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.

[apochronaut]

You will find that the bulb life will be dramatically reduced by running at overvolt.

I found your comment a bit odd, that " the microscope manufacturer wants the bulb that will last 10,000 hours" This rating would be for an led and some do but not filament bulbs. If you look the bulb # up, for your halogen bulb, or post it in the forum, you can find out just what the rated life is. Most are less than 200 hours.

Overvolting such bulbs can reduce their life to less than 10 hours, although they won't as you say, blowup.

[75RR]

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

Increasing the voltage over what a bulb is rated for decreases its life drastically.
On the other hand, reducing the supplied voltage increases its life exponentially.

If you need to increase the illumination, you are better off using a higher rated bulb and running it slightly below the rated voltage.
Reducing the max supplied voltage by 10% or 15% below the rated voltage is enough to increase its life by many hours.

See formula on first page of the pdf: http://www.microscopy-uk.org.uk/mag/art ... ersion.pdf

Higher rated bulbs produce a lot more heat so they are usually placed in an external lamphouse.
If you need more illumination in an internally placed bulb, located under the light port for example,
you might want to consider a LED conversion.

Remember however that with good quality microscopes, the rated voltage of the supplied bulb is enough to illuminate
the sample in all illumination techniques the microscope was configured for.

It would be nice to see photos of the microscopes and what you have done to them - words can be a little dry ...

[mrsonchus]

Hmm, it can be an easy conversion if that's what you need or would like -
although 75's comment is spot-on in my experience - "Remember however that with good quality microscopes, the rated voltage of the supplied bulb is enough to illuminate the sample in all illumination techniques the microscope was configured for."

Here's a picture of the time my big-O's halogen blew and I popped in an LED without any wiring needed,


Also I converted the 20W 6V halogen of my other 'scope using an LED psu, a £10 controller, a £2 torpedo-switch and a nice LED in place of the original halogen - I just stuck the assembly onto the side of the 'scope with tape and it worked perfectly. Easily put back when I sold that 'scope on - the the re-connection of 2 wires in the 'scopes base and the built-in system was back in action.

Here's the post link of the whole thread - viewtopic.php?f=12&t=2619&p=22583&hilit ... ion#p22583

I now use that rig to power my Orthoplan's external lamp housing with a halogen 40W 12V bulb - similarly stuck onto the side of the mighty 'scope and no need for the large and heavy Leitz psu...


Can we see some actual pictures of your set-up old chap?

John B.

[apochronaut]

don't forget that the phrase " making them brighter" was included in the original post. I suggest that all led conversions be put to the test of 100x DF, if one wants to know just how effective they are.....maybe even 100x phase?

[billbillt]

Thanks John B. for showing one again you conversion procedure.. It was certainly worthwhile and doable.. LED conversion is generally a painless operation..

BillT

[mrsonchus]

Aha! That's true Bill, to a point. But, there's one thing I can say with experience, I prefer halogen as a light-source.
I prefer it as I find the LEDs (although I've also tried the 'soft-white' type) have a harsh blue quality and also can be very hard on the eye - they seem to cause a sort of glare effect that tires my eyes at least, long before I have finished a 'session' at the 'scope.

I currently use 12V 60W halogen bulbs bought from the supermarket (at a cost of £6 for 4) in my Orthoplan's model-100 light-box to a very satisfactory end. I now also use one of those 'variable ND filters' used for cameras - simply placed over the field-iris top glass and used to very easily alter the brightness of illumination whilst keeping the halogen at its 12V design voltage. This works supremely well, not a single problem with this method for me.

Of course I don't need to consider heat levels with the external 100 light-box, actually capable by design of accommodating a full-on 100W halogen.

p.s. I've taken many comparison images with the 'variable ND filter' vs the Leitz 'proper' ND filters that I have - and could see absolutely no difference - none. The cheapo variable ND has effectively given me a continuously variable ND filter as it's name suggests! That surprised me as it was extremely cheap to buy - I think about £11 as I remember - and I was very sceptical indeed, but thought It would be so useful that I took the chance and bought one - it's perfect! No more tormenting my halogen with adjustment or swapping combinations of ND filters in and out, or suffering the light colour-changes that altering the halogen without using ND filters gives.


John B.

[AndyMilman]

I've read the comments and they're correct. I really don't know how long a halogen bulb is supposed to last when used at the rated voltage but increasing the voltage will reduce the lifetime. But the bulbs are cheap and easy to replace. OTOH, I don't want to replace them every other minute.

HOWEVER,

I accidentally connected my favorite microscope--which has both upper and lower lights--to a regulated power supply without turning down the voltage to 12 V or so. Instantly, two bulbs were gone to Halogen Heaven (I switched from one to the other when I saw no light when I turned it on). The good news is that nothing else happened--I just melted the two bulbs. (The power supplies shut themselves down in case the current gets too large, or there's a short circuit, to prevent melted wires and fires).

THE BAD NEWS

If you're going to exceed the rated voltage, be careful!
But some overvoltage (maybe to 15 V instead of 12) may safely provide more light.

BUT NOW GOOD NEWS!

In the meantime, I discovered that I can buy 50 W, 12 V bulbs for a dollar or so (if I buy ten--why not?). They have G4 pins, so I should be able to put them into the smaller housing* and run them at the nominal voltage. If the lamp housing doesn't get too hot, things should work out. I usually don't run a bulb for more than a few minutes at time without needing to look at something else for a minute; I try to remember to turn off the light when I'm not using it.

The ultimate problem, for me, is that the more common Meiji microscopes that have episcopic illumination only use 6 V 30 W bulbs, which don't provide enough light for looking at dark, non-transmitting things--like mold growing on a layer of agar. New, higher-power vertical illuminators are well over $1300 USD or so. So I'm looking (flailing?) around to find a cheap way to get more light on the subject. I don't have the bulbs yet, so I'm a bit concerned that they might not fit in the housing.
----------------------------------


*Meiji uses larger lamp housings for 50 W bulbs than 20 or 30 W.

[75RR]

I accidentally connected my favorite microscope--which has both upper and lower lights--to a regulated power supply without turning down the voltage to 12 V or so.

I realize that was an accident, but if you want to extend bulb life you not only need to limit the voltage to your bulbs to around 85 to 90 percent of the rated voltage but you also need to feed in that voltage gently by slowly increasing and decreasing it from and to 0 v.

The ultimate problem, for me, is that the more common Meiji microscopes that have episcopic illumination only use 6 V 30 W bulbs, which don't provide enough light for looking at dark, non-transmitting things--like mold growing on a layer of agar.

I think you may be confusing episcopic (reflected) illumination with diascopic (transmitted) illumination.
You seem to be trying to punch through opaque subjects with over-voltaged transmitted light (i.e. from below). Is that right?

Photos of what you are up to would help to clarify this.

[billbillt]

I don't see how anyone that does electrical work around microscopes can get by without a cheap multimeter to verify voltages before applying it to the bulb.. It will save a lot of trouble..

BillT

[mrsonchus]

Yet another case of a picture being worth a thousand words I think. Can you post some images which will really help the very knowledgeable fellows here to help you with your specific needs?

As mentioned, perhaps clarify your terminology too. The two (most would regard as 'main') methods of illumination/observation are :
1) The light passing through the subject from below and being observed from above - the light having travelled through the subject - 'transmitted' or 'diascopic' illumination.
2) The light having 'bounced off of' the subject - 'reflected' or 'episcopic' illumination.

John B.

[75RR]

I don't see how anyone that does electrical work around microscopes can get by without a cheap multimeter to verify voltages before applying it to the bulb.. It will save a lot of trouble..

We don't know that he doesn't - the burnt bulbs were an accident due to an oversight - power supply voltage setting was 'on' when plugged in.