Small Genset - Can it mate to shore power port?

Davidasailor26 · Mar 26, 2022

sunlover said:
1st Question: I'm thinking of getting a small genset for emergencies. 1000Watt. Can I mate to the shore power port? My concern is the mismatch between the 120V to 12V DC converter as the converter is sized to pull more amps off the shore power then the genset can produce. Do I need to mate the genset to an appropriately small converter for charging batteries?

2nd Question: This is an inverter generator. Has anybody opened these up, (voided the warranty), and used the DC power directly?

You can get a 15 amp to 30 amp AC converter so you can connect the AC output to your shore power cord. The 1000 watts on the AC side should be adequate for running your shore powered battery charger.

The DC output, in addition to likely being very low amperage, is probably not regulated at a good voltage for battery charging. You need something that can put out many amps at about 14.3 volts (depending on battery temperature and chemistry), then cut back to the mid-13 volts when the batteries are charged. Battery chargers are designed to do that, and regulated cigarette lighter style outputs are not. Internally within the generator the DC side before the inverter is probably not at a usable voltage either.

Edit to add: As always, consider the safety implications of a gas powered portable generator, including CO risks from the exhaust and station wagon effect.

Tom J · Mar 26, 2022

Sorry, but I am a little confused here. Why would you open up the inverter generator? The AC is supplied at the outlet of the generator. By opening up the gen, you might get access to the DC produced but not in a usable form.
You can always use a shore power plug adapter to run an extension cord from the gen. Depending on the state of charge of your batteries, the battery charger (converter?) might want to draw more than the little genset can deliver, though.
For my money, about 300w of solar panels would provide a steady state of charge and be quieter and more convenient to boot.

Ralph Johnstone · Mar 26, 2022

sunlover said:
Can I mate to the shore power port?

Unless you have a fail safe means of tying the generator into your shore power connection, you run the risk of connecting you generator to your utility power provider. Both sources of power will be out of phase with each other. This will result in your generator instantly rotating on its axis to get into phase with the utility power resulting in injury or worse to any bystander. The final condition of the generator I'll leave to your imagination.

Davidasailor26 · Mar 26, 2022

Ralph Johnstone said:
Unless you have a fail safe means of tying the generator into your shore power connection, you run the risk of connecting you generator to your utility power provider. Both sources of power will be out of phase with each other. This will result in your generator instantly rotating on its axis to get into phase with the utility power resulting in injury or worse to any bystander. The final condition of the generator I'll leave to your imagination.

I assumed he meant to connect the generator to the shore power inlet when actual shore power was otherwise unavailable. Concur that you certainly don’t want the generator powering a circuit that’s also powered by shore power. That would be a bad day.

jviss · Mar 26, 2022

Ralph Johnstone said:
Unless you have a fail safe means of tying the generator into your shore power connection, you run the risk of connecting you generator to your utility power provider. Both sources of power will be out of phase with each other. This will result in your generator instantly rotating on its axis to get into phase with the utility power resulting in injury or worse to any bystander. The final condition of the generator I'll leave to your imagination.

Ralph, what are you talking about? He's only asking if he connect the generator output to the shore power inlet of his boat, not back-feed the grid!

To answer the OP's question, yes, you can do this. If you try to pull more than 1kW you won't be able to, and the generator will brown out or cut off. No problem.

Meanwhile, there should be plenty of power to charge your batteries.

dlochner · Mar 26, 2022

Are you asking about a real generator or one those cheap “generator inverters“ that have recently sown up all over the internet?

dlochner · Mar 26, 2022

sunlover said:
Yes, cheap Home Depot propane Genset as a backup.

Please share a link to the product. It may not be hat you want.

Davidasailor26 · Mar 26, 2022

What size is your battery charger? If your objective is a way to charge house batteries I’d probably just rely on my alternator to augment the solar, assuming you have a dedicated start battery. If you don’t then I think you’re better off with a jump pack for emergencies than porting that generator around. At 700 running watts it’s probably enough to run your battery charger. If you have a 20 amp battery charger you’re probably going to be running the generator at about 40% load.

dlochner · Mar 26, 2022

sunlover said:
btw, I did invest in a 350 watt Renogy solar system, so this is just as a security blanket.

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If you read the specs, this is only a 700 watt generator, or about 8 amps (700watts/12v =~8 amps). That is not very much power.

Realistically, there are no quick and dirty solutions to provide enough electrical power to a boat's systems. The system needs to consider the consumption, storage, and generation of power, as well as a good monitoring system. In the absence of a deep dive into your electrical system, its use, and your sailing habits, no one can offer an informed opinion on whether this will meet your needs or not.

The 8 amps is not really enough to do much. It won't run AC, it will provide about half the power to run the refrigeration, it won't do much for charging batteries efficiently (especially AGM or deeply discharged FLA batteries), and it will likely annoy the neighbors in the anchorage.

Start at the beginning, what type of sailing do you do? How often and how long are you away from shore power? What is your consumption? Do you have a good battery monitoring system? How are your batteries? Age? Type? Capacity? What kind of alternator do you have? Is it adequate to charge your batteries efficiently?

When you have the answers to those questions, you can begin to reasonably, safely, economically design your electrical system to meet your needs.

Ralph Johnstone · Mar 26, 2022

jviss said:
He's only asking if he connect the generator output to the shore power inlet of his boat, not back-feed the grid!

sunlover said:
Can I mate to the shore power port?

My first impression was an EITHER/OR connection. I wanted to be sure he understood the predicament if these two should ever connect. Sort of like people who install an on board generator without the proper disconnect for each source.

Johann · Mar 26, 2022

dlochner said:
If you read the specs, this is only a 700 watt generator, or about 8 amps (700watts/12v =~8 amps). That is not very much power.

Realistically, there are no quick and dirty solutions to provide enough electrical power to a boat's systems. The system needs to consider the consumption, storage, and generation of power, as well as a good monitoring system. In the absence of a deep dive into your electrical system, its use, and your sailing habits, no one can offer an informed opinion on whether this will meet your needs or not.

The 8 amps is not really enough to do much. It won't run AC, it will provide about half the power to run the refrigeration, it won't do much for charging batteries efficiently (especially AGM or deeply discharged FLA batteries), and it will likely annoy the neighbors in the anchorage.

Start at the beginning, what type of sailing do you do? How often and how long are you away from shore power? What is your consumption? Do you have a good battery monitoring system? How are your batteries? Age? Type? Capacity? What kind of alternator do you have? Is it adequate to charge your batteries efficiently?

When you have the answers to those questions, you can begin to reasonably, safely, economically design your electrical system to meet your needs.

Some good advice… some bad math

A 700w generator can produce around 50 amps at 12v DC.
What is a “converter” in this context? RV slang for a battery charger? A DC power supply?

BigEasy · Mar 27, 2022

If you have decided to use a portable generator onboard, a Honda 2200 can run any appliance, power a 40 watt charger, and run a 12000btu air conditioner. Honda has become become the standard for portables. I am sure that you have already investigated the merits/ dangers of portable generator use on boats.

jviss · Mar 27, 2022

Johann said:
Some good advice… some bad math
A 700w generator can produce around 50 amps at 12v DC.
What is a “converter” in this context? RV slang for a battery charger? A DC power supply?

This 700W generator can't produce around 50A at 12VDC, because it doesn't have a DC output.

The "converter" people refer to in this thread it just a plug adapter, to allow you to connect this generator's AC output to your boat's AC shore power inlet.

dlochner · Mar 27, 2022

Johann said:
Some good advice… some bad math
A 700w generator can produce around 50 amps at 12v DC.
What is a “converter” in this context? RV slang for a battery charger? A DC power supply?

Isn't the first time my math has been off. :facepalm:

It is about 6 amps @120v, and about ~58 amps @ 12v. One of these days I'm gonna buy a calculator.

Johann · Mar 27, 2022

sunlover said:
I have no interest in the air conditioner. I just want to top off batteries if the solar panels don't keep up.

What is the 120v AC to 12v DC converter?

If you have a 12v marine battery charger that accepts 120v power you should only need an adapter cord for the genset to shore power inlet. A 700w generator will have no problem with a 40 or 50 amp 12v charger as BigEasy said.

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kloudie1 · Mar 27, 2022

If you use an extension cord (in addition to the short adapter pigtail) to better position the generator, make sure it is 12 gauge wire to decrease voltage drop.
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