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diy solar

Need a tool recommendation

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Sean Steele

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Aug 28, 2020
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I need an inline USB current display with adjustable current limiting capability. I am finding lots of meters but can't really tell for sure if any of them allow for setting a current limit. I want to make a USB powered heating device but want to limit the heat. Once I come up with the desired current, I plan to make a dedicated circuit from components.

I will be using a 5v 1watt heating pad but it heats up to 80C. I'm looking for room temperature.
 
If I understand correctly you have 2 wires (red/black) from the USB that'll be 5 volts
you want to limit the current instead of a device that will turn it on/off based on a temperature probe?
 
This will adjust current what you want to specifically look for is an LED driver as they have a potentiometer to set your current to a specific rate

but what you really want is a temperature sensor to just on/off it as we said above
or
or
https://www.aliexpress.us/item/3256805325622897.html (seems pretty versatile?)
(haven't used/tested either but pretty similar to one I have had for several years.. just random chinese chip and works fine)


These things work well too, and it's a bit easier
you plug it into mains then flip stuff on/off with that, you can plug a USB dongle in it to turn on/off your 5v thing
 
Last edited:
Thank you all. I knew this forum would set me straight. I probably should have mentioned that this was not a normal use case like a battery warmer. However, I suppose my use is pretty similar. I've seen rv tank warming pads with thermocouples on them could I use something that simple? I don't have room in my application for much in the way of circuitry.

EDIT: That LED driver is tiny. Smaller than the current limiting circuit I was looking at. I am looking into the other suggestions.
 
I've seen rv tank warming pads with thermocouples on them could I use something that simple?
Click to expand...
uhh sounds like it, if the thermocouple is connected to some sensor that turns on/off?
like a heating blanket has? those work fine too

I did link a current driver, which is an LED driver that you can use though if your original method is where you want to go with this. There are a million different ones but all the LED ones set a specific voltage and a specific current or else the led will burn out since it's a diode
 
Sean Steele said:
Thank you all. I knew this forum would set me straight. I probably should have mentioned that this was not a normal use case like a battery warmer. However, I suppose my use is pretty similar. I've seen rv tank warming pads with thermocouples on them could I use something that simple? I don't have room in my application for much in the way of circuitry.

EDIT: That LED driver is tiny. Smaller than the current limiting circuit I was looking at. I am looking into the other suggestions.
Click to expand...
oh just saw your edit, yea I don't think you will get smaller than that chip other than having the controlling of it external of where ever your heating goes
what you can do is after you wire it, take a big piece of heat shrink for large wires and put it over that led driver and use a heatgun or w/e to shrink the heat shrink tube over it and it'll be pretty good for outdoors/waterproof
also squirt some silicone in the openings on the sides lol
 
He said room temp so I guess 70f / 21c?
I'm wondering what he is doing that like 3cm device is already pushing his space limits hahaha
 
I'll tell you if you promise not to steal my idea. Lol. A friend of mine is tired of having hard butter in the morning after leaving it out overnight in her camper.

So, we want to add the heating pad to the bottom of a butter dish and power it by USB.
 
hahaha nice
You know I'd recommend the old school coffee mug warmer and just kick it on 15-30 mins before wake up time

I guess it's more complex and you could do that with your pad too, instead of leaving it on 24/7 I see why the temperature probe is hard too
but if you do a current limiter and the inside temp of the room changes... or there's more air movement... then the device won't be setting the correct temperature

It is plugging into an outlet though and a timer device could have all the logic there instead of needing a bulky-ish temperature probe down by the pad

some of them already around
www.seriouslytrivial.com

Electric butter warmer/softener DIY

I like to keep my butter on the kitchen counter and have been searching for a way to keep it soft–at least not rock-hard–for years. The problem got significantly worse after I moved to …
www.seriouslytrivial.com www.seriouslytrivial.com
 
I would start with an LM34 temperature sensor. These put out 10mV per degree Fahrenheit (700mV at 70F).
If you live in the civilized world the LM35, the Celsius version might be more appropriate.
https://www.ti.com/lit/ds/symlink/lm34.pdf

Then I would buy one of those Chinese digital voltmeters, one capable of reading down to millivolts, that has a programmable under/over voltage alarm relay.
That will read out directly in temperature, and you can program into it the required set point for the heater.

I made myself a very nice bedroom digital thermometer using an LM35 and a digital amp meter display.
The amp meter display was supposed to read up to 50 amps from a 50mV current shunt. So it read directly in degrees, and tenths of a degree Celsius.

Something like that with an adjustable set point alarm output should be ideal.
 
Last edited:
That's a cool sensor
I guess if you had the opposite of something like that a resistive heating pad can just be directly connected as the voltage goes up the heating would go up and push the voltage back down lol
 
gotbeans said:
hahaha nice
You know I'd recommend the old school coffee mug warmer and just kick it on 15-30 mins before wake up time

I guess it's more complex and you could do that with your pad too, instead of leaving it on 24/7 I see why the temperature probe is hard too
but if you do a current limiter and the inside temp of the room changes... or there's more air movement... then the device won't be setting the correct temperature

It is plugging into an outlet though and a timer device could have all the logic there instead of needing a bulky-ish temperature probe down by the pad

some of them already around
www.seriouslytrivial.com

Electric butter warmer/softener DIY

I like to keep my butter on the kitchen counter and have been searching for a way to keep it soft–at least not rock-hard–for years. The problem got significantly worse after I moved to …
www.seriouslytrivial.com www.seriouslytrivial.com
Click to expand...
Believe it or not, the USB coffee warmer was the first thing we looked at. They are supposed to keep the coffee at 120 to 135°F. That's thru a ceramic mug. I'd imagine a butter dish would get a bit too warm. Maybe if we wanted to have melted butter for lobster. Lol

P.S. I sent her that diy dish. There was also a discontinued battery powered unit that was $60. Seems like a really niche item. I'm hoping to make something a bit more approachable for boondockers.
 
Yea you'd have to only turn it on a few minutes for the butter, why I'd do like 15 before waking up or w/e then just turn off

don't worry though I won't steal the idea hahaha I leave my butter in the fridge/freezer ?
 
Warpspeed said:
The lowest temperature one I could find operates between 20C and 35C which is still too hot.
https://www.ebay.com.au/itm/134717853932?hash=item1f5dcf50ec:g:enYAAOSwEIxk-Rp5&amdata=enc:AQAIAAAA0FwywohbUkEd+A/vWzzDziuRsS6e7ELdV4tR6mc7Zg4F+jUkWDZ4y/F+QmGAj0DUQIJPan+qAVhkzJ+V8YXjb3kmNPKxxRao4C8/MTNKZPvUcvX3ePggPAGXqMGKJsLaWL0eL6yDKkRGJxQbRZ/Wq1hgp8Le1myhsO8Mdcda5Y+gYZem6uQ+k31U1f1AzSA/UzWiLozUenPgKgx7GKspFH/KdFWs5PEqadRiDU/Z7JwM2S7a8ScuxRlm4OLuTOIVDV9rEVpZHCaJ09qAI+FiOHE=|tkp:Bk9SR5TXw5GIYw
Click to expand...
The link I shared had 15C and 20C options. I'm no electronics engineer. In the interest of keeping this circuit simple I was hoping to connect this online with the heating pad. Given the low wattage and low voltage, would this be possible/recommended?
 
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