Convert a flat screen TV from main voltage(110V AC in the US) to 12V DC for boat - Page 1
Forum section: electronics / projects

author: superdmp
author_rank: Newbie
timestamp: July 17, 2016, 07:24:55 am
content: Hi all,I'm trying to help my father outfit his boat with some power efficient electronics (new toy of his, hobby of mine). I'm trying to build 12V DC step down / boost plugs for the various items he wants on-board, and am struggling with the flat screen TV.The current configuration is as follows:Boat power from 12V battery bank (charged using only solar, wind, and occasional engine use)Inverter to 110V AC - lose a minimum of 10%, most likely closer to 30%+ with his budget inverterTV Internal converter from 110 AC back to some DC voltage - Lose another 30%+ depending on efficiencyThis means, 60% of the power is wasted (heat heat heat), and if I can improve this, I can increase the usefulness of his boat batteries dramatically.I'm having trouble finding the schematics for the two flat screens he already has, and am even striking out at finding schematics for a budget flat screen to replace one or both of the current flat screens. All of the flat screens seem to do the power conversion internally, rather than having external wall-warts with easy to replace DC output specs. Does anyone know where I can find the electrical schematics for some moderately sized flat screen displays or even full TV's?I thought about just opening one up and putting a meter to work, but I don't want to do this half @$$. I need to make sure the pwoer I am supplying is precisely the required voltage, and is in sufficient wattage to run the TV reliably.Thanx y'all

author: tautech
author_rank: Super Contributor
timestamp: July 17, 2016, 07:56:36 am
content: Quote from: superdmp on July 17, 2016, 07:24:55 amWelcome to the forum.Just do that ^^^You'll likely find only a couple of power rails, probably 5 and 12V.The SMPS is usually a separate PCB alongside the main board and either edge connected or with a jumper loom.If you're were going to set it up as a dedicated LV unit you could remove the SMPS and "shoehorn" your own creation in its place with the required regulated supplies of course.

author: kripton2035
author_rank: Super Contributor
timestamp: July 17, 2016, 08:05:16 am
content: yes just open it and look around for voltage suppliesalso the brand and model of the TV can most of the times give schematics that help to see all voltages supplies and not forgot one in the process.

author: Seekonk
author_rank: Super Contributor
timestamp: July 17, 2016, 11:50:19 am
content: I found an older LCD TV that gad a single 12V power supply. I feel those are pretty rare. One thing I found that the 12V was very sensitive to voltage variation and would dim the screen. Many TV will work on DC. I power mine with broken inverters that I just removed the H bridge and just powered it on raw 140V DC. There are some boost converters that can generate 80V and that may be enough.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 17, 2016, 12:12:03 pm
content: Quote from: Seekonk on July 17, 2016, 11:50:19 amIn this case, it's best to bypass the rectifier bridge from the equipment; not only to further minimize losses, but to prevent it burning because the dissipation is now in two diodes 100% of the time, not divided on 4 diodes 50% duty cycle each pair, like on AC.

author: saturation
author_rank: Super Contributor
timestamp: July 17, 2016, 12:49:49 pm
content: Most marine grade TVs or monitors have DC input for power sources.So your questions suggests you are converting a non-marine grade TV for use on a boat, beware it may not last long even if you rarely use it; land based electronics are not made to withstand 100% humidity, salty air, or twisting forces from rocking boats. If the TV is cabin mounted, there is a high chance it will be damaged by the rolling of the boat. The larger the screen the worse this is; its only balance by the size of the boat, which counters the rolling effect, such as yacht size. Laptops by nature being designed to be portable, are more hardened for marine use and in practice, they work very well; stand alone monitors not so.Now if you have a temperature controlled cabin to mount non-marine grade electronics in, then it will last longer until you dock the boat and shut off the environmental controls, but you also shut off most electronics then too.I suggest you get a marine grade monitor or use a laptop with the largest screen possible. They are not that expensive anymore and beware 'marine' grade products that are really not marine grade; the best clue is they are marine grade is the chassis are made to take abuse, they have glare or sunlight filters, are reasonably splash aka water resistant and are pre-built to use 12-24VDC as a power source. Inside they have marine grade conformal coatings, outside higher grade UV coatings, covered or water proof accessory connectors, shock mounted PC boards and marine grade wiring.We buy them cheap, because they last only 3-5 years in time, due to the harsh environment. They'll last longer in fresh water, aka lakes, and large crafts, yachts and up, than salt and boats that ply the open oceans.http://www.walmart.com/ip/Pyle-Plmrm71w-7-Active-Matrix-Tft-Lcd-Marine-Display-White-800-X-400-plmrm71w/45947307?wmlspartner=wlpa&selectedSellerId=51&adid=22222222227033394985&wmlspartner=wmtlabs&wl0=&wl1=g&wl2=c&wl3=71927553296&wl4=pla-119477401016&wl5=9007285&wl6=&wl7=&wl8=&wl9=pla&wl10=100362769&wl11=online&wl12=45947307&wl13=&veh=sem

author: Kilrah
author_rank: Unknown
timestamp: July 17, 2016, 01:01:27 pm
content: It's pretty unlikely you'll find schematics, so yeah opening and probing is the best thing to do.You're likely to find a number of rails, 24V/12V/5V/3.3V are common, the "selection" in your particular unit will determine whether it's practical or you should just stay with the inverter.

author: Richard Crowley
author_rank: Super Contributor
timestamp: July 17, 2016, 01:27:55 pm
content: More likely on larger screen sizes (not mentioned here?), you may find that while the electronics will operate on 12V (or even lower), but the BACKLIGHT will want a higher voltage. I agree that using an ordinary domestic display in a marine environment will condemn it to premature failure. That is why they make marine-grade products.

author: aandrew
author_rank: Frequent Contributor
timestamp: July 17, 2016, 02:47:47 pm
content: Quote from: superdmp on July 17, 2016, 07:24:55 amI very seriously doubt your 60% loss numbers. That would mean that if your TV was drawing (for easy numbers) 100W, you would need a 250W inverter and the thing would be getting **HOT**.Before you go and reinvent the wheel, have you done any actual power measurements and calculate what your actual losses are? You might be pleasantly surprised. No sense going through all this work only to gain another 15m of TV time and risking the TV with a hacked up DC/DC supply.

author: Kilrah
author_rank: Unknown
timestamp: July 17, 2016, 03:02:22 pm
content: Yep.For a start, the following is wrong since 0.7*0.7 = 0.49, so your loss in this case is 51%, not 60%.Quote from: superdmp on July 17, 2016, 07:24:55 amThen an SMPS in a consumer device wouldn't be as bad as 70% efficiency, actually in many places they are legally required to be better than 85% at nominal load. Your inverter even cheap is pretty certainly >80% too.Using 85% and 80% gets you to 32% loss instead of the 60% you're picking out of the blue.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 17, 2016, 03:20:21 pm
content: Quote from: Kilrah on July 17, 2016, 03:02:22 pmYeah; 70% efficient SMPS in a monitor would also be pain in the ass to design, with all that cooling required, resulting in a larger, heavier and more expensive product. Miniaturization is the cost-saver in modern consumer electronics, and that necessitates rather good efficiency; even then, there often are capacitor lifetime problems due to heat. 85% would indeed be a good first-order approximation, 80% could be used as a worst-case approximation (ignoring low-load situations), but 90% is well within reality.--Quiescent power draw is a bigger issue. If you want to switch the monitor off from it's "soft" power switch, you may have several orders of magnitude more losses with inverter + original PSU, than a properly designed new DC/DC. But I don't know if this is a problem. The easiest solution is to turn the monitor off from the inverter side.BTW, have you analyzed what happens when you lose isolation in all devices when you convert them using highly efficient non-isolating DC/DCs? Ground loops no-one ever designed for are a possibility. Just saying, not sure if it causes any issues.

author: Seekonk
author_rank: Super Contributor
timestamp: July 17, 2016, 03:33:19 pm
content: At my camp, I don't use a central inverter. Each one is pretty much dedicated to a device and appropriately sized. At low power, the fans make up a significant amount of power. I eliminate all fans and allow free air cooling. Powering from the plug has advantages. Diode loss is pretty minor.

author: Artlav
author_rank: Frequent Contributor
timestamp: July 17, 2016, 10:12:25 pm
content: I would think your best bet is to open the thing up and take a look.With luck it would be a separate one-sided board with clearly labeled voltages and no complications.With less luck, you'd have a controlled power supply with PWM inputs to control the backlight inverter's brightness.Be aware that it's a bad idea to feed "unregulated vehicular 12V" into "electronics 12V" - there is a reason automotive stuff is rated for 9-32V with 40V spikes, and i would guess a boat would have a similar type of wiring.

author: LabSpokane
author_rank: Super Contributor
timestamp: July 18, 2016, 12:54:00 am
content: I'm betting that the "marine grade" cost of a mission specific TV includes the cost of designing for automotive load dump and (lack of) power quality.One of many primers:http://www.ti.com.cn/cn/lit/an/snva681a/snva681a.pdfThe short story is that you have to protect the hell out of the TV power inputs since the boat/automotive voltage ranges from around 3 to 60V.

author: Isad
author_rank: Frequent Contributor
timestamp: July 18, 2016, 05:06:14 pm
content: Somthing you could do is replace the CFFL tubes with LED stripi did this to a old monitor and convertet it to 12V yeah i had tomake a 12v to 5v converter for the logic and the led arent dimmablebut all in all it works great i use it in my office when i want to test anythingofc i doubt its gona survive the marine grade weather cuz the salt water willmake it fail pretty fast but you could try to coat evrything with glue or make itwater proof for that maters but i doubt its gona help anything.

author: saturation
author_rank: Super Contributor
timestamp: July 18, 2016, 06:30:28 pm
content: As general information, a key item in marine grade electrical power are floating or isolated supplies; devices are not grounded to the hull of the ship as part of their electrical power system. The water surface is a conductor; the engine, props and shaft are all conductors and allow current to flow through it and around the ship and is not part of the power supply for the ships electronics but necessary to ground to prevent shock say from lighting strikes or static electricity. If AC and DC are supplied on a ship, they are essentially separate and isolated.If non-marine electronics are used on boats and ships, insure too that isolation is maintained. Neutral and ground paths of any AC powered device must not be connected, e.g. surge protective elements within their power supplies that connect neutrl and ground should be defeated.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 19, 2016, 04:29:00 am
content: Quote from: saturation on July 18, 2016, 06:30:28 pmElectrical code specifically prohibits connecting neutral to ground downstream of the distribution panel. Any surge protective devices between hot/neutral and ground are to remain an open circuit under normal conditions. Thus it's a non issue with code compliant devices.

author: superdmp
author_rank: Newbie
timestamp: July 21, 2016, 07:11:08 am
content: Wow, some OUTSTANDING advice. I'm going to think over a few of the suggestions, including either opening her up and just seeing if I can replace the internal converter with my own 12v step up and step down as well as regulating the 12v precisely; also looking at just purchasing a pre-made marine grade unit.Thank you again, looks like I found the place for my electronics hobby fix,Dave