Battery Charging

[John Gilbert]

I use both the boat engine and an onboard generator to charge batteries. The engine is equipped with an 85-amp alternator. The generator produces 30-amp power. I am curious about the relative efficiencies of the two charging systems. I have been assuming that the generator will take longer to accomplish a full charge based upon its amp rating, but am not sure whether the AC power it provides changes its charging performance relative to the DC input from the engine. Any thoughts will be appreciated - as you can see, things electrical are not my forte.

 

[Don S/V ILLusion]

Think of it like filling a bucket with water. You have two different "hoses" flowing at different rates but we don't know what size bucket, i.e., what size your battery bank is. The smaller the bank, the less the difference is between your two charging sources.

Also, a 85 amp alternator virtually never puts out anywhere close to 85 amps. It's more like 30 amps typically under normal charge so comparing them further muddies the hose water (pun intended).

 

[jviss]

First, with the outboard generator, you are probably limited by the output of the battery charger you are using; most shore power chargers are relatively low output devices, usually around 10 Amps. At that current, even with a very modest house battery size, it could take 12 hours or more to fully charge.

With your engine-driven alternator, it depends on how it is regulated. If it is simply an internal regulator, it could also take a very long time to fully charge a house battery, since the output of the alternator will not be sufficient to efficiently and quickly charge a deep discharge battery bank. These are usually designed to just top off a starting battery, and provide some electrical power while the engine is running.

What size is the house bank? What type of batteries?

Your best bet would probably be to get an external, "smart" regulator, and have your 85 Amp alternator converted to external regulation. That way, you could charge two Group 24D, 75 AH battery in about 1.5 hours (depending on how smart the regulator is - many of them are not so smart!).

 

[Stu Jackson]

Alternators, regardless of how they are regulated, will not completely fill up your house bank. Generators would have to run a loooong time to do so, also.

Only shorepower or solar or wind will COMPLETELY fill up your bank.

This is because of battery acceptance.

http://forums.catalina.sailboatowners.com/showthread.php?t=114054

The different efficiencies you're asking about have more to do with when you use them. Your engine on the hook isn't as good as using your generator, and you wouldn't use your generator when motoring, right? Use the right charging source at the appropriate time.

Unless we know how your alternator is regulated and how big your shorepower charger is, and whether it is a true 3 stage charger, we can't answer your basic question (Don's right).

 

[jviss]

Alternators, regardless of how they are regulated, will not completely fill up your house bank. Generators would have to run a loooong time to do so, also.

Only shorepower or solar or wind will COMPLETELY fill up your bank.

I must say Stu that while this may be correct in some sense, it is not a meaningful distinction at this level of discussion. Many boats, like mine, are never on shore power, and that they may never get that last smidgen of capacity charged up simply doesn't matter. The only reason you might get there with shore power is that it stays in float mode for so long, since you are plugged in so long.

Fast battery charging with a large current source is actually better for lead acid batts. A three stage charger puts about 80% of the batter capacity back
at close to 1/3 C (capacity), so 100 A for four 24D 750 AH batteries. This should be a constant current charge until you hit the acceptance charge voltage, typically 14.2 V; Acceptance charge is constant voltage, and should stay at that voltage until the charging current diminishes to about 2% of the battery's capacity, at which point it's essentially 100% charged, and you switch to float mode.

This is vastly simplified, since battery types, condition, battery temperature during charging, and more factors influence this.

But for basic house battery use on the hook, and to answer the original poster's question, "I am curious about the relative efficiencies of the two charging systems" - the engine-driven alternator with an external regulator is the correct answer (note he says he has two alternatives, a generator and the engine charging system).

 

[jviss]

put some wrong info in this note, so I deleted it.

 

[Stu Jackson]

Then if he uses his generator, how does he connect to the batteries? If he uses the 12V output, he'd get ziltch of a charge. Most folks using generators plug 'em into their shorepower inlets to their shorepower chargers. We don't know how he's doing his.

I don't disagree conceptually with your earlier analysis - it's the difference between FULL and almost full. Not worth splitting hairs. Or the last 2%...

 

[jviss]

Then if he uses his generator, how does he connect to the batteries? If he uses the 12V output, he'd get ziltch of a charge. Most folks using generators plug 'em into their shorepower inlets to their shorepower chargers. We don't know how he's doing his.

I don't disagree conceptually with your earlier analysis - it's the difference between FULL and almost full. Not worth splitting hairs. Or the last 2%...

You're right, Stu, brain fart.

 

[Maine Sail]

But for basic house battery use on the hook, and to answer the original poster's question, "I am curious about the relative efficiencies of the two charging systems" - the engine-driven alternator with an external regulator is the correct answer (note he says he has two alternatives, a generator and the engine charging system).

Jviss,

An external regulator will only add float features, temp compensation and other features like "small engine mode", soft ramp up and remote sense. They will not get to 80% SOC any faster with all else equal. Most all "dumb regulated" alts built in the last 20+/- years have absorption voltages of 14.2 -14.6v.


We really need to know how the OP's generator "charges". Is it via a built in alternator, some gen sets have them, or via a shore charger off the AC output. If an AC shore charger or alternator we'd need to know what the amp rating is.

If I had to take a stab in the dark my guess is that the gen set charges via an AC charger which is likely under 30A, if factory installed. If in bulk mode the engine alt would likely charge faster but above 80% SOC the bank may be taking less than the 30A of the shore charger so running the engine alt is just wasted energy.

 

[jviss]

Not sure I follow you, Maine. The most important feature my smart regulator added was a bulk phase, which is high current up to the acceptance voltage set point, which is adjustable; mine is set for 14.3V. This bulk phase puts 80% of the capacity back quickly. Charging would be much slower with a simple regulator.

 

[Maine Sail]

Not sure I follow you, Maine. The most important feature my smart regulator added was a bulk phase, which is high current up to the acceptance voltage set point, which is adjustable; mine is set for 14.3V. This bulk phase puts 80% of the capacity back quickly. Charging would be much slower with a simple regulator.

Jviss,

You've been a victim of marketing hype and misleading information from the external regulator manufacturers. ALL regulators, smart and dumb, do both "bulk" and "absorption".

If you want to get a better handle on how these voltage regulators work, and what they really do, minus the marketing, fell free to read this:


Musings Regarding External Regulation (LINK)

 

[jviss]

Jviss,

You've been a victim of marketing hype and misleading information from the external regulator manufacturers. ALL regulators, smart and dumb, do both "bulk" and "absorption".

If you want to get a better handle on how these voltage regulators work, and what they really do, minus the marketing, fell free to read this:


Musings Regarding External Regulation (LINK)

Maine, with respect, I disagree. I don't think I'm a victim of marketing hype, nor do I think the purveyors of external smart regulators are charlatans. These things really do work, and really do allow faster charging of batteries than the stock internal regulators.

The internal regulator in the alternator I have was set for 13.6V or so, and even if it was set for 14.4, I doubt it would have supplied enough field current to produce the 100A that the alternator is thermally rated for. (By the way, it is field current that determines the alternator output, not field voltage; and, this is usually done with a pulse width modulated waveform in IC regulators). While it is true that when presented with a low enough equivalent resistance load, both the internally regulated and externally regulated alternators will be going 'all out,' and be bulk charging, the external regulator may be managed to drive the load harder, and with remote voltage sensing, battery temperature and alternator temperature sensing, drive the load to the limit of system performance, and charge much faster than an internally regulated alternator.

If you are regulated to 14.4, with no float mode, don't you think you could can damage your batteries, or at least shorten their life? While I sail whenever possible, I have motored entire days to complete a leg of a trip when where was no wind.

 

[Stu Jackson]

The internal regulator in the alternator I have was set for 13.6V or so, and even if it was set for 14.4, I doubt it would have supplied enough field current to produce the 100A that the alternator is thermally rated for.

This was the "discussion" Maine Sail and I have been having for years. Older alternators with internal regulators were set for too low a voltage to charge meaningfully. MS corrected me many times until the light bulb above my head finally lit!

My OEM Motorola on our M25 had a 13.6 V output and could only meaningfully charge with the Auto Mac which came with my boat. I could see the charging voltage from a panel analog volt meter which I checked with a DVM at the house bank, and the Auto Mac showed the amperage output of the alternator. With the Auto Mac backed off but still on, all I got was 13.6 V with less than 25A AO, until I turned the rheostat.

It seems from Maine Sail's investigatory journalism that a 14.4V internally regulated alternator will provide pretty much the same charge between 50% and 80% SOC.

I agree that lack of a float feature could be an issue on loooong motor trips. But wouldn't battery acceptance control that, too, since I think we all agree that unless run for that looooong motor tip, no alternator will ever reasonably get beyond 80% input (to a point where float would kick in, meaning just getting to float is NOT really full)? There's that pesky 2% again, eh?

And if I'm motoring for a long time, my fridge is on anyway.

 

[jviss]

...no alternator will ever reasonably get beyond 80% input...

Stu, I don't understand this, can you please clarify?

 

[Maine Sail]

Maine, with respect, I disagree. I don't think I'm a victim of marketing hype, nor do I think the purveyors of external smart regulators are charlatans. These things really do work, and really do allow faster charging of batteries than the stock internal regulators.

it was not meant as a personal slam on you at all. I just get frustrated when I am called in to trouble shoot a customers install where they spent $1500.00 - $2000.00 on an alt upgrade and get no faster charging. They do work and have many great features and I install a LOT of them.

The internal regulator in the alternator I have was set for 13.6V or so,

Then in your case it would charge faster as I mentioned in that piece.

and even if it was set for 14.4, I doubt it would have supplied enough field current to produce the 100A that the alternator is thermally rated for.

I've yet to come across an internal regulator that could not produce enough filed voltage and the resulting field current to hit the alternators max rated output.

(By the way, it is field current that determines the alternator output, not field voltage; and, this is usually done with a pulse width modulated waveform in IC regulators).

Exactly and at 7 volts less current will be produced than at 10.5 volts which is where most Balmar regs max out on the filed voltage. As the field voltage rises and falls so does the field current.

While it is true that when presented with a low enough equivalent resistance load, both the internally regulated and externally regulated alternators will be going 'all out,' and be bulk charging, the external regulator may be managed to drive the load harder, and with remote voltage sensing, battery temperature and alternator temperature sensing, drive the load to the limit of system performance, and charge much faster than an internally regulated alternator.

Again with all things being equal, they usually won't, and I have not seen this in multiple real world experiments. With batt voltage sensing this CAN greatly increase charging if the system has a voltage drop between the B+ and battery. Was working on a boat yesterday with a 1.2V drop between the alternator and battery bank. It had a Balmar regulator but of course it was installed incorrectly, as many are, and did not sense the batteries that were under the v-berth. The only way to fix this sytem would be with an external regulator and battery sensing or to wire an internal reg to sense the batteries not the B+.

If you are regulated to 14.4, with no float mode, don't you think you could can damage your batteries, or at least shorten their life? While I sail whenever possible, I have motored entire days to complete a leg of a trip when where was no wind.

I am regulated to 14.4v with no float mode and our batteries are ending their fifth season. This spring after a 20 hour load test they were still at 97-98% of Ah capacity from new. I also did a capacitance and SG test on them and all were in agreement and passing with flying colors. I add water perhaps once per year, if that. The previous batteries lasted 6 years and 2872 engine hours of dumb charging at 14.4 volts on a 24/7 five year live abord cruise by my friends, whom we bought the boat from... Cars drive around all day long at 14.4-14.6 and the batteries last a long time. The factory battery in my wifes 2003 Honda Pilot lasted until we traded the car one month ago. That alt put out 14.5-14.6v. If your reg is set to 14.6 then you'll use more water if you run the engine that long.

Again, my post was not meant in any way as an insult to you directly just more of a frustration I ome across on a regular basis with alternator charging..

 

[Stu Jackson]

Stu, I don't understand this, can you please clarify?

I think what I mean is that first we need to read the rest of that sentence: i.e., that pesky (remaining) 2%.

Sure, if run indefinitely, an alternator will provide enough charge to go past the start of the float stage and finish it, the way shorepower chargers do when left plugged in overnight or longer. I see it with my Link 2000 and have discussed this for a long time in my "Gotcha Algorithm" topic, which I am sure you've read.

It's just that in the real world, and how people use their boats, an alternator will NOT completely fill up a house bank. Only solar or shorepower will do that. Maine Sail has also discussed this many times.

And don't get me wrong either, I have an externally regulated 100A alternator with a Balmar MC-612 regulator, and I like the way it works, and enjoy the Small Engine Mode feature when the banks are really depleted. Saves a lot of wear and tear, and ya can't get that from an internally regulated alternator.

 

[Stu Jackson]

Again with all things being equal, they usually won't, and I have not seen this in multiple real world experiments. With batt voltage sensing this CAN greatly increase charging if the system has a voltage drop between the B+ and battery. Was working on a boat yesterday with a 1.2V drop between the alternator and battery bank. It had a Balmar regulator but of course it was installed incorrectly, as many are, and did not sense the batteries that were under the v-berth. The only way to fix this sytem would be with an external regulator and battery sensing or to wire an internal reg to sense the batteries not the B+.

This is a perfect example of real world issues. Like, take me, for instance!!!

I took the "shortcut" route of having the battery sense wire connected to the AO when I installed our MC-612. As you know, we also have a Link 2000. By habit, I would check the voltage at the regulator, and the amperage at the Link. Always looked fine to me.

Last week, after two grueling days of motoring, I happened to check the voltage at the Link 2000, and GUESS WHAT?!?. I was losing almost that same 1.2 V that Maine Sail described.

Just yesterday (really, honestly:naughty I bought a length of wire to finally install the battery sense wire to the bloody batteries, just like the instruction manual tells you to do.

I spent a week checking connections and confirming the integrity of my AO wiring, grounds, the shunt - you name it.

I finally came to this same conclusion, and all because: first I'd been lazy in the installation, and second, because while I have great instrumentation, I'd only been using the AO voltage display at the regulator and the amperage at the Link, not reading the voltage at the Link 2000 while the alternator was working - until last week when I thought "Houston, we have a problem!"

The battery sense wire goes in tomorrow.

Too bad there's not a "humble pie" emoticon!!!

Thanks, Maine Sail.

 

[jviss]

Datapoint

Just a data point on automotive regulator set-points. I just measured the voltage on my BMW X3, idling, and it's at 14.000 Volts. How's that for German precision! So, not 14.4V as some are. It moved up to 14.15 at 2500 RPM. Solid at 14.000 at idle, only jumping around by +/- 2 or 3 mV, and that could have been noise.

 

[Maine Sail]

Just a data point on automotive regulator set-points. I just measured the voltage on my BMW X3, idling, and it's at 14.000 Volts. How's that for German precision! So, not 14.4V as some are. It moved up to 14.15 at 2500 RPM. Solid at 14.000 at idle, only jumping around by +/- 2 or 3 mV, and that could have been noise.

Interesting data point but seems awfully low. Our M3 was 14.4v +/- about 0.3V... Were all accessories off?

 

[jviss]

Yes...

...just sitting there idling, daytime running lights, but everything else off, even the radio.