transformer psu questions

I have a pretty strong transformer and I'm wanting to know if it will work. Its not a very common transformer. On the primary side it has one 0v, one 120v, and one 220 and on the secondary side it goes in this order 24v-0v-12v-0v-12v. The info on it is. Brand: Top Mark E1HLWA11 (24v/11A) I'm trying to figure out how to hook it up for my printrbot. I can't find any info online and I have spent days on it, if not weeks. Do I need a bridge rectifier. If so can I make one out of diodes. Also I have a bunch of power caps but the largest ones I have are about 6600uF. I need to figure out voltage for the power caps as well as the amount of uF's I need combined. I know there is a calculation you can do but I'm disabled and I can't figure this out. I would really appreciate some help thanks.

I wasn't able to find any info on the model you note above, so I'm not *quite sure what the hookup would be, but it *should be pretty straightforward.

It appears to be for connection to a single phase 120/220 source. if you're in America, for instance, you could use either, in Europe, probably just the 220, since normal wall outlets are, afaik, 20 in Europe. If elsewhere, the local standard will apply.

The "0" input is a bit sketchier to me, since that *could mean ground or neutral, although I suspect it's the neutral. (A clear picture of the terminations would help immensely in correctly identifying its purpose)

The output you've noted indicates that it can be connected as a bipolar (+/- 12VAC) or unipolar (24VAC) supply, depending on which connections you employ

Yes, you need a rectifier to generate usable DC voltages. In fact, you need quite a bit more for anything beyond a rough shod supply, high in ripple voltage. Minimally, you'll need a (or two) capacitor(s) following the rectifier to smooth the output.

you can either create a discrete rectifier using individual rectifier diodes or an integrated circuit bridge. The diodes should be selected to pass at least as much current as the transformer will deliver.

Note that voltage losses from the rectifier will cause your output to droop below any presumption of (for instnace: 24VAC >> 24VDC) . The losses will depend on the diodes/rectifier used.

If this transformer's output is going to be used to power things like an arduino or other electronics elements, you'll want to employ suitable regulators beyond the initial rectification and filtering stages, to bring the power supply into compliance. Of course, there will be losses there too...

I'd also remind you that both the input and output sides of the transformer should be fused, to ensure safety, and the chassis should be properly grounded.

Sorry, I can't advise you on the specific values associated with any of the components in your homemade supply. But as you said, the info and equations are out there. Google it.

Thank you for your help. I used to be into all kinds of electronic stuff but I had a bad brain hemmorage. So I have little short term memory and its hard for me to figure things out that I used to find easy. None the less here I am trying as hardas I can with the limited budget and limited brain function. My Dr. Said it is good for me to try to do this stuff again so here I am. I will take a picture asap and give you as much info as I can into my setup. Any help you can give me is greatly appreciated. Thanks.

Here are some pics of the transformer and my setup I'm building. I'll try and take some of it apart if you need better pics.

Sorry to hear about your injury. To say "that sucks" is probably an understatement, but I hope you get my drift...

Hmm... It appears as if you already have things at least partially wired up, so I'm a little confused. First off, don't take it apart. You appear to have a functional power supply, or at least the basic makeup for one.

Have you used a voltmeter to see what the output connectors provide?

Not so sure what's hiding under the baseplate, but wiring from the transformer travels underneath, so it may be that you already have a rectifier and possibly regulators tucked underneath.

I'd suggest tracing the wiring (unplugged of course) to see if you can generate a basic schematic of what's already there. You may already be "ready to go".

Okay I'll spend a lil bit of time putting together a basic skematic for you and I'll post it online. Thanks for your help it really means a lot to me and getting back to electronics is getting back to the old me.

These are the colors of the wires I have and that came on the transformer. I don't have the 2nd fuse wired yet, or the 2nd plug in. I might have more fuses also if needed. I think the 2nd plug will be used to power that mini-power strip in the case. This mini power strip is powering USB power as well as power for the arduino etc. If it was you how would you set it up. I also don't have a rectifier or caps installed yet. Thanks.

fwiw, the input side fuse should be inline with the hot side, not the return. Otherwise, failure of the fuse does not remove power from the assembly, so a person sticking their hand in (or some other short circuit) will allow current to flow from the ac main into that "load", should it be connected to neutral through another path, intentional or otherwise...

120 (Hot) >> fuse.>> switch >> transformer ("120"), in that order.

Can I put a fuse between the hotside like you said as well as one on the return. I think I've seen it. I know My power caps need to be roughly double the voltage but about how much if should I use.

Thats a nice trafo, where did it came from, ups?

The 24vac would be peaks of 24*1.414-1.8(2 diodes drop) ~32.18 vdc. You should check if stepper driver ic and voltage regulators you use are ok with that (32-33v peaks). Should be about top limit for some at least, so heatsinking them might be required.

For caps depends what level of smoothness you want, but for 11a and 32vdc and 100hz imo try put at least 20.000uf. Maybe 30.000 if you want to go a little extra and have space for a little derating. Take a look at the rating of the diode bridge rectifier max instant current, if that is too low and the capacitance is too big, the instant current drawn at power up will burn the diode bridge, which i belieev is known as "blow up switch" - or smth like that. You can mitigate that if needed (ntc inrush limiter on main live), but probably at this level you wont need to. On the other hand if capacitance is too small, wont fill the space between the waveform peaks enough and the output will have a larger ripple. That shows up under a good load, but not just with ouputs left floating.

Fuse should be on the "live" wire, thats the one with the ac voltage on it. But after all, some cords can be plugged the other way in the mains socket, so it might end up on the other line in such a case. I am aware that 120v countries might have that 3 plugs wall socket, but for the 240vac ones with 2 and safety ground on clip wirings on the side, you can reverse the plug to have it either way, which changes the live side and the neutral. So fuse place isnt all that important generally speaking, it will interrupt the circuit in the primary winding of the transformer, regardless which side it is placed.

Edited 1 time(s). Last edit at 02/01/2013 03:18AM by NoobMan.

For caps bank i think i forgot its 60Hz supply in your case, hence x2 is 120 instead of 100. So for 100 math says 17000uF and for 120hz drops down to 14000uF(ripple3.21), but that seems kinda low to me, so i think better go with 20.000 (ripple2.29) or 30.000uF (ripple1.53). Hope i got my math right. If you go higher you might get the "blowup switch" problem.
Good luck!

REPRAP SQUAD, regarding selection of your primary filtering cap

read >>> this <<< link to get started back on the right path. Regardless of your injury, fact is, even most of us who've been working in the field professionally for decades still have to go back and reference materials. At least I do. I don't recall every detail of every method or principle I've ever learned. I recall much of it, but particulars can get fuzzy over time when we don't use them on a daily basis. There's only so much room in the noggin for info. :-)

I don't want to sound hard, but the only way you'e going to recover your skills is by using them. They're still there, it's just that some of the connections have been severed. Write the equations down. This will help rebuild the paths. If you have a calculator capable of storing equations, use it. This will help with not remembering as well, for the obvious reason that it at least stores it close by. If you don't have a calculator of the type I suggested, purchase one. Student level graphing calculators are dirt cheap, and they hold many equations.

As for the other issue, regarding fusing, please consult the NEC, as it's the fundamental governing document in the USA for design of safe circuitry. And it can be applied to any 120VAC country with at least a high degree of impunity. You can do whatever you want, since this isn't (afaik) a commercial device. If it is...

personal note: If a wall outlet swaps the hot and cold lines, then it is (at least in the USA), in direct violation of every electrical code I've encountered over the past several decades, so maintaining the standard method ensures that except in cases where someone has accidentally mis-wired the outlets or a self-aggrandizing, boorish nimwit has decided he knows more than professionals, you'll have created an instrument which is safe when standard, NEC approved wiring is in use, and should it end up in the hands of someone else, they won't be unpleasantly surprised.

EDIT: Regarding fuses on both the AC hot (Line) and return (Neutral), tell me this. Supposing that you used a fuse on both the line and the neutral, what would happen if the fuse on the neutral side blew and the line side didn't? Rhetorically speaking (since there is really only one right answer) Would the device be safe? Or would it remain a hazard?

Edited 1 time(s). Last edit at 02/01/2013 11:13AM by xiando.

So if my memories don't completely fail me this is basically the order in which I need to wire it. Also I think the reason why I can't find any info on this transformer is because it was made to custom order. I got it out of a really expensive concert light. I have some 8v and 10v dual secondary ones too.

Oh I forgot to label the three circles after the bridge rectifier are capacitors run in parallel.

There isnt other info that would be much usefull regarding transformer, coils voltages, wire thickness, and offers 250w in secondary. Schematic looks ok, it cant get much simpler than that.

If you make 5v out of those 32vdc peaks the linear regulator will have to burn out the difference, hence will both heat up a lot and have terribad efficiency. If you have some 8-10vac secondary thats great to use for lower voltages and fairly easy. But our electronic isnt typically taking separate lines for logic level so it would be a bit messy to implement in our case, and would have to hack the boards. In case you would need 9-12vdc you can add them later.

Ya I was looking through a bunch of my transformers, a bunch of them I believe to be custom made at the factory for commercial use and I found a huge 24 v with just a 115v. Two wires in primary and two wires in 2ndary. The other owe I found is 115v and on the 2ndary it has 8v and 10v both are pretty heavy duty. So I got to try and figure out which I will use for heat bed, extruded, motors etc. I have laptop and wall warts for the more fragile boards etc.

So you want to use a 2nd trafo for bed? Normally to switch the bed reprap uses a mosfet, but to do that you need to have same power source, e.g. same transformer even if they are from different windings. In case you have one transformer for reprap and steppers, and a 2nd separate transformer for bed, their grounds can well be at different levels, so you can only use a relay to switch the bed. Though the good news is if you use a relay then you can use AC instead dc, so you can use windings directly without anything on them. Probably best would be a SSR for ac, that is with zero crossing for minimal switching problems, so it will switch on and off only when wave passes trough zero, and would have to use bang bang instead of pid control, but thats quite ok, pid for bed isnt rly needed.

If it was you out of these 3 what would you use. Would you use one or a combination of them. Thanks.

Few indications about which one can deliver max power:
1) perhaps should start with this: the one who has most appropriate secondary rating, e.g. if one gives more than 24vac then its probably disqualified for this purpose (24vac is already dangerously close to the top) of what we can have. Also at the minimum, 8-10vac is just 10-12vdc, and if you want 12vdc then get an atx psu and save yourself the trouble, so that one gets disqualified.
2) the weight (kg) or size of the metal part: the E and I parts are to concentrate the flux, so the biggest one in first picture seems biggest in this sense so probably it can transfer most power in this way. Though its hard to say since should of have all 3 in same picture to be able to compare sizes correctly, it does seem like double the size of the 8-10vac one. This is rough approximation coz there are differences in permittivity of different materials used here which may change things a little but we cant measure that anyway.
3) the wire thickness of the secondary winding (not the wire soldered to it, the winding inside) that is going to be used for power: a thick winding wire indicates it can deliver more amps than a thinner wire; use caliper or just compare wires side by side; if biggest/heaviest one has also thickest wire in its winding, then its a winner.