L297 for unipolar?

[pminmo]

Actually I believe the point he is making is the L298 when used in conjunction with the L297 typically implements current limiting as the L297 has the comparitor and logic for chopped current limiting. If you are driving it from some other logic, you would either have to implement it in another way, or not have current limiting. You could drive a L298 via a parallel port just as a H bridge. You could also implement a L298 with a micro that has an analog comparitor and use that as part of a solution.

[Mcgyver]

Since I threw up some pics here before, thought it would be a good place for an update. hobbies are moving at a snails pace these days (work work work) but I have completed the boards. A transformer has been acquired, secondaries removed and magnet wire is in the trunk of my car.

Phil, with the HV 297-8 boards what voltage on the transformer should i try for and is it an rms or peak voltage - ie what should my multimeter show when set to read AC?

oh yeah, one more... I understand its a good idea that the large capacitor have a resistor across it so that it slowly discharges after the unit is turned off - I'm guessing it has to be high resisitance and high wattage - any suggestions on what to use? thanks

EDIT: Phil, I found the PS on your site! why is the R1 so low?? as the ohms approach zero, isn't it a short? I would have though it need to be a high value, so I'm obviously not understanding this

[pminmo]

Mcgyver,
Your boards look great! At 470 ohms, R1 still takes 5 or 6 seconds to drain a big cap at 32 volts. R1 is a bleed off resistor, you don't actually have to have one. If you don't have one, and have a big filter cap it will take 20 or 30 seconds to actually bleed the voltage to zero if there is no load. True, you don't want to low of value for r1, but at 32V 470ohms is only 68ma.
Transformers are typically rated at rms value. If you get a 24V transformer that means it should provide 24Vrms at the rated load. When you convert it to DC via a Full wave bridge, multiply the transformer value times 1.414 and subtract 1.4 (assuming a filter capacitor) for the DC value. 24 * 1.414 - 1.4 = 32.5V These values are approximate as transformers outputs vary depending on load, and the 1.4V diode drop will vary depending on recifier and load.

[eidos]

Originally Posted by aduri Without the L297 and sense resistance you hav'nt the current control. The stepper motor works in current not in voltage. Escuse me for my bad english

stepper motor works in current ??
HAaaaarggg !!!
OHMS law is changed ?

[pminmo]

aduri Without the L297 and sense resistance you hav'nt the current control. The stepper motor works in current not in voltage. Escuse me for my bad english :

Originally Posted by eidos stepper motor works in current ?? HAaaaarggg !!! OHMS law is changed ?

Edios,
I think what he mean't was the L298 alone has no mechanization to do current limiting without the L297 or equavalent circuit. And that you should pay more attention to the current rating of the a stepper motor. He admits english is not his strong point. Heck if I tried to read and answer questions in Italian.......

[contactirfu]

Hi Phil

planning on a board the one u have on ur site the ones with L297 rated at 7 amps for unipolar I found some 3.34 amps per phase unipolars sanyo denki ones resistance aropund 1.1 ohm half coil so what voltage to run at iam weak in electronics just give me the formula or i am too lazy to find it out...... ok then i have the motors do u think ur board will do the job on these motors well if u have any more info on the circuit i mean any documentation like u have for the break out board pls share it out as u have done foir the others ....... do we require a chopper board for the motors when using the board or do u need the resistors in series with the motors well let me know i am polanning on starting the build soon.....

regards

Irfan

[contactirfu]

U know what i am a very bad typist make many typo errors and hit enter before goin thru the typed out words...................

[pminmo]

I have addressed your question on my website board:
http://pminmo.com/phpBB/viewtopic.php?p=98#98