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 Post subject: Dynamotor B+ power supply
PostPosted: Feb Fri 20, 2004 12:56 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 620
Location: Lyons, Kansas
Greetings folks: I am rather new to this forum, having posted only a time or two, but I have lurked on these topic for some time. A hint that I would like to share involves getting various voltages out of a dynamotor. Many collectors may have dynamotors in their junkbox that are not getting used. There is a photo in the gallery of what I have done to my 24 volt dynameter. This photo shows the whole story of how I took a twistlock, choke of unknown henris, and a handful of 1N4741 zeners to get voltages that step down 11 volts at a time. I ran the dynamotor on 12 volts and got 150 volt output instead of the rated 250 volts at the 24 volt jeep design. It ran my Crosely XJ easily. Just something you can do to put a dynomotor to work.<P>------------------<BR>steve


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 Post subject: Dynamotor B+ power supply
PostPosted: Feb Fri 20, 2004 2:04 am 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34326
Location: Sandpoint, IDAHO 83864
One thing I have done for years is to run 28 volt dynamotors at reduced voltages to get reduced output voltages. Some of the surplus WW2 aircraft dynamotors are quite handy in this respect. Get one that puts out about 500 volts and you have a source of power at anything between about 100 to 500 just by controlling the input voltage.<P>I viewed the picture of what you built and I must state that to be extremely careful. Dynamotors are not like ordinary vacuum tube rectified power supplies that will only provide a limited amount of fault current in case of a short. A dynamotor has inertia and some of the larger ones can provide an extremely large amount of fault current if shorted briefly. If anybody doubts me, just get one up to speed and briefly short it out with an insulated screwdriver. The resulting arc is most convincing. There is no such thing as a "slight electrical shock" from a running dynamotor!<BR>I state this from nearly 40 years of playing around with various dynamotors in many different milsurp sets. I do not wish to see anybody hurt as a result of playing around with these things. <BR>Curt------------------<BR>Curt, N7AH


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 Post subject: Dynamotor B+ power supply
PostPosted: Feb Fri 20, 2004 2:56 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 620
Location: Lyons, Kansas
Wow! I'm glad to hear that caution about the amperage of those things! I did run an ac/dc radio on it for a short while, just for curiosity. It ran fine. So I did see that it puts out a good kick. The only problem I had was the motor whine, which came through. I think it was mostly mechanical instead of electrical. Maybe better cushioning or stabilizing the dynamotor to kill vibration would help that. Or do I need new brushes?<P>------------------<BR>steve


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 Post subject: Dynamotor B+ power supply
PostPosted: Feb Fri 20, 2004 6:58 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34326
Location: Sandpoint, IDAHO 83864
Completely eliminating dynamotor whine can be a frustrating experience. Any commutated motor or generator will create the whine by nature of the brushes/ commutator switching that goes on. In a dynamotor, you have at least two sets of brushes, often on some dynamotors as much as four sets, so the problem only gets worse. The secret is to make sure the commutator is clean and the brushes are seated properly. Also make sure the brushes are free to move in their holders and are of sufficient length to apply the proper tension to the commutator. New brushes often need to be "run-in" for a few hours so they seat properly. Watch the commutator for grooves and any possibility of the mica insulator sections might be raised enough above the segments to cause brush flutter.<BR>Make sure the rf bypass capacitors (often mica types installed right at the brush holders) are good. Keep the bearings properly lubricated with a channeling type grease, and do not overlubricate, as it will get thrown out of the bearing and wind up on the commutator.<BR>Shielding of the dynamotor often helps, and locating it at a distance from the set often helps. Shielded cables also help to keep the noise down.<BR>As for acoustical noise...remote location is about the only solution, or else just get used to it. I have to run the dynamotor for the ART-13 transmitter outside in a lined wooden box to be able to stand the noise. It sounds like a vacuum cleaner motor when running. (I wonder if the fact that it was made by Electrolux has anything to do with it?)<BR>Dynamotors can be a lot of fun. Just keep them maintained and be careful.<BR>Curt<P>------------------<BR>Curt, N7AH


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 Post subject: Dynamotor B+ power supply
PostPosted: Feb Fri 20, 2004 8:42 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 620
Location: Lyons, Kansas
Thanks, Curt, those are some good ideas. That old dynamotor, as you can see from the picture, came right out of storage and probably hadn't been run since WWII. I fixed it up several years ago. I am going to rework it: paint it, rewire it, shield it to make it safer, make it nice. A capsule of grease came with it - stored in one of the ends - along with a new set of brushes. <BR> You know, when I first opened the ends of that old war relic, and found those capsules, it kind of gave a person a feeling of discovering something of history. I didn't know what was going to be in them. If anyone has an old dynamotor in their collection - check it out. They are neat, rather unrecognized, pieces of radio equipment.<P>------------------<BR>steve


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 Post subject: Dynamotor B+ power supply
PostPosted: Feb Fri 20, 2004 11:17 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34326
Location: Sandpoint, IDAHO 83864
Steve- what exactly is the model number of the dynamotor pictured? It looks somewhat like the DM-33 or DM-35 dynamotors. DM-33 dynamotors nowadays are worth big bucks. It was the transmitter dynamotor for the popular Command Sets. Used to buy them brand new in the box for $4.98, but Fair Radio Sales was asking $75.00 for one a while back!<BR>Curt<P>------------------<BR>Curt, N7AH


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 Post subject: Dynamotor B+ power supply
PostPosted: Feb Fri 20, 2004 11:48 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 620
Location: Lyons, Kansas
Curt, this is a Continental Electric Co. DM310A. I was reading in an old Popular Science magazine from about 1950 how they were recommending that folks buy these surplus dynamotors and revamp them for the motors. They would take off the high voltage armature, put a pulley on the shaft, and run their small lathes, grinding wheels,etc. Guess that just makes the surviving dynamotors more valuable. They are still under-appreciated, not recognized for what they are, and still in danger of being thrown out in my opinion. But, when you think about it, that may be true of most radio equipment also. <BR> <P>------------------<BR>steve


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 Post subject: Dynamotor B+ power supply
PostPosted: Feb Sat 21, 2004 12:55 am 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34326
Location: Sandpoint, IDAHO 83864
Yeah, I have heard of that sort of butchering. In fact some hams took the BD-77 dynamotor, which was originally 14 VDC input and 1000 VDC output and center drilled the shaft and put a pulley on one end and drove it with another fan belt off their car engines. That would provide enough output power for a pretty powerful signal back in the days. Nowadays, you would not even be able to find a place to put anything like that under the hood of modern vehicles. The only real bad thing I ever found with dynamotors was the large starting current they draw. It is oftentimes enough to shut down a current limited power supply. I almost always float a lead acid battery across the supply to handle the starting current.<BR>Curt<P>------------------<BR>Curt, N7AH


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 Post subject: Dynamotor B+ power supply
PostPosted: Feb Sat 21, 2004 3:37 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3430
Location: Olympia WA USA
If you junk any old dynamotors, remember that some models of B&D drill motors use the exact same size brushes.<BR>I have rebuilt several from old dyno brushes, and they worked just fine.<BR>FrankB<P>------------------<BR>


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 Post subject: Dynamotor B+ power supply
PostPosted: Feb Mon 23, 2004 6:28 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34326
Location: Sandpoint, IDAHO 83864
Thanks for the note Frank. However, in my case it ususally is the opposite. I am needing dynamotor brushes instead. Maybe I will look into the cheap B&D electric drills that are always showing up at yard sales for a buck or two.<BR>Curt<P>------------------<BR>Curt, N7AH


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 Post subject: Re: Dynamotor B+ power supply
PostPosted: Mar Wed 30, 2016 2:00 pm 
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Joined: Feb Wed 10, 2016 5:16 pm
Posts: 22
Gentlemen, I have in my possession the radio and dynamotor for a 1933 Packard. I have restored the Packard and am thinking of restoring the radio and dynamotor as well. The Packard is a six volt positive ground system. The dynamotor is mounted on a steel base plate and is rubber mounted and has what appears to be a filter capacitor can and a transformer on one end of the unit all mounted to the base plate. I detect no shorts with my DMM. So I applied 6 volts from a battery using a dim bulb setup (a 6v auto sealed beam headlamp bulb) with no joy. Probably the brushes are not seated on the armature. In any case, I am in need of some sort of schematic diagram for the dynamotor. There is no name plate data anywhere on the dynamotor unit and the only info I have is that I bought all the piece parts that came with the 1933 Packard radio including the dynamotor. Any suggestion where such a dynamotor schematic could be found? I have the radio schematic which shows the dynamotor connection points with a B+ of 220v and the connections for the A+ for the heater filaments. I plan to restuff the capacitor can and ohm out the stepdown (I assume it is a stepdown) transformer for the A+. Since the dynamotor showed no life after applying 6v positive ground, I plan to disassemble the dynamotor and go hunting. Should be fun! Any thoughts on a dynamotor schematic with caps and transformer?

Bob


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