Startrite 352 phase conversion

[ScouseKev]

I'm looking for a Startrite 352 Bandsaw, but most seem to be 3 phase and 1 hp.

I know they can be converted using an inverter, but i'd like to uprate the power too.

My question is.... Is it fairly straight forward to fit a single phase motor? ..... will it then need a new on / off switch?

Many thanks in advance.

 

[flh801978]

I have a couple of startrites both with inverters ( VS is very usefull)

On your model is the bottom wheel belt driven...if so its easy to fit a new motor
Direct drive not so easy
You will need a new direct on line starter if you going single phase
Having said all that I dont think on mine i've ever been short of power

Ian

 

[woodpig]

I believe three phase motors are more powerful for a given size. If you are limited by size then you may actually have to fit a lower HP motor if going single phase.

 

[paulm]

A few years back I converted my startrite 351 or 352 (can't remember !) from the original 1.5hp single phase to a nice meaty 3hp single phase, pretty easy to do, not expensive and now munches through anything without stalling even green timber at full depth of cut

I sourced a motor from Goldcrest Technologies on ebay and the chap was very helpful indeed, cost around a hundred pounds at the time including a new pulley wheel as the drive shaft was a different diameter. I upgraded the drive belt at the same time to a nice meaty fan belt from Halfords as the original was a bit weedy for the extra power, and put in a 16 amp cable run and socket to power it.

Don't know about the switchgear aspect though from 3ph to single.

Cheers, Paul

 

[jolly1]

a 3 phase starter can be used if the operating coil is 240 volt. The starter would require a 3 phase and neutral supply, or a small control transformer in the starter.
If an overload is fitted then you need to take the single phase and series it through the 3 phases

 

[dickm]

a 3 phase starter can be used if the operating coil is 240 volt. The starter would require a 3 phase and neutral supply, or a small control transformer in the starter.
If an overload is fitted then you need to take the single phase and series it through the 3 phases

Think you mean parallel it, not series? But if the OP goes for a higher hp motor, I suspect that even in parallel, the 3p OL won't have enough capacity and will keep tripping.
I parallelled the contacts on my 352 using a 1hp SP motor like the original 3p,and it worked fairly well, but finally decided just to fit the right replacement switch. From memory, it's a Danfoss and not that expensive.
Changing the motor is a doddle, since it's just a standard foot mounting.

 

[jolly1]

no I mean in series if you connected then in parallel then each element will only see 1/3 of the current which means you could with a 60% overload. The only reason for series them is any decent overload unit will have an out of balance element, must see the same current in each phase. So single phase appears as an out of balance in a 3 phase unit.

Motor footing is dependant on the motor frame size, which should be to a standard.
Speed is dependant on the number of pairs of poles

So N =( Hz x Sec/Min) / number pairs of pole

for a 2 pole motor is 3000 rpm minus the slip say 5%

For clarity I mean series thro the overload unit
________

 

[ScouseKev]

May be i should have said this right at the beginning....but....i have no electrical experience at all !

Most of this advice has gone over my head.

Who would i need to get to do a job like this done professionally? Doesn't sound like your average domestic spark.

A new 352 is well over a £1000 so buying new is not an option.

Anyone got one they are thinking of selling?

 

[jolly1]

It depends on the electrician, if they could do it. The mechanical bit could get a wee bit complex, there should be a fame number though not always. Which allows matching of the physical parameters. But even more important is to get the
motor speed correct,
induction motor speed cannot be controlled by voltage reduction. If you can find a small motor repair shop they could most likely do it, look under armature winder.

 

[Harbo]

The switches are by Danfoss but now very hard to find. I had to fit a new NVR from Toolstation on mine.

Rod

 

[ScouseKev]

Thanks for all the advice.

Im out of my depth here so i'll be looking for pro to do it i think.
cheers

 

[beech1948]

hi kev,

Just before you go down the proffesional sparks route the thing to understand is:-

1) CXan your motor be wired for 3 phase 230v.....if so dom it. To learn how then go to OWWM.org and see everything electrical....its a US site but tackles these issues daily and 3 phase from 230v to 600v...ouch. Its really quite simple and should be shown by a diagram attached to your motor control box.

2) Stay with 3 phase just mnove wired to 230v 3 phase. Then add a VFD which will convert 230v single phase to 3 phase 230v. The advantages are many a VFD will give you speed control, most can be programmed to give a slow start up and a sudden stop etc etc.

Just stay 3 phase and keep it simple.,

 

[dickm]

no I mean in series if you connected then in parallel then each element will only see 1/3 of the current which means you could with a 60% overload. The only reason for series them is any decent overload unit will have an out of balance element, must see the same current in each phase. So single phase appears as an out of balance in a 3 phase unit.

Still not convinced! My reasoning for paralleling was that each of the 3 phases was taking (roughly) 1/3 of the "total" current, and so if the trips were in series, unless they could be adjusted to take 3x the OL current, they'd be tripping all the time on single phase 'cos they'd all be taking 3x the current. Or are we at cross purposes?
Like I said, it worked for me, although it did trip occasionally, hence going for new switch.

 

[jolly1]

Sorry but you are in error.
Overloads have two function
1 Overload typical set 110% flc Full Load Current
2 Un balance where more or less current in one element due to a motor winding fault, or bad connection or loss of a phase which will cause winding damage,

Lowest cost type are thermal (heaters) which operate a bimetallic element all 3 elements move in relation to each other providing the sum of the currents = zero (Kirchoffs Law)
If one phase is down that element will not move hence will trip
The other type is magnetic core balanced transformer.

In 3 phase say red is at peak positive then the other two phases will be negative values but sum to the same magnitude as the positive (but negative) so result is zero.

In single phase in parallel then say the current is 9 amp (makes the sum easy) then as it flows to the parallel connection then each element see 3 amps. So as far as the overload see then motor is only running at 1/3 of the load.

connection would be the live series thro the overload unit and the neutral bypasses it
contactor live goes through one pole neutral thro another, 1 pole has no connection.
Or thro the red phase in on the contactor out the red overload loop back to the yellow input connection to contactor out from yellow of the overload loop back to the blue input connection out of the blue overload to the motor

Regarding currents as you describe it is dependant on the motor connection star or delta connected, the tripping occurring could be due to tired o/load or the connections were causing a slight imbalance