Run the water heater from the inverter?

[Trawlerman]

Assuming that your alternator is current limited to no damage itself, you should have no problem running as you indicated. While it is true that you will experience a net loss of power from your battery bank while the tank is heating, the element thermostat will cycle off once the temperature is met. I assume you will not actually be using hot water for significant periods of time, so there will be lots of time for the alternator to catch up with the battery charge. Remember, the average watt-hours required is much less than the instantaneous watt-hours while the element is active.

 

[richvanf]

We often run the boat for 4-5 hours at a time, and it's not unusual to run it for 8 or more. But in the next 30 days or so, we may be looking at running it non-stop for about 140 hours, to cover the distance from the USVI to FL. (If the Bahamas don't loosen their restrictions, we have to go around them.)

I don't want to run the generator more than I have to, and everything that we'll need for a long passage like that is either DC, or runs off the inverter. Except the watermaker and the water heater. I expect to run the generator and watermaker for about an hour every other day, which will heat up some water, but in between, with the main engine running and charging the house bank, what about running the water heater from the inverter?

I would turn it on only once the house bank is fully charged, but then just leave it on all the time, so as it draws power from the house bank, the alternator will keep the house bank topped up.

Inverter: Magnum 3000 watt model.
Water heater: Seaward S1900E - 1500 watts, 120 volts.
ME alternator: Balmar 205 amp
House bank - 760 amp hours (8 GC batteries, not yet 3 years old)

The amp calculators I find online refer to something called the Power Factor that's necessary to calculate amps, and from what I can tell, a resistive load like a water heater is 1.0, or very close to it. Assuming 0.9 for the Power Factor, the water heater will draw about 14A AC, or 140A DC.

Thanks for any input. (Except for any input like "just go through the Bahamas - they'll never know!". Not doing that.)

Note that 760 AH is at the 20-Hour rate. Discharge time is not linear; the battery efficiency drops as the load increases. As long as the generator is running when the water heater is, there's not a problem. If you're interested I can give you the equation for the discharge time for GC batteries.

 

[mvweebles]

So rather than rely on opinion and off-cuff, I ran a similar Excel model to what I did to size my solar array for off-grid (XLS files are not permitted attachments, so JPG is attached). In short, I came up with an energy usage profile for an underway boat of about 45A/hr on average. This accounts for A/P, multiple MFDs, running lights, etc.

To the OP: no problem. Have a nice trip. You don't need to do a thing, and you don't need to worry about running your water heater.

- Peak load on Inverter w/Water Heater running: 2200W, or under 75%
- Average demand on Alternator is 42%. Assumes Water Heater cycles on 20% of the time which is likely an overly safe assumption in your climate
- Peak demand on Alternator is right at 160A, which is at the 80% threshold. What this really means is your batteries will rarely be used as a buffer.

Personally, using the Balmar Alternator in a manner that is well within its design specs sounds like a much better idea than putting an extra 150 hours on a generator (with a TCO of around $4.50-$5.00 per hour of operation).

 

[BrianSmith]

I fail to see the problem. A generator on board should be operational and if its operational there should be no restrictions in using it. To heat up water from your house bank via the inverter makes no sense at all. Your batteries are your safety in case you develop a problem with power generation on board. That happens often enough. Dont sacrifice that because you are afraid of running the generator. If you have a generator problem, just have it fixed. Good luck.

It's not a problem, and I don't believe it was presented that way. The generator works great, and I run it almost every day to make water, heat water, and top up the batteries. But in this particular situation (running 6 days non-stop), with the main engine running all the time and with a big alternator, I was just exploring the possibility of heating water w/o running the generator. No point burning diesel if I don't have to. Waste not, want not.

 

[BrianSmith]

Ok I wil throw in my 2 Euro cents

we have 2 hot water heaters the original , which is electric and engine cooling
the other is diesel continuous hot water
Both are. run from the batteries, and having a victron inverter, I have it programmed to automatically turn on the generator when the SOC of the batteries falls below 70%

Now how much energy do you need to heat up your 20 gallon
1 gallon is 8.3 Lbs
you want it at 120F. so lets say the cold water is 55F, so the delta is 65
the heat capacity f water is 1BTU/1F
the heat needed. is 20 * 8.3 *(120-55) *1. = 10,790 btu

which translates into 3.2 Kwh
add some losses ..so to heat the whole tank you need about 4KWH

so about 2 1/2 hrs to fully get it warm @ 1500 watt =
@12 V = 125 amps. (333 amp hr)
and @24V 63 amps. (160 amp hrs)

so now you can see it is not that difficult...

always look to the numbers.
you have a 200 amp alternator so I don't see any issue...

That's excellent! Thanks for laying it out so clearly! I'm still trying to wrap my head around all the variables in any electric computation.

BTW, the water is about 80 F, so there's way less heating to be done. Makes the math even better!

 

[BrianSmith]

This morning the Bahamas opened for transit. No stopping. Check on line.

Not true, unless you have information since this release from their Ministry of Transport on April 10, saying "No boats shall enter Bahamian Waters for whatsoever purpose until further notice, without prior written consent of the Competent Authority pursuant to Par. (15) hereof." Paragraph 15 tells you how to request permission, which I submitted as soon as I could after learning of this, and I've heard nothing back, nor do I expect to.

The confusion seems to be that they're allowing foreign vessels that are already in the Bahamas the freedom to leave, which they didn't have before this. But no new entries.

https://blog.bahamasmarinas.com/202...tocols-for-boating-in-the-bahamas-april-2020/ (scroll to the bottom to read the actual Release from the Bahamas).

 

[BrianSmith]

Why not just buy a 5 gallon solar shower for $25? Or if you need more than five gallons of water, buy two or three solar showers. Then replace your Seaward water heater to a hybrid version when you get back to Florida.

I have one already. Where do you propose we go to take the showers? We use the solar shower now to take showers on the swim platform, but I sure as heck am not going to let any of my crew on the swim platform while we're underway.

 

[BrianSmith]

Along the lines of some of these suggestions that obviously didn't understand the actual question, here is mine: Buy a new boat!

Thank you!

 

[BrianSmith]

So rather than rely on opinion and off-cuff, I ran a similar Excel model to what I did to size my solar array for off-grid (XLS files are not permitted attachments, so JPG is attached). In short, I came up with an energy usage profile for an underway boat of about 45A/hr on average. This accounts for A/P, multiple MFDs, running lights, etc.

To the OP: no problem. Have a nice trip. You don't need to do a thing, and you don't need to worry about running your water heater.

- Peak load on Inverter w/Water Heater running: 2200W, or under 75%
- Average demand on Alternator is 42%. Assumes Water Heater cycles on 20% of the time which is likely an overly safe assumption in your climate
- Peak demand on Alternator is right at 160A, which is at the 80% threshold. What this really means is your batteries will rarely be used as a buffer.

Personally, using the Balmar Alternator in a manner that is well within its design specs sounds like a much better idea than putting an extra 150 hours on a generator (with a TCO of around $4.50-$5.00 per hour of operation).

View attachment 101671

Excellent! Thank you!

 

[mvweebles]

Not true, unless you have information since this release from their Ministry of Transport on April 10, saying "No boats shall enter Bahamian Waters for whatsoever purpose until further notice

Why not go between Bahamas and Cuba? If you're not stopping anyway, looks like it's barely a diversion to stay south of the Bahamas' waters.

Curious minds....

Peter

 

[BrianSmith]

Why not go between Bahamas and Cuba? If you're not stopping anyway, looks like it's barely a diversion to stay south of the Bahamas' waters.

Curious minds....

Peter

Because I don't like the idea of 1000nm in open ocean, with no protection from wind and swell, and nowhere close to tuck in if we need to for some reason. (Engine trouble, medical emergency, unexpected bad weather.) Cutting across the Bahamas (for which we now have permission) gives us a lot of options for almost 1/2 the trip, and sets us up for an easy 1/2 day run to S. Florida from Bimini at the end. We also now have permission to make one marina stop, so we'll spend a night at Staniel Cay Yacht Club four days into the trip, for a nice break.

 

[High Wire]

I don't think you will have any problem with what you plan. Running the WH while the engine is running makes sense because you have the large alt. You will be on a long cruise so batteries will get topped off and stay there. If you get stuck at anchor somewhere due to weather, Plan B -Run the Genny. It only takes an hour of runtime to heat up the tank from cold. The tank will hold its heat fairly well.
FWIW, our 20 gal Raritan WH has an engine heat coil. By the 3rd day on the hook it might need to be powered for an hour of battery charging.

Enjoy your trip.

 

[OldDan1943]

Interesting the BH Govt permission for you to pass through their waters, take on fuel and maybe stop for one night, without going to customs. Of course, you must wear the quarantine flag and not step ashore. Can you order stores for delivery at the fuel dock>

Do you have that in writing?

 

[BrianSmith]

Interesting the BH Govt permission for you to pass through their waters, take on fuel and maybe stop for one night, without going to customs. Of course, you must wear the quarantine flag and not step ashore. Can you order stores for delivery at the fuel dock>

Do you have that in writing?

Yep. From the Bahamas Maritime Authority. We will clear customs at Staniel, but not leave the boat. We can get fuel if we want, and take-out from the restaurant, and two grocery stores will deliver stuff. We're very pleased that they're granting this permission when asked properly.