Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
Need to get constant 15v DC from a variable buss
- Thread starter gillbot
- Start date
Power one ( is a major power supply vendor. They have (as do many others) DC to DC converters. A quick search showed one with Vin = 50-220 VDC, Vo = 15 VDC, Io = 10 A.
That 0-volt lower limit may be a problem, unless you can ensure that you only hit 0 volts for relatively short durations.
If your supply was always greater than 15 volts, the supply is a snap. If it drops below 15 volts once in a while, it's a little trickier, you're forced into a switchmode supply that essentialy converts DC to AC so that it can be "transformed" up to a higher voltage, and then back to regulated DC.
If your supply spends a lot of time around 0 volts, then you'd need capacitors or something to maintain the voltage during the sags. If your supply spends a significant amount of time at 0 volts, you're screwed.
Can you provide some more specifics about the supply bus?
If your supply was always greater than 15 volts, the supply is a snap. If it drops below 15 volts once in a while, it's a little trickier, you're forced into a switchmode supply that essentialy converts DC to AC so that it can be "transformed" up to a higher voltage, and then back to regulated DC.
If your supply spends a lot of time around 0 volts, then you'd need capacitors or something to maintain the voltage during the sags. If your supply spends a significant amount of time at 0 volts, you're screwed.
Can you provide some more specifics about the supply bus?
- Thread starter
- #4
It should only reach zero when the unit is off. It's a high current DC supply buss and I want to tap off for some control voltages. I don't expect it to reach zero but I don't know it's true lower limit and it will sag significantly under heavy load periods.
automatic2
Industrial
Sounds like that supply is likely loaded with spikes/harmonics and other gremlins. Maybe consider a UPS that is driven off the bus.
A commercial DC/DC converter should be able to handle most reasonable disturbances. We're using them to protect the protection relay system on a turbine from the sometimes severe disturbances on the 110V battery. The products I've used in this application were either Schaefer 'C' Series for 110/110V isolated conversion, or Power One's EQ series for 110/12.0V isolated conversion. Both perform very well in spite of the "spikes/harmonics and other gremlins" which are revalent on the battery supply.
-----------------------------------
Start each new day with a smile.
Get it over with.
-----------------------------------
Start each new day with a smile.
Get it over with.
- Thread starter
- #8
There will likely be many spikes and dips in the voltage since it's unregulated. I can probably use a coil then a capacitor before the power supply to help smooth out the incoming feed.
Let me give you more information about what I'm trying to do.
The DC is generated by a gas motor driven three phase AC generator, which in turn goes through a 3 phase rectifier. The rotor for this AC generator is currently powered by a DC battery. (DC rotor spinning in the three phase AC stator)
I'm trying to tap off of the unregulated main DC buss to provide ~+15Vdc to recharge the battery and power the rotor during operation. This would allow a much smaller battery to be used and eliminate the need to change them often.
Let me give you more information about what I'm trying to do.
The DC is generated by a gas motor driven three phase AC generator, which in turn goes through a 3 phase rectifier. The rotor for this AC generator is currently powered by a DC battery. (DC rotor spinning in the three phase AC stator)
I'm trying to tap off of the unregulated main DC buss to provide ~+15Vdc to recharge the battery and power the rotor during operation. This would allow a much smaller battery to be used and eliminate the need to change them often.
Just a really daft thought:
Why not use a battery charger fed directly from the AC generator output across two phases, and avoid DC/DC conversion completely? DC/DC converters are expensive; battery chargers are relatively cheap becase they are a mass-market item.
Your small battery provides what we would call 'field flashing' on a large utility generating set to initially establish the output voltage, and then the set is self-sustaining by feeding a small proportion of its output back in to the field via the battery charger.
-----------------------------------
Start each new day with a smile.
Get it over with.
Why not use a battery charger fed directly from the AC generator output across two phases, and avoid DC/DC conversion completely? DC/DC converters are expensive; battery chargers are relatively cheap becase they are a mass-market item.
Your small battery provides what we would call 'field flashing' on a large utility generating set to initially establish the output voltage, and then the set is self-sustaining by feeding a small proportion of its output back in to the field via the battery charger.
-----------------------------------
Start each new day with a smile.
Get it over with.
- Thread starter
- #10
The supply on the AC side is just as unreliable as the DC side so nothing would be gained from tapping off there. It can also vary frequency since the motor changes speed based on load. For simplicity, I think the DC side will be easier.
Yes, the battery would flash the rotor to get the generator going. Currently however, the battery powers the rotor exclusively thus my desire to tap off the DC buss for power.
There will be a variable resistor in series with the supply so the output current can be regulated.
Yes, the battery would flash the rotor to get the generator going. Currently however, the battery powers the rotor exclusively thus my desire to tap off the DC buss for power.
There will be a variable resistor in series with the supply so the output current can be regulated.
- Thread starter
- #11
- Status
Similar threads