Thread: Doesn't hold standby power if I crank the car right away

Apologise to all for this long reply, but even this just skims over one of the problems with a PC in a vehicle – powering it.

The initial installation of a CAR-PC seems so simple at first glance, but in reality involves some serious thinking to overcome problems in the majority of PSU’s that behave like this and other system silliness in complex interfaced installations. If it were not for my initial use of STR (Suspend to RAM) I would not have noticed anything wrong with that part of the PSU initialisation (there was also a major noise problem with the M4 that I had to overcome).

Most installations end up with multiple ground points for various parts of the installation along with lengthy cable runs in a hostile electrical environment. It’s difficult in most installations to isolate the LCD ground casing, USB HUBS and amplifier chassis etc from the car frame (there are also reasons not to) and/or there are long earth connections joining two points. If a long cable connects the screen or other device to the PC then all kind of noise signals can develop between the two earth points, even with chassis grounding (and some case because of it.) RF pulse noise from the PC, HUBS, data lines and switch-mode PSU crawl over everything to some degree and the PC/PSU effects increase rapidly with a more powerful (power draw) system.

My installation has a small 14AH AUX battery that is “supposed” to maintain the PC and stop cranking voltage pulse/variations from upsetting the various microcontrollers when starting the car. Of course this depends on maintaining a correct state of charge in the AUX battery and comes back to how the system is used, wired and controlled. So every installation is different, and that’s without even getting into different Car design, charging systems, ground systems, chassis construction etc used by each vehicle maker which effects noise, starting voltage variations, pulse currents/voltage and chassis induced currents.

A lot of CAR-PC PSU units are supposed to run down to 6v or so (for brief periods like engine cranking) and they do, but that doesn’t mean the PSU wont spit the dummy for a few hundred MS just as it’s starting, in other words, it starts, stops (if in STR mode it drops +5v standby) and restarts, the end result is a failure to resume from STR.

I can only talk about my installation as without a block diagram, lead length and grounding etc I have no idea of your system connections, isolator or power switch timing. I think this is now at a point where my current basic power layout circuit is needed.



I ran 35A cable, both positive and negative, directly from the battery to an Alpine AMP mounted in the trunk. About 3 feet from the AMP I paralleled a Pos and Neg cable to the CAR-PC, also in the trunk but forward of the AMP.

The negative wire from the main battery and a short heavy chassis wire go to the same point on the CAR-PC chassis along with the negative cable from the AUX battery. The AMP is also grounded straight to the car chassis.

I spent a few days trying every type of chassis isolation and grounding scenario while measuring radiated noise, interference and audio noise, and this was the best layout. I would think this a pretty standard cabling connection for a lot of CAR-PC users.

Although my PC system only draws around 4A, in retrospect I could have gone with even heavier cable but it’s all I had at the time.

Now to the circuit, I designed my own Isolators as I had the bits in my junk bin and they cost me nothing. In reality you should only need one in this system, but I do NOT trust the M4 or any other PSU that is microprocessor controlled (or not) to drop the power in the event of a system failure to shutdown or other condition causing the main vehicle battery to bleed down to a critically low voltage.

I still like Diode isolation for a “SMALL” AUX battery as it allows the Car Battery to feed voltage during cranking without pulling current from the AUX. I do this in an attempt to maintain a voltage above 7 volts if the AUX battery is weak in charge and the PC is starting or has started. Of course you open the PC supply to positive voltage spikes from the cranking process; however that’s the reason you take a two wire feed directly from the battery terminals. The battery is such a huge low impedance load at that connection point so starting spikes should (I said should) be greatly reduced.

The forward voltage drop of around 450mV (for this device) across diode (D1) in that isolator is shorted by a Power FET when the voltage input rises above 13v, so it’s only a direct connection when current is flowing “into” the PC-AUX battery from the alternator and have a few mV drop across the FET/Diode when shorted.

The low voltage Isolator has a hold time so no matter how low the cranking voltage goes it won’t disconnect for 10 seconds. In this situation there is no sudden switching of input voltage to the PSU at the point of cranking.

However there is a rise in voltage as the Alternator voltage comes up and it depends on the state of the AUX battery, and therefore the AUX voltage, so there can be a sudden change. I believe that in my system this is the point causing a problem in the M4 and other PSU’s I have tried. When the AUX is just at the right voltage and the car is cranked just at the right time then the PSU does its double start silliness.

The second problem I found and posted long ago was the IGN line to the M4. If it swings at just the right time at start-up it causes the M4 to drop +5 standby if in STR. A cap and diode helped this problem but you are limited to the size of the cap unless you want the Power-off sense time greatly extended.

I also had a problem with my Monitor under the right starting conditions. The Monitor would be blank, would not respond to the remote, would not show the reverse camera and appeared dead. I supply the monitor with ATX +12v and +12v (nom) from the IGN switch. I have a reverse camera that is auto detected by the monitor when powered in reverse and so the monitor runs without the PC powered. When the ignition is off I can watch the status of the PC by keeping the screen powered by the PSU.

Removing and reconnecting power to the monitor made no difference. I found in the end that if I disconnected the main video cable and reconnected it to the PC the Monitor immediately displayed a picture. Seems that the PC does not see the monitor as it starts and only detects it when physically reconnected as above, however that does not explain why the Reverse camera and all controls on the Monitor appear dead, so maybe the video input circuitry locks on the monitor and only resets when it’s unplugged from the VGA port although you would think powering it on and off would unlock it.

The fix was that 10,000uf cap across the monitor supply socket on the PC case. It smooths out the sudden voltage fluctuation under some start-up conditions.

Now, at last, to the question you asked about what I rewired in the system to stop the majority of false start-ups. I initially has that low voltage isolator “sense input” switched via the ACC switch so that with the IGN was completely off, the Main battery was isolated. During cranking the ACC voltage is interrupted and that causes the low voltage isolator to switch and cause a sudden change in supply to the AUX battery. My design mistake was not having a 10 second delay built into the isolator.

When I modified the isolator I also decided to run the sense straight to the input supply and leave it powered at all times and have faith in the isolator, hey if it fails there is still the M4 low voltage drop out, is that built in redundancy? Or just redundant!

Those final two changes have made this so solid with STR, although I now hibernate the system instead. Another change was all USB devices now power up every time, where as I would occasionally get one (usually GPS) not initialising correctly. But it all relies on the AUX battery keeping a good state of charge, which is why I went to hibernate instead of STR. I have a few ideas to try down the track with powering only a couple devices in STR, but I’ve spent too much time on this project for now, besides it works perfectly at last so I just want to enjoy it, also the front and rear Hi Def web-cam drive-recorder is now working perfectly and completely embedded in the front end.

When you consider that I have 10 USB ports at the PC with 1 spare and one 4m lead to the front of the car with 3 x 4 Port Hubs on that and only 3 spare on those , that’s not a bad effort.

Hi OldSpark you hit the nail right on the head (but then I knew you would).

Wow - I've been complimented by a god! (Your M4 work blew me away. Then there are other threads....)

Your "..depends on maintaining a correct state of charge in the AUX battery... " caught my eye and I thought "I bet its diodic (isolation)". And yep, it seems to be (ie, D1, excluding its FET, and the other FET).
Even Schottky diodes are usually a minimum of a 0.3V drop (at low currents) and IMO that will make a reasonable difference even if the alternator is at 14.4V.


IMO - as a general rule and for most set ups - relay interconnection is the best. They have the lowest voltage drops so should ensure the most equal battery charging.
Then comes the control aspect which should be automatic - ie, only when the system (alternator) is charging. (Though additional manual control(s) can be desirable and added.)
And control usually has to be voltage sensing for stator systems (permanent magnet rotors etc) as per marine and some others (eg, some RVs & bikes), but otherwise IMO charge-light controlled. (That have no complicated timing or delay requirements, nor arbitrary voltage thresholds - unlike voltage-sensing systems.)

Even for non-charge-light systems (marine etc, and maybe some new vehicles), my preference would be to detect current on the alternator output (say above 100mA or 1A) as that indicates charging and - like the charge-light system - should not require delays etc. (For pedanticness, I might add direction - ie, current into the alternator means a faulty alternator (power diode) and hence no dual/multi-battery interconnection should occur, but that's another issue...)

Initial or reconnection delays are easy to add, but that is something I question. (IE - the desire for "priority charging" is bullsh! (Except in certain specific circumstances, but then IMO simply disable the normal charge-light etc control in those situations.))

Hi again, I think you’re overestimating my expertise! But thanks for the tongue in cheek position of merit!

I have been reading you conversation on quite a few threads (and learning some things about batteries along the way) it’s great to read and learn from the findings/teaching and obvious experience with these systems that you bring to the forums.

You mentioned the FET in my installation and of course with this I don’t have any Diode voltage drop when charging, well if you want to be accurate around 15mV across the FET/Diode combo.

The reason I wish I had used even heaver cables is the small but significant drop across the run to the AUX battery, especially when it’s down a bit (drawing more current) and the trips are short. I’m getting just on 14v at the battery, so I’ll see how it goes with use and time.

My CAR-PC now displays charge current to the AUX battery, voltage right at the battery terminals and isolator switching points. It can alarm on over current or charge failure and disconnect automatically as well if needed (hey, I could code it so I did.)

But as I said at the start of my previous post, the more you go into it the more complicated you realize it is (as you show in your posts ) and why some systems give so much trouble. Like all technical subjects it’s very hard to fully cover then in depth on a forum, but we try to make sense, I hope!

Tee-hee. As I said, you blew me away. You had the (testing) equipment, and the REALITY of the situation. That was far better and of greater significance than any limited or theoretical crap I could have added.

As to the "Geez, there's more to this than what I first thought!", I'm trying to think of a situation that isn't like that. (Especially when critical of colleagues etc LOL! )

If only there weren't all those exceptions to the universal rule!

I try to correct misunderstandings or lack of knowledge - especially when it leads to (long-term) inferior or expensive solutions, and especially when it results from misleading propaganda by the ignorant or - IMO worse still - those out for self gain (greed).


But as you say, we try to teach. And learn.

MickZ (with apologies to antimatter & others for this diversion...)

Firstly your name has been mentioned/sought on Laptop DC car charger noise (page 2).

Second, the real reason for this reply....

Originally Posted by Mickz

I have been reading you conversation on quite a few threads (and learning some things about batteries along the way)...

I got to thinking... is Bill Darden's Car And Deep Cycle Battery FAQ a better source than me for batteries?

When I found it years ago, I was rapt! IMO it was one of the best public sources I had seen - if not the best - and one of the few I had no disagreements with.
Finally about a year ago I read it properly and fully. And I reckon it is the best (still; & that I know of - not that I've needed to look further except for other specifics), and it is generally the only source I link others to. I still use it to check some things (like wtf was the voltage for Calcium or Gel or...) and it has even modified my former rule of 30% discharge for cranking batteries to Bill's 20% discharge limit.

Upon that re-read, I thought Bill presented so much info in a concise way. He did not have my verboseness, yet managed to so much ancillary stuff.
My only concern would be that whilst I may see what he means, will others? Can I read between the lines, or will others still manage to misinterpret, or misapply something in a different context or application?
[ EG - Not that this is from that FAQ, but an audio-forummer mentioned putting his audio batteries in the engine compartment for greater heat and hence greater capacity. Knowing that a 10°C might increase capacity by say 5% BUT that same 10°C HALVES the battery life - well, let's say I suggest spending a smaller incremental cost on a bigger battery! And considering an engine bay probably adds 30°C and hence you'll be replacing the battery EIGHT times as often... ]

But reading that FAQ from cover to cover - maybe skimming over the known-to-be-irrelevant sections - is that quicker, easier, and more thorough than my rambles?
I'm often tempted to simply refer to that FAQ or its relevant sections and then merely explain/answer what the poster then does not understand or understand its relevance to my point.

I do go further in some cases. EG - Bill does not address the paralleling of batteries - he palms that off (LOL!) to other references. (Though the applicable "theory" is contained in his FAQ.)
But that expertise I have - er, sorry, my opinion(s) - is augmented by, else simplified by knowing, Bills FAQ.

And damn Bill - he's updated again - it's now v.June13,2011 - my copy is V.April9,2011. What's the change this time?


BIG TIP: Just download his battery.zip (see 19. HOW CAN I PRINT THIS FAQ? if needed), put it in a suitable directory/folder; unzip it, and shortcut its "carfaq.htm". (eg: place in "D:\...\Batteries\BatteryFAQ\BatteryFAQ.v20110 409" or whatever suits your system.)

Originally Posted by OldSpark

MickZI got to thinking... is Bill Darden's Car And Deep Cycle Battery FAQ a better source than me for batteries?

OldSpark, thankyou X 100.

What a fabulous wealth of information. I’ve downloaded and placed with my other 30 directories of Car info. I’ve already started reading and jumping to graphs and info that caught my eye, going to read it all over the next few weeks. Thanks again for sharing and pointing us to that site.

Thank you both for adding so much useful information to this thread!

I have learned a lot that is for sure.

MickZ
Thanks for taking the time to write up and post a drawing of your setup, you have given me some ideas on ways to further enhance my setup (even though its working flawlessly).

I feel it's a shame to have shelved the M4-ATX even though the plethora of issues i faced because it wasn't as forgiving as the Opus150.

But in the end i happily have a reverse camera working (through USB) and STR functioning everytime.

Now on to handsfree bluetooth and getting my 3g data card working.

You guys rock!

Hi antimatter, just an update on the M4-PSU.

After my final mods just a few days ago, I finally have the M4 reliability resuming from sleep under all engine cranking conditions. It has been in sleep for close on 40 hours now with the occasional wake up to restart the dumb 18 hour +5v standby limit of the M4. I did a lot of engine cranking tests and some driving before that and it has worked perfectly.

However I though you may be interested in something I discovered.

I have a battery charger/power supply I built for general work. It’s an unregulated unit with 100,000uf of big filter caps. Tops out at 14.9v no-load and drops to 13.5v @ 25A. The result of no active regulator is a very tiny amount of 100Hz AC impressed on the DC voltage. If this is connected to the vehicle battery the Car-PC will not resume from sleep, it drops the +5v STB the instant it switches on – just like it does if there were a problem going into sleep mode. It will run perfectly from a cold boot with the supply connected.

Anything I do with the charging system and vehicle cranking does not bother the M4 at all now.
It suggests to me that they are not monitoring the input state correctly in the M4 and only confirms my findings that certain slight variations of the input at just the right time and rate of change will make the M4 drop its +5v standby rail.

Mine is now working great in this rewired installation. But as always, time will tell

The mods are in the last few post of my worklog, also some interesting results from my relay and fuse holder voltage drop tests are there as well.