Railpower 1300 testing

[peteski]

A correction on VA.... on a 60 VA system,  the product of volts and amps is NOT always 60, the definition of VA used by manufacturers is that there is at least ONE point where volts times amps equals 60.

You can make NO assumptions of the amps at any particular voltage...

Now, in reality, the one place you can be almost sure of the rating not being achieved is at max amps...

This rating has been used for a long time, and it's really kind of like using the diagonal measurement on a TV screen to make it seem bigger...

Greg

Volt-ampere (VA) is a power rating, usually of similar value to Watt-rating of a device.  For technical details see https://en.wikipedia.org/wiki/Volt-ampere
Quoting the above link: Volt-amperes are useful only in the context of alternating current (AC) circuits (sinusoidal voltages and currents of the same frequency).  So this is the maximum power consumed by the throttle's transformer on the 120V AC side.  Since there are some losses in the transformer, it will provide slightly less than what it consumes.  The rating on the DC output will be probably around 5 Watts total.  That will be at the maximum output voltage.

[Doug G.]

So is this a 1300 in disguise?

Accessories: 19 VAC
Track Power: 0-16 VDC
Total Power: 7VA
Model: SDK-789

Other than the 16 VDC, the specs look the same.  Also, they use triangular tamper proof screws.

There's no guarantee but it is almost for sure an MRC product and is probably very similar, if not identical, to the MRC 1300 with an overload circuit added to drive the overload LED.

Most of those inexpensive transistorized packs are very basic, like the original transistor packs of many years ago.

Doug.

[MK]

Thanks Doug.  I got it for $10 new at a train show a few years ago to test DC locos before I decoderize them.  Now I'll be extra careful and not run DCC stuff with it.  There's really no reason to since I have my Zephyr.

I did call up Athearn tech support about a month or two ago and they were very adamant about it having no pulse injection at all when I inquired.  I think I'll trust you guys more. 

[mmagliaro]

I haven't had time to draw up the schematic yet.  But I can tell you this, there is a transformer, 4 diodes, one resistor,
and one Darlington power transistor, plus the speed control pot.  That's it.  There's no filtering, no caps.

There is a Polyfuse in there for overload protection, so all you would have to add to get an "overload light" would be 1k ohm resistor and LED wired across that Polyfuse.  The LED would light any time the Polyfuse "opens".  And I know this because I've used that exact same trick myself 100 times for an overload light.  (Okay, not 100, maybe like, 12, but...)

I forgot I hadn't posted the 1300 scope pics.  Here they are:

[mmagliaro]

"Output 15DC" is very likely RMS, which means pulses (or spikes or whatever you might call peaks) will be higher.

Edit: I see Peteski already covered this. But it bears repeating, since electronic devices will be much more sensitive to the peaks of unfiltered DC than motors.

Typical. Traditional "power packs" were studies in minimalism in order to maximize profit.

It is.  Reading the full-throttle DC with a voltmeter shows about 14.5 on the 1300.  That's the average, not the peak.

[Doug G.]

Must be the Darlington causing the odd output waveform, huh. None of the other components would do that from a transformer sine wave output.

Doug

[metalworkertom]

Ok here is the other Tech II and Tech III comparison  tests , these were done with a 60 ma bulb as load as this is close to what Max used . First is the Tech II 2800 and 1440 these are producing the same wave forms. The 2800 is dual cab . Specs on the 2800 are 10.6 vdc variable  ,14.8 vac for cab 1, 10.6 dcv variable for Cab 2  both total va are 8.5. The 1440 specs are 14 vdc variable , and 13 vac total va 18 . Each photo is at 25% ,50 %, 75% and 100% throttle hopefully the photos will be in correct order.

[mmagliaro]

Must be the Darlington causing the odd output waveform, huh. None of the other components would do that from a transformer sine wave output.

Doug

I highly doubt this.  More likely it is the way they have the 4 rectifier diodes in the circuit.  I do not know if they are wired into a conventional full-wave bridge rectifier formation, and I bet they are not.  When I get a minute to trace the PC board and make up the schematic, we'll know for sure.  But I bet it's just the way the diodes are arranged.


Tom:
Those plots confuse me.  They all appear to be from the 2800.  Are you saying that the 1400's plots were the same? 
Okay.

Well, it looks to me like more of the same.  The peaks are nowhere near 25v.  So far, the 1300 is the only one anywhere near that high.

Are there any other models out there we should cover?  Anybody got a tech 7 they can scope?

[up1950s]

Maybe it's not so much what the 1300 has , but how it differs from the others . Is the 1300 so simplistic compared to all the others ?

[mmagliaro]

Maybe it's not so much what the 1300 has , but how it differs from the others . Is the 1300 so simplistic compared to all the others ?

Aren't those just two ways of saying the same thing? 
Yes, the 1300 is much simpler than the others.    But I don't think that matters.  A simple sine wave supply would work fine.
And two other models (1400 and 2800) have the same wave form.  The big difference is the peak amplitude of 25v.

[MK]

Max, did you get any pictures of the insides of the 1300?  If you did, can you post them?

[up1950s]

Aren't those just two ways of saying the same thing? 
Yes, the 1300 is much simpler than the others.    But I don't think that matters.  A simple sine wave supply would work fine.
And two other models (1400 and 2800) have the same wave form.  The big difference is the peak amplitude of 25v.

I understand that , and thank you for extending your wallet , time , and expertise proving that . The point I was trying to make is what is the missing circuitry or component that stops the 1400 and 2800 from going to 25 . Might it be the value of something , or some circuit that clips the peak voltage ? This sure must be great news to Jason , having an independent study bolster his statement . Well done Max , and thank you .

[peteski]

One thing that has not  been done was to scope out the low voltage AC output from the transformer (the accessory terminals will work for that). This will put to bed any notions that there is something missing in the DC circuit that makes the voltage higher.

I'm also confused by metalworkertom's post. So which throttle did he scope out?  He seems to vaguely mention few models.
I venture a guess that whatever model's photos of the internal circuit he posted, it will be similar or identical to the 1300 as the oddball waveforms on the track output seems ot be the same as in Max's 1300.  Scope out (or measure the AC accessory voltages) on both throttles! 

[mmagliaro]

One thing that has not  been done was to scope out the low voltage AC output from the transformer (the accessory terminals will work for that). This will put to bed any notions that there is something missing in the DC circuit that makes the voltage higher.

I'm also confused by metalworkertom's post. So which throttle did he scope out?  He seems to vaguely mention few models.
I venture a guess that whatever model's photos of the internal circuit he posted, it will be similar or identical to the 1300 as the oddball waveforms on the track output seems ot be the same as in Max's 1300.  Scope out (or measure the AC accessory voltages) on both throttles! 

I have scoped the 1300's transformer secondary, but not with a load on it...
The peaks are at 27v.  It reads on a conventional DVM as 19.5v AC, which would be the RMS value.

[metalworkertom]

Here are the Waveforms for the Tech III 9500.
Specs are 20 VDC variable 19VAC 20 VDC fixed.
Actual meter readings 21.14 VDC variable 19.61 VAC 22.03 DC fixed.
Tested at 25% 50% 75% 100%