12V inverter - Page 1
Forum section: electronics / general

author: akis
author_rank: Frequent Contributor
timestamp: December 07, 2014, 10:58:58 am
content: I am looking to buy a good quality inverter to use in my car. I already have a very old one, it claims to be 300W with transients of 1000W but it is not. It can barely cope with 50-60W, I have to plug in devices one at a time else it does not even start. We then bought a brand new "300W" from Halfords (auto spares shop in the UK) and it was even worse, it would not even power my laptop adapter without the laptop connected!I need a converter that will provide cleanly over 100W with no problems. The cigarette lighter sockets are rated 15A so we are talking maximum 180W out of the sockets, on the load I would expect no more than 150W.

author: G7PSK
author_rank: Super Contributor
timestamp: December 07, 2014, 03:50:41 pm
content: I have also found that it depends on which socket in the car you use, On my car you can get 150 watts but the one at the back my inverter shuts down if 40 watts are applied.

author: Lightages
author_rank: Unknown
timestamp: December 07, 2014, 03:57:11 pm
content: Samlex makes good ones. I don't know where to get one in the UK.http://www.samlexamerica.com/products/ProductDetail.aspx?pid=469

author: MarkL
author_rank: Unknown
timestamp: December 07, 2014, 05:42:44 pm
content: Quote from: Lightages on December 07, 2014, 03:57:11 pmI second that. I have several different models of their pure sine wave inverters and they all work great and they are reasonably priced.Another good inverter is Exeltech:http://exeltech.comA little more expensive, but very well designed and made. I have their XP125 purchased 14 years ago and never a problem.

author: akis
author_rank: Frequent Contributor
timestamp: December 07, 2014, 07:27:43 pm
content: I live in the UK we do not get many US products, presumably due to the ridiculous taxes. Do you know that for an item to come from the US to the UK, the importer/customer will pay US sales tax, shipping costs, UK taxes on the gross (including tax on tax and tax on the shipping costs), incur ridiculous delays at UK customs as well as pay extra charges to the courier companies for "customs clearance charges". The UK customs treat everything from the US as if it has come from some sort of terrorist country whereas you can import anything from the far east no probs.Therefore, everything in the UK is made in China. It is a challenge to get something non Chinese in the UK.So I ended up buying a "best seller" from Amazon, hoping it will work else I will return it. It is rated 300W, but I only plan to draw less than 70W. Still I wonder if it will work at all.In addition from my experience and people's comments these inverters make lots of noise as soon as you try to pull any power, and you must add devices incrementally else they trip during startup and refuse to start.So I was thinking how hard will it be to make my own. Take an old 300VA troidal transformer, make a 12V p2p square wave generator or sine wave if needed, plug it to the transformer backwards and job done. The square wave would have good efficiency.

author: SeanB
author_rank: Super Contributor
timestamp: December 07, 2014, 08:04:11 pm
content: Buy some Anderson plugs and wire them direct to the battery via a suitable fuse ( around 60-100A from most car audio shops) and you will have no issues with the voltage drop along the cable making it drop out. You do need decent cable though for the power leads.

author: MarkL
author_rank: Unknown
timestamp: December 07, 2014, 08:11:37 pm
content: Samlex is made in China:http://samlexgroup.comI would never connect anything I care about up to a square wave or even a "modified sine wave" (it's really a square wave) inverter.Good luck building or buying.

author: grumpydoc
author_rank: Super Contributor
timestamp: December 07, 2014, 08:25:35 pm
content: What do you wan to power from the the inverter?For some things a DC-DC converter or even using the "12V" direct would be a better solution.

author: akis
author_rank: Frequent Contributor
timestamp: December 07, 2014, 08:45:16 pm
content: Primarily I want to power my portable device which in its current version needs 12V-0-12V supply. So if I go the direct route, I need an "extra" 12V, isolated from the original 12V. Some sort of isolated DC-DC converter at around 50W. Then, my next version of my portable device will need 24V-0-24V supply. There, I would need two isolated, 24V DC-DC boost converters. But at home I use two isolated, mains, 240VAC to 12VDC / 24VDC adaptors. So in the end I thought it would be much simpler to have an inverter in the car and then I can plug *anything* to it, whetver I use at home anyways.I ordered this from Amazonhttp://www.amazon.co.uk/gp/product/B00INW611Y?psc=1&redirect=true&ref_=oh_aui_detailpage_o03_s00I did not check but would be very surprised if not made in China. And I do not expect a pure sinewave, but for sure it should be able to power DC adaptors as used on laptops etc, after all, this is the main target application for those inverters.

author: grumpydoc
author_rank: Super Contributor
timestamp: December 07, 2014, 09:01:58 pm
content: Well, it looks OK on paper.

author: madires
author_rank: Super Contributor
timestamp: December 07, 2014, 09:12:51 pm
content: An isolated flyback with +/-12V or 24V output would be a nice project and is no rocket science. I've built one based on a LM2577. Please seehttp://www.ti.com/lit/an/snva028b/snva028b.pdffor the basic idea. You might need another Simple Switcher for the required current.

author: akis
author_rank: Frequent Contributor
timestamp: December 09, 2014, 10:23:47 am
content: I have worked on the LM2679 Switcher and I must say it is not a walk in the park. Or to put it another way, it is OK up to 50% of rated power and then it collapses in various ways, including blowing the chip (the most common way to go). I have made numerous prototypes and built 4 copies of the final version. All 4 boards precisely the same, with exactly same components, have different current capabilities, from memory ranging from 2.8A to 3.8A, before the output collapses. In the end, to achieve my "5A" I paralleled two bards together connected via diodes. This works because as the LM2679 cannot give anymore, the output voltage decreases so the two boards balance out naturally.But I could never figure out why the "5A" was practically not achievable. The technical notes go on to pretend it is cake, but on some other application notes they do describe what I found out to be the case, oscillations on the diode that need to be swamped with a capacitor. And probably more things that can go wrong.All this to say that I believe that DC-DC at high amps is some sort of black magic :-)

author: theoldwizard1
author_rank: Regular Contributor
timestamp: December 20, 2014, 07:33:56 pm
content: There is a lot of junk on the market ! Some are the same thing with different labels.To me "good" mean "pure sine wave", although with out knowing how you are going to use it, it is hard to know if it s really a "requirement". Most things run "better" on pure sine wave.Check outKnurlgnar24's YouTube Channel. Lots of different inverter reviews.Quote from: SeanB on December 07, 2014, 08:04:11 pmBy far, THIS IS THE BEST ADVICE !For a 300 watt inverter I would use 12 AWG and a 30A fuse.

author: nowlan
author_rank: Frequent Contributor
timestamp: December 21, 2014, 02:06:59 am
content: I like watching that guy's reviews.Funky DMM he has too.