Overvoltage protection design ideas

[Longbow]

Re: Overvoltage protection design ideas

There IS an ideal solution to your problem, as described. A box of units cobbled together is not going to require high level engineering for you to get into operation. In fact, at this point you don't even know if your unit will function as expected over a long haul. You have a very common requirement for inrush protection. In this case you are not too worried about overloading the mains, but simply providing a soft start situation for your equipment. Thermistors are used industry-wide on all types of equipment and I recommend that solution because it is relatively simple, inexpensive and effective. The only difficult part is finding the correct resistance value and dissipation.

[Dannyx]

Re: Overvoltage protection design ideas

So basically there is no "ideal" solution and it's all about compromise from what I gather. The simplest form is to just put a zener diode across the thing you want to protect and have it blow the fuse if it exceeds the zener voltage. In a car, I assume this wouldn't work to protect a small electronic device because the thing would blow fuses every time when there's a spike over the zener voltage like when the car starts. Makes me wonder how headunits and amps are designed, since those connect straight to the battery, so they're constantly exposed to ramps and spikes.

[redwire]

Re: Overvoltage protection design ideas

LTC4366 used on a 24V truck electrical system, and they all died.
Lovely datasheet and the IC looks good but it cannot take any negative input voltage spikes- common occurrence in a car or truck. Have to add a bunch of circuitry for that, Fig. 8.

You can either clamp an overvoltage spike, turning it into heat in some component (i.e. TVS, MOV etc.); or you can switch off power or ride-through the overvoltage like the LC4366. The MOSFET gets very stressed in linear-mode trying to regulate say 24VDC out and 250VDC input spike.

[Badee]

Re: Overvoltage protection design ideas

that sure is interesting. any new updates about it?

[Dannyx]

Re: Overvoltage protection design ideas

That LTC chip looks very interesting and fit for the purpose. Had a look at its datasheet - looks complicated in there but I'm sure I'd be able to pull through. Soldering hasn't been an issue to me for quite a few years on, so no worries there It actually HAS to be small, since space inside my enclosure is very limited....I'd still need the series pass element to be bolted to a heatsink which requires additional space, so I'm not sure if it's doable at the end of the day...

[ben7]

Re: Overvoltage protection design ideas

The simplest thing I can see doing is to connect a suitably sized power transformer across the AC input before the UPS transformer, and connect the output of the power transformer in series, anti-phased, with the UPS transformer primary winding. This will reduce the input voltage that the UPS transformer sees, thus reducing it's output voltage.
(Note that connecting the output of the power transformer in-phase with the AC will INCREASE the voltage the UPS transformer sees.)

Of course, this might cause more voltage drop during high loads, but it will give you headroom so that if the mains input is higher, you won't violate the DC-DC regulator input voltage ratings.

As for other solutions, there are ICs made by some manufacturers that can drive FETS, used as electronic fuses, or surge stoppers.
Check the LTC4366 as an example.

-Ben

P.S. In the case of the LTC4366, you'll need to make sure the FET can handle the power dissipation if/when there is a surge. So pick a FET that has a large SOA (Safe Operating Area). You'll need to make sure you set the overvoltage timer, so that the transistor is kept under it's SOA. (SOA varies, depending on time and power dissipation.)

P.S.2. The LTC4366 is a small chip, dunno if you would be able to solder it! Linear Technology has some other similar chips, possibly in a larger package, so you should check out their site.

[Curious.George]

Re: Overvoltage protection design ideas

[QUOTE=Dannyx;794687]The automotive power system discussion you initiated, despite digressing slightly from the original topic, is VERY interesting, as me and my colleague often tackled it and had slightly different views. For instance, I must admit I'd have lost the argument, because I used to believe that when the car starts, the huge load caused by the starter makes the overall voltage drop (which it does, no doubt){/QUOTE]

Considerably. And, the drop can vary with the state of the battery, ambient temperature (cold weather halves the battery's capacity and doubles the apparent size of the engine, behind the starter), integrity of connections (think: corrosion), etc.

but never considered that it actually "kicks back" and causes a "+" surge. We'd always discuss the reason of fried poorly designed car accessories, especially cigarette lighter chargers, and I'd always claim that there's no way they got killed by OVERvoltage, since it doesn't (shouldn't) occur, but apparently there is some truth to this so I should reconsider....makes a whole lot of sense now.

This is also true when driving relays/solenoids, etc. (think: hood/trunk releases, door locks, etc.)

I believe it widely depends on the car, and we assume modern ones have more sophisticated power systems in them, though even older ones SHOULD have.....something to at least reduce this effect - think of a diode across the starter...stupid and utterly rubbish, of course, but just for the sake of argument something along those lines

A one-size-fits-all solution isn't practical. Cars vary. Cars are "maintained" by folks with a variety of different skillsets, etc. And, owner/operators aren't particularly saavy, either (ever see someone "jump" a car by putting the cables on BACKWARDS?? If the stuck vehicle's battery is truly shot, it won't put up much of a fight against the fully charged battery that's trying to reverse it!)

And, failure of one "massive snubber" would be a disaster for all the other bits of kit that could be compromised by a voltage surge (newer vehicles have electronics IN each headlight, ECU, ABS, window controller, etc.)

So, when designing for that environment, you condition power coming into your "module" to protect against the crap that could exist outside. Then, protect yourself from any bad things you might do within your module (e.g., RCD snubbers across all of the door lock solenoids that you are driving)

Then, all you have to worry about is temperature, corrosive fluids, someone accidentally wacking your module with a hammer, ... fun stuff!

[petehall347]

Re: Overvoltage protection design ideas

auto-transformer . check min against max of supply and working voltages of unit .

[Dannyx]

Re: Overvoltage protection design ideas

[Note I'm speaking in generalities and not addressing the specifics of your design]

Correct, I know that's your style

The automotive power system discussion you initiated, despite digressing slightly from the original topic, is VERY interesting, as me and my colleague often tackled it and had slightly different views. For instance, I must admit I'd have lost the argument, because I used to believe that when the car starts, the huge load caused by the starter makes the overall voltage drop (which it does, no doubt) but never considered that it actually "kicks back" and causes a "+" surge. We'd always discuss the reason of fried poorly designed car accessories, especially cigarette lighter chargers, and I'd always claim that there's no way they got killed by OVERvoltage, since it doesn't (shouldn't) occur, but apparently there is some truth to this so I should reconsider....makes a whole lot of sense now. I believe it widely depends on the car, and we assume modern ones have more sophisticated power systems in them, though even older ones SHOULD have.....something to at least reduce this effect - think of a diode across the starter...stupid and utterly rubbish, of course, but just for the sake of argument something along those lines

[Curious.George]

Re: Overvoltage protection design ideas

When talking about said load, are we referring to what's attached to the transformer or to what's attached to the PSU module that's ALREADY attached to the transformer ?

For the purposes of the protection circuit discussion, the load is whatever is "downstream" from your switch. When you abruptly open the switch, you are "dumping" the load. This can have repercussions for the "supply" (whatever is upstream from the switch) and the "load".

If the supply is a "commercial power supply/module", it may not be designed to tolerate such a dramatic change in the load (this is a separate design criteria besides volts, amps, weight, operating temperature range, etc.) E.g., some supplies are designed with a minimum load in mind and if that load is not present, the supply misbehaves.

The load can also see unexpected conditions on the power rails if the supply suddenly "disappears".

Folks thinking about designing automotive products often think the electrical "noise" (spark plugs, etc.) is the challenging aspect of that environment (ignoring the temperature range). But, in fact, the "load dump" that occurs every time you start the car (and the starter motor STOPS spinning) is the real hazzard. Instead of designing for ~16V (a 14.4V charged battery), you have to deal with this huge inductive voltage spike appearing on the "12V" power rail. If the battery is brand-spanking new (low output impedance), it can help tamp this down (assuming the wiring takes this into consideration). But, as the battery ages, its output impedance increases to the point where it has less effect on damping that spike.

[The battery typically won't care about the spike but the electronics in your infotainment system probably will!]

Either way, I can imagine that if the power module is powering something and it suddenly gets disconnected, it can cause a spike to show up at the input (at the bridge rectifier's output that is - the very first stage of the DC section). Is this why you were asking ?

I would imagine disconnecting the input to the power module would be have little consequences. But, you'll have to explore that possibility by looking at the characteristics of the "load" that the module presents to whatever supplies it with power. Likewise, you have to consider whether you are using high-side switching or low-side and any sneak paths that can remain when the switch(es) are open.

[Note I'm speaking in generalities and not addressing the specifics of your design]

[Dannyx]

Re: Overvoltage protection design ideas

When talking about said load, are we referring to what's attached to the transformer or to what's attached to the PSU module that's ALREADY attached to the transformer ? If we're talking about the transformer, then the load is the module itself and the bulk caps, so I believe it's a capacitive load IMO.
If we refer to the load of the module, then it's intended to power various devices, ranging from inductive ones like coils and motors to resistive ones. Come to think of it, I really should check if the module has a diode on its output to protect it from coils and stuff trying to discharge back into the supply....

Either way, I can imagine that if the power module is powering something and it suddenly gets disconnected, it can cause a spike to show up at the input (at the bridge rectifier's output that is - the very first stage of the DC section). Is this why you were asking ?

[Curious.George]

Re: Overvoltage protection design ideas

Good day folks. Some of the wonderful people here may know that a while back I mucked about with one of those Ebay PSU modules and I'm just about ready to wrap the build up now, having completed a nice case for it, until I thought of something: so I'm powering it with a UPS transformer which puts out 36v, which is rectified then fed into the input pins of the module. The module says it can handle up to 50v, which I can only hold as correct, since the input does get fairly close to that (around 48-49v) and I haven't had any funny issues during testing. However, I definitely don't want to push it and I imagine if the mains input to the transformer goes up slightly (say 240v instead of 230v), the output would also increase since there's no regulation on the output of that rectifier.

What is the nature of your load as it will also impact the instantaneous voltages that you see on the power supply rail?

So I had a look around to see how I could avoid such issue and found this....Seems simple enough and I actually thought of something like that even before running actual searches: get a zener close to the intended maximum voltage and a FET and build up that little circuit. If the output gets over the zener threshold, the zener conducts, the FET closes and blows the fuse...would this work ? Trouble is I'm not sure how stable my mains voltage really is, which means that if I set the "trip" voltage (Vz) to be too "strict", this setup would blow fuses all the time whenever the unregulated output goes a hair over Vz and the FET becomes conductive which would be a pain....imagine that happening when you're powering something on the bench and it just cuts out on you like *poof*... If Vz is too high, the output is already too high for the module also and the circuit becomes useless since it trips too LATE....

See the above question.

Approach no. 2 is this: I also thought of modifying this circuit a bit and build a regulator to ensure the supply NEVER goes above 50v like this: feed the unregulated 50v into a transistor, then put the zener on the base, so now, the transistor is conducting all the time under the value dictated by the zener - something like 48v (if such a value exists).

You may not be able to do this without carefully selecting a transistor for a high enough beta as the zener will limit the amount of base current you can provide to the pass transistor. Remember, the zener now has ~48V across it so any current through it (multiplied by 48) will determine the amount of power that IT dissipates! This puts a limit on the high end for the zener current.

I know that there must be a minimum current flow through the zener in order for it to regulate, so if my input is 48v, the zener value will have to be lower than that, but I just chose a round value for argument's sake. Problem no.2 is that the transistor would have to be HUGE. Correct me if I'm wrong, but at 15A which the maximum possible current draw through this PSU module (let's just leave it at that, since it may not be achievable in reality) the series transistor would dissipate over 700W (48v*15a = 720w !), so it's not practical in the slightest. It's unlikely I'll ever need that kind of power, plus I doubt the module could deliver it reliably to begin with, but like I said: worst case scenario for example purposes.

The transistor dissipates whatever the drop across it is times the current through it. So, if you're only dropping a few volts across it, then the power dissipated is "a few volts * 15A". The only time it would dissipate ~700W would be if the drop across it was ~48V (i.e., if the output was shorted!)[/QUOTE]

You appear willing to tolerate the power source being disconnected in the event of an OV condition (instead of trying to clamp it to a safe voltage).

Why not put a "switch" in series with the supply and open it as soon as the voltage climbs out of spec? Of course, a relay would be slow but you can use a pass transistor or a FET for the job and get near instantaneous disconnect.

Note that you have to also consider that the voltage on the output isn't always the same everywhere along the wire. There are effectively propagation delays et al. caused by wire inductance, wire resistance, etc. that cause the voltage seen at point A to differ from that at point B -- potentially significantly! So, the point at which you are monitoring may not reflect the voltage seen by some critical bit of circuitry that you are presumably trying to protect. And, the voltage you see now may not reflect the voltage that is seen after the switch is opened (esp if you are "dumping" -- the sudden disconnection of -- an inductive load).

[stj]

Re: Overvoltage protection design ideas

you can get circuit-breakers that fit into the same hole as a fuseholder.
or you could use the hole for a trip indictator lamp.

[Dannyx]

Re: Overvoltage protection design ideas

I just measured my rectifier's output again to establish once and for all what I'm working with exactly and it's around 48v, since I wasn't sure exactly what it was. It's lower than the maximum input of that Ebay module (50v), but still a bit close for comfort....ok, realistically it can probably take more than 50v for brief moments, but I'm not quite willing to test it The PSU runs fine, I tested it, it's just that I'm thinking of spikes in the AC line causing spikes on the secondary too.

The original idea was to simply cut the voltage entirely when the threshold is reached, but then I started thinking more and more about some sort of active regulator that "clips" the excess voltage if it goes above 50v. Trouble is I couldn't find a viable solution that can operate at such high current and voltage (50v at 15a would be very demanding and space is also scarce so there's little room for ventilation and heatsinking). Assuming there WAS room for all that, I thought about using a zener to drive a MOSFET, but a gate voltage of 47v (the closest zener value) would exceed the maximum VGS of most FETs, making the task impossible.

There's another idea I had which still uses a zener, but couldn't find such design anywhere, so either I'm a genius and a pioneer or, OBVIOUSLY, the idea wouldn't function and is bad to begin with, hence why it's not presented anywhere: instead of an "N" series pass element, how about a "P" type and a zener AFTER it. When the voltage exceeds 50v, the excess Vin-Vz closes the base/gate of the pass element, shedding away that excess voltage....not sure if this would work in the slightest - there are probably many many things wrong here which would result in immediate destruction or no response at all.

I also thought about Op-amps for a while, but I ran into the same issue: driving the series pass element at considerable voltage, plus no op amp I researched can go any higher than 35v...

Switching regs are the norm nowadays, obviously...

[sam_sam_sam]

Re: Overvoltage protection design ideas

It would depend on what the rating on the resettable fuse there are two rating one working amperage and max rating if you hover around the working amperage might not trip for a long time where as regular fuse will blow and no power will be flowing where as a resettable fuse will still have current flowing through it when it trips

So I would use both but what you have to figure out is what the regulator fuse amperage needs to be to protect the power supply or the equipment in case the resettable fuse is to slow to trip

I have used resettable fuses before in power supply but I select one where the trip point is and use them in switching power supply where when it over current shuts down the power supply ( or the device that it is powering) the only problem with this is if the switching power reset itself and put power on it again)

I have a USB power supply that has 5 amp power supply where the USB cord shorted out at tip
that did not have a resettable fuse but after that happened I put in a 2 amp trip current which is about a little more than one amp working amp which lowers the current a little bit because the resistance goes up when being over loaded and heat up a lot just before it trips

I cooked the USB connector that was being over current and next USB connector was damaged if I had a resettable fuse it would have damage the resettable fuse instead

We have some crane battery operated magnet for pick up metal plate the 3.15 amp glass fuse would some time blow for unknown reason this has a transformer in it

Well I finally figured why this was happening it was that the extension cord that they were plugged into the connectors contact were worn out

I ended up hard wiring outlet near where they are sitting to be charged

I was going to put resettable fuse in line with the glass in these magnets if had not figured out what was happening

One note they do make 250 volt ac resettable fuses the maximum rating that I have seen is 3 amps and lower amperage one as well

One note it is some what hard to 15 amp resettable fuses that rated over 16 volts

Here is a data sheet for one these resettable fuses

https://cdn.badcaps-static.com/pdfs/...c3444c1a36.pdf


I hope this helps

[Dannyx]

Re: Overvoltage protection design ideas

How about using a resettable fuse for this purpose ? Trouble is, I already drilled holes for the traditional cartridge-style fuse holders, so what would happen if I had a PPTC AND a glass fuse in series ? Which would blow first ? I assume the glass one would still go, thereby making the resettable one useless....

[Dannyx]

Re: Overvoltage protection design ideas

What do you mean by over size resistors? You can have resistor and pot to adjust the trip point, we are talking about very low current to trip the gate.

I was thinking of the op-amp idea: since the output voltage is almost 50v and I'd set a low reference voltage on the - input of the op-amp like I discussed, it would take a resistor divider with very high values to step it down from 50v to like 2-3v close to the reference, but I actually calculated the values shortly after and they could be like 100k and 5k...

I'm not sure whether to go with the linear regulator idea or with the " full stop" idea.

[budm]

Re: Overvoltage protection design ideas

What do you mean by over size resistors? You can have resistor and pot to adjust the trip point, we are talking about very low current to trip the gate.

[Dannyx]

Re: Overvoltage protection design ideas

Use SCR (or SCR equivalent circuit using Transistors) as the latching device in DC circuit.
Example of how it is used:
http://www.electronics-tutorials.ws/...r-circuit.html
https://dmohankumar.wordpress.com/20...esign-note-21/

I see: a combination of relay and SCR. I assume in the schematic in the second example link, my "fault" signal would go into that free "input voltage" pin. I just ran into another issue of obtaining a small sample from a 48v rail, since a resistor divider would have to be "oversized" to drop it down to 2-3v. I may just go with the zener again.

[budm]

Re: Overvoltage protection design ideas

Use SCR (or SCR equivalent circuit using Transistors) as the latching device in DC circuit.
Example of how it is used:
http://www.electronics-tutorials.ws/...r-circuit.html
https://dmohankumar.wordpress.com/20...esign-note-21/