ITPS Regulation

**starfox** · 01-28-2004, 06:41 AM

The linear regulator on the ITPS is a low dropout linear regulator, it'll drop the car voltage ~1.3V (though this should increase a little with load). I think the designer chose to use it to help smooth out voltage spikes going to your DC-DC power supply, and to possibly reduce the voltage to your PSU so it isn't running out of spec.

I have a morex dc-dc psu and i've tested it down to 7V with a bench power supply. The 12V line is passed through, but the 5V and 3.3V lines are buck regulated and will be okay if the battery voltage drops to around 7V during a crank. If you have any 12V devices however you're going to run into problems.

If you want to use a PC with no 12V line, you must have a motherboard that doesn't check that the 12V is within spec on booting. I've tried disconnecting the 12V ATX line to several motherboards and only one will start if the 12V is not connected.

A possible problem is that some motherboards might actually shut off if the 12V line runs out of spec, even though the motherboard is not using the 12V line.

Ricky327: A friend's photoetched a PCB for running National simple switcher ICs, using data from webbench. It's ATX compliant, but the PCB is quite complicated and is really big (size of a DVD-ROM, and it's double sided with thicker than usual copper. Big because the components must be spaced out, else there's going to be interference between the inductors). It's going to be hell to drill the PCB and solder everything in.. also that sourcing inductors is going to be difficult....

**MikeH** · 01-28-2004, 08:31 AM

It still puzzle me why the ITPS/PW70 cant survive a crank when you dont even use a 12V device.

I don't know about the PW70, but the Morex/Casetronic PSU uses a TPS3510 supervisor circuit. It monitors regulated voltages for over/under voltage and provides a PWRON signal to the motherboard indicating that all is well. Perhaps the PW70 uses this to monitor the incoming +12v line and does not give a PWRON to the mobo if it is not there.

**BigRedBee** · 02-25-2004, 12:53 PM

I've been playing with an ITPS / PW70 / M10000 setup in my car, too. I've got a second battery, so surviving a crank has never been an issue. However, with the car off, the system would survive only a short time (30 minutes or so) before resetting. I suspect that the ITPS was only supplying 11 or so volts after it got done regulating the (best case) 12.6 volts of the fully charged battery. I further suspect that the motherboard and/or PW70A was unhappy with this low voltage on the 12 v. rail (even thought it doesn't make use of it) and resetting the system.

So, I took the plunge and bypassed the ITPS. Everything runs just fine: car on, car off, and car cranking!

**MikeH** · 02-25-2004, 01:04 PM

BigRed..
Thanks for the update. I agree, with a dual-battery system, AND a battery isloator, you should never have "surviving crank" problems. It's still puzzling why the PW70 is picky about low incoming +12v.

BTW, how/where did you install the battery isolator? Is it between the alternator and both batteries? Did you do the install or did you have someone do it for you? I haven't had the guts to mess with anything upstream from the battery........

**BigRedBee** · 02-25-2004, 03:58 PM

Alternator--> existing battery
\-----------> battery isolator ---> second battery --> carputer

Here's the site for the Hellroaring battery isolator I'm using. It was a snap to install. The biggest problem was finding space for the second battery under the hood.

Here are some pictures.

**quinxy** · 02-26-2004, 12:14 AM

I must admit, this whole ITPS thing has really been confusing. I just bought a PC for the car, and the P120A PSU and an ITPS. And I've been pretty surprised/confused by the behavior of the power supply and the ITPS.

The biggest shock was that I did NOT expect the ITPS to drop the voltage below 12v when the source was > 12 volts. For example, with the car's ignition off, the battery supplies 12.8 volts and the ITPS passes only 10.2 to the power supply. This 10.2 gets passed along to the 12 volt rail, which means my hard drive fails (I also didn't expect the 12 volt rail to be unregulated in the PSU). Those were my biggest shocks and biggest headaches. All of this means that I cannot operate my car pc with the engine off, which I never, ever expected, and don't really see as reasonable at all. Seriously, is this "reasonable"? I mean, I'm a programmer, and if I was to write "code" which did something like this the design decision would be called a "bug", since I'm taking an acceptable/reasonable input voltage and turning it into an unacceptable voltage for the PSU. There may be technical reasons why this happens, linear voltage whatever you call it, but, that doesn't make it reasonable/right. Am I wrong here? Were my expectations unreasonable?

And, more importantly, what do I do now??? I'm not an electrical engineer. I just want to have the voltage regulation protection of the ITPS, the shutdown controller function, and a proper 12 volts out of the ITPS. (I also just discovered the need for the second battery to survive car start, which I am still trying to figure out from other people's posts.)

Thanks to all!

Quincy

**Ricky327** · 02-26-2004, 12:26 AM

quinxy,

You are correct to say ITPS shoudnt have been released. The regulator it uses is just not suitable for car use...full stop. As been said before the PW70 should survive the crank even without the backup battery as long as you dont use the 12V rail from it.

I guess its only good for a shutdown controller but of course these guys are trying to get it to work as how it should perform...but unfortunately its not straight forward.

**adamis** · 02-26-2004, 03:32 PM

Umm the ITPS is perfect for what it is, not for what it isn't advertised as. The point of the ITPS and the PW-70 combination is it's a whole lot cheaper and compact then an OPUS. I'm not saying the ITPS is better then the OPUS but going this route is a way to be able to shoehorn everything into a double din dash and save 100 bucks. That's where the ITPS is good at, small size, small price, and works for 99.9% of what you need.

I spent a long time trying to get the ITPS to survive a crank, using batteries and stuff. After a couple of months I finally gave up realizing that I was working to solve something I hardly would ever use in the first place.

Honestly, how many times in a day do you need to restart your car? If it's because you wan't to be able to keep your system running while pumping gas instead of taking the keys out of the ignition, then by all means, keep working at it but save yourself the time and buy an oppus.

If you really don't need music playing while pumping gas and can wait the 1 minute and 30 seconds for the system to hibernate and come out of hibernation then go with the ITPS.

Really you can't compare an ITPS to an OPUS. They are like apples and oranges, two different products that are not even in the same price range.

**swellfellaT** · 02-26-2004, 07:32 PM

Originally Posted by adamis

I can't believe some of you guys still don't understand the ITPS. It is DESIGNED for an automotive application. Maybe it isn't right for your application for some reason but I have a feeling that most of the people who use the ITPS don't have many complaints with it's use in an automotive environment.

The ITPS when used with the PW-70 powersupply and an Epia M motherboard will not drop out if the voltage drops below 12 volts. I've had this thing down to 10.5 volts and it didn't drop out. I can run my system for a long time without the motor running to boot. Of course you do have to stick with the components the ITPS is designed for...

Keep in mind that the Epia motherboards don't use 12v (unless someone else can prove me wrong and I'm talking about just the board, not serial devices for the sake of keeping it simple). In this case the PW-70 doesn't need the 12 volts to safely get the 5 volts and 3.3 volts to power the motherboard. Also stick to laptop harddrives because they run off of the 5 volt rail and are better suited to rougher environments.

As for crank survivability no it won't survive a crank but it isn't advertised as being able to do such a thing. That is what the small battery is for.

So in my apparent and newly discovered ignorance (I'm one of those people you can't believe), I also think the ITPS sucks. Good as a shutdown controller, but that's about it. I recently bought one of these, and found that the input voltage (around 14.5-14.7 volts, and yes, my car has a very stable *dual alt./battery* electrical system) is so drastically reduced by the ITPS (to around 11.5-11.6 volts, sometimes less) that I can't even run one 3.5" hard disk. This is absolutely rediculous, as this particular drive only consumes between 7.2 and 8.4 watts of power. Some of us would prefer not to pay $200+ for a 60 or 80 gig laptop drive, leaving us with few options. I do understand the ITPS (I'm an electrical engineering grad student!), I just do not understand the over-regulation/voltage reduction that is in place. iTuner claims that this unit can run larger drives, even optical drives, but I'm not seeing this as being possible when the output voltage on the 12v rail is so far under spec. Who else is having this problem? I tossed the ITPS and built my own. Was mine just a particularly bad example? Or does the design suck this much?

**Ricky327** · 02-26-2004, 07:58 PM

Was mine just a particularly bad example? Or does the design suck this much?

Nope you are not alone, maybe adamis is a lucky one

Heck, I dont even own one but by just by looking at the circuit diagram as published in their site it is so easy to see the potential problems.

How is it possible to have a 12V regulator in the car when the input voltage is from V13.3? I bet this minimum voltage is never mentioned in the ads.