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PostPosted: Tue Dec 09, 2014 5:23 pm 
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Shawn wrote:
Be careful with low voltage...
Ohms law..When voltage goes down.Current(amps) goes up...
Low voltage/ high current usually creates more HEAT which is bad for electronics.


Generally speaking it doesn't do that. Ohms Law E/I*R
When voltage goes down in electronics so does the amperage; There is some 'funny stuff' that goes on with voltage regulators/converters where say in a laptop with an 11.4V battery runs the system, and 19V is the input that is converted to a lower voltage to charge batteries AND run the system; Where assuming it didn't have a low voltage disconnect(most do unfortunately for ME*) the system would draw more current to makeup for the overall shortfall in voltage to keep everything going the status quo; But never anywhere near levels where heat would be an issue(IMO); as remember the system IS running on 12V already; AND the closer two voltages are to one another the more efficient(Less waste heat) the conversion.

ie: buck step up adapter I posted earlier, may be 92% efficient going from 16V to 19.5V DC, but it's only ~80% efficient going from 12.2V to 19.5V.

I admit I get a lot of my info from actually testing myself looking at I/O voltages and current; But also my father was an electronics geek from the 60's,and has been a great help.


---

Just looking at https://en.wikipedia.org/wiki/Ohm's_law
I = V/ R
12V / 100 Ohms = 0.12Amps
10V / 100 Ohms = 0.10Amps

----

If I can't find a fellow who owns toughbooks and does these kinds of tests, I'm thinking I'll spend $80~ or so on a CF-T8 or similar just to test to see if it will run on a lower than rated voltage on the DC jack. The SU9600 CPUs are very power efficient with a TDP of only 10W; Granted theres much faster cpus that take the SAME power, but nothing anywhere near as cheap.


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PostPosted: Tue Dec 09, 2014 6:54 pm 
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But an electric motor will draw 10 amps at 220v and it will draw 20 amps at 110v. When I cut the voltage in half I double the amps draw. I work on them and do amps tests every day for a living.
Most Toughbook AC adapters say the exact same thing on them. At 120v they use 1.2a and at 240v they use .6a....

I misstated ohms law, and you are correct. When you lower the voltage, less amps will become available.

The resistance will remain constant. Therefore I believe the wattage used will also remain constant.
P= IE So 100 watts equals 15volts times 6.667amps, But 100 watts at 12volts requires 8.33 amps. So at 12volts the amperage draw will increase. This can increase heat depending upon several factors. Wire size etc..

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PostPosted: Thu Dec 11, 2014 5:26 pm 
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Shawn wrote:
But an electric motor will draw 10 amps at 220v and it will draw 20 amps at 110v. When I cut the voltage in half I double the amps draw. I work on them and do amps tests every day for a living. Most Toughbook AC adapters say the exact same thing on them. At 120v they use 1.2a and at 240v they use .6a....

I misstated ohms law, and you are correct. When you lower the voltage, less amps will become available.

The resistance will remain constant. Therefore I believe the wattage used will also remain constant.
So 100 watts equals 15volts times 6.667amps, But 100 watts at 12volts requires 8.33 amps. So at 12volts the amperage draw will increase. This can increase heat depending upon several factors. Wire size etc..

Yeah theres more than one way to 'skin a cat'... From the point of view of DC 'electronics', without the appropriate minimum voltage and the resistance of a circuit being the same, it simply will not operate(if V too low), run(not to discount errors), or shortout(V too high).

When we are talking power adapters/converters, they are designed to change the power values, so yes a 240V adapter will use half the amperage than 120V input and the output would remain the same; In this case the internals of the adapter must be able to handle the higher amperage.

Computers have quite a number of voltage lowering internals for various components, but this is all stepped down already from the system battery or main DC power source.

With regard to Electric motors, or transformers in many 120-240V power supplies it is simply a selection(physical or digital, but ultimately physical). The motor/transformer simply has X number of windings of wire around it, power running through it. At a different voltage, a switch connects at a different position in the winding(like the 110-220V switch on back of desktop power supplies). It's still Ohmns Law.

The only risk I am aware of is in motors/compressors where the voltage is lowered to a point where it won't quite turn over and sit there consuming power generating heat burning out the motor/fire.

--- But I digress, it is generally safe in electronics to test with lower voltages; 'blindly' higher not at all!. I've taken dozens of my new toys that I could not afford to purchase again/ruin and run lower voltages through them for various reasons/trials.

Assuming no toughbook geek with a multimeter and extra DC plug w/adjustable power adapter steps in with his results for his computers, I think I will purchase one Toughbook CF-T8 just to try it myself; Would prefer rugged, but for ~$80 for the T8 and 10W tdp cpu, should be a good low power item to test.


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PostPosted: Thu Dec 11, 2014 5:54 pm 
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What specific model do you want to use for long term?
It would be best to try the model you want as Toughbook internal hardware and BIOS's are very different.

I just had a thought....an end around solution maybe....
The problem to overcome would be the built into the battery safety monitor.
If you took a Toughbook battery (I am thinking CF30 or CF52) Pulled the lithium cells out and connected to the tabs that went to the cells directly.
The units I mentioned use a battery that is 11.65v With a small buck you could drop the 12v to 11.65 if needed. A standard 12v battery runs/charges at over 12v. The Toughbook would "think" it was running off a standard battery.

The mod would be entirely in the battery pack and you can put a regular battery in anytime you want.

You need to start with a good battery because Toughbook batteries have an internal monitor that locks the battery once a cell goes bad.

PM me your email address and I will hook you up with a CF30 schematic..

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PostPosted: Thu Dec 11, 2014 7:45 pm 
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I have a CF-29 MK1 with a cracked lid that would be a nice donor for this project. Why the MK1 is they are very long lived battery wise. Or at least that is the claim. It is magnesium however so the appropriate dry chem fire extinguisher would be handy.
I've been thinking lately how we are tied to our batteries. Toughbooks, telephones, radios....forevermore etc.

This is very interesting but I am on several other projects...namely trying to sell a Toughbook or two at a profit of any kind.....mapping for the fire department, hacking an android for mapping, my ewes are lambing, we just had a bit of rain.....6 inches in 24 hours......ad infinitum.

BTW wind storm with the rain and with the inverter "on" all night was at 25.7 at daylight this a.m. 23.7 when I crashed last night.

I've been running the Air403 for enough years to wear out a set of props. 24V >>>>the cabling runs through the 2" mast>>>goes through a switch to the batteries. On..freewheel..off. Off turns on the brakes. Had a couple down bursts last night that woke me up. 42MPH+ The 403 ...at a certain speed the blades are designed to warp and stall the unit. Which sounds like a hammer dragged along a tin roof.

Just general yaddling here...we need to wake up the Dwagon for information meteroic. Shawn knows who I mean.

Let me know PM of your needs. Like a MK1-29?

Sorry I don't do meters.

J'd

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PostPosted: Thu Dec 11, 2014 8:42 pm 
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He may be lurking I dunno.....He would definitely have more answers..
I do not have any direct contact info....Rick, Blair or Bill probably do.

Jeff, here's a simple test you can try on a well used unit...
On a CF/29/30/52 battery the two larger outside terminals are marked + and -.
Get a unit without a bottom cover and alligator clip a wire to each of the outside prongs on the battery connector of the laptop.
Connect the other ends of the wires to a 12v battery, observing correct polarity.
Grab a camera..video is better..
Hit the on switch and watch for the magic genie to appear..

It probably must have a "battery" or at least the circuit board to start..I am curious......

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PostPosted: Thu Dec 11, 2014 9:09 pm 
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Shawn wrote:
He would definitely have more answers..
I do not have any direct contact info....Rick, Blair or Bill probably do.


I have it somewhere . Will check when I get out of work in the AM

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PostPosted: Thu Dec 11, 2014 9:35 pm 
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Shawn wrote:
What specific model do you want to use for long term?
It would be best to try the model you want as Toughbook internal hardware and BIOS's are very different.


That's getting difficult to say; I'd like the fastest possible for the least amount of power use. It should also be pre-windows 8 to avoid that new bios stuff to restrict what can be installed on the system(not a problem in desktops yet, not sure about laptops,but does cripple tablets). I'm still a fan of Windows XP SP2(faster and more power efficient in many tests vs vista-7).

http://www.cpubenchmark.net/cpu_list.php

T4400 was typically my minimum, but in the hopes of finding super power efficient affordable used to try! I'm thinking u9600 u4100 might be worth a go.

There is this list which is the best(having still to find a low tdp):
https://www.cpubenchmark.net/power_performance.html

but which of those can be found in a system that works with XP still and be affordable is rather tricky since they are all so new and typically in tablets etc.

Shawn wrote:
I just had a thought....an end around solution maybe....
The problem to overcome would be the built into the battery safety monitor.
If you took a Toughbook battery (I am thinking CF30 or CF52) Pulled the lithium cells out and connected to the tabs that went to the cells directly.
The units I mentioned use a battery that is 11.65v With a small buck you could drop the 12v to 11.65 if needed. A standard 12v battery runs/charges at over 12v. The Toughbook would "think" it was running off a standard battery.


I've done that with an emachine e725 with some minor success; One problem is you must leave the cells in it and use a buck adapter(main point now) to maintain the voltage ; long term this would not be good for the cells; short term it's still using a buck adapter; I considered using a buck adapter for each bank of (usually) 3 in the battery to remove the cells completely but its a game of tricking to trick the controller...

Theres no real 'good'(imo) reason why in a system with a 11-13V battery can't run directly off a 12V battery/charger; they added this to most laptops to guarantee a specific charge rate and lesson confusion from users whos systems would run but not charge when an under Volted power supply was attached. Dell and I presume others went proprietary using a 3rd pin and actually exchanging CODE to verify a 'dell X power adapter'; Lenovo/IBM used just a resistor(what I use now on a thinkpad t400s off a step-up converter); same goes with USB 5v chargers, most devices look for a resistor of +-150 ohms on (if memory serves; built 2) the data wires to signify it's a 'charger', before the device will accept a charge from it.

This is why the 2003+-(maybe even todays, donno 'yet') 16V toughbooks, and other 16V laptops could be plugged directly into a 12V battery; they simply didn't install the voltage checking hardware on the DC in yet;

Shawn wrote:
You need to start with a good battery because Toughbook batteries have an internal monitor that locks the battery once a cell goes bad.


Interesting, so once that is 'locked/switched' it's not possible to replace a bad cell and keep on trucking? I disassembled a d800 battery and repaired a cell but it never strarted working again; I assumed it was a bad control board, but perhaps they are sabotaging any repairs!


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PostPosted: Thu Dec 11, 2014 9:52 pm 
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Shawn wrote:
Jeff, here's a simple test you can try on a well used unit...
On a CF/29/30/52 battery the two larger outside terminals are marked + and -.
Get a unit without a bottom cover and alligator clip a wire to each of the outside prongs on the battery connector of the laptop.
Connect the other ends of the wires to a 12v battery, observing correct polarity.
Grab a camera..video is better..
Hit the on switch and watch for the magic genie to appear..

It probably must have a "battery" or at least the circuit board to start..I am curious......


In the old days that could possibly work, but I highly doubt it with the lithium charge control boards and battery monitoring sensors... IT wouldn't hurt to try so long as ! one didn't apply a higher voltage than the fully charged battery that is in it. If I remember an 11.6v laptop battery floats/fully charged at 12.1V(battery status monitor for windows would report it). Applying more than the batteries max charge voltage in 'that location' *could be bad for something.

fun fun


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PostPosted: Thu Dec 11, 2014 10:00 pm 
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Correct. Any current generation Toughbook battery can not be re-celled at home..
Best battery life is probably a CF19...10.4 inch screen convertible..Some are rated for 6hrs or more battery life. .To me that probably means best power consumption.

You can decrease power use by disabling touchscreen or digitizer and and wireless or modems etc..Lowering brightness makes a huge difference...I say you want SSD and an LED backlight at the very least..Do your homework on power usage of wifi cards......

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