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Hi, For cable insulation resistance calculation, the equation goes: IR = K * log (D/d) [megaOhm-1000ft] where D = diameter of insulated conductor and d = diameter of copper inductor ICEA has some K numbers for PVC and rubber. But how is K calculated? It's nowhere explained. I've come...

Ok, thanks. I will look into the triac option. This sounds like a cheap way of doing it.

I didn't know the type of motor would be important in this case. I just wanted the voltage supply to the motor to be controlled without much manual operation. I don't know what type of motor this cooler has, I'll have to check with the manufacturer. I was thinking of a simple board with a...

The motor takes up to about 60VAC and 3.5A single phase. This non-manually adjustable voltage is a preferred method for future end users to run the cooler without spending a lot of time paying attention to the ambient temp and adjusting the cooler voltage themselves. It could potentially...

Hi, I have a cooler powered by a small motor. The cooler motor is adjustable 0-60V (the higher voltage, the colder the cooler gets). Since a soft start is preferred, I use a typical Variac to slowly turn the voltage up in the lab. However, I'd like to set up a simple input/output system...

Sorry, I don't know any more details regarding the specifics on how the cooler runs. Yes, in reality I think it's alright if the cooler runs less efficiently for a few hours if the backup source doesn't fit that +/-0.5Hz. But my boss would rather know the different options that allow it to...

Thanks again, itsmoked. With regard to this cooler...as far as I understand, there's a linear motor that drives a magnet ring. This magnet ring makes the piston oscillate back and forth with respect to the displacer in the cooler, and there's a certain degree of phase shift between the piston...

Hi, This is kind of a "spin-off" thread from the other one that I posted before. http://www.eng-tips.com/viewthread.cfm?qid=188842&page=3 I have a 2kW Sterling cooler load that needs a backup system, and the performance drops off sharply outside 60Hz +/- 0.5Hz. Besides UPS, "Itsmoked"...

Thanks for all the comments. I will look into the Honda inverter generator.

Sorry about being ambiguous in my previous posts. I'm trying to have a backup system to keep 10 units of Sterling cooler (200W each) running. Each sterling cooler only requires about 100V/2A single phase. So I'm only looking for a small generator, 2kW or so, not an industrial type of...

So is there some kind of frequency regulator that I can add to the output to make sure it stays within 60Hz +/- 0.5Hz? I've looked at frequency converters that can take 47-63Hz input and output 60Hz +/- 0.1Hz. But those are really expensive (~$3,000). Any other cheap (less than $500)...

For a diesel backup generator, what's the typical output frequency variation? I've read specs that say 60Hz +/- 5%. Is it typcially off by that much? In my application, the load is very sensitive to frequency variation. The performance starts dropping when it's outside of 60Hz +/- 0.5Hz...

I'm looking for a cheap current limiting device that will cap the current at 25mA from the 120V wall plug. I read that a PTC thermistor would do what I'm looking for. Has anyone dealt with thermistors? I guess I just need to look for one that allows normal operating current at 25mA, and...

The load, AC, and DC are all connected with ground wire for return path. I was just trying to show a rough presentation, and the text sketch didn't show up well.

I'd like to superimpose AC and DC sources into one wire for simulation on a smaller scale (100-120V AC&DC). I have a DC power supply to control the DC voltage output, and perhaps get 120VAC from the wall. My load has a choke that can filter up to 1000VAC and the rest of the device can take...

Can I use a contactor in series with the power source? So that I can program my own temp range?

Hi, What kind of device should I look for if I want to control the voltage source feeding a gauge based on temperature readings? What I'm trying to do is to ensure the internal temp of the gauge doesn't get too hot. So I want to have some kind of temp sensor to read the internal gauge temp...

Well, the DC part of it is supposed to go to the sensor gauge via the Wye neutral. I believe the thinking is so that there can be DC voltage supply to the sensor gauge at all times to monitor measurements regardless of whether the motor is running or not. What kind of effects would harmonics &...

I was just told by someone that you can send both AC and DC voltages down the same cable at the same time (to a Wye motor winding). There's a sensor gauge that requires DC voltage and has a lead connected to the Wye neutral. The guy's reasoning is that the motor only sees the AC components...

That makes more sense. So it's just a matter of naming the filtering device before or after the AC-DC conversion. Thanks.