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H bridge l298n in Parallel Burning Out After Some Time

rodolfoviolac

New Member
Hi Guys,

I have a college project where I need to controll a motor (27V / 3 A), I used a H Bridge l298n in parallel to support the current, It worked for while and then stop but I don't know what was wrong. Does any body know anthing that could help me?

The motor is a Maxon 118752 precision brush motor (20 Watts) operating at 27 V max. The motor offers a peak current of 3 A, with a maximum continuous current of 1.2 A.

Spec for the motor:
https://www.made-for-science.com/de/quanser/?df=made-for-science-quanser-2-dof-serial-flexible-joint-usermanual.pdf

My circuit Design:

Screen Shot 2019-12-03 at 8.34.41 AM.png
 

ronsimpson

Well-Known Member
Most Helpful Member
You should read the data sheet about what type of diodes on the output of the L298. The 1N4007s are not right.
 

rodolfoviolac

New Member
ronsimpson can you suggest me what diode I can use? Which schottky diode is good for this?
I have these schottky available: SB360, SB3200, SB5100E, SB560, SB5200, SB3100, 1N5819, 1N5822.
 
Last edited:

ronsimpson

Well-Known Member
Most Helpful Member
I would look for 1A 50V Schottky.
On Schottky diodes, don't put 45V on a 50V part. But 30V on a 50V part is good.
I think the diode will only see 3A for such a short time that a 1A part is fine. (I have little experience on motor drivers)
I just looked at a robot www sight and some people there are using 1A or 2A Schottky diodes. (they are not paralleling two drivers)
------
After rethinking this: If you are ordering parts get 2A. If you have parts try 1A.
I use Digikey.com as a search engine. You can look for Schottky Diode and then sort for 50 to 100V and 1 to 3A and they will give you a long list of parts.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Not sure how hot it gets, it is bigger. Runned for over 20 minutes...

View attachment 121894
Lick your finger, and touch the heatsink - BRIEFLY! - if it's too hot you'll hear a sizzling sound as the saliva boils away. Don't do it without licking (or wetting) your finger, as the thermal inertia of your skin/flesh means it will burn you before you have time to feel it.
 

gophert

Well-Known Member
Most Helpful Member
You are slowly killing one H-bridge, then the other goes instantly.

The L298 is a bipolar H-bridge. That means, as it warms up, the current flow tends to increase. Unfortunately, not all bipolar transistors are the same and each starts out delivering slightly different Vbe and Vce. of the two paralleled H-bridges, one will carry slightly more current than the other. That one that carries more current will warm up faster and carry even more current. Then it will fail. Then the other H-bridge will be overloaded and fail instantly.

solution,
1) assume use a more modern H-bridge driver that can handle the current you need.
Or
2) add a 1 or 2.2 ohm resistor at pins 1,2,3 and 4 of the L298.

Your design is similar to using one resistor to regulate current for two LEDs in parallel. Don't do that!
 

alec_t

Well-Known Member
Most Helpful Member

dr pepper

Well-Known Member
Most Helpful Member
I see the circuit drives the l298 with inverter gates, maybe theres a switching propagation thingy going on and the bridge has a hi & lo side on at the same time briefly.
At the risk of blowing another '298 you could run the circuit without the motor connected, if the '298 still gets hot then this is happening.
A fairly big electro across the 27v might also be good, then when the motor protect diodes conduct the 27v doesnt go all over the place.
 

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