LMD18245 picstep need help

[zoltan]

Hi,

I need help (again). I could not figure out from datasheet if I can mount two LMD18245 on the same radiator, which means their capsules to be electrically connected. I built 3 picstep modules and the radiator I found out is so big that is covering both LMD18245 and I do not know if I must isolate their capsules or not. Please, help.

Thank you.

Zoltan

[santiniuk]

Zoltan,

If I read your question correctly. Yes you can use a common heatsink for the two LMD's to attach to. I have 3 drivers. i.e 6 LMD's all sharing the same heatsink and working fine.

Cheers

[jwstolk]

i'll have a look...
on page 2 of the PDF, there is an image of the chip, with "PGND" marked on the cooling strip.
are the PGND's of both chips connected in your situation ?

looks like a nice chip! I just build my own (water cooled) H-briges from loose parts.
http://jwstolk.xs4all.nl/i/mill7.jpg

what sort of price are these chips ?
jaap.

[zoltan]

Thank you. Yes. They, pair of two, share the same heatsink.

Zoltan

[eidos]

Originally Posted by zoltan Hi, I need help (again). I could not figure out from datasheet if I can mount two LMD18245 on the same radiator, which means their capsules to be electrically connected. I built 3 picstep modules and the radiator I found out is so big that is covering both LMD18245 and I do not know if I must isolate their capsules or not. Please, help. Thank you. Zoltan

hi zoltan
can I help you? : -)
the mount surface that serves to dissipate the heat is electrically connected to the pin "5" PGND,
what the GND of the feeding of the motors is and has to be connected to the SGND.
you can connect together then on the same squanderer the 3 bridge without problems.

hi

[zoltan]

Hi,

Thank you all of you for help. I do not know the exact price of LMD18245, but they are expensive; extremely expensive for me if I would buy. These chips I got them for free.
Zoltan

[jwstolk]

Originally Posted by zoltan Hi, ... they are expensive; extremely expensive ... Zoltan

oh good :-) I spend about 20 euro / motor, would be a pitty if there is a chip for less...
and i noticed that most (cheap) H-bridge chips are limited to about 12 V, while i needed
at least 35V to get any current at all into my 12V motors at high speed.

[Garfield2]

Originally Posted by zoltan price of LMD18245, but they are expensive; extremely expensive for me if I would buy. These chips I got them for free.

Ahh I have a tube of 18 of them here, they're not that expensive considering what they do in such a small package. Also it depends greatly on where you get them from.

Unfortunately there isn't such a thing as a free lunch (at least without catches), if you want a good device with many features you have to be willing to part company with a little bit of cash. I've found that to build a complex circuit using many discrete components in an attempt to try and save money, I always end up spending much more money in dollars and time than I would by just simply buying the part I originally considered to be "to expensive" in the first place.

I'm suffering that same problem with my CNC mill, I've spent all this money on decent bearings, rails and steppers only to build the rest of the machine out of MDF and use all-thread for screws just to save a few dollars.

I'm now waiting till I can afford ballscrews and plate aluminium before I start to build and get the maximum value out of all my components rather than skimping on a few and wasting the money I've spent on the parts I have.

Cheers,
Alan.

[zoltan]

Hi Alan,

You are right and I fully agree with your point. "I am too poor to buy cheap stuff" a friend of mine is repeating all the time to me. Myself, I said too expensive for me considering my financial resources. Sometimes and for some people the budget constraints or limited finance is an answer to the question: "TO BE OR NOT TO BE?"

I am sure you agree. Otherwise, using LMD18245 is a very nice experience and it is a very efficient and good solution.

Zoltan

[jwstolk]

Originally Posted by Garfield2 ....they're not that expensive considering what they do in such a small package. Also it depends greatly on where you get them from.

I looked it up, about 16 Euro at Farnell, witch is indeed not bad for what it does.
I overlooked the LMD18245, as it is in a bit strange place in there catalogue. But i still think
i spend way less on parts, since you need two LMD18245's for each motor + all other
parts (big capacitors, cooling plate, etc.).

the TIP122/127 I used for the the H-bridges are about 1 Euro each, same for the big
BU208. (but that's not counting time of course)
jaap.

[eidos]

Originally Posted by zoltan Hi, Thank you all of you for help. I do not know the exact price of LMD18245, but they are expensive; extremely expensive for me if I would buy. These chips I got them for free. Zoltan

hi
I am completely of accord on how much you say
that motor drivers and very expensive, and keeping in mind that on a cutter cnc, at the most the half step can be used, the money spent for that microstep ICs is lost in departure.
in fact on my drivers alone use H bridge ST series, economic and efficient.
hi

[Garfield2]

Originally Posted by eidos I am completely of accord on how much you say that motor drivers and very expensive, and keeping in mind that on a cutter cnc, at the most the half step can be used, the money spent for that microstep ICs is lost in departure. in fact on my drivers alone use H bridge ST series, economic and efficient.

You've obviously never had resonance issues or used a microstepping driver before. Once you've had resonance eatting your motor torque with a full/half step drive and you switch to a microstepping one, you'll never go back to full/half again!

Cheers,
Alan.