# Your ultimate booster requirements



## rreiffer (Jan 14, 2009)

All,

This post was suggested by another members reply to one of my posts. So here I the question: if you could design your ultimate booster what specifications would you want in the booster?


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## Greg Elmassian (Jan 3, 2008)

15 or 20 amps, capable of 25 volts, self regulated output, ac or dc input (regulation on input not regulated). 

Adjustable short circuit protection, both in amps, and duration of short. 

Fan cooled. 

Rugged with heat sinks. 

Greg


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## krs (Feb 29, 2008)

Posted By Greg Elmassian on 21 Jan 2012 09:12 AM 
15 or 20 amps, capable of 25 volts, self regulated output, ac or dc input (regulation on input not regulated). 

Adjustable short circuit protection, both in amps, and duration of short. 

Fan cooled. 

Rugged with heat sinks. 

Greg 


For me the booster would have to provide at least 20 amps, even 25 amps, since I can buy a 15 amp booster already.
Output DCC voltage adjustable to 26 volts so that I can assure 24 volts to the motor if need be
Happy with just DC input, no AC input requirement - that should simplify the design of the DCC output regulation, reduce the cost of the input circuitry which doesn't need to rectify and stabilize AC and also reduce the power dissipation you need to worry about.

Rugged, of course, heat sink as required, but preferably no fan for me.

But I would want an opto-coupled input or some design so one cannot possibly get groud loop issues or such.
Output needs to go into a safe, high impedance output mode if there is no input to the booster
Need the cut-out for Railcom
Feedback compatible with the most common Central Stations if there is a short and the booster shuts down.
And most important, a short circuit protection arrangement that is pretty much foolproof at any output current level.

Best bet to identify requirements is to look at the various designs floating around and see what capabilities they have included.
A DCC volt and ammeter vor instance would be nice and that would only add a few dollars to the cost. 


Knut


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## Greg Elmassian (Jan 3, 2008)

If you have regulation in the output stage of the unit, then ac or dc input does not matter. The only way I can conceive of DC being simpler to do is if you regulate the input, not the output, not a good idea, does not work as well. 

Since you have output protection, you are for sure monitoring the output current. 

I should have included "at a reasonable price" too.. 

By the way, running over 24 volts on the rails is asking for warranty issues and performance issues on the rails, that's why the spec is 24 to the rails, and the decoder handles 27v... 

Regards, Greg


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## krs (Feb 29, 2008)

Posted By Greg Elmassian on 21 Jan 2012 05:18 PM 
If you have regulation in the output stage of the unit, then ac or dc input does not matter. The only way I can conceive of DC being simpler to do is if you regulate the input, not the output, not a good idea, does not work as well. 

Since you have output protection, you are for sure monitoring the output current. 

I should have included "at a reasonable price" too.. 

By the way, running over 24 volts on the rails is asking for warranty issues and performance issues on the rails, that's why the spec is 24 to the rails, and the decoder handles 27v... 

Regards, Greg 
I don't agree with you Greg.

If one allows AC as the input power source, that means that one now not only has to rectify that power feed and filter it which isn't exactly cheap at these currents and takes a fair amount of space - ie larger cabinet, but one also has much more of a power dissipation problem than with regulated DC as the power source.

That's the basic reason why Zimo went for DC input only on their new Central Station design.

A transformer as a power feed for DCC boosters and central Stations was used years ago because it was an inexpensive option and one could easily handle different global line voltages by using different transformers but with the low cost switch-mode power supplies now-a-days I don't thnk that is the right option any more.


Take the US for instance where the power grid voltage is reasonably stable, but even so, the nominal line voltage varies by utility. I have seen anything between 115 and 120 volts, and then one should allow a 7% or better 10% variation.

So for a power design one needs to handle an input AC line voltage of about 103 to 123 volts or the equivalent output voltage range of a 24 volt transformer (20.6 to 26.4 volts) plus the voltage drop through the transformer at 20 or 25 amps. That creates a power dissipation issue that needs to be handled which you don't get to nearly the same degree as with a regulated DC power supply.


I don't see any benefit, just additional cost, when using AC power as the input.

As to the DCC output voltage.
The NMRA spec is 22 volts, so from a warranty perspective maybe that should be the limit, but I would still ,like to get 24 volts to the motor - so a compromise might be to allow an internal adjustment to raise the DCC voltage for those who are using the newer large Scale decoders that can handle higher voltages.
Actually - I'm not sure which warranty you are concerned about. The Zimo Large Scale decoders are rated at 30 volts DCC, ESU LokSound is rated at 40 volts DCC.

Regards,

Knut


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## Greg Elmassian (Jan 3, 2008)

rectification is cheap, a 25 amp fw bridge is a couple of bucks 
filter chokes and caps are cheap too. 

look inside an NCE some time... did you look at the choke on the Aristo filter? 

I cannot see the logic in your example about the variation in the ac line voltage, same variation in input power goes for DC. Maybe you can tell me how the example is any different. Yes of course if you supply it from a regulated DC supply, it will be simpler, but then the power supply is more expensive... so overall the system may be MORE expensive... a big AC transformer is fairly cheap. Thus the reason for AC input also. This lets people use existing supplies, another cost saver. 

I'm worried about the decoder warranty, many just meet the spec.... remember most of us here are in the US and US manufacturers tend to follow NMRA specs 

Regards, Greg


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## krs (Feb 29, 2008)

The "requirements" I posted is what I would want to personally see in a DCC booster - that was a first pass off the top of my head without looking at this further. 
I would definitely not entertain to use a 20 or 25 amp 24 volt transformer to power the unit 
I rather doubt people have transformers with that kind of current capability they could re-use since there are no DCC boosters or Central Stations that provide that amount of current. 
Bridgewerks was one company that made a supply with that current capacity but they don't offer that any longer and it sure wasn't cheap. 

If I were to develop a DCC booster for commercial sale then I would at least do a basic Marketing study to make sure the correct trade-off of capability vs cost is made. 
That would include a "total package" cost study as I think Greg is suggesting - DC switch-mode power supply and DC-only powered DCC booster and AC transformer with AC powered booster. 
I took a quick google search for a 24 volt, 20 or 25 amp transformer in a housing that was UL approved but only came up with over $200 units. 

As far as the DCC output voltage is concerened, the important thing is that it's adjustable. I would still want it to be adjustable to at least 26 volts, wouldn't go quite as high as the new Zimo Central Station/booster 

Knut


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## astrayelmgod (Jan 2, 2008)

"a big AC transformer is fairly cheap." 

I don't know where you are buying transformers, but I searched DigiKey for 115V in, 24V, 25A out, non-toroidal transformers, and all I see are Signal MPI series specifically the MPI-650-48, which start at $192 quantity one, occupy about 5 inches cubed, and weigh nearly 15 pounds.


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## Dan Pierce (Jan 2, 2008)

Hopefully the new Zimo system with 20 amp capability will start shipping next month. (You tie the 12 and 8 amp outputs together). 
Need to check the specs to see if this unit like the ones in the past can be used as a booster.


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## krs (Feb 29, 2008)

Posted By astrayelmgod on 21 Jan 2012 11:43 PM 
"a big AC transformer is fairly cheap." 

I don't know where you are buying transformers, but I searched DigiKey for 115V in, 24V, 25A out, non-toroidal transformers, and all I see are Signal MPI series specifically the MPI-650-48, which start at $192 quantity one, occupy about 5 inches cubed, and weigh nearly 15 pounds. 
If I went the transformer route I would try to get a toroidal one.
They are smaller, lighter, more efficient, provide better load regulation - pretty much better all around, they just cost a bit more.


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## krs (Feb 29, 2008)

Posted By Dan Pierce on 22 Jan 2012 07:16 AM 
Hopefully the new Zimo system with 20 amp capability will start shipping next month. (You tie the 12 and 8 amp outputs together). 


Was the capability to tie the two outputs together to provide 20 amps ever officially confirmed by Zimo?
I know one could do that on the old unit, tie the two 8 amp outputs together and get a 15 amp (not 16 amp!) output.

On the new design there was still a concern if it could provide both, the full 12 amps and 8 amps at the same time on two separate outputs - being able to tie them together would be the next step.


Knut


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## lownote (Jan 3, 2008)

I'm no expert, but I would not want more than 10 amps unless there was rock-solid protection against shorts. I'm about to start repairing a USAT loco that shorted without me knowing it, burning/melting the sideframe and one of the connectors.

20 amps and you start to get into the range of a welding rig. I can just imagine a flash, a nasty smell, and a pile of melted pastic


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## Dennis Cherry (Feb 16, 2008)

Posted By lownote on 22 Jan 2012 09:07 AM 
I'm no expert, but I would not want more than 10 amps unless there was rock-solid protection against shorts. I'm about to start repairing a USAT loco that shorted without me knowing it, burning/melting the sideframe and one of the connectors. 20 amps and you start to get into the range of a welding rig. I can just imagine a flash, a nasty smell, and a pile of melted pastic 


I agree on 10 amp boosters is all you need and do not see why 24 volts is always needed. Your motors are rated anywhere from 12-24 volts depending on the manufacturer or model. How many of you really run your trains at full voltage, you would all be traveling at bullet train speed on many models and not a realistic speed. Current draw is what you want, but not put all your eggs in one basket. So I like the 10 boosters and use more than one if needed. Less magics smoke release if something goes wrong. Lose one of your boosters and you can still run on limited number of trains, have only one booster that releases it magic smoke and you are down until repairs are made.


Power Supplies: only use switching type, analog supplies are iffy in design to maintain the regulated voltage and current needed for our varying demand.



It is your decision what best works for you. This is just my opinion.


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## krs (Feb 29, 2008)

Posted By lownote on 22 Jan 2012 09:07 AM 
I'm no expert, but I would not want more than 10 amps unless there was rock-solid protection against shorts. I'm about to start repairing a USAT loco that shorted without me knowing it, burning/melting the sideframe and one of the connectors. 20 amps and you start to get into the range of a welding rig. I can just imagine a flash, a nasty smell, and a pile of melted pastic 
It doesn't really matter that much if the booster is 10, 20 or 30 amps - none of the wiring inside our locos or cars is laid out to carry that kind of current.
One needs a booster (and central Station) design that can recognize a fault current and trips accordingly.
Pretty much none of the Central Stations or boosters actually do that, they all have a very primitive over current protection that only trips if the booster current exceeds the booster rating.

Maybe Greg can comment on his more since I'm not that familiar with the typical North American boosters like NCE or Digitrax.
Say you are running a small train that draws 1.5 amps using a 10 amp NCE booster (or Central station) as an example and you get a derailment that gives you a resistive short that draws 9 amps from the booster.

Would the NCE short circuit protection trip?
From what I have read so far, the answer is No even though the fault current is six times the operating current.

A high current booster design needs to trip if there is a fault current, not just if the maximum current level is exceeded.


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## krs (Feb 29, 2008)

Posted By Dennis Cherry on 22 Jan 2012 10:37 AM 
I agree on 10 amp boosters is all you need and do not see why 24 volts is always needed. Your motors are rated anywhere from 12-24 volts depending on the manufacturer or model. How many of you really run your trains at full voltage, you would all be traveling at bullet train speed on many models and not a realistic speed. Current draw is what you want, but not put all your eggs in one basket. So I like the 10 boosters and use more than one if needed. Less magics smoke release if something goes wrong. Lose one of your boosters and you can still run on limited number of trains, have only one booster that releases it magic smoke and you are down until repairs are made.


Power Supplies: only use switching type, analog supplies are iffy in design to maintain the regulated voltage and current needed for our varying demand.



It is your decision what best works for you. This is just my opinion.


I already commented on the current aspect above.

As far as the voltage is concerened - I'm not saying 24 volts is *always* needed but in sone cases which have been discussed here on MLS as well, one needs that voltage for proper operation of some locos.


One can always turn down the DCC voltage (if the booster design is such that the output voltage is adjustable) - and even if it's not, one can drop the voltage using diodes or some other means, but if the output voltage is only 20 volts maximum and one needs 22 or 24 volts, it's pretty much impossible to increase that DCC voltage at low cost. 

Not only that, with DCC one sets the maximum voltage applied to the motor on a case by case basis so nothing is going to run at bullet train speeds regardless of the DCC track voltage unless you want this to happen.

And if one uses multiple 10 amp boosters - they are connected to different power districts not connected with the outputs in parallel - so if one becomes defective, one looses a power district, ie a section of the layout is without power, it's not a reduction of power of the whole layout.
10 amps for Large Scale tends to be marginal, even 15 amps per booster is much better.

Knut


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## rreiffer (Jan 14, 2009)

All, 

Please remember, I really don't want what you think others should want, but what YOU want. Therefore if you want 24V, put it in, if you only want 18V max, put that in! Thanks


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## Bob in Kalamazoo (Apr 2, 2009)

Posted By rreiffer on 23 Jan 2012 10:26 AM 
All, 

Please remember, I really don't want what you think others should want, but what YOU want. Therefore if you want 24V, put it in, if you only want 18V max, put that in! Thanks 
Ok Rich,

In that case, I want 24 volts and 10 amps. But if I was buying a booster and 12 amps was available for just a few dollars more I would go for 12amps. Not because I think i need it, but just because a little more is always better.








Bob
When should I expect delievery?


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## Greg Elmassian (Jan 3, 2008)

my 2 cents: 

you can melt stuff just fine on 10 amps. 

Going to 20 does not appear to make it any more dangerous. 

I've melted stuff really well on 5 amps. 

What I need to do is get off my butt and put the polyfuses in to protect from "derailment shorts" besides the obvious one to the decoder. 

Regards, Greg


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## krs (Feb 29, 2008)

Rich - 

before you get carried away, take a look what is available commercially - up to 15 amps 

and what is available as a build-it-yourself booster like this one for instance 

http://www.merg.org.uk/merg_resources/dcc/download/cbus-dcc/simple-booster/NB1B_1.pdf 

Knut


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## rreiffer (Jan 14, 2009)

Thank you everyone for the great input. As a side note I do have a 24v transformer that is capable of 200A and yes,I can weld with it! (it came out of some OLD computer gear I used to work on.)


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