Transformer Question?

[EricRN]

Hi all,

I need some help from someone with some electrical expertise. Does anyone have a sense of whether one might be able to use one of these plug-in transformers to generate a supply of 230V power for 3HP running power tools? I don't have a 230V circuit in my garage (only have one in the laundry room on the other side of the house to power the dryer), and I'm wondering if something like this might be a cheaper work-around than installing the 230V circuit. (I unfortunately would have to install another breaker box since I don't have the available outlets in my current breaker. I had an electrician here awhile back doing some other work, and he said I was probably looking at $700-$1000 worth of work to do that.)

Here's my concern, and why I think it probably won't work. First, I have a general apprehension for all things electrical. I'll do a lot of work around the house, but I always pay to have a licensed electrician do electrical work. So there's a general fear that this will cause my garage to blow up or catch fire. (Maybe I'm exaggerating.) Second, and more realistically, I've got 20 amp breakers. If the power tool is drawing 13 amps at 230V, that means it'll draw roughly 26 amps at 120V. I'm assuming that would require the transformer to draw 26 amps from the 120V circuit, which would pop the breaker. Basically, I'd never get to use the tool or would at best experience a large amount of frustrating outtages as the transformer and tool pop the breaker.

 

[monophoto]

I've got 20 amp breakers. If the power tool is drawing 13 amps at 230V, that means it'll draw roughly 26 amps at 120V. I'm assuming that would require the transformer to draw 26 amps from the 120V circuit, which would pop the breaker.

Exactly - 3 hp motor operating at 230v through a transformer will draw about 26 amperes at 115 volts, which exceeds the rating of the 115 volt branch breaker. Therefore, that approach won't work.

The first thing you need to check is whether the motor can be reconnected to either 115 v or 230 v. If it cannot be reconnected (and not all motors can), then your options may be limited to installing a new 230 v circuit. However, if the motor can be reconnected to operate at 115 v, then another option is to upgrade an existing 115 v circuit. But that's not a trivial chore - you would need to replace the breaker (replace the 20a breaker with a 30a breaker), but you would also need to replace the existing 12 gauge wire with 10 gauge wire, and replace the existing 20a receptacle with a new 30a receptacle. My experience is that it is always easier to install a new circuit than to replace existing wiring, and ultimately, you would probably want the flexibility of having both the 115v circuit and a new 230v circuit.

So my suggestion is to install a new 230v circuit.

So sorry, there's no free lunch here - - -

 

[EricRN]

Exactly - 3 hp motor operating at 230v through a transformer will draw about 26 amperes at 115 volts, which exceeds the rating of the 115 volt branch breaker. Therefore, that approach won't work.

The first thing you need to check is whether the motor can be reconnected to either 115 v or 230 v. If it cannot be reconnected (and not all motors can), then your options may be limited to installing a new 230 v circuit. However, if the motor can be reconnected to operate at 115 v, then another option is to upgrade an existing 115 v circuit. But that's not a trivial chore - you would need to replace the breaker (replace the 20a breaker with a 30a breaker), but you would also need to replace the existing 12 gauge wire with 10 gauge wire, and replace the existing 20a receptacle with a new 30a receptacle. My experience is that it is always easier to install a new circuit than to replace existing wiring, and ultimately, you would probably want the flexibility of having both the 115v circuit and a new 230v circuit.

So my suggestion is to install a new 230v circuit.

So sorry, there's no free lunch here - - -

I figured as much. Thanks for confirming.

 

[Charlie_W]

Easiest option is to run a heavy cable /extension cord from the dryer receptacle through the house to the garage when you want to use it. Note that the cable needs to handle the current draw plus some extra for the distance. Use appropriate plugs and receptacle.
I'm sure John T (electrician) will weigh in soon.

 

[leehljp]

Reiterating what Charlie said: HEAVY extension cable. 10 gauge might do, depending on the length; otherwise 8 gauge extension cords.

 

[Curly]

If the 3hp tool is only used occasionally, like a planer, you might consider a generator. It has the added bonus of being handy if there is a power outage for a while. If the tool is used often like a dust collector or lathe then you would be better off getting a proper sub panel in the garage from the main panel especially if you own the house.

 

[jttheclockman]

Not sure what you want me to tell you but they are not made to run industrial tools. They are made for small appliances.

Man will not go into the math for motors and inductive loads as opposed to resistive loads. 3HP motor on 230 is about 10amps.

Those telling you to run a chord from your dryer outlet are not taking in concerns of distance. That outlet is probably wired with #10 wire for a 30 amp outlet. Jumping up to a #8 chord does nothing. Where is the panel in relation to the garage?? It would be easier and more economical to run a seperate line to garage. Now if your panel is rated to add this outlet. If all slots are filled with breakers, it is possible to use mini breakers somewhere in there. But again a load management of your panel and service are need to know. I won't even go into ground fault need in a garage.

You say you use an electrician for other electrical work, well I highly suggest you do the same here. Many factors go into adding outlets or even sub panels. This may be an option for you too. Again the service size (+load management) and panel will determine extent of work plus the route that needs to be taken.

 

[EricRN]

Not sure what you want me to tell you but they are not made to run industrial tools. They are made for small appliances.

Man will not go into the math for motors and inductive loads as opposed to resistive loads. 3HP motor on 230 is about 10amps.

Those telling you to run a chord from your dryer outlet are not taking in concerns of distance. That outlet is probably wired with #10 wire for a 30 amp outlet. Jumping up to a #8 chord does nothing. Where is the panel in relation to the garage?? It would be easier and more economical to run a seperate line to garage. Now if your panel is rated to add this outlet. If all slots are filled with breakers, it is possible to use mini breakers somewhere in there. But again a load management of your panel and service are need to know. I won't even go into ground fault need in a garage.

You say you use an electrician for other electrical work, well I highly suggest you do the same here. Many factors go into adding outlets or even sub panels. This may be an option for you too. Again the service size (+load management) and panel will determine extent of work plus the route that needs to be taken.

Yeah, if I put anything in, it'll definitely be done by an electrician. Was just trying to figure out if there was a workaround since the electrician is so expensive here in the DC area. Seems like there's no free lunch, as someone else said. I either need to pony up for the extra circuit, wait to buy the tool until I do (had my eye on a 3 HP bandsaw), or decide to go with less power that will run on 110V. Better yet, maybe I just focus on the tools I got and getting good with those!

 

[jttheclockman]

3hp bandsaw?? Do you do alot of resawing large logs?? I resaw alot and use carbide blades on a bandsaw that is underpowered for sure 3/4hp but can do well 120volts.

 

[EricRN]

3hp bandsaw?? Do you do alot of resawing large logs?? I resaw alot and use carbide blades on a bandsaw that is underpowered for sure 3/4hp but can do well 120volts.

Haha. You are almost certainly correct that 3HP is probably overkill for me. A 1 3/4 bandsaw will probably serve me just fine. I want the band saw mostly for resawing--I use a lot of 6-inch or wider, 1/4 inch thick panels in boxes and whatnot, and I can't bring myself to plane down 4/4 stock and losing all that work. Trying to resaw on the table saw always makes me nervous. I'm sure a 1 3/4 hp bandsaw could handle that resaw application with the right blade, but I've had enough experiences buying cheap and/or underpowered tools trying to save a buck, though, that when I see something with more juice in the budget that I have, I always try to make it work, and I'd seen that Harvey had their 3 HP model on sale.

For sure, the sensible thing for me to do is to not spend money upgrading the power supply, find a solid saw that will run on the voltage I have, and then spend the money saved on some boards.