Re: Bleeder resistor for power supply size?

I'm **not** an EE, but I did build a few linear power supplies for
those old S-100 computers. I did as Mariss suggested and switched the
power supply on and off on the AC side and let the computer drain the
capacitors, which it would do quite quickly.

I always put bleeder resistors on the capacitors anyway, figuring
that their real purpose was to bleed off the charge in the caps if
the rest of the system wasn't there to do it. (blown fuse, boards
pulled out, etc.)

I'll admit that circumstance was more likely with my old homebuilt
computer than with a stepper power supply, but that was my rationale
for wasting the current and generating the excess heat

Chris


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
<mariss92705@y...> wrote:

> Hi,
>
> This is one of those "how many angels can dace on the end of a pin"
> questions that come up again and again.
>
> A capacitor stores a charge (voltage) for a long time if there is

no

> load on it.
>
> That is not the way you are going to use your supply.
>
> You will have various drives and other loads on it and you will

turn

> the supply on and off on the AC input to your supply.
>
> With all these various drives and loads, your supply will very
> quickly discharge (<< 1 sec) when you shut off the AC supply.
>
> You never switch the loads on and off on the DC side. That is hard

on

> the switch and any electronics attached to it. You use the AC power
> input for that.
>
> You do that and there is no reason for a "bleeder resistor". It is

a

> pointless, sometimes expensive component that does precisely

nothing

> except get hot.
>
> Long and short, turn your power on-off at the AC side and let your
> drives be the "bleeders". They will do a better job than any

resistor

> and they will do it quicker and better for free.
>
> Mariss
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Damon" <damonfg@y...>

wrote:

> >
> > I found some amazing hang time in my system. When I was running
> > only a transformer,bridge, and caps (no motors/drivers) I had
> > 66VDC, shut down power and came back 48 hours later, it was only
> > down to 35VDC. With a pair of geckos and 1050oz steppers, it
> > bleeds down in about 10 seconds or so, entirely acceptable!
> >
> > -Damon