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Old 05-11-2004, 11:28 AM   #1
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switching vs. regulated power supplies

it's no secret that switching power supplies are, cheaper, lighter, and generally more efficient than their regulated counterparts.

well, i am wondering what the repercussions are when using this type of power supply on chargers, lathes, truers, motor run ins, etc. and, really, what the realistic chances are that we could see these repercussions.

it seems to me, that most of the aforementioned products specify a regulated dc source rather than leaving it open to any type. i would think the regulation to be most beneficial to chargers since they perform a sensitive operation.

what do we risk when using the more economical switching variety?

thanks in advance.

oh, and for anyone who cares, i found this page useful for a lightweight comparison between the two.

http://www.qsl.net/xq2fod/Electron/PS40/PS40.html
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Old 05-11-2004, 01:19 PM   #2
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Default Re: switching vs. regulated power supplies

Quote:
Originally posted by seaball
[B]it's no secret that switching power supplies are, cheaper, lighter, and generally more efficient than their regulated counterparts...........
A switching power supply also is regulated usually. Maybe you should talk about switching vs linear power supply. I donīt know of the USA but here a switching power supply is way more expensive than a linear one. Regarding lighter and more efficient youīre completely right but there are also some differences.

Main drawback I think is price. A switching power supply is way more complicated than a linear one so the switching unit is more expensive. But there are lowcost powersupplies like the ones used in computers (for private use) and the highend powersupplies as used for the industry. Lowcost units usually doesnīt have a very good efficiency, maybe bad filtering and reliability because of cheap electronic components and cheap design.
Other drawback is a switching power supply produces some electrical noise to the voltage output caused by the switching mode. For those guys without electronic knowledge, this electrical noise is something you could compare with dirty air at aerodynamics.

A more expensive power supply usually does have also a better filtering of that unwanted noise and also does performe better when input voltage is changing. This often happens at races.
A good designed switching powersupply should work as smooth as a linear one. So everybody should keep away from the ultracheap units. Iīm using the switching ones since about 10 years at least and never had a charger or anything damaged due to this. First I used the old Victor power supply and now switched to a Samlex.

As a general rule, power supplys used for radio base stations should be good enough for RC use also. Samlex is one of these brands.
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Old 05-11-2004, 01:27 PM   #3
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Also, Linear supplies are better suited for short burst high current applications... i.e. Motor Lathes, tyre truers, etc...

ALOT of switchmode powersupply's are NOT garunteed for use when driving electric motors.

Switchmodes are great for charging off though, I regularly hook into my friends 30amp supply... We have up to 6 chargers hanging off it each charging at 5 amps.
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Old 05-11-2004, 01:49 PM   #4
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ah, ok. i guess i had made the incorrect deduction that switching power supplies were inherently non-regulated. i see that is separate and independent of the type of output.

it seemed to me that when i was shopping for a "regulated dc" power supply, those that were termed as such were all linear. all the switching supplies neglected to have that adjective in their descriptions or titles.

cool, i think i'm squared away.

thanks again.
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Old 05-11-2004, 02:00 PM   #5
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Here in Denmark, Europe, switch mode power supplies also are a lot more expensive, than linear ones.

I've been using switch mode power supplies for charging for 4 years now, and I havent seen any problems by the concept. I will never use a linear PS for charging, simply because of weight and size.
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Old 05-11-2004, 02:18 PM   #6
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Quote:
Originally posted by Shadow_Rusty
Also, Linear supplies are better suited for short burst high current applications... i.e. Motor Lathes, tyre truers, etc...

ALOT of switchmode powersupply's are NOT garunteed for use when driving electric motors.

Switchmodes are great for charging off though, I regularly hook into my friends 30amp supply... We have up to 6 chargers hanging off it each charging at 5 amps.
Maybe driving electric motors seperates the good from the bad power supplys. But I donīt know why a switching one shouldnīt be suited for that use. A good designed unit does have fail safe functions like current limiting so this shouldnīt be a problem.

In reality Iīm using 5V switching PS for my lathe and an adjustable 3-5V PS for running in my motors. Didnīt have any problems even with motors using laydown brushes.
And be shure Iīm not the only one doing this.

But I talk about Mean Well or Melcher (Power-One) PS, not any cheap crap. You easily could get these industry units at Ebay for a good price.

But most guys arenīt running their motors directly at the PS. Most are using something like an Orion Motor Checker or similar or a motor run in function from their LRP or CE chargers for this. So if a charger can handle this inductive load why not a PS?

Beside this the Orion Motor checker and the LRP charger are switching DC/DC converters. Not too much different from switching PS.
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Old 05-12-2004, 05:11 AM   #7
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These guys in Germany make very good power suplies, switched and linear.
http://www.maas-elektronik.com/
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Old 05-12-2004, 07:47 AM   #8
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I use a 25 amp switching unit, I think it cost $90 US. A similiar non-switching unit was $150+. The switching unit is much more compact and lighter. I regularly drive 2 chargers, a motor checker, tire warmers, and discharger off of it with no issues. I'm guessing I'm pulling 22-23 amps when running motors and charging at the same time. The unit barely gets warm.

Honestly, if you're in the market for a new supply, I don't know why you wouldn't buy a switching unit. In the US they are significantly cheaper than the non-switching units.
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Old 05-12-2004, 06:12 PM   #9
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So a computer power supply would work? How many watts would you need?
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Old 05-13-2004, 02:19 AM   #10
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I'm doing fine with an old PC PS @ 200 W. I only use it for charging.
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Old 05-13-2004, 03:43 AM   #11
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Computer power supply conversion
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Old 05-13-2004, 09:12 AM   #12
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I donīt like those computer power supplies. About all of them do have a bad efficiency and this even decrease more as you have to put a high load at the +5V bus.
Also voltage output isnīt very clean. What I found with very much of the PC PS you wonīt get anything above 12V output, most of them even stay at 11V only or below. This is even with a high load at 5V. So not very much.
Another point is these PC PS arenīt that reliable as industrial switching PS. Look at the electronic used. About all of them use very little heatsinks for keeping the price low and if the inside fan stops working your risking your charger.

All in all itīs a cheap solution but also cheap quality and performance wise. I really wonīt use any expensive charger with those PS.
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Old 05-13-2004, 01:39 PM   #13
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I wont disagree with V12 on most of this, but since I'm on a tight budget

However, it not always a good idea to have higher than 12 V - because then the charger have to burn a higher effect into heat.

Example: 15 volt in, 9 volt over the batteries. 6 amps charge rate. Then there goes 9V*6A=54 watts into the battery. But there's also 15V-9V=6V over the charger. Multiply by 6A, and the charger have to burn 36 nice watts into heat. Where's the efficiency?

With 11,5V input, the charger only have to burn 11,5V-9V=2,5V*6A=15W.... Less stress on the charger AND in several cases, the option of charging few cells with higher amps.

Now, with only 11,5 volt input, it might be a problem to charge 8 cells packs. But some chargers, like LRP and CDC, have a step up unit built in, so in this cases, it's not a problem.

For my part, I started using the PC PS as a temporary solution. But it works good, so now I have used it for almost 2 years. When I at some point get an extra charger, I will upgrade to a better powersupply. But I wont one with adjustable voltage output.
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Old 05-14-2004, 04:12 PM   #14
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Cole Trickle

youīre right you donīt need an input voltage of 15V, this is too much. But 10,5 to 11.5V is what you will get from some PC PS and this doesnīt work with lot of chargers.
Every charger needs some voltage difference between input and battery voltage otherwise there is no correct charge. But as there are big differences in chargers construction there are also differences in this voltage difference. Same chargers as the Protrak are working OK even below 10V but some other including Robitronic and some Novak need a very high difference for working.

Beside this your math regarding battery voltage isnīt completely correct. A battery at end of charge will have usually more than 9V. If itīs a little older the voltage will be higher. Also battery voltage will be higher with higher charge current. This will result in up to 10,5V battery voltage. Also you donīt have to care too much about any voltage reading at the chargers display. This isnīt very true so you will have to use an external voltmeter for correct results.
The ideal input voltage is between 12 and 13V usually in most cases. But you īre right any voltage above the needed one will result in more heat at the chargers heatsink.

Regarding output voltage regulation every PS have one at least inside for factory setting. Usually Iīm adjusting this for the output voltage I prefer.

If the PC PS is working for you then itīs fine but it isnīt the ideal solution. I think itīs a risk using one if you didnīt choose one with a good design. But very few people here will know to much in this area. So you canīt recommand it to everyone.
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Old 05-14-2004, 07:44 PM   #15
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props for the good discussion. i got my answer, but i do enjoy the reading. good work.
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