At 11:54 AM 6/8/2005, skipp025 wrote:
>Most Astron Supplies will easily operate at 15 volts output if you
>mod the crow-bar circuit for the higher
>fire/trigger voltage. If fact, they actually work better at the
>higher output voltage.
Well, they end up with a bit less dissipation, due to the
input-output differential going lower.
Another good reason to use switchers.
>I WOULD NEVER DISABLE THE CROWBAR CIRCUIT IN ANY ASTRON SUPPLY
>UNLESS YOU WANT BBQ RADIO. (get my hint with the cap letters?) It's
>not a question of if, only when it will be required (unless you have
>one of the new generation regulator boards). I would not trust this
>type linear regulated high current supply to operate without a
>crowbar protection circuit.
If you have a large (relative to the power supply's output current)
battery across the terminals, the voltage won't get high enough to
trigger the crowbar (if the crowbar is properly set) until the
battery is damaged. A crowbar isn't really useful here, and just
adds potential problems.
Fuse the input of the supply appropriately, so that it will blow if
the output is held to maximum for 10 seconds or so.
See the buss guide called "Fuseology" on selecting fuses.
Even a full short on the regulator isn't going to bring up the
battery voltage much, and you won't see "BBQ RADIO" at that point.
Anything that is designed to live in a vehicle will tolerate 15-16V
on the input.
>Voltage (battery) back-feed to the supply terminals will kill many
>supply regulator circuits unless you know how to inspect the circuit
>design and retrofit the circuit to pass the reverse voltage source
>back to the filter caps (and any other low z sources on the input
>side of the regulator circuit)
This is a known fault of 78XX series regulators and similarly
constructed discrete linear regulators, but it's only an issue if the
battery is connected to a supply that is not turned on, and has
discharged it's input caps.
A 3A diode across the regulator fixes it nicely.
If you don't know the circuit, you can simply connect the banded end
to the input filter caps (16-35V ratings, 10,000uF or thereabouts)
and the other end to the output of the supply.
Yet another good reason to use a switcher. The only thing you'd be
"backfeeding" into would be the output filter caps.
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