# Power Supply



## rbrunne1 (Sep 22, 2007)

While searching eBay, I came across a couple of sources for cheap, switching power supplies:

http://cgi.ebay.com/18V-10A-DC-Univ...emQQptZLH_DefaultDomain_0?hash=item414b594e80

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=390041496727&ssPageName=STRK:MEWAX:IT

I know everyone covets an adjustable power supply, but there are other methods to vary the voltage.

I'm interested in anyone's comments on the suitability of these power supplies for HO slot car applications.

Thanks,

Bob B.


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## AfxToo (Aug 29, 2003)

Those would work very well, although the shipping from China brings the price up a bit. You could conceivably put 4 of these is a case with switching, fusing, and safer packaging and power a 4 lane track with 10A dedicated power per lane for less than $150. Not bad.

Varying output voltage after the fact, at the rated output voltage and current levels, can be very expensive because you need big and expensive components to handle the current. I know some folks are using variacs or router speed controls on the input side and counting on the power supply to scale the output appropriately. I haven't tested any of these variable input side solutions with either linear or switching power supplies so I don't know what the outcome would be.


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## CRC74Z/28 (May 14, 2009)

*cheap adjustable power supply*

I have considered trying one of these power supplies on my track.

http://cgi.ebay.com/90W-UNIVERSAL-Power-Supply-AC-Adapter-For-Laptop-Cord_W0QQitemZ230398294179QQcmdZViewItemQQptZLaptop_Adapters_Chargers?hash=item35a4cef8a3

Anyone tried this or have comments on why it wouldn't work.

Thanks
Chris


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## rbrunne1 (Sep 22, 2007)

AfxToo-I was hoping you'd chime in 



AfxToo said:


> ...the shipping from China brings the price up a bit.


The supplies are $29.80 to $32.99 Delivered :freak:



AfxToo said:


> You could conceivably put 4 of these is a case with switching, fusing, and safer packaging and power a 4 lane track with 10A dedicated power per lane for less than $150. Not bad.


Do you think 10A per lane is necessary? 




AfxToo said:


> Varying output voltage after the fact, at the rated output voltage and current levels, can be very expensive because you need big and expensive components to handle the current.


Varying the output side on a per lane basis makes it a little easier. A 10-25W rheostat would work - or I like the look of Philippe's "Cheap and easy Adjustable Voltage" using a rotary switch and diodes (see link) 
http://homepage.mac.com/pmarchand/cheap_and_easy_adjustable.htm

Thanks,

Bob B.


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## rbrunne1 (Sep 22, 2007)

CRC74Z/28 said:


> I have considered trying one of these power supplies on my track.
> 
> http://cgi.ebay.com/90W-UNIVERSAL-Power-Supply-AC-Adapter-For-Laptop-Cord_W0QQitemZ230398294179QQcmdZViewItemQQptZLaptop_Adapters_Chargers?hash=item35a4cef8a3
> 
> ...


Chris,

I don't see any reason why it wouldn't work. It's a clear improvement over the standard power pack and it packs more punch than the AFX Tri-Power Pack :thumbsup:

The Tri-Power Pack is 8V, 12V & 22V at 1A.

The UNIVERSAL Power Supply is rated at 3.5 - 4.5A.

Bob B.


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## AfxToo (Aug 29, 2003)

Yeah, even with shipping they are very affordable.



> Do you think 10A per lane is necessary?


Not for normal people. I was simply pointing out that for the price of a typical 10A linear supply (like an MG series) you could have 10A per lane. That's stout by anyone's standards.



> A 10-25W rheostat would work


If you don't mind the risk of running the rheostat beyond its maximum current rating. With 4 cars running steady state at 500 mA @ 18V and you are already at close to 36W worst case and 2A ... but chances are you would never run it near worst case because you would probably not run at less than 8 or 9 volts going to the track and box stock unmodified cars only pull around 250 mA. You can pick up 25W rheostats fairly cheap:

http://www.surplussales.com/potentiometers/rheostats/PotsRheost-3.html

I like to design for worst case just to be sure. Once you get into rheostats that can handle an ampere of more, they get very large and very expensive. Using a series of forward biased rectifier diodes rated at the max current or better are a safer way to go if you can live with stepped rather than continuous variability. I think this is a sound and proven approach.

I think these supplies look very intriguing and I may buy some of them myself.


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## rbrunne1 (Sep 22, 2007)

AfxToo said:


> I like to design for worst case just to be sure.
> 
> I think these supplies look very intriguing and I may buy some of them myself.


Agreed :thumbsup: Thanks for your opinion!


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## shocker36 (Jul 5, 2008)

Ive actually taken a 400 watt cpu power supply and used a the two 12vs to make 24 and put in a 3 way switch and resistors to come up with 24,20,18v. This was just a test to see if it would work now I just need 3 more power supplies. I just wasnt sure what would be the best voltage to run I hear 18 for tjets and 20 for other cars.


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## rbrunne1 (Sep 22, 2007)

shocker36 said:


> Ive actually taken a 400 watt cpu power supply and used a the two 12vs to make 24 and put in a 3 way switch and resistors to come up with 24,20,18v. This was just a test to see if it would work now I just need 3 more power supplies. I just wasnt sure what would be the best voltage to run I hear 18 for tjets and 20 for other cars.


Using a CPU power supply is certainly a cost-effective way to go 
They're compact, light weight, built-in cooling fan, clean power, etc. I guess I'm intimidated by the work required to modify them for slot car applications. Please post some pictures, schematics and instructions on how you did it :thumbsup:

I've found the required voltage to be very track, controller & driver dependent. With my 4x8 layout the cars were difficult to control with the stock controllers and wall-warts. The controllers were essentially an on/off switch and on was too fast. I swapped out the wall-warts for a 13.8V, 15A switching power supply that I already had and the controllability and fun improved dramically. 

I feel that T-Jets need a little more voltage and this has me looking for a new power supply and ways to adjust it. High amperage (> 10A), variable voltage power supplies can be expensive (> $100), so I'm exploring less expensive ways of achieving the same result - plus, I would like to be able to vary the voltage by lane to adjust for each driver's ability.

Better controllers would help too 

Bob B.


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## AfxToo (Aug 29, 2003)

In my opinion, the top "game changing" equipment mods you can do for your slot car enjoyment are:

1) Having a dedicated and permanent slot car table 
2) Installing a highly reliable and fully featured race management system
3) Having a controller that can work with _every_ car you own
4) Adding a variable power supply
5) Having the essential specialty tools like wheel and gear pullers and pushers (beyond screw drivers, oiler, and pliers)


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## rbrunne1 (Sep 22, 2007)

AfxToo said:


> In my opinion, the top "game changing" equipment mods you can do for your slot car enjoyment are:
> 
> 1) Having a dedicated and permanent slot car table
> 2) Installing a highly reliable and fully featured race management system
> ...


AfxToo - I couldn't agree more :thumbsup:

I've completed 1 & 2 and I'm moving on to 3 & 4


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## shocker36 (Jul 5, 2008)

I didnt make mine variable in the fact from 0-24v just made it so I had the voltages I wanted I plan on making 3 more one for each lane.


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