Coffee Maker Conversion - 110V - 240V - Page 1
Forum section: electronics / projects

author: ludzinc
author_rank: Unknown
timestamp: August 09, 2015, 12:10:37 pm
content: Wild idea time, please help me tear it down.I'm been asked if I can covert a coffee maker to run from 240V where it was originally designed to run from 110V.The electronics are simple and the conversion there is relatively easy, but it's the heating element that has me stumped.It's 15 ohms, and on 240V would draw 16A, which is no good for a 10A GPO.So I said it couldn't be done.But then I had an idea, i know dangerous things ideas...What if I used a diode to limit the supply to the heater? If it's only getting half cycles from the mains it's effectively running at half the voltage and thus would draw only 8A. The diode will need to dissipate 8A x 4Drop (call it 8W) in heat but I could bolt it to heating plate of the coffee maker.Can't be that simple, tell me what I'm missing.

author: BillW50
author_rank: Contributor
timestamp: August 09, 2015, 12:51:27 pm
content: Yeah that should work, but so would a 15 ohm resistor in series. Plus the resistor wouldn't unbalance the phase.

author: Kjelt
author_rank: Super Contributor
timestamp: August 09, 2015, 01:02:20 pm
content: Can the diode survive 325V reverse voltage?

author: Andy Watson
author_rank: Super Contributor
timestamp: August 09, 2015, 01:24:48 pm
content: Quote from: ludzinc on August 09, 2015, 12:10:37 pmPower is proportional to V². If you double the voltage you need to reduce t to one quarter cycle.

author: SeanB
author_rank: Super Contributor
timestamp: August 09, 2015, 01:31:12 pm
content: I would use a phase control dimmer to drop the current down, using a TRIAC and a simple phase switch, to drop the power to the element to half. You will need a true RMS meter to read the current to select the current to be the same as in the USA, after which you replace the variable resistor used to select on test ( probably around 47k) with a fixed value resistor closest to the value. You will need a simple LC filter on the mains to reduce noise. The thermal switches and such will probably be fine at 240V, as they typically are rated for 240V 15A rating.This is the common thing used in those ultra cheap eBay voltage converters, so you could just grab one, strip out the simple circuit inside and use it inside the case.Available ready to use as well, just remove the pot after testing....http://www.ebay.com/itm/AC-Step-Down-Voltage-Converter-Transformer-110V-220V-2000W-SCR-Voltage-Regulator-/121655856976?pt=LH_DefaultDomain_0&hash=item1c53410f50

author: onlooker
author_rank: Frequent Contributor
timestamp: August 09, 2015, 01:33:52 pm
content: Right, half wave will still double the power.You can use triac circuitry to better control the power consumption (and with fuse for fail safe).The other try is to serial a motor run capacitor (say, 50uf), but it may be overly bulky.Edit: OK,there is a similar reply posted when I was typing.

author: Zero999
author_rank: Super Contributor
timestamp: August 09, 2015, 01:48:29 pm
content: Quote from: onlooker on August 09, 2015, 01:33:52 pmYes but 50µF won't be enough. You need a 120µF capacitor or an 83mH inductor in series with the 15 Ohm heater to run it off 240VAC but it will be bulky.

author: onlooker
author_rank: Frequent Contributor
timestamp: August 09, 2015, 02:02:50 pm
content: QuoteIt is like serial 2 of the coffee makers. The extra 15 ohms dissipates ~700W. It is not what one wants.QuoteIn that case, it can be expansive too comparing to the triac solution.

author: Pjotr
author_rank: Frequent Contributor
timestamp: August 09, 2015, 02:52:25 pm
content: Whatever you do, a new coffee maker appropriate for the voltage at hand will probably be cheaper and ready to go

author: Siwastaja
author_rank: Super Contributor
timestamp: August 09, 2015, 06:37:33 pm
content: Try to find a 240V spare part heater or compatible heating element.If this is impossible, and you really want to do the conversion, the triac solution is probably the only sane. Although, it doesn'tneedto be phase angle controlled, you can use slower control if you want, passing a few full cycles. Fuses won't blow and the heater won't die if you run it for 100 ms at 4x power, then 300 ms off, or something like that. Diode is super easy but it's still going to be double the power.But phase angle triac controller - also called a lamp dimmer - is an off-the-shelf solution. Just pick one with enough current rating. As an added bonus, you can adjust the power.

author: IanB
author_rank: Super Contributor
timestamp: August 09, 2015, 06:47:19 pm
content: Look for a 240 V heater obtained as a spare part, or cannibalized from a discarded coffee maker, and retro-fit it?

author: ludzinc
author_rank: Unknown
timestamp: August 10, 2015, 03:50:27 am
content: Quote from: IanB on August 09, 2015, 06:47:19 pmTried that as a first step, no joy.

author: ludzinc
author_rank: Unknown
timestamp: August 10, 2015, 03:53:43 am
content: Quote from: SeanB on August 09, 2015, 01:31:12 pmThat is a great idea!Why am I trying to do this? It's a favour to some one who really loves this machine. And I like to solve problemsWill I actually do it? If I think the mod may in any way put some one's life at risk, oh hell no. For example my thought about the diode would run the risk of the heater plate coming live if the diode body were to short - so that's out.But a triac based dimmer? That could possibly mount inside in a nice box. An experiment to see how hot it gets is warranted at this stage!

author: ludzinc
author_rank: Unknown
timestamp: August 10, 2015, 03:57:20 am
content: Quote from: BillW50 on August 09, 2015, 12:51:27 pmOnly problem is the 15 ohm resistor needs to handle 960W. I can't find one big enough to fit inside the case

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 10, 2015, 04:24:22 am
content: Quote from: onlooker on August 09, 2015, 01:33:52 pmHalf-wave rectifier will cut the power exactly in half. That is what many cheap 230V to 115V converters use.

author: onlooker
author_rank: Frequent Contributor
timestamp: August 10, 2015, 04:32:22 am
content: True, but half of the power with 240vac is double of the power with 120vac.Not true, if you meant it will consume the same power as originally speced, unless you remove the DC bias/component by some means.

author: IanB
author_rank: Super Contributor
timestamp: August 10, 2015, 04:39:53 am
content: Quote from: onlooker on August 10, 2015, 04:32:22 amCan you translate that into English?OK, I guess what you are saying is this:Apply 240 V to a heater designed for 120 V. You will get 4x the power it was designed for.Half-wave rectify the 240 V AC. Now you will get exactly half the power as before. But this will still be twice the power that 120 V AC would have provided. The heater will still go into meltdown.

author: onlooker
author_rank: Frequent Contributor
timestamp: August 10, 2015, 04:54:42 am
content: Which part?For a resistor , Power ~ V*V, hence doubling the voltage leads to quadrupling the power dissipation.Now, if only half wave is in use, by symmetry, half of the quadrupled power is dissipated which is the doubling of the power dissipated under the original V.Anything incorrect?

author: IanB
author_rank: Super Contributor
timestamp: August 10, 2015, 05:19:34 am
content: Quote from: onlooker on August 10, 2015, 04:54:42 amNo, that all seems to be correct. I just had trouble following it on the first reading.

author: ludzinc
author_rank: Unknown
timestamp: August 10, 2015, 05:32:33 am
content: Quote from: IanB on August 10, 2015, 04:39:53 amAhDidn't think about it that way - I thought the diode would have the voltage and bring things back to 'normal'.The heater would not have melted down as there is a thermal breaker on it, but I can see now how it would have life tested the breaker.So another reason the diode is a dumb idea.Dimmer from eBay is ordered, I'll post about the experimental results when I get around to it.

author: SL4P
author_rank: Super Contributor
timestamp: August 10, 2015, 05:43:12 am
content: Keep in mind that the espresso pump motor will probably be wound for 110v/60HzThat alone could be a deal breaker, but all the other variables make this a less than desirable conversion.

author: han
author_rank: Frequent Contributor
timestamp: August 10, 2015, 05:57:01 am
content: Just buy step down autotransformer. safe and cheap..

author: gildasd
author_rank: Frequent Contributor
timestamp: August 10, 2015, 06:02:51 am
content: Quote from: han on August 10, 2015, 05:57:01 amWhere is the fun and learning in that?

author: BillW50
author_rank: Contributor
timestamp: August 10, 2015, 09:41:59 am
content: Quote from: SL4P on August 10, 2015, 05:43:12 amWhoa! Where did you hear there is a espresso pump motor? I thought we were talking about a classic coffee machine with a heater and a switch?

author: SL4P
author_rank: Super Contributor
timestamp: August 10, 2015, 09:45:08 am
content: Ol, i made the assumption 'why would you bother' reworking a glorified kettle !!I've made an ass out of me - without u being involved!!

author: BillW50
author_rank: Contributor
timestamp: August 10, 2015, 10:15:33 am
content: Quote from: ludzinc on August 10, 2015, 03:57:20 amOh I wasn't thinking of a resistor per se, but like a 100 watt 110V incandescent lamp bulb wired in series. Heck, a 220v bulb would work too, just dimmer. How cool would that be? A coffee maker with a built in lamp.

author: Andy Watson
author_rank: Super Contributor
timestamp: August 10, 2015, 10:27:48 am
content: Quote from: BillW50 on August 10, 2015, 10:15:33 amBarely tepid I would think!

author: Zero999
author_rank: Super Contributor
timestamp: August 10, 2015, 01:18:53 pm
content: Quote from: BillW50 on August 10, 2015, 10:15:33 amIn order for it to run at the rated power, you'd need a 960W lamp.

author: BillW50
author_rank: Contributor
timestamp: August 10, 2015, 03:46:19 pm
content: Quote from: Hero999 on August 10, 2015, 01:18:53 pmPerfect! Ten 100 watt 120v bulbs in parallel. Enough to light up the whole kitchen. Now we need two lighting bars attached to the ceiling with five sockets each.

author: Pjotr
author_rank: Frequent Contributor
timestamp: August 10, 2015, 03:58:31 pm
content: At least the neighbours are attended: Coffee-making in progress

author: rvalente
author_rank: Frequent Contributor
timestamp: August 19, 2015, 01:13:49 am
content: Go for the controlled rectifier. DDid not the industry controlled all those big chunky fat ass dc motors the hole 60's 70's and 80's until the IGBT technology starts spread?http://www.academia.edu/4984983/Single-Phase_Controlled_Rectifiers- Page 8

author: onlooker
author_rank: Frequent Contributor
timestamp: August 19, 2015, 02:11:12 am
content: If a 1:2 transformer that can handle required power is part of the scheme, why should one bother to use any controlled rectifier? A simply step-down transformer is all needed as someone already mentioned.

author: rvalente
author_rank: Frequent Contributor
timestamp: August 19, 2015, 02:16:42 am
content: Quote from: onlooker on August 19, 2015, 02:11:12 amForget the trafo, the equations are just the very same. I've not mentioned trafo in my suggestion, said controlled rectifier only.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 19, 2015, 02:26:38 am
content: Use a SCR and have it set to trigger near the peak. (A 320V or so SIDAC and 100 ohm or so resistor in series will work nicely.)

author: miguelvp
author_rank: Super Contributor
timestamp: August 19, 2015, 04:46:47 pm
content: Great coffee doesn't need a coffee maker, just get this and a 240V kettle.http://www.aeropress.com/product/aeropress-kit-copy/

author: Fred27
author_rank: Unknown
timestamp: August 19, 2015, 06:15:51 pm
content: +1 on the Aeropress.

author: jlmoon
author_rank: Unknown
timestamp: August 19, 2015, 07:47:50 pm
content: Think production... wire two identical coffee makers in series, get twice the coffee in same time and problem solved.

author: rikkitikkitavi
author_rank: Contributor
timestamp: August 20, 2015, 05:37:17 am
content: Regardless of how you solve the heater problem,I doubt that applainces for 110V are alowed to connect to 240V both from a regulation point, but also common sense that breakers, switches could possibly not be designed for switching 240 VAC, meaning you end up buying a new coffee maker real soon now...

author: Delta
author_rank: Super Contributor
timestamp: August 20, 2015, 06:51:23 am
content: Just have a cup of tea...

author: rikkitikkitavi
author_rank: Contributor
timestamp: August 20, 2015, 01:12:47 pm
content: Tea obvious answer from a Briton