How many Amps can my alt be putting back in

[jbinbi]

I have 2 x 80A alts. I am looking replacing my house bank, and hoping that someone can answer some questions below and maybe provide more info as well.

1. Say I have fla, 600ah bank, and I am down to 50%. If I run both alts for an hour, will I get 160 back into them, or will the alts give up because of heat before the hour. Is there an optimal rpm to run engine for max alt output vs. time?

1a. Say I have AGM/gels, same question

1b. LiPo/foam, I think it should take all 160 or whatever the alts are doing.

2. Same situation, but I am 75% SOC to begin with. Now I figure it is not just the alt that is limiting, but battery type with fla, getting to more exponential part of FLA curve. Alt can put out 160 to start, but what can battery take in at various SOC? There must be a curve for this somewhere?

2b. Same for AGm/gels,

2c. Same for LiPo/foam. I think for Li type chemistry it takes in as much as the charging source is putting out, curve is linear, not expo?

I use between 150-250Ah a day, and thinking of between 6-800 of battery capacity. When cruising, I normally need to use the engines for an hour to get in and out of harbor. Plus I have 500W of solar, but you might have 2 rainy/cloudy days. So even though I potentially have enough solar to be topping me off, I am curious to know what alts can give me. I only have a 40A battery charger, so that is my worst charging solution unless hooked up to AC overnight. Running the generator overnight vs. running the engine for 2 hours

[a64pilot]

Even then it’s more complex than your thinking. Do you have external regulators for those alternators? If not then that is going to really reduce charge current.
Plus you always run both motors?
Solar is the best answer, increase your charging with Solar. Next and I think a required back up is 100 amps or so of shorepower charger and a Honda, but if you have a generator, then go even bigger. I have 185 amps of chargers, 125 from an inverter / charger. 60 from a regular battery charger and a Kilowatt of Solar.

If I’m down to 50% SOC my 660 AH bank will only take all 185 amps for 10 min or so, then it’s voltage limited, I’m at absorption voltage with ever decreasing current. I’m AGM, gel will accept significantly less and flooded slightly less. You can’t charge Gel with high current, they won’t tolerate that.
I’m never down to 50% SOC though usually about 75% and at that SOC they will only start out accepting about 100 amps.

But you need to remember this, I don’t care if you have 1000 amps of charger if your trying to get to 100% SOC, it’s going to take 6 hours so so to do that, big chargers only help initially, but acceptance rates soon taper off.
That is when Solar comes into its own, it just sits there day after day silently pumping in power to the bank.

To get to 100% every day, it takes me 30 to 60 min of generator running first thing in the morning, then I can shove 50 to 100 amps into the bank, then Solar can spend the rest of the day dribbling in the full charge.
Summer time I don’t need any generator run time, only need it in the depths of Winter.

So I would double your Solar and get a big shorepower charger, best way to go there in my opinion is with an inverter / charger, then you have a good big inverter too, but keep your current charger as a back up, or run them both.

Don’t think of your engines as a charge source, of course take advantage of them when they are running, but don’t run them to just charge batteries, especially with stock alternators.

[S/V Illusion]

It’s kind of an academic set of questions given how much we don’t know about the charging curve of the alternators you have. Rather than rely on guesses here and theoretical opinions, it’s easy to find out definitively using a simple clamp meter to monitor charging current.

[noelex 77]

In practice the numbers can be quite variable, so you are better using something like a clamp-on multimeter or battery monitor to measure the real numbers.

Stock alternators are typically not very good at delivering substantial current as they heat up.

For an 80A stock alternator perhaps 40-45A continuous is about average. This will typically need around 1500-1750 rpm. You will generally need an external regulator to achieve these numbers other than at low SOC. However, these results are very variable depending on the alternator.

A 600 Ahr lead acid battery bank may be expected to accept the output of both engines (90A) up to around 70 -75 % SOC, but it is sensible to run high house loads during the charging phase, which will consume some of the power and extend the % SOC where the full alternator output will be accepted.

For catamarans it is more common to run just one engine, especially if the goal is efficient charging so the charging current will drop to 45A less the house loads. You are likely to reach a SOC around 85%+ before the battery acceptance becomes the limiting factor.

Lithium batteries will accept a great deal of current so the full output of the alternators may be accepted up to 95%+ SOC, but they tend to deteriorate more rapidly at these high SOC so it is sensible to stop charging sooner.

Please treat these numbers as ball-park figures, but they might help your initial planning until you can collect some real world numbers from your particular installation.

[jbinbi]

Appreciate the answers, am not holding anyone to anything here, it is an internet forum;-). Standard stock Hitachi alt that came with the lagoon.

Was hoping that running both engines for an hour at 50% could get me to 75%, and solar would get that up to 85%+ by the end of the day. The load is pretty much instruments during the day, fridge 24hr all the time, and short bursts of microwave in the morning and dinner time.

If I use the AC, then generator is going but the charger is only 40A. I guess I should look at a larger charger.

I am asking this as the other alternative is to go Li at 800Ah. In this case my hope is that I could put back 150Ah from the alternators in a hour?

BTW, if I need to use the engine all day, then I am running 1 engine. But to get in and out of the harbor for an hour, both running, at 1700 rpm I am doing 6+ kts using 1 gph with both, so no biggie on fuel to use both.

[barnakiel]

The battery is the limiting factor.


Your alt can put as much out as it does before it overheats. But when the batteries are not deeply discharged, the batteries limit the alt (unless you boost the voltage with some trickery).


Lithium batteries can take plenty of ooops from start till near full, so you may want some kind of decent overheat circuit on the alt.


b.

[a64pilot]

No, your better off with Solar than with LFP and using the engines to charge. To start with to go LFP, every charge source excepting maybe your Solar has to be replaced.

With enough Solar, most all of your loads can be covered, and a little generator or motor usage early in the morning can cover any short falls due to weather etc.

If your counting on your motors to charge, first your going to need new alts and regulators. That’s over $1,000 per engine including serpentine belt kit to go with a good 100 amp alternator.
Then your going to need to motor everyday, or run the motors everyday.

He has space for Solar, he can add Solar and not have to run anything, excepting maybe bad weather days, and then in my opinion he would be better running the generator with a big inverter / charger, because who doesn’t want a nice big pure sine waver inverter?

Stock alternators don’t do much for charging, biggest reason is that they don’t output absorption voltage, they output a lower fixed voltage, and because of that the batteries charge slower.

Now if the way you use the boat is to spend several hours every day motoring around, then sure drop the 2 grand into good alternators and charge that way. But if you stay at anchor for significant periods, then Solar is the killer app.

[CarlF]

There are a lot of ways to skin this “cat” but a few comments:

1. so called “Small Case” alternators like yours drop off very quickly from heat. Consider two options a) replace the belt with serpentine belt and put in a Balmar AT alternator that does not fade as quickly b) Install a 2nd belt and a 2nd large case alternator that will handle heat better (Balmar has such kits for many engines). You only need to do this on one engine.

2. AGM’s are not a good choice for people not plugging in every night. Gels can be better but have their own issues. Firefly’s or Lithium will require much less engine time due to better charge acceptance and will last a long time in 50% discharge use patterns.

3) Running a genset for a 40amp charger will leave the genset lightly loaded. It will waste fuel and carbon up. Get at least a 100amp charger to load up the genset. A better idea might be something like a Victron Multi with 3kw inverter and 120 amp charger.

[BlackHeron]

You either need a lot more solar (or also perhaps some.wind) -or to lower your daily power consumption.

Or get a real genset with a large inverter-charger and resign yourself to running it a couple/three hours a day.

Trying to produce that much AH and charge lead-acid batteries from mere alternators every day (doesn't matter how big they are or having fancy external alternators) from diesel sailboat engines is like trying to pull a small fishing boat on a trailer with a gigantic dump truck using 50' of anchor chain to hook it up with. Sure, you've got plenty of truck but the rig isn't ideal.

It's the wrong tool for the job and hard on an expensive dumontruck running all those hours with no real load on it. Operating a big dump truck isn't cheap -a little pickup with a proper trailer hitch would be much more appropriate for that towing job

[jbinbi]

Thanks. My generator is a honda, which is a pita to take out and use and put back.

I have looked at adding in a nextgen, which is a 10-12k deal, so if I could up the engine Amp output via a Balmar system for 2k, that is not a bad thing.

I have 500W of solar over the dink, I can't add more there, but could add 2 more flex panels on the bimini top, so I could get this up to 800W.

However, I have seen several new boats with all Li, even running the AC (800AH of Li), saying they can get the battery bank up quickly with solar and engines in the morning. If you use 400Ah overnight, and have 2 100A Balmars, plus 800 W of solar, and going to be motoring for 1 hour when you get up, my thought was if I could get 200A back into the battery with the alts, then let solar maybe get another 100+ during the day, I am pretty darn close to the 400Ah taken out. Not worried about replacing existing electronics, I need new batteries, I have 2 Victron Mppts , and the charger that came with the boat.

[Sternwake]

The health of the batteries also plays a part in how much amperage they can accept, and how long that amperage requires to reach absorption voltage, where amps taper to maintain that maximum voltage without exceeding it.

Newer healthier batteries accept more for longer before reaching absorption voltage.

How many PSOC cycles accumulated since last true full recharge also plays a part in how much amperage batteries can accept at the voltage reaching their terminals, and how long that amperage takes to bring the batteries to absorption voltage, and also how long it takes once in absorption for the batteries to reach the ideal 100% state of charge.

Keeping the alternator cooler can keep its amperage output per RPM, higher.

Inline blower fans pushing air into engine compartment aimed at alternator can help a good amount in keeping them cooler, but the amperage the fans pull, is amperage not going into the batteries, when still below absorption voltage

I've been inside a 50/120 chrysler alternator of late 80's vintage lately. It was rebuilt, poorly, prior to my ownership.

The aluminum rectifier plates use the alternator casing as a heatsink. These rectifier plates were painted, on this mating surface, and heavily dimpled on their bottoms. They used a thick wad of Zinc oxide grease to aid thermal transfer, but the two small retaining screws, could never exert enough pressure to squeeze out extra grease they used, for more metal on metal contact, and better thermal transfer. When i scraped off the zinc oxide it was a huge amount, at least 5 ML per plate. Very little direct metal to metal contact, so the casing was not acting as good heatsink for the rectifiers/ diodes, also not very much surface area for passing the ground to alternator body, which likely aided in undesirable heat generation at higher outputs.

I've removed that paint between these mating surfaces, and the dimples, got both mating surfaces smooth and flat, and very little Arctic Silver thermal grease was required to fill any remaining gaps. This alone should greatly increase thermal transfer to the casing from the diodes/rectifier and should help keep it cooler for longer and make more amperage.

But the stator also generates a lot of heat and the alternator casing also acts like a heatsink for the stator, the diodes transferring their heat to the casing more efficiently, means the casing will be suckinglheat less efficiently from the stator, to some unknown degree.

Cooler Diodes waste less amperage as heat.

Also this Alternator's external fan has a large gap between alternator body and the blades, reducing the amount of cooling air the fan can pull across the rectifiers, and through the alternator. I intend to lessen this gap. More airflow means cooler alternator, means more amperage potential and a more long term reliable alternator.
In theory anyway. i do not have enough 'before' data to prove my ministrations will be effective

My point is, your 80 amp alternators were never intended to output 80 amps continuously, but a little spit and polish can likely help them shed the heat they develop. The S&P can also aid in faster depleted battery recharging, while adding reliability and longevity. Getting inside them before leaving, also removes some mystery and increases confidence that you can find any potential future issues, should they fail in the wild blue yonder or perhaps see that potential existing issues now, like deep grooves in the slip rings mean they are not to be trusted now, much less in the wild blue yonder when they are going to be asked to work hard, often.

More amperage delivered early in the day means a better chance the solar can finish the job by later afternoon, minimizing PSOC cycles, extending battery longevity and the amount of juice one can use that night.

[noelex 77]

Originally Posted by jbinbi

Standard stock Hitachi alt that came with the lagoon..........

I am asking this as the other alternative is to go Li at 800Ah. In this case my hope is that I could put back 150Ah from the alternators in a hour?

Originally Posted by jbinbi

and have 2 100A Balmars, plus 800 W of solar, and going to be motoring for 1 hour when you get up, my thought was if I could get 200A back into the battery with the alts,

Unfortunately, you cannot simply multiply the output rating of the alternator by engine run time to calculate the amp hour output. This is common mistake when planning an electrical system.

The alternator rating is a maximum output. A small frame alternator will not deliver this output continuously. This is a limitation of the alternator output so this still applies with batteries that have a high charge acceptance rate such as a lithium battery bank or a reasonably discharged lead acid bank.

With a one hour run time at cruising revs you can expect around 40-45AHrs out of each of the engines with a stock Hitachi 80A alternator and around 70Ahrs from a high quality small frame 100A alternator. These are ballpark figures, but they assume a good quality installation and batteries (and/or loads) that can accept all the alternator can dish out, so your are unlikely to do much better. The engine will also need some time to warm up and cool down at lower revs so you will need a slightly longer run time to allow for this.

[Augi]

Originally Posted by jbinbi

I have 2 x 80A alts. I am looking replacing my house bank, and hoping that someone can answer some questions below and maybe provide more info as well.

1. Say I have fla, 600ah bank, and I am down to 50%. If I run both alts for an hour, will I get 160 back into them, or will the alts give up because of heat before the hour. Is there an optimal rpm to run engine for max alt output vs. time?

1a. Say I have AGM/gels, same question

1b. LiPo/foam, I think it should take all 160 or whatever the alts are doing.

2. Same situation, but I am 75% SOC to begin with. Now I figure it is not just the alt that is limiting, but battery type with fla, getting to more exponential part of FLA curve. Alt can put out 160 to start, but what can battery take in at various SOC? There must be a curve for this somewhere?

2b. Same for AGm/gels,

2c. Same for LiPo/foam. I think for Li type chemistry it takes in as much as the charging source is putting out, curve is linear, not expo?

I use between 150-250Ah a day, and thinking of between 6-800 of battery capacity. When cruising, I normally need to use the engines for an hour to get in and out of harbor. Plus I have 500W of solar, but you might have 2 rainy/cloudy days. So even though I potentially have enough solar to be topping me off, I am curious to know what alts can give me. I only have a 40A battery charger, so that is my worst charging solution unless hooked up to AC overnight. Running the generator overnight vs. running the engine for 2 hours

Checkout the Integrel System described by Nigel Calder at the link below.

The system not including installation costs $12K. It sounds like $12K plus installation is more than you want to spend but the system is designed to deal with all the issues involved with what you are trying to accomplish. If the efficiency is what is claimed in the video the $12K plus installation upfront might be worth it depending on your intended use/ intended length of use

Minimum size propulsion engine needed is 40 HP. I think Mastervolt provides the alternator/ generator.

https://www.youtube.com/watch?v=0uTNjfb3MNQ

The good news is that Nigel Calder seems to be a high ethics guy, has an excellent and long track record and is not for sale. It does appear that he has a financial motive to see the success of the product. But I think there is a pretty good chance if he backs the system, the system is OK.

[Augi]

Originally Posted by Augi

Checkout the Integrel System described by Nigel Calder at the link below.

The system not including installation costs $12K. It sounds like $12K plus installation is more than you want to spend but the system is designed to deal with all the issues involved with what you are trying to accomplish. If the efficiency is what is claimed in the video the $12K plus installation upfront might be worth it depending on your intended use/ intended length of use

Minimum size propulsion engine needed is 40 HP. ]I think Mastervolt provides the alternator/ generator.[/COLOR][/COLOR]

The good news is that Nigel Calder seems to be a high ethics guy, has an excellent and long track record and is not for sale. It does appear that he has a financial motive to see the success of the product. But I think there is a pretty good chance if he backs the system, the system is OK.

What I said above is incorrect. Victron provides supporting equipment for the Integrel System not Mastervolt. Victron does not provide the Integrel generator / alternator. I don't know who does or if Integrel makes the generator alternator themselves.

[johnn33]

Part of Triskell Marine in Cornwall, UK
https://triskelmarine.co.uk/integrel/
John