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pros & cons of 12v-to-18v DC-to-DC converter for Cappucino PC

I will be using a Cappucino mini-PC for the brains of my new robot project.

I originally bought it when I got the Evolution Robotics ER1 about 3 years ago, and went whole-hog on accessories, etc. Evolution published the idea of using the "mini-book" and running it on the ER1's 12vdc power supply ( 12 vdc 5.4 A-hr SLA battery ). The Cappucino has an AC-DC power supply that outputs 18vdc, and 18vdc is listed as the input voltage on the website's specs for the machine. Ever since then I have been curious as to whether it "just happens" to run OK on 12vdc, or am I stressing it somehow by doing that.

Now that I am building a new bot from scratch, I'd like to do everything right. Which leads me to the following questions:

1) Is it safe to run the Cappucino on 12vdc ? Does anyone know ? (My inquires to the Cappucino website itself along these lines just went unanswered a couple of years ago.) How does this affect a full compliment of USB devices plugged in to it? Perhaps someone knows the "real" manufacturer of the Cappucino & can point me in the right direction ?

2) I am trying to have everything run on 12vdc or lower, nominally. I'd really hate to be forced to have 18vdc simply for the PC when everything else is being spec'd out to 12vdc, but if it turns out that 18vdc is best, what are the pros and cons of using a 12v to 18v DC-to-DC converter ? ( I've seen this approach on the Cappucino site when they marketed the PC for use as a car computer system. )

If anyone has experience with any of these issues I would be grateful to hear some of your wisdom ! Thanks ! JCD (Pogo)

Reply to
pogo
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Here are some links to references for the above post:

Evolution Robotics ER1 Mini-book PC Project:

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Cappucino PC website:
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Reply to
pogo

Wouldn't ya know it ?!?!? Just a few minutes after I posted this thread, I discovered that SaintSong is the actual manufacturer of the Cappucino PC. Of course, I have emailed them my questions re 12vdc vs. 18 vdc.

Here is their website, FYI:

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(Oops. Posted this outside of the thread. My apologies.)

Reply to
pogo

"pogo" wrote in news:Ib3tf.18682$ snipped-for-privacy@bignews2.bellsouth.net:

I've been using LDO voltage regulators instead of the standard volt regulators. I want to save on battery weight. cya

Reply to
newtype

I learn something new almost everytime I get a reponse on here! Hot dawg!

So using LDO regulators allow the battery to last a bit longer than standard regulators, & therefore you can use a lighter weight battery, right ?

Reply to
pogo

I found an article on LDO here, for those that are interested:

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Reply to
pogo

Hi!

This doesn't make much sense I'm afraid. First, the power loss on *any* linear regulator is proportional to the voltage drop and the current. If you're making 5V out of 9, and your current is 2A, than you will dissipate (convert to heat on the regulator) (9-5)*2 = 8W. It doesn't matter if it is an LDO or not. The only case an LDO can help is if your input and output voltages are close. Every linear regulator has a minimal voltage drop that it needs for proper operation. For LDOs this is lower. So, LDOs *can* be used in applications where normal regulatros can't and in those applications they are more efficient. But in any particular application where both could be used, their efficiency is the same.

Second, if I understand this correctly the OP wants to make 18V out of 12V. That is, the output is higher than the input. No linear regulator will do that. You will need a (step-up) switching regulator.

My suggestion is to open up the case, find the power supply chip in the PC and look up it's datasheet. Chances are it is used in it's standard configuration and the datasheet will give you a good starting point to figure out what it can handle and what it can't.

My guess is that your +12V line internal to the PC will not be kosher, but the rest (+5V, +3.3V) are fine (can you measure them?). If that's the case, than try to figure out what the 12V is used for. In this PC the hard-drive and the CD-ROM look like laptop devices and hence are running from 5V exclusively. Your RS232 transcievers might need +/-12V, but most likely they don't. Again, find them and look up the datasheets. But even if they are, they probably don't care much if the 12V is only 10 or so. That leaves the CPU.

In Socket370 systems the CPU power supply is usually run from the 5V line, but uses the 12V to generate the gate-voltage for the MOS-FETs. Again, find the chip, and look up the datasheet. Also look up the datasheet for the MOS-FETs. What you will most likely find is that the gate-source potential on the upper-side MOS-FET for the CPU power should be 12-5=7V. If your 12V line is below spec, let's say 10V, than your gate-potential will drop to 5V. That's most likely OK though border-line. It will increase the channel-resistance of the MOS-FET and will result in increased heat-dissipation on it. You might not be able to run the fastest CPU on the board full-speed, stable. Worst case you can burn out the FET and destroy your motherboard (unless you know how to replace the demaged part). Note however that there are socket370 systems where the CPU is powered from the

12V line. I honestly would doubt it in your case, but you never know until you looked.

If you in some way can look up the max current specification on the 12V line, you can make a pretty good guess at what the CPU power supply is running from (provided that the HDD ad CDROM are indeed 5V only). If the power supply can't supply more than 1A on the 12V rail, than your CPU is powered from the 5V line for sure.

Regards, Andras Tantos

Reply to
Andras Tantos

Hi and thanks for the info!

1) What are you saying doesn't make much sense ? You mean the article on LDOs ? Or doyou mean what I am trying to do ? 2) Are you using Socket370 as an example, or is it somehow related to the Cappuccino system ?

Thanks again because it's all one big learning curve ! JCD

Reply to
pogo

The question about " 12vdc or 18vdc input power "

12vdc or 18vdc can all be used, but 18vdc is a more suitable specification as for Cappuccino, so we suggest you to use 18vdc better. You are always welcome to contact us whenever you think it is needed. Best regards,

SaintSong Customer center

Reply to
pogo

What doesn't make much sense is this: "I've been using LDO voltage regulators instead of the standard volt regulators. I want to save on battery weight." Unless you change the voltages in your system, moving from standard to LDO regulators won't save you much.

From the website it looked to me that both Cappuccino systems are Socket370 ones. (one is a i810 and the other is a i815 based system). P-VI/Athlon and higher power supplies usually use the 12V rail to generate the CPU voltage.

Regards, Andras Tantos

Reply to
Andras Tantos

Now *that* is some very valuable info to me! Thanks !

Reply to
pogo

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