Hello DEL you said: wait for a while before you rush off and do it .

Probably a good idea. I would be the last one to shoot you down for offering my favorite type of solution cheap down and dirty.

I have concerns over this one however, possibly we need some collaborators on this. AC voltage is rated as equivalent to the heating value of DC voltage. The actual peak voltage for a 120 V AC circuit is 171 V, with the actual potential continuously varying.

I Have never actually built a AC to DC converter to power motor. I have however done the same thing on a smaller scale for control circuits. Besides the bridge rectifier, generally I use A voltage regulator, and a capacitor.

Most of the time I am converting 24 V AC to a lower DC voltage say 10 V. The drop in voltage is of course accomplished by the voltage regulator and the capacitor is primarily used to smooth out ripple.

The use of a bridge rectifier exclusively I believe to be problematic. The voltage would be continuously varying and peeking at over 170 V.

The components I use in the control circuits are extremely inexpensive, the posters required current capacity seems to be relatively modest so assuming voltage regulators are supplied at the necessary voltage they may not be too expensive. Capacitors are cheap so it may be possible to easily build a regulated unit.

If a voltage regulator is either too expensive or unavailable in that value a combination of resistance and capacitance should work, that is assuming the motor current is relatively constant. The right combination would of course require a little calculating, and probably some trial and error.

I'm not necessarily saying you're wrong, but I am assuming from what I know that there would be problems related to simply rectifying the AC voltage. So hopefully someone will post who has knowledge of the availability of regulators in that value and possibly their expense.

Yeh...
My gut feel is that the inductance would probably help smooth out the peak currents. Adding a big smoothing capacitor will increase the mean voltage and thus probably the mean current.

Note extensive use of 'probably'
It will be interesting to hear how it works, it will be safe enough as long as a little caution is used.

There maybe weird load/speed/frequency synchronisation effects?....whatever you do don't drop below 50mph ....BOOM... oh no, that was just a movie . Maybe Sandra Bullock can help me with my experiments?

Del

Del

Well Dell: my cat is extremely upset with me for questioning you, so to satisfy her I will have to say it looks like my concerns were unjustified.

One way or the other it looks like I'm going to have to go get a bridge rectifier. As I said I've never tried to do this before. For the life of me I cannot figure out where the 105 V is coming from.

Even if I consider the 120 V AC as a constant there should only be a 1.2 V drop through the rectifier, (I believe there's a .6 V drop on each side of the bridge).

Generally I'm working with relatively high amperage AC circuits. So except for the occasional control panel I have to work with or designed, I don't do much with the smaller component level stuff anymore.

So until I get my rectifier and set up my little experiment if anybody wants to enlighten me where the 105 V DC value is coming from, it looks like I need a little education.

Okay pounce see I told the other cat he was right stop meowing.

Take the average voltage of a rectified sine wave. (It looks like camel humps).

sqrt(2) (Vac) (integ sin(x)dx from[0-pi] )/pi = .9 (Vac)

.9 (120) = 108

Now subtract a couple diode drops, and at the currents you will be drawing it will be 1 to 1.5 volts per diode ....Ie 108-2 = 106 volts.

However there will be some additional distortion from the current wave form and you will get marginally less.

Adding caps changes the wave form and if it is sufficient you get smaller camel humps because the cap holds up the voltage.

The following is a bunch of "loose" rules of thumb, but they will definitely get you into the ball park.

Example:

motor current 1 amp, desired ripple is 10 volts. Caps supports wave form approx for 1/240 of sec (crest to when next diode conducts). I amps is assumed almost constant due to motor inductance.

I = c dv/dt

1 = c 10/(1/240)

c= 416 uF

Now recalculate Average voltage with changed waveform. You will need to do a piece wise integration from crossing to peak, then on the discharge of the cap.

Hope you get the idea.

And if you get low DC filtered Volts out of Bridge:

Then Boost 110VAC to anything upto150VAC using a 2AMP Variac .

Be careful :Brush to Common=110VAC .Common to HI terminal=110>150VAC by gradual boosting!

After the full wave rectifier, just add an electrolytic cap of 250 volts working or better (experiment with the value, start with around 5 MFD) is placed across the output (watch polarity!!) to smooth the "lumpy" DC, the voltage will probably be up around 150-170 volts!!

You may need to add a choke in series with the motor to drop the voltage down a little to the values required.....

Experiment!!

Make sure the bridge rectifier has a high rating. For a 1A FLC motor, a 5A or 10A bridge rectifier should suffice; the 10A for preference.

Safe diode selection:

I max = 10 A for diodes are the ones that could survive the motor inrush (starting) current.

V nom >= 2*1.42 * 120 V = 340 V

Hello Guest,

As Del the cat has suggested, the easiest way is to use a bridge diode, and you will find explanation plus basic circuit here.

The Diode assembly would need to have a PIV (Peak Inverse Voltage) of 600 Volts, because you are using it with an Inductive load = a motor.

You don't advise your location, so it is difficult to give you a local supplier for such an item.

Have a look here:

25 A 600 PIV BRIDGE RECTIFIER 25 AMP BRIDGE. 600 P.I.V. 1 1/8" square. Read more CAT# FWB-256

$3.50 each

The reason for using a much larger Amperage and Voltage Bridge Rectifier unit, is so that you then should not require a heatsink, and the starting current of the motor will also not overload the Rectifier unit.

As you can see, these are very cheap, but do require soldering ability, along with a measure of understanding of electronics.

If you need further help, reply here with

Kind Regards....

Hello Sparkstation:

I need to post faster, since we were both posting at about the same time you could've answered my concerns in your post. Since you are now the third collaborator do you think a voltage regulator and capacitor should be added to the circuit? If you think that would be a good idea, have you got any idea as to the expense. The regulators I generally use are probably about two bucks.

For those of you on the bottom side of the world that is two US dollars. I just had to get the first tongue and cheek remark in.

PS.Please reply quickly,Save me a trip to RadioShack for some diodes,The only part I am missingTo collect some empirical data.

A diode,A diode,My kingdom for a diode.

Hello YWROADRUNNER

Thank you for your speedy response, as our Posts crossed.

As you say, a Voltage regulator and capacitor could be added to the circuit.

My concern is that the Topic Poster perhaps has only a very basic knowledge, and each additional added part makes the circuit more complicated.

The capacitor would be in circuit, to maintain the output of the bridge rectifier/regulator more towards the Peak value of DC.

The Regulator would require to handle the "Back EMF" from the motor during operation, and also the motor starting current, plus running current.

All in all, that's why I suggested the 25Amp 600PIV Diode Bridge, which although not ideal, because the Topic Poster's budget is minimal, costs the least to do the job.

Without further information regarding the soldering and other abilities of the Topic Poster, to have the absolute minimum to do the job, is IMHO, best.

Kind Regards from far away....

Del has it. If he puts a bridge rectifier on 120 VAC, he'll wind up with about 105 VDC. The motor will run a little slow, but the OP probably doesn't care.

Mr. Crews,

As others have posted you ought to be ok with a bridge on this motor. You won't have speed control this way but it should turn and not burn.

When you say "no budget"...do you really mean absolutely no budget? I have the little fractional hp Bodine gearmotors on several machines in my plant and run them with cheap little Minarik drives. Typically around US$100-$150 or so plus a cheap 5k pot and you have better control than the no control a bridge is going to give you.

If you just need a single speed run and want to go with the bridge, respond back here and when I go in Monday morn I'll pull one of my Bodine motors out of the bin and stick a bridge to it for an hour or two. Shouldn't be any problem but I'm always game to see how much smoke they can stuff inside things.

Hi,

Go to the local hardware store and purchase a 5 dollar lamp dimmer which is ususally a controlled rectifier which will put out DC at voltages from close to zero and up to the 130 VDC for your motor. It will make the motor a variable speed unit. If you want, go to WW Grainger and purchase a simple motor speed controller which is essentially the same as a lamp dimmer.

george

I've done that before, but many dimmers use a triac, so you need to stuff that through your diode bridge. A scope will identify the output very quickly.

For a commercial motor control you don't use any additional caps on the output, you let the motor have the ripple. The inductance of the motor smooths the current significantly. You will get about 105 DC volts average from the 120AC. (More detailed and you may loose a few more volts from the diode bridge).

Wouldn't you need a 1:2 transformer between the 110VAC and the Rectifier?

For a number of years I built machine controls that included a Bodine motors that was very similar to the unit described by the original query. We used a KB Electronics speed controller which included two bridge rectifiers much like DEL described. See www.kbelectronics.com for a wealth of details. The Bodine motors were ordered with the field coil wires and brush wires brought out seperately. The incoming 120V AC was rectified and one rectifier fed the field coils while the other circuit included a PWM to adjust the speed. Both bridge rectifiers. the controls also included a reversal switch plus a dynamic brake resistor.

Bodine is a top supplier.

It may be cheaper and more practical to sub out the DC motor for a same frame # 120v AC motor.

Your original post did not indicate a need for speed variation but if required, a plug in variable speed AC control is avilable...lower speeds will reduce torq but since is a gear drive it may be over engineeredto a motor HP that is "off the shelf" for Bodine. Depends on your real load.

Of course if this a learning project my sugestion may not be applicable.

MR. GUY

No, DC motor produces relatively fixed torque per amp. Lower terminal volts will produce lower speed and power, but torque will remain the same for the same amps.

Jeff, you don't say if there is a Field winding or permanent magnets, use a full wave bridge rectifier rated 200 volts 6 amps from radio shack, you could have second rectifier on the field winding, then put a light dimmer on the ac line feeding the F.W B. going to the armature/brushes leads and have variable speed drive

I think this is the one.

From

http://www.bodine-electric.com/Asp/ProductModel.asp?Context=13&Name=33A-W%20Series%20Parallel%20Shaft%20DC%20Gearmotor&Model=6152&Sort=11221

It looks like a permanent field magnet.

Wow...

My students did this using 600V 8 A diodes without any filters.

Somebody listed less than 4 USD bridge, #17 sent ironical note.

120 Vac in USA could be 100 to 125 V 60 Hz so for safety reason be ready for a small "ohmage", 1 A resistor at front of the rectifier. Can be done with a Fe wire. Install also > 1 A fuse, better CB (circuit breaker). This is a concept, test your prototype adjust values so you will learn using hands-on experience. Final product should looks professionally to give you 100% satisfaction.

I'm stuck on this. Does anybody know whether a reducing gearhead would look more like a capacitor or like an inductor?

Work load, real power, resistance. Neglecting backlash and torsional resilience.

no way you can do this ,without killing yourself. the dead.

i have a question for any of you.

i'm planning on buying an amatek 3300 for wind generator it has 130 vdc output and 25 amps i own an inverter charger that has an input of 110 vac , it has an output of 13.9vdc to charge the bateries(floating point which means , when batteries are charged it stop charging but keeps a refresh charging pulse for a short time at difrent intervals of time to avoid discharging) if the 110 vac are missing the inverter enters inmediatly (you dont notice the change when the power from the grid is gone because the inverter comes in so fast) now the question, how can i make the 130 vdc from the ametek to go into the 110vac input of my inverter?.

i'll get my ametek as soon as i solve this question.

thanks , manny

I just tried this today with a 130v DC, rated at .5A, motor just using a bridge rectifier. It is rated at 25 amps and does not get hot. The "smoothness" is not critical since it is going to be used a drive motor for a rotisseree in a smoker grill.

Low budget, that's the way I like it...

BP

Georgia Pacific Electrician

Bravo

This is the way - experiments...tests.

Hello everyone,

I just bought a bodine 4535 42A5FEPM-5N Right angle DC gear motor off ebay.

Specs:

130 VDC

1.8A

250 RPM

42 LB-in

10:1 ratio

Duty CONT

My problem is i only have 7 days to return it if it is defective, but i dont have any means of testing it right now.Money is tight this month so it will be awhile till i can get a KBWS-15.Taking the advice of some of the members here, I went to my local electronics stores, and nobody carries any bridge rectifiers that are 25A/600V.The best i could find was 6A/200V, 4A/400V or 25A/50V.My question is since i dont have time to order from mouser, or digikey, Would it be possible to use multiple bridge rectifiers to get the same effect as the larger rectifiers? And if so what would be the best way to do this?

Jeff! It's funny b/c now I need the SAME information.. haaa. I have the exact motor you have (130 vdc at 1 amp) and want to convert to use for a mini ferris wheel for the holidays. (yeah, I know it's stupid ). My question to you, if you are still on the forum, is 'did you get yours working and if so what did you end up doing?' I am thinking about the bridge rectifier (only found a 400v at 25amp) a POV cap to shorten the 'humps' during phasing and a voltage regulator (still can't find a 130 vdc regulator). Please, let me know what you did. Thanks!

Todd in NC