Author Topic: What's inside an MRC Railpower Tech II 2500  (Read 5555 times)

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mmagliaro

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What's inside an MRC Railpower Tech II 2500
« on: June 11, 2014, 02:13:10 AM »
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I always wondered, and I always suspected they were just a few simple components and a rheostat.
But no.  They actually are a full-on "transistor throttle", which I was happy to discover.

I was looking over the insides of one for a friend, and I have never been able to find photos of the guts of these
things on the web, so I thought I'd post them.

I was a little surprised to find no primary-side fuse in there.   If the main transformer starts to go, but doesn't fully short out
to blow your house breaker, it could start getting really hot and cause big trouble.  So on this one, I put in a fuse holder.
I also have to replace the thermal auto-resetting glass breaker.  It doesn't trip anymore, even on a dead short.

Otherwise, the pack works fine.







« Last Edit: July 02, 2017, 12:45:44 PM by mmagliaro »

peteski

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Re: What's inside an MRC Railpower Tech II 2500
« Reply #1 on: June 11, 2014, 03:39:00 AM »
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I gutted one of those years ago and used the shell for a TAT V throttle I build from an article in MR magazine.  So on the outside it looks like a regular throttle, but it really is a super-duper throttle.  Kind of like Chevy Vega with a 350 V8 motor.   :D
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LV LOU

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Re: What's inside an MRC Railpower Tech II 2500
« Reply #2 on: June 11, 2014, 09:39:30 AM »
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 I just stuffed all that,with all the functions,momentum,brake,ETC,minus the transformer,into a walkaround..

brokemoto

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Re: What's inside an MRC Railpower Tech II 2500
« Reply #3 on: June 11, 2014, 10:44:08 AM »
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All of the TECH II s have a transistorised throttle.  MRC advertised them that way when they introduced them.  I like this line and consider it a shame that MRC discontinued it.  The TECH III followed rapidly by the TECH IV line supposedly superseded these.  MR was unimpressed with the TECH III and outright panned the TECH IV.  I wonder if MRC ever addressed the concerns that MR expressed.

My favourite of this line is the 2400 with its ON-OFF pulse switch.  The 2800, the dual control pack, has a discreet pulse.  It is stronger than the pulse on the 2400 (with switch to ON, of course), but it is still discreet.  The 2500 has quite a strong pulse, compared to the other two.  It is my least favourite of the three.

Still, Thank you for the photographs and anbalysis.  Thank you for the 'heads up' on the factory breaker.  If that fails and a short develops, there could be big trouble.   

As always, your tutorials and illustrated essays are informative and useful.  I have benefitted from more than one 'heads up' contained therein.

Joetrain59

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Re: What's inside an MRC Railpower Tech II 2500
« Reply #4 on: June 11, 2014, 05:59:41 PM »
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Anyone have a link to the MR reviews of Tech IV packs? What's wrong with them?
 Thanks,
 Joe D

JMaurer1

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Re: What's inside an MRC Railpower Tech II 2500
« Reply #5 on: June 11, 2014, 06:27:23 PM »
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RMC did a review in April 2001, but I couldn't fine any reviews from MR
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mmagliaro

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Re: What's inside an MRC Railpower Tech II 2500
« Reply #6 on: June 14, 2014, 05:17:06 PM »
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Does anyone know definitively how many amps of current the 2500 can deliver before the overload starts tripping.
The rating is 16VA, which implies, at 12v, about 1.25 A.

In testing this thing out, I do note that it has a mighty heavy pulse at lower speeds.  I use 60 Hz sine pulses in my own
throttles, but the 2500's are too heavy for my taste.   The start-up and slow-speed running are excellent, but
it makes for lots of motor noise, and I bet, lots of motor heat if you run at those low speeds for extended periods.

peteski

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Re: What's inside an MRC Railpower Tech II 2500
« Reply #7 on: June 14, 2014, 07:18:39 PM »
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Does anyone know definitively how many amps of current the 2500 can deliver before the overload starts tripping.
The rating is 16VA, which implies, at 12v, about 1.25 A.


Are there any markings on the breaker?  You might be able to find its rating.
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mmagliaro

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Re: What's inside an MRC Railpower Tech II 2500
« Reply #8 on: June 14, 2014, 07:59:00 PM »
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Are there any markings on the breaker?  You might be able to find its rating.

Yeah.   SB601G1BK  I have been digging pretty hard.  I finally found out it is a Sylvania "bimetallic thermo protector"  (that's what they
called it).    I found a part selection guide here:
http://www.ultimheat.com/Museum/section1/1970%20Sylvania%2020111013.pdf

From what I can divine there, these things are designed to open based on heat AND current.  They do not really give
current ratings for these devices.  Now, I suspect that glass device is tucked in where it is so that it will get heated up
by the main power transistor down there, and will open if that transistor starts to overheat, regardless of
the current draw on the power pack.  I suppose that's a nice way to design it, but then again, it wasn't working, and I don't see any
broken mounting or glue that was supposed to hold the glass capsule against the transistor. 

I was surprised at how hard it was to actually track that down.   It needs to be replaced, because it no longer opens,
even on a dead short.  Something else I was shocked to discover.   I added a primary fuse.  On a dead short on the track terminals,
this thing blew a ONE AMP primary fuse (because the thermal protector never trips anymore).
Hmmmm 1 amp... 120v.... loosely speaking, that's 120 watts of power dissipated in the primary of that transformer.   
This means that without that bimetallic thingy working, that transformer could get reallyhot (remember, it didn't have a primary fuse in there before).
I put a 3A fuse in there, and then the primary fuse did not blow with the track terminals shorted.   

Question:
So... it was drawing less than 3A, but more than 1A.  Your house breaker will not trip, yet that transformer could become
dangerously hot, couldn't it?   Is there something I'm missing here?   

All the more reason I'm glad I added a primary fuse.

peteski

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Re: What's inside an MRC Railpower Tech II 2500
« Reply #9 on: June 15, 2014, 02:07:30 AM »
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Yeah.   SB601G1BK  I have been digging pretty hard.  I finally found out it is a Sylvania "bimetallic thermo protector"  (that's what they
called it).    I found a part selection guide here:
http://www.ultimheat.com/Museum/section1/1970%20Sylvania%2020111013.pdf

From what I can divine there, these things are designed to open based on heat AND current.  They do not really give
current ratings for these devices.  Now, I suspect that glass device is tucked in where it is so that it will get heated up
by the main power transistor down there, and will open if that transistor starts to overheat, regardless of
the current draw on the power pack.  I suppose that's a nice way to design it, but then again, it wasn't working, and I don't see any
broken mounting or glue that was supposed to hold the glass capsule against the transistor. 

I was surprised at how hard it was to actually track that down.   It needs to be replaced, because it no longer opens,
even on a dead short.  Something else I was shocked to discover.   I added a primary fuse.  On a dead short on the track terminals,
this thing blew a ONE AMP primary fuse (because the thermal protector never trips anymore).
Hmmmm 1 amp... 120v.... loosely speaking, that's 120 watts of power dissipated in the primary of that transformer.   
This means that without that bimetallic thingy working, that transformer could get reallyhot (remember, it didn't have a primary fuse in there before).
I put a 3A fuse in there, and then the primary fuse did not blow with the track terminals shorted.   

Question:
So... it was drawing less than 3A, but more than 1A.  Your house breaker will not trip, yet that transformer could become
dangerously hot, couldn't it?   Is there something I'm missing here?   

All the more reason I'm glad I added a primary fuse.

Interesting info about the circuit breaker.  But it is not just the ambient temperature which opens the breaker. Heavy current (which occurs during a short circuit) will also heat up the bimetallic strip and it should cause it to open.  Elevated ambient temperature will speed up this process.

As far as the 1 A fuse blowing on the primary side, did you use a fast-acting or slow-blow fuse?  Usually slow-blow fuses are used in transformer circuits.
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LV LOU

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Re: What's inside an MRC Railpower Tech II 2500
« Reply #10 on: June 15, 2014, 09:18:01 AM »
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 Max,I just took a 2800 Dual Power apart.One side was dead,I used what was left of the other side to make a tiny walkaround for a portable logging railroad I'm working on.I think I still have the circuit breaker,if I do,you can have it...
   I have several of these packs,though,and I always felt that they tripped way too easy.If I ran this 2800 with say,2 Arnold FA's,it would trip after about two minutes,the pack was barely warm,and they were only actually drawing maybe 1/2 amp.If I was changing that,I'd be looking for one from some old HO trainset pack..

mmagliaro

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Re: What's inside an MRC Railpower Tech II 2500
« Reply #11 on: June 15, 2014, 08:50:20 PM »
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Lou,
I think that could have a lot to do with where the glass capsule is placed.  If it is blowing far too easily, I would try positioning it away from  everything, so it is hanging in free air.


All:
I found one on eBay, although it is not the same rating.  It tended to open at around 1 AMP which is just a little too
low.   I did the "unrecommended" move of putting two of them in parallel.  It is usually not such a hot idea to put two
fuse devices in parallel, because they don't necessarily act exactly the same, nor give you exactly double the current rating
(if that is your intention in paralleling them).   But in this case, with a fairly crude auto-resetting device, it seemed to really
do the trick.  They are soldered, so there is no issue with contact looseness or corrosion, and although they may not
exactly split the load 50/50, I'm sure it's darn close.   As they heat up, one will open before the other, but then all the load
is carried by the remaining one, so it opens in very short order after that (as in a fraction of a second).
In practice, on a dead short, they give no indication that there are even 2 devices in there.   You hear the "boing" of the metalic
strips, the red overload light comes on, and the output shuts off.   They will keep cooling, overloading and re-tripping as long
as the short is present, which is exactly how it acted with a single device.

The big difference is that it will run 6 engines without any annoying intermittent tripping (total of about 1.1 amp).
The intent isn't that they necessarily handle 6 engines.  I just wanted the thing to function around the 1 amp mark
without any nuisance tripping.

(I think if I owned this thing, I would get rid of that capsule thing entirely and just put a conventional manual-reset pushbutton breaker
on it.)

Peteski: I did use a fast-blow fuse.  But still, is that normal for the primary of the transformer to draw an amp or even 2 amps at 120v,
when the secondary is only supposed to have a capacity of about 1.5A at 12 volts?    Or...
is the issue that on a short, there's an instant where the magnetic field on the primary side goes near infinite, but immediately
settles back down.    Is that your rationale behind the slo-blo fuse?




alhoop

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Re: What's inside an MRC Railpower Tech II 2500
« Reply #12 on: June 15, 2014, 10:41:23 PM »
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" Is that your rationale behind the slo-blo fuse?"
Yep, that and inrush current. A transformer has all the component parts as
a motor, and like a motor , exhibits a inrush when energized.

Al
« Last Edit: June 15, 2014, 10:51:05 PM by alhoop »

mmagliaro

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Re: What's inside an MRC Railpower Tech II 2500
« Reply #13 on: June 15, 2014, 11:02:16 PM »
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" Is that your rationale behind the slo-blo fuse?"
Yep, that and inrush current. A transformer has all the component parts as
a motor, and like a motor , exhibits a inrush when energized.

Al

Well, inrush wasn't the issue here.  It didn't blow at turn-on.  It would blow when I shorted the secondary.
I still don't really understand what happens in the primary's electric field to cause this.
Perhaps one of you gents will enlighten me.   :)

What I see is that the secondary is designed to provide perhaps 1.5A at 16V.  Okay, let's say it is generously
rated heavier than that to avoid failures, so  2 x 1.5A x 16 = 48 watts.
On the primary side, at 120V, we have  48 watts = about 1/2 amp.  So how does it blow a 1A fuse?


peteski

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Re: What's inside an MRC Railpower Tech II 2500
« Reply #14 on: June 15, 2014, 11:39:32 PM »
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Well, inrush wasn't the issue here.  It didn't blow at turn-on.  It would blow when I shorted the secondary.
I still don't really understand what happens in the primary's electric field to cause this.
Perhaps one of you gents will enlighten me.   :)

What I see is that the secondary is designed to provide perhaps 1.5A at 16V.  Okay, let's say it is generously
rated heavier than that to avoid failures, so  2 x 1.5A x 16 = 48 watts.
On the primary side, at 120V, we have  48 watts = about 1/2 amp.  So how does it blow a 1A fuse?

I am not familiar with the details of transformer theory. There might be a current spike in the primary when the secondary gets shorted  (similar to inrush current).  But I don't know for sure.  Your power rating calculation is close. There is some power loss in the transformer, but that should not be double of the output rating.

Do you have a meter which could measure the short circuit AC current of the secondary?  I'm curious what the reading would be.

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