# linear power supply or switching power supply



## Ovalhead (Nov 20, 2010)

I'm in the process of updating the 1/64 - 4 lane - speedway's power supply with a 30v / 20a regulated / variable unit. I'm confused as to which one to get, some are saying go with the " switching " including the manufacturer ( they sale both ) but at the same time, some veterans of this hobby say " linear ". 

Can someone please explain to me what I am looking for ? 

Thanks in advance,
Cliff


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## Hornet (Dec 1, 2005)

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## Ovalhead (Nov 20, 2010)

Thanks for your advice and information Hornet, I need it.

Cliff


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## partspig (Mar 12, 2003)

One good reason to NOT USE a switching power supply to power HO slot cars is that they have higher AC ripple and are noisier than a regulated linear DC power supply. For those that just don't understand what ripple is, it is AC feedback, witch makes the DC power on them "dirty", Or DANG!, why the heck are my pickup shoes turning so black, so quickly!! JMHO


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## Hornet (Dec 1, 2005)

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## northwest slot (Dec 1, 2009)

I'd go with the linear power supply, much more quite.


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## AfxToo (Aug 29, 2003)

Practically speaking, either type of DC power supply can be used if you are using it as it was designed to be used. As Hornet said, slot cars are pretty low tech devices and if they were intolerant of low current capacity, noisy, unregulated, low quality power supplies then every car run on the power supply included in the race sets would be at risk. But most any set car runs quite well on most any set power supply.

If you want to improve on the race set power supply there is nowhere to go but up. How far up is up to you and your wallet. The characteristics you want in a DC power supply are high current capacity, low noise, voltage regulation over a wide range of current, ability to operate at very low current levels, short circuit protection, and convenient hook-ups. Some optional things you want may also want include adjustable voltage output, current limiting, voltage and current meters, efficiency, low weight, small size, affordability, and even programmability. 

If you shop around you can find, and you should be looking for, power supplies that are designed for benchtop or lab use. These are standalone power supplies that are intended to be used with a wide variety of devices with a wide variety of current requirements. You'll find both linear and switch mode power supplies that are designed for this application. 

In general linear power supplies are more expensive, larger, much heavier, much less efficient, and produce cleaner (less noise) and better regulated output than switch mode power supplies. However, if you use a switch mode power supply that is specifically designed for benchtop or lab use you'll find comparable specs on those units, but you'll find they demand comparable prices too.

The wild card is using switch mode power supplies that are purpose built for a specific application, like a PC or entertainment device, for slot car use. Unlike linear power supplies or benchtop power supplies in general, switch mode power supplies are often built for a specific device with a specific current load. Switch mode supplies often have a minimum current load requirement and if you don't put enough of a load on it the output will either lose regulation or be absent. Early PC switchers suffered from this and were unusable at near zero load. Fortunately most commodity switchers today have been designed to work with no load and low load conditions. Most slot cars don't place much of a load on a power supply, so running a slot car from a commodity switch mode power supply is like using the switch mode power supply in its least optimal, least regulated, lowest filtering efficiency part of its operating range. Linear power supplies tend to follow the opposite pattern, being optimized for operation from low load up to the upper limits where they start falling off. Switch mode supplies also fall off on the high end (of current demand) but they can also fall off on the low end unless they are designed not to.

The main drawbacks to linear power supplies are cost and weight. Figure about a pound per amp at the voltages we use. The weight alone adds to the total cost if you are paying to ship it. Linears are also very inefficient because they consume power regardless of load. The advantages are that the better benchtop units produce very clean output with very good regulation over a wide range of current loads. 

Are switch mode power supplies usable for slot cars? Absolutely. If you are looking at benchtop or lab equipment switchers then you should have no concerns at all. If you are repurposing a switcher from say a PC or laptop or commercial equipment, make sure it will work in very low current situations and does not require a dummy or ballast load. You can determine this by seeing if it has a minimum current requirement or simply by experimentation or evidence that someone else has tried it and it works. Most modern repurposed switchers should be fine and more than good enough even if they are not quite as clean as what you'll get from a linear supply.


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## partspig (Mar 12, 2003)

Thanks Afxtoo for the technical explanation. JMHO, bottom line is you are gonna get what you pay for, switching or linear. And no, my shoes do not turn black, as I use a linear power supply. It cost me 100 bucks for 14-21 volts at 10 amps. My power supplies are over ten years old and are still working OK.


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## Hornet (Dec 1, 2005)

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## Ovalhead (Nov 20, 2010)

tang tang 1628, alright guy's, I'm all ears, pencil and paper................ :woohoo:

Thanks for all this input !

Cliff


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## AfxToo (Aug 29, 2003)

> AFXToo,here's the link to some 45 dollar switching supplies,what's your opinion of these as a fairly cheap upgrade for the majority of guys.


No way to tell since there are no specs listed and the brand is a mystery. TDK-Lambda, which is a good quality brand, makes a switcher with the same rated output (DPP480241) and a full spec sheet and the retail price is $180-$200. The output ripple/noise is around 100 millivolts (one tenth of a volt) with 1% load regulation, and it weighs 4 pounds. It's also Class B EMI rated which means you can use it in an office/home environment. It's also DIN rail mountable which would make mounting it under a track table very easy. Many 24V supplies are only rated Class A EMI, which is for industrial environments.

A high quality linear supply from a domestic manufacturer (like Acopian and its 24PT20) can easily set you back at least 3X the cost for the same rated output versus a switcher. With the linear you are talking 1 millivolt (one one-thousandth volt) ripple/noise, 0.05% load regulation, and 38 pounds. If you are Bill Gates and want a killer 18VDC supply to conform to HOPRA standards the TDK-Lambda 18PH36 36 amp linear would be a great choice and lighten your wallet by a grand.

The infamous "Galinko" power supply, which is really an MG PS10, is somewhat popular with slotters. It is a linear supply in a benchtop form factor. But the specs will tell you that it isn't much better than a quality switcher at about the same price, but at $150 this comes as no big surprise. I have one and it's been reliable and I have no complaints. 

So is taking a $60 chance on a 24V 20A power supply shipped direct from China a good deal? Hard to say. You can get a name brand with warranty for $200 or look around for a budget linear supply. I'd want a peek at the spec sheet and at least some feedback from existing customers before taking the chance. It could be a good deal and save you enough to put a down payment on a RTR Fray TJet. Or it could be a brick.


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## cwbam (Feb 8, 2010)

Any details how to wire up?

http://cgi.ebay.com/ws/eBayISAPI.dll...=160461609153=
DC 24V 20A Switching Power Supply Transformer Regulated

What about lower voltage 12 volt 18 volt?

thank you


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## Hornet (Dec 1, 2005)

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## Hornet (Dec 1, 2005)

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## usdra (Jan 23, 2007)

The new supplies are far above & beyond what they once were. I run switching supplies on my drag strip with high powered full neo cars and have no issues at all. They produced less than a .3 (3 tenths of a volt) of A/C ripple. I have since added a capacoitor to each lane to increase amp storage for the high amp draw cars & now have virtually no ripple. http://home.comcast.net/~medanic/Tech-PS.htm This is a very good article that explains it all. 
This is what I use on my drag strip http://cgi.ebay.com/ETA-24-VDC-20-A...037?pt=LH_DefaultDomain_0&hash=item3366d462bd


Eric
www.mobydiditperformance.com


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