trying to convert dc power


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Old 12-06-03, 10:07 AM
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trying to convert dc power

Hello!

I have a question that applies to DC power, and trying to step it up.

I am working on an insulation blower. The engine on it is set up for starting and charging with 12 volts. There is an electric clutch on the insulation blower that uses 12 volts. There is a humidity sprayer that uses a 24 volt DC solenoid to energize it. I need to get 24 volts to that solenoid somehow. AC power is not available. I can use 2 batteries, but I need them both to be able to charge from the 12 volt alternator on the engine. So, I am thinking I can either parallel the batteries or isolate them, as long as both get the 12 volt charge from the engine, but I need a series connection to get my 24 volts DC. I figure diodes will be needed to do this, but I can't seem to figure out what I need to do. Anyone have any ideas?
 
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Old 12-06-03, 11:09 AM
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Run two circuits, one in parallel for the 12 volts, the other in series for the 24 volt leg.
 
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Old 12-06-03, 11:23 AM
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Will that allow proper charging, since they will be connected both ways? There won't be backfeed through the series connection?
 
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Old 12-06-03, 12:33 PM
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I'd like to know how you would hook 2 batteries in series and parallel at the same time. I would be better if you could change the 24v relay to a 12 volt relay. Perhaps a starter solenoid would work. It could certainly handle the current.
 
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Old 12-06-03, 01:25 PM
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It is a flow solenoid. It actuates a valve that turns on water. No starter solenoid will work. I wish it were that simple .
 
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Old 12-06-03, 02:45 PM
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This is DC so you dont have to worry about reactance in the coil. In other words the coil will have a fixed resistance and by running it on a lower voltage you wont burn it up. So why not see if itll work on 12v anyway.
 
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Old 12-06-03, 07:55 PM
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Re: trying to convert dc power

Cheese - There's a bunch of ways to do this but none to easy. I suggest a purpose built device. Do a Google search for "Zane voltage doubler". OR "zaneinc.com" for the manufacturor.
 
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Old 12-06-03, 11:15 PM
grignon
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Most manufacturers of solenoid actuated valves offer their product with a variety of coil voltages-AC and DC. Get the manufacturers name off the device and look them up. a replacement coil shouldn't run more than a few bucks.
 
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Old 12-06-03, 11:26 PM
grignon
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Most manufacturers of solenoid actuated valves offer their product with a variety of coil voltages-AC and DC. Get the manufacturers name off the device and look them up. a replacement coil shouldn't run more than a few bucks.
 
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Old 12-07-03, 12:08 AM
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I think I may have figured out a cheap and easy way to do this. I have a power inverter...12 volt to 120AC. I also have a 120AC to 25 volt DC transformer. Any reason I shouldn't use the combination of these to make the 24V needed?
 
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Old 12-07-03, 08:12 AM
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A DC to DC converter will work best. Your power inverter idea will also work, but youll need a full bridge rectifier and a filter after the transformer most likely to clean up your AC enough for the coil to work.
 
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Old 12-07-03, 10:16 PM
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The owner of the unit was ready for it before I was able to read your reply Trinitro. I used the 12vdc to 120vac inverter, and the plug-in 120vac to 25vdc transformer. It ran the unit just fine. What kind of filter would you have suggested? Since it is working, is there still a need to install the filter? Would the solenoid coil overheat or burn up without it?

The owner of the insulation blower has a job lined up for monday, and needed it today (sunday) so he could send his crew out with it. I connected everything and tested the voltages with a DVOM, and it all looked good and when connected, it worked. It needs to be reliable though, so if you have any idea that this might cause problems, please let me know. Thank you!
 
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Old 12-08-03, 06:49 AM
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I was late with my reply...since it is now already Monday.
If your transformer will output 25 Vdc there is no need for the filter (for your application, the coil is not a particulary demanding piece of equipment). I strongly suspect you do have a AC to DC transformer unit, or your coil would not have worked very well. AC will constantly oscilate, which will make your coil oscilate also. That's why coils need DC. At the same time all coils have an "on" voltage and a "off" voltage. A coil may say it needs 24V to operate, but it will probably need 24V to turn on, but as long as the supply is at least, let's say 20V it will still stay on. In another words, as long as the voltage you apply ranges between 20V and 24 volts your coild would turn on and stay on. That's why a very smooth output (from the power supply, in this case the transformer) is not required.

A filter will basicallly take the 25V AC supplied by a transformer and "convert it" to DC. Usually it starts with a across the line film capacitor, followed by a full bridge rectifier, and then by a LC filter usually (an inductor and 1 or more capacitors, usually electrolytics). It's the capacitors that really do the filtering, the inductor is there mainly to buffer and protect the capacitors. A filter will always decrease the AC value (24 Vac may only end up being 20 Vdc), so generally a 24 Vdc power supply will have a 30 or higher Vac transformer.
 
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Old 12-08-03, 11:03 AM
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Ok, now I see where you're coming from ...I guess you didn't see that the transformer is in fact AC to DC. The 24 volts is DC, to the coil. So a rectifier & filters shouldn't be needed. Thank you for your help, and thanks to all who replied!
 
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Old 12-08-03, 04:49 PM
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Hmmm – The inexpensive power inverters I’m familiar with do not provide a sinusoidal output voltage. Rather they output negative and positive square waves, or the “modified sine-wave” type output a +/- staircase voltage. Either way the output includes harmonics of the fundamental frequency of 60hz. There would be no concern of damage to the solenoid as the step-down transformer and rectifier isolate it. The step-down transformer, depending on its design may be adversely affected. The harmonics may increase the eddy currents in the transformer’s core generating additional heating. If you did not hear a buzzing sound from the transformer, you’re probably OK.
 
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Old 12-08-03, 09:53 PM
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No, I didn't hear the transformer buzzing. The solenoid coil buzzed a tiny bit, but I assumed that to be normal.
 
 

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