Have to switch inverter off and on to power up pc

mbowler · 08-14-2000, 11:09 AM

Here is my setup in my car as of yesterday. I have a 140 watt inverter from wal-mart. The on button is on at all times and wired to a relay that turns it on with the ignition, when I turn on the car my pc doesn't turn on always. Sometimes (usually) I have to flip the inverter off and on 2 or 3 times to get the pc to turn on. Is the pc not getting enough initial power to turn on or what. By the way, the full power light is on on the inverter from the beginning

Chris Snyder · 08-14-2000, 12:15 PM

Some inverters will automatically shut off if they aren't getting enough voltage, which would happen when you start your car. I'm not sure of any way around it.

wizardPC · 08-14-2000, 07:21 PM

you need a bigger inverter. most power supplies require at least 150 watts, and most of the power supplies sold today require around 250 watts. you can get a 300 watt inverter at wal-mart for about $60.
I had a similar problem a while back when i put a VCR in my truck (long before i found this site and discovered what i could really do). Sometimes the VCR would come on, but not always. i had a 300 watt inverter, but the VCR required a power spike of 7 amps to start (which is 770 watts). i got me one of those energy star compliant ones and had no further problems. my point is you need a bigger inverter regardless of what the problem is, and if you do that and still have problems then your computer needs a spike to start. and no, i dont know how to fix that other than getting an energy star compliant system

Aaron Cake · 08-15-2000, 09:51 AM

Quote:

Originally posted by wizardPC:
you need a bigger inverter. most power supplies require at least 150 watts, and most of the power supplies sold today require around 250 watts. you can get a 300 watt inverter at wal-mart for about $60.
I had a similar problem a while back when i put a VCR in my truck (long before i found this site and discovered what i could really do). Sometimes the VCR would come on, but not always. i had a 300 watt inverter, but the VCR required a power spike of 7 amps to start (which is 770 watts). i got me one of those energy star compliant ones and had no further problems. my point is you need a bigger inverter regardless of what the problem is, and if you do that and still have problems then your computer needs a spike to start. and no, i dont know how to fix that other than getting an energy star compliant system

You are quite wrong. While it's true that a supply may be rated at 300W, that is the MAXIMUM power it can produce, not the average draw. Most PCs use only about 100W, REGARDLESS of the size of their power supply. Power supplies will draw a large surge at start up. If your supply draws enough to trip the inverter's cutoff, then you need a better supply. A lot of people are using 150W inverters without any problems at all.

Of course, the real fix for all this is to use a DC-DC converter.

------------------
Aaron Cake
London, Ontario, Canada

Player: Cyrix 200, 32MB RAM, 10.2Gig Quantum HD, Onboard EtherNet/Sound/Video, Custom Lexan Case, Win95 Kernal w/Custom Player
Car: '86 Mazda RX-7 w/Basic Performance Upgrades

ToesToes · 08-15-2000, 11:43 AM

Okay i had this exact same problem with my 300watt porta-watt. What happens is that there's not enough power for your inveter when you're starting the car. So what you need to do is to turn the inverter on a after you start your call. I found i needed to wait ~5 seconds with my car.

What i did was to buy a switch and wire it to the inverter. Start up your car, and flip that switch to start the inverter. If you inverter is already in a convient place, then you don't need to do this, but if it's mounted out of the way.. this will fix it.

Toes

mp31500 · 08-15-2000, 02:33 PM

I had to go with the 300 watt inverter also. Picked it up at Walmart for around $60. I just found out a few days ago that I can leave it running with the jeep off and it will keep the computer running during starting!!! The inverter low batt. alarm sounds but it keeps everything running. Great for short trips or to get gas. I even left it on for over an hour at lunch by accident. Not sure what the max time would be before the inverter cuts power.

mbowler · 08-15-2000, 02:36 PM

I actually just discovered this. I found that if I let the car sit in accessory power for a few seconds and then turn the car on it works fine, as opposed to just switching the ignition directly on from the off position. I posted another topic (need a way to delay a 12v signal). I am now looking for a way to have the power delayed a few seconds on it's own. Any ideas? A reply to my other topic suggested a solenoid for police car shotgun locks. I would imagine there is an easier way. I thought maybe a capacitor, but I don't know much about actual electrical parts.

Probedude_2000 · 08-15-2000, 11:06 PM

Mbowler,

If you're interested, check out my auto off (also provides a delayed power on and a switch closure for atx motherboards) board at my website.
http://www.dschmidt.com/autoooff.html

Bj · 08-20-2000, 09:23 AM

Hey Guys. It's obvious you guys don't know much about car electrics. I'm using a 60W inverter that runs all my stuff without a problem in the world. Why? Because I have a proper cable run. Use some big cable like 4AG stuff to go from the battery directly to the inverter, so when you start your car, there is no major voltage drop to the input of the inverter. This is your problem. Don't use a cig lighter socket or any tacky systems like that, do it properly and it will work every time. My battery voltage can drop to 9V and the inverter will still not trip out when I start the car. Try it. Use a heavy gauge cable from the battery post directly to the inverter and you'll notice a BIG difference.

Check out my modified inverter power supply if you also want a boost in inverter efficiency. http://home.primus.com.au/bravo

and go the the bjblaster section of the projects page.

Hope this clears a few problems up.

Probedude_2000 · 08-20-2000, 10:36 PM

BJ,

60W/12VDC = 5Amps max that you are pulling. Even if startup power was twice that (120W) you'd only be pulling 10Amps max (assuming 100% efficiencies). 4 ga is insanely overkill. 10ga wire is good for over 20Amps (or 240W continuous).

Back to your statement about voltage drop, the real reason your battery voltage drops during starting is due to the STARTER! The starter is NOT being supplied with power through the wire feeding your inverter, so beefing this wire up does NOTHING to increase the voltage to your inverter during cranking.

The only reason your setup works is that your inverter does not automatically shutdown when the voltage drops during cranking. You even said that your inverter does not shutdown when your battery is down to 9V. The majority of inverters out there shutdown when the battery voltage is about 10.5- 11.2V.

This is the reason your setup works. Has NOTHING to do with the heavy gauge wiring.
From your web page it would seem you would have figured this out already. Nice work on your web site BTW.

. . . Respectfully disagreeing with you.

[This message has been edited by Probedude_2000 (edited 08-20-2000).]

[This message has been edited by Probedude_2000 (edited 08-20-2000).]

Probedude_2000 · 08-21-2000, 11:00 PM

I ran the numbers for various wire gauges for a 10 ft length of wire.
Assuming a 5A current draw, here is the voltage drop over 10ft of wire for these gauges
4 ga = 0.01 volts
8 ga = 0.03 volts
10ga = 0.05 volts
12ga = 0.08 volts
14ga = 0.13 volts
16ga = 0.20 volts

So, assuming your inverter and computer is on while you are cranking, and your starter drags down the battery to 10.5 volts, if you used 16 gauge wire, the voltage at your inverter would be 10.3 volts.

Even if your used 4ga wire your inverter would only keep running if your inverter's circuity let it continue to run down below 10.4V, which isn't likely to begin with. Again, most I've used cut out between 10.5V and 11.2V.