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connecting dc supplies in parallel for more current
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. |
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 ? 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 |
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 |
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... |
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... |
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 |
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 |
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 |
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"Jim, N2VX" wrote in message . ..
On 27 Oct 2003 19:02:07 -0800, (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 ? I did it with 2 of them and it worked OK. As you described use a separate rectifier on each and combine the rectifier outputs. Start scrounging hamfests, etc. for electrolytic capacitors. You can't have too much filtering. In this case more is better. For a regulator use a 7815 IC to drive several 2N3055's. ARRL handbooks have a good example of 2N3055's in parallel. 5 2N3055's on a decent heatsink will run nice and cool. Scrounge for heatsinks, too. They tend to be cheap at hamfests because most people are appliance operators. And if you want to make life easier for the rectifiers add a soft start cicruit using a relay. The handbook has an example of it. Good luck and 73, Jim A 7815 would give 15 volts, wouldnt that be alittle high? A 7812 would be a little low, so i thought of a 723 ang just adjust the voltage to 13.8. |
On 29 Oct 2003 10:16:56 -0800, (clc) wrote:
"Jim, N2VX" wrote in message . .. On 27 Oct 2003 19:02:07 -0800, (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 ? I did it with 2 of them and it worked OK. As you described use a separate rectifier on each and combine the rectifier outputs. Start scrounging hamfests, etc. for electrolytic capacitors. You can't have too much filtering. In this case more is better. For a regulator use a 7815 IC to drive several 2N3055's. ARRL handbooks have a good example of 2N3055's in parallel. 5 2N3055's on a decent heatsink will run nice and cool. Scrounge for heatsinks, too. They tend to be cheap at hamfests because most people are appliance operators. And if you want to make life easier for the rectifiers add a soft start cicruit using a relay. The handbook has an example of it. Good luck and 73, Jim A 7815 would give 15 volts, wouldnt that be alittle high? A 7812 would be a little low, so i thought of a 723 ang just adjust the voltage to 13.8. You get 15 - (transistor drop + balancing emitter resistor drop). I got 14 volts out of it. That's in the range of car charging systems and I've measured that much on some cars with the engine running. There's another setup where you get IC regulator voltage + transistor drop + resistor drop, using PNP transistors. Check the handbook for details. Power PNP's are less common and it's hard to beat the venerable 2N3055's price and availability. How about a LM317? As I recall they are good for more current than 723's and easy to use. Regulator current at the IC is (output current) / (transistor gain) Then you can adjust to get 13.8 on the output. 73, Jim |
On 29 Oct 2003 10:16:56 -0800, (clc) wrote:
"Jim, N2VX" wrote in message . .. On 27 Oct 2003 19:02:07 -0800, (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 ? I did it with 2 of them and it worked OK. As you described use a separate rectifier on each and combine the rectifier outputs. Start scrounging hamfests, etc. for electrolytic capacitors. You can't have too much filtering. In this case more is better. For a regulator use a 7815 IC to drive several 2N3055's. ARRL handbooks have a good example of 2N3055's in parallel. 5 2N3055's on a decent heatsink will run nice and cool. Scrounge for heatsinks, too. They tend to be cheap at hamfests because most people are appliance operators. And if you want to make life easier for the rectifiers add a soft start cicruit using a relay. The handbook has an example of it. Good luck and 73, Jim A 7815 would give 15 volts, wouldnt that be alittle high? A 7812 would be a little low, so i thought of a 723 ang just adjust the voltage to 13.8. You get 15 - (transistor drop + balancing emitter resistor drop). I got 14 volts out of it. That's in the range of car charging systems and I've measured that much on some cars with the engine running. There's another setup where you get IC regulator voltage + transistor drop + resistor drop, using PNP transistors. Check the handbook for details. Power PNP's are less common and it's hard to beat the venerable 2N3055's price and availability. How about a LM317? As I recall they are good for more current than 723's and easy to use. Regulator current at the IC is (output current) / (transistor gain) Then you can adjust to get 13.8 on the output. 73, Jim |
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"Jim, N2VX" wrote in message ... On 27 Oct 2003 19:02:07 -0800, (clc) wrote: Start scrounging hamfests, etc. for electrolytic capacitors. You can't have too much filtering. In this case more is better. For a regulator use a 7815 IC to drive several 2N3055's. ARRL handbooks have a good example of 2N3055's in parallel. 5 2N3055's on a decent heatsink will run nice and cool. Scrounge for heatsinks, too. They tend to be cheap at hamfests because most people are appliance operators. And if you want to make life easier for the rectifiers add a soft start cicruit using a relay. The handbook has an example of it. Good luck and 73, Jim Here is the article (schematic link at bottom) http://www.seits.org/features/pwrsup.htm KBT Info page on linear supplies http://www.kbt-dc-supplies.com/index.php and Astron schematics are already on the Internet http://www.repeater-builder.com/rbtip/astron-index.html Greg w9gb |
"Jim, N2VX" wrote in message ... On 27 Oct 2003 19:02:07 -0800, (clc) wrote: Start scrounging hamfests, etc. for electrolytic capacitors. You can't have too much filtering. In this case more is better. For a regulator use a 7815 IC to drive several 2N3055's. ARRL handbooks have a good example of 2N3055's in parallel. 5 2N3055's on a decent heatsink will run nice and cool. Scrounge for heatsinks, too. They tend to be cheap at hamfests because most people are appliance operators. And if you want to make life easier for the rectifiers add a soft start cicruit using a relay. The handbook has an example of it. Good luck and 73, Jim Here is the article (schematic link at bottom) http://www.seits.org/features/pwrsup.htm KBT Info page on linear supplies http://www.kbt-dc-supplies.com/index.php and Astron schematics are already on the Internet http://www.repeater-builder.com/rbtip/astron-index.html Greg w9gb |
Connecting transformers in parallel is sometimes a risky business,
Some big power distribution transformers are sometimes connecting in parallel with some external inductance to reduce the imbalance. Take a separate smallish transformer with a centre tapped low voltage secondary winding. Connect the centre tap to the load and the two end of the small transformer to the respective hot terminals on the main transformers. The primary of the smallish transformer is not connected, but can contain quite voltages. =========== Question : With a load having 2 connections , with the centre tap connected to 1 connection of the load ,where to connect the other connection of the load ? Frank GM0CSZ / KN6WH |
Connecting transformers in parallel is sometimes a risky business,
Some big power distribution transformers are sometimes connecting in parallel with some external inductance to reduce the imbalance. Take a separate smallish transformer with a centre tapped low voltage secondary winding. Connect the centre tap to the load and the two end of the small transformer to the respective hot terminals on the main transformers. The primary of the smallish transformer is not connected, but can contain quite voltages. =========== Question : With a load having 2 connections , with the centre tap connected to 1 connection of the load ,where to connect the other connection of the load ? Frank GM0CSZ / KN6WH |
On Thu, 30 Oct 2003 11:31:22 -0000, "Frank Dinger"
wrote: Connecting transformers in parallel is sometimes a risky business, Some big power distribution transformers are sometimes connecting in parallel with some external inductance to reduce the imbalance. Take a separate smallish transformer with a centre tapped low voltage secondary winding. Connect the centre tap to the load and the two end of the small transformer to the respective hot terminals on the main transformers. The primary of the smallish transformer is not connected, but can contain quite voltages. =========== Question : With a load having 2 connections , with the centre tap connected to 1 connection of the load ,where to connect the other connection of the load ? To the "cold" end of both main transformers, which are connected together. You have to connect the primaries in such a way that the "hot" ends of the secondary of each transformer is in the same phase, thus the voltage of the hot end of each secondary is nearly equal and the centre tapped choke will take care of the rest. In three phase systems, connect the star points of the transformers together, which is also used as a return for single phase loads. A balancing CT choke is needed for each phase and also in this case you have to observe the primary polarity when connecting the primaries. Paul OH3LWR |
On Thu, 30 Oct 2003 11:31:22 -0000, "Frank Dinger"
wrote: Connecting transformers in parallel is sometimes a risky business, Some big power distribution transformers are sometimes connecting in parallel with some external inductance to reduce the imbalance. Take a separate smallish transformer with a centre tapped low voltage secondary winding. Connect the centre tap to the load and the two end of the small transformer to the respective hot terminals on the main transformers. The primary of the smallish transformer is not connected, but can contain quite voltages. =========== Question : With a load having 2 connections , with the centre tap connected to 1 connection of the load ,where to connect the other connection of the load ? To the "cold" end of both main transformers, which are connected together. You have to connect the primaries in such a way that the "hot" ends of the secondary of each transformer is in the same phase, thus the voltage of the hot end of each secondary is nearly equal and the centre tapped choke will take care of the rest. In three phase systems, connect the star points of the transformers together, which is also used as a return for single phase loads. A balancing CT choke is needed for each phase and also in this case you have to observe the primary polarity when connecting the primaries. Paul OH3LWR |
Connecting transformers in parallel is sometimes a risky business,
Some big power distribution transformers are sometimes connecting in parallel with some external inductance to reduce the imbalance. Take a separate smallish transformer with a centre tapped low voltage secondary winding. Connect the centre tap to the load and the two end of the small transformer to the respective hot terminals on the main transformers. The primary of the smallish transformer is not connected, but can contain quite voltages. =========== Question : With a load having 2 connections , with the centre tap connected to 1 connection of the load ,where to connect the other connection of the load ? To the "cold" end of both main transformers, which are connected together. You have to connect the primaries in such a way that the "hot" ends of the secondary of each transformer is in the same phase, thus the voltage of the hot end of each secondary is nearly equal and the centre tapped choke will take care of the rest. In three phase systems, connect the star points of the transformers together, which is also used as a return for single phase loads. A balancing CT choke is needed for each phase and also in this case you have to observe the primary polarity when connecting the primaries. ======================== Tnx Paul , for the very useful info ,which I have filed for future reference. Frank GM0CSZ / KN6WH |
Connecting transformers in parallel is sometimes a risky business,
Some big power distribution transformers are sometimes connecting in parallel with some external inductance to reduce the imbalance. Take a separate smallish transformer with a centre tapped low voltage secondary winding. Connect the centre tap to the load and the two end of the small transformer to the respective hot terminals on the main transformers. The primary of the smallish transformer is not connected, but can contain quite voltages. =========== Question : With a load having 2 connections , with the centre tap connected to 1 connection of the load ,where to connect the other connection of the load ? To the "cold" end of both main transformers, which are connected together. You have to connect the primaries in such a way that the "hot" ends of the secondary of each transformer is in the same phase, thus the voltage of the hot end of each secondary is nearly equal and the centre tapped choke will take care of the rest. In three phase systems, connect the star points of the transformers together, which is also used as a return for single phase loads. A balancing CT choke is needed for each phase and also in this case you have to observe the primary polarity when connecting the primaries. ======================== Tnx Paul , for the very useful info ,which I have filed for future reference. Frank GM0CSZ / KN6WH |
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 ? It should work fine, but your DC output voltage will end up higher with the addition of the required filter cap. Voltage across the cap will be about 26 volts, no load. Parallel the output of the bridges, install a big filter cap, and run the resultant voltage to a voltage regulator. Do not regulate prior to paralleling the supplies! Your regulator can be an LM317 or 7812, with pass transistors in a "collector wraparound" configuration. I'll describe such configuration below, using a 7812. You can parallel a number of pass transistors - I'd use 4 2N3055's (2N3055's because I have a lot of them) with a .1 ohm 5W resistor in each emitter leg. You can use a 7812 with 2 or 3 diodes in the ground leg between the leg and ground, connect the output of the 7812 to the parallel xsistors collectors. The base of the transistor goes to the input pin of the 7812. From there, a 2 ohm 1 watt resistor connects to the + side of the cap where the emitter resistors also connect. If you look at the 7812 datasheet application notes, you will find an example of the circuit there with a single pass transistor (and thus no emitter resistors) and no diodes in the ground leg. http://www.national.com/ds/LM/LM340.pdf The pass transistors have to handle about 205 watts (12.8 volts * 16 amps) so you need a good heatsink for them. You also need to heatsink the 7812. The LM317 circuit is essentially the same. Look at its datasheet. You won't need the 2 diodes in the ground leg, but you will need to add a couple of resistors. |
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 ? It should work fine, but your DC output voltage will end up higher with the addition of the required filter cap. Voltage across the cap will be about 26 volts, no load. Parallel the output of the bridges, install a big filter cap, and run the resultant voltage to a voltage regulator. Do not regulate prior to paralleling the supplies! Your regulator can be an LM317 or 7812, with pass transistors in a "collector wraparound" configuration. I'll describe such configuration below, using a 7812. You can parallel a number of pass transistors - I'd use 4 2N3055's (2N3055's because I have a lot of them) with a .1 ohm 5W resistor in each emitter leg. You can use a 7812 with 2 or 3 diodes in the ground leg between the leg and ground, connect the output of the 7812 to the parallel xsistors collectors. The base of the transistor goes to the input pin of the 7812. From there, a 2 ohm 1 watt resistor connects to the + side of the cap where the emitter resistors also connect. If you look at the 7812 datasheet application notes, you will find an example of the circuit there with a single pass transistor (and thus no emitter resistors) and no diodes in the ground leg. http://www.national.com/ds/LM/LM340.pdf The pass transistors have to handle about 205 watts (12.8 volts * 16 amps) so you need a good heatsink for them. You also need to heatsink the 7812. The LM317 circuit is essentially the same. Look at its datasheet. You won't need the 2 diodes in the ground leg, but you will need to add a couple of resistors. |
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