I was wondering if you fed 120vac to a 240 vac welder, what would the voltage be on the secondary windings?
Could it be low enough to power a DC outboard motor after you rectified the AC output from the welder.

Use output to power a 24 vdc electric motor for boats. Or a 12v motor, or 36 v motor..

I seem to recall open circuit, 240vac welder has about 70 vac on the secondaries.

 

You'll need a l-o-o-o-o-o-ng and absolutely waterproof mains extension lead if you plan to power your boat's motor like that . Sounds potentially lethal.
Datasheets for welders should specify the transformer output voltage.

 

Have you tried welding in the rain? It hurts
+=

 

I was wondering if you fed 120vac to a 240 vac welder, what would the voltage be on the secondary windings?
Could it be low enough to power a DC outboard motor after you rectified the AC output from the welder.
I seem to recall open circuit, 240vac welder has about 70 vac on the secondaries.

Is this a SMAW stick welder, as this is of no use to use as a general purpose transformer as the secondary is loosely coupled by a shunt, this allows the voltage to collapse and a constant current enough to provide the weld pool.
Max.

 

Boats have generators, I have a 6500 watt 120vac gen.
Batteries would be exhausted in a few hours of use, and an AC charger could not keep up, I don't think with power demand.
The idea came up on a boating forum about a get home motor if your main engines quit.
So how would you power a DC electric boat motor from an AC generator?
My quick thinking was a common AC arc welder uses an ac transformer.
And transformers can modify AC voltage.

I have an old Sears Craftsman 240vac AC welder with primary and secondary windings. I recall reading open circuit volts was 70 vac. And under load dropped to 24 v or something like that?

Current is adjusted by an arm that moves a steel core in and out of the windings or it moves the windings, I think.

 

My quick thinking was a common AC arc welder uses an ac transformer.
And transformers can modify AC voltage.

As I already stated a stick SMAW welder is of no use as a general purpose transformer!
Is this what you are referring to?
You need one that has normal primary-secondary coupling.
Max.

 

As I already stated a stick SMAW welder is of no use as a general purpose transformer!
Is this what you are referring to?
You need one that has normal primary-secondary coupling.
Max.

I do not know what is a SMAW welder??
Ok, I suppose it is.
However, I have been into my old Craftsman arc welder, and it has primary and secondary coils. I bought it around 1980. the secondaries are really large diameter copper wire coiled up.

https://en.wikipedia.org/wiki/Shielded_metal_arc_welding

This video shows how I remember it being the transformer.
Mentions a magnetic shunt.
At about 3 minutes. Mine is a lot bigger than this one.

 

So how would you power a DC electric boat motor from an AC generator?

The first question I would ask myself was how much power do I need? I have seen what I call a trolling motor rated in horsepower so you choose a motor to fit your needs for your boat. For example to get the performance of a 3 HP engine running on petroleum one motor I saw had an input power of 1.0 KW and propulsion power of 480 Watts. Many of the better ones include lithium batteries with higher voltages, like about a 30 Volt 18 AH battery. The merit to the higher voltage is a lower current draw motor.

You mention your boat has an on board 120 VAC 6.5 KW Generator so I will venture this is not a small boat. Your boat size and how fast you expect it to travel need to be figured in for an electric motor HP rating. The higher the motor voltage the less current it will draw for a given power. Before I would try to hack a welder I would just buy a inverter type power supply, along these lines, Powermax 110 Volt to 12 Volt DC Power Supply Converter Charger for Rv Pm3-55 (55 Amp) which can be had for about $120 USD and will weigh a heck of a lot less than a welder which for the reasons mentioned likely will not give you what you want. You can also get 24 vold flavors. Before anything though you need to know the actual voltage and current you want and need.

Ron

 

Why not just get a sail boat. Then you don't need all that fancy equipment.

OR wind your own transformer. Just be sure you learn about winding them before you go attempting it. It's not as straight forward as you might think. As Max alluded to, shunt bars control the current. The voltage is a result of the changing current.

OR find a transformer that puts out the power you need. There's tons of them around if you know where to look. Old stereo's have multi-tapped transformers that MIGHT put out enough power to run a small electric motor enough strength to get you home - provided you're not fighting a water current or a wind.

Friend of mine got a hold of a speed boat. The engine was toast but he planned on putting a trolling motor on it and go out on the lake that way. I told him I'll sit on the shore and watch the wind blow him across the lake. I'm not making this stuff up! He REALLY thought he could do that. Big and light - the wind is going to move that around quite a bit. And he planned on a car battery to get him around. Not for long I told him.

 

And don't forget "duty cycle" that's the amount of time a welder can be used.. For example a 40% duty cycle at a given current means you can only use it for 4 minutes out of 10.. See if yours has a duty cycle rating on it..

 

And don't forget "duty cycle" that's the amount of time a welder can be used.. For example a 40% duty cycle at a given current means you can only use it for 4 minutes out of 10.. See if yours has a duty cycle rating on it..

I thought he was talking about something like the old Lincoln "tombstone". Did they even have a duty cycle on them? I know the new made in China type do but the old ones?

 

And don't forget "duty cycle" that's the amount of time a welder can be used.. For example a 40% duty cycle at a given current means you can only use it for 4 minutes out of 10.. See if yours has a duty cycle rating on it..

Duty time won't matter for a welding transformer, the current load of a DC outboard motor is going to be much smaller than welding wire.

 

The first question I would ask myself was how much power do I need? I have seen what I call a trolling motor rated in horsepower so you choose a motor to fit your needs for your boat. For example to get the performance of a 3 HP engine running on petroleum one motor I saw had an input power of 1.0 KW and propulsion power of 480 Watts. Many of the better ones include lithium batteries with higher voltages, like about a 30 Volt 18 AH battery. The merit to the higher voltage is a lower current draw motor.

You mention your boat has an on board 120 VAC 6.5 KW Generator so I will venture this is not a small boat. Your boat size and how fast you expect it to travel need to be figured in for an electric motor HP rating. The higher the motor voltage the less current it will draw for a given power. Before I would try to hack a welder I would just buy a inverter type power supply, along these lines, Powermax 110 Volt to 12 Volt DC Power Supply Converter Charger for Rv Pm3-55 (55 Amp) which can be had for about $120 USD and will weigh a heck of a lot less than a welder which for the reasons mentioned likely will not give you what you want. You can also get 24 vold flavors. Before anything though you need to know the actual voltage and current you want and need.

Ron

That looks like a real nice charger.

Well, looking at the negative reviews, people are saying it maxes output at 30 amps?

 

That looks like a real nice charger.

Well, looking at the negative reviews, people are saying it maxes output at 30 amps?

The idea was just to serve as an example. Looking at the price it was off the boat from China. This is a little known secret but the Chinese do not use the same globally accepted definition of an amp. The world accepts the ampere was defined as one coulomb of charge per second. The Chinese seem to have a smaller colomb than the rest of the world.

Seriously though I would look towards a SMPS with substantial overkill they are much lighter than trying to use any transformer for your application.

Ron

 

I thought he was talking about something like the old Lincoln "tombstone". Did they even have a duty cycle on them? I know the new made in China type do but the old ones?

Here's a pic from my 1980 Lincoln tombstone and it shows a 20% duty cycle. This is why I mentioned it, I thought it was higher than 20%, but none the less this will shut down if I exceed the rating..

 

Here's a pic from my 1980 Lincoln tombstone and it shows a 20% duty cycle.

Oh, you have a new one! Mine is from the 1960's or maybe even older, I got it used in the 70's. No mention of duty cycle.

 

Here's a pic from my 1980 Lincoln tombstone and it shows a 20% duty cycle. This is why I mentioned it, I thought it was higher than 20%, but none the less this will shut down if I exceed the rating..

I assume there is no timer, it shut down due to heat?
Again, a DC motor load could be half or less the typical output of an arc welder when arc welding with rods, so why then would there be any more duty cycle significance.

 

Per my post #4 observe the example Lincoln SMAW shows 79v open circuit voltage and 25v at typical welding current indicating the voltage collapse when loaded due to the shunt.
Max.

 

I assume there is no timer, it shut down due to heat?

No with duty cycle it's up to the operator to watch the duty cycle. Like Max is saying this isn't what you want for a motor power supply.

If you have AC available on board, why not make a "trolling" motor that runs on AC? I'd start out getting a submersible sump pump and a propeller, and make an adapter to put the boat prop on the pump shaft. With a submersible pump the hard part is already done for you.
https://www.walmart.com/c/kp/submersible-sump-pumps

 

Or use the pump as a jet. As much power as the pump puts out, jetting the output or modifying it to turn a prop - the output is going to be the same. Why cannibalize the pump at all?