Ways to Destroy a New Power Supply - Page 1
Forum section: electronics / beginners

author: chephato
author_rank: Contributor
timestamp: July 24, 2020, 02:30:18 am
content: I am contemplating getting a Rohde NGE102B as my first dedicated bench power supply. It's a bit pricey yes, but I've spent time looking at most of everything else out there and am fairly unimpressed with the quality. Everything below 200USD seems like cheap Chinese crap and if I'm going to spend upwards of that might as well go for the long run and get something I'll be happy with for a few years and have a good experience using it. Hence the NGE.So, as I am a beginner, is there anything during usage of a power supply that I should be aware of? Never had one, so not sure what will happen with even the simplest of accidents. For example, shorting the leads, my assumption is current will go to max and voltage will drop but do I risk something blowing/heating up too heavily inside? What if I want to blow a capacitor every now and then to get my adrenaline up? Would it be stupid to do that on an NGE-quality supply for risk of blowing it too?The NGE is supposed to have some safety measures so my assumption is it should save me from my own stupidity but shrug, give me some advice, please?Thanks in advance.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: July 24, 2020, 03:23:56 am
content: Decent psus are pretty much made to look after themselves with the current limiting and temperature protection.Yes you can blow stuff up or even light a fire with one and it wouldn't be harmed by doing this. I use to power an electromagnet sometimes to sort screws.One thing I would be careful of is charging up batteries with them. Someone connected a battery backwards to one that I saw, it was a kit psu and all the output stage was destroyed by this. (Wasn't me honest, I repaired it.)I quite like the GW Instek for a mid range linear bench supply.Also a twin channel is handy for quite a few things, if you can afford it.https://www.tequipment.net/Instek/GPE-2323/DC-Power-Supplies/

author: SilverSolder
author_rank: Super Contributor
timestamp: July 24, 2020, 03:07:11 pm
content: Quote from: HackedFridgeMagnet on July 24, 2020, 03:23:56 amAlways put a diode in series with the battery when you do that? - a CV/CC bench supply is an AWESOME battery charger!

author: pigrew
author_rank: Frequent Contributor
timestamp: July 24, 2020, 03:40:35 pm
content: Some switch-mode power supplies are very unhappy with capacitive loads. I've damaged a Keithley 2602 by attaching capacitors. Other's (Keysight B2900A), I've seen become unstable with capacitance. The amount of capacitance doesn't have to be that high, either. Sometimes 100 uF can push them into destruction.I'm not sure what the specs of the R&S NGE102B are, and I didn't see any notes about capacitive loads in its manual, so I guess you're probably safe?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 25, 2020, 01:07:13 pm
content: I've to a simple Gophert 32V5A SMPS thingie and used it as a battery charger.I also connected it in reverse to a car battery. (accidentally of courseand it survived.Unfortunately it has a bit of a weird interface. You can set which digit to change with the rotary encoder, but after some short time it often goes back to the least significant digit. This is very annoying if you want to make a measurement, make a note, then do a measurement with another voltage.Any decent lab power supply should be short circuit proof. In the old days, it was very common to set the current limit to a known value was by shorting the thing and adjust the knob until the value was right.There are some abuse video's of the Korad KA3005. Even Dave reviewed it, and managed to blow one up. It was a design fault and got quickly revised.

author: bdunham7
author_rank: Super Contributor
timestamp: July 25, 2020, 01:48:48 pm
content: Quote from: SilverSolder on July 24, 2020, 03:07:11 pmOne diode voltage drop (and its uncertainty and variability) would seriously affect setting the maximum charge voltage on a Li-ion cell or battery.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 25, 2020, 02:04:57 pm
content: A decent lab power supply does not care about capacitive loads or a voltage source (like a battery) at the output. If it dies from such normal use, just throw it away, it was junk.The extraordinary claim about connecting 100uF to the power supply output destroying the power supply would require extraordinary evidence. (Of course, ignoring complete piece-of-shit power supplies which can die onanything, but OP has said they are not going to buy those, which I think is a good idea.)OP is right not to look at the crap; for some reason, the market is still saturated with those ~$50 to ~$150 linear relay-clicking supplies with varying levels of apparent fanciness in displays etc., these have a track record of doing completely random things like not obeying current limit below about 1V, or not at all, or dying from any disturbance, such as the user trying to do normal things with them.For proper products, Injecting a large, high-energy (not current limited) overvoltage beyond the maximum output voltage specification (for example, connecting the mains accidentally to the output) would likely blow up even a well designed supply.Apart from that, short circuit is not an error condition but normal operating condition, overcurrents by definition cannot happen (unless the supply isalready broken) because lab supplies have CC mode, they usually deal with overtemperature...

author: SilverSolder
author_rank: Super Contributor
timestamp: July 25, 2020, 02:08:53 pm
content: Quote from: bdunham7 on July 25, 2020, 01:48:48 pmGood point. I've found that as the charge current drops, the diode drop tends towards zero so you end up with a longer charge period, but the final voltage is "good enough for Australia" and safe!You could parallel a suitable resistor if getting to an exact voltage (faster) is important.I should have mentioned that I generally charge very small cells e.g. 120mAh or less.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 25, 2020, 02:12:26 pm
content: Quote from: SilverSolder on July 25, 2020, 02:08:53 pmThen this resistor allows reverse current to flow, just limiting it to some lower level (which cannot be arbitrarily low, or the cell would not charge up quick enough again) and if the supply design blows up on reverse current, even quite small current can be destructive.Better just to accept the small voltage drop of the diode, or use a decent supply which can handle voltage at the output.Diode is a good idea if you leave the charging unattended for a long time (not recommended, of course) because if you lose power, even if the supply can handle voltage at its output, it can draw some current, which would eventually drain the cell.

author: exe
author_rank: Unknown
timestamp: July 25, 2020, 04:23:52 pm
content: One thing to watch out is that some power supplies do not like attached battery when switched off. Some power supplies may sink some current when off. Also attaching a battery in reverse may damage it. In other words, be careful when attaching an external power source.Most lab power supplies are slow in regulation, so they won't oscillate with, e.g., external capacitance. More specialized devices (e.g., those with external sensing, or high-speed power supplies) may put some limits, this should be mentioned in the datasheet.

author: ArthurDent
author_rank: Super Contributor
timestamp: July 25, 2020, 04:25:34 pm
content: Quote from: bdunham7 on July 25, 2020, 01:48:48 pmYou can use a mosfet instead of a conventional diode for nearly zero forward voltage drop as these video shows. The first is simplest and gives a good explanation of how it works but the second is better and offers better protection.https://youtu.be/IrB-FPcv1Dc