Dual Power Pack for G Scale Model Railroad.

[gnm109]

Hello all,

About 15 years ago, I switched from an HO Gauge layout to a G Scale Layout. I built it indoors on the second floor of my barn. It has approximately 150 feet of track around the wall of a 20 X 24 room.

I needed a larger power supply than the two vintage 1 amp Troller units that I had been using since 1981 when I started the first HO layout. I wanted a dual pack and I decided that 5 amps would give ample capacity for even the longest trains.

Some research on the internet found a nice schematic. It’s shown here with a list of the components and their values:

http://www.aaroncake.net/circuits/supply.asp

I also decided to use two LM338K adjustable voltage regulators. They are inexpensive and will easily handle up to 5 amps and more at 1.2 to 32 VDC.

The 1.2 V caused my locomotives to start moving so I added two 5 ohm resistors to the output on each side to bring the voltage down to zero. They only get slightly warm when in use.

Some scrounging at the local surplus stores located the necessary parts, including the capacitors and 5 amp transformers. I wisely bought two extra transformers and I’m glad I did, since both stores are sadly now out of business.

I’ve been very pleased with my Dual 5 amp Power Pack since it’s been running. It hasn’t needed any repair since I built it. Operation is very smooth due to the very clean DC that it provides.

I would encourage anyone to try building one. Just be careful when handling the capacitors since the values are rather large. They are needed to smooth the DC output of the bridges and they work very well.

 

[garrymartin]

Well done, I tried and failed to build something similar however I am more than happy with the Helmsman set up I run now

 

[gnm109]

Well done, I tried and failed to build something similar however I am more than happy with the Helmsman set up I run now

Thank you for the kind words. While I am well aware of the elements and qualities of DCC and wireless systems in general, I find that analog DC suits my solo railroading style very well. Besides that, I enjoy hand building items. I am beginning to scratch build some of my own rolling stock. So far, I have built two flat cars and I've just begun a wooden box car to go with my ready-made rolling stock. I will post more when I've gone a bit farther.

Regards.

 

[Dtsteam]

Very interesting thanks. Its good to see that you've added meters - current draw in large scale does vary wildly and its a good early warning sign of trouble. I'm with you on the clean DC if circumstances permit.

 

[gnm109]

Very interesting thanks. Its good to see that you've added meters - current draw in large scale does vary wildly and its a good early warning sign of trouble. I'm with you on the clean DC if circumstances permit.

Hi,

The largest Locomotives on my layout are the USA Trains GP7/9's. They are built with dual motors. When underway, they use just under 2 amps at 8-10 volts. This is with 10-12 cars attached. The meters are important since you can detect short circuits immediately. I also sometimes use the track power to test various DC units and as you say the meters are very useful for that.

 

[Rhinochugger]

Yes, the usual point of dificulty with home built power unit/controllers is the overcurrent protection.

In my case, it was fractionally too slow, and used to upset one of the chips sending the controller into permanent top speed mode. It could be cured by unsoldering all the components and re-connecting them - so was ditched after the second time the thermal cut-out operated.

Jeff Helm of Helmsman says that he had to introduce a slight delay into his overcurrent protection circuits, to stop the controller being too jittery.

 

[gnm109]

Yes, the usual point of dificulty with home built power unit/controllers is the overcurrent protection.

In my case, it was fractionally too slow, and used to upset one of the chips sending the controller into permanent top speed mode. It could be cured by unsoldering all the components and re-connecting them - so was ditched after the second time the thermal cut-out operated.

Jeff Helm of Helmsman says that he had to introduce a slight delay into his overcurrent protection circuits, to stop the controller being too jittery.

Hello,

I've had no difficulty with overcurrent protection to this point. The transformers on each side (A and B) are quite large physically and are rated at 5 amps each. They are protected with simple 10 amp Buss fuses and I've yet to have one of them blow out. Typically, I will see no more than 2 amps with a train underway so overcurrent hasn't been a problem.

The key is to over build so that you have plenty of capacity. The LM338K voltage regulators should be mounted on heat sinks and there should be ventilation around them. The designer of the circuit mentioned that a fan would probably be in order. I decided to simply cut holes in the case and cover them with mesh to get some ventilation. That seems to have worked.

 

[Neil Robinson]

I think a concern isn't so much about protecting the power supply itself as protecting the load on the output.
For example a derailment could cause sufficient current to flow through a locos electronics to damage them yet the same current not be sufficient to overload any power supply components.

 

[gnm109]

I think a concern isn't so much about protecting the power supply itself as protecting the load on the output.
For example a derailment could cause sufficient current to flow through a locos electronics to damage them yet the same current not be sufficient to overload any power supply components.

Sure, it's possible. In use, the derailment would have to be such that the track was shorted across the rails. In such a case, I would always be present and would shut down the power immediately so that nothing would burn up.

To prevent damage, one could put a small fuse or other overload protection in the DC lines supplying power to the track. It has yet to happen, but as you say, it could.

 

[Mark]

Looks like a nice job! I work with an american manufacturer of G-scale power packs, and we make a similar unit:

Ours has a bit more power, but similar approach with meters for voltage and current for each track.