Thread: System Restarts whenever I start my car

1. Originally posted by Tony S:
<STRONG>Yeah, Jeff knows what he's talking about. That's exactly why your PC keeps kicking off/on. In fact, the voltage fluctuations could really mess with electronics if your ignition system didn't temporarily cut out when you turn the key. Going straight to the battery negates the ignition cutout. I, too, plan on hooking straight to the battery.</STRONG>

Actually, hooking straight to the battery might not help you that much. I had my box setup so that it was powered from the cig outlet that goes to the back seat. It was not hooked to the ignition, but it was hooked up to the battery through smaller gauge wires. I put a big filter cap right at the MpegBox input. Because the wires that go to the cig outlet in the back seat have more resistance than the ones going directly to the battery, when I started my car, my box would NOT restart. This was because the capacitor stores some charge. When the car starts the voltage at the battery drops a little bit. The capacitor then has to discharge either into the MpegBox or into the starter through the higher resistance lines. It chose MpegBox because current chooses the quickest path to ground, and that was through MpegBox instead of the higher resistance lines to the starter. I then connected my Mp3 player directly to the battery through 12 gauge wire. Then every time I started the car the unit WOULD restart. The low resistance path straight to the battery that didn't have to go through the fuse box (source of more resistance) made it so my filter cap discharged directly into the starter motor instead of keeping MpegBox alive..

The bottom line:
Batteries have what is called "internal resistance" If you battery is new, chances are it has a lower internal resistance. (lower resistances are good) Picture a voltage source that is Exactly 12 volts. Then picture a small "internal resistance" resistor in series with the battery. If that resistance is say, 0.1 ohms if you draw say 50 amps to start you car the voltage AT the battery would be 7 volts. (12 - 50*0.1) You can see if that internal resistance gets very big at all, it won't matter how well you connect to that battery and avoid the ignition. The starter motor is connected to that battery A LOT BETTER than running 5 feet of 14 gauge wire is. If you look at the starter one most cars, you see the positive terminal of the battery going right to the starter solenoid relay. And it is 6 gauge or so wire.

So, yes a new battery might solve the problem because its internal resistance will be low. (That's why you hear "test the battery under load") You are testing the internal resistance of the battery. As batteries get older, their internal resistance gets bigger. Unless you want to buy a new battery all the time, it won't fix your problem. Instead, you can do what I mentioned above, use a diode to block the path back to the starter motor, and use a capacitor to store some of the charge so your Mp3 unit will not be affected but transient power surges. You can do this on your stereo too if you don't like it turning off when you start your car.

I hope this makes sense and I didn't bore anyone to tears with EE jargon..

Jeff_

2. You're right again. I actually didn't finish my thoughts in my last msg b4 this one. I was @ work so had to cut it short for an issue. Anyway, I plan on hooking right to the battery but using some type of timed relay to start a few seconds after the engine turns over. By then the voltages should steady out enough. That, or the capacitor setup will work, yes.

3. So what size Capacitor and diode do I need to get to hook this up? I dont have this problem but I wanted to hook up a capacitor anyway just in case...

4. Jeff: Sounds like your car is having battery issues. I don't know what type of supply you are using, but you shouldn't need a tank circuit to keep your player from restarting. If you voltage falls below 9V during cranking, you have a problem somewhere.

5. I was reading about the installers who developed the install instructions for the Clarion AutoPC and they suggest that a 1/4 farad capacitor should be used to on the Acc line to the PC to prevent exactly this. The "tank" circuit probably does the same thing. By installing it on the Acc line it should prevent the power from feeding back to the starter as the ignition switch already isolates these 2 circuits.

(sorry about not being around for a while, the whole Northpoint DSL fiasco has me without an ISP right now. By the way, I like the new layout of the board.

6. Im at work so I cant give a whole big write up as to why these things happen, but there are miltiple reasons for the rebooting...

Wire guage used on the power leads to pc, loss of voltage / amperge due to cranking, a surge when the starter makes contact... lots of reasons, I built a similar circuit to isolate the pc from the car electrical when cranking. you could easily modify this to act as an aux (switchable ) power source for the pc while using it w/o the car running.

Note the use of this circuit assumes that you have determined the reason for the rebooting is because of the drop out during cranking, and not because of a faulty supply, bad wireing or something else.

There realy is no need for a special gel cell aux batery, I used a small 7 amp sealed lead acid - cost 17.50 it can run my pc for about 40 min.

Schematics - http://www.hjnetworks.com/car/auxpwr.htm

7. Originally posted by Aaron Cake:
<STRONG>Jeff: Sounds like your car is having battery issues. I don't know what type of supply you are using, but you shouldn't need a tank circuit to keep your player from restarting. If you voltage falls below 9V during cranking, you have a problem somewhere.</STRONG>
I wish I chould show you guys what it looks like on an oscilliscope. Like I said, I have killed my battery several times, so I AM having battery issues. Does that mean I need a new battery? Only if I am not happy with its 75 percent performance and want to spend 60-100 bucks. With a few bucks in components, a tank circuit keeps me from spending this kind of money, I can probably get another year from my battery. My supply cuts out at 10.5 volts or so, and it only needs a few hundered nanoseconds at that level to shut down. Like I explained above, it is very easy for a good battery to realize a 2 volt drop when you starter is drawing 50 amps.

Just the other day I killed my battery again. (left the cars PA hooked to the CB radio on for 3 days) I had to push start my car going. I drove home from Oregon State and stopped to get gas at the local Pilot. Got gas, ran in to pay, came back, started the car, the radio cut out but the player kept going. I'll think I'll pass on a new battery for now.

Jeff_

8. Remember, starting your car with a damaged battery will burn out your starter and stress the rest of the electrical system.

For what it's worth, I have looked at my car's starting voltage with a scope. The lowest voltage seen was just above 10V, right when the solenoid clicked in. The highest was a spike of about 360V, when the solenoid disengaged. Bear in mind that this is with a Crane CDI ignition (20A load at all times) in addition to the regular stuff.

9. It definitely sounds like a battery and/or starter problem to me. Most car batteries should be able to handle cranking and still keep the battery voltage above 8 volts. Otherwise, this would pose a real problem for the vehicle electronics such as fuel injection controllers and the like.

I've been using a custom-built ATX DC-DC PSU for about 4 months now and have never had any problems. The computer never reboots or hangs when I start the car. It is connected to the battery at a junction block in the trunk that is used for my amplifier as well. I ran 8AWG wire to the battery, and the car PC uses 12AWG wire from the junction block and back to ground.

Several times I have left the computer on by mistake while in class and came back over an hour later and was able to start the car just like normal (and the PC didn't reboot then either!) My system draws about 2.6 Amps while running.

The best advice I have is to run some heavy-gauge wire directly from the battery (through a fuse of course!) to your car PC. You can place a relay inline if you like, or use an ATX DC-DC converter like I do. Also, it is very important to find a good solid grounding point for the power supply. Remember, the voltage travels in a circuit between the battery, the power supply, and ground, so a good ground is just as important as the power lead. Plus if your ground is weak, the power supply will try to complete the circuit through other sources (i.e. your head unit or amplifier through the RCA grounds) which could end up damaging something.

Also, have your battery load tested or get one with more cold cranking capacity if you still have problems. The Optima battery mentioned above is an excellent choice in terms of high durability and low maintenance. You can even mount these batteries upside-down or sideways (they have gel instead of liquid inside). I've even heard of them working with the outer case cracked open during an accident.

10. Originally posted by Aaron Cake:
[QB]Remember, starting your car with a damaged battery will burn out your starter and stress the rest of the electrical system.

QB]

My car has no problem starting. It starts everytime without sounding like it is straining, the capacity of my battery has been decreased from use. When I get the chance, I'll post the data from my Tektronix TDS3054.

I think what it comes down to is my cars DC to DC converter was designed for use in laptops where the operating input voltage ranges from 11-16 volts. You guys are using supplies that allow an input voltage from 8 -16 volts.

I don't remember ever saying that my cars voltage was down at 8 volts during starting. I said that it could happen if the internal resistance of the battery got very big.

Also, My car is not fuel injected. It is my guess that the folks at Honda found a good way to deal with batteries (that are standard non-sealed non-gel cell batteries that are a few years old) in a way such that the cars computer and electronic systems don't fail from small transient dips down to 8 volts or so. Doesn't the most stress on a battery and electrical system occur from Jumping a car? Connecting a battery with full charge (and the others car charging system) directly to a battery with no charge, talk about a lot of current.

What is so wrong with using a diode and a capacitor if it works and solves the problem?

Jeff_

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