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  • 12V electrics question.

    I am looking to rig up a kind of extractor system, ghetto style in my Garage but using 12V rather them mains. The reason for this is I have quite a lot running on the mains although not usually all at the same time, so that's not so bad but I am thinking "green" and hoping to charge a battery to run it form a Solar panel.
    I did do this once before (Without the panel) in an old garage I had and it worked fairly well so long as it was plugged into the mains through a battery charger but that kind of defeats the purpose. Also it would spin like hell when you switched it on but gradually get slower otherwise until the battery was completely flat, which I would prefer not to have.
    So I am hoping to find some kind of voltage reducer/regulator that I could use with it, I suppose ideally with 2 or 3 speeds the fan could be run at and just an old vehicle radiator fan which I will build some kind of cowling for to the nearest source of fresh air. I am able to do 12V wiring, mains not so much unless I have detailed instructions, can anyone recommend what I should use though and how it should be wired? What I mean is what kind of voltage reducer, where would I get it from, scrapyard, E.Bay? Thanks

  • #2
    How much flow do you need? what are you extracting?

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    • #3
      What supply cable size/length and what size breaker is feeding it?

      Unless you really are running at a constant 120/130% up on what the supply is capable of, then I find it hard to believe that air extraction is going to 'break the camel's back'.

      For example- 12" Expelair (about the best there is!) will shift well in excess of 1000 m3/hour, at a loading of 85 watts. If, for example you had a 2.5mm3 3 core supply, then (at a sensible distance) then you could reasonably expect to be able to run 3.0Kw of equipment, and an additional 85w is hardly going to make much difference.
      Now, if you wanted to put a water heater, for example, in the garage- then that's a different scenario....

      Surely you don't need anything more powerful than that?

      If so, then you could go down the 12v route; using batteries to power the fan, and leaving them permanently connected (via a timer) to a charging system that will charge from 240v overnight.

      (I really can't see the latter providing you with the performance & reliability that you'd need though, as using a 12v fan of similar performance to the 12" above, and drawing 85w would mean a 7amp loading on 12v. If that was running all day, then it would just about flatten even a 110Ah deep-cycle battery, and you wouldn't be able to recouperate that capacity reliably, night after night. A charger capable of supplying that amount of current would seriously shorten the life of the battery)

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      • #4
        I don't really know much about what the garage elecrics are capable of, it was built in 1993 and has an armoured, underground cable from the house but it seems to be wired from a spur in the Kitchen rather than directly from the fusebox. Watts, amps and so on are a bit of a mysery to me I am afraid. I had an electrician look at it once and he said it was really just a domestic garage set up. He seemed to know what it would take to sort it out but when I asked him to do it he became very ellusive and it just didn't happen. I have a 3HP 16 amp compressor that he advised me would be too much for the system, I have had it for years and it's really too big for me, so I really just wanted to be able to run it for the purposes of selling it. I would like to do some spray painting but I am a long way off that at the moment, insullation required more heat, more equipment and so on. The fan idea came form talking to someone I know about air chambers and it seems by just moving the air around you can keep a car drier, so I thought what about a fan to move air about a bit and see if I can keep the whole garage drier. I do have a few batteries lying about that only get used occasionally for jump starting and they seem to last in spite of the abuse they get, abuse being getting left lying around for ages then charged in a rush when needed and flatted again, only to be charged again. I shouild say they were originally taken out of cars because they were supposed to be past their best then. If it worked then I could look at more or bigger as extractors. Maybe I should just find another electrician and see what he would recommend, given what you are saying that a fan wouldn't really use that much power anyway?

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        • #5
          So you don't want to Extract the air, just move it around?
          I think Machine Mart will prob sell what you're looking for.

          Going back to the supply; Is the spur that you've mentioned 'Fused' or not (ie, a 20a double pole switch?)

          If it's fused- then 13a (give or take a percentage, because a 13a plugtop fuse isn't a quickblow fuse) is gonna be all you'll get.

          Back to the compressor which you say is 3hp, intending to be run from a 16a supply.
          As 1hp=746watts, then 3hp would be in the region of 2200w, or about 9.5a.
          Now as you know, a motor of this size fed from a basic pressure switch will draw considerably more than it's rated current (from memory, about 6x) during it's run-up, and this is what's likely to blow a 13a fuse, and from this point of view it would be beneficial for you if you Don't have a Fused Spur in the house and therefore protected by the 32a (??) breaker in the board. (I'm not suggesting that you change a fused spur for a 20a switch, but if it's already there.....).

          You don't say what cable length (or size) from the house, but assuming it's not particularly long, then I'd say that you've got sufficient supply to run the compressor, some lights, and the fan. Anything else, and you've gotta switch off the compressor. And don't even think about electric heating, or a kettle

          One other suggestion- I wonder if it's worthwhile changing the oil in the compressor (and maybe even change for a lighter grade, especially if it's not used intensively) so that the run-up in cold weather will be quicker. This very issue is cooking us in work at the moment with our compressor suffering with little use (so it's not staying warm between cut-in's), and the overheat reset is tripping regularly

          Btw- the rating plate on the motor will give the amperage draw in amps (Prob both 415 and 230/240v, the latter being the higher figure)

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          • #6
            Originally posted by Rubberdubber View Post
            Maybe I should just find another electrician......


            So we were waiting to taxi, when the cabin crew announced that the Pilot wasn't happy with a fault on one of the engines, and that we're gonna be delayed by a few hours whilst they find another Pilot

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            • #7
              But inrush current will be higher than the running draw - bottom line power requried for equipment is pretty much a constant. P=IV so the lower the voltage the high the amp draw.
              240v kit will draw less amps than 12v, by a factor of 20! This is why industrial kit is 3 phase & 415v - to spread the load.
              Panthero Coupé quattro 20vt
              Indigo ABY coupé
              Imola B6 S4 Avant

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              • #8
                [QUOTE=Error404;929362]But inrush current will be higher than the running draw


                I did say that.....
                From memory, about 6x.

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                • #9
                  Originally posted by Error404 View Post
                  This is why industrial kit is 3 phase & 415v - to spread the load.

                  I also said that

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                  • #10
                    Ok I will try to clarify, incidentally this is all excellent information and much appreciated if not always completely understood, will leave calling in any new pilots for now
                    So length of cable spur to garage is about 7 metres. The spur is just a 13 amp fuse and I think from memory what the electrician planned to do was take away this spur and wire directly to a higher rated breaker in the fuseboard and I can see from what you say why this is what he wanted to do. THe downside of the current set up is if the fuse blows, which it does currently every time the compressor tries to fire up. The complressor is OK for house electrics and worked fine at my last house/garage, so not 3 phase. I have a small 2 fuse box the Garage with one for the lights and one for sockets and I also have a small compressor, basically just for blowing up tyres, air impact gun doesn't last 5 mins with this. There are 5 4ft flourescents, one separately switched so normally just the 4 on and I have hand lights and one mobile light pole with 3 LED bulbs if I need more light in a particular area without having to hold it. Double cockets are dotted about, 5 or 6 from memory but rarely are there that many in operation at any given time. there are also 2 halogen security lights outside which run from the Garage. At the moment I just do light mecanical repairs, evenings and weekends but I would like to do more and maybe some paintwork. Should maybe have mentioned I had a Propane space heater but it's pretty small and relatively useless in the size of teh garage mainly because of teh apex roof space which is open at present. I plan to put in an nsulated ceiling at least, so I am only trying to heat downstairs, maybe even divide this into smaller areas that can be closed off.
                    I did know with the big compressor that the problem was the higher draw on power at start up and what you have explained clarifies why this is. I didn't know different oil would make a difference, it hasn't had an oil change in years so that may be a good idea, what oil would I need? I will also have a look at the rating plate and report back.

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                    • #11
                      So- Fluorescent lighting & propane heating are No problem.
                      Might be worthwhile changing the Halogen external floodlighting for 30w LED units (regardless of the lack of supply to the garage- it's a No-Brainer anyway. Going back only a year or so, LED lighting for the masses just lacked a bit of development, but I think we're there now....)

                      A 7m cable length is absolutely nothing to worry about!

                      If you can look closely at the outer sheath of the armoured cable, you'll find info 'moulded' into it, repeated every metre. It'll give all sorts of info, but the important thing is the CSA, which I would expect & hope to be at least 2.5mm. It'll also tell you how may conductors, again hopefully 3.


                      Have a look, and either reply here, or PM me

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                      • #12
                        OK will have a look, I saw the plate on my compressor today whilst servicing the wife's car. Thought to myself I would get a bit of paper and a pen before I went back in and write down the info, you guessed it, I forgot. Next time I am out, I will do all kinds of wonders......hopefully

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                        • #13
                          I don't think you will have an issue with load on this. Extractor won't draw that much power. If you change lights to led it will reduce demand too. If you want the extra load it would be worth getting the sparky to update the wiring
                          Greg

                          S2Forum.com Administrator & Webmaster

                          '93 Coupe with a few tweeks

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