Tokiwa T60 portable

[Jonathan Wood]

Hi all,
Ive acquired one ot these portables and wondered if anyone had successfully modified one to soft start? I’ve not tried firing it up yet as the little info I’ve gathered all point towards them having a vicious hard start . It’s a split phase single ph motor , so not sure a VFD would be the best option even if I manage to find a single ph VFD. I’ve been thinking a series resistor with timed relay might be best bet ? Incidentally, the framing mech on these machines seems insane , are they supposed to work ?! I’d like to get it working as apart from the startup concerns the machine is in amazing un used condition ( and yes , there probably is a reason for that !) best wishes , Jon

[Jim Cassedy]

I used a pair of those Tokiwas at an outdoor film event back in the late 1970's. I don't recall the start
up being especially rough, but it was a long time ago. They were rented from a big camera store in
New York, that also sold them. After using them, I remember liking them enough that I really wanted
to buy at least one for myself, but at the time, it was beyond my budget.

Either Simplex or RCA (or maybe both) used to have a quasi-soft start on their projector motors by
putting a large wire-wound resistor in series with the start winding of the motor. It was either 40Ω @
70W, or 70Ω @40W. . . (I can't remember which), but i do recall making that motor modification on a
home projector I owned a long time ago and it did work to reduce the start-up jerk.

> EDIT: I found a diagram for the circuit I described. It was a 40Ω/70W resistor.
RCA_ProjMotorDiag.jpg
This circuit was used by RCA on their 1040 ¼hp sound head drive motors.
(110Vac here in the USA)

[Jonathan Wood]

Hi Jim , thanks so much for that , it’s really helpful . I will give it a go . Re the start-up I’m just going by what I’ve seen on YouTube and from what I’ve gleaned from these pages. I’ll try connecting it once I’ve changed the oil and lubed it up and see how it behaves . Your circuit diagram is very helpful though . Jon

[Mark Gulbrandsen]

I had one back in the mid 1970's. Mine had a jackrabbit start too, and it was somewhat hard on old safety film as well, so I didn't keep it very long. As far as softening the start up, definitely do what Jim said to start out...

[Paul H. Rayton]

Here's another schematic of "slow-start" circuitry. This was done for me by a colleague (Robert Simonton), way back in 1991. He drew it for 2 different power configurations: one for 3-phase @ 208-volt (sometimes found for 35mm projectors), and also for conventional 120 volt single-phase power. In each case, there are heavy resistors inline during the initial startup, which are then removed from the circuit (using a time-delay relay) after 3 to 5 seconds, i.e. after the starting up projector has reached (or almost so) the full running speed.

As you can see, the load resistors are, in this arrangement, defined as variable, and one can adjust the operating resistance to whatever resistance amount provides you a sufficient drop of the line voltage at initial startup so that the motor doesn't start off too fast. He specified the variable resistor to be in the range of 25 to 50 ohms, and have a minimum power rating of 50 watts. You may have seen such resistors before -- they're not tiny. They cut the voltage by brute force, just "resisting" the line voltage to a degree (and getting warm in the process.)

Once the desired resistance has been determined (say, hypothetically, 35 ohms?), a fixed resistor of that value can be used instead. Functionally, it would work the same but it would make for a more compact and cleaner installation.

The time delay relay needs to be adjustable in the range of ~2 to 5 seconds, with the actual delay time to be determined by observing the ramp-up speed of the projector system. These details are also fully detailed in the drawing(s). As it turned out, I actually never needed to use this arrangement after all, so this specific one is a bit untested in actual service, but it's entirely consistent with other such resistance-dependent voltage-drop slow start circuits I've encountered. The special bonus here was his inclusion of the details for both single and 3-phase installations:

Slow-start circuit for proj. by Rob't. Simonton, 1991, enh2.jpg

[Jonathan Wood]

Thanks Mark and Paul , that’s really helpful . The schematic Paul sent looks similar to how it’s done in the ped version of a Vic 5 . I might not need the timer though as the motor has a centrifugal switch which should bypass the start winding as soon as it gets near speed ? Jon

[Jim Cassedy]

I might not need the timer though as the motor has a
centrifugal switch which should bypass the start winding as soon as it gets near speed ?

That's how it was done in the RCA schematic I posted. It relied on the centrifugal switch to
cut the start winding & resistor out of the circuit. In some installations I've seen the resistor
mounted in a box or enclosure on or along side of the motor, and on other installs I recall
seeing the resistor mounted inside an oversized switch box attached to the projector pedestal.

[Tony Bandiera Jr]

At the UK voltage of 240v you might need to double (or at least increase) the resistor values (say 75 ohms on 240v instead of 40 ohms on 120v) but you'll still need to experiment to find the best value. I'd recommend getting a 100 watt, 100 ohm variable resistor. Connect incoming live to one end and the motor output to the sliding tap. Start with the tap 3/4 away from the live end and try to start the motor. If it is too slow or doesn't start, move the slide closer to the live end. Repeat until you find the soft start time you want. Disconnect the resistor without moving the tap, and measure the resistance between the tap and live end. You can then fit a fixed resistor closest to that reading, or leave the adjustable one in place.

[Jonathan Wood]

Thanks Tony , that sounds like a good idea . I think I’ll need to get a 110 v transformer for it as the motor is rated 100/50 or 110/60 with two sets of pulleys to suit the chosen frequency. I’m hoping 110/50 will be ok as 100/50 transformers are more expensive over here . Thanks again !