Voltage Advice Needed

[PaulQ]

So in other words: The voltage should be the same or slightly under the original. The ampere should be the same or above the original.

So exactly the opposite of what I have.

You need to determine the maximum amount of current this device will draw. It is entirely possible that the original power supply was capable of providing much more current than it would ever need. It's possible that the original power supply was designed to supply power to the device with certain peripherals attached that you're not using. You should check the labels and printing on the CDX to see if it indicates what it will draw. As for the voltage, .5 volts over will, in all likeliness, not create any significant problems. I'll bet that most cheap universal power supplies fluctuate at least that much either way during normal use.

[eslapion]

Voltage isn't as important as amperage; most devices can handle a higher than rated voltage (or even lower), but not enough current could cause damage.

WRONG!

There are devices which accept AC which will not have too much of a problem with slightly higher voltages. The same is true of devices that use UNREGULATED DC voltages. But if you go too high then damage will occur.

However, many devices such as the VIC-20cr, the Commodore 64 and drives with external power supplies such as the 1581, 1541-II and the CMD family of FD drives require REGULATED DC voltages. With these devices going only ONE VOLT TOO HIGH can completely cripple the device.

There was a thread about a 1541-II damaged this way in the Hardware and tech section.

[eslapion]

Voltage isn't as important as amperage; most devices can handle a higher than rated voltage (or even lower), but not enough current could cause damage.

Really? I had heard that it was more dangerous to supply more voltage than needed, whereas you can provide more amps than needed (but not less as you say) and the device will only draw those amps that it needs.

i.e. I direct you to my "sick 1541-II" thread where the faulty power supply was sending 8v on what was supposed to be a 5v line. The extra 3 volts were causing several chips to malfunction and possibly fried one.

The fact that you read 8 volts on your power supply is indicative of the fact that the regulator inside the power supply is dead. However, you measured this voltage when your drive was disconnected from that power supply.

In reality, when your drive was switched on and running, the actual voltage the supply fed to it was probably more like 6 volts. That, in fact, is plenty enough to cause very serious damage.

[eslapion]

Usually most IC's will be hurt more by under-voltaging them. Think about overclocking modern CPU's... you normally increase the voltage to get the transistors to switch fastter. In turn, it runs hotter.

But the .5v difference on the power supply probably isn't a big deal, since it most likely has regulators inside the unit, anyway.

The big deal is whether .65A less of available current will damage either the unit (because the voltage will drop as the power supply cannot keep up with the current draw) or the power supply will fizzle out because it's being stressed too much, and possibly blow'd up the unit.

I'd try to find a power supply that more closely matches the original in amperage.

WRONG!

See Boray's post.

Altough higher voltages WILL make CMOS circuits react faster, the VIC-20 and Commodore 64 uses NMOS technology which does not deliver higher performance when fed higher voltages.

Feeding higher voltages to pentium series of processor can make them go slightly faster and run hotter but we're talking about increases in voltages in the range of 0.025 to 0.1 volts. Any higher can permanently damage them.

To less current will make the voltage drop because there isn't enough to provide for the demand. Lower voltages will simply prevent the chip from running at all...

[eslapion]

What about those "Universal Power Supply"s from Radio Shack? They read:

Power Voltage DC 3, 4.5, 6, 7.5, 9, 12 V (1000 mA)

The focus on Voltage made me think that it was the most important thing. If I find an off brand replacement, I'm likely to have some difference...
...and "1000mA"? Does 1000 Milliamperes out meet my needs? Are these things frying equipment?

These things provide UNREGULATED DC voltages. They should NEVER be used with devices requiring REGULATED DC voltages.

Devices requiring regulated voltages will usually require 3.3V, 5V and/or 12V.

As you can see, batterie replacers like this type of power supplies almost never provide 3.3V (and specifically 3.3 and not 3 volts) or 5 volts.

[eslapion]

... As for the voltage, .5 volts over will, in all likeliness, not create any significant problems. I'll bet that most cheap universal power supplies fluctuate at least that much either way during normal use.

WRONG AGAIN!

(at least for devices using regulated power)

A properly working power supply for a 1541-II/1581 will provide 5V and 12V with a tolerance of about 1% with the drive turned off. It will still provide the same voltages with 1% tolerance with the drive turned on.

In other words, if the voltages vary by more than 2% (in the case of 5V power supplies, that amounts to 0.1 volt) between a full load condition and a no load condition then the regulator is considered faulty.

In reality, the voltage variation for a modern switching power supply which has a minimum load rating between minimum load condition and full load condition is usually less than 0.2% or 0.01 volt.

All TTL technology chips (the 74LSXXX and 74FXXX chips used in the VIC, 64, 128, Amigas and even pre-pentium era PCs) as well as allmost all legacy CMOS (memory, CPUs and custom chips) chips are designed to operate reliably between 4.75 and 5.25 volts. Below that they don't work reliably and above that they can be damaged.

[gklinger]

Five posts in a row with two "WRONG!"s and one "WRONG AGAIN!". Reading this thread is like watching the The McLaughlin Group.

[6502dude]

Five posts in a row with two "WRONG!"s and one "WRONG AGAIN!". Reading this thread is like watching the The McLaughlin Group.

[PaulQ]

[Jeff-20]

No, seriously, thanks for the info. I've played it a few times briefly just to test it. I will hunt for the correct power supply. That Cheers pic just cracked me up!

[idrougge]

... As for the voltage, .5 volts over will, in all likeliness, not create any significant problems. I'll bet that most cheap universal power supplies fluctuate at least that much either way during normal use.

WRONG AGAIN!

(at least for devices using regulated power)

Yes, but things using standard black wall-warts, and not custom Commodore supplies, will have voltage stabilisers inside, because it would be suicidal for the electronics to rely on a cheap wall-wart to supply exactly the required current and voltage.

[6502dude]

Cliff from cheers....ROFL


Good character, but that guy really got type cast.

[Victragic]

Hilarious.. everyone has their pet peeves. Don't get me started on ebay (oh wait, I did already).

still at least there's a point to be made in that someone might fry their Commodore gear if they do the wrong thing. Namely me, who only knows that electricity is generated by large mythical Gods banging their hammers on rocks when they are angry.

Digg.com on the other hand - if you can find one thread that doesn't involve pointless name-calling, random abuse and pedantic whining over the use of terms like 'lappy' instead of 'laptop' then please send me a link.

Oh, and btw - surely because we have 220v here all I need to do is plug in 2x 110v power adapters in the same socket to balance out the power?

[dave01253]

I won some stuff on ebay recently. I have 2 power supplies

one same as this

http://centsible.com/images/ebay/c64psu.jpg

and an old beige wedge type one.


The black one says 3-83 on the bottom. I assume its a date code but I had no idea that these were made that long ago. its the same as the ones packaged with the 64c but black. I'm just testing it with an old board that doesnt work. it draws power as some chips get warm.

ii get 9.5 ac and 5.01 dc

lets see what I get when its been on a while....


the beige wedge has obviously been opened and glued shut again.

don't like those.

[eslapion]

Yes, but things using standard black wall-warts, and not custom Commodore supplies, will have voltage stabilisers inside, because it would be suicidal for the electronics to rely on a cheap wall-wart to supply exactly the required current and voltage.

WRONG!

I have a very nice internet router here and a USB video capture box. Both use a nice little switching power supply walwart.

Both walwarts are rated for 5V 2A and the symbol on it says it is regulated. Just for the fun of it, I checked inside and apart from two small ferrite beads to remove RFI, there is no protection whatsoever. Both the router and the video capture box could be destroyed by feeding them anything above 5.25 volts.

For historical information, the C64, the VIC cr, the Commodore 128, the Plus 4 and C16 have no such protection. Feeding them too much voltage on the power input pins where they expect 5V will destroy them too.

I also have a Video to VGA converter N6 from viewsonic. It uses 12 volts and it requires regulated voltage. It too has no internal protection whatsoever and it too uses a walwart. Any voltage above 12.6 volts can destroy it. Feeding it in reverse polaroty will destroy it too.

Switching walwarts DO provide the exact required voltages. As for current, what you need is equal or above... Which means, yes, I CAN use a 500 watts ATX power supply rated for 30 amp on the 5V to power up my internet router which consumes less than 2. It will work fine but... what a waste.

Added edit:
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I also have a USB hub that uses a 5V switching walwart and it too is totally unprotected internally.

Many mobile phones use switching regulated walwarts to charge them. Using any voltage other than the one specified on the walwart could destroy the phone.