Dual alternator and oversize alternator success (or failure) stories

[S/V Alchemy]

Originally Posted by Jammer

I'm trying to think through alternatives based around a bank of 8 L16s, roughly 1200 Ah at 24 volts; C/5 would put me at 240 amps.

This got my attention. I have a bank of six L-16s, about 1185 Ah at 12VDC and I'm looking at a Mark Grasser alt for my Beta 60. But I also have a double PTO and could throw a couple of 90 amp alts of the standard "small" case on the engine easily enough and have a belt-and-suspenders approach. Still researching...

[john61ct]

Originally Posted by a64pilot

charging generator that could output serious amps as in hundreds or less cause it's variable. turn it way up at anchor to charge that LFP bank and put a good load on the motor, and turn it down when motoring so as to not overload the motor

No need for that function to be done mechanically, with an alt, a derating VR can do that, turn down amps output while holding V setpoins constant.

The NOS ex-Hummer 24V 400-570A units regularly go for under $500 delivered on eBay. Heavy though, and will use 20-30HP by themselves pumping out that 15kW

Not nearly as elegant as Eco-tech, but you did say Monster.

[Jammer]

Originally Posted by john61ct

Alts just need an off switch for field current, no significant power taken unloaded.

I think he was posting about permanent magnet alternators, which lack the convenient "off" feature as there is no field.

[RaymondR]

Originally Posted by Jammer

larger pulley = higher belt speed = less force for same amount of HP


HP = force x distance / time


Larger pulley, more distance less force for same HP

Yep, went through all this with a 3GM30 and finally decided that the best way to do it was with a jackshaft to the back of the engine where there was lots of room above the gearbox to fit the alternator.

The side load issue can also be mitigated by using a small toothed belt fitted in front of the crankshaft pulley driving a big pulley on the jackshaft then reverse the process at the aft end where there is plenty of room to fit a big roller bearing to take the side loadings. I was also going to belt drive some other stuff off the back end of the jackshaft and there was plenty of room back there to fit it.

[DeepFrz]

Jammer, 8 Trojan L16s would give you 870 ah at 24v.

[briblack]

We fairly recently upsized our alternator capacity on our 46' center cockpit. It has a 4JH2-TE Yanmar, and had an old 100 amp Balmar for the house bank, and the stock 55 amp Hitachi for the start. We moved the Balmar to where the Hitachi had been, and installed a new 200 amp 94-series Balmar on the stbd side. With a Balmar regulator to control both, and Blue Sea Systems relay to interconnect so both. The house bank is 7 Fireflies, so acceptance is not a limitation. We've seen 250 amps into the batteries, if they're discharged enough. It's been pretty successful, and a good backup to our 1000 watts of solar. A limitation is that the batteries can heat up, particularly in the tropics. Got to have temperature sensing on everything.

[S/V Alchemy]

Originally Posted by Jammer

Thinking outside the box.


Here's the vision.

1. On a mono, it is not possible to install enough solar panels to meet electrical needs, at least not in northern latitudes, not with a below-deck autopilot, not without hippie-like conservation measures. Not without compromising windage, storm readiness, and appearance. Therefore, some sort of generator onboard is a necessary evil.
2. All sizes of DC alternator driven by the propulsion engine are smaller, lighter, and cheaper than gensets of equivalent capacity.
3. With today's hybrid inverter-charger technology, there are no serious tradeoffs in converting between DC and AC power.
4. Ditching the propane system entirely provides savings of cost, space, and weight that are greater than the incremental cost, space, and weight penalty of the necessary compensatory upsizing of the electrical system.
5. With an electric galley I arrive at a daily power budget of 4-5 kwh. With reasonable reserves this leads me to a FLA bank of 24 kwh (12 L16s), which at C/5 will accept a charge of 4.8 kw or, at 24 volts, 200 amps. This will conveniently allow sufficient charging with an hour of engine time assuming no solar; a modest amount of solar (600 watts in 4 panels of 150w each on the aft lifelines x 5 hour average = 3kwh per day) does reduce this to a twice-a-week thing.
6. Sizing is also driven by occasional needs to run the air conditioning on the hook or a dive compressor. Either of this is around 2kw or a little more (I have a nice 2cfm compressor I plan to move to a future boat)
7. Wind and water generators, despite many years of serious engineering effort by talented people, remain fiddly technologies of last resort

So, I'm exploring, on paper, the idea that ditching a genset (and the propane gear) in favor of the best available DC generators driven by the propulsion engine puts me ahead in cost, space, weight, convenience, reliability, etc. I'm challenging the received wisdom. I may back off and accept the received wisdom at some point, but I'm not there yet.

Wow. I have four solar panels (540W), a 400W wind gen, and will either go one big (200 amp) Mark Grasser alt, or two 100 amps (I have a double PTO) off a Beta Marine 60. This is to feed a mereL-16s (1185 Ah). Main draws will be a 12 VDC watermaker (probably a Cruise RO) and a NovaKool reefer with the BD50 Danfoss compressor. Full complement of LEDs, and the main draw will be the 4 KW radar, I would think. There's a robust autopilot on order, but under sail will be under vane. "Movie night" will depend on state of charge; otherwise, it's reading the classics...on paper. I find it's easier to keep stuff manual (foot pumps, LAVAC head) than to mix too much electricity and the sea, although an electric galley has some appeal.


It's interesting you've plotted this out, however.

[Rumpi]

Ok, I see people trade weight and convenience for efficiency.
My ideal setup for extended cruising would be PM starter/generator with clutch on the front end coupled with a lithium bank, plus a mechanical spring starter for black starts. Solar sized to only cover 24h of typical consumption.

[a64pilot]

You’ll get considerably more power from two 100 amp alternators than one 200.
I’d keep the Watermaker AC and run it off of an inverter when your motoring as much as possible and save your bank.
Your biggest consumer (excepting the Watermaker of course) will be your fridge, cause it runs always, the Radar not so much, plus modern Radar pulls very little current.
I think the majority of the power my 4G Radar uses is to spin it.

[model 10]

You could use an air gun, dive tank and starting fluid to start an engine in a black situation.

[a64pilot]

If you had decompression levers, yes.
I keep thinking that my Milwaukee angle drill that I use as a winch handle may have a shot too, but I don’t have decompression levers.
Maybe if I backed up the crank and it had a running start?
I will not use ether, too afraid of kickback

My plan if as ever get that stupid is to either crack open a beer and wait for Solar to do its thing, or pull on the starter rope on the little Honda, and let it do its thing.

[Rumpi]

My thinking is that with a starter/generator on the engine the normal electrical starter is not needed anymore. In it's place one can put a spring starter in case the drive electronics fail, or the clutch fails, or the batteries fail. It's standard procedure on lifeboats to have them and getting one from the shipbreakers is not that expensive.

On the other hand the whole setup is only viable if the diesel is small enough to ensure the PM generator loads it up properly and the batteries can accept the load. If the boat is big enough to have a motor over 40HP you either need a monster battery bank or a chemistry capable of beeing charged over 1C. Otherwise getting a small generator is the better option. After all how many boats need a generator over 20kW to charge their batteries?

[model 10]

Problems with low amps for a start can be overcome by putting any number of dead batts in series. 20v will make the starter sing. There is no damage if you don't have the rest of the boat connected too.

[Emmalina]

Funny thing is I want to remove my genset 8kw as all it was really used for was AC and a big fridge compressor. Now have 12v compressors and don't use AC (shock horror for our US friends) so if I take it out can put more batteries and a small petrol frame honda driving a couple of alternators as back up !

[john61ct]

Are there any "PM generator 101" resources, plain-Joe installed commercial products in the 2 to say 6kW range, not mor expensive than the regular sort?

Or are these just science project ideas at the low end?

What is the main practical advantage over high-end but standard type alternators in generating high amp DC?