15.2V 136.8W max pelts under-volting amps/watts?

[terramir]

Just need to know what current they will draw max at 4V and 6V
because I want to use 6 of these tec12709's (there cheap) and lower the voltage so there more efficient. the freezone had 2x 3 in series now I'm wondering what kind of current I'll be dealing with I think somewhere around 4 amps from each bank @ 12v (3x4V in series) total watts used like 68 if 4 amps is right. might actually do 3x 2x6V but I don't know what kind of energy they will use then.
well that's about it let me know if anyone's got the data I need
terramir

[Akula]

This seems pretty close to what you described.

http://www.customthermoelectric.com/...Q_spec_sht.pdf

SoI would say 4 amps is a good ballpark figure.

[zipdogso]

Just need to know what current they will draw max at 4V and 6V
because I want to use 6 of these tec12709's (there cheap) and lower the voltage so there more efficient. the freezone had 2x 3 in series now I'm wondering what kind of current I'll be dealing with I think somewhere around 4 amps from each bank @ 12v (3x4V in series) total watts used like 68 if 4 amps is right. might actually do 3x 2x6V but I don't know what kind of energy they will use then.
well that's about it let me know if anyone's got the data I need
terramir

Firstly where you buying 12709's I ask because 12709's don't have a Qmax as high as 136w...not when specs are correctly quoted anyway. it is not ebay by any chance ?
Show me where your buying them assuming it's online.

Akulas reference is wrong those sheets are for 12715's.

This is the closest sheet :- http://www.customthermoelectric.com/...W_spec_sht.pdf

as you can see 12709's are no where near 136w Qmax.

So if you do have 12709's at 4v I expect it will be a shade over 2amps for a single TEC.
and at 6v it's a shade over 3amps..... of course a lot will depend on your Dt.

[terramir]

Firstly where you buying 12709's I ask because 12709's don't have a Qmax as high as 136w...not when specs are correctly quoted anyway. it is not ebay by any chance ?
Show me where your buying them assuming it's online.

Akulas reference is wrong those sheets are for 12715's.

This is the closest sheet :- http://www.customthermoelectric.com/...W_spec_sht.pdf

as you can see 12709's are no where near 136w Qmax.

So if you do have 12709's at 4v I expect it will be a shade over 2amps for a single TEC.
and at 6v it's a shade over 3amps..... of course a lot will depend on your Dt.

Not saying Qmax saying max draw there is a difference.
12709's are supposed to have an Imax of 9A and an Umax of 15.4V,
15.4V x 9 = 136.8W consumption 12V times nine would be like 100W however that doesn't mean that's what it's drawing :S these things are a bit confusing. I wish I could find a full spec sheet for these things the best I can find and the 12709 is a different animal than a 12711 (different resistance and hence a different curve) is this http://www.bkbelectronics.com/pdf%20...-127120-50.pdf
anyways need some more info I understand what your saying about the qmax it's like 80, anyways I need more info on the power draw not the cooling power.
terramir

[zipdogso]

Not saying Qmax saying max draw there is a difference.
12709's are supposed to have an Imax of 9A and an Umax of 15.4V,
15.4V x 9 = 136.8W consumption 12V times nine would be like 100W however that doesn't mean that's what it's drawing :S these things are a bit confusing. I wish I could find a full spec sheet for these things the best I can find and the 12709 is a different animal than a 12711 (different resistance and hence a different curve) is this http://www.bkbelectronics.com/pdf%20...-127120-50.pdf
anyways need some more info I understand what your saying about the qmax it's like 80, anyways I need more info on the power draw not the cooling power.
terramir

Oh I see it is you clouding the issue....it is more normal to quote the Qmax than the max consumption.

If they are 12709's the spec sheet I quoted is correct...they are 12709's.

here it is again:-
http://www.customthermoelectric.com/...W_spec_sht.pdf

The actual power draw will depend heavily on your Dt. As your linking multiple TECs 0.25 amp either way can make a lot of difference to the outcome especially when undervolting as you can see from the sheet.
At 4v you will be forcing the initial Dt low (10-20) range which of course requires more current, and the cooling wattage would drop below 30w
At 6v the difference in Dt is not so great. You should still expect to initially be in the low 20's - top 10'.

I say initial Dt because that is what it is - it is determined initially by the power level the Dt is further altered by the load you apply to the coldside relative to it's Q at that operating point.

Spec sheets are really only for ballpark figures to determine operating points not for accurate determination of any figure.
The only way to get accurate figures is to run the TEC at your determined operating point.

[terramir]

Oh I see it is you clouding the issue....it is more normal to quote the Qmax than the max consumption.

If they are 12709's the spec sheet I quoted is correct...they are 12709's.

here it is again:-
http://www.customthermoelectric.com/...W_spec_sht.pdf

The actual power draw will depend heavily on your Dt. As your linking multiple TECs 0.25 amp either way can make a lot of difference to the outcome especially when undervolting as you can see from the sheet.
At 4v you will be forcing the initial Dt low (10-20) range which of course requires more current, and the cooling wattage would drop below 30w
At 6v the difference in Dt is not so great. You should still expect to initially be in the low 20's - top 10'.

I say initial Dt because that is what it is - it is determined initially by the power level the Dt is further altered by the load you apply to the coldside relative to it's Q at that operating point.

Spec sheets are really only for ballpark figures to determine operating points not for accurate determination of any figure.
The only way to get accurate figures is to run the TEC at your determined operating point.

ok I'm looking at all these charts and well what confuses me is the higher the deltaT to higher the amp draw is, shouldn't be the other way around, i.e. as long as the delta T is low shouldn't it draw higher amps in order to increase the deltaT and then slowly as the delta T reaches the max for the voltage given shouldn't the power draw decrease? the way these charts are written it seems like that the higher the temp difference is the higher the current draw period. Could you clear that up for me?
Also I needed the max amps it will draw in order to design the controller circuit, because the mosfet or relay I will use as a switch needs to be able to handle the current throughput. so that's why I need the I max @ 4 volts, because I'll have three tec's in series so when they max let's say 3amps @ 12V (because it's in series that would be 36W x 2 banks would be 72 watts which would be more than the freezone which draws 56W max. @ 6 volts that would be 3banks x 2 it then estimated let's say 4 amps x 12V times 3 banks this would be 48W x3 banks= 144W this would double the power draw from the tec cooler. I just need to figure out the max values so I can plan for the max power demand, I understand that the better I cool the hot-side of the tec's the less delta T there will be and the less overall power will be drawn from the circuit. by those same figures if I modify the freezone and wire the tec's there in a way so they draw 6V then the max wattage would increase 2 fold, it seems if I go by the other example.
I'm just trying to figure out what I need to plan for in the current department.
terramir

terramir

[zipdogso]

ok I'm looking at all these charts and well what confuses me is the higher the deltaT to higher the amp draw is, shouldn't be the other way around, i.e. as long as the delta T is low shouldn't it draw higher amps in order to increase the deltaT and then slowly as the delta T reaches the max for the voltage given shouldn't the power draw decrease? the way these charts are written it seems like that the higher the temp difference is the higher the current draw period. Could you clear that up for me.

terramir

Your not reading it right...it looks fine to me the higher the Dt the lower the amps....what you looking at ?

The volts are the vertical axis and the amps are horizontal. So looking at 4v with a Dt of 60º (which is ridiculous in the real world you will never get it.) current draw is 0.75amps and at Dt of 20º (more like what you will probably get) it draws 2 amps.

[terramir]

exactly the higher the temperature difference the lower the amps how does that make sense because wouldn't it take more effort to keep that temperature difference going :S
terramir

[Akula]

The way to read those graphs is really to start with the voltage vs. current graph. Your voltage is determined by your power supply, which unless you are specifically using a constant current power supply, will be a constant voltage. Your amperage is determined by the dT across the TEC element, in other words your ability to remove heat from the hot side of the element.

You can think of it like lifting a load up a cliff with the dT being the height of the cliff and the heat removed from the cold side (Qc) being weight that is lifted. The higher the cliff the more power required to lift that load to the top. The trick with TEC is that just like in real life, the rope used to haul the load up the cliff has a weight of its own. Moving 1 Watt across a dT of 5 degrees takes less power than moving the same 1 Watt across a dT of 10 degrees. The kicker is 1 Watt across 10 deg C takes more than twice as much power than 5 deg C. In other words, as your dT increases your efficiency decreases, you need more rope.

I hope that analogy wasn't too convoluted.

[zipdogso]

exactly the higher the temperature difference the lower the amps how does that make sense because wouldn't it take more effort to keep that temperature difference going :S
terramir

Firstly the graphs are merely for determining whether a said unit can achieve the cooling your looking for and then find an operating point to achieve the cooling you require. They are no use what so ever once a unit is running except to confirm an initial manufacturers spec.
Running specs must be measured

TEC's are heat movers they dont actually chill.

It is all about movement of heat...heat moves more easily from a hot object to a cold object than from a hot object to a warm object.

Heat naturally moves from hot to the cold but in a TEC it is electrically induced to move the other direction. That's the trick that allows TEC's to remove heat from objects. The greater the difference in temp between the cold and hotsides the easier it is for the TEC to move the heat and consequently requires less current. So it figures a low Dt requires more power at the same operating point.

An often forgotten point is the Dt with TECs refers only to the temp of the hot and coldsides and doesn't involve any external temps.
Dt is initially pegged by the operating point and the thermal heat inefficiencies of your mounting etc. and then constantly further adjusted, going both up and down, by both the load on the coldside and the level of cooling on the hotside and both of these can be further altered by other factors.

So for you to try a get a max for current would require you to determine the lowest Dt at your chosen operating point. Short of using Dt=0, which wont neccessarily solve the problem as it is possible in extreme cases to have negative Dt, the only way to accurately determine it is to set up your TECs and measure it.

[Akula]

Heat naturally moves from hot to the cold but in a TEC it is electrically induced to move the other direction. That's the trick that allows TEC's to remove heat from objects. The greater the difference in temp between the cold and hotsides the easier it is for the TEC to move the heat and consequently requires less current. So it figures a low Dt requires more power at the same operating point.

You have it backwards zipdogso, heat moves naturally from hot to cold and the greater the dT between the hot region and cold region the greater the flow. When you want to pump heat from a cold region to a hot region is requires more power as the temperature difference increases.

This is why TEC lose efficiency as the dT increases. To move the same thermal load as the dT increases the electrical power supplied to the TEC must also be increased. This increase in electrical power increases the resistive heating (P = IV) in the TEC element and the whole process becomes less efficient, because the TEC is pumping the heat from the cold side to the hot and the resistive heat. Eventually the system reaches a steady state.

[terramir]

yeah That's what I thought but this is why this thing about the current draw being smaller the higher the deltaT is doesn't make sense to me :S
terramir

[zipdogso]

yeah That's what I thought but this is why this thing about the current draw being smaller the higher the deltaT is doesn't make sense to me :S
terramir

Read my last post again properly.....

I am well aware heat goes hot to cold I said as much...BUT in a TEC it is electrically induced to go the other way...if it didn't the TEC would not remove any heat !!! Heat has to flow from the coldside to the hotside.
Remember heat movement is determined by the current flow, TEC's work connected either way round with the flow relative to the +ve/-ve

My explaination for your apparent misunderstanding is correct.

[Ultrasonic2]

Presuming you're applying umax and imax then if you apply no load to a TEC it will logically use less electricity than if the TEC is fully loaded.

So a TEC achieving a delta of 69 while moving nothing will use less power than a TEC at a delta of o while moving Qmax+ ( which is rather logical if you ask me )

TEC's aren't mysterious objects that require us to ponder how they work. they have been around for ages and the FACTs have been widely published.

[Akula]

So a TEC achieving a delta of 69 while moving nothing will use less power than a TEC at a delta of o while moving Qmax+ ( which is rather logical if you ask me )

A TEC with a delta T at Tmax does have a significant load on it. The load is from the resistive heating of the element its self. It may not be moving heat from the cold side to the hot side, but it is blocking heat from moving back to the cold side.

[Ultrasonic2]

A TEC with a delta T at Tmax does have a significant load on it. The load is from the resistive heating of the element its self. It may not be moving heat from the cold side to the hot side, but it is blocking heat from moving back to the cold side.

This certainly isn't a rebuttal to what i wrote ( im not sure it's meant to be )

At dTmax no load is applied to the cold side Ch of the TEC. The TEC is moving nothing from Ch to Th. Though at this point the TEC is consuming Pmax !

let me quote the definition of dTmax from a TEC manufacture
tetech.com



The maximum obtainable temperature difference between the cold and hot side of the thermoelectric elements within the module when Imax is applied and there is no heat load applied to the module. This parameter is based on the hot-side of the elements within the module being at 300 K. In reality, it is virtually impossible to remove all sources of heat in order to achieve the true DTmax. Therefore, the number only serves as a standardized indicator of the cooling capability of a thermoelectric module.