run a 1200w water heater with 900w Generator

[Franziska]

Btw. they make less powerful heating cartridges/elements for waterheaters.
Change it for a smaller one.
Disadvantage you need to run the genny longer.

Originally Posted by sgtPluck

Pardon me if this is a silly question, but I've never owned a portable generator until now.

If I run a 900w generator, then connect shore power cable and turn on my water heater (1200w element) will it just heat up more slowly or could it cause a problem?

[Cadence]

Originally Posted by mitiempo

Will not have to. Shore power not connected, just generator.

In that case the breaker in the gen, will trip. It's install a smaller element, if one can found for your water heater of get a larger generator. The third option is taking cold showers,
If you have a large enough inverter you could run the heater off of that while running the gen. through a charger to the batteries. It would eliminate some battery discharge.

[capn_billl]

Originally Posted by RaymondR

The correct solution here is to leave the electricity alone and get your local welder to make you a calorifier sleeve to fit in the exhaust of your genset. You'll also need a pump to circulate the hot water to the water heater tank. That way you can use the whole 800 watts to charge your batteries whilst the waste heat heats up your shower water. You'll double your return on the gas you are using.

What this guy said, except getting hot water from a portable air cooled generator is going to be difficult.

Better if you don't have a powerful enough onboard generator to run your boat's AC requirements (several Kilowatts), just put a heat exchanger on the engine.

[CarlF]

Again, a 240v 1200 watt heating element will only draw 300 watts when connected to 120v. I'm still not sure which heating element the OP has.

[RaymondR]

Originally Posted by capn_billl

What this guy said, except getting hot water from a portable air cooled generator is going to be difficult.

Better if you don't have a powerful enough onboard generator to run your boat's AC requirements (several Kilowatts), just put a heat exchanger on the engine.

A copper sleeve which slides into the exhaust with a water jacket around the outside and inlet and outlet hose tails. Hot exhaust gasses heat the water. and it is circulated through the tank with the circulation pump. Since it's going to be pressurized by the water system but does not have to pump against a head I'd use a glandless, magnetically coupled pump and will use a Bosch pump to circulate it and daylight switch it via my solar controller.

I am in the process of running 1/2" copper pipe around the outside of my solar panel farm, which I'll paint black, to solar heat my shower water.

[Liberta T48]

If I understand how you are planning to deploy, no...it won't work. I'm not a marine electrician/systems guy...I will tackle plumbing, carpentry, mechanical and just about anything else - EXCEPT electrical. For safety, I would consult a licensed electrician with marine experience.

[dady]

Originally Posted by Captain Bill

You will most likely fry the generator if it doesn't stall. It might not fry instantly but it probably will before you have hot water. I'm assuming 120v water heater, but if you replace the element with a 240v 1200 watt element it will only draw 600w at 120v. It will just take a while longer to get to the temp you want.

Amazing answer my friend! Use the ohm law and you can calculate anything
Best Regards

[JimmyDarci]

Consider buying the Honda 1200 generator AND the 1200 twin unit. One can carry the load but Honda allows you to combine these two units (1200+1200). You can power a small city on this configuration and the Honda’s are smart in that they sense overload better than most. No, I do not sell Honda, I do swear by the units, however. Added benefit is that you can take the units with you for home use or camping and the twin configuration allows each unit to be easily carried (I recall each unit at 48 lbs).

[searenity38]

I would strongly advise that you add
"Sailboat Electrics Simplified" by Don Casey to your boat library.

[dady]

If you follow this picture is enough
Best Regards

[sgtPluck]

Originally Posted by searenity38

I would strongly advise that you add
"Sailboat Electrics Simplified" by Don Casey to your boat library.

Haha, I DO have it back in storage in US, along with the Calder book and This Old Boat. Will have to re-read it. But it's so much easier to post dumb questions here and get quick answers (and some friendly abuse)


Thanks for all the responses, clearly this was a dumb question, I ain't gonna do it.

As you were.

--OP

[EngNate]

Originally Posted by Captain Bill

You will most likely fry the generator if it doesn't stall. It might not fry instantly but it probably will before you have hot water. I'm assuming 120v water heater, but if you replace the element with a 240v 1200 watt element it will only draw 600w at 120v. It will just take a while longer to get to the temp you want.

When a 240V heating element is run on 120V, power will be reduced by 75%, e.g. a 1200W element will produce 300W.

Why?: Watts = Volts x Amps, reducing voltage by half causes current to be reduced by half, half the volts x half the amps = 1/4 the watts.

[Pete7]

Originally Posted by RaymondR

A copper sleeve which slides into the exhaust with a water jacket around the outside and inlet and outlet hose tails. Hot exhaust gasses heat the water. and it is circulated through the tank with the circulation pump. Since it's going to be pressurized by the water system but does not have to pump against a head I'd use a glandless, magnetically coupled pump and will use a Bosch pump to circulate it and daylight switch it via my solar controller.

I am in the process of running 1/2" copper pipe around the outside of my solar panel farm, which I'll paint black, to solar heat my shower water.

Hmm, just be aware of this tragedy:

https://www.bbc.co.uk/news/uk-england-34810360

[noelex 77]

Originally Posted by Captain Bill

You will most likely fry the generator if it doesn't stall. It might not fry instantly but it probably will before you have hot water. I'm assuming 120v water heater, but if you replace the element with a 240v 1200 watt element it will only draw 600w at 120v. It will just take a while longer to get to the temp you want.

Originally Posted by dady

Amazing answer my friend! Use the ohm law and you can calculate anything
Best Regards

Amazing, but wrong .

A 1200w element at 240v will have a current of:
5 A

Therefore the resistance of the element is:
48 Ohms

At 120v this same resistance will have current of:
2.5 A

Therefore the heating produced has a wattage of:

2.5x120= 300w

Carl had the correct answer in post #34.

[pendragon]

Never heard such stupidity..
If you connect the shore power and your gen set together. The genset will blow up, or the shore power fuse will blow, as they will not be in phase with each other.