Down-Sizing the Motor on a Used Sander

A shop owner can get a great deal on a used wide-belt, but he doesn't think his shop has the amps to run it. What are his options for matching his power to the machine? September 17, 2008

I have an opportunity to purchase a repo'ed Sunhill 2 head sander which has 25hp and 20hp drive motors. I only have single phase 200 amp service which will not provide enough power. Upgrading the service to the building is not an option so I was wondering if changing the motors to a lower hp would work. The unit is four years old in good condition and sells new for approximately $20,000 including tax. The bank wants $,1000 for it.

Forum Responses
(Solid Wood Machining Forum)
From contributor S:
I don't think you would gain anything by changing the motors. A three phase motor will develop the horsepower it needs, depending on the load you place on it. In other words, you can load the machine up to any level of current draw. So a smaller motor will still require the same amperage to accomplish the same amount of work.

Staying under the 200 amp limit is going to significantly drop the capacity of the machine - exactly how much is difficult to determine. It will depend on a combination of things: the width of the material being sanded, the amount of material you are trying to remove, the species of lumber, and the rate of feed.

Single phase motors are expensive, and generally unavailable in higher horsepower, and they suck a lot more juice. The largest single phase motor WW Grainger offers is 14HP, and it draws 57 amps at full load.

If you elect to stay with three-phase motors (which is really your only logical choice), you'll also need a converter to make three phase out of single phase. Bear in mind that such a converter also consumes power.

A 25HP, 230 volt, three phase motor shows to draw 68 amps at full load (remember, you don't have to operate the motor at full load). The 20HP motor needs 54 amps for full load. You could also reduce the current draw by only using one head (obviously). You'll also need to collect the dust, which will require some sizeable HP all by itself. And don't forget the feed motor and its power requirements.

A good investment would be to have a knowledgeable electrician look at your situation and advise you accordingly. No doubt the $1,000 purchase price is attractive, especially if the machine is located within driving distance. Can you buy it and store it until you get moved to a different shop? If I were you and had an extra $1,000, I'd buy it, if for no other reason than to use it as incentive to move to a better shop.

From contributor S:

Maybe I spoke too soon - after adding it all up, you might be able to operate this machine at near full load. Even at half-load, you’re still about a thousand times better off than hand sanding.

You have 25HP at 68 amps, 20HP at 54 amps, 5HP (feed) at 15.2 amps, 10HP dust collector (assuming three phase) at 28 amps.

That totals 165.2 amps. That (in theory) allows you 35 amps to operate the three-phase converter and any other load, such as lighting. Just don't count on using any other equipment concurrently with the sander, and don't expect to be able to fire-up all these motors at the same time. Consult an electrician, then buy it.

From contributor R:
I run a 18 hp 3ph on a 30hp converter that I built. The converter and my 3ph buss bar are on a 100amp single ph breaker and I’ve never had any problems. Start one at a time and you’ll have plenty of power. Plus that’s a good buy.

From contributor P:
I read your post and a few things jump out at me; Sunhill, 3ph / 1ph service, no warranty, modification.

You are a cabinetmaker and I'm sure a very good one. Each minute you spend modifing this machine takes away from the business that makes you money. How much you give (within reason) for a machine has little to do with the worth of it, if it does what you need it to do and requires little repair. Sunhill is not going to fix or replace any part that is damaged by an electrical mistake. They may not even have the part any longer to fit the machine, according to the age.

As stated earlier, electric motors are expensive and when changing from Chinese motors to US motors, you must also modify the mounting system as well as change all starters and possibly transformers. We are not talking cheap. They say the happiest day a boat owner experiences is the day he buys it and the day he sells it. It may be the same with this machine if you decide to get it.