www.robowars.org

RoboWars Australia Forum Index -> Technical Chat

Power Supplies
Goto page Previous  1, 2, 3, 4  Next

Post new topic   Reply to topic
  Author    Thread
andrew



Joined: 16 Jun 2004
Posts: 3110
Location: Castle Hill, Sydney. N.S.W


 Reply with quote  

Thats alright George. Andrew or just Welchy will do (as i am known now). I am going for this charger as iots dirt cheap and that plus the beehive and jaycar one covers me pretty well all round.

About the power supply Tim (who rocks) from team hell bent offered to give me a computer power supply thats about 12 amp and such all for the cost of shipping and some extra to modify it etc.

Ill get that one probably so all up a nicad charger for less than 100 Very Happy. sounds good to me.
_________________
Andrew Welch, Team Unconventional Robotics

Post Sun Aug 01, 2004 9:42 pm 
 View user's profile Send private message Send e-mail MSN Messenger
Nexus
Experienced Roboteer


Joined: 17 Jun 2004
Posts: 903


 Reply with quote  

Noticed on the Oatley website on the same page as the scooters, 1st item.
150 watt surplus power supply.
Its only $12 Dollars and with mods it claims to handle 12.8 volts at 25amps.
Here are its details if anyone would care to pass a thought if it was worth trying.
I am not an experienced hobbyist but would like 25 amps cheap.

NOTE: for experienced hobbyists only!!! For 9.6-12.8VDC @ 25A add a 4K7 Resistor in parallel to R51 and connect the 5VDC outputs in series, Don't forget to isolate the GND connection from the chassis etc. Size: 220mm(L) X 70mm(H) X 100mm(W).
_________________
Bots that do not destroy you, only make you stronger.

Post Sun Aug 01, 2004 10:17 pm 
 View user's profile Send private message
Nick
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW


 Reply with quote  

It looks like Andrew, err, Welchy is all sorted. For anyone else needing big amps at small bucks, have a look at this link: http://gallery.bcentral.com/GID5085587P3243565-Featured-Products/Mean-Well-S-250-Watts.aspx

The price is in USD and there would be shipping on top, but the price is pretty good for a 13.2V / 250W supply. Jaycar sell the 240 W model for double the price (I have 2) and their 600W supply looks interesting for people with multiple Triton type chargers.

I'm sure there must be better deals out there somewhere, but I haven't seen them yet, so my next PSU is coming from Mean Well...
_________________
Australian 2015 Featherweight champion
UK 2016 Gladiator champion


Last edited by Nick on Mon Aug 02, 2004 12:35 am; edited 1 time in total

Post Sun Aug 01, 2004 10:21 pm 
 View user's profile Send private message
Spockie-Tech
Site Admin


Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


 Reply with quote  


quote:
150 watt surplus power supply. Its only $12 Dollars and with mods it claims to handle 12.8 volts at 25amps.


Someone cant do their maths. 12.8volts x 25 amps is 320 watts.. more than double the rating.. and thats assuming 100% efficiency. I've noticed Oatley can get a little spec-happy on occasion, but most of their stuff is OK.

It sounds like you are running the power supply at more than double its rating with that mod. If its well made, it should take it for a while, but unless its german (they always overengineer things), I wouldnt expect it to crank 25 amps for long. but thats ok, 10-15 amps is all most builders need unless you want to charge 5+ batteries at once.[/quote]
_________________
Great minds discuss ideas. Average minds discuss events. Small minds discuss people

Post Mon Aug 02, 2004 12:22 am 
 View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
prong
Experienced Roboteer


Joined: 19 Jun 2004
Posts: 839


 Reply with quote  

here is the actual ad.

(USED) 150W POWER SUPPLY: FDK Brand, model # PEX668-31. This compact high current power supply has two internal 60mm fans and two STD IEC mains connectors (1x Male and 1x Female). Input: 100-240VAC @ 6.6A 47-63 Hz. Output: +5VDC @ 25A, +12VDC @ 2.3A (Max. 4A), -12VDC @ 0.25A. Outlet: 100-240VAC @ 4A 47-63 Hz. Total Max. continuos: 150.2W. Total Max. output: <15 Sec.: 174.2W. Two or more of these power supplies could be connected in series and modified for higher output voltages but the GROUND connection would have to be isolated from the EARTH (GND is connected to Earth via the chassis and may be connected elsewhere). NOTE: for experienced hobbyists only!!! For 9.6-12.8VDC @ 25A add a 4K7 Resistor in parallel to R51 and connect the 5VDC outputs in series, Don't forget to isolate the GND connection from the chassis etc. Size: 220mm(L) X 70mm(H) X 100mm(W).

It is a bit confusing to read but i take it to mean that to get 12v at 25 amps you need to run two power supplies in series. Still thats only 24$, so pretty cheap!

Post Mon Aug 02, 2004 1:10 am 
 View user's profile Send private message Send e-mail
Totaly_Recycled
Experienced Roboteer


Joined: 15 Jun 2004
Posts: 1346


 Reply with quote  

All of the power supply mods ive seen so far either mod the board to get 13.8 volts at about 5-7 amps depending on the suply used and dont use the 5 volt section
All the ones that use the 5 volts section use 3 of them in series and they then wind down the 5 volts on each one to about 4.6 volts or alternativly use a couple of big diodes in series with the out put to drop of some volts ..
Here are some i have come across .. but for all the inexperianced builder's please don't even take the cover off a power suply unless you know exactly what you are doing or have an experianced techi with you to supervise unloading the caps ect .. these things can still be live when switched off.....

http://www.antennex.com/preview/archive3/powers.htm

http://www.qsl.net/aa3sj/Pages/PC-Supply.html

Post Mon Aug 02, 2004 2:50 pm 
 View user's profile Send private message
timmeh
Experienced Roboteer


Joined: 20 Jul 2004
Posts: 2523
Location: Victoria


 Reply with quote  

Hey guys i have found a power supply at dick smiths 13.8v @ 20!!!!!!! amps for $99 how good is that and it is a more solid design then those little tin boxes with lots a holes in em it looks more like a car amp.
At the moment i am tinkering with a pc power supply that if it works should give out about 12 amps i will test it with a multi metre when im done to see if im right!
_________________
Tim Team Reaper.

Post Mon Aug 02, 2004 6:26 pm 
 View user's profile Send private message Send e-mail
Nick
Experienced Roboteer


Joined: 16 Jun 2004
Posts: 11802
Location: Sydney, NSW


 Reply with quote  

Were you looking at this one? http://www.dse.com.au/cgi-bin/dse.storefront/410dfb0407a75d522740c0a87f9c068d/Product/View/M9814

Its a DC-DC conterter, not a power supply - I shearched the DSE site and found nothing else that matched...
_________________
Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Post Mon Aug 02, 2004 6:40 pm 
 View user's profile Send private message
timmeh
Experienced Roboteer


Joined: 20 Jul 2004
Posts: 2523
Location: Victoria


 Reply with quote  

Yes thats it sorry didnt see that part about the 24 to 12v thing on the price tag it just sed 13.8v 20 amp power supply must have got it mixed up or something owell.

With the pc power supply mod what dose \Solder the 6 power resistors to the 5V load wires. The power resistors should be wired in parallel (side by side). mean? what end gos to what.You connect a wire from the 5v supply to one of the power resistors with the rest joined in parallel and what do you connect the other end of the last resistor too?

And dose this have any affect on how many amps you get from the pc power supply? ass the person Some guys say you can do it with fewer resistors. My testing shows 2 x 10 Ohm 1OW resistors gives about 3.5A continuous 4 x 10 ohm 10W resistors gives about 4.5A continuous 6 x 10 ohm 10W resistors gives about 7.5A continuous; more might be better,


http://www.mattsrcstuff.com/PCPS.htm
_________________
Tim Team Reaper.

Post Mon Aug 02, 2004 7:09 pm 
 View user's profile Send private message Send e-mail
ffej
Experienced Roboteer


Joined: 22 Jun 2004
Posts: 595
Location: Kurrajong, NSW


 Reply with quote  

The other side of the resistor bank needs to go to the ground rail. Essentially all your doing is creating a dummy load, as the PC PSU will not output the maximum it can on the 12V rail without some load on the 5V rail. ATX PC PSU's need an additional dummy load on the 3.3V rail for the same reason.

The more resistors you put across the 5V rail in paralell, the lower the total resistance, and the bigger the load placed on the rail. Some power supplies require more of a load than others to get the maximum output on the 12V rail, hence the "more (resistors) might be better" conclusion.

Also, the bigger the load, the more heat your going to be dumping through the resistors, so keep cooling in mind when placing them.

BTW, I dont mean to be rude, but if you dont completely understand what you are doing, should you really be attempting to mod a power supply that connects to the mains, and could turn lethal should something go wrong?
_________________
Jeff Ferrara
fb@ffej.net

ffej.net

Post Mon Aug 02, 2004 10:10 pm 
 View user's profile Send private message Visit poster's website Yahoo Messenger MSN Messenger
timmeh
Experienced Roboteer


Joined: 20 Jul 2004
Posts: 2523
Location: Victoria


 Reply with quote  

i do understand what im doing but i just wasnt sure about what the other end of the load resistors connected to as im not touching the ac part of the power supply ect not altering it im just modding the dc part which is safer but its not the volts that kill you its the amps so i still have to be carefull i know.

Thanks for helping me now i will finnish my power supply i couldnet get any 10 watt 10 ohm resistors so i just got a few 5 watt 10 ohm resistors i under stood that the resistors make a dummy load i just didnt know how that would increase the amps on the 12v line
_________________
Tim Team Reaper.

Post Mon Aug 02, 2004 10:24 pm 
 View user's profile Send private message Send e-mail
ffej
Experienced Roboteer


Joined: 22 Jun 2004
Posts: 595
Location: Kurrajong, NSW


 Reply with quote  


quote:
The resistors are like a electric magenett arent they? a wire that is coiled around that connects the - to the + they use power but dont short same sort of concept am i right?


Sort of, the resistors your using would most likely be ceramic, which is ohmic, meaning the resistance shouldnt change with diffenced in heat (it does, but in theory it shouldnt).

Resistors, funnily enough, resist current flow, but they are still conductors. The higher the resistance, the less the current can flow at a fixed voltage (ohms law). When you short a power supply, you give an "easy" path for the current to travel from positive to ground, meaning one of very little resistance. Copper is, to some extent, a resistor, and an electromagnet, theres so many copper windings, that the resistance ends up being quite high, reducing the current flow.

No idea if that answered your question . . .
_________________
Jeff Ferrara
fb@ffej.net

ffej.net

Post Mon Aug 02, 2004 10:53 pm 
 View user's profile Send private message Visit poster's website Yahoo Messenger MSN Messenger
Spockie-Tech
Site Admin


Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


 Reply with quote  


quote:
its not the volts that kill you its the amps so i still have to be carefull i know.


This is an oft-quoted saying of basic electrical theory that doesnt quite tell the whole story, and can lead people into a false sense of security..

Yes, it takes current, not voltage to stop your muscles (and your heart), but as long as humans have dry skin, our resistance is fairly high, so a low-voltage power supply is incapable of flowing many amps through you, regardless of whats is capable of supplying when hit with a low-resistance load. If it were otherwise, a 12v car-battery (capable of many hundreds of amps) would be lethal to the touch.

Likewise a Van-deGraaf (or other static) generator that can generate 10,000 volts or more is not dangerous, because despite its ability to spark-jump 10 centimeters of high-resistance air (so skin is no problem for it), it doesnt have the ability to supply any high amount of current (flow) to back up its high pressure (voltage).

But 240v is certainly enough to cause a decent current flow through skin resistance, even more so if your skin is only slightly moist, and back it up with the ability of the wall-power circuit to supply 10 amps or more (not to mention the momentary higher currents from the charged capacitors in a power supply) and you have a lethal combination of volts to cause the flow, and the amps to feed it.

In a linear (transfomer) power supply only the primary side of the main power transformer is operating at line (240v) voltage, and the filtering caps are on the low-voltage side of the transformer, so you just have to keep you fingers away from the 240v stuff.

However, in a switch-mode. a large part of the circuitry is floating at the mains voltage and has big caps charged to this voltage, so even hours after you have powered it down, it can still be storing a dangerous wallop.

An analogy for you. low voltage - high current power is like a bucket of water thrown at you. a big splash, but not with any real pressure pushing it. High Voltage - low current is like a potato/cap gun, it goes bang and moves fast, but doesnt have killing force behind it. Medium voltage & high power is like a bullet. the speed and force combined is deadly. Think water-jet cutting machines compared to your garden hose.

The electronics techies arent repeatedly warning you about them just because we're scare mongers you know. These things are far more dangerous inside than your electric toaster is, at least when you unplug the toaster, its safe. Not so with a PC power supply.

I strongly second what Jeff (nightshade) said. If you need parallel resistors explained to you more clearly, you do NOT yet have the electronics knowledge to go tinkering inside this sort of equipment, leave it to the professionals, they're a lot cheaper than a heart-defibrillation treatment in the hospital is.
_________________
Great minds discuss ideas. Average minds discuss events. Small minds discuss people

Post Mon Aug 02, 2004 10:53 pm 
 View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
Spockie-Tech
Site Admin


Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


 Reply with quote  

For anyone not concerned about 240v power yet. have a look here.

http://www.drmegavolt.com/underpages/warning.html

Line power is not for inexperienced people to play with !


Actually the whole dr.megavolt site is pretty cool too.. but heed his warnings.
www.drmegavolt.com
_________________
Great minds discuss ideas. Average minds discuss events. Small minds discuss people

Post Tue Aug 03, 2004 8:29 am 
 View user's profile Send private message Send e-mail Visit poster's website MSN Messenger
timmeh
Experienced Roboteer


Joined: 20 Jul 2004
Posts: 2523
Location: Victoria


 Reply with quote  

On my pc power supply the 12v- and the 12v+ give out 22.3v @ 9.9amps tested with a multi metre black wire on the 12v- and red wire on the 12v+ and the 5v- and the 5v+ give out 9.2v @ 3.9amps this is without any resistors just the - and + lines from the 12v and the 5v

why is the 5v and 12v giving out more voltage?

I could go the 12v+ and the 5v- combined for 15v which is the right voltage for the triton ass 22.3v is to much but i only get 6.5amps

Is there some sort of dial i can put on the 22.3v to turn it down to 12v without loosing amps?
_________________
Tim Team Reaper.

Post Tue Aug 03, 2004 2:48 pm 
 View user's profile Send private message Send e-mail
  Display posts from previous:      

Forum Jump:
Jump to:  

Post new topic   Reply to topic
Page 2 of 4

Goto page Previous  1, 2, 3, 4  Next

Forum Rules:
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum

 

Last Thread | Next Thread  >
Powered by phpBB: © 2001 phpBB Group
millenniumFalcon Template By Vereor.