# AC/DC Adaptor Electronics/Electricity? **URL:** \ **Category:** Factual Questions\ **Created:** [May 22, 2002, 4:38pm UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325 "2002-05-22T16:38:40Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![H8\_2\_W8](https://avatars.discourse-cdn.com/v4/letter/h/c77e96/32.png) [@H8\_2\_W8](https://boards.straightdope.com/u/H8_2_W8)\ **Post date:** [May 22, 2002, 4:38pm UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325/1 "2002-05-22T16:38:40Z")
We received this Panasonic portable DVD player as a gift: > **[Panasonic DVD-LV70](https://www.crutchfield.com/p_133DVDLV70/Panasonic-DVD-LV70.html?s=0)** > > Portable DVD/CD player with 7" LCD screen We have a 6-7 driving trip with our little 2.5 y/o, leaving Friday and we went ahead and bought two DVDs for him (Thomas Tank and the Muppet Movie) but the battery in this player lasts 4 hours and we won’t be able to recharge before we get to our destination. So, this is the official AC/DC Car Adaptor for the player, but it is $129!!! > **[Panasonic DY-DC95](https://www.crutchfield.com/p_133DYDC95/Panasonic-DY-DC95.html?a=&s=0&id=detailed_info)** > > Car power adapter for Panasonic portable DVD players Why wouldn’t a regular 9V car adaptor I get from Radio Shack work for this thing, assuming the jack fits the unit? Are there any amp or ohm considerations? (I obiviously don’t know enough about electronics- hence this post) What’s this about negative/positive ground and car fires?!?! Is this a scare tactic so you spend $100 more than is necessary? Any help will be appreciated - - - ---
**Author:** ![3waygeek](https://avatars.discourse-cdn.com/v4/letter/3/e95f7d/32.png) [@3waygeek](https://boards.straightdope.com/u/3waygeek)\ **Post date:** [May 22, 2002, 5:06pm UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325/2 "2002-05-22T17:06:01Z")
Any adapter that can supply 9V at at least 2A (the same output as the Crutchfield unit you mention), with the proper plug, should be OK. For example [this Radio Shack unit for $17.99](http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F004%5F018%5F000%5F000&product%5Fid=273%2D1815) should do the trick. Don’t worry about the positive/negative ground thing – all current production cars are negative ground, and have been for as long as I can remember. ---
**Author:** ![Mikahw](https://avatars.discourse-cdn.com/v4/letter/m/e9bcb4/32.png) [@Mikahw](https://boards.straightdope.com/u/Mikahw)\ **Post date:** [May 22, 2002, 5:26pm UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325/3 "2002-05-22T17:26:47Z")
the adaptor for that DVD player uses a nonstandard rectangular plug. If you can find another adaptor that supplies 9V at at least 2A that has the nonstandard plug, it’d work. I doubt you’ll be able to find one, though. ---
**Author:** ![H8\_2\_W8](https://avatars.discourse-cdn.com/v4/letter/h/c77e96/32.png) [@H8\_2\_W8](https://boards.straightdope.com/u/H8_2_W8)\ **Post date:** [May 22, 2002, 5:35pm UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325/4 "2002-05-22T17:35:47Z")
Looking at this picture of the player, the 9V input isn’t rectangular though, so where would that plug go? > **[Panasonic DVD-LV70](https://www.crutchfield.com/p_133DVDLV70/Panasonic-DVD-LV70.html?s=0&id=morephotos&pi=2&display=XL)** > > Portable DVD/CD player with 7" LCD screen ---
**Author:** ![Mikahw](https://avatars.discourse-cdn.com/v4/letter/m/e9bcb4/32.png) [@Mikahw](https://boards.straightdope.com/u/Mikahw)\ **Post date:** [May 22, 2002, 5:40pm UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325/5 "2002-05-22T17:40:45Z")
Hmm, that **is** weird. Are you sure that that plug works with that player? Well, in that case, the plug from radio shack should work, as long as the DVD player’s socket isn’t some oddball size. ---
**Author:** ![GaryM](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/garym/32/241_2.png) [@GaryM](https://boards.straightdope.com/u/GaryM)\ **Post date:** [May 22, 2002, 5:51pm UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325/6 "2002-05-22T17:51:29Z")
OK, reading the specs on the “official” adaptor, it provides 9 volts at 2 amps. If Radio shack has a unit that provides the same, you are all set. You don’t need to be able to handle 24 volt inputs, just 12 volts. Some Radio Shack adaptor/converters use their system of interchangable plugs, so physically mating to the DVD player shouldn’t be a problem. However I’m not sure that Radio Shack has a DC to DC converter that provides 2 amps. A look at their on-line catalog shows nothing rated at more than 1 amp. The unit linked to by **3waygeek** is only rated at .9 amp Examine the DVD player and see if it really can only handle 9 volt input. Some DC devices can actually handle a range of input voltages. An alternative would be a DC to AC inverter along with the AC adaptor/charger that came with the unit. Some of these units are pretty inexpensive and you’d have a device that could be used on any AC powered device. Well, any device within the capacity of the unit you bought anyway ---
**Author:** ![H8\_2\_W8](https://avatars.discourse-cdn.com/v4/letter/h/c77e96/32.png) [@H8\_2\_W8](https://boards.straightdope.com/u/H8_2_W8)\ **Post date:** [May 22, 2002, 5:54pm UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325/7 "2002-05-22T17:54:18Z")
Mik - I think it is the correct item since it is listed as the adapter for portable Panasonic DVD players and is under the accessory listing for the LV-70 unit. I wonder if they have the wrong picture of the adapter, because the pictures of the player look correct. I think I’ll take the unit into a Radio Shack and see if they can find something that will power it and fit it. If not, H8\_2\_W8\_Jr. can watch the cows go by his window after the battery dies, because I’m not paying $129 for 2 more hours of Muppets. thanks guys! ---
**Author:** ![Running\_with\_Scissors](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Running\_with\_Scissors](https://boards.straightdope.com/u/Running_with_Scissors)\ **Post date:** [May 22, 2002, 8:27pm UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325/8 "2002-05-22T20:27:33Z")
Judging by the price and the size of the adapter, the Panasonic-branded adapter is probably regulated. I wouldn’t try to replace it with a Radio Shack adapter. What you could do is get yourself a power inverter - this provides a 120V outlet, so you can plug in whatever you want, including the DVD player’s AC adapter. I bought mine a few years ago at a warehouse club for about $45. They sell them in various capacities, but the smallest one should be fine for this purpose. I use it for my laptop so I don’t have to pay the exhorbitant fees for a car adapter for it (plus, it’ll still work when I buy a new laptop). Amazon has several listed, starting at around $50 - just search for **power inverter**. ---
**Author:** ![DarkScooterPie](https://avatars.discourse-cdn.com/v4/letter/d/b3f665/32.png) [@DarkScooterPie](https://boards.straightdope.com/u/DarkScooterPie)\ **Post date:** [May 22, 2002, 9:42pm UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325/9 "2002-05-22T21:42:34Z")
Two thing: Polarity does matter. Radio Shack and other adapters comes with different plugs (the end that plugs into the DVD player) and you can them with positive on the inside and negative on the outside. You can also get the with negative on the inside and positive on the outside. Instead of getting a DC to DC convertor, I recommend you get a DC to AC convertor. You should be able to find them in Radio Shack, most car part stores and some computer stores. Then you can just use the AC plug that came with the DVD player. This is the way to go if you also have a need to recharge your laptop, or decide to bring a VCR or a home base video game with you on future trips. Jim ---
**Author:** ![DarkScooterPie](https://avatars.discourse-cdn.com/v4/letter/d/b3f665/32.png) [@DarkScooterPie](https://boards.straightdope.com/u/DarkScooterPie)\ **Post date:** [May 22, 2002, 9:56pm UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325/10 "2002-05-22T21:56:48Z")
Two thing: Polarity does matter. Radio Shack and other adapters comes with different plugs (the end that plugs into the DVD player) and you can them with positive on the inside and negative on the outside. You can also get the with negative on the inside and positive on the outside. Instead of getting a DC to DC convertor, I recommend you get a DC to AC convertor. You should be able to find them in Radio Shack, most car part stores and some computer stores. Then you can just use the AC plug that came with the DVD player. This is the way to go if you also have a need to recharge your laptop, or decide to bring a VCR or a home base video game with you on future trips. Jim ---
**Author:** ![3waygeek](https://avatars.discourse-cdn.com/v4/letter/3/e95f7d/32.png) [@3waygeek](https://boards.straightdope.com/u/3waygeek)\ **Post date:** [May 22, 2002, 10:14pm UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325/11 "2002-05-22T22:14:07Z")
> [@](#): > > \*Originally posted by GaryM \* > **The unit linked to by 3waygeek is only rated at .9 amp** Thanks for catching that – I misread the specs. I’d thought the DVD took 12VDC in, and that adapter can supply 3 amps at that voltage. I’d thought of suggesting a DC/AC inverter, as **DarkScooterPie** and **Running with Scissors** did, but in my experience, these devices tend a bit toward the bulky side, and can put out quite a bit of heat, which can be a consideration if you have young kids or pets in the car. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [May 22, 2002, 10:56pm UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325/12 "2002-05-22T22:56:27Z")
I took a look at the voltage converter. Based on the specs it looks like a linear voltage regulator attached to a big heat sink. You could build the same in one evening. Let’s see… the maximum output is 9V at 2 A, right? Maximum car battery voltage is around 14V. A 9V linear regulator should work fine. [www.mouser.com](http://www.mouser.com) has the regulator you’re looking for. They have two versions: part no. 511-L78S09CT, which is a TO-3 package, and part no. 511-L78S09CV, which is a TO-220 package. Both are rated at 9V / 2A / 150 °C. The former costs $1.46; the latter costs $0.46. Now let’s assume you’ll be using L78S09CV… most TO-220-packaged devices have a junction-to-ambient thermal resistance of around 40 °C/W _without_ a heat sink. Given that the regulator will dissipate up to 10 W, and assuming the ambient temperature won’t exceed 30 °C, the regulator’s junction will be 430 °C(!). This is way above the 150 °C “safe” limit for such a device. So you’ll obviously need a heat sink. I would use a heat sink that is rated at no higher than 10 °C/W. In fact, just get the biggest heat sink you can find (they’re cheap). Mouser part no. 532-529802B25 will probably do just fine. Better yet, get the TO-3 regulator and use heat sink 532-500403B00. Then add a fuse and you’re done. Total parts cost (minus enclosure): approx. $10.00. And I do not believe Mouser has a $$ limit. (Of course, there are “better” options. A DC-to-DC converter would be much more efficient, and a DC-to-120VAC converter would be very convenient. But my goal was to come up with a _cheap_ solution.) ---
**Author:** ![Running\_with\_Scissors](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Running\_with\_Scissors](https://boards.straightdope.com/u/Running_with_Scissors)\ **Post date:** [May 23, 2002, 1:07am UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325/13 "2002-05-23T01:07:04Z")
> [@](#): > > \*Originally posted by 3waygeek \* > \*\*I’d thought of suggesting a DC/AC inverter, as **DarkScooterPie** and **Running with Scissors** did, but in my experience, these devices tend a bit toward the bulky side, and can put out quite a bit of heat, which can be a consideration if you have young kids or pets in the car. \*\* The one I have is quite compact (probably no more than 2.5" x 5" x 8"), fits under the passenger seat, and generates only a small amount of heat under normal (i.e. with a laptop plugged in) load. It does have forced air cooling, but the temperature of the case and the air coming out is never more than “slightly warm”. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [May 23, 2002, 3:03pm UTC](https://boards.straightdope.com/t/ac-dc-adaptor-electronics-electricity/110325/14 "2002-05-23T15:03:46Z")
> [@](#): > > \*Originally posted by Running with Scissors \* > \*\* > The one I have is quite compact (probably no more than 2.5" x 5" x 8"), fits under the passenger seat, and generates only a small amount of heat under normal (i.e. with a laptop plugged in) load. It does have forced air cooling, but the temperature of the case and the air coming out is never more than “slightly warm”. \*\* The problem I have with DC-to-120VAC converters, especially the _cheap_ ones, is that they tend to put out a really crappy waveform; it usually looks more like a square wave than a sine wave. Some devices won’t care, but others will. I’m not sure how a portable DVD player will respond… assuming the unit has an internal switching power supply, I would guess it probably won’t care, since the first stage is usually a simple rectification stage. But maybe I’m wrong. Can anyone else shed light on this issue?