output from transformer is coming not as expected

[Brumby]

So - just to confirm - your meter was in series with the 7 ohm graphite pencil - and this combination was then connected across the power supply being tested?  Thus the total load will be 7 ohms plus the resistance of the internal 10A shunt.

This cannot be right.  The maths simply does not work for transformer 2 and transformer 4 - even just using the 7 ohms as the total load.

Using Ohm's Law:  V=IR  rewritten as I=V/R

Thus: 20V DC / 7 ohms = 2.86A
and... 19.8V DC / 7 ohms = 2.8A

as such, these are maximum possible values and neither of these agree with the current readings given.

Something is wrong.


Can you please show us exactly how everything is connected when doing these current measurements.

[VickySalunkhe]

As soon as i turn on the psu the graphite used heat up and smoke used to come and the current rating increases drastically
I have given you the highest rating of current before the graphite has torn out leaving the circuit open.(ALL THIS HAPPEN WITHIN COUPLE OF SECOND)
So I don't know what is the actual resistance as the graphite heats up i think resistance will come down thus giving out more current

But the main task which was to test whether transformer can give out 5A or not was completed so i gave out the readings which i have got

[VickySalunkhe]

Final readings of motor connected to vehicle body and tested it by using a load of 70kg on the vehicle

70 meter long wire between main supply and psu
15 cm long wire between psu and controller
Width of wire  1mm

Transformer 1 (12-0-12v 5A)                                    Transformer 2 (12-0-12v 5A)
RATINGS WITHOUT LOAD
30V AC OUT                                                                      14.8V AC OUT
26.7V DC OUT (AFTER RECTIFIER)                                 13.01V DC OUT (AFTER RECTIFIER)
40.7V DC OUT (AFTER 6.6mF capacitor)                        20V DC OUT (AFTER 6.6mF capacitor)
RATINGS WITH CONTROLLER,MOTOR, THROTTLE (NO MECHANICAL INPUT ISGIVEN TO THROTTLE)
36V DV    0.06A                                                                 17V DC 0.11A

Transformer 1&2 in series
Without load      58.6V
With some input to throttle and controller, motor is connected
52.5V      0.05A
44.1V      0.55A
38V         1.11A
35V         1.45A
After 35V controller stops to give any power to motor and starts from 52V again


Transformer 3 (12-0-12v 5A)                                    Transformer 4 (0-12v 5A)
RATINGS WITHOUT LOAD
29.9V AC OUT                                                                  14.5V AC OUT
26.6V DC OUT (AFTER RECTIFIER)                                12.7V DC OUT (AFTER RECTIFIER)
40.8V DC OUT (AFTER 6.6mF capacitor)                       19.8V DC OUT (AFTER 6.6mF capacitor)
RATINGS WITH CONTROLLER,MOTOR, THROTTLE (NO MECHANICAL INPUT IS GIVEN TO THROTTLE)
36.1V DV    0.06A                                                                 16.8V DC 0.11A

Transformer 3&4 in series
Without load      58.5V
With some input to throttle and controller, motor is connected
52.5V      0.05A
44.4V      0.55A
38.4V         1.15A
34V         1.5A
After 34V-37V controller stops to give any power to motor and starts from 52V again

1+2   connected parallel with 3+4
53V         0.05A
47.9V      0.57A
43.9V      1.2A
37.1V      2.62A
42.2V      1.75A
49.6V      0.55A
36V          2.85A


As soon as the voltage drops down between 34V - 37V motor starts from starting i.e, 52V
Current reached to 2.6A max with a load of 70Kg on vehicle
With all 4 transformer connection


With 2 transformer connected serially
Max 1.36A current is attained


But theoretically i can get 7A of current
But practically current i am gettung is 2.6A
That's the problem
Plz help me to resolve the issue if any


Thanks

[StillTrying]

"After 35V controller stops to give any power to motor and starts from 52V again"

As the motor controller is expecting to be powered by lipo batteries it's probably switching off to protect the lipo batteries from over discharging.
I don't think you'll be able to get the current much higher than you already have from a transformer and bridge rectifier.

[VickySalunkhe]

I don't think you'll be able to get the current much higher than you already have from a transformer and bridge rectifier.

But why?
The configuration of transformer i purchased should deliver (5A) for what they are made for right?

Or is it like
In a center tap transformer
If 1,3 wire is joined with a bridge rectifier we get half the current for what the transformer was made for.

[Ian.M]

No.  If from an honest manufacturer, a transformer fed from a supply of its nominal primary voltage can supply its full rated RMS secondary current into a resistive load, without overheating if cooled as specified, and without the secondary voltage dropping below its rated value, *HOWEVER* a bridge rectifier followed by a capacitor is *NOT* a resistive load, even if there is a resistive DC load after the bridge rectifier.   You have to apply the derating factor of 0.62 for this configuration, as shown in  the PDF I linked back in reply#44:

Take a look at the Hammond Transformers Design Guide for Rectifier Use
...

That derating factor can be confirmed by circuit analysis, either manually or by SPICE simulation.

Therefore your 5A RMS transformer secondaries are only good for fractionally over 3A DC, when used with a bridge rectifier and reservoir capacitor.

[IanB]

I disagree. There is no derating factor for this application. The derating factor protects against overheating, it does not limit the maximum current the transformer can produce. For short periods of maximum load all that will happen is that the transformer might get a bit warm.

I think instead we have to look to the 70 m long wire. This was said to have a resistance of 3 ohms in a previous post. Is this resistance for just one leg, or for out and back combined?

5 A through 3 ohms will drop 15 V, and 5 A through 6 ohms will drop 30 V. This will drastically limit the voltage the motor sees when you open the the throttle and put a load on it.

[VickySalunkhe]

Therefore your 5A RMS transformer secondaries are only good for fractionally over 3A DC, when used with a bridge rectifier and reservoir capacitor.

Thats what i am worried about sir
As per your saying
I should get 3A from one transformer
But i am getting 1.3A from it
Which is the problem

[IanB]

Get your 70 m wire, join the two conductors together at one end, then measure the resistance between the two conductors at the other end. What is the total round trip resistance of the wire, out and back?

[VickySalunkhe]

Sir today i have tried to replace the 70meter wire with 30cm wire
But there was not any major difference between the readings which i have posted today only...

[Ian.M]

The derating factor is applicable if you dont want to burn up your transformer in continuous operation.  Transformers are not fussy pieces of silicon, they are Iron, Copper and usually plastic insulation, and they tolerate brief overloads well as long as the deep winding temperature stays under the maximum temperature rating of the wire insulation.   Better manufacturers will even specify permissible overload factors and duty cycles.

Therefore your 5A RMS transformer secondaries are only good for fractionally over 3A DC, when used with a bridge rectifier and reservoir capacitor.

Thats what i am worried about sir
As per your saying
I should get 3A from one transformer
But i am getting 1.3A from it
Which is the problem

You can get UP TO 3A continuously without burning out your transformer, and probably 6A for a few seconds, but that doesn't mean your motor controller *will* draw 3A (or 6A).

I think instead we have to look to the 70 m long wire. This was said to have a resistance of 3 ohms in a previous post. Is this resistance for just one leg, or for out and back combined?

5 A through 3 ohms will drop 15 V, and 5 A through 6 ohms will drop 30 V. This will drastically limit the voltage the motor sees when you open the the throttle and put a load on it.

I agree that much of the problem is the wire resistance.  1mm dia wire is near enough 18AWG, which if made from good quality electrical grade copper should be about 21 milliohms per meter.  For 140 meters (70 m there and back), that comes to almost exactly 3 ohms.

[VickySalunkhe]

Get your 70 m wire, join the two conductors together at one end, then measure the resistance between the two conductors at the other end. What is the total round trip resistance of the wire, out and back?

5 Ohm

[Ian.M]

Can you confirm the 1mm wire diameter?  Also, what's its strand count and individual strand diameter?   Stranded wire can have up to 1/3 more resistance than solid wire of the same diameter, due to its packing fraction (i.e. the voids between close packed circular strands), but that would only account for 4 Ohms of resistance.  If you are measuring 5 Ohms and its not a measurement error, and the diameter is actually 1mm, it implies the copper is crappy, with a bulk resistivity 25% higher than pure electrical grade copper.

[WaveyDipole]

I had a look at the photo and am concerned as to how TX2 is wired. It is difficult to tell on the photo but I fear that there may perhaps be some confusion because instead of red-blk-red as per TX1 and TX3, TX2 has the opposite, i.e. blk-red-blk. It is difficult to tell which wire goes to the right side of the terminal block, but the direction of loops in the black wires seem to suggest that one of the black wires is wired into the left side of the connector block but has had a length of insulation stripped back at its mid point (just left of exit point of the red wire) and then the end of the topmost black wire loops back and its end is wrapped around this same point. The red wire then seems to go to the right terminal of the connector block. I hope that is NOT what is going on here and perhaps this is the bare end of one black dangling loose above the other and obscuring the insulation otherwise that TX would be getting really hot! The red wire should be the center tap and ought to be left disconnected. The two black wires should be connected to the connector block, but apologies if I have mis-interpreted the picture.

[VickySalunkhe]

Can you confirm the 1mm wire diameter?  Also, what's its strand count and individual strand diameter?   

Wire diameter 0.83mm
Strand count   10
Strand diameter   0.3mm

[Ian.M]

There's something wrong there as the sum of the strand cross section areas (CSA) comes to more than the overall CSA calculated from the overall diameter.

70m of a solid pure copper wire of 0.83mm diameter would be 2.174 ohms, so with the loss due to the voids between strands 5 ohms is in the right ballpark for 70m x 2 wires.

That wire is ludicrously thin for the purpose - 2.5 mm² mains flex would be a far better choice, and I would strongly advise at least 2000uF per Amp bulk decouping at the motor controller as I bet it draws high current pulses.

[VickySalunkhe]

Sir can you plz
Tell me how you calculated all this calculation
And what do they mean?

And what minimum diameter wire shall i use for this purpose
Thanks

[Ian.M]

resistance = resistivity × length / area
area=Pi*(d/2)²

Wikipedia says: Pure Copper electrical resistivity = 16.78 nanoohm·m (at 20 °C)

The rest is just simple maths.

In practice it will be worse than the calculation gives because the copper wont be 100% pure and the overall diameter makes no allowance for the voids between strands.

The minimum wire diameter is determined by how much voltage drop your application can tolerate.   Calculate the maximum wire resistance you can tolerate then look through a cable manufacturer's catalog for a cable with a low enough resistance per meter to be under that after multiplying by the total wire length there and back.

[VickySalunkhe]

The minimum wire diameter is determined by how much voltage drop your application can tolerate.   Calculate the maximum wire resistance you can tolerate then look through a cable manufacturer's catalog for a cable with a low enough resistance per meter to be under that after multiplying by the total wire length there and back.

Sry
But I didn't get any of this sir.

How would i know how much minimum voltage drop my application can tolerate or what does it mean actually?

How would i know what is the max wire resistance i can tolerate?

How would i know what diameter wire can support 5A current and have minimum resistance.....

[Damianos]

Most of the presented measurements seem a little or a lot strange!
For example, the voltage with a 50mA load is six volts lower than what measured without load!
It is not clear where the measurements are done. Are these on the controller or at the output of the circuit?

You forgot to say what are the types of the rectifiers. Have you found a datasheet of them?
Are the transformers of any "special" type? What is showed on their labels?
Are all the capacitors of the same type/model? What is their working voltage rating?

How is the circuit constructed, under the cartons? Is possible to show a photo?
Are connected the components with very thin wires? There are mentioned measurements with and without the capacitors, how are they connected and it is so easy to disconnect and reconnect them?
... ...

One more test that you can do, is to try to measure the ripple voltage of the power supply. Set your meter to AC voltage, measure at the output without and with a little load, on each of the four and the entire combination of them. [with capacitors connected]
If an instrument with peak detect is available, the above will be more informative.

[Brumby]

The minimum wire diameter is determined by how much voltage drop your application can tolerate.   Calculate the maximum wire resistance you can tolerate then look through a cable manufacturer's catalog for a cable with a low enough resistance per meter to be under that after multiplying by the total wire length there and back.

While straightforward to many of us, I was concerned that this was too much of an ask from our OP.  So, rather than set them on a difficult task, I had a look at the cable they have at hand.

From the photo, it would seem the OP is using a mains rated cable - thick white sheath with red and black insulated wires within - but that it would be at the lower end of current carrying capacity.  My guess is it would be for lighting circuits.  Also, at 5 ohm for 140m it works out as 0.036 ohms per metre.  With 10A current that is about 0.7V drop per metre of twin cable.  So long as the cabling throughout the supply is of at least this gauge and the total length from the transformers to the load is less than, say, 2m I can't see a 1.5V drop being a problem.  Going heavier gauge is never a bad idea - but this should work for testing.

Questions to OP:
 1. Is all the wiring connecting all your components of this gauge or thicker?
 2. What is the total length of wiring from the transformer to the load?  (Just answer for a single wire - and we will double it for any maths.)

How is the circuit constructed, under the cartons? Is possible to show a photo?

This is something I have wondered as well.  In the photo, I don't see any soldered joints, just the terminal blocks used to connect the transformers.  How are the connections we can't see being made?  If you are simply twisting wires together, then there is going to be a lot of potentially poor connections, especially for pulling currents of 5A and more.  Heavy current connections need to have very good contact or you will lose a lot of power.  The terminal blocks are a good move, but what else are we not seeing...?

Request to OP:
 3. Can you please show us a photograph of the hidden wiring?

It is not clear where the measurements are done. Are these on the controller or at the output of the circuit?

This has been a problem from the very outset.  Where you measure a voltage is important and for higher current situations can be absolutely critical for understanding what is actually going on.  There is also the issue that we are not seeing the complete setup, so there may be some hints or obvious errors that are invisible to us.

Request to OP:
 4. Can you please provide a schematic of the entire circuit - from the supply, through the controller to the load?  (Do not try to look inside the controller - just show the connections to it.)

One more test that you can do, is to try to measure the ripple voltage of the power supply. Set your meter to AC voltage, measure at the output without and with a little load, on each of the four and the entire combination of them. [with capacitors connected]

This would be an interesting - and useful - test.

With no load, we would expect this AC voltage to be pretty small and, essentially, insignificant.  When this DOES become interesting is when you put a load on it.  I would be interested to see what it was like at around 1A load current.  The actual current isn't hugely important - but if you can measure it accurately, that will help in doing some math.  Oh, and don't forget to do the DC voltage measurement as well.

Request to OP:
 5. Can you test the supply as suggested showing:
    a) DC volts, AC volts - with no load  and..
    b) DC volts, AC volts, DC amps - for a load current between 0.5a and, say, 3A

[Connoiseur]

Suggestion to OP:

You can make your own crude resistive load from nichrome wire wound on a suitable former like ceramic tile or a mud brick, although personally, I prefer brick as it does not crack on heating. Nichrome wire is easily available in most of the electrical shops as heater wire rated 1500W at 230V. Alternatively you can buy a rheostat of suitable rating.

In practice it will be worse than the calculation gives because the copper wont be 100% pure and the overall diameter makes no allowance for the voids between strands.
 

I beg to differ. Commercial copper wires available today have more than 100% of IACS conductivity. Also, the area mentioned on the wire (at least the ones IS 694:2010 certified) is the actual area of all the strands combined, so the "packing void factor" is ruled out. But yeah, the temperature may not be 25 deg. C at OP's location, so the resistance will be a bit higher.

[Ian.M]

In practice it will be worse than the calculation gives because the copper wont be 100% pure and the overall diameter makes no allowance for the voids between strands.
 

I beg to differ. Commercial copper wires available today have more than 100% of IACS conductivity. Also, the area mentioned on the wire (at least the ones IS 694:2010 certified) is the actual area of all the strands combined, so the "packing void factor" is ruled out. But yeah, the temperature may not be 25 deg. C at OP's location, so the resistance will be a bit higher.

IACS commercial grade annealed copper: 17.241 nanoohm·m, 
Wikipedia's figure for Pure Copper: 16.78 nanoohm·m, both at  20 °C.
Modern commercial grade copper is between the two, due to process improvements since the IACS standard was set in 1913.

I would no longer bet on cheap wire being made with pure commercial copper - if its made of low purity recycled copper, contaminated with brass, solder and other metals, its resistivity can be significantly higher, before the impurity level rises to the point where the decreased ductility adversely affects the wire drawing process.

Also the O.P. quoted the wire diameter as 0.83mm (presumably measured), which I then calculated the area from, as the strand diameter and count was inconsistent and did not give the CSA.  Therefore I stand by what I said.

[VickySalunkhe]

First i have done some changes in the circuit with wires
which resulted in increase of output current by 1 amp i.e, max i can get is 3.5A from my psu. But still its half way down considering the fact my output current will be 62% of rated current value.

and an update in readings of previous wire  used  length of wire was 35 meter sorry, but because of some confusion i told you 70 meter earlier

Wire used between psu and controller
and between capacitor, rectifier.....
TOTAL length of wire used back and forth 1.9 meter
Diameter of wire     2.5 mm
No. of strands         36
Strand diameter     0.33 mm

same wire was used between main supply and psu for carrying 252 V AC
Length of that wire 37 Meter [of one wire   double it for two wires]
resistance of above wire (two wires connected) 1.3 ohm

1. Is all the wiring connecting all your components of this gauge or thicker?

Previously wire was thin of 0.83mm  but now as i have said earlier because of changes done
Thicker wire .

2. What is the total length of wiring from the transformer to the load?  (Just answer for a single wire - and we will double it for any maths.)

TOTAL LENGTH  both side  1.9 Meter ( don't  double this value)

How is the circuit constructed, under the cartons? Is possible to show a photo?

 3. Can you please show us a photograph of the hidden wiring?

IMAGES ATTACHED OF CONNECTION AND HOW MULTIMETER IS USED AND WHERE.

4. Can you please provide a schematic of the entire circuit - from the supply, through the controller to the load?  (Do not try to look inside the controller - just show the connections to it.)

IMAGE OF SCHEMATIC ATTACHED

One more test that you can do, is to try to measure the ripple voltage of the power supply. Set your meter to AC voltage, measure at the output without and with a little load, on each of the four and the entire combination of them. [with capacitors connected]

5. Can you test the supply as suggested showing:
    a) DC volts, AC volts - with no load  and..

Transformer / Circuit                DC VOLTAGE                  AC VOLTAGE                  Full Circuit 58.6V 128.6V 1 & 2 (IN SERIES) 58.2V 127.6V 3 & 4 (IN SERIES) 58V 127.6V transformer 1 39.2V 85.7V transformer 2 19.2V 41.8V transformer 3 39.4V 86V transformer 4 18.93V 40.8V     b) DC volts, AC volts, DC amps - for a load current between 0.5a and, say, 3A Full Circuit 1 & 2 (IN SERIES) 3 & 4 (IN SERIES) 56.8VDC      125VAC     0.05 A                56.1VDC      123.2VAC     0.05 A                55.8VDC      122.9VAC     0.05 A 46.5VDC      99VAC     1.5 A 49.1VDC      108.2VAC     0.5 A 49.8VDC      109.3VAC     0.5 A 43.5VDC      95VAC     2 A 43.5VDC      96.2VAC     1 A 44.6VDC      98.1VAC     1 A 37VDC      81VAC     3.4 A(MAX) 42VDC      92VAC     1.16 A(MAX) 43VDC      94.3VAC     1.17 A(MAX) Readings for full circuit are not accurate as i was not able to take readings on specific current value as i have taken for half circuit I have some doubts now despite of changing the wire which can handle 10amps psu is not able to supply even 7A I have strong doubt about the center tap transformer i think i have read somewhere by connecting wire 1 and 3 we get half the rated current is that true ? All the connections are rigid now so there will be no leakage current think so... TWO MORE REPLIES ARE ADDED BECAUSE I WAS NOT ABLE TO UPLOAD ALL THE IMAGES BECAUSE OF POST RESTRICTIONS

[VickySalunkhe]

Two more images

need to upload two more
was not able to do so because of post restriction
sorry for inconvenience