Automatic Switch for 12 volt Cooler?

paulstamserpaulstamser Solar Expert Posts: 86 ✭✭✭
I need help on how to find or make a voltage regulated on/off switch or relay for a 12 volt cooler wired into my home PV system.

Here's the situation: I have a small remote stand-alone 12 volt PV system with limited battery storage. In winter I use natural refrigeration, but in summer I am able to run a small Coleman 12 volt thermo-electric cooler (uses 4.5 amps) with the excess output of my PV array. I can cool it down to the low 30s F. and it stays fairly cool overnight since the cooler is in my root-cellar.

Right now I am regulating it with a simple on/off switch. That is, when the sun is fully on the array I turn it on (about 10:30 am), but on cloudy days or after the sun is off the panels (around 4 pm) I turn it off. Just a flip switch.

But, I would like to make it automatic in operation. That is, when I forget, or go away for the day or overnight the cooler will turn on and shut off automatically depending on system voltage; whether or not the sun (or bright overcast) is hitting the PV array. But I don't know exactly how to do this. I know that I need some kind of automatic switching device or relay that will turn the cooler on when my system voltage is above a certain level (say 13.5 volts) which means the sun is shining good, and then automatically turn the cooler off when the voltage drops to 12.6 volts meaning the sun is gone and battery voltage is getting too low.

Question: Is there off-the-shelf adjustable voltage on/off switch/relay such as described above? Something I can install in the cooler circuit of my household PV system? It needs to be adjustable so I can set the turn-on/turn-off voltage points at the best possible levels for my system so the battery remains fully charged. Does such a unit exist? If so, where can I buy one?

Or doesn't such a unit exist and I have to make my own?

Any advice very much appreciated!

Thanks
«1

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Automatic Switch for 12 volt Cooler?

    This probably won't be the answer you are looking for.

    There are charge controllers such as this SunSaver http://store.solar-electric.com/ss-6l.html which have a Low Voltage Disconnect which might handle it. You'd need exact figures on how much the 'frige draws and a technical answer on what the controller can handle on its LVD terminals.

    This relay driver http://store.solar-electric.com/moredr.html might be adaptable to your use.

    Or this voltage controlled switch: http://store.solar-electric.com/volconswit.html

    If nothing else, a simple timer: http://store.solar-electric.com/fldctico.html

    That's just some of the possibilities pulled only from the host NAWS web site.

    Maybe you might want to consider a 3-way 'frige from an RV, and perhaps upgrading the system so the batteries aren't in danger of low voltage? Whatever else, allowing them to discharge and stay low for any significant length of time will shorten battery life.

    Am I correct in assuming your cooler isn't temp regulated? If so, it's probably using more power than necessary.
  • BB.BB. Super Moderators, Administrators Posts: 29,639 admin
    Re: Automatic Switch for 12 volt Cooler?

    One other, more expensive option is a Battery Monitor. Some (like in the Xantrex series) can be programmed to turn on and off based on Battery State of Charge (i.e., turn on at 90% state of charge, and turn off at 80% state of charge.

    My guess though--is you should also look at something else besides the thermal electric cooler... They are terribly inefficient--and many have motors that will not last very long in continuous service.

    There are small coolers that have a real refrigeration compressor (example, don't know anything about brand).

    Or, various sizes of propane / RV fridges...

    Or convert a reasonably efficient device to a fridge:

    Chest freezer as a chest refrigerator

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,314 ✭✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    I second the opinion of the efficiency of the Thermal Elect. Cooler. 4.5 amps, around 50 watts. A small Propane fridge with a 12 vdc heating element that draws about 100 watts is available. (Also not a very efficient use of electricity! only for example. A small fridge like that might have a duty cycle of ~50% if the installation was good. Say 1.2 kwh/day.

    Your 54 watts chugging away 24/7 would burn 1.27 kwh/day so even with the inefficiencies using electricity to power a absorption fridge. The same fridge might burn ~2-300 btu/hour for the same 50% duty cycle, or ~3000 btu/day. (a gallon of propane has ~79k btu. That 3000 btu might cost ~$.15-.20 per day.

    https://americanrvcompany.3dcartstores.com/Portable_c_223.html

    https://americanrvcompany.3dcartstores.com/Portable_c_223.html

    Tony
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    here is the circuit for what you need it is ajustable to any low voltage point to turn off something and is adjustable to any point above that to turn back on again
    You connect the sense wire and the 12v wires to the battery.. for most purposes.. the link is marked H/L and L/H in its present position the most likely to be used it switches at a lowering voltage..example batt drops from 12.6 to 10.6 it will switch something on/off then it turn on/off again at a higher voltage both settings are independant .. if link in the L/H position it switches something on rising voltage.. I dit it so it could be used for auto uses of voltage sensing fot things like turbo cooling. extra fuel mix.. etc.. This position has almost no uses that I can think of for solasr/battery/wind
    You must use a multiturn variable resistor for the 1meg ohm
    Sorry I dont sell them.. but its an old design of mine have used for years.. but it uses easily available parts.
    But if you go into manufacture of them and make a million please be kind enough to send me a litle to buy a beer or two
  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Automatic Switch for 12 volt Cooler?

    Think this fits the bill ready made to go :D

    http://www.solarconverters.com/product_frame.html

    Then look at voltage controlled switch

    HTH Nigel
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    Maybe you can find a 12v timer switch for low cost.

    I am not a fan of the Peltier coolers as they are pretty inefficient, but they have their place in some applications.
  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Automatic Switch for 12 volt Cooler?

    Opps this would have been a more suitable link :blush:

    http://store.solar-electric.com/volconswit.html
  • BB.BB. Super Moderators, Administrators Posts: 29,639 admin
    Re: Automatic Switch for 12 volt Cooler?
    nigtomdaw wrote: »
    Opps this would have been a more suitable link :blush:

    Don't sweat the earlier link--posting of links to other sites are fine (even competitors) as part of our ongoing education. We are just trying to avoid being being a free advertising site for people who spam for personal profit (as this forum is funded and maintained by NAWS).

    And that other site was the Mfg. site anyway--NAWS is one of their retailers. ;)

    -Bill B. as Moderator
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    It costs $78 to buy the voltage switch if you read post #5 mine you can make one for less than $20.. all very cheap parts.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    jonp,
    not everybody has the ability or knowledge to tackle making that. yes, there are many here that could, but the majority would rather not try it. btw, the zener going to the 7808 could blow out easily with it's current configuration.
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    HUUUH? that 16v zenner is not likely to fail anytime its 16v the most likely highest input 15.5v and it has a 1n4004 to reduce that .7 v..
    have made many of these over the last 15 years and NEVER one failure and have given that circuit to many others that have built them (sometimes only half built as they not need the low to high part) and no one has had a problem.

    many have been used in vehicles for various uses thats why the other low to high setting,, for switching things like extra boost at different throttle settings, water cooling inlet etc.. that circuit can survive almost any 12v situation.
    layout of the circuit is not critical..
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Automatic Switch for 12 volt Cooler?

    Just curious... what is the purpose of the 16V zener. My first thought was "no current limiting resistor" but it's only "seeing 12V (or 11 something. You say 11.6. I always used .7 as the drop across a forward biased silicon junction, but no matter.) Transients perhaps?

    K
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    you hit it craig as i noticed no limiting resistor. i do wonder if it's even needed at all because as was pointed out it is used in configurations that do not present that high of a voltage, but if it ever did it would blow.
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    No limit resistor is needed as I said the input is never likely to be above15.5 volts as its connected across your 12v battery.. Also the 1n4004 which serves the main purpose of protecting the circuit against connecting it the wrong way.. has a secondary purpose drops the input by .7v So with that zener to blow would need a battery voltage above 16.7 volts.. if that happened you would have far more serious problems to worry about than the voltage switch failing..
    And as I said have NEVER had a circuit failure yet ..so feel confident if no failures in 15 years you can sefely build it as is and expect it to work ok for you also..but if you want to you can put a 10 ohm resistor after the 1n4004 and just before the zenner.The zenner only provides transient protection to the regulator.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    very good on the transients and if the zener would pop, even from a strong transient, the circuit itself would still function so nobody would ever know it did pop. as i said there are few that would build the circuit, but it's still nice for those that would endeavor to do it.8) transients are optional:p:D
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Automatic Switch for 12 volt Cooler?
    Or doesn't such a unit exist and I have to make my own?

    It looks like a simple build to me. It's been many, many years since I etched a PC board. About 20. There must be products/systems available these days would provide secure construction (beyond breadboard) for a circuit such as this.

    Perhaps the OP has the skill to construct such.

    This schematic goes in my archive! Thanks John P!

    Craig
  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Automatic Switch for 12 volt Cooler?

    Corr $69 a real deal breaker for a solution to a members problem

    Im not a electronics guru, so I suspect others are not so too,, by the time youve bought all the gear soldering iron anti static mat , magnifying glass , a life, sos
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    If you want to simplify it a bit if used for solar and not in a vehicle you can leave out the input 1n4004 the first 16up cap the 16v zenner diode the 10k and 22k resistors on the inverting half of the ic
    I have seen people make them ok on "vero board"

    Sorry you have to design and make your own"transient generator":D

    And for those havng sleepless nights just worring about if that input zenner will ever fail and you not know.. take the following recomendation from the Steel Wool Knitters Association of Nebrasca (north east division). LEAVE IT IN YOUR PARTS DRAWER .


    Most people who are into solar as a hobby would have items like pliers ,soldering iron 10lb rock breaking hammer.. king sized screwdriver.(for the IC in question an antistatic mat is not required)
    Some people even make their own solar panels and wind generators..mabe they get some satisfaction from that??? mabe they not worried they mabe using their life un profitably??
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Automatic Switch for 12 volt Cooler?
    nigtomdaw wrote: »
    Corr $69 a real deal breaker for a solution to a members problem ;)

    Im not a electronics guru, so I suspect others are not so too ,,,, by the time youve bought all the gear soldering iron anti static mat , magnifying glass , a life, sos 8)

    Why is buying a solution a no no, OB, X, MNS, Samlex, MNS, Trimetric, Studer, Morningstar, Solar Converters, Magnum, and others a problem ?


    in defense of those that it has been said have no life, i say you couldn't buy those items that you have listed without them. there's nothing wrong with buying something too as not that many are into electronics and there's nothing wrong with not being into electronics. but there's nothing wrong with making something too if it performs the purpose.
    gee, bring up about a zener and it's a federal case that branches out. your circuit is appreciated john and feel free to post any other circuits you may have. do not take anything personally or insultingly with my zener observations or inquiry for talking about the circuit is actually healthy to do as new and improved ideas and circuits come from it. even if that doesn't happen it allows a better understanding of the circuit even to those that are not into electronics.
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    its all ok I never feel insulted by anyone here..And besides ive been insulted by "experts" for almost 50 years so you guys dont have much chance:D
    Ive been an electronics tech mostly in audio (amplifiesr) and 2 way radios and wiring up electronics on luxury boats above 100 ft.. have come across almost every problem at sometime..
    I know not all are interested in making things even simple things,, but some of us do, so I just give the ideas or circuits for people to use or not use..
    If someone can redisign any circuit I give .. go for it ..

    Really you would be supprised how many people over theyears have asked in many places about voltage switches... They just dont seem to be redily available or if they are they cost more than the remainder of the project..
    most I have made have been as Isaid for vehicle use.. but I use one to turn on a grid battery charger if my solar panels have not charged up the batteries. for whatever reason.Otheres use them to switch from battery/inverter to grid if battery voltage drops too low. Or simply turn off a battery load if low voltage and turn it back on when battery charged.
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: Automatic Switch for 12 volt Cooler?

    Please! Everyone! The OP asked if he might have to build his own! To me, this suggests that he has the equipment and skills to do so. John P gave him a solution. So did others with "off the shelf" products. Let the OP make his choice.

    K
  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Automatic Switch for 12 volt Cooler?

    No Life:blush: a bit harsh and obtuse, Im guilty, as charged, and I apologise again :blush: But i bet the possible self build project wouldnt be far behind $ wise.

    The OP had a problem and I gave a relatively low cost solution, others gave new routes to solve the problem,

    I am sometimes bombastic and need a slap on the face for which I say to Neil

    Thanks 4 keeping me in check ;)

    To John P I tip my cap also!

    Nigel never too old to learn.
  • icarusicarus Solar Expert Posts: 5,314 ✭✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    If I was slapped every time I made a suggestion that wasn't fully in keeping with the Original Post I would be black and blue. I do think it is appropriate on some occasions to point out what to me at least is a viable alternative solution to a problem. In doing so I think we all are exposed to "outside the box" thinking that allow us to look at problems and solutions in a different light.

    I will admit that there are times when I (and perhaps others) have been too far out of line and Bill and Niel have had to rein me in. I guess the point of this forum and the learned members is to help one another out, but also to allow us to see other solutions and to perhaps learn.

    As Nigel stated so good,,, Tony old,, maybe not too old to learnt new tings!;)

    Tony
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    huh? a slap? i thought it more my being bluntly honest in my opinion. if that slaps you i guess i don't know my own strength. points are well noted and taken all the way around and it's all in helping the op.:cool:
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    Some times we get carried away with getting too involved with minor technicalities of a device or a project. Sure it sometimes good to exchange information of a technical nature with other technical minded people. BUT in doing so the person that asks about the original question many times does not understand all that is being said and goes away confused with what he sees as conflicting information,, so he then does not know what he should do or use.
    To give an example I do posts on another similar site to this.. A person asked ..I have 2 solar panels from different manufacturers 1 is rated 17.5v 3.6 a the other 18v and 3.9a. can I use them in parallel..? my answer based on that info.. he is not building something critical he has most likely been given or got cheaply the 2 panels.. so replied yes it be ok.. well that was the start of about another 10 posts saying it not good idea and others going into discussions about I not explained that the highest rated panel was now degraded by the lower rated panel. A whole lot of pointless useless argument. So confusing that the OP came back and said he not now know if it ok.... for many people a simple "yes" "no" is adequate even if not 100% accurate... can you jump off a table safely to the floor"yes" can you jump from from a 5 story building roof to the ground"no".. no need for long discussions about how you could damage yourself if you land at wrong angle when jumping from table.
    Before we post replies to another persons suggestion to the OP it is wise to stop and think .. is that reply adequate for that person..(if it simple question its unlikely he is knowlegable about electrical things so is not going to understand a highly technical oriented answer.) if "yes" then say nothing more.
  • mike95490mike95490 Solar Expert Posts: 8,431 ✭✭✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    If it's a thermoeletric cooler, and you KNOW you have surplus power in the summer, just pull one panel from the array, to feed the cooler. It can handle low voltage, low current just fine, nothing more needed than 2 wires.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • GreenerPowerGreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    OK! I'm going to add some entropy to this thread.

    My 2c, the thermo-electric cooler is not as efficient as the propane fridge but in term of economy, if the OP has already got it, it's not worth spending $$$ for a propane fridge. This cooler won't run 24/7, it just run to as necessary to maintain the internal temp. When the place is un-attended, if the door is thermally sealed pretty good, I doubt that it would use much power. The OP also wants it to run after sun down unless the battery is getting discharged to some point.

    Here is another circuit that the OP could use:
    BatteryMonitor.jpg
    Some explanation of how the circuit works.
    * LM3914 is configured for "DOT" mode (vs bars i.e. pin 9 MODE is no connect)
    * R1 sets the sink current of the LED drivers of the LM3914 to ~67 mA to drive the relay coils.
    * R2 (with R1) sets the reference voltage to 15V.
    * R3 (with 10 internal 1K resistors of the LM3914) makes a voltage divider to have the LED drivers to monitor 10V-15V in 0.5V step.
    * R4/C1 make a ~ 1 sec time-constant ramp up to help reset the relay during starting up. The input voltage would sweep from 0 to the battery voltage. The "low dot" that connects to the relay would reset it and makes it open on start up. C1 needs to have voltage of 20V or higher.
    * Once the battery voltage gets to the "high dot" connection, it would set the relay to make it close. The relay stays closed until the battery voltage gets down to the "low dot" connection.
    * Some programmability is achieve by connecting the "set" and "reset" coils of the relay to approriate LED driver pins.
    * The referenced relay contact is capable of 8A @ 250VAC. If the amperage is not enough it could be used to drive a 12V auto-relay to connect the battery to the fridge.

    The parts can be purchased from :
    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LM3914N-1-ND
    http://parts.digikey.com/1/parts/749194-relay-mini-pwr-2-latch-3vdc-pcb-dsp1a-l2-dc3v.html

    This controller - http://www.futurlec.com/CarBatteryMonitor.shtml - (not 100% sure in term of driving currents) can also be used with the above relay. Just pull out the LEDs and connect the relay coils similarly. Not sure what the steppings on the battery voltage monitored.

    Disclaimer - use these at your own risk.
    GP
    PS: Changed the supply voltage to 18VDC instead of connecting to the battery to maintain 15VDC reference. Hopefully a 18VDC wall brick can be used if 120VAC is available. If not a small 50W MSW inverter can be used with the 18VDC brick
  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Automatic Switch for 12 volt Cooler?

    Hi GP long time no see, your post is over my head but I like my new Karma aka Niel+ electronics+ others.

    Niel dont kick off Im warming to the other side, PS a slap in the UK is just a ticking off, I warrented it u and you gave it....................... I accepted it, no big deal. the Atlantic sometimes looses itself in translation ..................


    Love and Kisses ( PS Not Gay in Any Way) ( but being Gay is OK ) As F As I Concerned

    Nigel:p
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    :roll: what are we going to do with you nigel?:confused::p
  • westbranchwestbranch Solar Expert Posts: 5,153 ✭✭✭✭
    Re: Automatic Switch for 12 volt Cooler?

    Neil, I don't know what to do either..... but we need to check his lungs now for some foreign substance rather than pump his stomach...
    ( I remember a reference from Nigel long ago about too much Vino Tinto and not enough sleep)
    as I think he is hallucinating..:roll:

    sorry Nigel, couldn't pass the opportunity up.. tutt tutt;)

    Eric
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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