dc motor control

[henjulfox]

Hello,

I'm trying to drive a 1/2 HP 90 VDC motor to test motor conversion output. I've hooked it directly to 12 and 24 volt battery banks which works well on the low range, but not enough power to get near the high range.

Any thoughts on the results of house current 110VAC to a light dimmer switch, then rectify to DC? This is only for short term testing so I'm not worried about efficiency or long term burn-out.

-Henry

[Opera House]

I don't think it would work UNLESS you also put a lamp load in front of the rectifier.  The notor back EMF would prevent proper triggering of the RC time delay control.  The lamp would insure that the load returned to zero between cycles.

[Nando]

1)Use a dimmer BUT place a full wave rectifier at the output and then use a large storage capacitor, you need at least 50,000 ( preferable 100,0000 microfarads at 250 volts, load this with the motor and as well, a resistive lamp of around 40 to 100 watts.

Ideally, you should have an isolation transformer ( 1 KW).

With a full wave rectifier you need to use the negative and the positive outputs to drive the motor and without transformer you need to make sure that there is not a connection of the motor body to a ground or a possible current should occur.

Nando

[Opera House]

Some small cap might be a nicety(10uF)to reduce some spikes, but you would get better control with pulsing.  SCR DC speed drives never use caps.  A large cap could dangerously overspeed the motor with 160 volts.

[drdongle]

I have done this but used caps of only a few hundered uF, worked fine.

[oztules]

If you are not after variable speed, just a full wave bridge (tiny noise suppression  capsif you want) will give your motor around it's 90Vdc

A lot of small american built floor scrubbers had just this style of system in them (240v ac driving a 180v dc motor straight through a bridge rectifier) in the 70's through to the late 90's...... never understood why they did dc brush motors when induction  ac would have been more reliable... they were mains powered machines..

If you want to control the speed in steps then different caps in series with the ac input will do it.

 Its  not nice, but very effective....

beware of earthed brushes. check isolation first, however it was probably designed with the above dc system im mind. ours were honeywell 180vdc 500W .

..............oztules

[Jerry]

Hi Henry.

I posted a story some time back on this subject. I use tredmill motors as a drive motor for motor conversion tests. I had looked at the Harbor Freight router speed control ($10 to #15?). I took the HF apart and part for part it was identical to my lite dimmer.

Next I took an old car amplifier heatsink and mounted the dimmer to it with some heatsink compound. I added an AC receptical at the end of the heatsink.

The output is fed to a fullwave bridge rectifier then the DC is off to the tredmill motor. Since the RPM on the tredmill motor is 6,000 tops, I used a small belt pully on it and a large belt pully on the motor conversion.

I also used my Lazer Tack to take rpm readings, Fluke true rms for voltage reading and an amp meter.

I tried the big caps but that didn't work well. Go without the big cap.

If you would like to use my complete setup just e-mail me or call or come buy the store. The hole things been setting on a shelf for a year now.

Heres a few pictures. I hope they're not to big? Please forgive if they are?

With the added heat sink this controller works very well. I had no heat problrems  at all.

                          JK TAS Jerry

[maker of toys]

at a guess:  DC motors lug down better without heating up too bad.  a 1 phase AC induction motor  can be lugged down too far, reengaging the start windings. . . . A dc motor will just lug until it can draw enough current for the torque demand.

-dan

[oztules]

I had the same guess Dan, but what pulled me undone,  was when is in the latter nineties they did indeed change over to induction motors, and the rest of the machines design didn't change, ....and the thing worked exactly the same......

............oztules

[henjulfox]

Jerry,

Long time no chat!

As I read it you did exactly what I was talking about. AC to dimmer to rectifier to motor and it works fine. Excellent. Looked like one leg of the dimmer output went to the rectifier, one directly to the motor. Or do both legs go to separate rectifiers? My drive motor at 1/2 HP is on the small size but has the big advantage of a generator tachometer attached to it. I just read the voltage (X 20) to get the RPM.

I almost have enough information to share to make it worthwhile to stop by the store for a visit. Been playing with ECM's. You are right - the 1/2 and 3/4 HP's are nice but the 1HP is where the real power is. I couldn't beat unmodified Jerry blades on the 1/2 HP but for the 1 HP I'm getting more power with 4 blades at 33 degrees pitch. Put 6" extensions on the Jerry blades last weekend and still doing better with the steep 4 blades though my testing site is next to a large tree that is leafing out and may be skewing my test.

-Henry

[Jerry]

Hi Henry.

Just wire the dectifier as though it was the lite. then send its DC output to the motor.

Is your 1 hp 4 blade 33 degree ECM with extension still with stock wire scheem or have you made some coil reasignment mods?

The mods worked best for me plus using higher speed blade formate. I would think with 4 blades,extensions and 33 degrees that thing would spin from a sneez at 50 ft LOL.

I'm at the store thursday. Come on by I'll show you the F&P and my extensions.

What kinda #s you gettin from the 1 hp ECM?

                        JK TAS Jerry

                         

[Nando]

Capacitance depends on the power to be supplied and possible the behavior of the motor itself.

The addition of the capacitor size cleans the overall performance and I base the capacitance value on the motor size and current plus motor stability.

You may have used a few hundred microfarads BUT you did not give any further information to really determine if your statement is practical and real for this case.

Just saying:

"I have done this but used caps of only a few hundered uF, worked fine.

Carpe Vigor, Dr.D"

IS NOT ENOUGH to really accept your statement

Nando