Starting up a DM-21 Dynamotor
 

Dear Friends,

I just picked up a BC-314-G (MW version of BC-348). It came out of
the estate of a long deceased ham so I don't know how recently it was
used. I would like to begin the restoration process and will start
with the dynamotor. I have read TM11-850 N which covers this radio
and the only maintenance mentioned for the dynamotor is one drop of
oil in the bearings.

If I'm going to start up a dynamotor that hasn't been run in a long
time, does this one drop of oil in the bearings sound sufficient? Is
there any other recommended maintenance to get this thing lubed
properly so I don't burn up the bearings when applying power? Also,
it's a 12 - 14v dynamotor. Is it recommended to start it on very low
voltage and increase it slowly to the recommended operating voltage?

Thanks for any help you guys can give me!

73,

Derek
WB0TUA

Give her a couple of drops of oil, and fire her up at full voltage.
If the bearings are a problem, they will make themselves known.
Bearings for these things are easily available from Grainger, etc.

The dynamotor should snap right up to full speed. If it doesn't
then there is a problem.

Do not try and run the dynamotor at less than full voltage. Doing this
will cause the current, which is what burns things out, to be too
high.

-Chuck, WA3UQV

Derek Cohn/WB0TUA wrote:
Dear Friends,

I just picked up a BC-314-G (MW version of BC-348). It came out of
the estate of a long deceased ham so I don't know how recently it was
used. I would like to begin the restoration process and will start
with the dynamotor. I have read TM11-850 N which covers this radio
and the only maintenance mentioned for the dynamotor is one drop of
oil in the bearings.

If I'm going to start up a dynamotor that hasn't been run in a long
time, does this one drop of oil in the bearings sound sufficient? Is
there any other recommended maintenance to get this thing lubed
properly so I don't burn up the bearings when applying power? Also,
it's a 12 - 14v dynamotor. Is it recommended to start it on very low
voltage and increase it slowly to the recommended operating voltage?

Thanks for any help you guys can give me!

73,

Derek
WB0TUA

You might want to pull the end caps and take a look at the bearings
and brushes before firing it up. Put in a few drops and rotate it by hand.
Dynomotors are very reliable, and its probably in good condition.
Make sure you have a strong battery! The starting current is huge.

Steve W6SSP

Derek Cohn/WB0TUA wrote in message
om...
Dear Friends,

I just picked up a BC-314-G (MW version of BC-348). It came out of
the estate of a long deceased ham so I don't know how recently it was
used. I would like to begin the restoration process and will start
with the dynamotor. I have read TM11-850 N which covers this radio
and the only maintenance mentioned for the dynamotor is one drop of
oil in the bearings.

If I'm going to start up a dynamotor that hasn't been run in a long
time, does this one drop of oil in the bearings sound sufficient? Is
there any other recommended maintenance to get this thing lubed
properly so I don't burn up the bearings when applying power? Also,
it's a 12 - 14v dynamotor. Is it recommended to start it on very low
voltage and increase it slowly to the recommended operating voltage?

Thanks for any help you guys can give me!

73,

Derek
WB0TUA

First I'd make sure that I could turn the rotor by hand and then check the
conidtion of the brushes and commutator. If the old lube is dry you might
try adding a drop of good oil (turbine oil available at appliance stores)
and see if that frees it up. Next start it with no load and see how it
comes up to speed. If it's quiet and running smooth I'd apply the load.
Don't use too much oil, a drop or two is usually all you need.
regards
hank wd5jfr
"Derek Cohn/WB0TUA" wrote in message
om...
Dear Friends,

I just picked up a BC-314-G (MW version of BC-348). It came out of
the estate of a long deceased ham so I don't know how recently it was
used. I would like to begin the restoration process and will start
with the dynamotor. I have read TM11-850 N which covers this radio
and the only maintenance mentioned for the dynamotor is one drop of
oil in the bearings.

If I'm going to start up a dynamotor that hasn't been run in a long
time, does this one drop of oil in the bearings sound sufficient? Is
there any other recommended maintenance to get this thing lubed
properly so I don't burn up the bearings when applying power? Also,
it's a 12 - 14v dynamotor. Is it recommended to start it on very low
voltage and increase it slowly to the recommended operating voltage?

Thanks for any help you guys can give me!

73,

Derek
WB0TUA

....[snip]....
If I'm going to start up a dynamotor that hasn't been run in a long
time, does this one drop of oil in the bearings sound sufficient? Is
....[snip]....

I recently put a 30-year-old brand-new squirrel-cage fan into service
(I bought it in the early 1970's and never got around to installing it),
and it was pretty "stiff" until I dripped about 10 drops of light oil
into each of its two "oil here" holes. After that, it would start on
"high" but didn't want to start on "low"; another 10 drops in each hole
and it seems to be working fine now.

--Myron.
--
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
PhD EE (retired). "Barbershop" tenor. CDL(PTX). W0PBV. (785) 539-4448
NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol)

If your fan has "oilite" bearings, a porous sintered bronze material,
the bearings will only stay free for a short time after a reoiling.
This is because the pores in the oilite get clogged up with hardened
oil, and metal particles. This keeps the oilite from providing a
continuous (though tiny) amount of oil on the shaft. Oilite works just
like a wet sponge does. It leaves a smear of oil on everything it
touches.

One good way to rejuvenate oilite bearings is to remove them from
their housings, and wash them thoroughly in lacquer thinner. After
they dry, set them in a small puddle of light motor oil, and heat
to 150F (NOT OVER A FLAME!) a light bulb makes a good heat source.
When they cool, they will suck up a proper load of the oil, and will
be good to go for a long, long time.

One other thing to note, the shaft to bearing clearance must be small,
a few thou for a 1/4 inch shaft. If the clearance is too much, the
shaft will rattle about in the bearing and make lots of noise. Usually
on a worn out motor, with oilite bearings, the shaft will be what has
worn.

-Chuck, WA3UQV

wrote:
....[snip]....
If I'm going to start up a dynamotor that hasn't been run in a long
time, does this one drop of oil in the bearings sound sufficient? Is
....[snip]....


I recently put a 30-year-old brand-new squirrel-cage fan into service
(I bought it in the early 1970's and never got around to installing it),
and it was pretty "stiff" until I dripped about 10 drops of light oil
into each of its two "oil here" holes. After that, it would start on
"high" but didn't want to start on "low"; another 10 drops in each hole
and it seems to be working fine now.

--Myron.

"Steve" wrote in message
...

Make sure you have a strong battery! The starting current is huge.

Steve W6SSP

AH, the olden days! I used to have (still have a couple
laying around) a DM35 running my mobile Lettine 240.
It would dim the headlights at first keyup. I popped a few alternator
diodes, too, until I went with an extra battery and heavier alt. I wouldn't
want to trade those
days for the new, but it's fun to remember.

Some years ago, a ham buddy and I were scrounging around in his storage shed
and ran across a BD77 dynamoter unit--1000 volts @ 350 mils (I think)---.

"Hmmm, I wonder if it will start".

We carried it into the shop and hefted it up onto the workbench (sucker was
heavy!), and hooked it to a
surplus 150 amp supply. After all those years, we forgot
about the startup torque on one of these bad boys and touched the positive
terminal. The dynamotor proceeded to JUMP off the table causing us to go
into a dance of
the wayward dynomotors! We both were hopping around the floor frantically
trying to keep the thing off our
feet!! The torque was terrific-way more than the old DM35s I was used to.
We put the thing back in the shed and I think it is still there today!
Yeah, yeah, I know, we
should've anchored it down! LOL!

73

Jerry

Way back in the late '50s, when Hams still used dynamotors in their mobile 75m
rigs (also mil suprlus based), the story was that you shouldn't spin up a
dynamotor without a load on the B+ output -- otherwise the excessive voltage
would short out the windings.

I played with one from one of those made-for-Russia WWII sets, spun it up
several times with no load, and never saw a problem. Maybe the original lytic
cap across its output leaked enough to provide a good load :-)

BTW, re the guy who had the 1000 VDC unit jump off his workbench -- lucky he
didn't made a desperate grab at it, and catch it by the output terminals ...
Mike K.

PS: Once, my old-fashioned soldering iron (pluggied in and heated up) started
sliding off my bench. I grabbed it just in time to ... you know the rest.
Still hurts my hand to think about it.
Oscar loves trash, but hates Spam! Delete him to reply to me.

Mike Knudsen wrote:

PS: Once, my old-fashioned soldering iron (pluggied in and heated up) started
sliding off my bench. I grabbed it just in time to ... you know the rest.
Still hurts my hand to think about it.
Oscar loves trash, but hates Spam! Delete him to reply to me.

Like the guy over in alt.sysadmin.recovery who was doing some solder
work without benefit of clothing, and shook a blob off the iron.

Murphy's Law operated perfectly.

--
1 Bryant (B) = 4577 books; 1 Ha'bryant = 2289 books
1 Sitter (or Room) = 1104 books; 1 Dinky = 161 books
1 Wallshelf = 23 books; 1 Bedside = 17 books
-- Robert Uhl, in asr

knudsenmj posted:
PS: Once, my old-fashioned soldering iron (pluggied in and heated up) started
sliding off my bench. I grabbed it just in time to ... you know the rest.

Still hurts my hand to think about it.

I did that in the late 50s. Fortunately a knowledgable old-timer was on the
job with us and introduced me to the use of vinegar on burns. We had no
doctors available. Vinegar killed the pain and left no scars.

Don

"N2EY" wrote in message znip
snip
Not really - the Ancient Ones just threw the switch and let 'er whine!


Nah, we used to use a Ford starter solenoid back when they were made tough!
Try it now, and they will burn up!

I burned up two trying to get switching for a 700 watt mobile amp. Hadda go
for a heavy duty, extra cost one!

Jerry



73 de Jim, N2EY