# Tag Info

45

Unless you can guarantee that all the contacts will close and open at exactly the same instant of time the only safe current you can assume is 2A - that is, the capacity of the first contacts to close, or the last contacts to separate.

43

A thermal imager is very useful in this situation. They are not terribly expensive these days. If you don't have one, a bare finger can be substituted for a sensor. ADDITION: There are also Thermochromic Paints for different temperature ranges that can be used to identify hot spots.

42

Sixty-four little relays were turned on by a key; One soon welded shut and then there were sixty-three. Sixty-three little relays started glowing bright blue; One of them turned black and then there were sixty-two. Sixty-two little relays bore of amps a metric ton; One said he'd had enough and then there were sixty-one. ... (I can't be bothered to write ...

33

Hint: resistance is not just a matter of cross section, but also of length. Would you expect the jumper cables to work if they were say, 10 meters long? What about 100 meters? You got my point. Even if the contact surface is very small, the effective length of the contact is very short. One could argue that having flat, rounded surfaces would lead to a ...

29

I haven't seen anybody else mention temperature. Perhaps you left the default 10 degree rise in the online calculator? That's pretty conservative. A 20 degree rise isn't that bad in a lot of situations. And if you aren't running the highest current continuously, it's quite possible even a higher temp rise would be acceptable, since it will have time to ...

29

Here's the datasheet that should be linked from your question. I shouldn't have to look for it. Each mosfet should handle 32 Amps That's with $V_{GS}=10$V You set $V_{GS}$ to $5V×\frac{R_2}{R_1+R_2}=4.54V$, you really want as much voltage here as you can (5V seems to be your maximum). If I were you I would change $R_1$ to 10~50Ω and \\$...

27

You could use a PCB current probe. A search showed up the following. Figure 1. A TTi current probe. The probe-head is held on the PCB trace under investigation and the output can be monitored on an oscilloscope and, presumably, in the case of DC on a multimeter. Figure 2. The probe head. I have never heard of a "Fluxgate Magnetometer" before and I doubt ...

25

Here's what will happen. When you activate your relays for the first time, the first one to close will have its contacts welded together by a massive overcurrent. Soon enough, other relays will close and hopefully distribute that current more or less evenly. When you deactivate your relays, they will all open except the one with welded contacts. Since it ...

24

Assuming the supply is putting out a large current (eg. hundreds of mA) you can follow the voltage gradient from the supply using a voltmeter on its most sensitive range. When you find the minima on the net (or plane) you've found the sink (Vcc) or the maxima on the ground net. Kind of a manual implementation of a steepest descent optimization algorithm.

19

Another solution for boards is to make the trace as wide as you can afford (even if it's narrower than calculations, as long as it's not too much so). Make sure the entire trace is NOT masked, then solder-coat the trace, so you have a nice convex bead of solder running the length of the trace. It's probably not the best solution, but I've seen it used in a ...

19

Ghetto FLIR: Squirt some low boiling point liquid (like flux cleaner) on the board. See where it boils. https://www.youtube.com/watch?v=t5fICjcaJ3E#t=13m19

19

Have you noticed how the clamps get hot after a jump-start? That means power is lost, it ends up in those clamps. You're right the connection isn't ideal so power is lost but not so much that anything melts or explode. What is there to explode anyway? Nothing :-) You wouldn't want to make that huge starting current flow for more than a minute as the clamps ...

19

Do note that this IC has been discontinued and not recommended for new designs, they recommend the ACS723 instead. It also comes on a 30A version on the exact same package. PCB trace calculators rely on basic assumptions: Long distributed traces. Thin conducting layers. Acceptable application temperature rise given board geometry and trace placement For ...

17

My question is this: is this phenomenon something that truly exists, or is it simply an internal "old wives tale" with little to no basis? Well, do the math. If you sink let's say 100 A into a steel conductor of let's say 50 mm² diameter, what is the voltage over 10cm of that conductor due to ohmic resistance? So yes, Ohm's right, and if you put a lot of ...

15

15

It's simple: manufacturers make what customers will buy! It's the same reason why Ferrari won't put a trailer attachment at the rear of their cars... Price is a very important part of this, of course, and price is tied to silicon area, process, yield, and of course packaging. For example, an opamp with +/-12V supplies and 1A output current will dissipate ...

14

Look at page 4, fig.12, graph of safe operating area. That is exactly what you need. You are talking about single pulse, right? You didn't mention any repetition or timing at all. If you open mosfet hard, say Rdson is 0.85mOhms. In case of 1000A the Vds will be less than 1V, so you have to look at the left side of graph. There is no line for 100ms pulse, ...

13

You seem to overestimate the effects of current on conductors. Let's take a regular AWG17 wire for example, which is a mere 1mm² of copper. Guess how much current it can take for 1 second before blowing up? Now check if you guessed right. Jump start clamps have a contact area of about 5mm², and the teeth are cooled by the thermal mass of the rest of the ...

12

There is a spray for that. Google "cold spray electronics" and you will find many hits, like this one Spray the stuff on and watch where it disappears most quickly. That is the point generating the heat - ergo drawing too much current. This stuff has other troubleshooting uses - should be standard in any well equipped electronics lab. I found a video on ...

10

You'll need to couple the square wave with a capacitor to the transformer because standing DC voltages will just cause heat but there is no problem feeding a transformer with a square wave in principle. In practice, if you fed a 60Hz "power" square wave to a transformer, the higher order harmonics in the square wave would mean that a regular AC power ...

10

At 1600A, I expect that you are approaching this problem from the wrong choice of switching components. TO-220 N-FETs soldered to copper boards seems insufficient for this application and the large number of devices means that probability of component failure is high and can be cascading. For motor drive applications, module-packaged FETs may be more ...

10

What you are describing, as i understand, seems completely reasonable. Ground references can often change due to some substantial current flow and finite resistances of the conductors in use.This is simply due to Ohms law. If you can draw an analogy between different parts on your cars chassis to different points on a length of PCB trace we can compare this ...

10

You're not allowed to parallel. You can't parallel through relays because you can't parallel generally. In US NEC, it is disallowed except for currents so large that single wires are not readily available. I don't have a cite but I'm sure the EU model codes have the same rule, since it's a basic physics problem. And even then, each paralleled ...

9

You might try searching for solderable bus bars. They come in various sizes and shapes. You can solder them down to the PCB, and they provide masses of current carrying capability.

9

I don't know how you came up with needing 5 V, but it sounds like a bad idea. You have a big efficiency problem, so spending a bit more on power electronics will make things easier and cheaper in the long run. First, I would not bus around power as low as 5 V because that will require too much current. Having a roughly 48 V bus sounds like a much better ...

9

Your question applies to virtually all high current ICs and power devices. It is clear that the leads themselves are thick copper wires, and the capability goes far beyond 20A. Many power FETs can handle pulse current in the 100's of amps for example. Providing PCB traces to allow this current to flow has almost nothing to do with the capability of the ...

9

The field from 2000A flowing in a conductor will be quite significant, and linear with the current. Just dangle an analogue output Hall effect IC close to the cable. Better still, have two Hall effect ICs, one either side of the wire. Align one up, one down, so they both read the conductor field in the same direction, but read external fields in opposite ...

8

No, your rail shape is not good at all the gap between the rails should be small as possible, and the contact area between the rails and the armature as large as possible. You've maximized the former and minimized the latter. But it's also not the problem keeping it from working. Here are the issues, with number 3 being the most important, but the others ...

8

From the notes underneath that part of the datasheet: Notes a. Repetitive rating; pulse width limited by maximum junction temperature (see fig. 11). Fig. 11: From this, you can see that for 80% duty cycle (Duty factor, D = 0.8) we are beyond the scope of the graph (it only covers D <= 0.5). For that reason, you will need to work within the ...

8

So you have a rail shorted hard to ground. In my experience this is usually a soldering problem. My technique is to hook the rail in question up to a bench PSU. Set the voltage limit at the normal operating voltage of the rail and the current limit to about 1 amp. The current is something of a compromise, too low and the volt drops will be difficult to ...

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