Using the L293D to drive large motors

[Bondfire]

Hi pple,

Is there any1 who has used the L293D motorcontroller IC (or similar)to drive a large motor?

Generally, these IC's are used to drive small motors as they only supply 500mA; however cost being a major factor in my work, i need to use these IC's to drive a motor that draws 3A at no load and 14A at full load.

Is there any way in which i can increase the drive current of the L293D, perhaps using ULN2003A or someother way? I have no alternative but to use the L293D.

Thanks in advance
Bondfire

 

[williB]

is that 14 A continious current..?
because you say that you have no choice but to use the L293D but you are gonna have to use some power transistors on the design with the L293D so why not start with them and go from there...

 

[bloody-orc]

yes you should use a H-bridge with power transistors.
Search googel wor schematics

 

[Bondfire]

Sorry for my ignorance pple but i hadn't any idea that i had to use power
transistors...the L293D is a H bridge driver and all schematics that i have
seen had the IC directly interfaced to (small) motors so i thought that
i could interface it directly to a slightly larger motor by increasing the
drive current of the IC..perphaps using the ULN2003A and then using a pullup resistor to boost the ULN's output current.

Am i totally on the wrong track????

Bondfire

 

[DirtyLude]

What they're saying, is it's easier to get rid of the H-Bridge chip and create your H-Bridge using power transistors. An H-Bridge is not a complex curcuit, and it's easier to create it from scratch using big transistors or MOSFETs rather than trying to up the performance of a L293D.

 

[Bondfire]

Oh that i know...i've used relays and transistors for control circuits they they don't have a very long useful life...so thats why i am using these ICs..thanks anyway

Bondfire

 

[Exo]

integrated H-bridges that can get upto 14A don't exist as far as i know of.
You're far better of building them with a couple of N-channel fet's.
google for H-bridge desing , you'll find lots of hits.

 

[DirtyLude]

Transistors don't have a very long useful life? Why not? (That's not sarcasm, I really don't know)

Most of the H-Bridges now use MOSFET's anyway.

 

[Bondfire]

Sorry i was vague..wot I meant was that students are sometimes careless and accidently burn these Mosfets quite frequently so they have to be changed all the time...i wanted to design a motor controller that students can use without doing that...the L293D has thermal shutdown capability; if it gets too hot, it will just disable itself...that was what i meant by saying Mosfets don't last long....i've seen too many Mosfets getting burnt...beats me how.

 

[Nigel Goodwin]

Sorry i was vague..wot I meant was that students are sometimes careless and accidently burn these Mosfets quite frequently so they have to be changed all the time...i wanted to design a motor controller that students can use without doing that...the L293D has thermal shutdown capability; if it gets too hot, it will just disable itself...that was what i meant by saying Mosfets don't last long....i've seen too many Mosfets getting burnt...beats me how.

You just need to design the controllers acordingly, however making them more 'student proof' will cost a great deal more money!. You might consider buying commercial ones, firms like 4QD sell them, but it's not a cheap item!.

Bear in mind the stall current of your motors, if the off load current is 3A and full load 14A, it's a pretty big motor, stall current it probably going to be something like 100A.

 

[J Paul]

the only way i can see it being done with the chip is to have the chip drive power transistors of some sort, probably the bigger and more robust metal can ones mounted to a really beefy heat sink.

14 amps, just how big is this robot? i'm using a couple of motor/gearbox setups from BG micro (the 9.95 ones) and they draw hardly any power even at full load, yet my robot probably right now weighs in around 30 pounds or so mostly due to the three 6v 10Ah SLA batteries.

 

[gurgalesci]

I concur

I agree with J Paul on the use of large robust metals for working the very large motors. That should give the motors some juice and opportunity to run. Maybe the bigger the motors the better. But, robust metals are the best.

I have a new issue that I need help on: what if your motors are very small, like a volume of only 4 cm small? What should I do then? Should I get non-robust metals to work it? Should I do the opposite of what a large motor would require? Please, someone help me, I need answers to my puzzling question.

 

[J Paul]

something that small should be easily run by the l293's, i'm using just one to drive the two motors on my robot max which i described above. i think last time i checked current draw each motor pulled less than a quarter amp each. no problems whatsoever. yet

i think the rating on the l293's is .5 A per full h-bridge, and since there's two on each chip you're all set.

 

[gurgalesci]

Hey, thanks. I tryed it and it work splendidly.

 

[bryan1]

There's a newer H-bridge driver chip that replaces the L293 it's the SN754410NE chip from TI. This chip can deliver 1 amp to the motors but you can also piggyback them to double the output current. I've found a heap of info on the net and I was lucky enough to get 10 samples to play with.

Cheers Bryan1

 

[Bondfire]

Thx for the tip.

Can you tell me where i can get the schematics for putting 2 of these IC's in parallel for increased current?

 

[J Paul]

all you need to do is set one on top of the other and solder the leads to each other, at least that's what was told to me a while back.

 

[Bondfire]

Thats quite a delicate task...one mite end up burning the IC...is this the
same as putting the 2 IC's in cascade?

 

[J Paul]

not sure.

 

[bryan1]

eh Bondfire checkout this link on stacking the chip https://www.acroname.com/robotics/info/ideas/stacking/stacking.html

cheers Bryan1