Thermo electric pcb power supply

[keeney123]

Re: Thermo electric pcb power supply

Yes I applied heat sink compound to both sides hot and cold. The hot side gets a little warm but can be touch with hand no problem and the cool side is blowing cold air on both Peltiers. The outside fans and inside fans are blowing and functioning find. The thermo-couple I believe may be a K type from the coloring? I disconnect it from the power supply measure the resistance across the wires and the resistance measures 10K to 14K when turning rheostat inside the refrig. 10K is full cold. When I leave the thermo-couple disconnected and turn on, Op Amps seem to float. This can be see in the output voltage about 2 volts. I connected a 150K ohm rheostat in parallel with the thermo-couple and turned it down and monitored the current in the output, current stayed steady at 2.5 Amps. Also, I have attached and example of a constant voltage constant current chip by TI. If you look on page 15 you will notice how the output current stays the same for any give output voltage.

[budm]

Re: Thermo electric pcb power supply

BTW, did you apply heatsink compound and does the heatsink get warm at all?

[keeney123]

Re: Thermo electric pcb power supply

How I read the specs. are if the hot side is at 25 degrees C and one applies 12 volts to the Peltier then 4 to 4.5 amps will be drawn through it.

[budm]

Re: Thermo electric pcb power supply

This is not a linear supply but a switching supply using Pulse Width Modulation to control the duty cycle. Unfortunately I do not have 50 watt resistors otherwise that would be a good idea. I do have excess of old computer tower power supplies that have a 12 volt output that can drive several hundred of watts power. I will have to get this from a friend. I have no O-scope to look into the modulation circuit. I just have a multi-meter no schematic. This is in a B&D cooler that B&D does not list on their site nor are their any parts listed for it. I was helping a friend with this refrig. When I got it, it was not cooling. I measured the voltage going to the Peltiers and it measured 12 volts so I took the Peltiers out and ordered the same devices and then it cooled, but only to 60 F. The manual says that maximum cool is 37 F when ambient is 70 F but I think the power supply is under designed. I put attachment of Peltier specs on.

We know that it is regulated SMPS power supply (I already drew the simplified diagram, and it really does not matter if it is regulated switching power supply or regulated linear power supply, it is just the power source that should maintain 12V output up to the load current spec), and it is regulating and maintaining 12V output with Peltier (load) connected to it, if it cannot handle the load the voltage would not maintain at 12V, the current draw from the power supply is dictated by the load if the Voltage is maintained which it does in this case.
For example if you have 12W lamp connected to this power supply, it will only draw 1A so you cannot make it draw more current than that, if you connect 48W lamp then it will draw 4A from the power supply.
The amount of the current draw is based on the delta of the temperature.

[Behemot]

Re: Thermo electric pcb power supply

Peltier only cools on one side when it is sufficiently cooled on the other, otherwise the efficiency drops radically. And even properly cooled it is not very efficient and consumes lot of power. I would say this is more of a cooling problem.

[keeney123]

Re: Thermo electric pcb power supply

This is not a linear supply but a switching supply using Pulse Width Modulation to control the duty cycle. Unfortunately I do not have 50 watt resistors otherwise that would be a good idea. I do have excess of old computer tower power supplies that have a 12 volt output that can drive several hundred of watts power. I will have to get this from a friend. I have no O-scope to look into the modulation circuit. I just have a multi-meter no schematic. This is in a B&D cooler that B&D does not list on their site nor are their any parts listed for it. I was helping a friend with this refrig. When I got it, it was not cooling. I measured the voltage going to the Peltiers and it measured 12 volts so I took the Peltiers out and ordered the same devices and then it cooled, but only to 60 F. The manual says that maximum cool is 37 F when ambient is 70 F but I think the power supply is under designed. I put attachment of Peltier specs on.

[budm]

Re: Thermo electric pcb power supply

It is 12V Regulated power supply, so the if the Peltier is only drawing 2.5A then that is what it is drawing. You can easily verify if the Peltier is OK or not is to hook it up to 12V car battery and check the current draw.
Right now the 12V output is still at 12V and did not drop, right? if that is the case then it is the Petier itself is not drawing the current.
Constant current power supply the voltage will go up or down to force the regulated current to flow through the load when the load resistance changes.
You can also use 3 Ohms at least 50 W resistor to simulate 4A current draw on the power supply.

[keeney123]

Re: Thermo electric pcb power supply

If constant current supply voltage will drop. If constant voltage supply current will drop. I thing this is a constant voltage supply. I have no schematic, but did trace out the front circuit and tried biasing transistors so they would turn on sooner but the control circuit shut everything down.

[keeney123]

Re: Thermo electric pcb power supply

The Peltier Max.about 14.5 Volt, Max.6.5 Amps provide voltage supply will not deliver more than 2.5 Amps at 12 volts.

[budm]

Re: Thermo electric pcb power supply

So what is the spec of the Peltier? If you have 12V power source that can handle the current draw by the LOAD, the load will draw what ever it needs as long as the power supply can handle it, if the power supply is weak then the output voltage will drop.

[keeney123]

Re: Thermo electric pcb power supply

Nothing blew up but the results was the same not enough current to the Peltier. Must be a current control circuit monitoring output current. Next step is to try a old tower computer power supply directly to Peltier devices and see if they will pull 4 amps apiece.

[keeney123]

Re: Thermo electric pcb power supply

I found that replacing the 2 ohm resistor that is color coded to be 200 ohm with a 200 ohm would not work so I replaced the 2 ohms. I replace both transistors with J13009-2 and that worked fine. The problem I am having is that the 2 Peltiers drawing only 2.5 Amps each and that is not enough to cool down the 1.7 cu ft refrig. I found that ERL-28 has two isolated secondary 12 volt coils on the output that are tie together, so that only one coil it providing energy at a time. I am going to configure them so both are being used at the same time which may give me more current at the same 12 volts. I will have to float the secondary of the coil, but keep the gnd. for the 12 volts. To do this I will have to get a Schottky dual diode with a common anode. I will use NTE6244 to do this and also replace the other Schottky dual diode with NTE6240 and see if anything blows up.

[keeney123]

Re: Thermo electric pcb power supply

I do not know if this pertains to same problem, but I have been working on a B&D Thermo-Electric Refrigerator with a power supply board that is suppose to be a Haier RF-5210-60. I found a shorted T6, J13007-2 transistor. It was shorted from base to emitter. With further investigation I found that the bias resistors to both T6 and T7 J13007-2 transistors were miss marked. Both resistors were Red, Black, Brown with a 5% gold tolerance band. When I took these out of the circuit and measured them with a Ohm meter they read about 2 ohms. So this causes me to wonder how many others power supply boards have this problem?

[TedofCroton]

Re: Thermo electric pcb power supply

Hi All,

I basically have the same device as Aaron and was thinking to try the same thing(connect a 220 to 12v adapter(from another appliance or something)). Alternatively, would anyone know where I could get a replacement power supply that has 3 12v outputs and one 12v 3 prong for the temperature regulator?

Spare parts in the wine fridge world aren't very liquid and was thinking to just swap another in. Does this make any sense at all?

Thanks in advance.

[budm]

Re: Thermo electric pcb power supply

I cannot tell until I see the bottom side to see how the low voltage is generated to run the temperature control circuit section.
It looks like it uses similar circuit I drew up in post 11, and the temperature control also runs off 12V. He can try as you suggested to see if the control section will still function.

[momaka]

Re: Thermo electric pcb power supply

I see two transformers, the large one looks like for the 12V may be 4~5A capacity, the smaller transformer next to the brown cap I cannot tell if it is transformer or inductor

To me, this looks like a half-bridge design driven by a 494 or 7500 controller. Most likely, the bigger transformer in the center is for the step-down, and the smaller one next to it is for driving the two BJTs attached to the heatsinks on the left. The fact that there is a brown polypropylene cap on the primary tells me that this is more than likely such design. Probably very very similar to AT computer PSUs.
Under the main transformer is another heatsink with another component on it - my guess is this is the 12V rectifier. If it's a 3-pin device and is marked on the PCB as "D###" (where "###" can be any number), then this is most likely a dual common cathode diode. To eliminate guessing, more detailed pictures would be required. We will also need pictures of the under side of the board to see how everything is connected.

If the design really turns out to be like that, then all you will really need is a powerful diode (rated for at least 6A or more) to feed through to the 12V rail.

[Aaron The Tinkerer]

Re: Thermo electric pcb power supply

Hmm...good point. I was assuming that since the fans and Peltier are getting 12vdc that the temperature control function also is controlled by 12v. The fridge, while in cooldown/full power mode, draws 68 watts so the Peltier module itself is probably a 60-watt (nominal) module, probably a TEC1-12706, so that large transformer is probably 5 amps.

[budm]

Re: Thermo electric pcb power supply

You need to find out if the temp control section also runs of 12V or the main SMPS transformer also has another low voltage winding for making the low voltage to run the temp control circuit. I see two transformers, the large one looks like for the 12V may be 4~5A capacity, the smaller transformer next to the brown cap I cannot tell if it is transformer or inductor, need to trace out the board.

[Aaron The Tinkerer]

Re: Thermo electric pcb power supply

The board also has temperature control so it does not drive the Thermo full on all the time, so if you feed the module with 12V to the cooler module, it will run on full mode.

I understand that, but isn't there a way to feed it 12v before the temp. control section, essentially bypassing the converter section? I definitely need the temp. control function because I don't want it running full-on all the time.

[budm]

Re: Thermo electric pcb power supply

The board also has temperature control so it does not drive the Thermo full on all the time, so if you feed the module with 12V to the cooler module, it will run on full mode.