# PDP-11/70 Boards

Mike Katz bitwiz at 12bitsbest.com
Wed Dec 8 17:14:07 CST 2021

```That would depend on the type and size of wire (solid core, stranded,
strands of stranded, etc.).

On 12/8/2021 5:06 PM, pbirkel at gmail.com wrote:
> Seems to me that the actual coil resistance will limit the max-current at lower voltages.  20 A through wire sized for 1 A seems ... unlikely?
>
> -----Original Message-----
> From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of Mike Katz via cctalk
> Sent: Wednesday, December 8, 2021 5:58 PM
> To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>; wrcooke at wrcooke.net
> Subject: Re: PDP-11/70 Boards
>
> More accurately up to it's rated wattage "Power = Voltage * Current"
> after all.
>
> If you have a 100W max variac you can draw 20A @ 5V (approx) but only 1A at 100V.
>
> On 12/8/2021 4:44 PM, Mike Katz via cctalk wrote:
>> "As a general rule, a variable transformer (Variac) can provide full
>> rated current at any output voltage. So a 2.5A unit can provide 2.5 A
>> at 1V, 10V, 120V, etc. With a 20V output, that is 50 VA (Watts, sort
>> of)."
>>
>> Up to the current rating of the variac.  When you draw more current
>> than the transformer can deliver then the voltage will sag.
>>
>> On 12/8/2021 4:22 PM, Will Cooke via cctalk wrote:
>>>> On 12/08/2021 3:58 PM Rob Jarratt via cctalk <cctalk at classiccmp.org>
>>>> wrote:
>>>> So, to supply the bricks on the bench, would a variac rated at 2.5A
>>>> be OK? I am not sure I know how much current the bricks will draw at
>>>> 20VAC, and at what voltage the 2.5A rating is given. Otherwise,
>>>> would this do the trick?
>>>> https://cpc.farnell.com/block/steu250-48/transformer-250va-230-400v-
>>>> 2-x/dp/TF01418?st=24v%20transformer
>>>>
>>>> Thanks
>>>>
>>>> Rob
>>>>
>>>>
>>>>>> JRJ
>>> As a general rule, a variable transformer (Variac) can provide full
>>> rated current at any output voltage.  So a 2.5A unit can provide 2.5
>>> A at 1V, 10V, 120V, etc.  With a 20V output, that is 50 VA (Watts,
>>> sort of).
>>>
>>> Will
>>>
>>> "I was born not knowing and have had only a little time to change
>>> that here and there."
>>> Richard Feynman
>

```