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 Post subject: Re: Battery Radio Power Supply
PostPosted: Nov Sat 16, 2019 6:29 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2044
Location: Weimar, Texas
JnTX wrote:
Mike,

These are the results of my simulation. I assumed a temperature rise of 25C in the transformer so the windings would be at 50C. That much temperature rise would make the winding resistances increase by about 10%.

Voltage on C1: 4.5VDC
Voltage on C2: 119VDC
Voltage on C4: 90VDC (Assumed to be clamped by the string of zener diodes)
R1: 1.8K, 1 watt
Zener current: 4mA to 16mA depending on the radio load

Primary 1 current: 44mA RMS
Transformer load: 5.3VA

You can check your results against my simulation when you get your supply going.

The main concern with the above is the primary 1 current. The transformer is designed for a current of 25mA for each primary winding. The temperature rise in primary 1 will be more than 3 times the design point.

Jay


Thanks Jay, I didn't mean to disappear. Work took over my life for a little bit. It'll be Thanksgiving week (maybe after) before I can try the radio out but I'll check the readings and report back

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Mike


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 Post subject: Re: Battery Radio Power Supply
PostPosted: Nov Sat 16, 2019 6:33 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2044
Location: Weimar, Texas
Marcc wrote:
If you are designing for a specific radio, using salvaged transformers. One PSU I made for three UX201A's used fixed regulators 7805 for filament and 7905 for bias on separate windings. HV was a reversed 240V primary transformer and used two LR8's. One for HV and one for 45V 7805 cooled using a small CPU heatsink fan blowing onto its heatsink but also venting the entire housing. Totally uncomplicated.

Marc


If this was my radio I'd be doing this differently. The irony of this post is that I think I'm going to fab a board for ten 9V batteries in series and stuff them in one the vintage looking battery box. Same with the filament voltage. Both fused of course. I may still give them the AC option but I'll need to know that it's not going to erupt in flames :shock: :D

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It's hard to solve an equation if every term is an unknown.

73
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Mike


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 Post subject: Re: Battery Radio Power Supply
PostPosted: Nov Sat 16, 2019 6:44 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2044
Location: Weimar, Texas
infzqi wrote:
...
New calculations, accounting for winding resistance, using Schade's full wave center tap graph that I believe to be appropriate also for the full wave bridge [1].
Designing for 16 mA shunt zener regulator current at no load on 90 volt output. 12 mA maximum load on the 90 V output.
The results are very similar to JnTX's Microcap simulation result. I'm sure that either method is close enough.
It would be interesting to learn the actual measured voltage across C2 with the radio load on the supply.

Results:
Dc voltage across C2: 131 volts (JnTX gives 119 V)
R1: 2.2 k 10% 2 watt. (JnTX gives 1.8 k 1 W)
Primary VA: 5.75 (192% of VA rating of 120 V winding of Tamura 3FD-410) (JnTX gives 5.3 VA).
120 V secondary VA: 3.4 (113 % of winding rating).
LM317 dissipation: 1.35 watts.

(For a new design a transformer such as a Triad FP10-1200 or a Signal DP-241-5-10 would be more suitable than the Tamura 3FD-410).

Method:
Dc voltage at C2:
120 vac secondary voltage x 1.4 = 170 V ac peak volts.
Rs = secondary resistance + reflected primary resistance. Using hot resistances given by JnTX, = 333 + 396 = 729 ohms Rs.
(reflected primary resistance = 396 ohms because primary to secondary ratio is assumed to be 1.0).
Using JnTX's figure of 16 mA as nominal current to be supplied.
Estimate of Rl at C2: 140 V / 16 mA = 8700 ohms.
Ripple angular frequency x C2 x Rl = 308
Estimate Rs / Rl = 729 / 8700 = 0.084
Estimate Edc / Eac peak = 0.78 (prone to variation in reading of graph)
Estimate C2 voltage = 0.78 x 170 V = 132.6 V across C2.
Revised Rl = 132.6 V / 16 mA = 8287 ohms.
Revised Rs / Rl = 729 / 8287 = 0.088
Revised Edc / Eac peak = 0.77
Revised C2 voltage = 170 x 0.77 = 131 V (12 volts higher than 119 V Microcap simulation figure)

R1 resistance:
131 V - 90 V = 41 V across R1.
41 V / 16 mA = 2562 ohms = R1.
Subtracting 10% from the 2.562 k R1 resistance in order to permit 16 mA at maximum R1 resistance gives 2.306 k. 2.2 k 10% is commonly available. 2.2 k - 10% = 1980 ohms. 41 V / 1980 = 21 mA. 21 mA squared x 1980 = 0.87 watt dissipated by R1.

120 volt secondary VA:
131 V x 21 mA = 2.75 watts dc power.
2.75 W / 0.81 transformer utilization factor for full wave bridge rectification [2] = 3.4 VA
3.4 VA / 3 VA = 113 % of winding rating.

5 volt secondary VA:
5 x 1.4 = 7 V dc
As wired, the 5 V secondaries are parallel, rated at 1.2 amps total. The assumption is made here that the resistance is small enough to be disregarded in this application.
250 mA filament current + 20 mA LED current = 270 mA
7 V x 270 mA = 1.9 watts.
1.9 W / 0.81 TUF = 2.35 VA

120 volt primary VA:
3.4 VA + 2.35 VA = 5.75 VA
5.75 VA / 3 VA = 192 % of winding rating.
5.75 VA / 120 V ac = 48 mA (very close to JnTX's figure)

LM317 dissipation:
7 V dc - 1.5 V dc = 5.5 V drop across LM317
5.5 V x 0.25 A = 1.35 watts.

[1] Landee, Davis, Albrecht, Electronic Designers' Handbook, 1957, pp. 15-10 to 15-18
[2] R. Visintini, "Rectifiers", Power Converters for Particle Accelerators, CERN course book, 2004, p. 141

Hopefully no significant errors.
-------------
WB5HDF


I'll take a look at these posts again when I have access to Excel (or equivalent) and make a "data sheet" to fill out and document what the PSU does with the actual radio I restored. When I get home I have to remake two pulleys and a shaft for the pulleys on the lathe. I guess I don't have to, I want to. What I made will work but I know where the flaws are and it's bugging me.

Here's my first attempt at making anything on a lathe (pulleys for the dial chord. The originals are wood and one is broken):

Image

Image

This is how I set the groove depth every time. I made both pulleys at once then parted them off individually

Image

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


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 Post subject: Re: Battery Radio Power Supply
PostPosted: Nov Sat 16, 2019 7:57 pm 
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Joined: Nov Tue 14, 2017 5:09 am
Posts: 2013
Location: Austin, Texas
Nice work.

I think the first work I did on a lathe was to turn down the tuning capacitor drive pulleys for a Crosley TRF. They were pot metal and still looked good but had grown a bit. I was having a hard time getting them down to size and finally realized that the pot metal was expanding almost as fast as I could cut it. I made some new pulleys out of brass.

Jay


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 Post subject: Re: Battery Radio Power Supply
PostPosted: Nov Sun 17, 2019 2:11 am 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2044
Location: Weimar, Texas
JnTX wrote:
Nice work.

I think the first work I did on a lathe was to turn down the tuning capacitor drive pulleys for a Crosley TRF. They were pot metal and still looked good but had grown a bit. I was having a hard time getting them down to size and finally realized that the pot metal was expanding almost as fast as I could cut it. I made some new pulleys out of brass.

Jay


Thank you. I really enjoy using the lathe. I'm going to recut the spindle. The spindle is fine but I used 3/16" hex stock and I should have used 1/4". It's a simple piece (that's the makings of famous last words right there)

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


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 Post subject: Re: Battery Radio Power Supply
PostPosted: Nov Wed 27, 2019 12:37 am 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2044
Location: Weimar, Texas
My plans to do a detailed test have unraveled a bit but I have some data:

Primary: 122 VAC
Current: I'm using a Sencore Powerite for AC power. The meter range setting is 0-1.5A. The meter worked the last time I used it and it's sitting on 0. I'll slip an AC meter inline for current in a bit.

DC: 82.15V @ 12.2mA

Voltage is much higher than 82 when the load is off so I raise the AC until I get close to the 100V max DC input of the load, then as I increase the load the voltage drops and current rises (it's some kind of magic, or physics :) ). It's been settled out at 82VDC and change @ 12.32 mA.

Temperatures after about 30m are:

Ambient: 79°
Transformer: 101°
Current limiting resistor: 106°

I'll let it run for an hour or more and see what it's doing.

Image

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


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 Post subject: Re: Battery Radio Power Supply
PostPosted: Nov Wed 27, 2019 2:49 am 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2044
Location: Weimar, Texas
Everything is still hanging around the temps that I posted an hour ago. I checked the voltage drop across the 4.7k resistor and got 54VDC (137 - 83). I didn't verify the value for the resistor and used 4700Ω to get .0115A or 11.5mA.

One thing I can't do is vary the load. The Dynaload is rated at 100V / 10A and just a slight change to the fine setting drops the voltage significantly. The finest marking on the amp meter is 20mA.

edit...

:? Dang it... I didn't have a load on the filament side of the transformer so the test wasn't of much value. I'll have to tackle that another time.

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


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 Post subject: Re: Battery Radio Power Supply
PostPosted: Dec Sun 08, 2019 12:52 am 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2044
Location: Weimar, Texas
After more than a little frustration I decided to fix the power plug on the radio, connect the power supply to the radio (it's been recapped), and see what happens. It ran for about 30m before I took some shots with the Fluke TiS camera.

Those are here: LINK
Page 1 and 2 are of the power supply board
Page 3 and 4 are of the radio, specifically the cap that goes from the volume pot to the grid of the 1H5 (detector, avc, AF tube). The cap was only 81°F but it was hotter than it's surrounding.

All in all the board doesn't seem that hot. The VR for the filament voltage, with a heat sink, was about 147°F - 150°F and that was the hottest.
Plate voltage settled around 88V. Filament was adjusted to 1.5V

I checked all of the tubes on my Hickok and they passed with flying colors.

But the radio has an interesting problem. Initially, with the tuning lever at the bottom of it's travel I heard white noise, aka static. So far so good. I don't have the dial cord strung yet so I manually moved the tuning lever up and, in places, it started squealing. Like so:

https://youtu.be/BIJdgG5JKDE

Got any ideas?

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


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 Post subject: Re: Battery Radio Power Supply
PostPosted: Dec Sun 08, 2019 6:07 am 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2044
Location: Weimar, Texas
I shrunk the board down

Image

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


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