Rewiring microscopes and making them Brighter

[AndyMilman]

I have collected more than a dozen Meiji microscopes, many of which have dead power supplies. Replacing one of them with a new Meiji power supply is beyond my resources, so I tried making my own. It was surprisingly easy. In essence,

1) I disconnected what wires I needed to, added a new plug to receive 12 V wiring, and ran the wires to the light socket (in the microscope, that is). I sometimes added a dimmer that I found on eBay and a switch to turn it on and off.

Finding an adequate power supply was easy: 12 V and 50 W or more will do the trick. Again, on eBay.

2) The whole thing cost less than $100, and so far has worked well.

3) I have some microscopes with illuminators both on the top and bottom. This required me to drill a hole in the base at some out-of-the-way position, add a switch to the circuit, so I could switch between them.

So far, it works well. I wouldn't try to sell it to a University research lab; but if it stops working, I can fix it. Since it's only 12 V DC, there's little worry for safety. I've re-done four or five so far (which will be for sale at some point) with no trouble.

MORE LIGHT!

Many of the things I look at won't transmit light; they must be illuminated from the top. The problem with this kind of illumination is that it may not work well with subjects of low reflectivity. Normally, Meiji uses 30 W 12 V halogen bulbs in the smaller lamp houses. This may not be enough.

But the microscope manufacturer wants the bulb that will last 10,000 hours! I'd not mind changing one every 100 hours if needed. So I took out a regulated power supply and tried running the bulb at higher voltages: the 12 V bulb even worked at 24 V without exploding. Fifteen to 17 V gave almost as much light, and may let the bulb live longer.

Even if it is a bit unconventional, increasing the light output by increasing the voltage seems to work. The obvious worries that the lamp housing will become dangerously hot or the wiring will melt so far are unfounded. But no one should be complacent about it.

Does anyone else have experience replacing the power supplies on-the-cheap? I'd like to know if there are problems I haven't thought of, or solutions to these problems, or yet, better approaches than mine to increasing the brightness.

[75RR]

So I took out a regulated power supply and tried running the bulb at higher voltages ...

Using a higher voltage than the bulb is rated for reduces bulb life drastically.
You are better off using a higher rated bulb and running it at a slightly lower voltage.
10% to 15% lower than the rated voltage is usually enough.

Have a look at this article, particularly the first part that has a formula for rerated bulb life:

http://www.microscopy-uk.org.uk/mag/art ... ersion.pdf

Note: Higher rated bulbs do produce more heat and are therefore usually placed in external lamp-houses.

One way around this, if you want to increase light output for internally located bulbs (directly under the light port) is to convert to a LED.

[AndyMilman]

Further thoughts on brighter bulbs


I'm still working on increasing the brightness of Meiji vertical illuminators.
They originally were intended for 6V, 30 W bulbs (and come from the ML2000 series).
They're not as bright as what I need for viewing dark biological specimins--like mold on a grape--
episcopically.

LED Bulbs

I bought various LED bulbs, but I had limited success. The problem is that there's only limited space in the housing, and
the LED arrays were either too large or the bulb was too long.

50 W Bulbs

Meiji makes a 12 volt, 50 watt version of the housing that it uses on the more expensive of its ML5000 series episcopic microscopes, but they're
almost impossible to find. They use a G6 (approx. 6 mm spacing of the wires). The smaller housings that I have need a G4.

I found some 12 volt, 50 watt bulbs with a 4-mm spacing of the wires (G4; they also come in G6). This works great, except that the Meiji housing
is relatively small. Overheating was going to be a problem.

My first thought was to add some heat sinks. This was easy, just requiring some thermal paste and a threaded hole in the housing.
It still got hot, but not to the point (I hoped) that it would start a fire. Then I added a small fan on the top (held on with two
screws) and that works great. The housing is cool enough that you can hold your hand on it.

I don't know if the fan alone would be sufficient; I haven't had the time to try it yet.

[apochronaut]

I have been playing around with a conversion on an old microscope from an 18 watt tungsten , to a 50 watt halogen and have considered fan cooling as well.

but

I am concerned that one could easily create a condition using a fan, of uneven cooling of the quartz envelope of the bulb, which would lead to uneven redeposition of the tungsten back to the filament and subsequent premature failure and or internal blackening of the bulb.

I just wonder whether passive cooling might be the best. There are small 12v. thermoelectric cooling plates available quite cheaply( as low as 3.00), that can be used a s heat sinks.