Pro/Forums - View Single Post

Rich W · 01-25-2001, 02:13 AM

Yes, that sounds about right. And you were measruing correctly...

Now when you say that the output voltage stayed at 18.5V, that is less than the RMS values of the transformer(s) you have (I calculated that earlier to be 20V RMS, that's how I came up with that 29.7 V reading...) So, the voltage is below the RMS voltage of the transformer.. I don't know much about this case, but I know that it isn't too good.. both for the life of the transformer, and the 'quality' of the DC current... ie, there will be LOTS of ripple. Can you read to me the value of the capacitor? If you can, I think I can dig up an equation that will give the percent ripple of the power supply (ripple is how much the current varies... with a small load, the ripple will be less.. as the load increases, ripple will increase... a bigger capacitor can help). When ripple gets above anywhere from 5% to 15%, weird things can happen to the peltier.. either it won't cool as well as it could, or it might under go 'thermal stress'.... that occurrs when the power is cycled at a frequency less than 1kHz to 2kHz.. and that is bad for the peltier after a while. Can you measure the voltage output while attached to the peltier with the voltmeter in AC mode? Lemme know what that reads.

As for ther performance of the peltier, that is how it should behave when properly cooled.... becareful not to have the peltier exceed about 80 deg C though... at that temp (normal) peltier modules will be destroyed because that is the temperature at the solder which holds all the tiny modules inside will melt at. Some 'high temp' modules can whithstand up to 200 deg C, but by far most are 80 deg C modules.

Also, I'll make up a chart here in the next few days that might clarify some things... we'll see.

LMK...
Rich W.

01-25-2001, 02:13 AM	#22
Rich W Cooling Neophyte Join Date: Feb 2000 Posts: 77	Yes, that sounds about right. And you were measruing correctly... Now when you say that the output voltage stayed at 18.5V, that is less than the RMS values of the transformer(s) you have (I calculated that earlier to be 20V RMS, that's how I came up with that 29.7 V reading...) So, the voltage is below the RMS voltage of the transformer.. I don't know much about this case, but I know that it isn't too good.. both for the life of the transformer, and the 'quality' of the DC current... ie, there will be LOTS of ripple. Can you read to me the value of the capacitor? If you can, I think I can dig up an equation that will give the percent ripple of the power supply (ripple is how much the current varies... with a small load, the ripple will be less.. as the load increases, ripple will increase... a bigger capacitor can help). When ripple gets above anywhere from 5% to 15%, weird things can happen to the peltier.. either it won't cool as well as it could, or it might under go 'thermal stress'.... that occurrs when the power is cycled at a frequency less than 1kHz to 2kHz.. and that is bad for the peltier after a while. Can you measure the voltage output while attached to the peltier with the voltmeter in AC mode? Lemme know what that reads. As for ther performance of the peltier, that is how it should behave when properly cooled.... becareful not to have the peltier exceed about 80 deg C though... at that temp (normal) peltier modules will be destroyed because that is the temperature at the solder which holds all the tiny modules inside will melt at. Some 'high temp' modules can whithstand up to 200 deg C, but by far most are 80 deg C modules. Also, I'll make up a chart here in the next few days that might clarify some things... we'll see. LMK... Rich W.