AC ADAPTOR REPLACEMENT - Page 1
Forum section: electronics / repair

author: bfi1714
author_rank: Newbie
timestamp: July 10, 2019, 09:55:56 am
content: Hi! I'm looking for a possible replacement for this American AC adaptor, check the Imgur links. This adaptor is used for my automatic cat feeder and till now I've being using it with a bulky step down transformer. However, now, I would like to get hide off the transformer and use a proper Australian adaptor. I found a 9VDC 1A adaptor, but I'm concerned that it may damage the feeder electronics as on the original AC adaptor, the output current is shown as 120mA DC.Please, any help is appreciated.https://imgur.com/a/9GmNEZ7https://imgur.com/a/sSBw9BUMany thanks,bfi1714

author: ahakman
author_rank: Regular Contributor
timestamp: July 10, 2019, 10:24:20 am
content: You can use any 9V adapter that's AT LEAST 120mA (and center positive on the plug). Using an adapter with a higher current rating than the original is fine.The current rating of an adapter tells you how much current the adapter COULD supply (should the load draw that much) before the voltage of the output falls. So if the original adapter can supply 120mA, the load probably draws less than that, say 100mA. Your replacement adapter COULD supply up to 1A, but if the load never draws that much, it's not an issue.What would be an issue is if the original adapter could supply 1A, but you tried to run it from an adapter that could only supply 120mA - that would probably not work.

author: coromonadalix
author_rank: Super Contributor
timestamp: July 10, 2019, 10:28:32 am
content: As a start measure the connector barrel to be sure, your positive is at the center in your photos, you surely can find a matching switching transformer who could do 100-240v automaticallyAnd yes the 120ma is the current limit of your old adapter, you can substitute it with say an 500ma one.

author: Electro Detective
author_rank: Super Contributor
timestamp: July 10, 2019, 11:10:49 am
content: Go to a Jaycar or Altronics store nearby, or online if you must, and get a REGULATED 240 volt AC to 500ma DC adapterand fit the matching plug, set up to be DC positive (+) Tipand DC Negative (-) on the outside barrel,a multimeter, or a friend with one that knows the deal, is amust haveto confirm thisIt's very important not to stuff any of that upIf you're not sure, take the lot to the store and request to speak to someone knowledgeable about such matters,avoiding any s*** kicker 'fast sale' counter turkeysshark baitthat pop up from time to time in retail establishments500ma and regulatedwill ensure an excellent constant output of 120ma, or whatever your device -really- pulls,not always what's written on the stickerGood luckand we are here in case of drama you and the cat/s don't need

author: bdunham7
author_rank: Super Contributor
timestamp: July 10, 2019, 05:48:28 pm
content: Quote from: bfi1714 on July 10, 2019, 09:55:56 amI'd be a bit more careful than the previous posts suggest. You MAY be able to just use any old 9VDC adapter with the correct polarity and everything MAY be fine. Or, it could go poof! The nominal voltages on adapters often don't reflect reality and you need to more accurately characterize the old adapter and the device and then you will know what is acceptable. For example, looking through my box of spare adapters and parts the other day for a similar project, I found a 5 VDC adapter that had 5.1 VDC open circuit, while another rated at 3.7 VDC had 10.3 VDC open circuit! Certain setups have matched adapters that count on the load of the device to bring the voltage down where it needs to be--these are often transformers--and others have very flat voltage/current curves--typically SMPS. So you might need to characterize the load as well! I'm sorry this is so complicated and I don't want your cat to starve, but this is an engineering forum after all!If you want to keep it simple, just measure the open circuit voltage of your current adapter. If your replacement adapter has a similar open circuit voltage or less, you will likely be OK. I would expect your cat feeder to be somewhat tolerant of voltage variance because I presume it has a motor that runs intermittently--which means the design can't count on a steady load.

author: Electro Detective
author_rank: Super Contributor
timestamp: July 10, 2019, 11:35:54 pm
content: Let's try that again, and welcome to further debate if I'm NQR on this (a path traveled countless times btw)A 500ma bog standard AC toRegulatedDC adapter may cost a few dollars more (and maybe not)but gets rid of those open circuit vs loaded up concerns of 'good enough/hey, it works' penny pinching and or Approval Friendly manufacturers unregulated adapters.bdunham7's cat feeder device will receive the required 9 volts at any current/load demand, be it steady and or fluctuating, from the sticker rating of 120ma max or less,or more if required up to a generous reserve of 500maand...keeps the show on the road at 9 volts DCduring freaky AC voltage fluctuations from 180 to 260 volts during peak and off peak demand in the street/suburbWhy gamble on an unregulated cheapo that may work 'ok' out of the box, and cash out later, or cause the cat feeder drama?@ bdunham7, do you have a photo of the cat feeder's DC requirements? Does it specifically state 9 volts DC at ???maI've used these before, and even though I prefer old school transformer based ones, they work greatwww.jaycar.com.au/switchmode-plugpack-9vdc-1-66a/p/MP3484This one has a fixed positive tip (assuming it's listed plug dimensions/specs are same as yours) and ready to go.www.altronics.com.au/p/m8925c-powertran-9v-dc-2a-fixed-2.1mm-tip-appliance-plugpack/This one is cheaper, 500ma and should suffice:www.altronics.com.au/p/m9273a-powertran-12v-dc-0.5a-fixed-2.1mm-tip-appliance-powerpack/The more 'ma' the better I reckon, and you can use them with low or higher powered devicesFWIW: I'm here to pitch for the cats, so they don't miss out on a feedand or whiff a smouldering adapter.

author: bdunham7
author_rank: Super Contributor
timestamp: July 11, 2019, 02:53:31 am
content: Quote from: Electro Detective on July 10, 2019, 11:35:54 pmI'm not the OP, I feed my cat manually via the all-it-can-eat method. Regulated wall warts at 9V may be not-so-common, but to go even further, there's no guarantee that the original one provided regulated 9 volts, or even close to that. I've done a fair amount of wall-wart swapping and things are generally OK without too much trouble, but there are devices that just use (cook, actually) a battery for voltage regulation. IOW, they may depend on the voltage falling off under load. Sounds silly, perhaps, but I'm dealing with one right now--an it isn't an as-seen-on-TV cat feeder, it is a $1K precision drafting tool with a power supply system designed by a third grader. In my case the supplied power pack reads "4.5 VDC 200mA". And, if you were to use a regulated, precision 4.5 VDC supply, it would not work properly and would not charge the battery. It actually needs 6.0 VDC or so at a minimum of 6 (yes, six) milliamperes plus whatever current you would like to float thru 4 2/3AA NiCd cells--which are, of course, boiled dry...Anyway, short of re-engineering while the cat goes hungry, the adapters you have posted will, most likely, work fine if the device does not use batteries.

author: Electro Detective
author_rank: Super Contributor
timestamp: July 11, 2019, 09:03:32 am
content: Apologies for the mistaken OP 'oops'and yes, adapters for powering and charging batteries are another topic to be covered,or already have been perhaps'Third grade designers' should get daily doses of 'time out' in the bathroom, based on some of their iffy ~work~ I've come acrossok cat supporters, so what's the plan if there's a power failure in the area? UPS backup? (PURE sine wave type please)and what to do with cat staff that forget to top up the feeder ?