Rebooting on Ignition startup

[mhawley]

I posted this question several weeks ago, I have found out some new information and wanted to see if anyone had any new ideas.

My Z1 is in a diesel truck. I have to turn the key on to start the glowplugs and cylcle the fuel pump. While this is going on, the z1 boots up. The process lasts about 30 secs, and then I turn the key to start the engine when there is a voltage drop to run the starter. The voltage in the power line(Ignition Accessory) to the z1 drop to less than 1 volt. This causes the z1 to reboot. The voltage drop is only for about 1 sec. There is another power line to the z1, this one come directly from the battery and is hot all the time, it powers the memory. It only drops to about 10 Volts during engine startup. I have been researching this and it seems to be a big problem with the Car PC people who do not like to have there Car PC's reboot on car startup.

 

I have seen several possible Solutions:

 

1. Simplist: Install a simple switch between the ignition power line and the z1, then wait till the engine is running and turn the z1 on manually.

 

2. Tank circuit. I was wondering if anyone had any experience with this. apparently it is a circuit that senses the voltage in a primary line and when it drops below a certain voltage switches to an alternaltive battery to keep the voltage at a set level, and then switches back to the primary circuit when the voltage returns to normal. I was thinking of using the battery circuit that provides memory power to the z1 instead of a seperate battery for the 1 to 2 secs that it needs the alternate power.

 

3. Capacitor. Could this be configured to provide power for the 1-2 sec. that the voltage drops to less that 10volts. One of my concerns is what happens to the power in the capacitor when the ignition is switched off, does the the Z1 continue to run till the capacitor looses its power or could it be set up to where the unit shuts off when the ignitions is shut off?

 

4.Diode. I'm not real sure on all the operation of it, I seems like it does something to prevent spikes. I believe it stores spiked energy and then disipates it at a later time, sort of the reverse of what needs to happen in this case, but could this some how be configured to keep the voltage on the side of the z1 from dropping below 10 volts?

 

There seems to be a lot to technical and electrical expertise on this board, so I was hoping some of the knowledgeable folks could help.

[ducatiboy]

It's not a problem for it to reset, other than the annoyance for the driver for it to completely boot up just to restart.

 

I think your best bet is the capacitor. You want something to hold up the voltage while you crank over your car (or truck). The problem is just putting something in across the 12v switched line and ground it would try to supply power to the whole truck and unless it was the size of a toaster it would drop so fast it wouldn't matter.

 

So it would need a diode to keep it from feeding the rest of the electrical system.

 

And yes, when you turned off the truck it would keep the Z1 on till the cap drained off. But if you choose the value correctly, it shouldn't be too long. How long do you crank over your engine? 2 seconds? 5? You choose the size of the cap to only be just longer than that.

 

I guess the first step would be to measure the current the switched 12V line feeds into the Z1.

 

Not to be too much of a schmuck, mine are all installed and this isn't a real important thing for me to find out so I'm not super inclined to rip it out to measure it. Although one of mine is installed in a F250 with the diesel, so I know what you are talking about, but I just live with it.

 

so if anyone wants to measure the amount of current a running Z1 draws on the 12V switched line we can come up with a cap and diode which should keep it alive long enough. I have some extra caps laying around which should work, I just don't want to go poking around trying some without doing the math first.

[ducatiboy]

1. Simplist: Install a simple switch between the ignition power line and the z1, then wait till the engine is running and turn the z1 on manually.

 

Technically this is exactly what you have now, just that it boots once before you would flip the switch.

[cntrylvr79]

if I remember correctly the z1 pulls around 100ma on the accy line.

[ducatiboy]

The other problem is that, I wonder how low the voltage can go on the cap before the Z1 resets.

 

Even with a 5V drop over 5 seconds, I'm still getting a cap the size of my forearm. And you would need to put a resistor in front of it so that every time you cranked the key it wouldn't have a super in-rush of current.

[bdmpastx]

You really think that the reset is due to voltage drop and not due to the accessory part of the ignition switch being turned off momentarily? I know that mine reboots due to the accessory being turned off on startups. You wouldn't normally notice it on a gas car but I know this due to installing car alarms and such. When you crank over a car, the accessory power is turned off when the starter is actually being turned over so that you can use all available power to turn over the engine. There are several ways that you could bypass this functionality. You could do as you say and add a capacitor and a diode to the accessory (switched power line (Red Wire)) of the radio only. And I am not talking a huge capacitor that you see for car stereos running huge amps and such. Or you could put a jumper wire and two diodes from the start circuit to the red wire of the radio. One diode would need to be on the switched line and one on the jumper. So that no feedback gets to the starter in normal condition and no vice versa so that no feedback gets to the other accessories in a start condition.

[ducatiboy]

You really think that the reset is due to voltage drop and not due to the accessory part of the ignition switch being turned off momentarily?

 

Yes, it drops from 12V to 0V. But with a cap, the voltage will drop slowly over time depending on the time constant of the circuit. So one would need to know the capacity of the circuit and how low of a voltage the Z1 can tolerate before it thinks it's time to shut off. When that line goes from 12V to 0V almost instantly that's enough. But will it shut off if that line was 5V? 10V? 2V? I don't know, it depends on it's sensing and input for that line.

 

I also don't know what a slight voltage drop (or a slow voltage drop) would do with the z1. Can it handle it?

 

I know that mine reboots due to the accessory being turned off on startups. You wouldn't normally notice it on a gas car but I know this due to installing car alarms and such. When you crank over a car, the accessory power is turned off when the starter is actually being turned over so that you can use all available power to turn over the engine.

 

Yah, it just drops the voltage very quickly.

 

There are several ways that you could bypass this functionality. You could do as you say and add a capacitor and a diode to the accessory (switched power line (Red Wire)) of the radio only. And I am not talking a huge capacitor that you see for car stereos running huge amps and such. Or you could put a jumper wire and two diodes from the start circuit to the red wire of the radio. One diode would need to be on the switched line and one on the jumper. So that no feedback gets to the starter in normal condition and no vice versa so that no feedback gets to the other accessories in a start condition.

 

Well the size of the cap will depend on the voltage of the system (which we do know is 12V -15V ish). Generally the rule of thumb is 2x the voltage of the system for safety. We need to know what the current draw of the Z1 is and according to cntrylvr79 it's 100mA. So now we need to know how long you want to keep the Z1 alive, I'm guessing 2 - 5 seconds. And how low of a voltage the Z1 needs to keep it alive. I'm going to try to run some numbers, but I'm thinking it's going to be a huge cap.

 

We would also need a current limiting resistor for the cap so it doesn't try to charge instantly and a diode to keep it from feeding back to the rest of the car. We only want to keep the Z1 alive.

[ducatiboy]

Some quick math, I came up with at a 5V loss over 5S you would need about a 0.1F or a 100,000uF cap. And at 25 volts you would get something in the 20+ cubic inches size range Panasonic sells them:

http://www.panasonic.com/industrial/com ... ES_DNE.pdf

 

Of course if we only need 2 volts we can get away with a .03F or 30,000uF cap. These are pretty beefy caps and most likely would have some amount of leakage (constant drain on your battery).

 

This might not be the best solution.

 

Instead of holding up that line constantly (which I went down this because all the wires are at the Z1)... how about a relay which would switch the red (switched) 12V to the wire that becomes energized when you crank the engine.

 

You put a relay in line with the red switched, signal to the relay to switch goes to the energized wire when you crank the engine. When that happens the relay switches the red 12v switched from where it's normally at to the energized 12v line for the starter, when that goes away it switches back to the normal 12V switched line. You would put a small cap between the relay and the z1 to keep up the voltage during the very quick transition. Based on the sensing of the Z1, you might not need it. It would be, lets guess 50ms to switch. You could probably do that with a 1-2uF cap or so.

[madmanfrommars]

I was actually going to suggest something like that with a relay connected in series, although I'd think that the capacitor would have to be bigger then 1-2uF, thats a very small capacitance. You have to keep in mind that there would be power losses due to the resistance of the wires, so it would need to be even bigger then we calculate.

 

We'd definitely need the actual values to plan something like this out. Can you take a multimeter and take voltage/current readings of how much power the unit draws normally and at what values it reboots at? From that, it would have to be determined how big the capacitor should be.

[ducatiboy]

I was actually going to suggest something like that with a relay connected in series, although I'd think that the capacitor would have to be bigger then 1-2uF, thats a very small capacitance. You have to keep in mind that there would be power losses due to the resistance of the wires, so it would need to be even bigger then we calculate.

 

We are only at 12V and drawing 100mA (according to cntrylvr79). With this voltage and current and short wire lengths, I would bet the resistance of the wires is so minimal that you won't need to put it in the equation.

 

If 100mA is measured with some length of wires (couple feet) then we can assume a 120ohm impedance for the Z1 (at least with this line for sense).

 

If we assume that a large relay would take 50mS to switch, that puts the voltage drop of just over 2 volts for that time for a 2uF cap. 1uF puts it at 5v drop. I don't know what is needed to keep it alive.

 

So thrown in 10uF cap. I don't know how long the switch from one source to the other would be. But I'll bet it's pretty short.

 

We'd definitely need the actual values to plan something like this out. Can you take a multimeter and take voltage/current readings of how much power the unit draws normally and at what values it reboots at? From that, it would have to be determined how big the capacitor should be.

 

I can't cause they are installed in vehicles at the moment. If you don't believe cntrylvr79, then if someone would like to measure the 12V switched to make sure, that would be cool. I can get to this eventually but not right away. And I don't feel like buying a 3rd Z1 for more tests

[Deep Throat Jr]

What if you used a time delay relay with a 5 second delay. Use the trucks Acc wire to trigger and hold the relay. have the relay switch B+ to the Z1 Acc input.

 

Just my 2 cents

 

DTJ

[cntrylvr79]

Why not just do it the easy way and tie the red wire into an ignition wire in the truck instead of using the accy wire that it's tied into. The ignition wire in the truck winll not lose power when the engine is cranked. If you want to keep the retained accessory power for the radio that's a fairly easy thing to do with a couple relays and a diode or 2.

[ducatiboy]

What if you used a time delay relay with a 5 second delay. Use the trucks Acc wire to trigger and hold the relay. have the relay switch B+ to the Z1 Acc input.

 

Just my 2 cents

 

DTJ

 

Sure that would work too, but it would require more smarts or another RC circuit to slowly drop the power to whatever relay to give it that delay. But yes, something like that would work.

[ducatiboy]

Why not just do it the easy way and tie the red wire into an ignition wire in the truck instead of using the accy wire that it's tied into. The ignition wire in the truck winll not lose power when the engine is cranked. If you want to keep the retained accessory power for the radio that's a fairly easy thing to do with a couple relays and a diode or 2.

 

I don't know what wires are available in a vehicles wiring, at least not as much as you do... but the last thing I came up with was 1 relay and 1 cap (a rather small one at that too). How is a "couple relays and a diode or 2" easier? I guess I would need to see what wires were available with the key on and off and what had 12V and what didn't, there might be an easier way that what I last posted.

[cntrylvr79]

Well going out on a limb here, based on his other posts this is a 2000 Hummer H1. At the ignition harness there should be a green wire. This wire will show +12volts when the truck is on and also +12volts when the truck is cranking. So run a fused tap of that wire to the z1. Now provided that the voltage in the truck doesn't drop below 10.2 volts the z1 will stay running while the engine is cranking.

 

Ducatiboy. The 10.2 volts is based solely on my d1. The z1 may be a little different.