Generator, replace or not

My northern lights 5kw has died, I like to hear thoughts on replacement vs using the space for battery bank and sizable inverter? If I go the battery option where can I find information on what to buy and install?

Depends how is your boat set up? I need my genny to run the boat. A/C, electric stove, HWH etc.

Think about how you will keep the enlarged battery bank fed. Especially if staying in one place multiple days,meaning no alternator input. And calculate the loads you need to service, to see how much input you need.

A combination of a large solar array and wind generator to feed the batts may work. All that battery, plus a solar panel set up,and wind generator,will involve expense,so you need to do a cost comparison, new set up vs generator repair/replacement.

Personally, I`d renew the generator. I also have some useful solar but even a big solar system could have trouble with hungry items,like stoves.

What killed the 5kW? Very fixable machine in most cases.

You are looking at around $12K +/- to replace if it is relatively easy access. I would fix if possible. What happened?
Sure you can go battery/inverter but what are you going to charge the bank with? On my boat with a 8 cu ft refrigerator, one overnight at anchor sucks out about 120 Ah from the bank. Cruising at 1700 rpm will top up the bank in a few hours the next day. Now if you stay put a second night, you need something engine powered or solar to recharge the bank. Running the main in neutral for hours is a bad choice.

Don't know what kind of boat you have, but if most like it typically have gensets, I would discount yours about $10,000 in comparing it with other similar boats with gensets.


Listen to Ski's advice. Unless it was trashed by a salt water dunking or threw a rod or similar catastrophe, the NL's can often be rebuilt much cheaper than replacement and a whole lot less than $10,000.



David

As others have noted... unless you can reach out and shake hands with a connecting rod from the engine room, a rebuild would be the best course of action, IMHO.

Without more information on the failure, engine or generator end. Major failure such as engine block / crankshaft destroyed vs won’t start using excessive oil, it’s hard to give decent advice.

captDJ said:

My northern lights 5kw has died, I like to hear thoughts on replacement vs using the space for battery bank and sizable inverter? If I go the battery option where can I find information on what to buy and install?

Click to expand...

I have thought about what I would do if my NL5kw died, and it does look the solution includes bigger batteries and solar. But it also includes changing the heating system to hydronic so as to make hot water. Total = $not cheap.

So when my gen hydrolocked last summer (don't ask), the result was one of the valves becoming stuck open, and after 30 years, it was time to do a top-end overhaul. Head removed, machined, new valves, springs, seats, injectors, head bolts, glow plugs, gaskets/seals, injectors ++.

Total $1500, all labor mine except head work.


Ready for another 30 years

Thanks to all, seems to have had a stuck valve which the piston hit and broke the valve rail? Plus soot in the cooling system which could point to a cracked block, estimate was 3-5k to fix.
I was thinking about replacing my a/c with one that requires less amps that the inverter could power and replace the fridge with an ac/dc unit.
Another option would be to remove/install myself and have a shop rebuild.
Oh and it’s tucked in tight between the mains with a 16” square to access.

"Back of an envelop" estimate for running an AC unit or heat pump off an inverter. /Really/ rough numbers.

Really roughly, I approximate an AC unit or heat pump as having a wattage power requirement of a little more than 10% of its BTU rating. So, for example, I'd ballpark a 16,0000btu unit at 1600W + "a bit", so maybe 1700W.

1700W is doable by many common inverters. It doesn't leave much headroom, but it is clearly doable.

But, how much battery is required? 1700W @ 12V is about 140A. That's about as much energy as one can draw from a pair of 6V golf cart batteries (parallel for 12V) in an hour at about 75% discharge. Again, really rough.

So, again really roughly, one would need 2 golf cart batteries for each hour one wants to operate a 16000btu AC unit or heat pump for heating. Want to run it for 4 hours per day? You'll need about 8 batteries. 6 hours per day? 12 golf cart batteries.

Golf cart batteries cost $150/each. A box for each pair of batteries, probably costs $60, or $30/battery. Maybe another $20/battery in wire. $200/battery in all. $2,400 for the battery bank. Maybe another $500 for the inverter. With taxes, etc, probably right around $3,000 for the set up.

If you want half as much AC capacity, you can cut that in half, 50% more, multiply by 1.5. Run it for half as long per day, cut it in half. Twice as long per day, double it. You get the idea.

But...don't forget that you need to recharge those batteries. 12 batteries might need 1200 amp-hours @ 12V. If one could dump the whole of 2x60A alternators into them, that would be 10 hours to fully charge. But, the charging efficiency might be, in really rough numbers, 50%. That would be 20 hours to charge. Not at all reasonable.

What if we just charge them to 70%. Well, then we are discharging from 70% to 30%, using 40% of the battery capacity. Before we were using 70% of the battery capacity (100% - 30%). So, we need 70/40= 1.75x as many batteries -- 22 batteries and boxes. Wildly guessing as above, $5,250 in cost.

What about the charge time? Since batteries charge ore efficiently earlier on, charging to 70% probably only takes really roughly 15hrs. Upgrade from 60A alternators to 150+A alternators, and that is down to 6 hours.

Lets say we want to charge the batteries in just 4 hours. Anything more than that would be hard on the batteries. That would be 1200 amp-hours / 4 hours = 300 amps/hour. That probably means north of 2x 175A alternators -- basically the equivalent of a 4.2kw generator! Those might be $750/alternator. Maybe $1000/alternator after making other needed adjustments. We're up to $7,750 to do this without a generator -- and the need for batteries every few years. I'd think for $7,750 one can get a rebuilt generator installed.

Even if I introduce one friendly piece of reality -- the HVAC might only have a 60% duty cycle (compressor on 60% of the time, wildly guessing), this $7,750 is still just a little shy of $5,000.

These numbers are obviously very, very, very approximate and rough and compound a bunch of error. But, my point is this. It is easy to get enough inverter to run an AC unit, even a large one. But, it takes a huge amount of battery to run one for any length of time. And, that is a much bigger expense that needs to be repeated every few years as the batteries need replaced.

But, even with that, there is just no fast way to charge that much battery from that depleted a state to a near charged state on a daily basis underway. It just takes time.

It is very reasonable to operate without a generator. But, this does involve limiting long-running major loads like HVAC. Even short bursts of loads, like a few minutes of microwave can be fine. But tings like AC? Would need to be really limited.

You are not going to be able to supply an air conditioner compressor, fan and water pump with a battery/inverter setup for any useable length of time even with the main engine running. So your air would become a shore power only benefit. If you want air away from the dock, you will need a genny.

"On my boat with a 8 cu ft refrigerator, one overnight at anchor sucks out about 120 Ah from the bank."


Unless you only do it once in a year , or travel every day, surely a new efficient reefer might save currency?

captDJ said:

Thanks to all, seems to have had a stuck valve which the piston hit and broke the valve rail? Plus soot in the cooling system which could point to a cracked block, estimate was 3-5k to fix.
I was thinking about replacing my a/c with one that requires less amps that the inverter could power and replace the fridge with an ac/dc unit.
Another option would be to remove/install myself and have a shop rebuild.
Oh and it’s tucked in tight between the mains with a 16” square to access.

Click to expand...

If you do rebuild, make sure you figure out what caused the valve to fail. Salt water back up through a poorly designed exhaust system is probably the biggest cause.


And there is no way you can run a normal 16,000 btu A/C from batteries and an inverter for very long.


David

captDJ said:

Thanks to all, seems to have had a stuck valve which the piston hit and broke the valve rail? Plus soot in the cooling system which could point to a cracked block, estimate was 3-5k to fix.
I was thinking about replacing my a/c with one that requires less amps that the inverter could power and replace the fridge with an ac/dc unit.
Another option would be to remove/install myself and have a shop rebuild.
Oh and it’s tucked in tight between the mains with a 16” square to access.

Click to expand...

With a quote of $3 to 5 to fix, plus surprises, I could argue strong for a new one. There's new ones in the 5K range for way less than $10k. Then you have a new one.

You no longer need a genny for marine air conditioning. I brought this up to the northern lights dealer last week at the boat show. There are currently three major boat manufactures selling boats with dc systems that run solely off the battery bank. Average energy consumption is between 250 and 400 watts an hour for 16k btu. Depending what you use the genny for though its probably worth fixing. That unit weighs less than a set of 8ds and gives you the most options. Inverters, chargers, solar and lithium batteries combined with the new dc systems look to be the future solution but the price is still pretty high for consideration in a retrofit.

Wow, you are all awesome! After your kind advice I realize I need a generator to be happy away from shore power.
First I’ll remove and then assess new unit or rebuild? Good news is I just found the shop manual online so the process begins, thanks again for the great input.

If money is no object, lithium batteries totally change and arguably tip the equation. But $$$$$.

I believe it was water in fuel that took out the one cylinder, original generator died because of salt water through the coffee can exhaust (PO). I installed this one w/o a raycor (my fault) and I won’t let that be the case again, which ever goes back I will put a water filter on first, costly education.

cafesport said:

You no longer need a genny for marine air conditioning. I brought this up to the northern lights dealer last week at the boat show. There are currently three major boat manufactures selling boats with dc systems that run solely off the battery bank. Average energy consumption is between 250 and 400 watts an hour for 16k btu. Depending what you use the genny for though its probably worth fixing. That unit weighs less than a set of 8ds and gives you the most options. Inverters, chargers, solar and lithium batteries combined with the new dc systems look to be the future solution but the price is still pretty high for consideration in a retrofit.

Click to expand...

No. A 16,000 btu marine A/C system draws about 14 amps, raw water pump included. That is 1,700 watts. At a typical duty cycle of 33% which will be more like 100% on a hot sunny day, that is about 560 watts or 13,000 watt hours in 24 hours. It will take about 3,000 watts of solar to replace that on a sunny day and about 1,000 AHs of Li battery capacity or double that for AGM or FLAs to cover you at night, early morning and late afternoon when solar doesn't do much.


Like I said over on the electric boat thread: you need lots of batteries and more efficient (about 30-40% rather than the current 18%) solar panels to run A/C from batteries and solar power.


David

cafesport said:

Average energy consumption is between 250 and 400 watts an hour for 16k btu.

Click to expand...

I'm sorry, but the math just doesn't add up. 16k BTUs is equal to almost 4.7k watts. so to get by on 400 watts an hour, your air conditioner can only run about 5 minutes every hour -- and that's assuming nearly 100% efficiency.


Ain't no way you are going to get by in Miami with your A/C only running 5 minutes out of every hour!

Cafesport,

Can you by any chance point me to info on those units?

My thinking is that the 400W number might be an average across the whole day -- including morning and evening. In other words, a 16000btu unit would be about 400W at 25% duty cycle.

The unfortunate thing about expressing the load that way is that most of that usage will be during the hot parts of the day. So, using it all day at an "average" of 400W might be, in terms of energy, almost the same as using it for "only" a few hours a day, at the hottest times of the day.

The challenge with expressing the wattage that way is that it doesn't let one compute the energy drain for the afternoon, when you actually want to use it.

captDJ said:

My northern lights 5kw has died, I like to hear thoughts on replacement vs using the space for battery bank and sizable inverter? If I go the battery option where can I find information on what to buy and install?

<snip>

I was thinking about replacing my a/c with one that requires less amps that the inverter could power and replace the fridge with an ac/dc unit.

Click to expand...

With a degree in Electrical Engineering and an ABYC E-11 certification to boot (the latter is as valuable as the former), I have attacked this same question over and over again for about 30 years. I revisited it again last year in the context of LiFePo batteries and also Carbon Foam.

My (personal) conclusion: If you want to run air-conditioning, you must have a generator. Forget about trying to do it with solar/inverters/batteries/whatever.

You could try to 'replace your A/C unit with one that requires less amps', but you'd get less BTUs. Yes, A/C compressors and the motors that drive them have gotten somewhat more efficient over the last 2-3 decades, but the newer refrigerants are less efficient, so that has been a zero-sum-game.

I understand the desire to get rid of an internal-combustion engine and replace it with electro-chemical storage (batteries) and a bunch of silicon (inverter/charger) technologies...but if you actually sit down and do all the math and analyze all the costs (including maintenence), a diesel powered generator is still the best option.

Sometimes, the newer/sexier technology isn't actually 'better'.

Then again sometimes...it is. For example...the (somewhat) new 'rare-earth' magnet DC generators are amazing. With these beauties, the engine spins up (or down) to match the power demand. Under most conditions, the engine is spinning so slow you can't hear it.

The total packages are about 2/3rds the weight and use 1/2 the fuel of old-school fixed-rpm generators. Acquisition cost-per kW (including DC-DC converter) is ~20% higher than conventional AC generators, but TCO is substantially lower.

One (made-in-the-USA) manufacturer is Polar Power -- there are a number of others.

https://polarpower.com/products/dc-generators/#tab-id-1

I like the idea of DC. If starting with a clean sheet, a good design for a boat system could be drawn up. Especially getting away from 12v and going higher to limit amps in cabling.

But the rub shows up in a few points:

1. Safety, not many have been killed by 12V, but get much over 24V and up, and now you can get zapped. I have been bit by 32V when sweaty and it could have been bad. I am quite sloppy with 12V and am still kickin'.

2. Switching. I know contacts running DC become more problematic with higher volts. I don't really know the details (mech engr here), but when I worked in power plants and submarines there were differences with AC and DC switching in the higher voltages.

3. Incompatibility with off the shelf household type stuff. Forces you to either buy specific for DC, or run a large inverter to run AC loads. Like aircon.

4. Forces some sort of conversion when on shore power, depending on how much AC stuff you have and how much is DC.

I looked at that DC gennie, I guess I don't understand how it is regulated. Output is DC, but then is variable speed. As I understand permanent mag gennies (really a rectified alternator, right??) if the speed changes, so does the output volts. That is what is nice about a unit with slip rings or rotor/stator variable excitation. Reg changes exciter volts, output volts follow.

PM gennie can be used with fast switching inverter tech (portable Honda) to put together a decent AC waveform. But that is AC, this thing is DC.

Interesting stuff, though.

A neat (admittedly biased) white paper addressing some of your questions. I will be an early electric adopter on boats, it's right on the edge today. Still always will need diesel gen to cross an ocean. Though we should not make this thread into an elec boat debate, belongs in it's own.

https://polarpower.com/products/dc-alternators/ac-vs-dc/

PS: I thought 48V was fairly safe but at the limit. Am I wrong?

I spoke with this guy at the Miami boat show last week. Interesting stuff, seems to be a good quality product. If you use the generator budget for lithium batteries and electrical upgrades, it might work. No affiliation here, it seems this might be what the OP was looking for.

www.tmdmarine.com


Rafe

The 48V answer I rely on....

https://www.quora.com/What-is-the-safe-limit-of-DC-voltage-for-humans-to-touch

Personally I would go with a traditional generator whether you repair the current one or replace it with another new or used one. My reason is that you may be willing to deal with some unique setup if you go to sell the boat having a “standard” setup will be easier to sell than “unique”.

Ski in NC said:

I like the idea of DC. If starting with a clean sheet, a good design for a boat system could be drawn up. Especially getting away from 12v and going higher to limit amps in cabling.

But the rub shows up in a few points:

1. Safety, not many have been killed by 12V, but get much over 24V and up, and now you can get zapped. I have been bit by 32V when sweaty and it could have been bad. I am quite sloppy with 12V and am still kickin'.

2. Switching. I know contacts running DC become more problematic with higher volts. I don't really know the details (mech engr here), but when I worked in power plants and submarines there were differences with AC and DC switching in the higher voltages.

3. Incompatibility with off the shelf household type stuff. Forces you to either buy specific for DC, or run a large inverter to run AC loads. Like aircon.

4. Forces some sort of conversion when on shore power, depending on how much AC stuff you have and how much is DC.

I looked at that DC gennie, I guess I don't understand how it is regulated. Output is DC, but then is variable speed. As I understand permanent mag gennies (really a rectified alternator, right??) if the speed changes, so does the output volts. That is what is nice about a unit with slip rings or rotor/stator variable excitation. Reg changes exciter volts, output volts follow.

PM gennie can be used with fast switching inverter tech (portable Honda) to put together a decent AC waveform. But that is AC, this thing is DC.

Interesting stuff, though.

Click to expand...

Ski, I think you misunderstand.


The DC output of the generator is never used 'directly' by any device except the DC-to-AC converter (A.K.A. the common 'inverter') and (sometimes) a DC-to-DC converter.


If you are familiar with the newer Honda 1000i and 2000i portable generators (where the 'i' stands for 'inverter'), it is the same concept. These little generators produce a variable-voltage DC output which feeds an inverter, which is why they call them "inverter-generators".


https://www.consumerreports.org/inverter-generators/pros-and-cons-of-inverter-generators/


Now, in a standard 'oldschool' AC genset, the engine always has to spin at an RPM that produces >>exactly<< 60 Hz, so, for a 4-pole generator back-end this would be 1,800 rpm. If it's a 2-pole generator it would be 3,600 rpm. For european markets, 1,800 rpm/60Hz generators are spun more slowly to produce 50Hz at 1,500 rpm or 3,600 rpm 60 Hz generators are slowed down to 3,000 rpm. This generator produces alternating current by virtue of it's commutator-based design, and the current 'alternates' at a frequency dictated by the engine/armature rpm.


Bottom line, these generators produce a constant voltage and frequency, while the output >>current<< varies with load. The engine will be spinning at 100.00% of rated RPM even if you are only using 5% of the rated output power.

The new DC generators produce a constant current, while the DC output >>voltage<< varies with load. Because the alternating current (and it's frequency) is produced by the inverter's electronics (and not by the spin-speed of the armature), the new DC generators can spin at whatever rpm is 'right' for the load, this takes advantage of the torque curve of the engine. So....if the demand for power is only 5% of rated load, the engine will spin very slowly. Likewise, the engine will spin faster as more juice is needed.


There is absolutely no safety issue because (a) at any given power level, DC in intrinsically safer than AC -- remember Edison vs. Westinghouse? and (b) the higher voltage DC goes directly to the inverter and it doesn't connect to anything else in the boat.



Hope this helps...

Confusion

denverd0n said:

I'm sorry, but the math just doesn't add up. 16k BTUs is equal to almost 4.7k watts....

Click to expand...

No Denver, you misunderstand.

An air-conditioner (marine or otherwise) is a thermal >>pump<<, it is not a thermal energy source. In the case of a Marine A/C unit, what it does is to soak up heat from the cabin air and 'pump' that heat into to the water that flows across the condenser. The energy needed to 'pump' heat from one place to another is much lower than the energy needed to actually >>make<< heat.

This is hard for many to grasp -- it may be easier (though not technically correct) to think about a marine A/C unit as extracting "coldness" from the water and moving that into the cabin air.

A technically accurate way to understand this is to think about a 16K BTU A/C unit as being able to >>MOVE<< 16,000 British Thermal Units out of the cabin air and into the water (or the reverse, when in 'heat' mode).

Look at the actual energy consumed by a 16K A/C unit and you will see it is about 13 amperes at 120v which equals about 1.5kW, nowhere near 4.7kW.

Or...if you are really skeptical, feel the temperature of the water coming out of your A/C outlets and notice how much warmer that water is than what went in. The heat in that water is what was pumped out of your boat's cabin air.