anyone here had anything to do with 3 phase inverters ?
(for those that dont know they change the freqency of the power output so you can run things like motors faster/slower etc...)
I want to run fans inside fridges faster than they normally go....
whats my chances itll all run ok ?
if I just use the normal fan motor that comes with the fan blade might it struggle to push the fan any faster ?
if I use different more powerfull motor (say a 200w motor instead of a 70w) will that be more reliable ?
I need to swap 3 x 1200w 12v 3000rev fans for some I can run from mains voltage... can run on single or 3 phase....
to buy the right single of 3 phase motors there Ã,£250+ each :(
where as I can get morots rated to 1700rpm for Ã,£10 each :D
anyone got any experience / input ?
(p.s. Im thinking about one in a fridge thats non-critical to try first, itll be sucking ait over the motor at about 0C... and the ones in the freezers I plan to do later on will be at ~ -18C)
The company I work for supply variable speed drives as part of their range, and I commission them sometimes :lol:
Most motors these days are rated 50/60 Hz so you can certainly get an extra 10 Hz out of the motor, if the drive lets you do this. How much extra grunt you get out of the system depends on the motor sizing relating to the load, as youve guessed. Generally speaking there is a fan curve defining the air flow versus speed, and I would suggest youll get an extra 10-20% if you follow the curve up - within these constraints I would say the fan blade will limit the extra gain more than the motor, unless the motor is undersized.
If the motors are belt connected youve a chance of changing speed by changing pulley size too.
Youve got 1.2kW 12volt fans? :shock: Where does the 100A come from?
The 1700 rpm motors arent going to drive your fans anywhere near the required rating if the fans normally run at 3000 rpm. Youd best also check that the proposed motors will run ok at -18 if the air is being dragged over them.
thanks, I was starting to think no-one would reply :o
(second opinion as always a big help!)
the 12v fans are one a freezer unit thats built onto the front of a box from the back of a lorry... theres a huge 3 phase motor running 24/7 that drives a fan, the compressor motor and a big alternator that powers the 12v side....
but Id like to convert it all to run from the mains in the way a normal fridge does. (its not used at the moment so Ive got some time to fiddle with it)
Im thinking normal fridge fan motors are only 1/8 hp or so... so if I use 1hp motors maybe theyll do it ?
I might be better off looking around and seeing if I can find some motors with fan blades to suit.
hmm, Ill have a look around at some prices ;)
If you can physically disconnect the 12v fan motors from the fan spindles then maybe you could use the cheap mains motors with those fans, if you can mount the motors with an appropriate fanbelt/pulley arrangement.
If the fan is only 100W (1/8 hp), youd never bother with an invertor, itd cost too much. I would have thought that sort of fan would have an integral motor, thats not removable.
Picture of the current arrangement?
no pictures at the mo, Ill get some tomorrow tho :)
the problem is, you need to push enough air through the evaporator grill to stop it icing up... they ice up pretty quick if they dont have a good "blast" of air coming through them :)
the current 12v fans are a separate motor and fan setup, with the fan fixed onto the motor shaft.
will post some pickies tomorrow showing fan blades pitch etc..
got pics.... cant get them from cam right now tho :s
long story short, I didnt fit the unit, and I trusted my brother when he told me they were 1200watt fans... (i know its a huge ass alternator on there)
there only 1200watt, there 14v and 140watt, so 10 amp right ?
so Im thinking id be better just picking up a PSU on ebay then replacing the fans ?
~14v, min 30amp (comething a bit bigger would be better right?)
quick look on ebay and theres a couple to choose from :)
aiming for 40amp plus thof or some head room, and theres a coupld of small solenoids I can run from it instead of swaping them for ac ones like I was going to :)
good job you asked greg, youve saved me a small fortune and a load of work !
first thing that tends to go wrong with electric motors are the bushes, then the bearings, rewinding the coils isnt that common but is still relativley easy to do, it just takes time and wire.
Dont forget that an electric motor takes more current during spin up and then settles back on the juice.
^^ was already thinking about that, going for a min of a 40amp psu... and can always step start the fans, 1 then 2 then 3, they only take 2 sec or so to start up :-)
These 14v fan motors are DC arent they? So you cant make them run any faster anyway (ac inverters only work on synchronous ac fans). If theyre off a lorry then obviously theyd be designed to work off the vehicles electric system, which is why I was kinda worried about the 100A..:lol:
Having a higher current psu wont give you any more speed of course, just a bit more headroom. If you want more air flow youre going to need faster motors or more fans.
Make sure your switching devices to allow the dc feed to the fans are suitable for switching 20-30A DC to an inductive load, as the dc feedback will be really high when switching off - arc erosion of contacts leading to welding together eventually. You might need some sort of capacitor/surge suppressor across the switch contacts.
Or just use a big ass lightswitch :lol:
I suppose, in retrospect, that itd be possible to increase the speed of the DC fans by over-volting them, much as were used to decreasing the speed of cpu fans with lower voltage. The risk would be higher winding temperatures, but given your application that may not be a problem...
You might be able to try a 12-20v supply and run them at 18v to see if you get any beneficial air flow increase. There will be a point at which you dont get much more flow for speed increase, beacuse of the fan curve.
oops, I should have cleared that up... if I can stick with the normal fans Ill run them at stock speeds...... only wanted to speed up the replacement fans I was thinking of using :)