Im still trying to come up with a high current DC supply for my mobile HF rig.
I have 4 - transformers that are all the same part number, there output is 4amp
at 18.5 vac. I want to hook a bridge to each & then connect the DC outputs of
each in parallel to increase current to my regulator circut.
I should end up with 17 - 18 VDC @ 16 amps. Does this sound like it would
work ok, Im not sure about paralleling DC supplies ?

You can probably make it work with matched parts, but you will need
somevery good heatsinking and a crowbar circuit in case one of your pass
regulators shorts out.

You should really look at using an ASTRON SS30 or SS30M (M has volt and
amp meters). One was for sale on one of the swap boards recently. I have
two and they deliver the current without any strain or heat. As far as
RFI noise, they are also very quiet. ARRL did a write up a couple years
back on various switchers and this one was the quietest. 25 amps
continuous, 30 amps intermittent. I run mine to 20 amps all the time and
the fan switches on for a short time, no sweat.

clc wrote:

Im still trying to come up with a high current DC supply for my mobile HF rig.
I have 4 - transformers that are all the same part number, there output is 4amp
at 18.5 vac. I want to hook a bridge to each & then connect the DC outputs of
each in parallel to increase current to my regulator circut.
I should end up with 17 - 18 VDC @ 16 amps. Does this sound like it would
work ok, Im not sure about paralleling DC supplies ?




--
Joe Leikhim K4SAT


"Jazz is not dead. It just smells funny." -F.Z.

clc wrote:

Im still trying to come up with a high current DC supply for my mobile HF rig.
I have 4 - transformers that are all the same part number, there output is 4amp
at 18.5 vac. I want to hook a bridge to each & then connect the DC outputs of
each in parallel to increase current to my regulator circut.
I should end up with 17 - 18 VDC @ 16 amps. Does this sound like it would
work ok, Im not sure about paralleling DC supplies ?


That should work OK. If you want a regulated supply then connect the
regulator after the combined DC
voltages. That way you don't have to be concerned with the possible
reverse current through one
of the regulator circuits.

Bill K7NOM

clc wrote:
Im still trying to come up with a high current DC supply for my mobile HF rig.
I have 4 - transformers that are all the same part number, there output is 4amp
at 18.5 vac. I want to hook a bridge to each & then connect the DC outputs of
each in parallel to increase current to my regulator circut.
I should end up with 17 - 18 VDC @ 16 amps. Does this sound like it would
work ok, Im not sure about paralleling DC supplies ?

Why don't you connect the transformers in parallel and rectify /
stabilize the total AC current?

Hans

Hans wrote:

clc wrote:

Im still trying to come up with a high current DC supply for my
mobile HF rig.
I have 4 - transformers that are all the same part number, there
output is 4amp
at 18.5 vac. I want to hook a bridge to each & then connect the DC
outputs of
each in parallel to increase current to my regulator circut.
I should end up with 17 - 18 VDC @ 16 amps. Does this sound like
it would
work ok, Im not sure about paralleling DC supplies ?


Why don't you connect the transformers in parallel and rectify /
stabilize the total AC current?

Hans

There is a "chance" that the voltages won't be exactly the same. As a
result you can
have circulating currents in the transformers from that difference. The
diodes solve
that potential problem.

Bill K7NOM

just paralleling up the power supplies will probably not result in any
power exceeding the power supplied by the transformer with the largest
swing.
let me describe this for you:

your rectifiers act as switches, whenever the voltage across them
exceeds 0.6 volts (for silicon diodes), they will conduct. now you
connect the anodes of two rectifiers that are driven from the other
side by a voltage generators. If you imagine that one of the two
diodes are driven by a voltage source that is higher than the other by
0.6 volts, then the diode will never switch on as the other diode will
reverse bias this diode. so, simply paralleling up the dc outputs may
not work. A 0.6 volts difference between two transformers is almost a
given.

my recommendation to you would be to wire up the primary windings in
parallel and the secondary (18v) windings in series. That way, if the
phase is proper you will get 18-0-18v (36 v) across the two
secondaries. A bridge will get you 18V.

Something like this :

----+-3|
| 3|C--------------||---+
| 3|C |
| 3|C------+ |
-+--|-3| | |
| | | +-------+----O 18 DC +v
| | |---- Gnd | |
-|--+-3| | | ===
| 3|C------+ | === filter cap.
| 3|C | |
| 3|C--------------||---+ Gnd
-+----3|

this uses just two of the four transformers. besure that the voltages
of the secondary are in phase. (you will not get more than a volt or
so if the are not). there is probably a way to also utilise four
transformers, it is in the corner of my eye, but the above given is a
cookbook recipe.
However, if you require 36v, then it is a simple matter to extend this
by using two supplies with secondaries in series on each side of the
rectifier bridge.

- farhan

Hans wrote:

clc wrote:

Im still trying to come up with a high current DC supply for my
mobile HF rig.
I have 4 - transformers that are all the same part number, there
output is 4amp
at 18.5 vac. I want to hook a bridge to each & then connect the DC
outputs of
each in parallel to increase current to my regulator circut.
I should end up with 17 - 18 VDC @ 16 amps. Does this sound like
it would
work ok, Im not sure about paralleling DC supplies ?


Why don't you connect the transformers in parallel and rectify /
stabilize the total AC current?

Hans

There is a "chance" that the voltages won't be exactly the same. As a
result you can
have circulating currents in the transformers from that difference. The
diodes solve
that potential problem.

Bill K7NOM

just paralleling up the power supplies will probably not result in any
power exceeding the power supplied by the transformer with the largest
swing.
let me describe this for you:

your rectifiers act as switches, whenever the voltage across them
exceeds 0.6 volts (for silicon diodes), they will conduct. now you
connect the anodes of two rectifiers that are driven from the other
side by a voltage generators. If you imagine that one of the two
diodes are driven by a voltage source that is higher than the other by
0.6 volts, then the diode will never switch on as the other diode will
reverse bias this diode. so, simply paralleling up the dc outputs may
not work. A 0.6 volts difference between two transformers is almost a
given.

my recommendation to you would be to wire up the primary windings in
parallel and the secondary (18v) windings in series. That way, if the
phase is proper you will get 18-0-18v (36 v) across the two
secondaries. A bridge will get you 18V.

Something like this :

----+-3|
| 3|C--------------||---+
| 3|C |
| 3|C------+ |
-+--|-3| | |
| | | +-------+----O 18 DC +v
| | |---- Gnd | |
-|--+-3| | | ===
| 3|C------+ | === filter cap.
| 3|C | |
| 3|C--------------||---+ Gnd
-+----3|

this uses just two of the four transformers. besure that the voltages
of the secondary are in phase. (you will not get more than a volt or
so if the are not). there is probably a way to also utilise four
transformers, it is in the corner of my eye, but the above given is a
cookbook recipe.
However, if you require 36v, then it is a simple matter to extend this
by using two supplies with secondaries in series on each side of the
rectifier bridge.

- farhan

You can probably make it work with matched parts, but you will need
somevery good heatsinking and a crowbar circuit in case one of your pass
regulators shorts out.

You should really look at using an ASTRON SS30 or SS30M (M has volt and
amp meters). One was for sale on one of the swap boards recently. I have
two and they deliver the current without any strain or heat. As far as
RFI noise, they are also very quiet. ARRL did a write up a couple years
back on various switchers and this one was the quietest. 25 amps
continuous, 30 amps intermittent. I run mine to 20 amps all the time and
the fan switches on for a short time, no sweat.

clc wrote:

Im still trying to come up with a high current DC supply for my mobile HF rig.
I have 4 - transformers that are all the same part number, there output is 4amp
at 18.5 vac. I want to hook a bridge to each & then connect the DC outputs of
each in parallel to increase current to my regulator circut.
I should end up with 17 - 18 VDC @ 16 amps. Does this sound like it would
work ok, Im not sure about paralleling DC supplies ?




--
Joe Leikhim K4SAT


"Jazz is not dead. It just smells funny." -F.Z.

Paralleling DC supplies can be problematic if they are regulated supplies and
not designed for paralleling. Another solution to consider is using a deep
cycle battery and a charger. Works fine, even during a power outage...