Battery bank charging

[CaptBud]

Can anyone explain why we charge DC battery banks using an AC generator which actually produces AC, operating at 1800 RPM for 60 cycle sine wave then run it through a Charger/Inverter unit which in turn supplies a DC current to the battery bank? When the propulsion engine is running it also uses an alternator to charge the battery bank while underway. Wouldn't it make more sense to operate a small diesel charging engine at low operating RPM turning a "DC Generator" to charge a "DC battery bank". Unless there are a lot of AC appliances onboard that need more power than can be drawn from an inverter there is really no need for an AC generating system.

 

[Bacchus]

Just my opinion but most gens are installed and sized to do much more than charge battys. In fact if just charging that is generally too light a load on a gen as they are recommended to run st / close to 50% load.
I think you are correct in that if charging is the only purpose there are more efficient ways of doing it.
I think the reason auto DC generators have given way to alternators is an economic & reliability one. Solid state diode rectifiers pretty simple and inexpensive and eliminate brushes and comutators.

 

[CarlF]

Until recently, batteries and inverters couldn't handle large AC loads like air conditioning - that's why most gensets are installed - not battery charging.

But you now now have an alternative. Niger Calder's Integral system use a 9kW DC alternator running off the engine. With a big Lithium bank you can get rid of the genset.

https://integrelsolutions.com

 

[kchace]

DC generators are very inefficient

 

[FF]

The small Hondas and other mfg have the right idea. The engine RPM set by the load , not a fixed RPM.

The throttle device from a welder could be adapted to any small motor to create the charge voltage desired.

The portable units are about 3 decades advanced from boat gensets.

For folks that want fast DC charging installing a good sized alternator 120A to 300A belted on the front of the current genset would require finding the HP available from the front of the engine from the engine MFG and purchasing a pulley for multiple belts.

A 3 or 4 stage Voltage regulator added would speed the charge process.

 

[ranger58sb]

Unless there are a lot of AC appliances onboard that need more power than can be drawn from an inverter there is really no need for an AC generating system.

Like a couple fridges, aircon, water heater, icemaker, a bazillion AC outlets (TV, stereo, laptops, etc.)... and an all-electric galley including cooktop, coffee maker, microwave/convection oven...

Yep, many will run on an inverter, maybe or maybe not all at the same time...

Battery charging can almost become just a small sideline...

-Chris

 

[tiltrider1]

Cars used to have DC generators now they have AC alternators.

 

[CaptBud]

Let me clarify my intent......the object of my post is to have a charging system that eliminates the high RPM fuel and noise pollution created by an AC gen set. A DC gen set would not have to operate at 1800RPM and its only function would be to pump its output directly into the battery bank. My desire is to be able to stay on the hook longer without having to "cruise" or operate an AC gen for long periods to fully charge the battery bank. Never discharge a battery bank lower than 50%, and to be totally honest I have never been able to "fully" charge the house bank unless I plug into shore power. A boat should not be full of AC equipment if the intention is to stay on the HOOK for more than a day or two just relaxing without "noise pollution" while being able to sustain a healthy battery bank.

 

[FlyWright]

Let me clarify my intent......the object of my post is to have a charging system that eliminates the high RPM fuel and noise pollution created by an AC gen set. A DC gen set would not have to operate at 1800RPM and its only function would be to pump its output directly into the battery bank. My desire is to be able to stay on the hook longer without having to "cruise" or operate an AC gen for long periods to fully charge the battery bank. Never discharge a battery bank lower than 50%, and to be totally honest I have never been able to "fully" charge the house bank unless I plug into shore power. A boat should not be full of AC equipment if the intention is to stay on the HOOK for more than a day or two just relaxing without "noise pollution" while being able to sustain a healthy battery bank.

Sounds like you might need solar.

 

[AusCan]

If you don't require air conditioning or an electric galley there is little need for a generator of any type. I run everything on 12V and although I have an inverter, it is rarely used.

A single good quality 250W solar panel and MMPT charger tops up the battery bank to 100% every day when I'm on the hook and running a fridge, freezer, lights, fans, chargers etc. It requires nothing to operate other than daylight.

I have zero desire for a generator which would give me less space, and more maintenance, cost, complexity and noise.

I don't have an icemaker, so for cocktails I have to keep a bag of ice in the freezer. I can live with that.

 

[GoneDiving]

Can anyone explain why we charge DC battery banks using an AC generator.

Because a boat's DC load is typically trivial when compared to its AC loads when the generator is running. eg battery charging while AC cooktops, watermaker or HWS are running.

Let me clarify my intent......the object of my post is to have a charging system that eliminates the high RPM fuel and noise pollution created by an AC gen set.

I'm doing the same but by replacing the Gensets with solar and battery bank. I'm fortunate in that I have a large single pitch roofline so can fit ~6kw of panels. A 840ah @ 48v house bank provides surge capacity and a small Honda-esque genset will provide emergency back up should the sun disappear for weeks at a time. I prefer generic, easy to source and repair components so went with an AC vs DC genset.

A DC generator could be used in place of the panels if most loads were DC. However, most of my loads will be AC (keen diver, electric galley, residential refrigeration, teenage kids etc)

I don't see a huge benefit of DC generators over AC. It's still going to be noisy and fuel consuming. Variable speed inverter AC generators are available, though only in smaller sizes.

Good luck

 

[ranger58sb]

A boat should not be full of AC equipment if the intention is to stay on the HOOK for more than a day or two just relaxing without "noise pollution" while being able to sustain a healthy battery bank.

To each his own, especially when supported by regional differences...

But 95°F days with about 90% humidity here on the Chesapeake in July and August isn't really all that comfortable at anchor inside with no AC (aircon) running. March and November can have their frigid moments, too.

So maybe "Your boat should not be full of AC equipment..." but ours certainly is.

-Chris

 

[nwboater]

Can anyone explain why we charge DC battery banks using an AC generator...]

Unless you require a generator to run air con or electric range, DC generators make good sense. I replaced the AC generator in my trawler with a 6hp Kubota diesel driving a 150 amp alternator. It was very efficient. I particularly liked how you could match RPM/amp output to battery bank need. For example, It would deliver 100-120 amps for bulk stage then throttle back to 40-60 amps for absorption. Only negative is that it was loud w/out an enclosure.

 

[FF]

"Only negative is that it was loud w/out an enclosure."


Put in your dink.

 

[Portage_Bay]

Can anyone explain why we charge DC battery banks using an AC generator...]

Unless you require a generator to run air con or electric range, DC generators make good sense. I replaced the AC generator in my trawler with a 6hp Kubota diesel driving a 150 amp alternator. It was very efficient. I particularly liked how you could match RPM/amp output to battery bank need. For example, It would deliver 100-120 amps for bulk stage then throttle back to 40-60 amps for absorption. Only negative is that it was loud w/out an enclosure.

Was your DC gen an off the shelf buy it and install it unit? Or did you engineer and build it yourself?

My reason for asking is I have a dying AC gen and not a lot of need for AC. My AC loads can easily be handled by an inverter as they are on the hook.

 

[FF]

"Was your DC gen an off the shelf buy it and install it unit? Or did you engineer and build it yourself?

50DN™ High Output Heavy Duty Brushless Alternator | Delco ...

Almost any alternator output you desire is available at the local bus repair or scrap yard. 12V? 24V? 200A to 350A .

Stop by in FL and I will give you a 12V one.Too heavy to ship.

 

[Portage_Bay]

"Was your DC gen an off the shelf buy it and install it unit? Or did you engineer and build it yourself?

50DN™ High Output Heavy Duty Brushless Alternator | Delco ...

Almost any alternator output you desire is available at the local bus repair or scrap yard. 12V? 24V? 200A to 350A .

Stop by in FL and I will give you a 12V one.Too heavy to ship.

A generous offer FF. But I'll pass. I'm about as far away from Florida as I can get and stay in the continental US.

 

[ghost]

I put in a dc generator quite a few years ago. Single cylinder Kubota with 200 amp alternator. I wanted a small quiet easy way to maximize my charge cycle while minimizing charge time. The results were mixed. Biggest issue was that it was loud. I sound insulated my lazarette where it lives, and that helped but even with a water lift muffler I found the exhaust noise was not just loud but also had a sort of annoying tone. It did provide a nice large charge current. It also required to be manually started, which was a pain. I actually engineered an automatic start/stop/monitor device using an Arduino controller, but it still sits on a breadboard somewhere needing an enclosure and soldering... putting the whole dc gen together was fun, but assembling a pile of parts would be annoying for most folks. I wouldn’t recommend it unless you have a real reason. Converting ac to dc etc is no big deal, I think we get too hung up on it in many situations.

Since then I found a Northern Lights 5kw with sound shield. That now sits next to the dc gen and I put in underwater exhaust and you can stand next to the boat and barely hear it.

So theoretically I can run both or either now. For the fastest charge while also heating water, making ice, frig/freeze on high I should run both. I almost never do. The whole reason for minimizing charge cycle time was to enjoy the quiet. So now I pretty much just run the Northern Lights. Yeah, it will run a little longer, but who cares, it’s really quiet. So in the end, while I like having the capability, the reality was that the biggest problem I was actually trying to solve was sound. After maybe 3-4 days straight on anchor, I might cycle the dc gen, maybe.

Victron used to have a white paper about 10-15 years ago that laid out their vision before solar prices came down. They had a dc gen as a cornerstone to their vision, so I kind of went down that road as part of their vision experiment. While I have not yet added solar, I think that should be a component to most people’s game plan. I’ll add it when I’ve added a Bimini to create an intentioned location for the solar.

 

[GoneDiving]

So theoretically I can run both or either now. For the fastest charge while also heating water, making ice, frig/freeze on high I should run both. I almost never do. The whole reason for minimizing charge cycle time was to enjoy the quiet. So now I pretty much just run the Northern Lights. Yeah, it will run a little longer, but who cares, it’s really quiet. So in the end, while I like having the capability, the reality was that the biggest problem I was actually trying to solve was sound. After maybe 3-4 days straight on anchor, I might cycle the dc gen, maybe.

My genset is pretty obnoxious not only because of the dB readings but also because of the drone and vibration it sets up throughout the vessel. I realise newer models are much better. However, for the same cost I can build a substantial solar generator and make much better use off the fuel, space and maintenance time. It will also generate power even while I'm not on the vessel. No more boarding 2 days early to turn on fridges, HWS etc.

 

[firehoser75]

CaptBud,
If your goal is to be able to stay on the hook longer, not "murder" your batteries by not fully recharging them often enough, and avoid the loud, long run times needed by an A/C generator, then solar is definitely the way to go.
I installed 2 x 285 watt panels, flat on the roof of my pilothouse. My house bank consists of 6 golf cart batteries for a capacity of just over 600 amp/hrs. My energy use is almost 100% 12 Volt and consists of fridge/freezer combo (8 Cubic foot RV style), separate Engel freezer, LED lights, AIS runs continuously for anchor alarm, and various smaller loads like recharging cell phone and other devices.
Throughout the late spring to early fall, we reach a full 100% charge (which is very good for battery longevity) by 1-2 PM most days. The times we don't are due to heavy fog or very heavy cloud cover. On those days, I run the generator for about 1 hour to top up (bulk only) the battery bank and heat the water.
Solar is silent, works any time the sun is up, and requires very little maintenance, and is one of the few methods that will get your bank totally recharged to 100% without lengthy run times of either the engine or gen set. (or marina plugin).

Solar sounds like it is "just what the doctor ordered" for your wants.

 

[FF]

One advantage to using a DC gen set is IF the inverter is large enough power the AC loads simply installing the same size DC power source on the main engine gives a superb cruising generator .

No worries about an underway engine RPM change , and the system not providing 60 CPS .

 

[SteveK]

Tom, Can you estimate on the hook time the panels extend the battery use before a recharge is needed. Looking for a return on investment.
For instance if my house bank now lasts 3 days, do the 2 panels you have add a day or more?

 

[Capt Ray]

Someday someone will come up with a quiet way to make DC from panels that get energy from the sun.

 

[SteveK]

Someday someone will come up with a quiet way to make DC from panels that get energy from the sun.

I am guessing Captain Obvious was already taken?

 

[IfItsWorthDoing]

Re. Integrel system

FWIW, I checked with them as I was hoping to use their kit but was advised my 20hp Diesel engine would be too small to mount even the Integrel Lite on - they work with engines of 40hp upwards only ...

 

[koliver]

Tom, Can you estimate on the hook time the panels extend the battery use before a recharge is needed. Looking for a return on investment.
For instance if my house bank now lasts 3 days, do the 2 panels you have add a day or more?

Since Tom hasn't answered, I will.

My system is a pair of 160watt panels. When on the hook I lift them up from vertical to horizontal, but there is still some shading of one or the other, from the Bimini or the mast and radar. Tom has more wattage and less shading.
My controller is the cheaper one, Tom has MPPT, I think, as he recommends that kind.

While on the hook, I run a fridge and a freezer, and everything else in the boat is DC too.

My wattage is more than I need to keep the batteries up all summer long, so it isn't a mere extension of the number of days between recharges at the dock, it is an elimination of the need to plug in, altogether.

If I ran an AC fridge I couldn't get away with the system that I have, as the loads would be too much.

Tom's system is bigger and better and his loads are likely little different than mine.

 

[SteveK]

Thanks Keith
I have a DC fridge, use AC from inverter for cell phone, computer, toaster, coffee. The rest is lights, flush, winch, cooler (heavy draw) etc, the usual. I have done 3-5 days before batteries want to be charged at 11.5V. If I start the engine the alt pegs at 60 amp and continues at about 40. That replaces 40 amp per hour running.

I am having trouble understanding the output of these panels. 100 watts are anywhere from 6-8 amps. With a 5 hour sun window that is 30-40 amp hrs.

Perhaps if asked like this,
If I use 100 amps, will a 300 watt panel charge at ~20 amp per hour average for 5 hours to refill the battery.

 

[SteveK]

Just found this link, it has a calculator to determine what I need for panels to meet my needs

 

[koliver]

Thanks Keith
I have a DC fridge, use AC from inverter for cell phone, computer, toaster, coffee. The rest is lights, flush, winch, cooler (heavy draw) etc, the usual. I have done 3-5 days before batteries want to be charged at 11.5V. If I start the engine the alt pegs at 60 amp and continues at about 40. That replaces 40 amp per hour running.

I am having trouble understanding the output of these panels. 100 watts are anywhere from 6-8 amps. With a 5 hour sun window that is 30-40 amp hrs.

Perhaps if asked like this,
If I use 100 amps, will a 300 watt panel charge at ~20 amp per hour average for 5 hours to refill the battery.

Mine are rated at 19amps. That will only happen in direct, bright sunlight, and to maintain that amperage you will need to be adjusting the aim frequently. I solved the "what will be enough" problem by putting on a pair of 160w panels, to be kept vertical most of the time, in the theory that my loads will be satisfied by a single 160 watt panel. So far, the pair are working out well.

 

[chrisjbell]

Saw a few people mention putting together something themselves but I looked at a boat once that had a small diesel DC generator on it - pretty quiet, really low fuel usage. Something like: this one ... there are other manufacturers, this was just one of the first that popped up for me