Digital Potentiometer and Power Supply

[cmore082]

Hi, and thanks for helping me

I purchased Tusotek Auto DC-DC Constant Current Boost Buck Converter Voltage Regulator 6-35V to 1-35. I am trying to find digitally control the boost buck converter by replacing its 100K potentiometer with a 100K MCP41100 digital potentiometer. I tried using the digital potentiometer with Arduino and the DC-DC booster and it worked, but the booster does not go as high as with the original mechanical potentiometer. Would you know why I the digital potentiometer is no working as intended? What are the factors I must consider if I want to control boost buck converters with a digital potentiometer? Specs of the mechanical potentiometer can be found in the following website (scroll down): http://www.aliexpress.com/item/Trim...ohm-Variable-Resistors-100pcs/1596795967.html

 

[(*steve*)]

the digital pot will probably not work correctly if any of the voltages on the digital pot terminals are outside the power supply rails for the chip.

 

[cmore082]

Hi Steve,

Thanks a lot for the useful input. You are awesome and of great help!

I took new measurements of each heating element. Each heating element (120 mm length 15 mm wide) at its max load of 3V and 1.5A generates 60 celsius. Say I want to have three of these heating elements on the chest (Circuit 1), three on the back (Circuit 2), and two on the stomach area (Circuit 3). I am wondering what is the best set up for the design. Looking at one circuit individually, say circuit 1, would it be best to connect the heating elements in series or in parallel?

Once we find what is the best set up for each circuit, how should we connect all circuits (parallel or series)?

It would be awesome to have a portable battery source that can supply power to the jacket. That's why I was wondering if I would have to use a dc booster.

I greatly appreciate your expert advice. Thank you!

 

[(*steve*)]

Since you have an even number of these, I'd run pairs in series.

Do you have a link to the datasheet for the digital pot?

A simpler approach may be to set the voltage to the max for the elements and use a microcontroller and a mosfet to vary the power using pwm.

An advantage of this is that you can individually control the elements if you wish.

 

[cmore082]

Since you have an even number of these, I'd run pairs in series.

Do you have a link to the datasheet for the digital pot?

A simpler approach may be to set the voltage to the max for the elements and use a microcontroller and a mosfet to vary the power using pwm.

An advantage of this is that you can individually control the elements if you wish.

Hi Steve, I hope all is well. Unfortunately I do not have the datasheet for the heating elements. I am going to follow your advice with using PWM and a mosfet. I would like to have 3 heating elements on the chest, another 3 in the back, and two in the stomach. I was thinking that it was best to connect each element of its region in series. Then connect all 3 circuits in parallel to a source so if a circuit fails, the others can work. If I am right, the schematic would look like the picture attached to the thread. I am thinking of controlling each circuit with a mosfet and an arduino. I also found affordable li-on batteries that have 4800mAh 3.7V

Suppose we want to keep all 8 elements at full capacity for 3 hours, how many batteries would I need? Could you please explain why you came to that conclusion. On a final though, could we use a dc booster to booster the voltage of the batteries so we use less batteries?

Thank a lot!

 

[(*steve*)]

if the strings are not the same length you can't put them in parallel without the shorter string hogging current. You might end up with a fiery hot stomach and barely warm chest and back.

a simplistic calculation of power is that each battery can provide 3.7 x 4.8 Wh of energy. The heat pack consumes energy at a rate of 3 x 1.5 x 8 W. Dividing the energy (Wh) by the rate (W) gives you the duration (h).

In your case it's 17.76 / 36. This is 0.4933, or a tad under 30 minutes. An added problem is that the resistance in the battery will reduce this. However, since this simply adds more heat, if you can position the battery where the heat is not wasted.

Assuming this is the case, you would need 16 or 17 batteries for 8 hours at full power.

 

[(*steve*)]

and with that, I simply repeated the answers you got in another thread.

try not to do that.

 

[cmore082]

if the strings are not the same length you can't put them in parallel without the shorter string hogging current. You might end up with a fiery hot stomach and barely warm chest and back.

a simplistic calculation of power is that each battery can provide 3.7 x 4.8 Wh of energy. The heat pack consumes energy at a rate of 3 x 1.5 x 8 W. Dividing the energy (Wh) by the rate (W) gives you the duration (h).

In your case it's 17.76 / 36. This is 0.4933, or a tad under 30 minutes. An added problem is that the resistance in the battery will reduce this. However, since this simply adds more heat, if you can position the battery where the heat is not wasted.

Assuming this is the case, you would need 16 or 17 batteries for 8 hours at full power.

Hi Steve,

Thanks a lot for the input. Sorry about the posting of another thread. I am new to forums. Not everybody replies to threads.

I have a question. How would the set up of the battery pack affect the performance of the circuit. For example, I understand that setting up the batteries in parallel increases current and in series increases voltage.

 

[(*steve*)]

your resistors require 3V to draw their rated current. Keep the voltage close to 3V x the number of resistors in series.

I recommended 2 in series, so have pairs of batteries in series.

this is not a trivial question. There are many variables.

 

[cmore082]

your resistors require 3V to draw their rated current. Keep the voltage close to 3V x the number of resistors in series.

I recommended 2 in series, so have pairs of batteries in series.

this is not a trivial question. There are many variables.

Thank you Steve!