MadModder
The Shop => Electronics & IC Programing => Topic started by: snub on March 21, 2012, 11:42:36 PM
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I bought a couple of different PWM's and am looking for advice on which one to use. Both were $11.00 ( shipping included! ). The first one is rated at 6 amps and the reason I like it is that it comes enclosed in a case with tabs for easy mounting. I opened the case so I could inspect the guts. Not much in there, and no heat sinks.
(http://i53.photobucket.com/albums/g62/mithslew/PulseWidthModulator003.jpg)
The other side:
(http://i53.photobucket.com/albums/g62/mithslew/PulseWidthModulator002.jpg)
The other one is rated at 10 amps and has 2 large heat sinks and a lot more 'components'...:
(http://i53.photobucket.com/albums/g62/mithslew/PulseWidthModulator005.jpg)
The motor I'm using only draws about 2 amps so either one would work.
I don't know a lot about electronics, but my gut instinct would be that the second one would be a better choice, just based on the fact it has 2 heat sinks and more 'stuff'. But, I could be wrong.
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Try the first one first. If it lets out the electronic smoke, use the second one. Cost $11 to try it.
They are pretty efficient so they usually don't need much in the way of heatsinking. And 2A is not much.
FWIW
Jim
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I like the way how they have tried to disguise those 555 timer chips? would only cost about 50p to repair if they blew
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Hi Snub
unless you need to fit it into a small space , I'd go for the 10A one
the motor may only take 2A when its working
but what does it take at switch on or if you stall the motor ?
John
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Hi Snub
It may be worth checking that the pwm's have a diode accross the motor for back emf protection. The motors are a purely inductive load at turn on and as the pulse is removed will ring up to a high voltage if no clamp diode is present, possibly causing output driver failure.
Hope this helps
Best Regards
picclock
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Thanks for the advice, gentlemen. Not sure if there is a diode in the circuit. There is a component marked 'D4', which I suppose could be one. Here are some better pics:
(http://i53.photobucket.com/albums/g62/mithslew/PWM-E-Bay1.jpg)
(http://i53.photobucket.com/albums/g62/mithslew/PWM-E-Bay2.jpg)
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Snub
Yes, that's a diode. Looks like it may be either a 1N5408 or a UF5408 ..
At least on my pic it looks like an '8' for the last digit.
1000V Vrrm 3A. Good enough .. if it is one.
If you look at the traces under the circuit board, it should be effectively wired across the output terminals, cathode [ end with the bar ] to the positive motor terminal.
In fact, as it has 2 signal diodes and a few other bits, you may well find the contraption is based on the generic 555 Timer Chip PWM schematic.
Similar to this one ... maybe not exactly, but ...
http://www.discovercircuits.com/DJ-Circuits/simplepwm2.htm
It is a common practice to parallel off two [ or more ] MOSFETs to get more grunt .. which may be what you have..
BC
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Hi Snub ,
just to add to Bluechips reply
if the board is designed to work on more than 18V
I expect you will have a voltage regulator to supply the NE555 timer , on one heat sink
and a FET to control your motor on the other
John
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Very good point that, John...
Never occurred to me :scratch:
Which probably explains my habit of re-inventing the Direct Arc Furnace ... :bang: :bang:
:lol:
BC
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Thanks, again. The vendor states that this unit will work on 12-24-36 volts. I'll take a look and see how the diode is wired in.