help choosing solid state relay

Thread Starter

mobydick

Joined Nov 19, 2010
27
Hello
I have an old DC motor that used to drive Tension Test machine
The motor is 150V 4.5KW
The block diagram for motor driver :
block diagram.png
My problem is the motor rotates too fast .
I have done some googling and I get that the best way to lower the voltage is to use solid state relay before the rectifier
I have never used one before and There is lots of types for specific uses (inductive loads, capacitive loads…) and lots of control methods(zero crossing, random turn on,….) and I got confused.

Any recommendations will be appreciated
 
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MaxHeadRoom

Joined Jul 18, 2013
19,055
If using a motor on rectified DC you do not need the Cap, Especially using 3ph rectifier where the % ripple is less than 5%.
This will lower your peak DC.
An off the shelf SSR generally switches on/off, not variable.
Another alternative is a 3ph SCR bridge control.
Max.
 
Last edited:

Thread Starter

mobydick

Joined Nov 19, 2010
27
the capacitor is already installed
i want to lower the DC voltage even more
so there is no off the shelve phase control SSR
is bossible to make one
 

MaxHeadRoom

Joined Jul 18, 2013
19,055
What % of the current rpm limit are you looking for?
The 3ph SCR SSR circuit is one way or a couple of Buck/Boost transformers on two of the transformer outputs.
Another possibility is to reduce the secondaries by taking equal turns off of each.
Max.
 

Thread Starter

mobydick

Joined Nov 19, 2010
27
i have never dealt with big motors like this ,so i have no idea what is the current rpm limit
adding extra transformer will be too expensive
i want to cut rpm to half or may be more so i need to remove a lot of turns
adding external component will be the easiest solution
 

MaxHeadRoom

Joined Jul 18, 2013
19,055
I assumed automatically it was a P.M. field, it would not be a wound field by any chance?
Especially in that size of motor?
If it was, there is a simple answer.
Max.
 

ian field

Joined Oct 27, 2012
6,543
the capacitor is already installed
i want to lower the DC voltage even more
so there is no off the shelve phase control SSR
is bossible to make one
AFAIK: SSR and phase control modules are 2 entirely different things.

But you can get off the shelf phase control modules. A company I used to work for that made ultrasonic cleaning equipment used them as a cheaper alternative to variacs in a continuously variable generator.

Unfortunately I can't remember the make - the only SSR I can think of off hand is the Opto22.
 

MaxHeadRoom

Joined Jul 18, 2013
19,055
2 wires to the motor can still mean wound field if the voltage is fixed.
Yes Opto22 are SSR's, the 3phase SCR controllers are fairly pricey.
Depending on whether you are looking for variable rpm or just a lower fixed rpm.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
19,055
I presume you mean three Triac controllers in place of the SCR control?
It would depend on how the three transformers are connected, Star or Delta secondary?
One of the down sides with SCR control is miss-firing, especially in the case of power outage etc usually ending up in blown SCR or fuses.
Personally I would be looking at reducing the AC if fixed rpm is needed, or PWM if variable.
Max.
 

ian field

Joined Oct 27, 2012
6,543
I presume you mean three Triac controllers in place of the SCR control?
It would depend on how the three transformers are connected, Star or Delta secondary?
One of the down sides with SCR control is miss-firing, especially in the case of power outage etc usually ending up in blown SCR or fuses.
Personally I would be looking at reducing the AC if fixed rpm is needed, or PWM if variable.
Max.
I just assumed that an off the shelf phase control module would most likely have a triac in it.
 

MaxHeadRoom

Joined Jul 18, 2013
19,055
1ph 'Dimmer' style AC motor controllers have a Triac, which agreed you can operate ahead of a bridge.
But when getting in to 3phase control, the nature of the AC origin has to be known, Star-Delta?
Most of the first CNC DC servo motor controllers were a 12 SCR bank for reversal capability.
Now replaced with PWM.
Max.
 

Thread Starter

mobydick

Joined Nov 19, 2010
27
great dissection

so i should search for phase controller not SSR?
can't i use DC SSR after the capacitor?

2 wires to the motor can still mean wound field if the voltage is fixed.
i will look at it again
i will also look at the transformers to see the toopolgy

Depending on whether you are looking for variable rpm or just a lower fixed rpm.
just a lower fixed rpm



Could you get away with 3 individual phase controls - if you can find a 3-gang pot?
yes , that what i meant but using SSR(now phase controllers) not pot
 

ian field

Joined Oct 27, 2012
6,543
great dissection

so i should search for phase controller not SSR?
can't i use DC SSR after the capacitor?
A solid state relay is exactly that - it switches the power on and off in response to a control signal.

A phase control module switches on at some point on each half cycle of the AC waveform - the control signal tells it how early or late to fire on each half cycle.
 

MaxHeadRoom

Joined Jul 18, 2013
19,055
Check how the three transformers are connected Star/Delta, Star/Star etc, a possible change in the configuration can possibly lower the voltage to the acceptable level.
Max.
 

Thread Starter

mobydick

Joined Nov 19, 2010
27
Each transformer has 3 yellow and 2 black wires
1 yellow wire is not connected
1 yellow wire is connected to an input phase
1 yellow wire is connected to the other wires from the other transformers

1 black wire is output to the rectifier
The other black one is connected to the other wires from the other transformers
So I guess if the not connected wire is a center tap one the connection will be (Yy)
 

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MaxHeadRoom

Joined Jul 18, 2013
19,055
They appear to be connected Star-Star so this is the lowest voltage from them unfortunately.
BUT when they are powered, on one transformer, measure from the star connection on the input side to the 'open' (unused) connection and compare to the other used terminal, you may be able to use the alternative Higher primary connection and lower it that way, probably by half.
Max.
 

ian field

Joined Oct 27, 2012
6,543
AFAIK: SSR and phase control modules are 2 entirely different things.

But you can get off the shelf phase control modules. A company I used to work for that made ultrasonic cleaning equipment used them as a cheaper alternative to variacs in a continuously variable generator.

Unfortunately I can't remember the make - the only SSR I can think of off hand is the Opto22.
Found it - its a; Hyreg AR2/250-15.
 
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