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Measuring current draw
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elmegil



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PostPosted: Mon Jul 01, 2013 8:40 am    Post subject: Measuring current draw Reply with quote  Mark this post and the followings unread

Does anyone have a clever rig that lets you easily measure current draw? Both per module, and per supply (actually per supply is more important at the moment).

I have a 5U rack I've built, using the Analog Synth for the 21st Century supply for +/- 15V, a standalone Power One unit for 5V, and another standalone Power One unit for a couple of Euro modules (notably a Klee Sequencer) on the back side that use +/- 12V.

I'm using 1.5A fuses on the main that feeds all three supplies.

Yesterday I added "just one more" module, and started having problems. And I have another 19 units of width to fill in this rack Smile

The problem: I have a patch together for some ideas I was exploring with the Klee but have not yet recorded. After I added the most recent module I set that running and was playing around with it to see how I want to structure things (I'll eventually post it). Everything seemed OK for a little bit, but after a couple of minutes, the 15V supply "went out". I hit the power button, looked for smoke, didn't see or smell anything out of the ordinary, and turned it back on. Everything looked fine, but then in another couple of minutes, the same thing happened. I did it a third time, trying to find a source for the problem, and this time it blew the main fuse. I unplugged the new module, replaced the fuse, and ran it for a little bit more, but didn't have additional problems (though I to be honest I did not run it for an extended time, so there might still be something lurking).

BTW the new module had been tested and was working fine on the bench supply.

I'm expecting my current draw may be too much, or perhaps I'm having a heating problem, drawing too much through the 15V regulator, which is in open air but no heat sink.

I'd like to be able to measure the current draw, individually and in aggregate, but the only way I can think of involves hacking a power feed to get my meter into the path. I was thinking about something on stripboard that would let me do it, but I figured I'd ask if there is any other clever way to accomplish that which I'm not thinking of.
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piedwagtail



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PostPosted: Mon Jul 01, 2013 12:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
open air but no heat sink


I'd approach that first.

Robert
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elmegil



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PostPosted: Mon Jul 01, 2013 8:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

And it would appear that was the problem.

1) the regulators were both pretty darn hot after running for a bit

2) I put sinks on both the + and - regulators, and ran the patch for a good 10 minutes or more with no problems. Added the new module to the supply, ran for another 10 minutes and it seems like I'm set.

3) I'm still interested in any current draw measurement techniques, because I would like to have some idea what I'm pulling.
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isak



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PostPosted: Mon Jul 01, 2013 11:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

hi elmegil.

if you use Yusynth modules on each and every module Yves is saying in the schematics what is the current draw.
also in MFOS modules.

about checking the current draw your self...well, sorry, cant help.
but i wish to know as well Smile

Edit:
Quick google come up with this...
http://www.head-fi.org/t/39535/how-do-i-measure-current-draw

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piedwagtail



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PostPosted: Mon Jul 01, 2013 11:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Fastest solution would be four of those screw down banana posts with wire holes.


Posted Image, might have been reduced in size. Click Image to view fullscreen.


Normal operation a thick wire jumper between two on each rail.
Measurement time (individual or multiple) take out jumper and connect ammeter.

I'll implement that on my current re-build.

Robert
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Osal



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PostPosted: Tue Jul 02, 2013 4:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes, regulators need heat-sinks. Put them as big you can. From a set of temperature measurements I did, for passive dissipation, considering the worst case conditions that follows:(mains voltage fluctuations 10% high and ambient temperature 40 C) we shouldn't pull out more than 0.8A (I always refer to per rail). This is using big heat-sinks.
So, we should be moderate.

Edit: This is using a 36 VCT transformer (for +/-15V supply) and tested using LM317 regulators. I think that it is also applicable to the 7815 regulators.

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Osal



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PostPosted: Tue Jul 02, 2013 4:51 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
I'm using 1.5A fuses on the main that feeds all three supplies.

One fuse for the three power supplies?

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Osal



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PostPosted: Tue Jul 02, 2013 4:58 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:

3) I'm still interested in any current draw measurement techniques, because I would like to have some idea what I'm pulling.

You can make proves for your multimeter using crocodiles in their ends. Just measure the positive rail that use to be the one that consumes more current. You can check in a second measurement the negative rail. You could also use two multimeter for measure both rails at same time.

But remember that the connections must be reliable. If one of the supplies fail, it can damage components of the modules. So, considering this, it is better to use bananas as Robert already said.

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elmegil



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PostPosted: Tue Jul 02, 2013 5:39 am    Post subject: Reply with quote  Mark this post and the followings unread

Osal wrote:
Quote:
I'm using 1.5A fuses on the main that feeds all three supplies.

One fuse for the three power supplies?


The 15V has a fuse inline as well that came with the 36VCT Transformer. I did not have any other inline fuse holders so I put one fuse at the main.
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elmegil



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PostPosted: Tue Jul 02, 2013 5:54 am    Post subject: Reply with quote  Mark this post and the followings unread

isak wrote:
hi elmegil.

if you use Yusynth modules on each and every module Yves is saying in the schematics what is the current draw.
also in MFOS modules.


I have quite the random selection of modules, many of which have current draw information on Dave Brown's website (for example there are a couple wogglebugs), but some of which are completely custom, or built on stripboard from schematics, and so don't have specs easily available.
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elmegil



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PostPosted: Tue Jul 02, 2013 6:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Osal wrote:
elmegil wrote:

3) I'm still interested in any current draw measurement techniques, because I would like to have some idea what I'm pulling.

You can make proves for your multimeter using crocodiles in their ends. Just measure the positive rail that use to be the one that consumes more current. You can check in a second measurement the negative rail. You could also use two multimeter for measure both rails at same time.

But remember that the connections must be reliable. If one of the supplies fail, it can damage components of the modules. So, considering this, it is better to use bananas as Robert already said.


I believe all my 2164s are protected by diodes, but the chance of damage to other parts is high on the list of why I was concerned about the original failure. I was right there and immediately powered off each time I had an occurrence, and my patch at least is still fully functional, so I'm optimistic that I didn't cause any damage with my foolish lack of heat sinks.

I will think about how I might set up a stripboard that I can put inline with bananas, plug in my supply on one end and another supply cable going to what I want to measure on the other end.
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piedwagtail



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PostPosted: Tue Jul 02, 2013 8:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Just to clarify for anyone who is unfamiliar with the binding posts pictured above: they have a small horizontal hole through the shaft which is revealed when you unscrew the top section.

My suggestion is to place them close together for each rail and put a short thick wire through the aligned set of holes and then screw the top section down hard; that is pretty secure.Loop if you will to bind them together.

You could use banana to banana leads into the top but it's cumbersome and less secure.

Robert
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Osal



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PostPosted: Tue Jul 02, 2013 11:49 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
The 15V has a fuse inline as well that came with the 36VCT Transformer.
Im not sure if I understood. Is the transformer built with a polyfuse or something like that?

Quote:
I did not have any other inline fuse holders so I put one fuse at the main.

Consider the fuse as an individual protection for each transformer. To protect it from any short in the secondaries. Shorts after the regulators are protected by the same regulators.
So, I recommend to use a fuse, properly sized, for each transformer.

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elmegil



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PostPosted: Tue Jul 02, 2013 12:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

The 36V CT transformer used for the 15V supply is salvage. As such it has a number of secondaries that are other values that I'm not using. It had fuse holders in line with the primary and some of those outputs including the center tap of the 36V CT secondary, and I retained those. The main fuse is listed as 5A and the 36V secondary fuse is listed as 3A. This is as it was when I bought it, so I haven't felt I needed to change the values. I've included a photo below.

As stated before, I have no other in-line fuse holders, and no easy access to them (I haven't looked at Radio Shack lately, but their selection is generally poor for anything but the most common of items).

I have put them into my wishlist that I use whenever I do a new mail order, so I will eventually get there Smile. However, I'm not in a great hurry because the 5V and +/-12V supplies are barely used at all, and they're behind the overall fuse on the main, which is undersized relative to all this.


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Osal



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PostPosted: Tue Jul 02, 2013 2:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
The 36V CT transformer used for the 15V supply is salvage. As such it has a number of secondaries that are other values that I'm not using. It had fuse holders in line with the primary and some of those outputs including the center tap of the 36V CT secondary, and I retained those.

Interesting transformer! I have some questions if you could check it:
Is it full encapsulated also in the other side?.
What is its current rating?
Could you measure the actual AC voltage across the secondaries?

Quote:
The main fuse is listed as 5A

This must have a mistake. I explain how to calculate it in the second post here

Quote:
and the 36V secondary fuse is listed as 3A. This is as it was when I bought it, so I haven't felt I needed to change the values.

Since you are using the LM7815 regulator you don't need a fuse in the secondaries. The regulator has already short circuit protection.
You could use that fuse holder for the other transformer!

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Osal



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PostPosted: Tue Jul 02, 2013 2:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

I would try to use much larger heat sinks. If there is no room for two large heat-sinks, you could put a big one for the two regulators using insulating pads.
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elmegil



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PostPosted: Tue Jul 02, 2013 3:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

Osal wrote:
elmegil wrote:
The 36V CT transformer used for the 15V supply is salvage. As such it has a number of secondaries that are other values that I'm not using. It had fuse holders in line with the primary and some of those outputs including the center tap of the 36V CT secondary, and I retained those.

Interesting transformer! I have some questions if you could check it:
Is it full encapsulated also in the other side?.
What is its current rating?
Could you measure the actual AC voltage across the secondaries?


It is fully encapsulated, there's a sheet of metal on the other side as well.

I've made notes on the top as you can see in the photo, those were taken from the spec sheet I got with the transformer, written on there simply to make it more accessible.

So I have 36V CT at 5A, 4V CT at .5A, and 28V at 5A (no, that .5A is not a typo, it's listed as 500mA on my sheet)

I measured them with no load to distinguish for certain--the sheet says "yellow red/black/yellow red for the set I want, hence the "YBY" on the top--and the color difference left me uncertain so I measured them all. It's been a while, but the values were sufficiently close that it was clear which set was which.

You cant read the label clearly in the photo, but this is a TPZ81V001M by some japanese company.

One other oddity: the primary has a third tap as well, it is drawn as being close to the orange tap. The primary winding is white to orange.

I went ahead and attached a photo of the sheet....


Osal wrote:
elmegil wrote:

The main fuse is listed as 5A

This must have a mistake. I explain how to calculate it in the second post here


I can only say what I have in my information and what it says on the fuses. Smile I'm fairly sure these are not slow blow fuses, if that makes any difference. I definitely do not know the overall VA rating of the transformer. The primary is US Standard 110V/120V.




Osal wrote:
elmegil wrote:

and the 36V secondary fuse is listed as 3A. This is as it was when I bought it, so I haven't felt I needed to change the values.

Since you are using the LM7815 regulator you don't need a fuse in the secondaries. The regulator has already short circuit protection.
You could use that fuse holder for the other transformer!


That's a great idea; there's another in line fuse as well that's not in use, I should be able to use it as well, since there are two other separate supplies/transformers (12V and 5V are different units)


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piedwagtail



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PostPosted: Tue Jul 02, 2013 4:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

That has to be the biggest transformer used in Synth-diy!

I'd use both the 36V centre tapped and 28V secondaries you've got two supplies there.
x1.414 they are both capable of +/-15.
You must have enough current for anyhting you'll ever build!

Surprised the regs stood up for so long having to drop such high voltage without heatsinks.

I'd use large screw terminal household block to replace that black modernist sculpture of tape seen in the picture.

Robert
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elmegil



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PostPosted: Tue Jul 02, 2013 5:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Laughing

Physically, it doesn't seem much bigger than other toroids I've seen, but spec wise, yeah Smile

So without a center tap, I assume I'd be using the 28V in the way Ray Wilson does for the "wall wart power supply"? Half wave rectified for each polarity?

I'll find better sinks, those were what I had on hand. I have some others somewhere, but they're definitely less mass, so I didn't spend a lot of time looking for them.

I am still learning my way around these things, hadn't thought about terminal blocks Embarassed
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elmegil



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PostPosted: Tue Jul 02, 2013 6:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

So I now have some mica sheet heat sink insulators but I think I must have tossed the only sizeable heat sink that I had around--it was attached to some other salvage and I think I must have tossed it in the recycle bin. I'll have to go dig through some old PC heat sinks maybe....

The only other chunks of metal I have are all sheet metal, mostly aluminum plate I use for panels. Not sure how much mass I need to dissipate the heat though...

One other thing I'm not clear on with these: do I need to use thermal grease with the mica sheets?
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analog_backlash



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PostPosted: Wed Jul 03, 2013 1:30 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi elmegil.

From my somewhat limited experience of building PSUs, I have always thought that the mica washer itself introduces additional thermal resistance between the regulator IC and the heatsink, so thermal transfer compound is even more important here. This seems to be borne out by the attached document (which also explains how to choose heatsinks).

Another alternative is to use silicon rubber insulators as shown in this (UK) link:

http://www.rapidonline.com/Electronic-Components/Silicone-rubber-mounting-kits-32693

These claim to have good thermal conductivity and do not require heat transfer paste. I have not tried these myself, but it seems like a good idea.

Gary


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elmegil



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PostPosted: Wed Jul 03, 2013 5:23 am    Post subject: Reply with quote  Mark this post and the followings unread

That's exactly what I was unable to find in google last night, thank you Smile
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Osal



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PostPosted: Thu Jul 04, 2013 1:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
So I have 36V CT at 5A, 4V CT at .5A, and 28V at 5A (no, that .5A is not a typo, it's listed as 500mA on my sheet)

mmm, that sheet doesn't seem from the manufacturer. The transformer is big, but I don't think that it is big enough for these specifications. I would test it to be sure of its real current rating.

Quote:
You cant read the label clearly in the photo, but this is a TPZ81V001M by some japanese company.
One other oddity: the primary has a third tap as well, it is drawn as being close to the orange tap. The primary winding is white to orange.

Due that the transformer is manufactured in Japan, it could be to use it with the Japanese mains voltage (100VAC) or with 120VAC

Quote:
I can only say what I have in my information and what it says on the fuses. Smile I'm fairly sure these are not slow blow fuses, if that makes any difference.

Try to replace them by slow blow fuses.

Quote:
I definitely do not know the overall VA rating of the transformer.
We can determine it. Just a few power resistors and a multimeter reading AC RMS voltage. In addition a K-prove or an infrared thermometer would be great.
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Osal



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PostPosted: Thu Jul 04, 2013 1:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

piedwagtail wrote:

I'd use both the 36V centre tapped and 28V secondaries you've got two supplies there.
x1.414 they are both capable of +/-15.

Robert, 1.414 is the crest factor of an ideal sine but the sine wave of the mains voltage is not ideal.
Furthermore, due the voltage regulation of the transformer the wave at the secondaries is more distorted as more current runs in the secondaries.
For these power supplies we use, I would use the crest factor=1.3.

Then, we must subtract the rectifier voltage drop, the voltage ripple, the voltage dropout of the regulator and also we must add room for low fluctuations in the mains voltage. (It is not constant)

Usually for a +15/-15V power supply using standard regulators we need a 36VCT transformer.

More details: http://electro-music.com/forum/topic-51694.html

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Osal



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PostPosted: Thu Jul 04, 2013 1:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:

The only other chunks of metal I have are all sheet metal, mostly aluminum plate I use for panels. Not sure how much mass I need to dissipate the heat though...

I measured the temperature of LM317/LM337 packages in my PS1. Using an anodized aluminum sheet of 425mm*260mm*2mm, I estimated that the maximum current that the power supply can produce is 0.8A. (Considering the following worst case situations: 40C of temperature ambient and a 10% of high fluctuations in the mains electricity)
You could use a 3mm sheet and reduce the area by say 2. I guess. It need measurements.

The other way is to calculate it and use a commercial big heat-sink.

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