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You are welcome

Glad I could help!

Yes , yes and yes. However, there is no reason not to power the meter from the output of the boost converter in this device. I have seen that the voltage meter I used can be more inaccurate at 5V. A lm317 , lm334 or tl431 and associated components actually costs more than i wanted for this project , and is unnecessary for a tester when the component is only connected for a couple of seconds at most.If you look at my low ohm meter, I used a tl431 as a constant current source for that.Also I don’t feel that 3mA is enough current to light 10 white LED’s in series to be clearly visible . The concept was to make a universal tester for $3 including the box, connectors and components. Thank you for your comment and ideas.

@@Joftec The 3mA current will run through all 10 LEDs... if 3mA is enough to light one, it's enough to light 4398 leds in series, provided you have the voltage compliance. That's how series current works...

I said 3mA is not enough for them to be clearly visible, not that they would not light. Big difference.

Hi, schematic is coming in a short video soon. Just a resistor for current limiting , I want to keep it as inexpensive as possible. Thanks for your comment.

Hi, I was waiting for comments regarding the lack of circuit diagram, just like yours. Thanks. I will be doing a short showing the circuit diagram soon.

I think it is far easier and entirely more accurate to measure . I have seen toroidal transformers gestimated by weight, as it is practically impossible to measure the core, but not EI transformers where core measurements are relatively easy.

Glad it helped!

The actual metric value for the equation is 116.129323 as shown in the video . In very basic terms because the core you measure is not actually the core

It is basically derived from the formula shown near the beginning of the video.

@@Joftec ok. at 3:18 I see you assuming 50Hz and 2.60 turns/volt. But then at 15:43 there is a logical jump that eludes me

The actual design process is not covered in this video, the purpose of the video is to estimate the design power dissipation of an already designed transformer. The example at the start is an example of how the process works . For example when you measure the core size as shown in the video, you are not actually measuring the core because for the laminations to work they are individually insulated, this insulation therefore occupies space in the core and reduces the magnetic material in the core. These details are taken into account within the math . Hope that helps

Sure, it’s ok for estimating.

Yep, (mm²/116)² =VA or (inches² x 5.58)² =VA. Six of one, or half a dozen of the other, as my father used to say.

I agree it is close,but the actual derivative is 116.139323 in mm or 5.58 in inches. For estimates 116 is fine, for designs it is much better to be 100% accurate. The difference is quite small, but can be important when physically fitting the secondary ( usually, as the wire is thicker) winding onto the bobbin. The actual area available for the copper as apposed to how much copper can be wound in that area, can be and is different. During the design process, this is one of many factors which have already been taken into account when the finished product is estimated. Like everything else copper, laminations and time are expensive and transformers are for sure designed to be as cheap as possible, this means that they will perform at 100% of their design capacity with an agreed temperature rise in an agreed cabinet size/airflow. The copper and lamination quantity increase with size, therefore smaller is cheaper, but smaller is also hotter electrically and cooling efficiency so there is an exponent there too. Different manufacturers in different regions may also have different Bobbin/lamination sizes available,in the UK and both metric and inch sizes were freely available when I was doing this , this can make subtle differences in the area available for copper. Different regions have different standards for the insulation thickness on the copper, and even differing Amps per square mm for the copper itself, which is nuts, but true. So in summary, for estimates, which is the purpose of the video, I agree 116 for mm is acceptable. For designs 116.129323 is better, and for simplicity 5.58 is the best, for me anyway.

@@jonathanperry1583 That doesn't make sense to me, using 6 decimal places in mm, and only 2 decimal places in inches. 0.1mm equals approx 0.004 inches. if you wanted to be that precise, inches would need to have more decimal places. But the calculation was being used as a ballpark estimation of VA anyway, 0.1 mm makes little difference in the calculation. Then you would down rate the estimate by 10-20% or so, don't want to push the transformer to 100% of its estimated maximum VA.

Hi, yes there is . However this is far more problematic for several reasons, a couple being , 1. It is almost impossible to measure the cross sectional area of the core of a wound toroid as it is completely covered by the winding(s),insulation etc. 2. There tends to be a wider range of core materials, and thickness of coatings on the cores, which can mean large differences in core efficiency. I therefore do not want to endorse reverse calculation on a toroidal transformer. Hope that helps

@@Joftec Thanks and I understand the logic. The reason I asked is that most of the transformers in my junk/spares/gold box are toroidal

As I said in the video, the circuit is derived from a circuit supplied from a viewer. I did try it without the “ split rail “ and the results were in consistent. Adding the “ split rail “ provided much better stability of measurements , that is why it is there on my version of the circuit. As far as I am aware the gain of a non inverting op amp will wither be unity or 1+ (RF/Rin) , therefore to not have the additional 1 + .The inverting amp sets the required gain , 10 for example and not 11 , and the fact that the 602 is a dual device, why not use it fully and invert with unity gain. Seems the most sensible to me.

Hi, interesting question. As I touched on in the video , normally when designing a transformer the turns per volt and current required are calculated. The cross sectional area of copper is then calculated, and a suitable bobbin is selected based on that requirement.The actual math behind the calculation is relatively complicated, and the method shown is a simplified shortcut. Bobbin and lamination manufacturers follow the rules determined by the math allowing the shortcut shown to become true. Therefore in effect the only measurements needed are the ones shown and the overall width is irrelevant for the shortcut. As far as I am aware the overall width of the lamination is determined by the width of the central section of the E. I believe that roughly speaking the area of the outer “arms “ of the E are close to the inner section of the E. Therefore the overall width is roughly the centre plus 2x the arms plus 2x the gap for the winding. The gap for the winding is based on the area of the gap and its relationship to the current handling capability of copper wire for a given area. The really interesting part is that that value can and is adjusted depending on many factors including desired operating temperature, enclosure type, and cooling, for example . Hope that helps.

@@Joftec Wow, thanks, yes that helps!

Hi, it’s at the start, about 1 minute in

No I don’t think it can in standard form due to the output transistor .

You are welcome

Awesome, thank you!

Hi, I am not sure if I still have it. Could well have been recycled

Do you have a circuit ? I could possibly look into that. Thanks

@@Joftec Yes, I could share that with you. However, we would need to create a means to get it to you. I do not see your email address, on your channel details, and TH-cam will not allow me to post a link to a drop box. Do you have any suggestions?

Hi, email address added to channel details. Thanks

Hmmm, it’s not visible . Email address is joftechnical@btinternet.com

@@Joftec Thanks. Done. Enjoy!

Thank you.

Good to know. Thanks

Very welcome

I personally like build videos and enjoy watching them no matter how simple. But a shorter video with the schematic would suffice, considering that you’ve got it built and showed how it works on a video already.

Actually I realize this is a dumb question since you already showed how to use it in a video.

Do are most welcome - please subscribe if you have not done so.

Yes switch has to be on for charging, confirmed by the red charging LED

Hi, yes that may be the case. I do the calibration every time I need accuracy anyway .

Hi, Thanks for your great comments. It will work with both 12 and 15 volt transformers, of course depending on what maximum output voltage you want. I don’t know your level of knowledge, so sorry if I am stating the obvious, if you are using a standard iron core transformer EI type for example, they have terrible load regulation. By that I mean the that the output voltage of the transformer will drop depending on the load, and most importantly the power rating. For example if you have a 24v 72VA rated transformer, ie 24v output at 3A , the open circuit voltage could be over 30v dropping to 24v as the load increases. If you have a 200VA transformer for example, at 3A the output voltage will still be way over 24V. So in summary check the transformer voltage unloaded and loaded to make sure it fits your requirements.

@@Joftec Good advice there. It's a shame they cut costs by using useless opamps, very off putting for beginners. I'll get the op amps from Rapid electronics at just 49 pence each! They do a large range of toroidal transformers too.

You could file the button down a bit also. Or just round off the edges.

I used a slide switch for mine as the case I keep it in is a tight fit.

Hi, the switch was purchased from Aliexpress. I think it is called a Self Locking / UNlock Push Tactile Power Micro Switch . The size is 5.8mm x 5.8mm long button. Hope that helps

Thank you very much for your response, went ahead and purchased from aliexpress. Will have fun when it arrives.

Thank you sir

lol

Yes that is true, the charge indicating led confirms that too.

AliExpress, pretty sure they are available on eBay and probably others too

Good to know thanks

Same here. However, it can get locked up when attempting to test some 3 pin devices which o suppose are not in its database. The only way to reset it is to temporarily remove the cell or let the cell discharge. Therefore I put a switch on mine for reset purposes.

Hi, I think there are two things you need to watch out for here. If you watched the first part of the video the op amps supplied in the kit were unmarked, they could have been anything. I used genuine TI TL081 CP. Also the absolute maximum input voltage is 40 VDC, the circuit uses the 5v1 zener diode to offset the - side therefore the total input voltage is whatever the output is (smoothed DC from the rectifier) plus 5.1V. Therefore at 24vac @ 1.414 = 33.8V + 5.1 = 39V, very very close to the max input voltage. If you are using an EI type transformer, the output will for sure be higher than 24V unloaded . I also grounded the inputs of the op amp prior to switching on, as they are jfet, just to make sure they were totally off.

@@Joftec You are right about the transformer. It is an 220V to 2x12V E+I.But, the mains voltage is 230-240V here in Europe. So that was the cause of the failure, I know. But what drives me mad is that with the new opamps that I bought already are not working as intended. Right now I am waiting new ICs from Digikey, and I hope that will solve the problem. And I plan to use it with an 2x9V transformer that will be something around 27V input. Thanks for your reply.

Hi, measure the voltage unloaded. But if it’s a 220v primary and you are at 230-240 and an EI transformer I would guess your output is way over spec. Also remember these are fet input devices, therefore the inputs can be turned and possibly stay on via static electricity. Ground the inputs before power up, use static sensitive precautions also.

Common problem.

I am happy you feel this way, I was a little worried about making a video on this.

Thank you Carlos