Safety question on building an enclosure for a eBay DC to AC board - Page 1
Forum section: electronics / projects

author: Dan123456
author_rank: Regular Contributor
timestamp: November 04, 2023, 06:23:56 am
content: Hey allI bought one of those dodgy, el cheapo DC to AC inverters from EBay (I would provide a link but it is stupid long - just google “DC-AC Step-up 12V to 110V 220V Inverter Board 150W Converter Transformer” to see what I’m talking about)Basically, you feed it 12V DC and it has 6 different spots you connect to to get different AC (or in realty, high frequency square wave) voltages ranging from 20V to 220V depending on which spots you connect the wires.I’m not sure what the output current is likely to be but I want to build an enclosure for it because having the bare board just sitting there while running seems incredibly dangerous to me and would never forgive me self if my cat or nephew were to get hurtFor the DC input side, I am planning on just using a couple of banana plugs as I have heaps of them and don’t see 12V DC doing any damage, but for the AC output side, do you guys have any recommendations? I want to have all the outputs wired up to the outside of the enclosure so I can easily just plug in / unplug wires to each spot to get whatever voltage I need at the time.I was thinking maybe just speaker terminals just so the bare metal of the terminals isn’t exposed (example below)?https://www.jaycar.com.au/4-way-push-connection-speaker-terminal/p/PT3002?pos=2&queryId=f37e9dac24f6a74effe49195bebaa55bThe thing doesn’t need to be fully OSHA compliant or anything and any plugging / unplugging of wires would be down with it powered offI just want it safe enough to prevent anyone getting shocked if an adolescent were to decide to touch it or a cat were to rub up against it before I can slap them away etcAppreciate your thoughts

author: JeanF
author_rank: Regular Contributor
timestamp: November 04, 2023, 10:17:48 pm
content: Hello, that one ?https://www.ebay.com/itm/325451855905You can shorten ebay links by cropping right after the ebay item number. On the other hand, giving keywords as you did is maybe more future-proof, it will allow to find the product even after the ebay listing expires.Well, that thing doesn't look incredibly safe indeed. I know it's not what you asked, but personally I would not bring all the outputs to the outside, I'd solder PCB screw terminals to V0...V5 (they look like 5mm pitch) and put the whole thing in a plastic electrical enclosure, with a big label on the lid saying "DISCONNECT INPUT BEFORE OPENING" and a small hole in the side of the box for the output wires. That way, no live contacts can be touched from the outside, and a little reminder that doesn't hurt if it's late at night.Otherwise, speaker terminals could work, I think you could find versions with 6 or 8 contacts. Or a some shrouded banana plugs ? or loose pieces of insulated wire, each ending with a Wago 221 or 222? But that would not be very pretty.I'm curious, what's the intended use for this board according to the manufacturers? Powering a mains appliance from this sounds quite dodgy

author: coppercone2
author_rank: Super Contributor
timestamp: November 04, 2023, 10:30:38 pm
content: get real connectors for 120V.And buy crimped cables of thick gauge so its hard to break on the AC side.

author: Dan123456
author_rank: Regular Contributor
timestamp: November 05, 2023, 03:13:27 am
content: Quote from: JeanF on November 04, 2023, 10:17:48 pmThat’s the one! Thank youI had seen people get politely asked not to post short links in the past so wasn’t sure if I was allowed to do thatYeah, absolutely I intend on putting the whole thing inside a plastic enclosureThe thing looks like a bit of a death trap to me so I want no part of it to be exposed while it is turned onI am looking for a good option for a connector so can plug into each of the 6 spots that I can bolt / glue to the outside of the box so I never have to open it againI was thinking a 6 way (or a 2 way plus a 4 way since they seem easier to find) speaker one so I could solder a wire to each of the spots on the board and there would be no metal exposed on the outside of the boxI don’t really have anything in particular planned for the board at this pointProbably just play with it to light different light globes or what not (I.e. Neon etc.)I figured I could basically use it as a poor man’s variac for non-sensitive electronics and for $10-$15, figured it was worth having a play with (provided I can make it safe enough to not injure or kill anyone)

author: coppercone2
author_rank: Super Contributor
timestamp: November 05, 2023, 03:37:56 am
content: Get industrial rated connectors, speaker connectors are low voltage and made with speakers in mind.The safest option is to put the non pin sticking out IEC connector on it. Then use a cable to connect it to some breakout thing for prototypes. Like a special bread board with screw terminals on it and a replacable mounting plate. So if you wanna test a board or module that has 120V input, you take the mounting plate off, mount it to that with screws (expendable piece of FR4 sheet), install it, then wire it with short ring terminals. Then you would never be more dangerous then working on a open piece of equipment.I mean like IEC cable -> flat 18x12 inch polycarbonate plate with rubber feet that has a terminal block and cable strain relief on it, and mounting studs for the removable mounting plate. So then you mount a prototype to mounting plate securely with screws, then you wire it into the terminal block (i.e. possibly wago connector or spring loaded ferrule thing), then you plug it in. Then all the mains stuff is localized on the test board.that way its basically an assembled product before power on. Add a switch and fuse too.then you can also cover up all the HV connections with plates on top of terminal block before use, and add a cover on some nylon standoffs for long term teststhe usual problem is going to be a net of high voltage modules connected on a bench with random frayed wires...

author: themadhippy
author_rank: Super Contributor
timestamp: November 05, 2023, 04:02:25 am
content: On the 12v side for 150W output your going to need 12-13A ,are you happy with that sort of current going through your banana sockets?As to the output selection why not use a switch to select whatever voltage tapping you want

author: coppercone2
author_rank: Super Contributor
timestamp: November 05, 2023, 04:08:28 am
content: the right banana sockets can take that but I would only trust the good stuff. everything needs to be high quality/official/selected carefully. Making that reliable is difficult. and anything HV and banana is the safety banana now. maybe a long time ago you could have it, but its just not sold like that today!

author: JeanF
author_rank: Regular Contributor
timestamp: November 05, 2023, 08:13:43 pm
content: Also, note that this device generates a 20 kHz square wave output... Some ebay listings say "for resistive loads only", some don't. It is likely to cause harm to any devices that incorporate a capacitive input dropper, and won't work to power devices using an iron-core transformer, or a standard bridge rectifier (diodes won't be fast enough), with possible/probable damage to either your DUT or the transformer of your inverter board.If you wanted to power something based on a switch-mode power supply with this thing, you *could* add a bridge rectifier with fast diodes (suitable for 20 kHz) and that will convert your "inverter board" to a high voltage DC power supply, and many SMPS can work when fed by DC, but then again, extreme care is needed, HV DC is, just like HV AC, no joke. And as your inverter board has no overcurrent protection, the secondary of the inverter transformer will burn if there is a short in your DUT. So the fuse idea by coppercone2 looks like a good one.I think the cheap variacs from China (which have their problems too, you'll want to use them way below their ratings, control the wiring when you receive it, etc) are still better bang-for-buck than this

author: soldar
author_rank: Super Contributor
timestamp: November 05, 2023, 11:04:58 pm
content: Quote from: Dan123456 on November 04, 2023, 06:23:56 amHere's a link:https://www.ebay.com/itm/325451855905After re-reading the thread I see the link was already posted. Just to clarify, this is the basic link, the rest is info regarding your own session andshould be removedalways.