12VDC to 24VAC...Picaxe?

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212

Senior Member
Hello, I finally got a deal on a pan/tilt unit for my RF remote camera set-up. It said heavy duty, and yep, it is. The thing is about 14 inches tall and weighs 23 lbs! OK...so it might be a little over rated, but I have it now. It uses 24VAC for power, which comes from a 120VAC mains powered control box. I want to put the unit out in the woods, and mains power is not available. I know I could use an inverter to get 120V, then plug the control box into that, but I have Picaxe :) I'm sure some of you very smart, talented, and very helpful people would be glad to help a dumb old country boy with this...right????
 
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moxhamj

New Member
I think this might not be best done with a picaxe. Sure, you can do it and you can generate a 50 or 60Hz square wave and some big transformers etc, but a 555 can generate a square wave cheaper than a picaxe, and the waveform generator is only a tiny part of the circuit anyway.

This would have been a difficult problem to solve years ago, but the wonders of mass production mean that DC to mains converters are exceptionally good value. It seems wasteful, but stepping 12V up to 120 or 240V, then a transformer back to 24VAC is going to be the cheapest.

But what the picaxe can do is turn this circuit on and off with a relay. So you might get a message to pan or tilt, the picaxe turns on a big 12V relay, powers up the inverter, waits a second or so, then does the panning and tilting.

An old car battery would be a start for a 12V supply. Maybe solar powered? And the solar charging is going to need picaxe control, right?

So the picaxe is going to still have lots of work to do...
 
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212

Senior Member
Thanks for the reply Doc, but come on, can't we figure it out somehow??? I have lots of junk around to scrounge parts off of. I actually HAD an inverter, but measured the output voltage with the meter set to amps...doh! You should have seen how much smoke they had put in the box when they made it, and it all came out...

There will be several Picaxes in the thing when all is done. I want to, eventually, have the camera automatically turn to and zoom into remote sensors too...I just need power :)
 
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kevrus

New Member
You could use two 12v batts in series to give you 24v, and then a 555 as Dr_acula suggested to generate the ac. No issues then with stepping up the voltage.
If you don't need a perfect sine wave and can manage with a square wave then the circuit shouldn't be too difficult...there is also reset pin on the 555 which if held low will stop the timer output so this could be controlled from your picaxe
 
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westaust55

Moderator
I am of the same opinion as Dr Acula. Would only be considering a PICAXE or similar if variable frequency was required.

Have a look at this:
http://www.powerstream.com/inv-12dc-24vac.htm

Might also be worth making enquiries whether you can operate from 24 Vdc (ie two 12 Vdc batteries in series) as opposed to 24 Vac.
 
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leftyretro

New Member
westaust55 said:
I am of the same opinion as Dr Acula. Would only be considering a PICAXE or similar if variable frequency was required.

Have a look at this:
http://www.powerstream.com/inv-12dc-24vac.htm

Might also be work making enquiries whether you can operate from 24 Vdc (ie two 12 Vdcbatteries in series) as opposed to 24Vac.
Click to expand...

That looks to be a very useful and efficient power converter. Also a 24vac output could feed any common 120vac/24vac transformer wired backwards if one needed 120vac output. And the wattage output is high enough to be very useful for many applications. I wonder if the final pricing would be hobbyist friendly. ;)

Lefty
 
hippy

hippy

Technical Support
Staff member
First thing is to find out what the unit actually needs. It says 24VAC but I bet it doesn't run on AC internally. Reverse engineer the power supply circuit, find out what it delivers to the rest of the unit.

Often the labelling matches whatever plug-in PSU they are shipping rather than anything else. I've seen product labelled 15VAC which use a blocking diode and a 7805 which can work with 9VDC wall warts.

There are probably few low-voltage items labelled VAC which don't have a blocking diode or bridge rectifier immediately after the PSU socket and they can all be used with DC, with the great advantage it doesn't matter which way round +V/0V is connected. In this case you may be able to just connect a 12V car battery or two to get 24V. I'm sure a good part of it is in coercing people who don't know better to buy the manufacturer's recommended PSU.

An important thing not mentioned is the current drawn.
 
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Shack

Member
hippy said:
First thing is to find out what the unit actually needs. It says 24VAC but I bet it doesn't run on AC internally. Reverse engineer the power supply circuit, find out what it delivers to the rest of the unit.

Often the labelling matches whatever plug-in PSU they are shipping rather than anything else. I've seen product labelled 15VAC which use a blocking diode and a 7805 which can work with 9VDC wall warts.

There are probably few low-voltage items labelled VAC which don't have a blocking diode or bridge rectifier immediately after the PSU socket and they can all be used with DC, with the great advantage it doesn't matter which way round +V/0V is connected. In this case you may be able to just connect a 12V car battery or two to get 24V. I'm sure a good part of it is in coercing people who don't know better to buy the manufacturer's recommended PSU.

An important thing not mentioned is the current drawn.
Click to expand...
I agree with Hippy and I will be surprised if the unit does not run on 12v DC internally.

An easy test is to plug a 24v DC source into the same plug and see if the unit works. It will not damages the unit. Then try 12V. Or, you may need to open it up to see if there is a transformer and a bridge inside.

I also agree that you will probably find the battery life to be quite short. Overall, not too practical of an idea.
 
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papaof2

Senior Member
Is noise a factor?

212 said:
Thanks for the reply Doc, but come on, can't we figure it out somehow??? I have lots of junk around to scrounge parts off of. I actually HAD an inverter, but measured the output voltage with the meter set to amps...doh! You should have seen how much smoke they had put in the box when they made it, and it all came out...

There will be several Picaxes in the thing when all is done. I want to, eventually, have the camera automatically turn to and zoom into remote sensors too...I just need power :)
Click to expand...
Remember that any inverter will generate noise, both acoustical and electrical. I've been using DC->mains AC inverters since the days of synchronous vibrators generating 60Hz squarewave power. (One even had space in the case for a 12 volt car battery and included a charger - the current generation of small "power pack" units for jump starting car engines just have newer and smaller components.)

Will the acoustic noise be a problem where you are using the pan/tilt mechanism? Both the pan/tilt motors and the DC->AC inverter for it will make some noise. Will the noise be such that it scares the local wildlife away?

The electrical noise will have to be filtered to keep it away from the electronics.

I agree that determining the actual power needed by the pan/tilt mechanism will show the optimum way of powering it. If it runs directly from 12 or 24 volts DC, then an SLA/AGM battery and a small solar panel may provide long-term unattended operation.

Powering any device away from mains power is best done as efficiently as possible. Althpough I have an AC inverter for the car, I use a 12 volt->18 volt DC->DC unit to power the laptop when using it in the car - less acoustic noise, less current drain on the car battery.

Remember to protect your remotely located electronics from beasts and insects. Ants like certain kinds of electronics (they destroyed the outside temperture/humidity sensor of a wireless thermometer). Other insects nest in any sheltered place they can find. A pan/tilt mechanism that is in the open could become a riding toy for the squirrels.

John
 
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212

Senior Member
It's definitely powered by AC. Inside the control unit there is nothing besides a transformer and the four way switch. In the pan/tilt unit there are a couple of caps, but no diodes or anything to change the AC to DC. I did not look at the tilt motor, but it does use a little more than power than the pan motor on my meter. The controller does not swap wires to change direction, it just has a common and four others going to the unit. The little pan motor seems to have two separate sets of windings, one for each direction, and the tag says 24VAC 30 watt. It will be very easy to work with an RF remote.

Yes, noise is an issue, but I'll have the electronics inside an enclosure and that will help. I can't even hear the unit pan, but it does make a little noise when it tilts.
 

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jpyle1

New Member
24 volt

I have several security cameras that use 24 vAC, or 12 vDC. They have a well marked tri-pinned jumper inside the case to make the voltage selection. You might want to have a look inside , as many devices I have seen use this same ploy.
John
 
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212

Senior Member
We posted about the same time.. Nope, no jumpers in there to change, not much besides the motors and limit switches. I sure wish it was that easy though. Just for kicks I did try 24VDC...nothing :(
 
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westaust55

Moderator
As the motors are seemingly AC, two two cables are likely as:
1. Main winding, and
2. start winding - needs a second winding usually with a capacitor to get a phase shift for a magnetic field shift to start the rotor turning.
 
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Dippy

Moderator
Surely if the little motor 'sticky' says 24V AC then thats that? And you will need an inverter like WA's link.
Maybe kits or circuit diags are available for home-made?
 
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westaust55

Moderator
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papaof2

Senior Member
Also check your local auto parts stores. I picked up a 120 watt 12 volt DC -> 120 volt AC inverter for $5US after rebate last fall. These are probably not the ultimate in efficiency or waveform, but would be OK for driving the very small motors in the pan/tilt unit in intermittent service.

John
 
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212

Senior Member
I'm watching a few used inverters on....that bay site Dippy hates...

But...now what would keep me from using a different transformer in one, to give me 24V instead of 120V?? I need to read more about the Oatley Electronics offerings. Thanks for the links!
 
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boriz

Senior Member
Do you really need to go to all that trouble? Two RC hobby servos and a hot-melt glue gun works for me. A 6v SLA battery will last a long time and be perfect for solar charging.

Unless you have a big heavy camera...
 
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212

Senior Member
Big heavy camera is putting it lightly :D I have some board cameras, even a decent day/night camera, but my Sony camcorder blows them away in picture quality. It also has the time/date display, and a good zoom. I have the camcorder, an A/V transmitter, IR led array, camera controller, and lots of batteries in the case. All that must weigh around 15~20 pounds or more, and the Otterbox case itself ain't light. Now I'm gonna need an inverter in there too. One good thing is, it's anti-theft...who is gonna carry all that out of the woods.
 
hippy

hippy

Technical Support
Staff member
who is gonna carry all that out of the woods.

I'd be tempted. If you can carry it in, someone can carry it out. The camcorders I have weigh 5 pounds without batteries, with spare SLA's, tapes, sandwiches, bottles of water, probably all-in at 10 pounds. I'd upgrade to digital but full-size shoulder mount ENG-style gets you places members of the public often cannot :)
 
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212

Senior Member
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jpyle1

New Member
24vac/12vdc

Just for the curious about the dual vlotage, the picts show what kind of seperate power suply board there have. 8 were hit in a lightning strike. I revived 5 by just switching the jumpers to DC. Got to be half wave off of the 24vAC. Cameras made California, Im in Oklahoma,US

John
 

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westaust55

Moderator
jpyle said:
Just for the curious about the dual vlotage, the picts show what kind of seperate power suply board there have. 8 were hit in a lightning strike. I revived 5 by just switching the jumpers to DC. Got to be half wave off of the 24vAC. Cameras made California, Im in Oklahoma,US

John
Click to expand...
From the photo there are 4 diodes D1, D2, D4 and D5 plus Z1 ispossibly a Zener. So may well be full wave rectifier - but hard to tell without view of the track side of the board as well.

Lightning would have taken out at least 2 diodes if was full wave rectifier.
 
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