a ok , i get it,
By the way , anybody knows why My h_bridge, L298N get really really hot even with a heat sink and just 1.8 amp ?and yes it is connected to the 12v battery. Getting hot, and its not working anymore...
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a ok , i get it,
By the way , anybody knows why My h_bridge, L298N get really really hot even with a heat sink and just 1.8 amp ?and yes it is connected to the 12v battery. Getting hot, and its not working anymore...
Last edited by lerameur; - 14th January 2007 at 23:22.
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Country Fried
Hi Leramuer, sounds like the magic smoke escaped from that device. 12v x 1.8 aOriginally Posted by lerameur
= 21.6 watts, I assume thats the running current under normal load. That figure increases exponentialy when you reverse direction and that's a whole lot of heat. What do you have for a heat sink? Maybe in addition to more heat sink you should put in a thermal shutdown circuit.
JS
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If it was me doing a project needing an H-bridge, I'd skip the H-bridge and just go with a set up using a bunch of logic-level N-channel enhancement mode MOSFETs (try saying that 3 times fast), or P-channel, whatever. That way I know for sure I can drive whatever it is I need to drive. And if the MOSFETs get too hot even after putting a heatsink on them, you can always parallel them. Which gets me to thinking...have you tried paralleling a couple of L298N's? I haven't read the datasheet, don't know if it's possible (or even wise)...might work though.
And 12v @ 1.8a does = 21.6watts, but only if the L298N has resistance across it, zero resistance = zero load. Maybe the L298N isn't being driven hard enough. (Sounds like it's time to get my butt over to the datasheets so I know what I'm talking about here).
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I have a big ass heat sink, about 9 times he size of the chip.
I believe I was under th wattage recommended (or maybe just on it, cause the battery was fully charged at 12.85 and @ 1.9 amp 24.7 watt.
would that of killed it.
I looked at comse circuit for making my own H-bridge, but is seems a bit messy.
I have some IRFZ44N N mos, maybe get their brother P's and work with that, you have any schematic ?
I found this: http://www.armory.com/~rstevew/Publi...d/nch-brdg.htm
but I dont know
update:
I tried one IRFZ44N , it become very hot with just 5watt. I know I can put a heat sink, but this thing is suppose to support 94 watt. Is there somehting I am not getting ??
Last edited by lerameur; - 15th January 2007 at 05:39.
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to go back to my LCD problem , I am not using backlight. I thought you where refering to the contrast adjustment. nothing is connected to th backlight supply. IS this ,my problem , From the other post you mentionned, The gentlemen did not have a problen and the backlight was not connected. Mine does.
Last edited by lerameur; - 15th January 2007 at 06:51.
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Well, like I said, the only way something can dissipate heat is if it has resistance in the first place, zero ohms across a device = zero volts dropped across it = zero watts dissipated in it. If that MOSFET is a standard MOSFET, and you're driving it with 5v, it isn't going to work very well. You need a logic level MOSFET, one that's designed to be driven with 5v. And monster heat sinks only work well up to a point. You can only get rid of so much heat so fast, they got limits too.
Why not post a schematic...we'll get a better idea of what you're up to. (on a side note, I haven't gotten over to the L298N datasheet yet).
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well eventually I would like to use 15v at 2 amps, so that h-bridge might to be ideal for now.
To follow your idea on using MOSfet, I found a web site talking about the IRF540, which is very similar to the one I have IRFZ44N., Except they use Pmos also, I guess I can use 4 Nmos and using an inverter instead of using 2 Nmos and 2 Pmos.
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what about driving one L298 per motor instead of two motors ?
will it be creating less heat ?
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You got it, for the most part. In the end, you get 2 control lines, one for on/off, and one for direction. But, you will have to use 2 N's and 2 P's and an inverter (which you can also use a couple of small MOSFETs and a couple of resistors and make your own inverter from components rather than a 7404), N channel on top, P channel on bottom. Remember (in basic terms), N channel MOSFETs work by applying a ground to a circuit, P channel's apply power to the circuit.
And yes, some snubber caps and protection diodes, just in case. Motors are ugly in some ways...
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I put back the circuit together with one L298.
added caps, Its really hard to make them stick onto the motors, any thoughts?
Also it was not working at first, I realized that my Pic chip was not putting some pins at high. I changed the program so the pin output went from portC to portD and it worked. I reprogrammed the chip a few times, those couple of pins on PortC are not working no more. Can I revived them ? what happened..
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B A
Sounds good, how about some "B/A" bypass capacitors, or snubber diodes to protect those transistors, motors throw off some outrageous spikes which may well cause your bridge to get "Kentucky Fried".
Always better, I think.
Last edited by Archangel; - 15th January 2007 at 21:40. Reason: Add
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