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Author Topic: L298n voltage loss  (Read 1840 times)

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Offline Jak24Topic starter

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L298n voltage loss
« on: October 30, 2010, 05:33:32 AM »
Hi!

I just recently realized that the reason that my robot is slower than calculated, could be the voltage loss in the l298n.
I am using a 12v battery to power a (3)12v motors, and turns out the l298n gives the motor only 10.8 , so the loss is 1.2 v.
When my battery is fully charged (13,8 v) then it gives 12.6,
my question is:
Is there any way to get rid of the voltage loss, is there a better h-bridge chip, or are they all pretty much the same?

Thanks

Regards
Jak24


Offline DUKELancelot

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Re: L298n voltage loss
« Reply #1 on: October 30, 2010, 09:47:35 PM »
The LMD18200 H-bridge is what you are looking for. It uses MOSFETs so it doesn't get really hot like the L298 (which uses bi-polar transistors and provides a significant voltage drop to the motor).  It also has built in flyback diodes, so you don't need external diodes like with the L298.  The disadvantage is that there is only 1 H-bridge per package, whereas the L298 has 2 (a dual H-bridge).  This makes the L298 cheaper to use.

Also 1V do you actually thank that will make a difference. Did your calculations take into account weight, fraction and that the rated RPM of your motors is for no load , so under load they will drop a considerably amount like 20-30%.
 :P
« Last Edit: October 30, 2010, 10:07:17 PM by DUKELancelot »
Before you insult someone walk a mile in their shoes. Then your a mile away from them, and have their shoes.

Offline Soeren

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Re: L298n voltage loss
« Reply #2 on: October 31, 2010, 03:17:22 PM »
Hi,

I just recently realized that the reason that my robot is slower than calculated, could be the voltage loss in the l298n.
Easy to test - wire one of the motors around the L298 (i.e. let it get full speed) and compare.
However... Calculating the exact top speed of a vehicle is next to impossible unless ALL factors are known.


Is there any way to get rid of the voltage loss, is there a better h-bridge chip, or are they all pretty much the same?
There are lots of better bridges, but did you consider a relay and a single power MOSFET per motor?
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Jak24Topic starter

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Re: L298n voltage loss
« Reply #3 on: November 01, 2010, 03:09:26 AM »
Hi!
The LMD18200 H-bridge is what you are looking for. It uses MOSFETs so it doesn't get really hot like the L298 (which uses bi-polar transistors and provides a significant voltage drop to the motor).  It also has built in flyback diodes, so you don't need external diodes like with the L298.  The disadvantage is that there is only 1 H-bridge per package, whereas the L298 has 2 (a dual H-bridge).  This makes the L298 cheaper to use.

Also 1V do you actually thank that will make a difference. Did your calculations take into account weight, fraction and that the rated RPM of your motors is for no load , so under load they will drop a considerably amount like 20-30%.
 :P

Yeah that h-bridge might be a better consideration.
Hi,

I just recently realized that the reason that my robot is slower than calculated, could be the voltage loss in the l298n.
Easy to test - wire one of the motors around the L298 (i.e. let it get full speed) and compare.

I tested it like that, i got about 15% more speed


However... Calculating the exact top speed of a vehicle is next to impossible unless ALL factors are known.

Yeah, when i did my calculations I only considered the main factors, and i didn't consider things like:
loss in friction, losses in motor (as it doesn't always preform the nominal speed/torque) etc...

Is there any way to get rid of the voltage loss, is there a better h-bridge chip, or are they all pretty much the same?
There are lots of better bridges, but did you consider a relay and a single power MOSFET per motor?

wouldn't that only allow the motor to turn in one direction?

Thanks

Regards
Jak24
« Last Edit: November 01, 2010, 03:10:40 AM by Jak24 »

Offline Soeren

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Re: L298n voltage loss
« Reply #4 on: November 02, 2010, 04:50:13 PM »
Hi,

I tested it like that, i got about 15% more speed

Oh, then it's surely worth going for a better solution.


There are lots of better bridges, but did you consider a relay and a single power MOSFET per motor?

wouldn't that only allow the motor to turn in one direction?

No, the relay controls the direction and the MOSFET controls the speed.
Here is a circuit I've posted before.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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