CarPC Engine Crank

[MiniWalk§]

hey guys, i recenty installed a carpc into my car

the mobo is the VIA TC-10000 with the onboard 60W DC-DC reg

only issue being that despite being directly connected to the engine, the mobo is still rebooting when i crank the engine over,

powering info:
Optima D34 Yellow
Nissan SR20DE :P
5amp fused 12awg wiring (max the connector to the mobo would take)

im assuming the answer is going to be capacitors, but im leaving this one open to the electronics brains trust of OCAU

any help will be greatly appriciated

[led_blind]

When the engine cranks the amp draw will cause a drop in batery voltage. No idea how much but i wouldnt be suprised if it dropped as low as 10v (during crank) There are lots of ways around this, cap's will help but you may need something large. Personaly, i'd add another led acid battery.

For me, id take out your current power cable, add a diode to stop the current flowing into the starter engine on crank. Then connect it straight to the battery and run the carputer off that battery. I dont know how you power it off at the moment, but you probably have it sorted so you dont drain your car batt.

[MiniWalk§]

at the moment, it is directly connected to the battery via a larger cable that serves the headunit, the carpc, the touchscreen and the volt-gauge

the voltage doesnt drop below 10.8 from what ive seen on crank

another battery is not ideal, as space confines are already tight

current power off method is shutting down the mobo via windows

[CaveDog]

No real idea on crank for your carputer, but might I ask, why is it powered on before you are driving? Mine automatically turns on when the stereo (acc) is on, but I have never really had a need to have it survive crank. If you do build a simple solution, let me know...

On another note, if you haven't sorted a shutdown solution yet, try the PIN 8 on a serial cable trick. If you pump 5v into pin 8 on a serial cable, and set windows to think it hasa UPS connected, then when 5v is lost (say cut by a relay that is controlled by your acc line) the machine starts to auto shutdown.

Search MP3car.com forums for more details.

[Odje]

A small SLA battery or a super capacitor bank is all you need. Use a very high power Schottky diode or relay to stop the starter motor from draining your extra SLA battery or super capacitor. SLA option is the cheapest. Super Cap would be rather expensive. But I also agree as to why you turn your CarPC on before your engine is.

[MiniWalk§]

CaveDog -> i see ur in 3131 :P i live in mitcham 3132

it doesnt bother me too much regarding the engine crank, i was just wondering if it can be done more than anything.

shutdown method is start->shutdown :P

designed so it can run wihtout the keys in the barrel

explain more on this SLA business. it has my interest

[Odje]

Originally Posted by MiniWalk§

explain more on this SLA business. it has my interest

SLA=Seal Lead Acid Battery. It is the same type of batteries that are used in UPS's and alarms among other things, hence they are common, run of the mill and cheap. SLA batteries come in a wide range of physical sizes so you can select one that meets your space restrictions. Also, they can be charged very easily and are compatible with the car's electrical system without any charging circuitry. FYI the car battery is also a lead acid battery, just not sealed. The sealed version are for indoor use or where ventilation is not available. The non sealed type, ie car battery can vent hydrogen gas when being charged and can spill electrolyte if the caps are not screwed on tight.

[MiniWalk§]

mmk, starting to make a bit of sense,

how do i go about rigging the SLA battery into my mains ? and what kinda ampage fusable link am i needing ?

[Odje]

Originally Posted by MiniWalk§

mmk, starting to make a bit of sense,

how do i go about rigging the SLA battery into my mains ? and what kinda ampage fusable link am i needing ?

Use a high current horn relay, 20 or 30A or more depending on the load, to disconnect the SLA battery from the car battery when cracking. Connect the two positives of the two batteries together via the NC contacts of the relay, with a fuse of course. Connect the coil of the relay in parallel with the starter relay. When the car is cranking, the relay will energise and disconnect the two batteries.

You need to determine the load in order to determine the cable size, fuse rating and horn relay rating.

BTW: Ampage is not a word, try current rating instead. The ampage, wattage, metreage, etc police will be around soon.

[MiniWalk§]

max load of the carpc alone will be 5amps @ 12VDC

[Renza]

Originally Posted by Odje

BTW: Ampage is not a word, try current rating instead. The ampage, wattage, metreage, etc police will be around soon.

you forgot voltage!

could this be done with diodes instead of a relay?

[DarkYendor]

Originally Posted by Renza

you forgot voltage!

could this be done with diodes instead of a relay?

You could probably use a large diode to prevent the current flowing back into the cars electrical system - only problem may be charging (because the voltage to everything on the other side of the diode will be 0.7V lower). Still, if you're alternator puts out a solid 14.4V, you should be okay - the SLA might only be able to charge to ~90% though.

Otherwise, jaycar sells battery isolators - one might be suitable.

[rickbishop]

Aren't there dedicated carPC PSU's that are designed to deal with this sort of thing?

[Odje]

Originally Posted by Renza

could this be done with diodes instead of a relay?

Originally Posted by DarkYendor

You could probably use a large diode to prevent the current flowing back into the cars electrical system - only problem may be charging (because the voltage to everything on the other side of the diode will be 0.7V lower). Still, if you're alternator puts out a solid 14.4V, you should be okay - the SLA might only be able to charge to ~90% though.

A Schottky diode will have a lower voltage drop but still may affect charging as DarkYendor said.

[MiniWalk§]

Originally Posted by rickbishop

Aren't there dedicated carPC PSU's that are designed to deal with this sort of thing?

the motherboard that i have has an onboard dc-dc regulator, which doesnt use the ATX style input, it uses the common bullet style connectors youd find on discman etc