polarity reverser?

[pieman]

I need to buy or build a polarity reverser (is that the right term?). We have a gyrostabilized helicopter camera system. This runs off 24volts which is normally supplied by the Chopper. I have put together a devise which produces 24volts with a 12volts stepdown that can be used to power the system off mains or switched to 24volts for the helicopter power.

The problem is the power on different choppers is wired differently A+ or B+. I need to build a small circuit which will output 24volts A+ regardless as to which way round the 24volt input side is wired.

regards

 

[JBrock]

I don't suppose you could get away with a four-diode full-wave bridge?
Oh well, never overlook the obvious!

 

[pieman]

My knowledge is limited. Would this work as described ie

input A either OV or (24V) DC
input B either 24V or (0V)

Output X 24V DC
Output Y 0V

Is this a suitable circuit
Diode bridge - Wikipedia, the free encyclopedia

Would I need specific diodes?
Would this do the job?
VISHAY FORMERLY INTERNATIONAL RECTIFIER|36MB10A|BRIDGE RECTIFIER, 35A 100V | Farnell United Kingdom
its 100V 35A? system needed would draw upto 600W

Many Thanks

 

[Nigel Goodwin]

A diode bridge is perfectly suitable - as long as there's no othe rcontact between the item been powered, and the original power supply (such as a connection to chassis).

600W at 24V is 25A, so a 35A 100V bridge should be fine - but will probably require bolting to a suitable heatsink to get it cool enough.

 

[pieman]

There is a mains supply producing 24v too which can be used when there is no helicopter power and is selected by a switch this has a ground cable to the box chasis. Also the 24-12 stepdown has a chassis ground as follows

110V-240V AC----->ACtoDC 24volt transformer(grounded) ---->power to camera + feed to 24VDC-12VDC stepdown transformer(grounded) for monitors and VTR etc.

or by switch

24V DC in from chopper -----> power to camera + feed to 24-12 stepdown transforner(grounded) for monitors and VTRetc

What are the issues with these ground connections and the bridge?

Many Thanks

 

[Nigel Goodwin]

You need to know if the ground is connected internally in the camera system, if so a FAR more complicated switch-mode solution with isolation transformer will be required.

 

[Leftyretro]

There is a mains supply producing 24v too which can be used when there is no helicopter power and is selected by a switch this has a ground cable to the box chasis. Also the 24-12 stepdown has a chassis ground as follows

110V-240V AC----->ACtoDC 24volt transformer(grounded) ---->power to camera + feed to 24VDC-12VDC stepdown transformer(grounded) for monitors and VTR etc.

or by switch

24V DC in from chopper -----> power to camera + feed to 24-12 stepdown transforner(grounded) for monitors and VTRetc

What are the issues with these ground connections and the bridge?

Many Thanks

One thing that is not clear: "feed to 24-12 stepdown transformer"
DC current can not go through a transformer, only AC. Is this a DC to DC voltage convertor or 12vdc voltage regulator instead?

Lefty

 

[pieman]

24volts DC is provided directly by the chopper or from a mains 110/240AC-24DC transformer. This 24volts DC is then split to the main camera system but also stepped down to 12volts DC to power some 12volt gear such an HD video recorder and an HD operators monitor.

regards

 

[pieman]

http://www.media.f2s.com/IMGS/psrect.jpg

Maybe the above badly drawn circuit will clarify things many thanks. I guess the best place for this rectifier (marked green) if it will work is between the helicopter power input and the switch (mains converted power/chopper power)

Still trying to find out if the camera is grounded to the chassis or not

Many Thanks

 

[ccurtis]

The problem is the power on different choppers is wired differently A+ or B+. I need to build a small circuit which will output 24volts A+ regardless as to which way round the 24volt input side is wired.

How do you cope with this problem at the present time? If you cope with it by just connecting the power leads in reverse, manually, the system you are powering is not grounded to the chassis.