mot. 4 812 Netzgerat Powersupply EN

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Codex
Beiträge: 15
Registriert: 06 Jul 2017, 04:17

mot. 4 812 Netzgerat Powersupply EN

Beitrag von Codex » 10 Mai 2018, 14:22

Hi,

I just received an unused mot. 4 812 power supply, the 30173 1975. The ones sold in Australia have an Approval label stuck over the original bottom third of the top panel, see the picture attached.

In Australia, we typical have 240 V ac. At my house its typically above 245 V ac and sometimes 250 V ac. (There is a local power substation close to my building)

In the picture, you can see there are two Mot. 4 812s. One has been used a lot the other is like new.

With 244.6 V ac input I get the following output voltages.

Output of like new mot4. 812 with no load
10.58 V ac
-12.12 to +12.12 V dc

Output of often used mot4. 812 with no load
9.47 V ac
-10.53 to +10.53 V dc

With Elektronik-Bausstein Gleichrichter + RBII for a 120 mA ac load then there is about 25 mV drop on the 812 ac outputs.

I am a bit surprised that they have all most a 10% difference in ac output voltage.



Has anyone measured their output voltages in Germany?

Does anyone know if the Australian mot4 812 is the same as the Germany version of the mot4 812, do they have the same transformer coil winding ratio?

Are there any schematic diagrams or pictures of the inside of one of these?

Thanks
Michael
Dateianhänge
MOT4-812.png

Burkhard
Beiträge: 33
Registriert: 21 Okt 2015, 21:23
Wohnort: USA

Re: mot. 4 812 Netzgerat Powersupply EN

Beitrag von Burkhard » 12 Aug 2019, 16:08

It doesn't look like you ever got a reply, but I think I will "ping" the thread.

I'm in the USA with a 110 VAC input Trafo 811, but have a similar question. The nominal output voltage from the variable DC V output is supposed to be ≈ –6.8 → 0 → +6.8. I measure ≈ –10 → 0 → +10 V DC with a modern DVM. This was open circuit, but it only dropped a little (<1 V ) with motor load so it would seem to me to be too high to safely use with the classic "6V" Motors.

Likewise the side terminal (nominally 6.8 V AC) measures about 9.5 V AC RMS. With the load of a single incandescent bulb in a Leuchtstein, it drops to ≈9 V AC. I think this is still safe for the Gleichrichter (rectifier block) and the other Silberlinge which would be downstream of the Gleichrichter, but it bugs me that it AC output is so much higher than the specification.

I measured both the DC and AC outputs with another DVM and got the same results.

I'm not sure...
1. If this is a typical (normal) measurement that someone would expect when using a a modern DVM on one of these old Trafos?
or
2. Has something internal degraded over time which has caused both outputs to go so much higher than the spec? I realize that the Trafo's electrolytic capacitor used in smoothing the full wave rectified DC output probably isn't what it used to be, which would make the "DC" voltage a lot more "peaky" than it should be. And maybe (?) that would make the DVM read high. My instinct says a weak capacitor would cause the opposite effect (lower voltage, not higher), but maybe I am missing something. In any event. what about on the side (AC) output which should be 6.8 V AC, but measures more like 9.5 AC RMS? That doesn't employ (to my knowledge) a smoothing capacitor at all, and yet it seemingly reads high also.

Finally, I somehow obtained a Trafo 812 which I can't use as-is since it's 220V and we are 110V in the USA. Does anyone know if it is possible to open it up and move the input wires to different leg(s) and "convert" it to 110V input ?

Ahh, one more thing.... Is there a schematic available or any internal pictures for the 811/812/814?

thanks,
burkhard
Zuletzt geändert von Burkhard am 23 Aug 2019, 16:22, insgesamt 2-mal geändert.

vleeuwen
Beiträge: 1055
Registriert: 31 Okt 2010, 22:23

Re: mot. 4 812 Netzgerat Powersupply EN

Beitrag von vleeuwen » 12 Aug 2019, 17:26

You can try to open it and replace (modernize) the rectifier and capacitor.
I don't know I they were still using selenium rectifiers in these power supplies for toys in 1975.

I have several 814 but most of the time I am using modern power supplies.
The old motor also working in the 9V based fischertechnik system of today.
Only the old 6V lamps can give problems.

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uffi
Beiträge: 130
Registriert: 24 Jan 2014, 16:21
Wohnort: München
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Re: mot. 4 812 Netzgerat Powersupply EN

Beitrag von uffi » 13 Aug 2019, 18:18

The specification of these voltage values apply for the specified current load of 500mA. So, you should measure the voltages with a load of 500mA (=10 light bulbs in parallel).

juh
Beiträge: 299
Registriert: 23 Jan 2012, 13:48

Re: mot. 4 812 Netzgerat Powersupply EN

Beitrag von juh » 13 Aug 2019, 19:47

Well, the OP is probably long gone. Anyway, there are two low-res images of an opened 812 in this thread, not that I'd expect this to be of too much help.

Best
Jan
Meine fischertechnik Designs für den 3D-Druck: https://www.thingiverse.com/juh/designs

Burkhard
Beiträge: 33
Registriert: 21 Okt 2015, 21:23
Wohnort: USA

Re: mot. 4 812 Netzgerat Powersupply EN

Beitrag von Burkhard » 14 Aug 2019, 01:51

juh hat geschrieben:Well, the OP is probably long gone. Anyway, there are two low-res images of an opened 812 in this thread, not that I'd expect this to be of too much help.
Jan
It's better than nothing, although I am a bit confused on how to remove the Trafo's cover.
• In the old thread you referenced, it seems like the writer removed the rubber feet, drilled out the brass rivets they were hiding and then lifted the cover off.
• But in the fischerfriendsman picture, he drills a 2mm hole crossways on the side of the Trafo. Or maybe he drills one at each corner... not sure.

It seems to me that my output voltage is very high on both the AC and DC terminals (are some primary windings shorted and thus reducing the turns ratio?) AND there is a large AC ripple on the supposed DC output which suggests the inner smoothing capacitor isn't doing much smoothing. I'll try to get some pictures on an oscilloscope.

Thanks for any advice,
burkhard

juh
Beiträge: 299
Registriert: 23 Jan 2012, 13:48

Re: mot. 4 812 Netzgerat Powersupply EN

Beitrag von juh » 14 Aug 2019, 14:34

The thread pictures show an 812, the ffm pictures an 814. Maybe they use different mechanisms?

I once opened an 814 following the ffm method. IIRC, you drill one hole for each plug, 2mm refers to the depth not width, 2mm so that the screw will have enough grip to pull the plug out.
Meine fischertechnik Designs für den 3D-Druck: https://www.thingiverse.com/juh/designs

Burkhard
Beiträge: 33
Registriert: 21 Okt 2015, 21:23
Wohnort: USA

Re: mot. 4 812 Netzgerat Powersupply EN

Beitrag von Burkhard » 14 Aug 2019, 17:23

juh hat geschrieben:The thread pictures show an 812, the ffm pictures an 814. Maybe they use different mechanisms?

I once opened an 814 following the ffm method. IIRC, you drill one hole for each plug, 2mm refers to the depth not width, 2mm so that the screw will have enough grip to pull the plug out.
Oh, you are right... I think they are different! On the 811 (and I think the 812, but I would have to check the one I have) the sides of the case are smooth, without any openings or access plugs visible that can be drilled into in order to extract them. I only see rivets under the rubber feet (which need to be removed to see the rivets). Maybe I'll try drilling those out.

Here's a couple of oscilloscope images that show what is happening on the end (supposedly DC) output jacks of my 811. The AC side port is similarly high, but of course isn't rectified.
• In the first, there's no load. The output voltage seems too high and there is a LOT of AC ripple, +/– 5.9V on top of the DC component. I did attach a SIlberling Gleichrichter (rectifier block) which cleans up the ripple.
Trafo 811, max voltage on &quot;DC&quot; end port, no load
Trafo 811, max voltage on "DC" end port, no load
• In the second, I attached a classic era minimotor to the rectifier output. (not for very long, as I didn't want to damage the motor). You can see the motor load pulls down the voltage a couple of volts, but it's still pretty high, higher than seems OK to me for a classic vintage motor. Also, since the side (AC) port is similarly high, the Gleichrichter output without that motor load applied gets well over the 9.0 V +/– 20% (i.e. 10.8 V DC) specified in the design of the other SIlberlinge. And I don't want to smoke any of those!
Trafo 811, max voltage on &quot;DC&quot; end port, LOAD = classic minimotor
Trafo 811, max voltage on "DC" end port, LOAD = classic minimotor
My assumption is that there are two problems with the transformer:
1. The smoothing of the DC output is very poor, which I assume is because its internal 45-year old capacitor is no good. This should be easy to repair.
2. The output voltage is too high. I was guessing maybe some primary winding coils were shorted together, effectively reducing the turns ratio, but this is just a guess. I'm not sure if there could be any repair for this...

Thoughts? I know I should just use a modern power supply, but if I can fix the vintage stuff and learn a little in the process, that's much of the fun.

Thank you!

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