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Moose

National Electric Watch Cleaner - refurbing

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Hi all.

I have got a National Electric Watch Cleaner and as expected the heating element is bug***d (sorry, not working). Everything else is OK and the motor and bearings are nice smooth with good control from the speed dial. With a bit of TLC (and rattle-can black) it will provide me with good service.

Does anyone know if the heating element from the Elma RM80 (90) is a good match for this machine? It basically just needs to operate at mains voltage and fit into the space where the old element used to fit. I could use it without the heater and just bodge something with an old hairdryer to provide a warm airflow, but I am hoping that the Elma element could be used. Has anyone ever tried this?

I am going to re-wire it and makes sure it is up to current safety standards, as it still has its original (seriously old now) wiring scheme. New Jar seals will be needed but I have some aviation fuel/chemical grade 3mm rubber gasket material I can hand cut to suit, so that will be OK. The jars and lids are sound and just need cleaning (and the seals). And it has a complete set of baskets, which is a plus.

I have included a photo of the old heating element for a size reference. Unfortunately for me, Elma do not state size of their replacement element.

 

 

IMG_1539.jpg

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17 hours ago, yankeedog said:

are the heating coils removable?

I would say not. The entire assembly is and I was hoping to wire in the Elma Heater. Working on the assumption that you turn it on, it gets hot enough, you use it, then you turn it off again. I think the Elma element must be self regulating, or designed to operate at a certain temperature. Looking at the Elma spare part in the catalogue, there is a simple two-wire connection, same as this one.

 

IMG_1538.jpg

10.jpg

Edited by Moose
Added Elma Element image.

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It looks like an old fashioned stove element to me, or possibly a very old kettle element. What are the dimensions of the space it needs to fit in?

Is the thing on the metal disk a thermal fuse, or a thermostat?

If it is a stove element, then you might be able to adapt a modern one to fit.

https://www.ebay.co.uk/sch/i.html?_odkw=6%40+stove+element&_sop=15&_osacat=0&_from=R40&_trksid=m570.l1313&_nkw=6"++cooker+element&_sacat=0

 

https://www.ebay.co.uk/itm/futura-kettle-element/192929243765?hash=item2ceb7aa275:g:9oIAAOSwH5xc6nm3

https://www.ebay.co.uk/sch/i.html?_odkw=5"++cooker+element&_sop=15&_osacat=0&_from=R40&_trksid=m570.l1313&_nkw=kettle+element&_sacat=0

You may need to add in your own thermostat to get these to cut out at a reasonable temperature, I'm pretty sure you don't need to boil a Rolex to get it clean.

https://www.ebay.co.uk/itm/5PCS-KSD301-Temperature-Switch-Thermostat-50-C-150-C-Degrees-Celsius-NO-NC/272790891850?hash=item3f839aad4a:m:mqXL_j-yLhgkW5JDPzzM-ug

Edited by AndyHull

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Don't forget to ensure the thing is correctly earthed and that you are on an RCD protected circuit if you are testing any modifications, we don't want any hair raising incidents. Bangs and electric arc flashes may make good youtube content, but only if you are not part of the fireworks.

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BTW you can also buy kiln elements, in various power ratings, which might do the trick. Do you know what the original power rating of the element was?

Example -> https://www.ebay.co.uk/itm/AC-220V-2500W-Heating-Element-Coil-Pottery-Kiln-Furnace-Resistance-Restring-Wire/202496373526?epid=25030666425&hash=item2f25b97316:g:LW4AAOSwyiFb5PWO

 

 

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One further thought, if you are feeling particularly brave, you could purchase the nichrome wire and re-make the element, however you would need to know the specification of the original coil, its total hot resistance,  the gauge of the wire, its total length and the resistance per foot/meter of your chosen wire, so you could make something to match.

https://www.ebay.co.uk/sch/i.html?_from=R40&_sacat=0&_nkw=nichrome+wire&_sop=15

.. but a suitable kettle element (or perhaps two in series) and a suitable thermostat sounds like a much simpler substitution.

Edited by AndyHull

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The basic dimension is shown in the photo, 75mm diameter. The other “thing on a metal disk” is the replacement heating element for the Elma RM80/90.

What would be useful to know (but not information I can find online), is what diameter the Elma replacement is and, if it is also a 240 volt element.

if anyone out there uses an Elma 80/90 it may be easy to see it in the bottom of the drying chamber. Or maybe a circuit diagram was supplied with the machine.

At £45 for an Elma element, I’m not sure I want to take the risk of buying one just see if it will work.

Otherwise, I will just as likely refurb it without a heater, and keep an eye open to see what might come up. I can always blow some hot air in from a hairdryer or something to get a drying effect.

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it looks like all the sections are still there . it's just a coil of nichrome wire.Form the ends so that you can hook the sections together, it will work. for how long is anybody's guess, all you need is continuity.

Edited by yankeedog
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I dont know about the ID of the coils but you could also cut sections , of oh say 12 AWG solid conductor wire and insert them inside the coils connecting the sections together.just so it's inserted for a few turns on each side. it will get hot.

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If you decide to fix the existing heater I would tackle the problem as follows.

Count the coils.

Figure out the diameter of the coil.

The total length of wire in the existing coil is is Coil Circumference multiplied by number of coils or if you prefer...

2 * Pi * 'Diameter' * 'Number of coils' 

... since the diameter of the coil is much easier to estimate.

Nichrome wire is rated in Ohms/meter, this figure will be on the spool. The exact figure depends on the gauge of the wire,  so you should be able to work out the total resistance of a new coil.

The old coil can be cobbled together by twisting (not soldering) the coils together using bits of copper wire, per Yankeedog's suggestion.

You can then measure its approximate resistance, which should be close to what it was when new, or at least close enough for the purposes of this game.

You can probably get a rough estimate on the old coil's resistance using a micrometer to work out the wire gauge, then multiplying that by around the figure obtained from new wire of similar gauge, or even by guessing at 4 Ohms per meter.

More details here -> https://en.wikipedia.org/wiki/Nichrome

In other words, it should be possible to create your own coil, using a spool of cheap nichrome wire from ebay, a suitable round stick to form it on, and a little arithmetic. It can't be that hard, since the Victorians had this figured out long before we came on the scene. Mind you, they were still starching their hat brims with mercury, so perhaps health and safety wasn't their strong suit. 

Ohms law states that for resistive power in a DC circuit, Watts = V^2/R so you should be able to tell if you are in the right ball park with your calculations, based on that and your estimate of 200 Watts.

The fact that we are actually dealing with AC power and the fact that the resistance changes with temperature mean that this is an estimate, but probably close enough to tell if we are in gentle heating or explosive melt down territory.

I do, of course, completely absolve myself from any responsibility if your experiments set the cat's tail on fire, or result in lots of smoke and loud profanity. Also 240v AC is dangerous etc.

In summary, get the correct gauge of nichrome wire, wind the correct number of coils of the correct diameter, try it, but don't forget your safety glasses,  and work on a heatproof surface, since hot globules of exploding nichrome can be very "interesting".

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All excellent advice.

BUT...

I have decided to purchase a modern 200W PTC heating element. It looks much like the one used by Elma in their new machines. It's about 75mm by 35mm rectangle shaped and can be mounted on the existing heatproof plate without issue. As standard is gives me 200W heat output at 220/240 volts and is self regulating - all I need to do is turn it on and off. 

To be honest, I did consider re-constructing the original, but then if more modern (and safer) technology is available, I may as well use it. I suspect it is a better solution that trying to hand produce a new element for a 50's or 60's heating element, as interesting as that might have been to actually try. Bottom line is that what I need is about 200 watts of safe, controllable heating. A PTC heater is the safest option for me.

Mind you, if anyone out there wants my old element to try to repair it, they are welcome to it for the postage cost from me to you.

If anyone is interested, the cost of the element is only £25 from Farnell, vs £45 to get the official Elma element from HS Walsh. For my money, it's exactly the same thing, only the Elma version is mounted on a steel plate. If you take a look at my earlier photo, you can see the PTC heater mounted on the circular plate.

200w 220/240v PTC Heater

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