5, simply remove power from the ignition wire which powers the regulator. This will allow the field to collapse gracefully, without a high voltage spike.

Chris

Originally Posted by mbartosch

Agree, dropping field current is the safest way to properly shut down alternator charging. A simple NC relay in the field does the trick, but IMO it's better to cut power to the external alternator regulator. I remember that e. g. Balmar recommended against cutting field directly, and as field is driving a coil I definitely see the reasoning behind this.

[CatNewBee]

Originally Posted by Boatguy30

1500 watts seems out of whack with 600 amp hour battery bank. I'm no expert for sure but just curious on that ratio.

No problem for LFP. 1500Wp translate to barely 100A charge current at 12V, 600Ah LFP can be charged at 1C continously or 3C quick charge, resulting in up to 600A charge current / 1800A charge current, they wont even notice 100A comming in, you can throw at them 6 times more solar.

[john61ct]

LFP's longevity is greatly reduced by charging above 0.3-.5C rate, so 200-300A for a 600Ah bank.

Sure it will **accept** (demand, pull) at a much higher rate if the source makes that much power available, but allowing that not a good idea if you want to get anywhere near optimal lifespan.

The actual numbers are very dependent on temperature. Opposite of storage, hotter allows safer faster charging.

In some use cases may even be worth pre-heating the cells if fast charging is important.

As temps approach freezing, even 0.3C charging becomes dangerous. Colder and faster can cause real damage, even render that pricey bank instant scrap.

[CatNewBee]

Originally Posted by john61ct

LFP's longevity is greatly reduced by charging above 0.3-.5C rate, so 200-300A for a 600Ah bank.

Sure it will **accept** (demand, pull) at a much higher rate if the source makes that much power available, but allowing that not a good idea if you want to get anywhere near optimal lifespan.

The actual numbers are very dependent on temperature. Opposite of storage, hotter allows safer faster charging.

In some use cases may even be worth pre-heating the cells if fast charging is important.

As temps approach freezing, even 0.3C charging becomes dangerous. Colder and faster can cause real damage, even render that pricey bank instant scrap.

Ha ha ha, 100A on a 600Ah battery is 0.16C, not even near 0.3 to 0.5C.

[john61ct]

Yes, and what? I never said anything about the 100A, that of course is perfectly fine.

This however

Originally Posted by CatNewBee

LFP can be charged at 1C continously or 3C quick charge, resulting in up to 600A charge current / 1800A charge current

needed qualifying.

[nebster]

We charge engine start batteries (12VDC AGM) with a very small 120VAC battery tender running off our inverter running off our house batteries (52VDC LFP).

The inverter is always on, so there is no energy cost on the margin to spin it up.

The inverter achieves between 88 and 92% DC-to-AC efficiency depending on loads, but never any less than that because we have a decent baseline.

The trickle charger uses such a tiny amount of energy, in relative terms, that the losses in the whole charging chain are way down in the noise.

As usual, context matters. Once a system reaches a certain size, micro-optimizing may bring more consequences than benefits. To wit: in our case, we have only one*load attached to our 52V battery, the inverter-charger. That dramatically simplifies the battery management burden (and, in fact, in our case we are crazy and don't even use a BMS).

Redneck here, reporting for duty!

[sailingharry]

Originally Posted by nebster

We charge engine start batteries (12VDC AGM) with a very small 120VAC battery tender running off our inverter running off our house batteries (52VDC LFP).

The inverter is always on, so there is no energy cost on the margin to spin it up.

The inverter achieves between 88 and 92% DC-to-AC efficiency depending on loads, but never any less than that because we have a decent baseline.

The trickle charger uses such a tiny amount of energy, in relative terms, that the losses in the whole charging chain are way down in the noise.

As usual, context matters. Once a system reaches a certain size, micro-optimizing may bring more consequences than benefits. To wit: in our case, we have only one*load attached to our 52V battery, the inverter-charger. That dramatically simplifies the battery management burden (and, in fact, in our case we are crazy and don't even use a BMS).

Redneck here, reporting for duty!

Nebster,


Thanks for the validation. As I said when I first tossed this idea out, I don't have LFP and don't run my inverter more than an hour a day. But the idea sure seems to have merit to me -- or at least worthy of consideration before discarding it. And to you. So there are two of us in this strange world! Lol.


Harry

[Jef & Marin, Netherlands]

We are sailing in the tropics mainly. Solar is 1760W, LiFePO4 house battery is 540 Ah 12V.
The solar produces lots of Ah's. More than enough for our high energy use (washing machine, electric cooking on induction, dishwasher, big watermaker, breadmaker, water cooker for tea, even heating the boiler)


You might also get enough energy from solar, making charging from the alternators not necessary, and thus your system much simpler and cheaper.



And we like to sail; we hardly use the engines except to get in and out of anchorages.

For us, charging the house battery from the engines is often not necessary and not very useful. So the system is very simple:
- The 60A alternators just charge the start batteries.

- Solar charges the LiFePO4 house battery


It happened to us in winter in the southern Pacific that solar was not enough. Then we had to the generator. Also to run a fan heater because it was bloody cold.

Also, we have another fallback: the house battery can be connected to the alternators via a kind of emergency switch; there are diode splitters on the alternators. The current is somewhat limited by the cable run to the house battery.

This switch is only used manually. If you keep it connected continuously your start batteries will not charge adequately, or you LiFePO4 will be overcharged. This switch is also useful for emergency starting on the house battery, with a 3rd position bypassing the diodes.



The advantage is the simplicity of charging a mixed LA/LiFePO4 system.


If we would not have the generator that came with the boat, but did a new installation, it would be nice to have double alternators per engine, a small one for the start batteries, a big one for the LiFePO4.
Also I consider having just one start battery on our catamaran.
Especially if both start and house battery have the same voltage (to have a backup solution). First I would have to calculate cable size, starting current is 400A

[CatNewBee]

Originally Posted by Jef & Marin, Netherlands

We are sailing in the tropics mainly. Solar is 1760W, LiFePO4 house battery is 540 Ah 12V.
The solar produces lots of Ah's. More than enough for our high energy use (washing machine, electric cooking on induction, dishwasher, big watermaker, breadmaker, water cooker for tea, even heating the boiler)


You might also get enough energy from solar, making charging from the alternators not necessary, and thus your system much simpler and cheaper.



And we like to sail; we hardly use the engines except to get in and out of anchorages.

For us, charging the house battery from the engines is often not necessary and not very useful. So the system is very simple:
- The 60A alternators just charge the start batteries.

- Solar charges the LiFePO4 house battery


It happened to us in winter in the southern Pacific that solar was not enough. Then we had to the generator. Also to run a fan heater because it was bloody cold.

Also, we have another fallback: the house battery can be connected to the alternators via a kind of emergency switch; there are diode splitters on the alternators. The current is somewhat limited by the cable run to the house battery.

This switch is only used manually. If you keep it connected continuously your start batteries will not charge adequately, or you LiFePO4 will be overcharged. This switch is also useful for emergency starting on the house battery, with a 3rd position bypassing the diodes.



The advantage is the simplicity of charging a mixed LA/LiFePO4 system.


If we would not have the generator that came with the boat, but did a new installation, it would be nice to have double alternators per engine, a small one for the start batteries, a big one for the LiFePO4.
Also I consider having just one start battery on our catamaran.
Especially if both start and house battery have the same voltage (to have a backup solution). First I would have to calculate cable size, starting current is 400A

Congratulations, nice set up! We have the same experience with ours. A 8kVA Onan generator is way more efficient to charge the batteries quickly if ever necessary than the engines alternators.

[chubby]

Originally Posted by mbartosch

I chose to implement "option A", alternator directly charging the LiFePO4 house bank controlled by a Balmar MC 614 regulator.
The MC 614's "belt manager" in combination with the alternator temperature sensor takes care of limiting charging current to acceptable limits.
Our Balmar 6 series 150 A alternator typically puts out around 110 A when cold at moderate cruising speed (~2000 RPM) and is limited to about 90 A after a while when hot by the MC 614. Overall it works very well.

Charging the starter battery is done via a Sterling B2B charger from house bank, triggered by ignition and using a timer relay to make sure the battery gets at least one hour charge even if ignition is on for a few seconds. I chose a B2B charger in order to avoid slowly destroying the LA battery due to never reaching full charge if it were directly connected to the alternator output via the traditional battery isolator.

The entire setup works great so far for us.

i just wanted to give props for your engineering/systems blog on your website..
on scale of usefulness it is right up there with the nordkyndesign and marinehowto blogs.


..super helpful for those of us in the design phase of all this


(thanks)

[mbartosch]

Originally Posted by chubby

i just wanted to give props for your engineering/systems blog on your website..
on scale of usefulness it is right up there with the nordkyndesign and marinehowto blogs.


..super helpful for those of us in the design phase of all this


(thanks)

Thanks for the nice feedback, very much appreciated!