single phase starter

[Dagny]

Why am I having so much trouble finding a single phase starter 5 hp 24A screamer air compressor. screamer = any compressor 3400 or higher RPM.

Be nice if it had a fuse kit for pressure sw.

 

[rockwithjason]

why not use a 3 pole starter and bridge it?

 

[wyliesdiesels]

Theres plenty of 5HP single phase staters available.

rpm isnt a spec that the starter needs to have.

 

[Doug Arthurs]

I would just use a 3phase as mentioned and bridge the other two contacts on the overload.

 

[Dagny]

What do you mean run one of the lines through again. through the third pole?

 

[joe_padavano]

I just bought a 40A single phase starter for a 7.5HP motor. They are everywhere.
Type 5HP single phase motor starter into Google and a bazillion come up.

I'm curious why it is necessary to bridge the three phase starter for a single phase motor. The mag starter is just a relay. Single phase starter is a DPST relay, a three phase starter is a 3PST relay. The overload heater should trip if any one of the phases overheats.

 

[CompressorPros.com]

In case you haven't found one... 5HP Single Phase Starter

We get ours from Atlas Copco...used on BelAire, Chicago Pneumatic and other brands. In stock and would ship from Charlotte, NC

 

[wyliesdiesels]

What do you mean run one of the lines through again. through the third pole?

I just bought a 40A single phase starter for a 7.5HP motor. They are everywhere.
Type 5HP single phase motor starter into Google and a bazillion come up.

I'm curious why it is necessary to bridge the three phase starter for a single phase motor. The mag starter is just a relay. Single phase starter is a DPST relay, a three phase starter is a 3PST relay. The overload heater should trip if any one of the phases overheats.

Many newer overload relay blocks also have phase loss protection. SO if you dont jumper from T2 to L3, and connect motor leads at T1 and T3, so that current is sensed on all 3 motor lugs, the phase loss protection will trip right after start up.

 

[matt_i]

Here is the basic concept of using a 3 pole starter and maintaining the overload protection for a single phase motor.



There are a couple of classes of motor starter, there's the NEMA series and the IEC series. Both work quite well but the NEMA series is built for 50 years of hard work if you ask me. Very robust devices, I have bought several, already-used and they will be here after I am just a memory.

That said the IEC series will work without trouble in a residential-duty shop for a long time. You could buy those new at Automation Direct among many sources.

Important when buying any starter is specifying the coil voltage, which is equivalent to the control voltage you'll be using.

 

[Dagny]

On line was easy. I have accounts at three supply houses.All wanted to sell me 3 phase starter at 3 times the price.

 

[bczygan]

8911DPSG22V09

Bill

 

[joe_padavano]

Many newer overload relay blocks also have phase loss protection. SO if you dont jumper from T2 to L3, and connect motor leads at T1 and T3, so that current is sensed on all 3 motor lugs, the phase loss protection will trip right after start up.

OK, that makes sense. Thanks. I guess the older "heater" style would not have this problem, right?

 

[matt_i]

Thanks. I guess the older "heater" style would not have this problem, right?

Negative, Ghost-Rider

The whole point of having overload protection (even the classic discrete-element heater style) is so a motor that's unattended (lets say on a rooftop) that attempts to start on single phase won't fry itself and require a really difficult rigging and replacement job (bucking a 25hp motor across a roof is not fun!)

The heaters should be sized close to the motor's FLA (full load amps). This will almost always be exceeded when a 3phase motor tries to start on 1 phase, then cannot, sits there drawing mega current with a locked rotor until the motor windings short or something else burns up. But, the discrete elements get hot, like right now (!) and trip the mechanically latched contact that's tied to a bimetal strip-type-thingie. The NC contact for the overload goes open and the relay drops out, because the coil can no longer be energized. Motor saved.

Just pointing out that the single-phase issue is present on both modern styles with a little screw adjuster to set the current trip limit AND the classic discrete heater element style where you look in a catalog table and find it needs 3pc of B86 heater to work correctly.

Same issues will also be present should you get a machine which was wired for 480v 3ph and attempt to run it on 240v 3ph, even if the motor's windings have been configured correctly to run on the lower voltage. The current is more or less doubled on the halved voltage and the overload heaters don't like this. One can run for 1-2 seconds until the overload contact opens up.

 

[wyliesdiesels]

Negative, Ghost-Rider

The whole point of having overload protection (even the classic discrete-element heater style) is so a 3Ø motor that's unattended (lets say on a rooftop) that attempts to start on single phase won't fry itself and require a really difficult rigging and replacement job (bucking a 25hp motor across a roof is not fun!)

The heaters should be sized close to the motor's FLA (full load amps). This will almost always be exceeded when a 3phase motor tries to start on 1 phase, then cannot, sits there drawing mega current with a locked rotor until the motor windings short or something else burns up. But, the discrete elements get hot, like right now (!) and trip the mechanically latched contact that's tied to a bimetal strip-type-thingie. The NC contact for the overload goes open and the relay drops out, because the coil can no longer be energized. Motor saved.

Just pointing out that the single-phase issue is present on both modern styles with a little screw adjuster to set the current trip limit AND the classic discrete heater element style where you look in a catalog table and find it needs 3pc of B86 heater to work correctly.

Same issues will also be present should you get a machine which was wired for 480v 3ph and attempt to run it on 240v 3ph, even if the motor's windings have been configured correctly to run on the lower voltage. The current is more or less doubled on the halved voltage and the overload heaters don't like this. One can run for 1-2 seconds until the overload contact opens up.

Fixed it for you