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bkamen
Joined: 07 Jan 2004
Posts: 1615
Location: Central Illinois, USA
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| Using ECCP for TEC Control |
 Posted: Thu Sep 22, 2011 5:28 pm |
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Has anyone used the ECCP of a PIC for TEC control?
If so, did you use full or half bridge (driving a full bridge)?
I like the simplicity of the half-bridge mode (driving a full bridge) but it looks like the PWM cycle is always in a complementary mode (which doesn't look like it would mesh well for a TEC as the load.)
(In Full bridge, heating or cooling would be selected via REVERSE mode which seems like the right way for a TEC)
Just wondering what others' experience has been.
Thanks,
-Ben
EDIT: I should also add that the TEC will be used for regulating a temp (it will heat as well as cool the device)
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Dazed and confused? I don't think so. Just "plain lost" will do. :D |
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asmboy
Joined: 20 Nov 2007
Posts: 2128
Location: albany ny
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| Posted: Fri Sep 23, 2011 10:29 am |
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"TEC" ??defined as ?
thermo electric cooler ala Pelletier ??
i sure do get using PWM as a proportional heat regulator method in general
but in what way is PWM going to ( linearly?) adjust heating AND cooling?
are we talking about modulating the motor driver on some sort of acoustic refrigeration gadget??
Thermoacoustic heat pump??
OR running both a resistive heat element AND
a proportional valve for applying refrigerant ??
you sure have me puzzled with this one. |
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bkamen
Joined: 07 Jan 2004
Posts: 1615
Location: Central Illinois, USA
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| Posted: Fri Sep 23, 2011 10:39 am |
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| asmboy wrote: | "TEC" ??defined as ?
thermo electric cooler ala Pelletier ??
i sure do get using PWM as a proportional heat regulator method in general
but in what way is PWM going to ( linearly?) adjust heating AND cooling?
are we talking about modulating the motor driver on some sort of acoustic refrigeration gadget??
Thermoacoustic heat pump??
OR running both a resistive heat element AND
a proportional valve for applying refrigerant ??
you sure have me puzzled with this one. |
I love it when I can stump the masters!
Anyway - yes, TEC = Thermo Electric Cooler (Peltier) and as you know (for everyone else's benefit) they can be used to heat or cool depending on which way the current flows.
While I have tried it yet, the ECCP looks like in half-bridge mode, a duty cycle of 50% would equate to 1/2 the waveform coming out of PxA and PxB for the other 1/2 of the cycle.
More PWM in one direction would equal colder and more in the other would equal hotter -- the amount of "bits" towards one or the other would be split and resolution would be lost.
I decided that Full-Bridge was probably the best way -- but still wondered if anyone had done this yet just for comparison. Maybe there's something super neato about Half bridge mode I didn't consider... I guess it would work --- just maybe for lesser or lowercost applications.
To me, half bridge mode seemed like a sure "don't do this way" method. What are the thermal stresses (if any)?
ya know?
Anyway -- that's my story. I'm sticking to it.
-Ben
_________________
Dazed and confused? I don't think so. Just "plain lost" will do. :D |
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asmboy
Joined: 20 Nov 2007
Posts: 2128
Location: albany ny
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| Posted: Fri Sep 23, 2011 12:26 pm |
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i had thought TEC were different from ordinary thermocouple junctions.
as in --
is there not a DIODE effect that only allows only
uni-directional current flow - hence a defined hot and cold side ????
i had never heard or realized that there was any other possibility
that said - at least - unidirectionally for sure- no reason why a PWM source of excitation should NOT work to modulate the essential heat pumping action. |
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bkamen
Joined: 07 Jan 2004
Posts: 1615
Location: Central Illinois, USA
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| Posted: Fri Sep 23, 2011 12:32 pm |
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| asmboy wrote: | i had thought TEC were different from ordinary thermocouple junctions.
as in --
is there not a DIODE effect that only allows only
uni-directional current flow - hence a defined hot and cold side ????
i had never heard or realized that there was any other possibility
that said - at least - unidirectionally for sure- no reason why a PWM source of excitation should NOT work to modulate the essential heat pumping action. |
Right, in a normal unipolar fashion, it would be fine.
The ECCP looks like it's bipolar even in half-bridge mode where the direction bit may not apply (there's no setting for it if you look at the ECCP docs.
So in a single PWM cycle, the true part would be PxA active and the false part of the cycle would be PxB active.
I think that would work -- but it would be weird and less effective as a full bridge (and a Full-Bridge driven by half-bridge setup like shown in the PIC datasheets would be equally less effective as the half-bridge if you had 2 supply sources.)
Anyyyyway... I went with full bridge... but I'd still like to hear from anyone who did a temp controller using a TEC.
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Dazed and confused? I don't think so. Just "plain lost" will do. :D |
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