Alternator Size with LiFePo4

[john61ct]

Yes, specialist kit that, and priced accordingly.

Buying stuff from the likes of Maine Sail, Mark Grasser, Bruce@OceanPlanet, is a solid bet for do it right the first time.

My more generalized comment above was more wrt mainstream / stock / less expensive gear, in response to the earlier comment skeptical of the strategy.

[OceanPlanet]

Originally Posted by john61ct

Yes, specialist kit that, and priced accordingly.

Buying stuff from the likes of Maine Sail, Mark Grasser, Bruce@OceanPlanet, is a solid bet for do it right the first time.

My more generalized comment above was more wrt mainstream / stock / less expensive gear, in response to the earlier comment skeptical of the strategy.

Ah, right! Yes, your suggested strategy is a good one in that regard. I didn't read back in the thread, just firing off in a rush...;-)

[rgleason]

You are assuming that people know beforehand that their small frame alternator must be derated by a huge percentage. In my case I started with a stock 80A alternator on a Yanmar that was only putting out about 50 amps. I took my yard managers recommendation and went with the Balmar 165. It is derated about 20% and still overheats at any output over 120A. If I would have done more research I would have known better and gone with a different brand. Hindsight is great, but all I can do now is try to cool the alternator or relocate the diodes.

Using your current Alternator

Size of Alternator 165a
Belt Program B-3 (85% max output) - 140a - for alternator longevity
Reduced output due to heat 85% - 119a actual output

I had a similar discussion with Balmar about that alternator. I believe it has dual fans.
If you need greater output, try blowing air towards the rear of the alternator with a bilge fan, perhaps drawing cooler air up from the keel area. Also facilitate moving of air through the engine compartment. The gains may not be enough for you (it think it may be about 5-7amp improvement).

Then consider removing the diodes to a remote location with a small fan and aluminum heat dissipation. Removing the diodes improves air flow and removes the diode heat from the alternator. Good cooling for the remote diodes is also essential.

There are better remote diodes Mark Gasser, etc. which will be more effective and stay cooler but this is an off the shelf one from the auto industry, Quicktifier. (notice the difference in the size of the wires, compared to Mark Gasser remote rectifier!)

[rgleason]

Balmar is augmenting their AT Alternators with an XT Alternator with a
"braided stator wire design to generate exceptional output in the smallest possible area. The XT-Series produces slightly more power than our previous AT-Series 165A design and operaties 5o-10oC cooler. "


XT-Series and AT-Series Alternators | Balmar


Operating cooler could be a key to power output.

[john61ct]

redirect from here http://www.cruisersforum.com/forums/f14/lfps-charging-voltage-and-state-of-charge-211772.html

Originally Posted by Cpt Pat

Heat is the number one enemy of longevity, and the more cycles the more the cumulative degradation from heat.

Charging a LFP with an alternator that outputs relatively high charge rates may (and I suspect will) have a negative impact on LFP life. And here's the on topic part: Especially if you charge the cells to or above the 100% SoC point, where the partial energy converted to heat rises rapidly

Originally Posted by rgleason

Thanks Cpt Pat, good considerations, re alt charging & heat. What do you think of an ideal rated 170a alt charging at 130ah actual, to 200ah or perhaps a 300ah bank? Would have natural vents and tstat fan.

Personally I think the issue may go beyond heat. I would keep that alt de-rated to .3 - .5C in normal use, lower end better, unless a specific situation arose where I really needed to speed things up.

Just as with "don't draw lead banks below 50%", it's just a grey scale guideline, and I think violating it **occasionally** would have a minimal negative impact on longevity.

[tanglewood]

I think the real issue here is about finding a true, continuous duty output level for any given alternator, and recogniozing that for many (perhaps most) alternator that is NOT the nameplate rating.


It's not about what LFP wants, but about what an alternator can deliver on a continuous basis. LFP just gives the alternator the "opportunity" to operate at a continuous level.


The really unfortunate thing is that none of the manufacturers provide any of this information. They ideally should do what engine manufacturers do, and provide continuous duty ratings, and higher ratings for various not-to-exceed durations.

[john61ct]

Well there are heavy duty units that can and do put out their rating 24x7 if ambient isn't too high. Emergency vehicle units, military. . .

Even if the alt **can** put out 130A continuously, it will last longer if de-rated, so no harm in oversizing if you can, other than cost.

Plus then reserve capacity is there if your situation requires charging as quickly as possible.

[rgleason]

Yes, John. I am assuming the alternator will be oversized at least 15% for heat and 15% for longevity. If you were to start with 170a x .85 x .85= 122a
So to get 130a I would need a larger alt. about 185a. A large case with dual fans and fan/vent assist cooling would help and a remote rectifier mught be needed.

My goal is to charge 80-100ah in less than an hour of engine time

Assuming a charge rate of .5C I would need 200ah of LiFePo4. Assuming a charge rate of .3C then .3/100 = 333a bank would be needed. However much of that won't be used. The added size of the bank will simply increase the number of available cycles beyond the years you will use the boat.

What I've noticed is that LiFePo4 and any other batts are subject to user mistakes which affect the life span too!

In any

[rgleason]

A64 wrote
http://www.cruisersforum.com/forums/....php?p=2792569

... actual continuous power output from my 165a due to temp regulation is about 80 to 90 amps, I have mine set conservatively at 95C, w/ serpentine belt.

To achieve 100a it appears remote rectifiers will be needed or a larger alternator.

[rgleason]

The other concern when charging at faster rates, say .5C
http://www.cruisersforum.com/forums/....php?p=2790865

[rgleason]

Another concern when faster charging rates are used (.5C & greater) is heating up the batts and damaging the cycles.
http://www.cruisersforum.com/forums/....php?p=2790865

Perhaps it would be best to have a slightly larger bank, charge at 0.3C or 0.35C, and let a medium sized solar pv take care of the rest, to achieve 100a charge in 1 hour.

[john61ct]

Size the bank for your consumption needs, not to meet some arbitrary charging spec.

Your runtimes will be varying anyway, based on your usage of stored electricity, and your sailing patterns.

Remember to get away from the "need to fill it up" lead mentality.

[Q Xopa]

Originally Posted by rgleason

Another concern when faster charging rates are used (.5C & greater) is heating up the batts and damaging the cycles.
http://www.cruisersforum.com/forums/....php?p=2790865

Perhaps it would be best to have a slightly larger bank, charge at 0.3C or 0.35C, and let a medium sized solar pv take care of the rest, to achieve 100a charge in 1 hour.

Yes, if you have a say 300Ah bank and charge it at .3C /100A. Assuming you've only discharged to 25% DOD and go to 75% (ie 50%/ 150AHs of total capacity). Or 200A charge rate with a 600AH bank. Thats only 1.5 hours. Or a 45 min run in the morning and then another in the evening. More shorter runs. Or run in the morning and solar during the day. Plenty of ways to skin this power management cat if we know the guidlines.

[rgleason]

Thanks, that clarifies the factors.

Marinehowto.com has an excellent alternator review.
https://marinehowto.com/marine-alter...n-tips-tricks/
I thought I knew quite a lot about alternator installation, I learned some important things after reading it. Its worth reading multiple times.

[rgleason]

A64 has previously posted more info about his 165a installation down below. http://www.cruisersforum.com/forums/....php?p=2747348
He has a Mark Grasser J Series 165a which he says outputs 80-90 amps continuous. There are more details below. Getting good output is definitely a challenge, but if the output is too great you'll be spending alternator $ needlessly, or charging your LiFePo4 batts at too high a rate and loosing cycles.
There needs to be a good balence between daily use (80 to 140 for us), battery capacity C, rate of charge (.3C or occasionally when needed 0.35C to perhaps .4) and figuring out an actual continuous rating under hot engine and alternator conditions, as the alternator is installed which will meet those requirements.

200ah x .30C charging = 60a
200ah x .40C charging = 80a

270ah x .30C charging = 81a
270ah x .40C charging= 108a

It appears that my goal of charging 100ah in one hour will be quite costly, both because a larger LiFePo4 battery bank will be needed and the alternator required will be more expensive not to mention the wiring.

Keeping the SOC range to 75% to 25% indicates that a 200ah bank will have about 100ah available, which would be ok. We could charge that in the morning for 45 min, then partially offset loads during the day with solar PV and depending on the SOC at the end of the day charge for 45 min more.

With the 200ah bank I would have to adjust my continuous charge goal to 60ah-80ah which is definitely possible with a MG. J165.

The other improvement I intend to make eventually is to re insulate the refrigerator with 4" of new instead of 3" of very old which will reduce loads too.