Paid Job: Build this for me (two of them) - Page 1
Forum section: electronics / general

author: Larrikin
author_rank: Newbie
timestamp: July 19, 2025, 07:27:27 am
content: Firstly, I am not an electrician. I have had someone spec this for me. Basically I have an EV which produces a 100w USB C using the PD protocol. I want a device (two of them) that can leverage the USB C port and turn it into a cigarette adapter (female) which can produce up to 100w of power so I can plug in a portable fridge or anything else into the cigarette adapter that needs up to 100w. It will just draw what it needs to. Accordingly, this was drawn up for me as to how do to it (I don't know any of the tech details below but if you do, then you can probably do the job). I am told this is not a difficult job for those that are in the know.I need two of these.REQUEST: Fan‑less, palm‑sized USB‑C → 12 V/8 A cigarette‑lighter adapter (≈100 W) in a clean, finished enclosureI am after someone who can build me this:SummaryCar:USB‑C ports provide full 20 V × 5 A PD (100 W).Goal:power a device that could require up to ~90 W and other 12 V accessories where no factory cigarette socket exists.ConstraintsSilent:strictly passive‑cooled (no fan, no coil‑whine).Tidy:finished in a small, single‑piece enclosure with only one USB‑C lead in and one flush‑mounted cigarette‑lighter socket out. No loose boards or wiring visible.Faceplate / bezel should look OEM‑ish when tucked behind a seat or in rear foot‑well.Core electronics (supply or equivalent — substitutes ok if specs match)USB‑C PD trigger board — 5 A capable, selectable to 20 VExample:DAOKI PD2.0/3.0 Trigger Module (Amazon AU ASIN B091GGVS9Z).DC‑DC buck converter, potted, fan‑less: 9‑36 V → 12 V ≥10 A (≥120 W), ≥90 % efficientExample:XWST “waterproof” 12 V 10‑15 A module (Amazon AU ASIN B0CZLC7847).Sealed aluminium, passive‑cooled — no fan, <7 W heat at 95 W load.Panel‑mount female cigarette‑lighter socket, ≥15 A, centre‑pin positive, supplied with weather cap if possible.5 A / 100 W e‑marked USB‑C cable, 0.5 – 1 m. (I have spares if you prefer.)Enclosure options — pickone:(a) Hammond 1455C801 extruded‑aluminium case (80 × 54 × 23 mm)– Converter’s aluminium body can be thermal‑pasted directly to the case for silent heat‑sink.(b) Custom 3‑D‑printed PETG/ABS shell the size of a deck of cards, with:front face: flush cigarette socketrear/bottom: moulded strain‑relief for USB‑C leadinternal standoffs for PCB screw‑mount and thermal interface padInline mini‑blade fuse holder + 10 A fuse on 12 V output.Mechanical / wiring briefSet trigger to 20 V before installation.Keep 12 V run <10 cm; use 16 AWG silicone wire.Thermal‑pad or RTV‑bond converter’s metal back to enclosure wall so entire case acts as passive heat sink (target <55 °C surface @ 8 A).Provide cable‑gland or moulded strain‑relief on USB‑C lead for durability.All holes de‑burred; finish in black or dark grey for OEM look.Bench‑test spec (deliverable)Input: 20 V × ≤4.8 A (96 W) from bench USB‑PD supply.Output: 11.9 – 12.1 V @ 8 A continuous for 30 min, ripple <50 mV p‑p.Case exterior <55 °C, no fan noise, no audible coil‑whine.Verify inrush ≥12 A for 100 ms without drop below 11.5 V (to cover things like a portable fridge compressor start).Deliverables & quoteFinished, tested unit as described.Pictures of internal layout before final close‑up.Quote should include parts, labour, and estimated turnaround.Shipping to Melbourne, Australia.Please reply here or DM if you can build this, and include:Price breakdownLead timeAny questions / alternate parts you’d like to propose

author: PlainName
author_rank: Super Contributor
timestamp: July 19, 2025, 07:45:06 am
content: The test spec:QuoteSeems to be mutually exclusive. Perhaps you mean ≥4.8A.

author: Swake
author_rank: Frequent Contributor
timestamp: July 19, 2025, 08:40:06 am
content: What is your budget?Just asking because with all these 'specs' and proof of concept stages you're easily going to end up way over 10k (your choise of AUS$, USD, EUR, CHF) in development costs alone. After all, time is money and electronics engineers don't work for free... This cost is assuming you'll wave any and all responsibilities in terms of fit for purpose of the design (after all you're defining specs and parts), regulations, warranty, certifications, insurance and what not.ps: As far as I remember standard USB-PD is capable of 5 A max. If it is regulated directly to 12 V you'll have only 12 V x 5 A = 60 W (actually less counting conversion losses). This means you'll have to ask the USB-PD to deliver 20 V and then buck convert it to 12 V (probably 13,8 V as it is a 'car fridge'). Best case you'll end up with +/-85W out of such a contraption.ps2: Pretty sure your car has a 12V battery too. Keep it simple and pull a wire with a 15 A fuse on it from that battery into a socket and you're good.

author: voltsandjolts
author_rank: Unknown
timestamp: July 19, 2025, 08:53:34 am
content: This one does 50W apparently.https://www.youtube.com/watch?v=Q--qtl2sHmw

author: IanB
author_rank: Super Contributor
timestamp: July 19, 2025, 09:12:26 am
content: Quote from: Larrikin on July 19, 2025, 07:27:27 amFirstly, I'm really not sure you appreciate what someone would charge to make this for you. As a custom one-off job, the most significant charge would be the hourly rate, and it would take several hours to do this job, and therefore would cost way more than the cost of parts.Secondly, with the amount of detail you already have, this could be a home-build project where you build it yourself, which would result in a much more reasonable cost.Thirdly, it is not obvious that going through a two stage conversion process from car electrical supply to USB-PD supply to DC-DC converter would be all that economical or efficient. If the car already has a 12 V electrical system, it would be better to tap into that directly, as someone else suggested.My suggestion would be to find a local auto-electrician, and ask them to fit a 12 V accessory socket to your vehicle, if it doesn't already have one.

author: Psi
author_rank: Super Contributor
timestamp: July 19, 2025, 09:20:23 am
content: Sorry, i completely misinterpreted what you were trying to do.Have deleted my previous post that didn't make sense given you were trying to power from USBC not car battery.

author: Larrikin
author_rank: Newbie
timestamp: July 19, 2025, 11:56:32 am
content: Thanks to everyone who has responded so far.In simple terms, this is what I am trying to achieve but I have zero skills to do this myself.My car is an EV and has 100w PD USB-C sockets all through the car, but only has one cigarette adapter under the front passenger foot well. Hardly ideal for a portable fridge which would likely reside in the boot or in the back seat.I have USB C ports everywhere so I was hoping to get a device that plus into the USB-C socket and delivers 100w female cigarette adapter so I can plug something into it. All the ones I have found on amazon have a very low limit like 20w. There is nothing out there that does one as high as 100w. Is this even possible? I am after two of them.

author: Psi
author_rank: Super Contributor
timestamp: July 19, 2025, 12:31:43 pm
content: So the car is taking 12V or 48V from its accessory battery and buck/boosting that up to 20V so it can do 100W USB PD. And you want to take that 20V and step it back down to 12V?

author: Larrikin
author_rank: Newbie
timestamp: July 19, 2025, 12:38:22 pm
content: I am needing a cigarette adapter not a USB C adapter for my portable fridge. I only have a USB - C port which is capable of 100w PD, so that's what I am trying to achieve. I need to plug the fridge in but there is no cigarette plug to plug it into - only USB C.

author: voltsandjolts
author_rank: Unknown
timestamp: July 19, 2025, 02:14:14 pm
content: Just wait a while, someone will manufacture a USB-C fridge

author: jc101
author_rank: Frequent Contributor
timestamp: July 19, 2025, 02:26:48 pm
content: Something like this?https://www.amazon.co.uk/HATMINI-Cigarette-Lighter-Adapter-Adjustment/dp/B0DM694PJG

author: voltsandjolts
author_rank: Unknown
timestamp: July 19, 2025, 02:35:23 pm
content: Quote from: jc101 on July 19, 2025, 02:26:48 pmGood spot, but construction doesn't look like the claimed 100W.

author: jc101
author_rank: Frequent Contributor
timestamp: July 19, 2025, 02:39:34 pm
content: Well, shows they exist. I'm sure there are others available out there.For the price, worth giving it a try I'd have thought. I am resisting the temptation to get one and see what it's like.

author: Larrikin
author_rank: Newbie
timestamp: July 20, 2025, 08:52:42 am
content: Quote from: voltsandjolts on July 19, 2025, 02:35:23 pmI own one of those. Piece of crap and doesn't work. Also the wiring is so flimsy, there is no way it could carry 100W.I've also bought one of these and waiting for delivery on it:https://www.amazon.com.au/dp/B0CHJRCW2FBut again, reports say it can only do ~36W. Nothing like 100W.

author: Kean
author_rank: Unknown
timestamp: July 20, 2025, 09:08:12 am
content: Quote from: jc101 on July 19, 2025, 02:26:48 pmExcept that will quite possibly only supply 3A at 12V. Not many PD sources seem to do 12V at 5A, and many won't even output 12V at all. The 12V mode on PD has been removed from the USB PD spec.To achieve what the OP wants (close to 100W at 12V) then you would have to use the 20V 5A PD mode and a buck converter to get 12V at 8A - as per the description provided. I'm not sure that it would be practical to supply 96W at 12V anyway due to power losses, but if the fridge is pre-cooled before connection then it should not require full power.It is great that the OP has detailed requirements, but as mentioned that level of specific detail will actually push the cost up. I would not even bother to quote on this for a mate as there is too much risk that it doesn't meet their actual needs. Plus the time/cost to source components and put a quote together would likely exceed what the OP is probably willing to pay for a one-off. I would not want to use random sourced parts from Amazon.

author: Kean
author_rank: Unknown
timestamp: July 20, 2025, 09:27:08 am
content: On further checks a common panel mount cigarette lighter socket will not even fit on either of the suggested enclosures.The ones I have here (e.g Jaycar PS2020) need about a 26mm cutout and are about 36mm outer diameter on the face. It may be possible to get something smaller, like PS2004 which says 31mm, but unsure without having one in my hand. Even a non-panel mount lighter socket (i.e. corded) is over 25mm diameter.

author: jc101
author_rank: Frequent Contributor
timestamp: July 20, 2025, 09:36:02 am
content: I wasn't going to mention the socket wouldn't fit into the requested enclosure size...A lot also depends on what the EV USB ports can actually deliver too. They will probably be dynamic, depending on the state of the EV battery, and if the EV is awake or asleep. Lots of variables. The device may well need to shed the load if the socket renegotiates the connection.I've designed a number of USB sources and sinks, and quite like USB-PD. It's an interesting idea, but would need several safeguards to do safely.

author: voltsandjolts
author_rank: Unknown
timestamp: July 20, 2025, 12:36:01 pm
content: There are portable power stations with 12V cigarette socket outputs, and usb-c charging e.g.https://factorypure.com/products/bougerv-220wh-portable-power-station-for-refrigerators-new..maybe leave it charging while supplying the fridge.

author: jc101
author_rank: Frequent Contributor
timestamp: July 20, 2025, 12:39:52 pm
content: Quote from: voltsandjolts on July 20, 2025, 12:36:01 pmThat would be ideal I would have thought.Well done for finding that, my googlefoo let me down when trying to search for something like that.

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: July 21, 2025, 03:24:23 am
content: Quote from: Larrikin on July 19, 2025, 12:38:22 pmSo the current suggestions are to use a power bank or to have a mechanic wire in a second cigarette lighter socket directly from your 12v car battery.If a USB-C to cigarette lighter socket is what you end up deciding on, I'd be happy to do it; and there are a few questions I have.1: The case is too small to fit the cigarette lighter socket. You can see a mechanical drawing of one here:https://www.memoryprotectiondevices.com/datasheets/ZA2060/ZA2060-datasheet.pdfThey are about 27mm in diameter (your enclosure is 23mm high), and you'd want the case bigger than that for electrical isolation. Say about 36mm minimum. Likewise, you'd need the case to be wider. Is this acceptable?2: What is the temperature range this device must operate in? In FL, USA, our car gets up to 72C inside if we leave it in the sun -- and it's a silver colored car. A black one would get hotter.3: As you may be aware every form of power transformation brings with it losses. For example, gasoline to engine motion (kinetic energy), engine (kinetic) power to hydraulic power, electrical energy to chemical battery energy. Therefore, even if I or anyone else built this circuit, we'd be transforming the energy from 20v to 12v. That would involve some losses, climbing with temperature. The best buck convertors I'm aware of boast 93% efficiency. So, 100W in would be 93W out at peek efficiency (probably measured at 20C).I don't suppose this will be much of a problem for your fridge, but would this constraint of reality be acceptable to you? If you really need 100W, I would have to spec two USB-C inputs so that I could get the full power to your fridge.4: You specify as your sixth requirement, "Inline mini‑blade fuse holder + 10 A fuse on 12 V output." As should be obvious, you can't get 12V a 10A out of this port. 100W in cannot equal 120W out. That would be "free energy". So having a fuse of that size does not make sense. Moreover, because we are so near the limits of what the USB-C port of your car can provide in terms of current, any fuse would be pointless because the car's own internal USB-C over-current-protection would kick in long before any fuse would blow. So could we just abandon that requirement?

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: July 21, 2025, 03:41:21 am
content: Dear Mr. Larrikin,Here's a case I think would be much more suitable, R191-070-000. It's water proof, so there would be no need for potting the USB-C to cigarette lighter adapter, although I could still do that if you feel that it is necessary.

author: Psi
author_rank: Super Contributor
timestamp: July 21, 2025, 01:31:01 pm
content: Quote from: Simmed on July 21, 2025, 04:32:57 amoh, it's not 'difficult' that part is true. At least not in a general powersupply design sense. (There are still a few questions around if it's possible given USB-C limitations/efficiency) But assuming it's possible it's still going to be quite time consuming to get everything up to the standard needed to hand over a good product and charge money for it. And there are some additional requirements that can be annoying, like passive cooling, zero coil whine and waterproof.Someone with switchmode powersupply design experience could throw a first pass prototype circuit together and make a PCB for it in around a week or two. If they were designing it only for themselves they might stop at that point with a few bodge wires added in to make it work. If it goes unstable and fails after 3 weeks it's fine when it's your own thing with only yourself to blame. You can't do that when making it for someone else.When selling any item it requires a large amount of extra testing/tuning. The first design is almost guaranteed to have both obvious and non-obvious issues that need to be found and fixed by lots of testing. Probably needing 2 or 3 more circuit/PCB iterations.It could easy balloon to a month or two of work. Even at 50% normal hourly rate it's still going to cost at least $8k of time if everything goes well.One advantage OP has is that he doesn't need it designed to have a low BOM cost since it's not for manufacturing.So it's possible to use a really expensive DCDC controller IC that cost $10-20 each but does a good amount of the design work for you and has a good datasheet for figuring out optimal values for all the components.(i'm not volunteering to do it)

author: thm_w
author_rank: Super Contributor
timestamp: July 21, 2025, 08:46:56 pm
content: Quote from: Larrikin on July 19, 2025, 11:56:32 amCar audio shops regularly run low gauge wire from the front of the car to the back for subwoofers.It would also help if you specified the car model. Some EV's have the 12V battery in the trunk.

author: Someone
author_rank: Super Contributor
timestamp: July 21, 2025, 11:08:28 pm
content: Quote from: Psi on July 21, 2025, 01:31:01 pmAnd a consumer finish OEM aligned enclosure, that right there would be around half the expense.Like I can do it and already know all the electronics that will meet the specifications, but the customer will probably be unhappy with the texture of the enclosure. So the budget includes doing it 3 times to be sure.Several weeks and 10-20k as people are mentioning is where that is headed.

author: Psi
author_rank: Super Contributor
timestamp: July 22, 2025, 02:52:43 am
content: Quote from: Someone on July 21, 2025, 11:08:28 pmYeah, I'm assuming that because this is a one-off item the OP wants, rather than a mass-produced item. The case design can be hand-made which makes it so much easier than trying to make something for rapid production.Actually yeah, I missed seeing the "OEM‑ish" 'clean finished enclosure' requirements from the specs provided.I guess it really depend how OP defines that. Is very tidy DIY enclosure ok, or does it have to look like it was mass-produced etc...I definitely agree that enclosures are a pain in the ass when they need to look good. They're such a time sink for a part that doesnt effect functional operation at all.Some Hammond aluminum extrusion with PCB front/rear panels is what I would do for this sort of project, if it was me.They can look pretty tidy.

author: Zucca
author_rank: Unknown
timestamp: July 22, 2025, 03:09:31 am
content: Wondering how many ice bags and a "passive" cooler you can buy with the same amount of money for this project (including the car fridge).Anyway if you need 12V in a car make no sense to hunt for an USB C PD device. Look for a 12V in the car as already suggested, a fuse box is a good place to start.99% of cars EV included have 12VDC somewhere ready to go.

author: IanB
author_rank: Super Contributor
timestamp: July 22, 2025, 04:39:35 am
content: Also, a fridge in particular is an odd choice of device to power in a car. When you plug in a fridge, it will generally take a few hours to cool itself and its contents down to the desired temperature (and make sure it is a real compressor fridge, and not one of those fake Peltier things that are a waste of money). So a fridge is a long term, continuous load. You could reasonably find one in an RV or caravan or mobile home, where it is running all the time. But unless it is already pre-cooled, you are not going to just put one in a car and expect it to do much. A fridge is a 24 h/day kind of load. And that is going to put a lot of stress on a power supply that is more likely designed for intermittent loads. If you are just going to go on a car journey and have cool beverages when you arrive, you are much better off with a cool box and a bag of ice or some cold packs.

author: EEVblog
author_rank: Unknown
timestamp: July 22, 2025, 04:55:12 am
content: Quote from: Psi on July 22, 2025, 02:52:43 amYeah, the one-off nature makes this an expensive exercise, albeit fairly easily technically.I'm surprised if something like this doesn't exist.I'd even look at a small USB rechargeable battery bank with 12V lighter output, e.g.:https://www.snowys.com.au/rover-go-39600-mahhttps://kickassproducts.com.au/products/kickass-kickcharge-150wh-portable-power-pack-for-campingOr as others said, get an auto electrician to retrofit the USB-C with a 12V outlet. The 12V wiring is already going to the USB-C adapter which would be right behind the socket.

author: Kean
author_rank: Unknown
timestamp: July 22, 2025, 05:25:01 am
content: Quote from: ballsystemlord on July 21, 2025, 03:24:23 amInteresting. It has been a long time since I worked on auto-electrics, but how does that lighter socket mount? I presume using the rear bolt, which I'd say makes it hard to panel mount, and needs a cleanly cut and chamfered hole to look good.Maybe the MPD AS215 is a better option for a secure panel mounting and clean finish. That also has the weatherproof cap they requested. Very similar (probably identical) to the Jaycar PS2004 I mentioned.https://www.12v-parts.com/part.php?pn=AS-215&original=Auto&override=Auto