PocketJem Posted October 22, 2013 Share Posted October 22, 2013 Hi all We have a Le Maitre Mini Mist that operates on 110v, we therefore currently use a step down transformer to use this in the UK on 240v mains. How easy would it be to convert the Mini Mist unit to work on 240v AC so we could dispense with the bulky transformer? Can anyone explain what's involved and if parts are needed where they can be obtained? I suspect that it will be an expensive option to return it to Le Maitre. Or, as an alternative does anyone know of a very small and lightweight 1kva transformer that would power the unit rather than the large one we use at the moment. Cheers Link to comment Share on other sites More sharing options...
dbuckley Posted October 22, 2013 Share Posted October 22, 2013 It is likely the heater is directly connected across the mains input, and thus the heater is 110V rated, and other than heater replacement, this wont be easy to change. Thus the external transformer is the only reasonable option. Link to comment Share on other sites More sharing options...
Jivemaster Posted October 22, 2013 Share Posted October 22, 2013 Ask LeMaitre! but I suspect that the current system is as good as any Link to comment Share on other sites More sharing options...
Brian Posted October 23, 2013 Share Posted October 23, 2013 I can't remember what's inside a Minimist but what's fed from the mains? If it's just the heater then you should be able to stick a cheap 1kW dimmer on it (maybe even internally) and adjust it so that the heater is still fed at the 1k level. Link to comment Share on other sites More sharing options...
PocketJem Posted October 23, 2013 Author Share Posted October 23, 2013 Thanks for the replies. I'll pull the lid off it over the next few days and have a look at what's where. Link to comment Share on other sites More sharing options...
ianknight Posted October 23, 2013 Share Posted October 23, 2013 The heater is at 110v, a customer of ours has several 110v Mini's and asked for a cost to convert - LeMaitre will sell you a 230v block but the cost is about the same as a new machine - I'd carry on using a transformer. B-) Link to comment Share on other sites More sharing options...
Brian Posted October 23, 2013 Share Posted October 23, 2013 @ianknight Ian, can you remember if there's anything else in there which is voltage sensitive? Link to comment Share on other sites More sharing options...
csg Posted October 23, 2013 Share Posted October 23, 2013 its 15 years since I had a minimist open, but at that time there was nothing in there other than the heater connected via a thermal cut out across the mains, the only other electrical component being the heating neon. There is no electronic thermal management or fluid control in this machine. For a lighter stepdown, you could look at switchmode PSU options, or potentially as suggested above a compact dimmer that could be fixed by replacing the level pot with the appropriate value resistor. Link to comment Share on other sites More sharing options...
Brian Posted October 23, 2013 Share Posted October 23, 2013 Can someone check my calculation... I reckon that a 110V 1kW heater, run off 240V via a single diode will dissipate a power of 965W. Pavg = Vrms * Irms ...or... Irms = Pavg / Vrms = 1000/110 = 9.1A R = Vrms / Irms = 110/9.1 = 12.1 Ohms <- hot resistance of heater For half-wave rectified AC... Vdc = 0.45 * Vrms = 0.45 * 240 = 108v P = V * V / R = 108 * 108 / 12.1 = 964W So, if my sums are right, all you need is a single diode of suitable current rating. Link to comment Share on other sites More sharing options...
bigclive Posted October 23, 2013 Share Posted October 23, 2013 It's not as simple as a diode. The heater block will have a resistance of about 12 ohms which will pass about 20A at 240V giving a power dissipation of 4.8kW. With the diode it's only on half the time, so the dissipation will be 2.4kW which is twice its rating and will potentially result in rapid element failure or other damage. Link to comment Share on other sites More sharing options...
dbuckley Posted October 23, 2013 Share Posted October 23, 2013 Do not be tempted to connect 240V power to this heater, via a dimmer, or a diode. The electrical insulation of the heater is rated 110V, and both the schemes noted will produce an average voltage of less than 240V, but there will still be 240V mains across the heater for part of the mains cycle, and this voltage is higher than the heater is rated for. Danger Will Robinson. Continue to use a transformer. Link to comment Share on other sites More sharing options...
PocketJem Posted October 24, 2013 Author Share Posted October 24, 2013 Thanks Guys. Really interesting stuff. However, I want to be 100% safe and as such will continue to use the transformer... Until someone comes up with an absolutely foolproof and 100% safe method of conversion ;) Link to comment Share on other sites More sharing options...
ImagineerTom Posted October 24, 2013 Share Posted October 24, 2013 There is a 100% foolproof way of converting it - change the heater block from a 110v to a 230v one. Since essentially the only componant within a minimist is the heater block it's just not going to be viable. If you wanted to switch from unleaded to diesel fuel you'd just buy a new car rather than trying to swap the engine. Whilst the minimist was a great machine if you still want a portable "off mains" unit that can be charged from regular uk mains supply there's many other options out there now for surprisingly little money that beat the minimist. Link to comment Share on other sites More sharing options...
PocketJem Posted October 25, 2013 Author Share Posted October 25, 2013 There is a 100% foolproof way of converting it - change the heater block from a 110v to a 230v one. :D ** laughs out loud **, yes I can see the error of my ways. I figure we'll just stay with the 110v and transformer, it would appear to be by far the easier and safer option :) Link to comment Share on other sites More sharing options...
ianknight Posted October 28, 2013 Share Posted October 28, 2013 @ianknight Ian, can you remember if there's anything else in there which is voltage sensitive? Sorry for the late reply, I think there was also a small transformer which supplied the control electronics - probably the easiest thing to swap or it might just be a link to put the other primary in series. I stopped looking too deep when I found the cost of the replacement block to change it to 230V. Link to comment Share on other sites More sharing options...
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