WHAT IS A GOOD GENERATOR ??

[john61ct]

Originally Posted by Pizzazz

if you are an AC boat (cooking, watermaker, heating) use an AC generator. Keep the DC for small loads.

The context in which I brought this up is a 99.9% DC context, obviously focus is on efficient usage, avoiding AC mod-cons. That doesn't have to mean sacrificing comforts, just not being as wasteful as wealthy Americans are in S&B McMansions, more European / Japanese sensibilities.

Or glamping as opposed to scout-type camping.

I would never consider electric heat, except when load-dumping excess solar production to a HWS.

Cooking with electric, maybe 5 minutes a day on a microwave, otherwise solar or propane (but let's not derail on that please! )

Watermaking brings up a great idea, pulley driven unit off the same motor driving the alt(s).

Otherwise, the only significant load on the DC gen is charging the battery, ~5A when fridge compressor's running.

But with LFP requiring such short runtimes, maybe best to just stick to DC watermakers, apparently can get down below 2AH per gallon produced?

[a64pilot]

No, pure DC is steady. For instance you cannot transform DC.
AC power that is run through diodes is not really DC, it’s pulsed DC, you can run pulsed DC through a transformer. Old timey electronics used a vibrator to pulse DC so that it could be run through a transformer.

Assuming your primary function of a generator is to charge a LifePo battery bank, whether you generate AC or DC it’s not going to make much if any difference, reasoning is the banks acceptance rate will take if the gen is properly sized almost all of its output, so a DC generator isn’t going to be turned down to lower RPM as the banks acceptance rate tails off like a flooded LA bank will do. I can’t see any other advantage of a DC generator except for the ability to run at lower RPM for periods of reduced output.
Also a person that is attune to how a generator functions and who desires to minimize its run time is going to save up tasks that are energy intensive and do them during gen run times so it’s not going to run unloaded anyway.
For me that means charging batteries, making water, making ice, washing clothes and maybe heating some water for bathing. I keep my gen loaded between 15 and 25 amps the whole time it’s on.

So a DC generator makes AC power and converts it to DC I bet, maybe pulsed DC, while an AC generator makes AC power, that if your charging your bank you convert to DC, either way there are conversion losses? However I don’t believe these conversion losses are significant, if you lose 10% what does it matter?

[a64pilot]

If you weld with pure DC, it’s a smooth steady bacon frying sound and the magnetic field is smooth and steady.
Welding with an AC or a rectified DC machine the arc is staccato sound and feel and the magnetic field is obviously pulsed on and off very rapidly.

[Dockhead]

Originally Posted by a64pilot

.. . .However I don’t believe these conversion losses are significant, if you lose 10% what does it matter?

Yes. And because you convert power both ways on most boats, it comes out in the wash anyway. I agree with you -- I don't think it makes much difference.

The main thing I like about DC generators is the possibly of having a really, really simple one, which is really, really easy to fix.

That being said, my heavy duty AC generator is one of the most reliable pieces of gear on the boat. Never broken (knock on wood) in any way which I couldn't fix myself, in 8 years and thousands of hours of use, and those failures were exclusively banal diesel things -- fuel system, lift pump, heat exchanger.

[a64pilot]

Here is the thing.
An alternator is an AC generator however as it’s rectified to DC the Hz rate of its AC power is irrelevant so it can be run at different speeds.
A standard AC generator is a big alternator that the speed is maintained so that it outputs the correct Hz rate.

A difference is I believe a AC generator has a pmg or permanent magnet generator to make current for field excitation, where an automotive alternator use the automobiles battery to provide current for field excitation.

Th Wild card is of course the inverter / generator, it seems to combine the best attributes of both in one, the quality of AC made by a good one is apparently better than any standard AC generator, I don’t know why it’s not scalable to larger generators?

[john61ct]

Originally Posted by a64pilot

Assuming your primary function of a generator is to charge a LifePo battery bank

In the above use case, that is the only function. Assume minimum 600AH storage, likely double that or larger.

Originally Posted by a64pilot

I keep my gen loaded between 15 and 25 amps the whole time it’s on.

That must be @AC voltage? I'm talking DC here, @14V maybe 250A actual output as a minimum, with dual alts 500+.

Originally Posted by a64pilot

a DC generator isn’t going to be turned down to lower RPM as the banks acceptance rate tails off like a flooded LA bank will do. I can’t see any other advantage of a DC generator except for the ability to run at lower RPM for periods of reduced output.

Again, that may be a feature available from a sophisticated OTS unit, but for this case completely unnecessary, since as you point out the load is very constant.

As I said the biggest technical challenge, and it is not a big one, is getting the pulley ratio right. The only other one is cooling.

Given the high torque requirement at that constant load point, what is the lowest most fuel efficient rpm range for that engine?

Then, what is the rpm range for the alt(s) to output at 70-80% of rated maximum? Someone worried about a $3-400 alt may oversize a bit and stick to 50-60%.

Install pulleys sized accordingly, with top-notch serpentine belts.

A complete system shouldn't be more than $2K (at 500+A) although getting the first prototype done might be double that.

Replacement the power head, AKA new or reconditioning the OTS alts, is relatively cheap as chips, especially in less-developed locations.

Important to select the right engine, should be reliable and low maintenance.

[john61ct]

Originally Posted by a64pilot

the inverter / generator, it seems to combine the best attributes of both in one, the quality of AC made by a good one is apparently better than any standard AC generator, I don’t know why it’s not scalable to larger generators?

Sophisticated electronics are expensive, until produced in large quantities.

With lots of such gear going to unusually high voltages OR currents raises pricing exponentially.

[john61ct]

Originally Posted by Dockhead

The main thing I like about DC generators is the possibly of having a really, really simple one, which is really, really easy to fix.

Exactly.

For each of us, the day may come we need to get by in third-world conditions.

[newhaul]

Question; can I place a 150amp alternator on a volvo md2b and run efficiently? Or is that to big ?
Charging Fla 440ah bank Finnish with solar (400 watts) and or wind ( also 400 watts) .

[john61ct]

Figure 60-70A is the maximum actual load that bank will pull for more than 10-15 minutes.

Don't try it with single V belt, ideally serpentine if you ever upgrade to a higher CAR bank.

[kenbo]

Originally Posted by john61ct

Figure 60-70A is the maximum actual load that bank will pull for more than 10-15 minutes.

Don't try it with single V belt, ideally serpentine if you ever upgrade to a higher CAR bank.

John,

when you say serpentine belt do you mean flat, ribbed belt? I believe serpentine refers to the path the belt makes around the pulleys, minimum 3.

[john61ct]

I've heard 1 HP per 20A ? Elsewhere 30+, Obviously lot of variables involved.

Not least of which is that HP does not equate to torque, especially if you want to output high amps at low rpm

And note off your main engine, need good VR to control derating

And the ability to cut field current (Alt Off switch) at the helm, for when you need all the horses for propulsion.

[newhaul]

Originally Posted by john61ct

I've heard 1 HP per 20A ? Elsewhere 30+, Obviously lot of variables involved.

Not least of which is that HP does not equate to torque, especially if you want to output high amps at low rpm

And note off your main engine, need good VR to control derating

And the ability to cut field current (Alt Off switch) at the helm, for when you need all the horses for propulsion.

Ok I suppose I should have let everyone know what boat the motor is going in it's my defender. Came stock with atomic a4. Some had an md6 so about 12-15 horse stock. I'm installing an md2b at 23-25 hp. So have plenty of horses to run at hull speed and run alternator. But I'm going to have a pto setup for it ( like on riding lawn mower decks.)

[john61ct]

Originally Posted by kenbo

John,

when you say serpentine belt do you mean flat, ribbed belt? I believe serpentine refers to the path the belt makes around the pulleys, minimum 3.

Yes, handles higher torques than double V belts.

That's where I'd needing tech help, and obviously space is a critical issue for modding existing setups.

[kenbo]

Originally Posted by john61ct

Figure 60-70A is the maximum actual load that bank will pull for more than 10-15 minutes.

Don't try it with single V belt, ideally serpentine if you ever upgrade to a higher CAR bank.

I have a 460AH flooded bank and I have put 100-110 amps into that bank for over a half hour on several occasions. Depends on your depth of discharge and I admit I'm not a slave to the 50% DOD cutoff. I don't find it has as much bad effects as not fully charging them after every discharge cycle.