Peltier Help - (Solar Powered Cooler?)

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Re: Peltier Help - (Solar Powered Cooler?)

Postby judas79 » September 28th, 2016, 1:27 pm

Thanks a lot for the great answer it was totally complete and well explained. Could you take a look at these links to verify if I'm ordering the right hardware? I haven't ordered anything yet...
'buck' dc-dc converter
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http://www.ebay.com/itm/150W-12A-DC-DC-CV-CC-Buck-Converter-4-5-32V-24V-to-12V-19V-1-30V-Step-Down-Power-/252220643705?hash=item3ab9859979:g:5foAAOSwys5WVYG6

or
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http://www.ebay.com/itm/200W-15A-12V-Voltage-Power-Buck-Converter-Step-Down-Module-DC-DC-8-60V-TO-1-36V-/391456268942?hash=item5b249ca28e:g:HyIAAOSw65FXsXsd

and the capacitor
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http://www.ebay.com/itm/5-x-25V-1000UF-105C-Radial-Electrolytic-Capacitor-10x20mm-HP-/262556298829?hash=item3d21932e4d:g:NhYAAOSwqfNXnkSb

or
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http://www.ebay.com/itm/2-Pcs-1000uF-35V-105C-Radial-Electrolytic-Capacitors-Black-21x13mm-H1-/282057700358?hash=item41abf2f406:g:~CsAAOSwbsBXlblT
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Re: Peltier Help - (Solar Powered Cooler?)

Postby k-ww » September 28th, 2016, 2:05 pm

The DC/DC converters look OK.

On second thought, 4700 uf at 35V would be even better for the cap.
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Re: Peltier Help - (Solar Powered Cooler?)

Postby judas79 » September 28th, 2016, 2:55 pm

Many thanks again; I will do as you advised and order the bigger cap.
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Re: Peltier Help - (Solar Powered Cooler?)

Postby xgarb » September 4th, 2017, 4:10 am

Hi,

Did you get anywhere with this? I've been trying something similar on and off for years and have discovered that a solar panel and a peltier can be difficult to make work together.

I have a 100W panel (18V 6A)
Peltier - Voltage: 12V, Umax (V): 15V, Imax (A): 4.3-4.6A, QMax (W): 72W)
DC Converter - https://www.banggood.com/DC-DC-8A-Autom ... 69195.html (Input voltage: DC5-30V Input current: 8A (MAX)

At the moment I'm finding it works if, on the DC converter, I set the output current as low as possible and the voltage to be 12v without the load and then attach the peltier (with fan and heatsink) and slowly increase the current output to maximum. While I do this I can see the Volts increasing from around 6V to around 10V.

If I switch off the power from the panel and then switch It on again the voltage is around 5v and the fan barely spins. I'm not sure what is happening here. I need to find some way of increasing the current output to the peltier slowly.

If I try the same as above when there is less sun, the voltage slowly rises up to a point and then drops quickly. I guess something happens with the panel voltage when the peltier starts drawing too many Amps for the amount of sun.

I've ordered a capacitor but I'm not entirely sure how I would use this.

Another thing that I'm not sure about.. the DC converter gets really hot (too hot to touch) while I'm running the peltier.

I've attached a couple of files. One showing the system and the other showing how effective it is at dehumidifying.
Attachments
IMG_20170902_125246524.jpg
Condensation
IMG_20170902_125230719b.jpg
Overview - power is going right to left
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Re: Peltier Help - (Solar Powered Cooler?)

Postby k-ww » September 6th, 2017, 11:15 am

xgarb: Some questions and suggestions:

1) do you have the DC converter placed so that it is in the airstream of the pelter's fan? [every bit of cooling helps with such a little heatsink as on the DC converter.

2) with the DC converter running, I would measure from the 'arm' of the pot that controls the current limiting of the DC converter and make note of which side of the pot the arm goes to as the current limit is reduced, and the polarity of the arm of the pot from that terminal. I would then place the cap [4700uf or whatever you have] and wire it [observing the polarity] across the pot's arm and that terminal. This will give a 'soft start' function of sorts to the DC converter's current output. The output of the DC converter when you first connect it has to provide a lot of current to the peltier and this may cause it to go into self-limiting on startup with the current limiting set to maximum, or even exceed the output capability of the transistors inside [think of trying to drop the clutch on a manual transmission car at a dead stop, with the car in 3rd or 4th gear, and a small engine [VW beetle] - you will stall the car or it will move 'chug-chug'.

3) If you consider the solar panel as a battery that has an internal resistance that increases with a decrease in sunlight, that may help you understand what is happening to the output of the solar panel.
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