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From halogen to led
Posted: Sun Sep 12, 2021 8:57 pm
by Greg Howald
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
Re: From halogen to led
Posted: Sun Sep 12, 2021 9:37 pm
by viktor j nilsson
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.
Re: From halogen to led
Posted: Sun Sep 12, 2021 10:15 pm
by Greg Howald
Ok. I'll look that up. Thanks.
Re: From halogen to led
Posted: Sun Sep 12, 2021 10:46 pm
by Greg Howald
Found an ordered an led driver that can be added to the circuit. Thanks very much. I appreciate your input.
Greg
Re: From halogen to led
Posted: Sun Sep 12, 2021 10:51 pm
by viktor j nilsson
Which one did you get?
Re: From halogen to led
Posted: Wed Sep 15, 2021 2:07 am
by Greg Howald
I ordered the three I found on Amazon. Surely one of them will do the job.
Re: From halogen to led
Posted: Thu Sep 16, 2021 1:30 am
by farnsy
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.
Re: From halogen to led
Posted: Thu Sep 16, 2021 2:06 am
by Greg Howald
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
Re: From halogen to led
Posted: Thu Sep 16, 2021 5:14 am
by MicroBob
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.
Re: From halogen to led
Posted: Thu Sep 16, 2021 3:12 pm
by apochronaut
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..
Re: From halogen to led
Posted: Thu Sep 16, 2021 5:09 pm
by MicroBob
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?
Bob, who once had an electronic organ that received and played long or medium wave radio...
Re: From halogen to led
Posted: Fri Sep 17, 2021 2:10 am
by apochronaut
No nearby A.M. stations on amalgam teeth?
Re: From halogen to led
Posted: Fri Sep 17, 2021 3:42 am
by Greg Howald
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
Re: From halogen to led
Posted: Fri Sep 17, 2021 4:30 am
by Greg Howald
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
Re: From halogen to led
Posted: Fri Sep 17, 2021 7:52 am
by Hobbyst46
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.
Re: From halogen to led
Posted: Fri Sep 17, 2021 2:30 pm
by Greg Howald
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
Re: From halogen to led
Posted: Fri Sep 17, 2021 6:57 pm
by MicroBob
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
Re: From halogen to led
Posted: Sun Sep 19, 2021 3:07 pm
by Greg Howald
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.
Re: From halogen to led
Posted: Sun Sep 19, 2021 5:00 pm
by MicroBob
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.
Re: From halogen to led
Posted: Mon Sep 20, 2021 10:19 pm
by Greg Howald
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
Re: From halogen to led
Posted: Tue Sep 21, 2021 11:00 am
by Adam Long
Which dimmer did you get Greg? PWM?
Re: From halogen to led
Posted: Tue Sep 21, 2021 11:21 am
by Greg Howald
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.
Re: From halogen to led
Posted: Thu Sep 23, 2021 1:46 am
by Gatorengineer64
Great project, can we get a photo of the final result?
Re: From halogen to led
Posted: Fri Sep 24, 2021 12:05 am
by Greg Howald
I can post that after my current project is complete.
