I need a way to charge a USB device from the 12V socket indirectly to avoid the prius ground loop. Any ideas?
Ebay lists isolated 12V to 5V switching regulators. I would get the 'glue' logic (i.e., connectors, wiring, and housing) and assemble it. Bob Wilson
Buy one of these: DC DC Isolated Power Supply in 10 8 13 2V Out 5V | eBay Take to store and find a large 12V to USB charger like this: New Car Auto Charger Adapter DC 12V to AC Converter 220V Charger Power with USB | eBay Take the second unit apart and keep just the USB socket and housing. Epoxy the regulator to one side and run the 12V to the car 'plug' and the output to the USB pins. Double check the input and output polarity and test with a 9V battery. How soon do you need it? This is a simple build. Do you want me or any of our compatriots to toss one together for cost of parts and shipping? Know any high school kids taking electronics who need a project? Bob Wilson
I plug various things into my car. I actually need that and a reliable (won't burn out easily) 12v cig lighter splitter that has at least 4 cig ports out and 2 USB out for various electronics. I don't need it urgently. Perhaps I'd be able to put it together myself if I had more detailed instructions.
Uh Oh, changing requirements makes this much harder. The original requirement was to a ground isolated, 12V to USB (aka., 5 V) converter. The isolated DC-to-DC converter will accomplish that task. It just needs connectors which I would normally just adapt from another part that is not isolated: two leads to the 12V supply two leads to the USB connector No assembly required. Bob Wilson
The usual reason for avoiding a ground loop is a direct audio connection. One easy option is an audio isolation transformer. It takes no power and keeps the ground loops away: 3 5mm 1 8 Car Aux in Headphone Mini Jack Ground Loop Isolator Noise Filter | eBay Bob Wilson
I've isolated 12V power before by using a rechargeable battery-pack between the seats. I drew the power from the power-pack, which was recharged by the vehicle. In my application, the negative power-out contact was not common with the ground of the vehicle, but that may not always be the case.
I have a custom sound system in my car. I wanted to listen to mp3s, but modifying the MFD to allow this seemed too complicated and risky. So I installed a self-contained (except for power) sound system. A phone with 3.5mm out is connected via 3.5mm to a 12v amplifier, which is connected to 2 speakers via basic speaker wires. The amplifier is fed power directly from the 12v socket via a cig lighter splitter. The problem occurs when the phone is being charged via a USB cable connected to the car's 12v system. It causes the ground loop to be heard. Unfortunately, "filtering" the 12v electricity via a USB battery pack charger still causes the ground loop. If the battery pack is connected to the 12v system to charge the pack, but the phone is not connected to the battery pack, no ground loop. If the battery pack is not connected to the car 12v system, but the phone is connected to the battery pack for charging, no ground loop. If the battery pack is connected to the 12v system to be charged and also connected to the phone to charge the phone, I get a ground loop! I even tried using a laptop. I connected the laptop to the car's 12v system via a DC car charger compatible with the laptop's DC in requirement. Then I connected the phone to the laptop via a basic USB cable and got the ground loop! So the only way to listen to the music and charge the phone is by alternating connections. The battery pack can charge the phone or the car can charge the battery pack. Both at the same time cause a ground loop. The reason I brought up the 4-way or 5-way splitter is just to give people an idea of what I wanted to do in case they see a shortcut in the big picture. I have considered ground loop isolators, but they appear to hurt music quality. Also, any suggestions regarding a good 12V cig light splitter I mentioned?
Medical power supplies have to prevent ground loops that can kill a patient. But now we have a better requirement, not stated, but implied: Input: 10-14V DC @1 A Output: 5V @500 ma It would help to know if this USB device is a 500 ma or larger load. You typically want a power supply to not be overloaded for any significant period of time. So let's start with the first part: There are two, disconnected grounds, "Vin-" and "Vout-". But it is listed as "1W": UL,CE certified Size: 19.6x 6 x 10 (mm) Efficiency: 80%(max) Maximum isolation voltage: 1000V DC Input voltage: In 10.8-13.2v DC Output voltage: 5v DC Power: 1Watt Maximum output current: 200mA Minimum output current: 20mA Working temperature: -40~185 F So I checked their Ebay store and had no luck. So one option is to parallel three giving potentially 600 ma. but sometimes the output side regulators can 'fight' and let the smoke out. We would need to check the 'Application notes' and hard specs. But first, lets see if something might already be out there. So checking Ebay, I found: DC DC 10 24V to 5V 1 5A Car Isolated Power Supply USB Charging Board Converter | eBay This appears to be an integrated unit that does everything needed. No need to hack putting together a set of smaller parts. But some assembly is required: Buy part Take to Radio Shack and buy plastic box to house it 12V auto plug to power it grommet for plug wires nibble and mount part in box so USB port is available and mechanically solid and grommet fits take time, make sure solid mount for USB and wires make sense remove part from box run 12V leads through grommet hole in box solder 12V auto plug to board install board and cover Post photos of your part here. GOOD LUCK! Bob Wilson
The MP3 player is a cellphone and most of the chargers for it are rated at 1000mA so I wouldn't risk getting anything with fewer max amps. Thanks for doing the research. Looking at it now I'm wondering why I don't just get something like this: The cellphone generally has enough power to last a day in the worst conditions (extreme cold) so why not just use that? Any other ideas regarding the use of a solar panel to accomplish this?
Have you considered using a small 12VDC -> 120VAC inverter, feeding a 120VAC -> USB power converter, to provide your power? This would break the ground loop. Though I can believe other problems cropping up with common cheap consumer products, such as USB converters not liking cheap modified sine wave inverters, switching frequencies sailing through terrible ripple rejection, and others. This won't be nearly as efficient or compact as the isolated DC-DC converter solution Bob is pushing for, and quite possibly not as quiet either, but might work for someone not confident with building their own.
Idea ... the "cigarette lighter" plug is about the most ungainly, oversized, and low-contact-quality power connection you could think of. Ham radio geeks seem to favor compact powerpole connectors, where you can get various nifty adapters and a selection of power distribution splitters including the RigRunners, which let you individually fuse different connections to protect whatever gauge wire you'll be plugging in at each port. -Chap
I've used those in the past. Even brand name ones seem to be unreliable and horribly inefficient. 12V DC up to 120V AC of which I only need 5 DC.
I absolutely agree. Why are we still using nonstandard adapters made decades ago to somehow work with a plug designed for lighting cigarettes back when in-car portable electronics were not as common and when smoking in cars was common? Unfortunately, most of my equipment is compatible with this type of port and as long as it works I am not willing to invest serious $$$ to make it logical.
It is the two conversion devices in place of one that is inefficient. It isn't like the 120V-AC -> 5v-DC conversion throws away 96% of the power or is any more inefficient than the other stages. If this approach has had reliability problems, consider trying again with a real sine inverter, not the common cheap MSW inverters.
I took a quick glance at prices and it seems to be prohibitively expensive for what I am trying to do. There are more efficient, cheaper solutions, like the solar panel charger.
