....

Power dissipation issues:
You need to look at power dissipation when the transistor is saturated. In many datasheets, typical saturation curves are shown where Ib=Ic/10. Basically, you want to stick with that formula; whatever you expect to see as the collector current, provide 1/10 of that for the base current. If you fail to provide enough base current, the transistor will drop out of saturation, and power dissipation in the transistor will increase dramatically.

...
...

I struggle to understand this, but to no avail so far....

Is it not the main function of the transistor (at least in this circuit) to amplify the current? So that I(base) x hFE = I(collector)?

With my very limited understanding I would say it is important to keep the transistor out of saturation, so that the amplification occurs as expected.

What am I missing?

What would it mean if I say: "The power dissipation of the transistor is too high"? Would that be the same as if I said:
"The maximum power rating for the transistor is beeing exceeded"?

 

I struggle to understand this, but to no avail so far....

Is it not the main function of the transistor (at least in this circuit) to amplify the current? So that I(base) x hFE = I(collector)?

Take a look at the datasheet for the transistor(s) that you are considering.

Note that for the hFE specification, Vce is given as being 5v, 10v, etc.

Since P=EI, you need to keep either/both E and I low enough so that you don't approach your transistors' power dissipation limits.

With my very limited understanding I would say it is important to keep the transistor out of saturation, so that the amplification occurs as expected.

What am I missing?

You're missing the Vce specification given with hFE.

What would it mean if I say: "The power dissipation of the transistor is too high"? Would that be the same as if I said:
"The maximum power rating for the transistor is beeing exceeded"?

You really don't want to approach the maximum power dissipation rating for the transistor, unless you like smoke.

A transistor is said to be in saturation when a further increase in base current will not appreciably reduce Vce. The "rule of thumb" here is Ib=Ic/10. It's also what you will see for the Ib spec for virtually all transistors on the saturation plots.

By keeping Vce(sat) low, you minimize power dissipation in the transistor. Where you get in trouble with Pd is when Vce gets excessive; ie: transistor is out of saturation, and Pd goes up correspondingly.

 

Take a look at the datasheet for the transistor(s) that you are considering.

Note that for the hFE specification, Vce is given as being 5v, 10v, etc.

Since P=EI, you need to keep either/both E and I low enough so that you don't approach your transistors' power dissipation limits.



You're missing the Vce specification given with hFE.



You really don't want to approach the maximum power dissipation rating for the transistor, unless you like smoke.

A transistor is said to be in saturation when a further increase in base current will not appreciably reduce Vce. The "rule of thumb" here is Ib=Ic/10. It's also what you will see for the Ib spec for virtually all transistors on the saturation plots.

By keeping Vce(sat) low, you minimize power dissipation in the transistor. Where you get in trouble with Pd is when Vce gets excessive; ie: transistor is out of saturation, and Pd goes up correspondingly.

Thanks for the explanations - but I'm afraid I still don't understand. I lack basic understanding of semiconductor technology.

So I simply went with the P=EI approach and used the simulation applet to check all possible combinations (hopefully all) failure modes for maximum transistor power dissipation. I identified the maximum power point by using the scope function for each transistor, set to "Show Vce vs Ic" .
Then I calculated the maximum power dissipation.
The maximum power dissipation occurs when the imbalance between battery segments is just a little too weak to trigger the relevant opto-darlington. The highest power dissipation I could find was 34mW. That is less than half the rated input power dissipation of 80mW.
The output power dissipation should be negligible because there will only be about 12mA max flowing (it's rated to 400mA).

This is what the latest circuit diagram looks like:

And here the simulation of the "core" of the circuit and the code for the simulation applet at http://www.falstad.com/circuit/ :

$ 1 0.0010 0.529449005047003 55 5.0 50
t 240 128 304 128 0 1 -31.912614657462626 0.5697241042634721 192.0
t 192 176 256 176 0 1 -0.18515443923846855 0.6151787222655717 192.0
t 240 224 304 224 0 -1 50.71936672391769 -0.23060905724056813 186.0
w 240 128 192 128 0
r 128 128 128 80 0 10000.0
w 192 128 128 128 0
w 304 144 304 176 0
w 304 208 304 176 0
w 688 144 752 144 0
w 688 208 752 208 0
w 752 272 688 272 0
w 752 80 688 80 0
178 512 160 544 160 0 1 0.2 1.0086981205859048E-9 0.25 1000000.0 7.5E-4 10.0
178 512 320 544 320 0 1 0.2 2.4127439035570575E-9 0.25 1000000.0 7.5E-4 10.0
178 512 416 544 416 0 1 0.2 6.67405282710902E-4 0.25 1000000.0 7.5E-4 10.0
r 464 368 512 368 0 24000.0
178 656 320 704 320 0 1 0.2 0.002399880006089693 0.25 1000000.0 0.0010 5000.0
x 712 325 753 328 0 12 Relay 1
x 716 335 742 337 0 8 NC/NO
x 646 483 703 487 0 16 12V DC
w 240 224 192 224 0
w 352 176 304 176 0
v 688 448 656 448 0 0 40.0 12.0 0.0 0.0 0.5
x 733 410 827 414 0 16 Warning LED
x 738 435 793 439 0 16 on dash
x 823 87 911 96 0 40 IDeA
x 769 111 949 114 0 12 (Imbalance Detection Apparatus)
x 810 128 946 131 0 12 Vectrix version - untested
x 782 162 963 166 0 14 SSR 1-4 = ASSR-1228-302E
x 779 231 944 235 0 14 12V SMPS: 4A continuous
x 781 187 925 191 0 14 PNP : BC856 hFE=186
x 781 210 925 214 0 14 NPN : BC846 hFE=192
x 705 267 733 270 0 10 Tab 1
x 698 202 732 205 0 10 Tab 35
x 696 141 730 144 0 10 Tab 69
x 701 74 741 77 0 10 Tab 103
w 656 368 656 384 0
w 656 384 640 384 0
d 640 384 640 352 1 0.805904783
v 752 256 752 224 0 0 40.0 51.33 0.0 0.0 0.5
v 752 192 752 160 0 0 40.0 50.95 0.0 0.0 0.5
v 752 144 752 112 0 0 40.0 51.33 0.0 0.0 0.5
w 192 128 192 144 0
w 192 144 224 144 0
w 224 208 192 208 0
w 192 208 192 224 0
w 128 224 192 224 0
174 128 128 160 160 0 1570.0 0.5 Resistance
174 128 192 160 224 0 5840.0 0.5 Resistance
w 160 144 160 176 0
w 160 208 160 176 0
s 624 64 688 80 0 0 false
s 624 128 688 144 0 0 false
s 624 192 688 208 0 0 false
s 624 256 688 272 0 0 false
w 224 144 240 144 0
w 240 144 256 144 0
w 256 144 256 160 0
w 256 192 256 208 0
w 256 208 224 208 0
w 192 176 160 176 0
x 187 172 240 175 0 12 BC846(3)
x 231 124 284 127 0 12 BC846(1)
x 229 376 282 379 0 12 BC846(2)
x 183 428 236 431 0 12 BC846(4)
x 234 223 287 226 0 12 BC856(1)
x 234 478 287 481 0 12 BC856(2)
w 752 112 752 80 0
w 704 336 720 336 0
t 224 432 256 432 0 1 -0.20314499213033343 0.6151674680434169 100.0
t 272 384 304 384 0 1 -50.6974156964314 0.25252637358736507 100.0
t 272 480 304 480 0 -1 34.73981307552468 -0.5657860865863853 100.0
174 128 384 160 416 0 1570.0 0.5 Resistance
174 128 448 160 480 0 5840.0 0.5 Resistance
w 160 400 160 432 0
w 160 432 160 464 0
r 128 368 128 336 0 10000.0
r 128 528 128 496 0 10000.0
r 368 128 368 160 0 10000.0
r 464 112 512 112 0 24000.0
178 512 64 544 64 0 1 0.2 7.849921382031156E-4 0.25 1000000.0 7.5E-4 10.0
w 576 432 544 432 0
w 576 336 544 336 0
w 576 336 576 208 0
w 576 176 544 176 0
w 576 176 576 80 0
w 576 80 544 80 0
w 560 144 560 64 0
w 560 64 512 64 0
w 560 416 512 416 0
w 560 416 560 320 0
w 560 320 512 320 0
w 560 320 560 192 0
w 560 160 512 160 0
w 560 160 560 144 0
w 512 336 512 352 0
r 512 192 480 192 0 24000.0
w 432 240 432 192 0
w 512 464 496 464 0
r 512 448 480 448 0 24000.0
w 480 272 480 256 0
w 480 256 480 208 0
r 128 240 128 272 0 10000.0
w 128 240 128 224 0
w 128 272 192 272 0
w 128 384 128 368 0
w 128 496 128 480 0
r 368 448 368 480 0 10000.0
w 496 528 496 464 0
w 496 528 528 528 0
w 496 528 448 528 0
w 368 496 368 528 0
w 352 528 128 528 0
w 576 208 576 176 0
w 560 192 560 160 0
w 512 96 512 80 0
w 512 80 464 80 0
w 464 80 464 32 0
w 320 432 352 432 0
w 304 400 304 432 0
w 304 432 320 432 0
w 304 432 304 464 0
w 304 496 320 496 0
w 224 432 208 432 0
w 208 432 160 432 0
w 256 448 256 464 0
w 256 464 192 464 0
w 192 464 192 480 0
w 256 416 256 400 0
w 256 400 192 400 0
w 192 400 192 384 0
w 272 384 192 384 0
w 192 384 128 384 0
w 272 480 192 480 0
w 192 480 128 480 0
w 752 256 752 272 0
w 752 224 752 208 0
w 384 240 304 240 0
w 368 256 368 176 0
w 480 192 432 192 0
w 384 240 432 240 0
w 352 336 128 336 0
w 448 272 368 272 0
w 368 272 192 272 0
w 352 432 368 432 0
w 448 528 368 528 0
w 368 528 352 528 0
w 464 368 304 368 0
w 752 208 752 192 0
w 752 160 752 144 0
w 368 448 368 432 0
w 368 496 368 480 0
w 464 32 624 32 0
w 624 32 624 64 0
w 608 128 624 128 0
w 592 256 592 128 0
w 592 128 608 128 0
w 608 192 624 192 0
w 608 192 608 272 0
w 576 432 576 384 0
w 656 448 608 448 0
w 608 432 608 320 0
w 560 320 608 320 0
w 608 320 656 320 0
w 640 352 656 352 0
w 688 432 688 384 0
w 688 384 656 384 0
w 576 336 640 336 0
w 640 336 640 352 0
w 576 384 576 336 0
162 720 400 720 432 1 2.1024259 1.0 0.0 0.0
r 720 352 720 384 0 1000.0
w 720 448 688 448 0
w 720 336 720 352 0
w 720 384 720 400 0
w 464 448 480 448 0
w 464 448 464 496 0
w 464 496 320 496 0
w 352 336 432 336 0
w 352 176 368 176 0
w 416 256 368 256 0
w 432 256 416 256 0
w 720 432 720 448 0
w 688 432 688 448 0
w 608 432 608 448 0
w 448 272 464 272 0
w 512 336 496 336 0
w 496 336 432 336 0
w 608 272 496 272 0
w 464 272 480 272 0
w 480 272 496 272 0
w 512 208 480 208 0
w 496 336 496 256 0
w 592 256 496 256 0
w 496 256 432 256 0
w 368 272 368 432 0
x 468 139 547 142 0 12 ASSR-1228(1)
x 463 395 542 398 0 12 ASSR-1228(2)
x 516 95 521 97 0 9 1
x 519 189 524 191 0 9 3
x 516 108 521 110 0 9 2
x 519 206 524 208 0 9 4
x 549 174 554 176 0 9 5
x 548 159 553 161 0 9 6
x 550 79 555 81 0 9 7
x 553 62 558 64 0 9 8
x 518 349 523 351 0 9 1
x 517 366 522 368 0 9 2
x 518 463 523 465 0 9 4
x 520 447 525 449 0 9 3
x 549 429 554 431 0 9 5
x 553 317 558 319 0 9 8
x 551 335 556 337 0 9 7
x 550 414 555 416 0 9 6
w 528 528 592 528 0
w 592 528 592 304 0
w 592 304 624 304 0
w 624 304 624 256 0
w 128 80 368 80 0
w 368 80 464 80 0
w 464 112 304 112 0
w 368 176 368 160 0
w 368 128 368 80 0
o 39 64 0 34 80.0 0.00625 0 -1
o 40 64 0 34 80.0 0.00625 0 -1
o 41 64 0 34 160.0 0.00625 0 -1

 

How would you build the first prototype for this circuit?

Would it be worth the effort to make a PCB - or would it be better to solder cables to the copper side of a prototype board?

 

I think that the current breaking capacity of the relays RLY2 and RLY3 will almost be exceeded when switching off the full 102s battery voltage.
See the curve on page 1 of this datasheet: http://www.tycoelectronics.com/comm...ype=Specification+Or+Standard&DocLang=English

RLY3 is supposed to do the inrush current limiting and is less critically affected by this. The 100 ohm inrush limiting resistor limits the maximum current draw through the RLY3. The absolute maximum would be 153V/100 ohm = 1.53A.

Do I read the data sheet correctly when I calculate and interpret it like this:

With 0.75A through RLY 3 the voltage drop across the inrush resistor will be 100 ohm x 0.75A = 75V. That leaves 153V-75V=78V across the load which is sucking the 0.75A out of the battery. That data point is just underneath the Max DC load breaking capacity curve in the above linked data sheet.
Or is this a wrong way of looking at it? Would I need to look at 153V under 0.75A load?

RLY2 is even closer to the maximum DC current breaking capacity curve (if it can even be calculated like I did above).

Now to the main question of this post: Can I increase the DC current breaking capacity of these two relays by adding a capacitor across the input and the switched output as in the schematic below?

If that approach is not fundamentally flawed somehow, then how do I choose the appropriate capacitance for C1 and C2?

If these caps are too big, then switching the relay to "ON" could cause too much inrush current through the relay and damage the contacts - right?

And how about the "Bleeding Resistors" 1 and 2? Are they required? They seem to defeat the purpose of the relays, which is to completely shut down the electric system when it is turned off (the original Vectrix draws 7mA continuous form it's battery, draining it over several months to a voltage at which the stock charger cannot begin a charge any more).

 

I have had a play with the ExpressPCB program, below are the results.

There are probably still some errors in there, I need to check them again and thoroughly.

A question for those who have done this before: Roughly how much would it cost to have a single board like this produced?

 

I would make it myself for around $30 if you had to start from scratch.

Laser printer,
Iron (or Laminator)
weekly gloss newsprint type advertisement paper
a blank piece of FR4 double sided PCB material.
Some Ferric Chloride or Hydrogen Peroxide/Muriatic Acid solution.

Bill_Marsden just posted about his results with this method.

Doing double sided boards are a little tricky at first. Make registration marks to line up both sides if possible, and do "edge of material" lines.

 

Before you make your board, better make sure your traces are large enough to carry the maximum battery current expected, or your traces will act as fuses and melt.

Roman Black hosted UltraCads' free PCBtemp on his website:
http://www.romanblack.com/pcbtemp.htm
UltraCad no longer supports PCBtemp; they now sell a more capable version. However, this freeware version should keep you from burning up your boards' traces.

Did you know that ExpressPCB can provide an instant quote for making a prototype board?
Click on "Layout", then "Update pricing file"
Once the pricing file has been updated, click on "Layout", then "Compute board cost".En
Enter your location, select the options you desire, and it'll give you a price at the end.

 

Thanks guys!

ExpressPCB says US$125,- for two boards (no silkscreen layer) including $55,- for shipping to Australia.
Should be here in about 4 business days from ordering.

Making my own is an interesting option, I'll look into that. A trip to the local electronics hobby shop with the PCB layout should help - they sell DIY board making kits.

For now, the board needs careful checking and probably bit of refinement.

The traces are large enough unless I misunderstood something really badly.

According to the "PCB Design tutorial" by David L. Jones they are a lot larger than they need to be. The over 200A being drawn from the battery during acceleration do not go through this board. The maximum current spike will be the 153V/100 ohm = 1.53A inrush current when RLY 3 switches. And all connections to the main battery are through fuses with max 3.1A rating. I hope that covers it!

I'm actually more worried about having sufficient spacing between the traces - so that the 153V DC don't make it into the 12V parts somehow.

 

Does anyone have a good idea how to integrate a higher cutoff-voltage for the DC/DC converter into the IDeA? I contacted the manufacturer for the DVC75 which I intend to use, but they need at least an order for 50 DC/DC converters to make a custom version.

The standard-DVC75 http://deutronic.com/fahrzeugwandler/75-watt-pot-getr_data_de.pdf works with input voltages from 56V-154VDC; I would like it to quit when the voltage falls below 92VDC.

It is unlikely that no imbalance will occur when the battery voltage drops to around 0.9V/cell= 91.8V and therefore it is likely that the "Imbalance Detection Apparatus" will turn the DC/DC converter off when in "Automated Deep Discharge" mode. But I would like to have an independent safeguard against further discharge that turns it all off at about 92V.

Any ideas how to do this would be much appreciated!