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Workshop humidity

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Baldric08/10/2009 13:47:35
170 forum posts
16 photos
I remember someone mentioning somehwere that a dehumidifier in the workshop can help keep rust at bay, but on a timer is no use, it should be on a switch that comes in when the humidity reaches a certain level. Does anyone know where to get such a switch, preferably inline like a timed switch.
Robbo09/10/2009 22:18:27
1504 forum posts
142 photos
The easiest humidity switch to find ( they call them humidistats) is sold by the Air & Water Centre -    They do a plug in one, so you plug it into a socket and then plug your dehumidifier into the front of it..    Digital settings for the humidity level you want.    In the house it's usually 40 - 60%.
The big downside is that it costs £45 !!!!
Humidistats are fitted into a lot of bathroom extractor fans, so it may be possible to buy one of these more cheaply and cannibalise it.   However, the fan circuitry will probably only stand 1 or 2 amps, and the dehumidifier load will be more than this.
Probably best to Google "humidistat" and see what you get.
Robbo10/10/2009 20:02:17
1504 forum posts
142 photos
Part 2.
The last para of my previous posting got lost.   It said:
Most dehumidifiers (mine is an elderly model, like me) have a built in humidistat and an adjustable control dial, which may only be in numbers rather than %age humidity, but trial and error will find the setting you need.   Mine is like this, I leave it on the same setting and just leave it switched on all the time, it switches itself on and off as the humidity demands.
Eric Cox11/10/2009 11:04:54
537 forum posts
37 photos
A retro-fit controller can be found here
Douglas Johnston25/10/2009 11:32:19
760 forum posts
34 photos
I have been looking into the idea of using a  dehumidifier in my workshop for some time. The best type of unit seems to be the type that uses dessicant (not the simple silica gel filled containers that you need to revive every other day). These units work well down to to very low temperatures, unlike the compressor types.
                   The units can be run all the time on a humidistat but that can be rather expensive if your workshop is not well sealed to the outside air. The other problem is that of making sure that the temperature of your machinery is kept above the dewpoint of the air in the worshop.
                    The real problem is found when your machinery is cold (usually overnight) and the morning sun heats the air inside the workshop causing the dew point to rise above the machine temperature, since the metal machinery cannot rise in temperature at the same rate as the air. The result is condensation and the dreaded rust.
                    A well insulated workshop helps a lot in reducing the rate at which the air temperature changes inside the workshop thus helping to reduce the temperature difference between machinery and air.
                    I am in the process of designing a system which will switch the dehumidifier on only when there is a danger of condensation forming on metal surfaces so that the cost of running the system can be kept to a minimum.
charadam01/11/2009 23:40:58
184 forum posts
6 photos
5 years back, I was faced with the necessity of replacing an ancient eyesore, 12 foot x 7 foot creosoted tongue & groove shed that had apparently seen service as a cowshed.
At the same time, I happened upon a load of free breeze blocks and so the construction method was decided.
I won't go into the digging of foundations, the concrete mixer allowed to harden off when full, the Building Inspector who was (eventually) persuaded that his presence was superfluous and all the other happy memories.
The shed - for so it must be called - or the H&S will descend - ended up at 19' x 8' externally, cement rendered and divided internally by an insulated block wall to provide garden storage in 6' at the end.
The ridged roof was insulated with 6" of fibreglass mat and the walls with 30mm Kingspan sheathed in 5mm ply. The floor was quarry tiled on 125mm of concrete with rebar at strategic locations beneath the Chipmaster lathe and Boxford mill.
A 150 Watt dehumidifier with its own humidistat was installed as well as a 200 Watt oil-filled radiator for trace heating. A fan heater is present but is very infrequently used.
A rough and ready record was kept of the humidistat setting and after around 2 years, things settled down to where the 2 litre container is emptied 3-weekly in reasonable conditions and weekly in British weather.
The control was simply observation of any tendency for rust to begin and happily it is well-controlled at (I believe) reasonable cost.
Incidentally, 18 x 13 amp sockets are not enough in a 12' x 7' 6"  "shed".
V8Eng02/11/2009 19:43:52
1634 forum posts
32 photos
I own a machine which had been stored in an uninsulated, and not particularly well roofed shed for a few years.
This had been covered in ordinary bubble wrap, and was virtually rust free, anything not under the wrap had gone extremely rusty.
Can someone explain this, or was it just a fluke?
I've never had time to investigate making machine covers out of bubble wrap, but have often wondered if it might be something worth testing out properly, under controlled conditions.
Ian S C03/11/2009 09:07:25
7468 forum posts
230 photos
My workshop is a galvanised iron clad shed with no insulation,temperatures range from -10c in winter to +30c in summer,never had condensation problems ie no rust on tools,I suppose every thing stays at the same relative temperature,It would be nice to be a bit warmer in winter.IAN S C
Douglas Johnston03/11/2009 09:24:18
760 forum posts
34 photos
A couple of years ago I made a cover for my milling machine out of two layers of plastic sheet (cut from a cheap B&Q plastic  tarpaulin) with a layer of bubble wrap in between. The whole thing was stuck together with duck tape, and while it is a bit cumbersome it does appear to be effective in keeping the rust at bay over the winter.
                 Bubble wrap is an excellent insulator and provided it completely covers the machine it should prevent a large temperature difference between the metalwork of the machine and the surrounding air , when the air temperature rises quickly due to morning sun after a cold night. This keeps the metal temperature above the dew point temperature and thus prevents condensation.

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