From halogen to led

Here you can discuss different microscopic techniques and illumination methods, such as Brightfield, Darkfield, Phase Contrast, DIC, Oblique illumination, etc.
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Greg Howald
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From halogen to led

#1 Post by Greg Howald » Sun Sep 12, 2021 8:57 pm

One of my scopes is 20 watt halogen, and for others, it might be bright enough, but not so for me. I decided to convert to led.
Transformer output is 6.3 volts a.c. at 60Hz. Building a bridge rectifier was easy enough and I put in 3500 micro farads of capacitor strength and a large induction coil.
60Hz hum is still present using a 1 watt led. Not enough voltage for a 5 watt led. But at 5 watts hum is minimal. I have a 3 watt led coming and will have enough voltage to drive it so I'll see what happens with that. At low voltage I can see the hum but above 75 percent of brightness I can't see it any more. All of the cameras see the hum except the Amscope MU 1000. It seems to filter the hum out.
I have a ready made rectifier coming along with a 3 watt led, so I'll have plenty of experimenting to do.
Any suggestions concerning filtering out the hum?
Greg

viktor j nilsson
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Re: From halogen to led

#2 Post by viktor j nilsson » Sun Sep 12, 2021 9:37 pm

Greg Howald wrote:
Sun Sep 12, 2021 8:57 pm
One of my scopes is 20 watt halogen, and for others, it might be bright enough, but not so for me. I decided to convert to led.
Transformer output is 6.3 volts a.c. at 60Hz. Building a bridge rectifier was easy enough and I put in 3500 micro farads of capacitor strength and a large induction coil.
60Hz hum is still present using a 1 watt led. Not enough voltage for a 5 watt led. But at 5 watts hum is minimal. I have a 3 watt led coming and will have enough voltage to drive it so I'll see what happens with that. At low voltage I can see the hum but above 75 percent of brightness I can't see it any more. All of the cameras see the hum except the Amscope MU 1000. It seems to filter the hum out.
I have a ready made rectifier coming along with a 3 watt led, so I'll have plenty of experimenting to do.
Any suggestions concerning filtering out the hum?
Greg
Yes, use a constant current led driver. I like the Buckpuck and BuckBlock drivers.

Greg Howald
Posts: 1185
Joined: Tue Oct 20, 2020 6:44 am

Re: From halogen to led

#3 Post by Greg Howald » Sun Sep 12, 2021 10:15 pm

Ok. I'll look that up. Thanks.

Greg Howald
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Re: From halogen to led

#4 Post by Greg Howald » Sun Sep 12, 2021 10:46 pm

Found an ordered an led driver that can be added to the circuit. Thanks very much. I appreciate your input.
Greg

viktor j nilsson
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Re: From halogen to led

#5 Post by viktor j nilsson » Sun Sep 12, 2021 10:51 pm

Which one did you get?

Greg Howald
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Re: From halogen to led

#6 Post by Greg Howald » Wed Sep 15, 2021 2:07 am

I ordered the three I found on Amazon. Surely one of them will do the job.

farnsy
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Re: From halogen to led

#7 Post by farnsy » Thu Sep 16, 2021 1:30 am

I don't think making efforts to retain the original transformer are worth it. 12V A/C adapters (or 5V, if you prefer) are small and cheap. You can use a wall wart or an old laptop cable that you already own and run the 12V directly to a PCM dimmer so your LED always gets 12V or nothing--works with a great variety of LED bulbs. That's the normal way to do an LED conversion. It's really cheap and well-standardized and you never have mains power in your scope so if you mess something up it's not dangerous.

Super old, inefficient, humming transformers are something I can't tolerate, and 6V A/C is not real useful if you are converting to LED anyway.

Greg Howald
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Re: From halogen to led

#8 Post by Greg Howald » Thu Sep 16, 2021 2:06 am

Thanks. I do have the adaptor necessary and I have a. dimmer arriving on Monday. So far, what I have achieved is so much brighter that it puts the 20 watt halogen to shame. I'll just see what happens as other parts arrive and go from there. So far this has been rewarding.
Greg

MicroBob
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Re: From halogen to led

#9 Post by MicroBob » Thu Sep 16, 2021 5:14 am

Today many things are powered by 5V USB power - why not a microscope? Single white LEDs need around 3-4 Volts DC so 5V DC is already close. And a 5V powered microscope can be powered by a power bank or a borrowed USB charger in case one forgets the power supply.

apochronaut
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Re: From halogen to led

#10 Post by apochronaut » Thu Sep 16, 2021 3:12 pm

farnsy wrote:
Thu Sep 16, 2021 1:30 am


Super old, inefficient, humming transformers are something I can't tolerate, and 6V A/C is not real useful if you are converting to LED anyway.
I once had an old scope that came from the Emory School of Medicine, in Atlanta. It hummed " Goober Peas" incessantly, sometimes so loud that my dog howled. Drove me crazy! I sold it to a rapper around 2000 to use as a sampling source.
The one I use now, a Diastar with an on board transformer capable of handling a100 watt halogen output is quieter. When on full power for high rez. DF for instance, there is just an almost inaudible hum. It came from the Plant Introduction Station at Bethesda , Maryland and although I am not sure I think it is humming Lemon Tree but very low, similar to the Peter Paul and Mary version. Quite tolerable and pleasant compared to Goober Peas! Goober peas is a March, so understandable..
Last edited by apochronaut on Fri Sep 17, 2021 2:10 am, edited 1 time in total.

MicroBob
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Re: From halogen to led

#11 Post by MicroBob » Thu Sep 16, 2021 5:09 pm

Hi Phil,
shouldn't the advantage of a proper reseach stand be that the tune can be adjusted in a wide range and exchanged with just a few lever turns? :lol:

Bob, who once had an electronic organ that received and played long or medium wave radio...

apochronaut
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Re: From halogen to led

#12 Post by apochronaut » Fri Sep 17, 2021 2:10 am

No nearby A.M. stations on amalgam teeth?

Greg Howald
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Re: From halogen to led

#13 Post by Greg Howald » Fri Sep 17, 2021 3:42 am

This evening I took farnsey's advice and took out the transformer. The only thing I kept was the switch. I replaced the dimmer with a 500 ohm, 2 watt potentiometer so it could take the full load. I went with a 5 volt power block. When it came up it was beautiful and very bright. I was so happy to see a pure white background, not only with my eyes but with the camera as well. The pvm will arrive on Monday. I'll try that instead of the pot, but at this time I am more than pleased. Bring on the phase contrast!
Greg

Greg Howald
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Re: From halogen to led

#14 Post by Greg Howald » Fri Sep 17, 2021 4:30 am

Wow! Testing demonstrates the best Rheinburg, oblique and dark field imaging I have seen when compared to the eight other scopes I own. Thanks so much to all of you for your help. The frog just became a Prince.
Greg

Hobbyst46
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Re: From halogen to led

#15 Post by Hobbyst46 » Fri Sep 17, 2021 7:52 am

Bravo.

A constant current is really the best for LEDs but PWM can do the job. If using a PWM dimmer, and horizontal bands appear in the camera image, the exposure should be longer (slower camera speed) to prevent the banding.

Greg Howald
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Re: From halogen to led

#16 Post by Greg Howald » Fri Sep 17, 2021 2:30 pm

The constant current is ordered and I will install both that and the pvm. The pvm will arrive on Monday but the constant current driver won't be here til October. Tick. Tock. Tick. Darn!
Greg😆

MicroBob
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Re: From halogen to led

#17 Post by MicroBob » Fri Sep 17, 2021 6:57 pm

Hi Greg,
nice to hear that youv'e got a nice illumination now. The potentiometer might actually be a very good solution as long as you don't overload it. A resistor in line with the potentiometer might be useful to bring down the voltage and improve the adjusting of the brightness. Did you find a good solution for a heat sink? LEDs have a better efficiency than bulbs but still produce more heat than light.

Bob

Greg Howald
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Re: From halogen to led

#18 Post by Greg Howald » Sun Sep 19, 2021 3:07 pm

I stacked two one inch square heat sinks on top of one another to raise the light to an appropriate level. I think it will be sufficient.

MicroBob
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Re: From halogen to led

#19 Post by MicroBob » Sun Sep 19, 2021 5:00 pm

That sounds ok to me. It is advisable to use heat transmitting compound to make best use of the heat sinks. When the LED is well connected to the heat sink it will be fine as long as you can touch the heat sink for 10 seconds or so.

Greg Howald
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Re: From halogen to led

#20 Post by Greg Howald » Mon Sep 20, 2021 10:19 pm

The pvm came today. I went with 6 volts to a 3 watt led lamp. It looked a little dim until I centered the lamp.
What a beautiful result. The dimmer mounted without difficulty so there was no change to the case. Its just great. Thanks for all your help and advice.
Greg

Adam Long
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Re: From halogen to led

#21 Post by Adam Long » Tue Sep 21, 2021 11:00 am

Which dimmer did you get Greg? PWM?

Greg Howald
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Re: From halogen to led

#22 Post by Greg Howald » Tue Sep 21, 2021 11:21 am

I got the dimmer on Amazon. It is an in stock item and cost under fifteen bucks. It is 6 to 90 volt dc and the potentiometer is separate from the board. It works very well.

Gatorengineer64
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Re: From halogen to led

#23 Post by Gatorengineer64 » Thu Sep 23, 2021 1:46 am

Great project, can we get a photo of the final result?

Greg Howald
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Re: From halogen to led

#24 Post by Greg Howald » Fri Sep 24, 2021 12:05 am

I can post that after my current project is complete.

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