120VAC mains direct to DC plus 3A Current Limit

[Mosaic]

This is an attempt to use peltier modules direct from the 120VAC mains. 170VDC rectified and smoothed.
I will double insulate as the supply isn't isolated.

So far I am looking at using FET PWM with an input capability of 200VDC to generate around a 4A avg. with soft start current. I plan on using (3) series mounted 12V, 60W (peak) peltier units. This means a 0.1 ohm current sense feeding into a low pass and then the comparators.
The challenge is the control circuitry operates at lower voltages, eg. a TL494 PWM driver is good to about 40V.
The Tl494 might pull perhaps 20mA to operate so a resistance divider could drop the 170VDC supply to 1/10 to provide the TL494 power. Perhaps 3.5W additional heat load as a result.

A stock PC supply is a bit too bulky for the application space overheads.

thx

 

[alec_t]

Can't you use a small wall-wart as a low-voltage supply, plus opto-triacs to provide isolation of the control stuff?

 

[Mosaic]

That's n option. But triacs are chopping a 60Hz signal, then that'll get rectified and smoothed. Might have a high LF ripple at the current limiting end which makes a current sense control prone to swings.

I was thinking of rectifying and smoothing at the high voltage side (like a PC PSU) , then using a TL494 PWM (say 50Khz) direct into the Peltiers via the current sense. A low pass filter can then supply a stable average (current sense) voltage signal for the comparators. A 5A fuse in line with the Peltiers for protection.

 

[tcmtech]

If it was me given TEC module are pretty forgiving devices I would just capacitive couple the TEC's to the mains power. Once AC capacitor, one bridge rectifier one DC electrolytic capacitor and one resistor to bleed off the charge on the AC capacitor for safetys sake.

 

[alec_t]

But triacs are chopping a 60Hz signal

Not if you use integral cycle control with zero-crossing sense optos.

 

[Mosaic]

If it was me given TEC module are pretty forgiving devices I would just capacitive couple the TEC's to the mains power. Once AC capacitor, one bridge rectifier one DC electrolytic capacitor and one resistor to bleed off the charge on the AC capacitor for safetys sake.

Ok, won't there be heating etc. on the capacitor @ 3-4amps conduction?

 

[Mosaic]

Not if you use integral cycle control with zero-crossing sense optos.

Worth a try... how'd u suggest I do the avg. current control?

 

[chemelec]

Series Connecting Peltier Devices is Not very good.

 

[Mosaic]

Ok...given all the feedback.I figure this looks like the best option to use a pair of 60W peltiers. Safer and reasonably compact.
https://www.ebay.com/itm/AC-110V-22...ffType=OrderSubTotalOffer&_trksid=p5731.m3795

 

[chemelec]

Definately a Better Option.

 

[tcmtech]

Ok, won't there be heating etc. on the capacitor @ 3-4amps conduction?

No. Read up on how capacitors work in AC circuits.

 

[chemelec]

Ok, won't there be heating etc. on the capacitor @ 3-4amps conduction?

No. Read up on how capacitors work in AC circuits.No. Read up on how capacitors work in AC circuits.

I agree no heat,
But For 4 Amps at 60 hZ, you would Need a VERY BIG CAP.
Probably about 900 uf, Non-Polarized and Probably rated at 250 Volts.

 

[ronsimpson]

plan on using (3) series mounted 12V, 60W (peak) peltier units.

Dumb question:
Is that 3 (4Volt unites)=12V?
OR
Is that 3 (12Volt unites)=36V?

60W total, so 3 X 20 watt?
The numbers do not add up for me.

Do you have data on your Peltier unites?

 

[Mosaic]

60W 12V 5A units. Using 3 was for a lot of thermal margin and losses.

I'll go with 2 x 60W units at first to see if they're adequate for the job. I'll have to mock up the application, but I do have enough on hand to do it before I purchase the 120W PSU.

 

[ronsimpson]

I fond many supplies like this:

 

[chemelec]

Mosaic, CURIOUS, What are you trying to cool with these peltiers?

 

[Mosaic]

Got a couple pounds of solder paste in little tubs, hiding out in the kitchen fridge.

Making a new home for them in the workshop.

 

[chemelec]

I have made Many coolers with TE Devices.
You Might look at this:
http://chemelec.com/Projects/Peltier/Peltier.htm

Hope you have some GOOD Heatsinks and a Fan to keep the Hot Sides Cool.

 

[tcmtech]

But For 4 Amps at 60 hZ, you would Need a VERY BIG CAP.
Probably about 900 uf, Non-Polarized and Probably rated at 250 Volts.

Way too much. To power a 4 - 5 amp 36 volt load off of a 120 VAC 60 cycle power source you would need about 16 - 21 ohms of impedance which works out to around 135 - 165 uF which is easily doable with common motor or HID lighting ballast capacitors.

 

[chemelec]

Way too much. To power a 4 - 5 amp 36 volt load off of a 120 VAC 60 cycle power source you would need about 16 - 21 ohms of impedance which works out to around 135 - 165 uF which is easily doable with common motor or HID lighting ballast capacitors.

I was calculating for 4 Amps at 12 Volts.