My 80amp SCR Motor Controller

Discussion on general flowbench design

Postby cspeier » Sun Nov 01, 2009 3:59 pm

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bruce wrote:I'm wondering how much of an effect the SCR is having on max output of your motors?

I know with the HF or Payne control you don't get full output from the controlled motors.

Since you are controlling all the motors is it dropping the max output?

I thought of that myself. I know you have the ability to set the SCR in many different ways. it does have a line voltage compensation which puts a constant load on the SCR as voltage changes..

4.5 Line Voltage Compensation
The LPC
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Postby Tony » Sun Nov 01, 2009 4:16 pm

bruce wrote:I'm wondering how much of an effect the SCR is having on max output of your motors?

I know with the HF or Payne control you don't get full output from the controlled motors.

Since you are controlling all the motors is it dropping the max output?

The SCRs drop a fairly constant two volts just by themselves, that is unavoidable. It is where all the heat comes from.
But also, the firing circuit can never reliably reach right up to 100% of full timing, because that can cause triggering and misfiring problems right at full maximum power.

Something in excess of 95% of full power might be a realistic expectation.

It should be easy enough to compare the incoming mains, and motor voltages with a multimeter to see how much you are actually losing.
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Postby cspeier » Sun Nov 01, 2009 6:45 pm

Tony wrote:
bruce wrote:I'm wondering how much of an effect the SCR is having on max output of your motors?

I know with the HF or Payne control you don't get full output from the controlled motors.

Since you are controlling all the motors is it dropping the max output?

The SCRs drop a fairly constant two volts just by themselves, that is unavoidable. It is where all the heat comes from.
But also, the firing circuit can never reliably reach right up to 100% of full timing, because that can cause triggering and misfiring problems right at full maximum power.

Something in excess of 95% of full power might be a realistic expectation.

It should be easy enough to compare the incoming mains, and motor voltages with a multimeter to see how much you are actually losing.

I'm going to check line voltage in the morning. I will post the results.
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Postby cspeier » Mon Nov 02, 2009 9:26 pm

I didn't have time today, but will check line voltage in the morning.

I used the bench all day today. The head I was working with allowed me to flow at 28" with the sharp edge. I did find out real quick that a sharp edge is the ONLY way to have stable accurate readings! The hole I made was turbulant and fluctuating the cfm numbers.

The SCR got a 6 hour workout and worked flawless.

I have a servo on the way for the POT. Thinking I can adjust the depression with it. I'll keep everyone posted!!
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Postby cspeier » Wed Nov 04, 2009 12:18 pm

Voltage at the plug: 249v

Voltage drop across the SCR at full speed: .6 of a volt

Amps across the SCR: 22 total

Used this bench for 2 days straight logging appox 7 hours of bench time, worked flawless!
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Postby bruce » Wed Nov 04, 2009 1:23 pm

I picked up a similar control/parts off eBay over the past week and will be giving it a try as another option for the Payne Control/HF Control.

Later this year when I build another PTS bench (specifically for testing) I'll add this control to run all the motors.
"There is no more formidable adversary than one who perceives he has nothing to lose." - Gen. George S. Patton
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Postby cspeier » Wed Nov 04, 2009 8:52 pm

wing64k wrote:Chad,
How is the bench now,by reading the posts looks like youn got it sorted out.What kind of depression can you pull now.

Dean

Not nearly enough. I'm working on a 300 cfm head and can only pull 28".. I'm going to order 5 Lighthouse motors tomorrow. I like to flow SBC at a higher depression. However, the goal is to be able to flow a 500 cfm at 28".

FYI.. There are some 115923 Ameteks on Ebay for $45 each! New. Scratch and dent. I'd buy them but don't want to add relays. Buying the LH in a 240v is a simple solution.
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