Automatic Switch for 12 volt Cooler?

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  • GreenerPower
    GreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    #32
    Re: Automatic Switch for 12 volt Cooler?
    nigtomdaw wrote: »
    Hi GP long time no see, your post is over my head
    Hi Nigel, I see that now you've got your feet wet with the XW60.

    Maybe I need to explain more on the LM3914 for the OP benefit.
    Once the monitor voltage levels are set, say 10V=15V in 0.5V steps, the LM3914 would pull LED 1 pin low to turn it on once the input voltage is above 10V, LED2 pin would be pulled low if the input voltage is above 10.5V and so on. In "bar" mode, all LED pins below the threshold voltage would be pulled low to make the high of the bar grows as the voltage climbs up (the LEDs are connected from V+ to the LED pins). This mode is not useful since driving both coils of the relay would make it confuse to be open or close. The "dot" mode is chosen so that a single LED pin is pulled low i.e moving up dot as the voltage climbs.
    The relay used is a "bi-stable" type i.e. it doesn't need the coil to be constantly energized to stay open or close. A "low" LED pull would make it open and stay open as the "dot" move up. A "high" LED pull would make it close and stay closed as the "dot" moves higher or lower but not to the "low" setting.
    As for the setting of the voltage range to monitor and the steps, the LM3914 spec and internal diagram really to be studied. The PDF spec can be optained from the posted link.
    Hope this helps.
    GP
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  • nigtomdaw
    nigtomdaw Solar Expert Posts: 705 ✭✭
    #33
    Re: Automatic Switch for 12 volt Cooler?

    kk spanish for OK yes guilty as charged I guess I must leave the forum, TTFNF ,,,,,,,,,,,TatTatForNow, Im gone;) OP Im a luddlite . West branch Touchae but in a world of sprialling cost Vi stays stable :D

    Bye I will miss all of you:cry::cry:
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  • Kamala
    Kamala Solar Expert Posts: 452 ✭✭
    #34
    Re: Automatic Switch for 12 volt Cooler?

    Nigel! Don't go. Pleaaaase stay. We need all kinds. As idiosyncratic as they may be. Yes, I am linguistically Anglican. Como esta? Pardon, como estas usted? :D

    BTW... Where's the OP?
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #35
    Re: Automatic Switch for 12 volt Cooler?

    The one major drawback I see with this circuit is. you need a seperate 18v supply.
    and as drawn its not adjustable for set point and the problem of no hysteresis around the set point.
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  • GreenerPower
    GreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    #36
    Re: Automatic Switch for 12 volt Cooler?
    john p wrote: »
    The one major drawback I see with this circuit is. you need a seperate 18v supply.
    True, I was hoping 120VAC is available to use a 18VDC wall brick.
    Well, you make me thinking ... For the sake of discussing, not sure if the OP is still reading. The modified circuit below would run from the battery voltage. R2 changed so that the reference voltage is 10V. R4 changed and R5 introduced to scale down the battery input from 10V-15V range to 6.6V-10V range to the SIG input while still keeping the ~1sec time-constant. This circuit would run as long as the battery voltage is above 10.5 V
    ...and as drawn its not adjustable for set point and the problem of no hysteresis around the set point.
    the "adjustable" set points are the various LED driving pins of the LM3914. The limitation is that it is in 0.5V discrete steps but I guess this is not critical for the OP application. The hysteresis is provided by the "bi-stable" nature of the relay used - it's like an RS flip-flop, one coil used to "set" (connect), one coil used to "reset" (disconnect). The coil can be pulsed for the relay to change state, it doesn't need to be constantly energized. Input voltage jumping around the set point won't change the state of the relay until it reaches the other "set-point". The C1 cap also filters any spikes.

    BatteryMonitor1.jpg
    GP
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #37
    Re: Automatic Switch for 12 volt Cooler?

    But with the method of hystereses you propose its only .5v? so in fact that is really too close as soon as the load is removed the battery voltage would most likely go up that amount and reconnect the load.. therefore oscilate around that point...
    And I really think having to have a seperate power supply defeats the users needs of having the cooler running on battery/ies ? why not then just have a 120v to 12v power supply and nothing else??.having a coler connected to batteries and mains is kinda silly idea to my thinking...
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  • GreenerPower
    GreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    #38
    Re: Automatic Switch for 12 volt Cooler?
    john p wrote: »
    But with the method of hystereses you propose its only .5v? so in fact that is really too close as soon as the load is removed the battery voltage would most likely go up that amount and reconnect the load.. therefore oscilate around that point...
    You mis-understand this part John. Say the "reset coil" is connected to LED driver 5 (pin 15) for 12V cut-off and the "set coil" is connected to LED driver 8 (pin 12) for 13.5V turn-on. Once the battery voltage gets to above 13.5V the "set coil" is energized. If the battery voltage goes above 14V or below 13.5V, the "set coil" is not energized anymore but the relay stays connected (bi-stable or latching relay). Until the battery voltage gets to below 12.5V then the "reset coil" is energized and the relay disconnects. Once the battery voltage gets below 12V, the "reset coil" is not energized anymore but the relay stays disconnected.
    ... And I really think having to have a seperate power supply defeats the users needs of having the cooler running on battery/ies ? why not then just have a 120v to 12v power supply and nothing else??.having a coler connected to batteries and mains is kinda silly idea to my thinking...
    I am thinking the 120VAC is from an inverter for other things in the place, not grid power. Also I think I sneaked in the modification circuit on my editted post about the same time you posted this :)
    GP
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #39
    Re: Automatic Switch for 12 volt Cooler?

    ok I should have looked at it more carefully. but still dont think its a good way to design one
    (1) it needs an outside supply voltage 18v . and that is not usually available on cheap "plugpacks" wall warts whatever
    (2) it requires a relay not available everywhere. and very few people understand how they work. and they usually have low current ratings..most ive seen about .5a.. To switch a cooler module you need a 10a relay as you switching about 5a. So you need to then connect another relay.. more expense
    (3) the LM3914 is relatively expensive about 4 times the cost of the ic I used
    I costed all the parts for mine from retail catalogue incl board to make it on at $17.40 au the price of a similar built one in USA is $69 about $90 au.. So very cheap and easy to build and adjust and it can switch 10a with very available relay.. yours is going to cost if priced on parts here at about $29 au. plus ??? for the 18v power supply..
    And to show why I dont think the idea of a wall mains supply is desirable here is part of his original post..Here's the situation: I have a small remote stand-alone 12 volt PV system with limited battery storage
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  • SolarJohn
    SolarJohn Solar Expert Posts: 202 ✭✭
    #40
    Re: Automatic Switch for 12 volt Cooler?

    It's fun to tinker with electronics, I do it all the time. However, when I want something I can depend upon, and that uses little current for it's operation, I go for a commercial product instead of home-brew. When the power grid fails, and its freezing outside, I want my off-grid system to function flawlessly. For these reasons, I choose the Morningstar Relay Driver for the job. The Morningstar Relay Driver has other advantages as well: You have an upper and a lower voltage threshold to work with, and programmable delays. If you enjoy tinkering, have the time, and can tolerate the consequences of an unproven product, go for it. Otherwise, I would stick to well-designed and packaged products that have been tested and proven over time. Just my humble opinion.

    John
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #41
    Re: Automatic Switch for 12 volt Cooler?

    But here was a person with a simple cooler wanting something to turn it off when the battery gets too low.. he not wanting something that is connected to a huge solar aray that is powering his grandmothers iron lung machine..

    My design is very simple easy to construct uses very cheap and available parts. and as Iwould estimate more than 100 of them have been made by me and others I have given the circuit to Isay that is a proven design.. It was designed about 15 years ago .. I think that long enough
    And as I said its parts cost here is $17.40 compared to $90 if the $69 is worked on todays exchange rate.. a saving of $70 and mabe he will learn something from making it.. and if it did fail.. its not life threatening..
    its not like saying to him here is the design for a 5000w grid inverter ..now go make one ..:D

    Solar john mine has this also..You have an upper and a lower voltage threshold to work with
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  • GreenerPower
    GreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    #42
    Re: Automatic Switch for 12 volt Cooler?
    john p wrote: »
    ...(1) it needs an outside supply voltage 18v . and that is not usually available on cheap "plugpacks" wall warts whatever
    ...And to show why I dont think the idea of a wall mains supply is desirable here is part of his original post..Here's the situation: I have a small remote stand-alone 12 volt PV system with limited battery storage
    Points taken, that's why I provided a modified circuit to remove the need for a separate supply in my post #36 in this thread (got to solve this for an electronics geek like me, verified working as well ;) )
    (2) it requires a relay not available everywhere. and very few people understand how they work. and they usually have low current ratings..most ive seen about .5a.. To switch a cooler module you need a 10a relay as you switching about 5a. So you need to then connect another relay.. more expense
    (3) the LM3914 is relatively expensive about 4 times the cost of the ic I used
    I costed all the parts for mine from retail catalogue incl board to make it on at $17.40 au the price of a similar built one in USA is $69 about $90 au.. So very cheap and easy to build and adjust and it can switch 10a with very available relay.. yours is going to cost if priced on parts here at about $29 au. plus
    Well, those might be expensive and less available where you are. The OP is in the states, that's why I posted the links to get those parts from digikey. The relay contact rating is 5A for DC, probably too close for comfort, throw in an auto relay, the cost for all the parts needed plus shipping is probably < $20 US (yours is probably < $10 US here in the states).

    I don't doubt your circuit fits the bill for the OP needs, just want to offer a choice depending on the OP skills/comfortability in building electronic circuits. People tend to go with circuit that has less components.

    I doubt many readers here without electronic background would understand how either your circuit or mine works. You don't need to understand how a switching power supply works internally to use one.
    GP
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #43
    Re: Automatic Switch for 12 volt Cooler?

    I have had a look at your redrawn circuit.. I dont seem to have the specs on the LM3914. and cant remember them. but I used to use hundreds of LM3915s as VU meters for audio mixers..
    but wondering how the varying battery voltage is going to effect its performance?? or the ics outputs leds going to alter as the voltage of the battery alters?? meaning is the preselected led to turn off the relay going to happen as expected at 10v.. when its set point is done at 12v input?
    Another thing you have no flyback diode across the relay..??most ics blow out their outputs with back emf from relays..
    I always try to use solid state relays as they dont have that problem.
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #44
    Re: Automatic Switch for 12 volt Cooler?

    Solar john You telling me you woud use.. For these reasons, I choose the Morningstar Relay Driver for the job At an incredible $147 for the sole purpose of turning off a $50 cooler connected to a solar panel and battery???.. my god what would you buy if you needed to power a small room Air Conditioner.. A nuclear power station???
    I really have no understanding of why someone would humbly suggest someone should spend more on a switch than the remainder of the system is worth.....

    Did you read the original post???

    Greener Power came up with a similar solution to mine at a fraction of the cost of the item you think he should buy. and its relatively easy to build..
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,650 admin
    #45
    Re: Automatic Switch for 12 volt Cooler?

    Take it easy folks... There have been lots of well thought out solutions for the original poster to consider.

    Thank you everyone for suggestions and hard work.

    -Bill B. (moderator)
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • nigtomdaw
    nigtomdaw Solar Expert Posts: 705 ✭✭
    #46
    Re: Automatic Switch for 12 volt Cooler?

    See a $69 solution was real close:roll: and NAWS sell them, Im back ;)
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #47
    Re: Automatic Switch for 12 volt Cooler?

    ringtomdaw. I not quite sure how $69 us or ($90au ) is real close to $17.40au ???

    you all seem to forget the OP said it only very small system and those coolers are not expensive. and mabe even obtained some of the parts used.so to spend a lot on a switch to me is out of proportion .

    That is why 2 of us have been trying to give him the lowest price item.. and it appears from his post he could build one if the design is simple enough..
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  • Kamala
    Kamala Solar Expert Posts: 452 ✭✭
    #48
    Re: Automatic Switch for 12 volt Cooler?

    IMHO thread has become aberrant for this forum.

    K
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #49
    Re: Automatic Switch for 12 volt Cooler?

    I think thread should now be closed. As really we all have gone on way too far.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,650 admin
    #50
    Re: Automatic Switch for 12 volt Cooler?

    OK--I will lock the thread... Poor Paul (the original poster) when he logs in to read this thread (has not been back since the original post) will find his thread closed...

    Paul, if you want to add anything--please PM me and I will open it for your comments.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,650 admin
    #51
    Re: Automatic Switch for 12 volt Cooler?

    Good Evening Everyone...

    Paul is back and would like to continue the discussion in this thread.

    Please respect Paul's directions as he take this thread in a useful direction for him.

    Sincerely,
    -Bill B. Moderator
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #52
    Re: Automatic Switch for 12 volt Cooler?

    ok what does he want to know? will do my best to try to help and keep on topic.. hope others do the same.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,650 admin
    #53
    Re: Automatic Switch for 12 volt Cooler?

    Paul sent me a message yesterday and was very interested in continuing the discussion will be following up on the ideas presented--He will post when he has a chance.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • paulstamser
    paulstamser Solar Expert Posts: 86 ✭✭✭
    #54
    Re: Automatic Switch for 12 volt Cooler?

    I appreciate all the good replies. Thanks much.

    I will probably buy the ready made voltage cut-in/out switch. Altho I have tools, soldering iron, etc. I have never built a circuit board unit and don't even know what all the symbols mean and would have to study that. Plus I live in the middle of nowhere and getting all the parts would be another chore, etc.

    I would also like to reply to some of the other opinions posted:

    The Coleman 12 volt thermo-electric cooler (4.5 amps) is very efficient the way I use it. It only runs when I have surplus sun (not at night, cloudy days, etc). Propane? Why burn fuel and spend big bucks on a propane or an "efficent" 12 volt fridge when the under-$100 Coleman cooler (no freezer) does a decent job? Since I keep it underground in my root cellar it always stays cool, if not cold. That might not be good enough for some people, but it works well for me. And perhaps I got a good one, because I've been using it for several years now and the motor has held up.

    Speaking of propane refrigerators, I own an old Servel propane fridge I bought many years ago. But the idea of buying/burning propane in the summer to make cold drove me nuts and I stopped using it. And while the modern propane units are probably more efficient they still use a system counter to my keep-it-simple philosophy, which might be of interest to some.

    Rather than trying to duplicate a suburban lifestyle in the wilds (or as close to it as possible), I first adopted a 19th century lifestyle and then worked up from that level. That is, I burn wood, twigs, paper, and cardboard to heat my house and heat water. I pump my daily water with a hand pump and once every couple months run a gasoline engine pump for 10 minutes to fill a big upstairs tank for faucet (non drinking) tap-water. I have a dry "humanure" composting toilet. I devised a gravity shower which is wonderfully simple and works great. But I also have electric lights, inverters, radios, drill press, DVD player, computer, and until the digital switchover I even had TV. For refrigeration I use natural cooling in winter (the best!) and limited 12 volt cooling in summer as described in the OP. Since winters here are LONG and summers short it isn't a hardship. Overall, I use a "systems approach," that is, a diverse combination of both ultra simple low tech and modern high tech methods to solve daily lifestyle needs and problems. Like I say, it wouldn't work for everyone, but it works well for me.

    After getting back into this I might also upgrade my PV system this fall with another panel. I will almost certainly buy these items from the good folks who provide this useful forum. The last things I did to my home power system was upgrade to LED lights 2 years ago and in 2003 I had to replace the battery bank (4 lead-acid golf cart batts). Got 10 years out of the previous set.

    Thanks!
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