chemelec said:I have built and used Many Peltier devices ove the past 25 years.
A Pentium Heatsink is Definately NOT BIG ENOUGH, even with a fan.
If you want Effiency, You need to keep that Hot Side, Really Cool.
I would Not Recommend PWM.
Use a Thermal Detection Circuit to turn it Full On and Full Off as Necessary to maintain the temperatue required.
USE Lots of Insulation on your Water Tank.
A Zener is Not Appropriate for that kind of Supply Current.
Possibly a diode or two in Series, to just Drop the Voltage a Bit.
Or Better yet, Get a Better regulated Charger.
Nigel Goodwin said:Why would you want to PWM one anyway?.
It's essentially a 'heater', and like any other heater if you want to control the temperature you can use 'burst fire' control - turning it ON and OFF over a fairly long time period. For example, ON for 5 seconds then OFF for 5 secs, thus giving 50% rating.
The thermal inertia of the load smooths this out nicely, thus it's commonly used for heating elements.
Styx Posted: I dunno, I dont know much about peltiers, I was just pointing out if you did want to PWM one (say for current control) then there are ways so the peltier sees an almost constant current.
chemelec said:Styx Posted: I dunno, I dont know much about peltiers, I was just pointing out if you did want to PWM one (say for current control) then there are ways so the peltier sees an almost constant current.
Putting a large Capacitor across the output of a PWM Circuit will reduce the Pulse Effect. But What is your Point?
All that Effectively does is Average out the power. In Essence: With 12 volts in and a 50% duty cycle, You will average 6 volts out at whatever current.
Peltier devices work best at there Rated Voltage.
This produces absolutely No Bennifet to driving Peltier devices.
And you obviously don't understand PWM much either.
.Peltier devices work best at there Rated Voltage
Nigel Goodwin: Why would you want to PWM one anyway?.
It's essentially a 'heater', and like any other heater if you want to control the temperature you can use 'burst fire' control - turning it ON and OFF over a fairly long time period. For example, ON for 5 seconds then OFF for 5 secs, thus giving 50% rating.
The thermal inertia of the load smooths this out nicely, thus it's commonly used for heating elements.
chemelec said:Sorry to get you Overheated. Reduce your Duty Cycle.
chemelec said:And you obviously don't understand PWM much either.
chemelec said:I Never said you used a Capacitor.
But in essence your inductor circuit will give the same Effect. Averaging the power, resulting in Reduced Power and poorer efficiency of the peltier device.
chemelec said:I also Never said you Can't control Peltier devices with PWM.
I said or at least ment to imply: that it is not an efficient way to go.
As Nigel Said:
Nigel Goodwin: Why would you want to PWM one anyway?.
It's essentially a 'heater', and like any other heater if you want to control the temperature you can use 'burst fire' control - turning it ON and OFF over a fairly long time period. For example, ON for 5 seconds then OFF for 5 secs, thus giving 50% rating.
The thermal inertia of the load smooths this out nicely, thus it's commonly used for heating elements.
And in Reality, this is Still PWM, But at a Very Slow Frequency.
"In My Opinion": It is better to use this type of duty cycle, preferrably with even longer time periods. Also preferrably controlled by feedback by the required temperature.
WHAT I was dissmission was the statementppl have said that you should not PWM peltiers since they do not like being switched on and off very fast - I dont know much abt peltiers so cant comment
So Peltier "might" not like being switched ON and OFF, I demonstated a methed where they do not switch NO and OFF, but you then go and dissmiss me as not knowing PWM!!!Klaus said:I would have to agree there with chemelec, Peltier devices do not like to be switched on and off rapidly. Besides, there is no point in doing so since temperature variation for a mass of 4 litres of water are going to be slow anyway.
Styx said:WhY? because the method you and Nigel have mentioned might be all well and good for some situations (10s period) BUT it comes at the expense of temperature ripple
IF you could get peltier that could go down to -55 and also +125 then I would invest in a Peltier cooler.
WhY? because the method you and Nigel have mentioned might be all well and good for some situations (10s period) BUT it comes at the expense of temperature ripple
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