Thanks for reading. Im having some problems with my car system, which includes a 5" lcd, a hard disk and a 240v inverter. If found that if the lcd is on, and then the inverter is powered up, then the lcd will die untill I unplug it then plug back in, so I assume the inverter is producing some spikes or something when it powers up. This happens every time, however the hard disk has also powered down before (when another device on the inverter was unplugged.. I think) which cant be good for reliability. The LCD powersupply is a normal 317T circuit with 3 protection diodes (output->input, adjust->input, and one that appears to be input to input bypassing some resistors if current is reversed). Also 0.1uf capacitor on input, 1uf on output, both tantium. I have no idea what type of powersupply is used on the HDD enclosure. So far I seem incapable of openeing up the case... but think its switching type as it seems to be very efficient. So the question is how do I prevent this. I was thinking an inductor/choke/suppressor type thing might help (on the inverters plug?), but having never used them before.. I dont know.. Thanks Mark
are you running a pc in your car from an invertor? what invertor are you using? what pc? full specs, is it a laptop or a desktop, either way, give us the full specs. what 5" lcd? is it a 12v lcd? or a high a high voltage ac lcd running from an invertor? a 12v lcd would be the way to go obviously tell us these ^ 4 things, and anything else you can think of
not using a pc, just a usb hard disk enclosure (is arm based, has sd card slot, tv in/out etc...) http://www.rapidonline.com/producti...ier4=12V+DC/230V+AC+Inverters&moduleno=66840# thats the inverter. Only the hdd enclosure is ran from this. The LCD is a sony psone screen, needs 7.5v and is ran from the LM317T circuit, as described above. The wireless camera and reciver, are running on 9v (rated 12) with almost exactly the same power circuit - except its a LM338T for the extra current. These appear to have no problems with the inverter. edit: looks like they do have the same problem, and switch off when inverter is powered up. thanks
i get it now it seems that the invertor has a massive current surge at turn on, i doubt it is dropping the car's voltage too low, i'd say it's more of a case of the resistance of the invertor being so low that it is taking most of the current, not leaving enough for the lcd & camera circuits. can we not use the invertor? if it's 12v we can just make a little vreg circuit... would only be good when the car is on tho, probably not what you want, plus it would be good to have an invertor in the car for various things. i'd suggest adding one of those 1 farad caps, close to the car's battery, this increases the car's surge current capability. I wouldn't add any cap's to the invertor, it will only increase it's start-up surge. I would add capacitance to the vreg circuits you made aswell, right at the 12v input of each circuit, not far away from the circuit, right on it. More capacitance the better, try 1 x 10 000uf on the 12v input of each vreg circuit might be enough, if not then try 2 x 10 000uf on each. Replacing the gauge of wiring for the two circuits should help aswell, no point going past 8 gauge, 16 gauge each would be good i'd say. If both are getting voltage from the one supply cable then maybe go 8 gauge - what are they getting power from now? If they are just tapped into existing car wiring, then giving them their own 16gauge straight from the battery will probably be enough. Using a thinner gauge cable for the invertor can help, but you don't want to have a cable that get's warm or hot! Fitting a choke/coil on the invertors supply cable should help a little, again make sure it can handle the amps, you don't want one that gets hot! edit: the 1 farad cap is the expensive upgrade, so you might want to try all the other upgrades first, unless that's how you've got it already?
I doubt that... not in a car supply. Whilst I have no idea how much resistance there is from the inverter to the battery/alternator... its not enough to limit inrush current of a small inverter with no load connected. I was thinking there was a back-emf type spike on the 12v supply, from the inverter.
with no load either! well even 1 hdd isn't that much of a load i guess well either way fitting one or better yet 2 inductors/chokes in series on the invertor's 12v input will help a bit. It would actually be good to fit chokes on the 12v supply of the lcd & camera circuits aswell if it's a spike issue - these two chokes don't have to be high amperage, and a bit of resistance would be a good thing for helping to suppress the spike. btw, the lcd & camera circuit's have their own cable going straight to the battery? fused very close to the battery of course is the invertor running off the cigarette lighter or is it sharing the same supply cable as the lcd & camera? - if they are all sharing one cable then i'd say give them their own supply cable from the batt. and does it matter if the motor is running or not? what about having the motor running, hold the revs at about 3000rpm (so the alternator is making heaps of power), turn on lcd then turn on the invertor without a load - does the lcd stay on or does it turn off? repeat test with a load. If the lcd still turns off like this, AND it's not sharing a 12v supply cable with the invertor, but it's own ~16ga 12v cable from the batt, then it's most likely a spike problem. If 3000rpm cures the problem then it has to be a current supply issue. another thing is with the motor off, radio on, up loud, turn on the invertor, what happens? and repeat test with motor off & cd playing. If it's a spike there would have to be sharp noise on the radio when turning on the invertor, but if the cd isn't bothered then the noise can't be that bad can it?
If you want to limit inrush current, an appropriate NTC thermistor in the 12v line going to the inverter might solve the problems. It will need to be securely mounted (on a board) and kept away from anything plastic - so putting it halfway along the cable wrapped in tape is bad I'm not sure a 1F capacitor is really an appropriate way to solve the problem - kind of like taking a sledgehammer to the problem. Plus they are rather expensive and will draw a huge current of their own when connected across the supply (assuming that little widget on top of them doesn't limit inrush current). A quad of motor run caps proceeded by an NTC inrush limiter might do the trick if the 12v supply *is* somehow on the fritz, even better if you throw in a regulator afterwards. Edit; or you could always put a UPS on the 'mains' side of the inverter lol Edit2: <redacted > And, FWIW, the psu for the hard drive enclosure will be switch mode.... linear PSUs are h00ge & heavy, you'd know if you had one Edit3: So um yeah. Final thought on the matter, sounds like when you switch the inverter on, the capacitors in there are pulling huge amounts of current (only for a brief time though), which is causing the 12V supply (presumably ciggy lighter) to dip a little, which upsets the LCD. Does inverter THEN LCD work?
from what he described i thought there was a massive surge of current happening, hence the massive 1 farad cap option amongst my suggestions , i didn't think of using an ntc thermistor to limit surge! nice suggestion! from what i understand, switching the invertor on, then the lcd on is fine. I dunno if it's surge or noise or a bit of both giving trouble? I just wanna know the answers to the questions in my last post: the results of the tests i proposed and the detailed description of how it all is wired. I think these answers will give us a good picture of what is happening. I havent used a car invertor before, so i'm interested to find out what's happening here.
Nor have I ever used an invertor, I'm sure some practical experience would help. From the fact that switching the inverter on after the LCD killed the LCD but vice versa is fine, this suggested to me that turning on the inverter was drawing a large current from the car, quite possibly to charge up some large-ish caps inside, and while that was fine for the car it was pulling the 12v down a bit which was upsetting the LCD, as opposed to there being a back-emf spike (i.e. overvoltage as opposed to under) or similar. A voltmeter across the 12v supply might shed some light.
