You are not obligated to use the on-board fan. It's convenient and relatively quiet; but a duct could easily be connected to a remote squirrel-cage pull fan.
You are not obligated to use the on-board fan. It's convenient and relatively quiet; but a duct could easily be connected to a remote squirrel-cage pull fan.
Last edited by Luis-F-S; 12-Oct-2017 at 09:41.
In general, it's not the bulbs themselves that need the fan action, it's the everything else in the head... In fact, the bulbs were designed to run hot, and too rapid air flow over them can cause thermal shock that would weaken their structure, but inside the head can become like an oven, where plastics, wiring, lubes, etc are affected, and metal expansion/contraction + warping can happen, so the fan just pushes the heat from the air inside somewhat... (The parts still get warm/hot, but the cooler moving air around them helps them cool more evenly...) Many well designed heads used to be designed for convection cooling, where there was a intake vent area low in the unit that would draw cool air, but there was a chimney high up in the top where warm air would rise up out of the inside... Parts nearer the lamp area would heat more, but the heat would transfer away through the different metal parts, making the head metal a big heat sink that would get warm, but hopefully not too hot to the touch or stuff inside... (An upgrade for many heads is to figure what metal parts get hottest (and more likely to warp/distort), but where they meet the next metal part/panel, to remove the panel so the junction can be cleaned down to bare metals and a thin layer of heat sink compound is applied there so there is a better transfer of heat there, and throughout the unit...) And to re-position plastic parts, wiring, etc that are more heat sensitive lower in the head if they are not already, and away from the hottest panels/parts...
Many of the "muffin" type fans used in modern gear do not operate at mains voltage, but at reduced voltages fed from a tap in the P/S units, so look at the front of the fan itself and note the listed operating voltage (and if AC or DC), and a small supply (from a laptop supply, wall wart, etc) can be added to be left on during your printing session... You don't need a high volume fan, as you are just keeping the air moving inside the unit to prevent excessive heat build-up, and using a slightly under-voltage supply is OK, as the fan will turn slightly slower, reducing vibration... You should not need a hurricane force wind inside, as the fan is to just assist the "natural" cooling inside the head (and prevent hot air build-up)...
The round, black thermostat inside is a safety feature that cuts-off power if the unit got WAY too hot, but is there more for legal reasons, than operation, but as with any high output head, one should not leave it on longer than it is being used at that moment, give it a rest for 5 or 10 minutes if given a hard use, it got VERY hot on the outside, leave the ON cycles as short as possible, and don't use if you smell burning... (Set an operating ON time limit rule for any head and give it a shut-down break if longer like less than a minute on, etc...)
For rebuild/restoration, you can get high heat (ceramic based) engine paints from a auto or hardware store, or paints used to paint B-B-Q grills, DO NOT use vinyl replacement wire as it is not heat resistant, burns easily (like a smoky NASCAR rubber fire), while stinking like hell... Get some teflon coated wire, but note that teflon will just melt above 5 or 600 deg F, so no wires near the lamp or very hot areas... Get those fiberglass covered high heat tubing pieces for wires that run past or through very hot areas (don't allow wire insulation to touch or run along metal or anything hot inside)... After painting, there might be some smell from new paint out-gassing, but normal... Alway sniff for new weird smells when using... Run the head for testing before a printing session and check inside for melting, before a date in the dark...
The voltage regulation issue of the old P/S is only valid if if you use very short exposure fast color materials, or if you live somewhere that has terrible mains power (lights in your house dim/flicker often etc), but for B/W larger prints, the times are longer so a slight variation in power during exposure is negated, esp as mentioned, the head might be a little underpowered, but that helps you a little there, too...
Good luck with the restoration!!!
Steve K
When I rewired the head to serial I managed to use the existing wires apart from a small bit where the main runs into the head. Good idea to replace that with a teflon-coated cable just to be sure.
If the bulbs are not the main issue regarding the fans, I might install a little temperature monitor as per ic-racer's suggestion to make sure there is no heat build-up close to where the wires run. The thermoswitch in the CLS300 cuts the power at 80+ deg C (according to plaubel's manual) so anything south of that should be safe, assuming it's the same switch as in the CLS301. It's positioned next to the connection terminal.
I want to mention that all the problems of underpower, heat and big fans can be avoided with an LED head.
Today, I wouldn't spend my money in the restauration of a broken EST for b&w only.
Ritchie
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