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THE AM BULLETIN BOARD => Technical Forum => Topic started by: KC4VWU on September 14, 2017, 07:50:14 PM

Title: Dynamotor Info
Post by: KC4VWU on September 14, 2017, 07:50:14 PM
Hi Guys,
            Does anyone happen to know how to properly check the armature in a dynamotor? I'm working on a model DY-1, which is the mate to the ARC-5 receivers. Interested in the HV side (dynamo). There are 39 contacts on the commutator and by picking an arbitrary contact and one (nearly) 180 degrees from it there are 15 poles with varying continuity to the first, 19 with the second, and 5 which shows continuity amongst themselves. Can't figure out the rhyme or reason for this except for open circuit(s) in the winding. The motor side commutator checks from one arbitrary all the way round it's 26 poles with varying degrees of a small resistance slightly increasing upward to 180 degrees then back down to the starting point. This seems more like it. Not much about dynamotors in either handbook and online sources doesn't really get into specifics other than how important it is to clean and repack the bearings.

            The problem I have is that the output is only about half than what it is supposed to be, and after it runs for a minute or two, it drops by half again. This is open load test. Will not even begin to light a 25w bulb, which is slightly over its capacity, but should should show some signs of life. Only thing I can think of is I got the brushes back in wrong. I marked their positions, but failed to mark top and bottom, so they could have been installed upside down.

I'd like to install some new brushes, but want to make sure of the armature's condition first. Does anyone know where to get the brushes? Should be the same as ones used in it's army counterpart, the DM-32.

Thanks, Phil 

Title: Re: Dynamotor Info
Post by: KU8L on September 15, 2017, 12:44:46 PM
I am not familiar directly with the ARC-5 dyno's but we do a lot of commercial AC servo and DC motor/drive service here at out repair center.  Be sure there isn't rust or carbon built up on any armature or stator laminations--it can create shorted loop conditions internally.  Also, a hi-pot test to be sure the windings are not grounded to the core.  

Commutator service is tedious but critical if the comm is well used.  Carbon and debri must be removed from between the comm sections and the comm must be smooth and even and make good contact with the brushes.  We typically do this on a lathe with a commutator mill but it can be done by hand as well.

A decent starter/alternator repair/rebuild shop or a motor repair house can diagnose these pretty easily if you get really stuck.

Here is a a little video I saw re: service on these.



Title: Re: Dynamotor Info
Post by: W2PFY on September 15, 2017, 07:13:57 PM
Curt, what are the input voltages and how many amperes does it draw? Are you hooking the light bulb up to the output of the dynamotor? I have been playing with dynamotors for about 50 years as well as some very large motor generator sets used for charging industrial batteries and also large DC motor generators used for welding. It doesn't matter to some extent how large or small these devices are as they all operate pretty much on the same principals.

As far as the brushes are concerned, they should have somewhat of a concave shape on them where they meet the commutator. If they do not, they need to be seated with a brush seating stone. The seating stones come in several degrees of hardness but I think for small work, you would use a soft seating stone. It looks like they can still be found by googling them or get them at a motor repair shop. Properly seated brushes should not show too many sparks but all motors/generators will show some sparks depending on the load and the design. The soft stones are white in color. You should blow the motor out with compressed air when done. If you do need to turn the commentator, it will also be undercut where the mica between each copper segment is cut lower than the surface on the commentator, otherwise it will be spark city and that commentator will get so hot that it will melt the solder connections on the commutator   
Terry (

Title: Re: Dynamotor Info
Post by: Opcom on September 15, 2017, 09:43:05 PM
If I'm not mistaken, brushes get used to having the commutator pass them in a single direction, that is, they wear a certain way, and putting them back upside down can cause issues.

Is a growler appropriate for dynamotor rotor testing?

check out this video

This article seems good.

Title: Re: Dynamotor Info
Post by: KC4VWU on September 16, 2017, 02:48:16 AM
Well guys, looks like it is the HV side of the armature. Manual says to go around the commutator checking adjacent contacts and I found two places that show no continuity. Most showed a resistance of 25 to 26 ohms, and there were a few that showed about 130ish and quite a few others that showed around 13 ohms. Given the shape that the commutators were in, I'd say this one had a problem from the get go. Dosen't look like it's had much run time at all. I guess now it's an interesting paperweight. Onward ho! 

Title: Re: Dynamotor Info
Post by: KU8L on September 19, 2017, 12:49:41 PM
Sometimes open commutator segments just need to be re-soldered.

Title: Re: Dynamotor Info
Post by: KC4VWU on September 19, 2017, 06:26:47 PM
That thought did cross my mind. An open would seem more likely at the commutator contacts solder connection, but seeing it is the roadblock there. I'll have to find the jeweler's eyepiece and give it a good look over.   
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