AC to DC

Ken, use an AC transformer / controller to give you the variable voltage, then, on the output, use a bridge rectifier, available for Tandy and other electronic suppliers, ensure it has the current carrying capacity you need, and place an electrolytic capacitor, 1000uf across the DC output, ensuring correct +- polarity as marked on the device, and there you have it.

Here's a link to a wiki. http://en.wikipedia.org/wiki/Diode_bridge

What is the DC voltage for?

 

Dale H

Walthers Cornerstone oil pump #933-2705.  I want to feed it off of my 14v acc. power & convert it to 6 to 8 vdc.

 

Ken

Use the bridge rectifier described in this post

 

https://ogrforum.com/d...nt/15086404583225747

 

To reduce voltage after the bridge rectifier in series from the + circuit to the pump string together some 1n4001 diodes in proper polarity. Each diode in series will drop voltage by .6 volts.  Since it is a DC dropper only 1 string is needed. Dropping voltage with diodes is described here.

 

www.jcstudiosinc.com/BlogShowT...=413&categoryId=

 

Dale H

I understand the rectifier.   Does each diode drop the voltage .6 volts? Is there a variable type device that can be used to adjust the voltage down?

 

Thank You

Ken

Mount the string of diodes on a euro style barrier strip. Each . 6 volt increment drop will have a screw terminal where a wire can be inserted. You could tap multiple accessories off the string if larger 3 or 6 amp diodes are used.A string of 10 diodes would provide up to a 6 volt drop.

 

You could use an adjustable wire wound resistor but you would be guessing at the value.

 

You could use an adjustable LM317 voltage regulating circuit also with a pot in the adjusting circuit. This is more work than the above 2 solutions.

 

You could just put a single diode in series to the pump. With 14 volts AC in, the output would be half waved pulsed DC equivalent to about 7 RMS volts. Not sure how smooth it would run on this. Some PW type vibrator type accessories work better on this than AC. Each additional diode would drop .6 volts more.

 

In the middle of the board you will see a diode dropper using 6 amp diodes mounted on a barrier strip. In this application in activates the whistle or bell. The bridge rectifiers are used as droppers to provide a complete throttle for an automated layout. Click to enlarge.

 

Dale H

Search eBay for "LM317 converter" and there's one for $5.99 w/ free shipping from Asia so it may take a couple weeks.  It takes AC (or DC) as input and puts out adjustable regulated DC so you can fine-tune your DC pump voltage to 6V, 8V  or whatever.  The screw-terminal connectors should make hookup fairly simple.

 

Stan

 

that is a pretty good unit for the money,that will work also if the pump draws less than 1 amp. cant really build it yourself cheaper.

 

Dale H

Ken;

Not to detract from the good information so far, but here is another idea for you.

I have this same oil pump and love it, but I found it runs way too fast even at 6-8 VDC.

You may already have a surplus low voltage DC wallwart on hand, or another source of low voltage DC.

I installed a potentiometer in series in the power to the pump and turned it down so as to get a nice slow realistic speed. Works just great.

You can likely find a suitable pot at Radio Shack or any electronics jobber.

I think I used a 500 ohm, but almost any value in that range would work.

The current draw as I recall is around 200 ma. Very low.

Hope that helps,

Rod

Ken, as Rod suggested, if the supply rate needed is low amp, the use of one of those adjustable voltage wall plug transformers would probably suit you fine for that...mind you "adjustable" would be defined as "set outputs". I'm holding in my hand one of these...is a "PowerLine 1000mA{1 amp hour rate as I recall} universal AC adaptor for 3-12v DC and has a slide voltage selector knob which yields outputs of these set voltages...3v, 4.9v, 6v, 7.5v, 9v and 12v". This particular wall plug has different end plugs as well...think I swiped this from the wife's porcelain coke village power supply collection.

Just a thought..

NightFire Electronics has an adj power supply kit

for $7.99. Input is 3-18vac output is adjustable

and regulated from 3-15vdc. Kit number NF-1725

www.vakits.com

 

Thank you for all of your ideas.  I ordered the Asia Engineer module.  Hope it doesn't take to long to get here.

 

Thank You

Ken

I got a couple of those in about two weeks.  They are coming from China, so it does take some time.

I have 4 of these oil pumps. Wired them to a CW 80 transformer (accessories) and all they would do is "hum", I tried all at one time and each one, same result "hum"

 

I'm not sure if they were used or not, I bought them at my LHS at what I thought was a good price ( looking at the price on the box) but checked Ebay a few minutes ago and my LHS must still be laughing.

 

I tried to take the motor off (instructions indicated 4 screws I can see only 3) to grease but can't get it off.

 

Any help would be appreciated. The oil rig must me OLD because Walters doesn't list the item 933-2705.

 

Brent 

Per the OP's original request, he wanted a method to convert AC to DC since the typical transformer's accessory output is AC while the oil-pump motor apparently requires DC.

The more questions I ask ,the more I learn.  I assumed all accessories would work on a transformer. I did read on the oil pump that it was DC. I read a little about the CW 80 and found out all accessories are not run the same. Nuf said.

 

I have a MRC TECH II Railpower 1400  (I have a couple of HO trains in a box). I hooked the oil pump to the DC terminal ((output 14 VDC 18 VAC) and they worked.

 

Next question!! Is connection to 14 VDC, OK.  Before I ruin everything.

 

Thanks

 

Brent

I would lower the voltage until the unit just works reliably. From the 14 VDC I would add a string of diodes. A single diode from the 18 VAC would yield about 9 volts RMS pulsed DC. The pump may run on that,I do not have a unit to try..

 

Dale H

If the MRC DC output is fixed I agree with Dale, or if you are using the adjustable DC out you can control the DC voltage with the throttle handle.  G

Regarding the Asia Engineer converter, formerly known as LM 317 converter, I obtained a couple of these.  Mine are identical to the photo depicted in previous posts with one exception:  the input does not indicate AC and DC as in the photo.  It just says "In."  Am I to assume that the "In" means that I can still install both AC and DC?  Also which of the screws adjust the voltage--the tiny one on the blue electronic part or the larger screw on what appears to be the heat sink?

Yes, a full wave rectifier will convert AC to DC, and also pass either polarity of DC.  That's why they didn't feel the need to indicate polarity or power type, it'll take most anything.

 

The slotted screw on the blue part adjusts the voltage.  The other screw fastens the electronic component to the black heatsink.  And to my knowledge every blue adjustment control on these modules has a "slip" mechanism so when you reach the end-of-travel CW or CCW it does not hit a hard mechanical-stop but rather lets you continue turning in each direction but with no electrical effect.

 

Perhaps providing too-much-information but what I always found interesting about a bridge rectifier (as used on this module) is the DC input can be applied in either polarity to the input.  Yet, on the output side the +DC always comes out of the +output and the -DC always comes out of the -output!

You do know why Stan right?  G

I turned the slotted screw on the Asia Engineer converter that controls output voltage while it was connected to the transformer supplying input power. It did not change the illumination from the LEDs to which the converter was connected.  Is the voltage regulator on the converter only effective for DC input power?  Or are my units defective?

You have to turn it, and turn it, and turn it some more. It takes many turns to change the voltage output.

I think I've discovered the problem through experimentation.  Originally, I hooked the converter to a variable voltage post and set a voltage from the transformer, trying to adjust it up and down with the slotted screw of the converter.  I then tried hooking it up to the accessory posts of the transformer that are fixed voltage, and when I turned the slotted screw, it worked. 

It should work with a variable or a fixed input voltage.

Dave

that's a good schematic, Ive done both, purchased rectifiers and made my own.

great way to be able to run DC trains on my post war AC ZWs.