toroidal transformer output - Page 1
Forum section: electronics / beginners

author: V_King
author_rank: Regular Contributor
timestamp: November 28, 2013, 08:46:25 pm
content: Hello,I need an isolated and unregulated power supply for my stepper driver, 50V and 5A.There are quite a few toroidal transformers onfarnellAll of the transformers have double secondary coils and I wonder if I could just buy a toroidal transformer with 2X25V 5A output and connect the secondary coils in series, to have required 50V with 5A as I only need one tap (to save space and money). On the other hand, can I connect the secondary coils in parallel and have double the current.Or am I talking complete bollocks and need to go to the corner?Thanks.

author: Unknown
author_rank: Unknown
timestamp: November 28, 2013, 08:56:49 pm
content: Yes, if they have two separate output winding (as opposed to a single center-tapped winding which is usually indicated as 25-0-25), connecting in series or in parallel is both fine. Make sure to observe phase when connecting them in parallel.Another thing you may not be aware of is that DC voltage after full wave rectification / smoothing is a little under 1.4 times the AC RMS voltage (so rectifying 50 Vrms AC would give you about 70 VDC). Since there's no such thing as free lunch (aka conservation of energy), the maximum DC current that you can draw goes down by a little more than a factor 1.4 (because the caps don't draw a steady current), DCI = 0.6 * ACI is an approximate rule of thumb. All this is irrelevant if you're directly using AC.

author: peter.mitchell
author_rank: Super Contributor
timestamp: November 28, 2013, 09:24:19 pm
content: Is it required to be unregulated, or is that just a product of it being cheap? since transformers are labour intensive and have a lot raw materials, they haven't really come down much in price, for the equivalent price of the toroidal transformer im sure you could get a very nice, regulated, isolated SMPS.

author: V_King
author_rank: Regular Contributor
timestamp: November 28, 2013, 09:50:58 pm
content: thanks for answers.I am using industrial stepper driver made by kollmorgen.The manual says, it needs: 20 - 75 VDC recommended design center isolated unregulated type (or regulated + bus cap)I have very little experience with power supplies in the market, just general knowledge from uni.With toroidal transformer I can have a power supply for around £50. All the switch mode power supplies are almost £100 for the same power output.If you could recommend something better, with less tinkering and familiar price, I will be happy

author: mariush
author_rank: Super Contributor
timestamp: November 28, 2013, 10:01:36 pm
content: You can get 24v power supplies from eBay starting with 10-15$ :http://www.ebay.com/itm/Mean-Well-MW-AC-DC24V-50-100-350-400-600-1000W-1500W-Switching-Power-Supply-PSU-/370889628513?pt=LH_DefaultDomain_0&var=&hash=item565abe9b6124v 2.2a - 22.5$24v 4.5a - 28$24v 6.5a - 32$[..]24v 14.6a 49$These also have a voltage adjust pot allowing you to set them to 24v +/- 1-2vAnd these MeanWell power supplies are all over eBay just enter "meanwell 24v" and you find a ton of them. They output isolated 24v, they do the wattage but they're inefficient compared to regular pc power supplies (they have about 65-70% efficiency)There's also 48v power supplies from same company, 48v is a common voltage :http://www.ebay.com/sch/i.html?_odkw=meanwell+24v&_sop=15&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR2.TRC1.A0.Xmeanwell+48v&_nkw=meanwell+48v&_sacat=0

author: Psi
author_rank: Super Contributor
timestamp: November 28, 2013, 10:02:22 pm
content: Quote from: alm on November 28, 2013, 08:56:49 pmHe can use a center tapped 5A 25-0-25V to get his 5A 50V output, use each side and ignore the middle tap.

author: wraper
author_rank: Unknown
timestamp: November 28, 2013, 10:24:21 pm
content: Quote from: V_King on November 28, 2013, 09:50:58 pmMean Well NES-350-48 48V 7.3A $50 with free shipping

author: Unknown
author_rank: Unknown
timestamp: November 28, 2013, 10:44:49 pm
content: Quote from: Psi on November 28, 2013, 10:02:22 pmParallel gets tricky (hot), though.I agree that SMPS is probably the best (cheapest, lightest, most efficient) solution.

author: Psi
author_rank: Super Contributor
timestamp: November 29, 2013, 02:23:46 am
content: No paralleling required, it's just using a center tapped transformer as if it doesn't have the center tap.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: November 29, 2013, 02:28:53 am
content: What's the application exactly? If it's industrial(ish) than light, efficient and to a lesser extent price is not as important. Personally I much prefer a transformer supply in that application since it's robust and handles overcurrent gracefully. And the stepper won't care if there's a little ripple on the input. Also voltage=speed in stepper applications since it allows you to accelerate quicker.Otherwise, I can see the SMPS argument, as long as it doesn't trip out.

author: V_King
author_rank: Regular Contributor
timestamp: November 29, 2013, 10:01:26 am
content: thanks for the suggestions. Will consider chinese power supplies for the future, unfortunately now I need the power supply next week.Paul, the power supply is needed for lab tests, and all the power supplies we've got here are 30V maxrobustness and simplicity are two most important aspects - tests not always go as planned

author: David_AVD
author_rank: Super Contributor
timestamp: November 29, 2013, 08:58:39 pm
content: A lot of those cheap Chinese (clones of Mean Well) are pretty crappy. Lots of EMI and poor reliability.