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Author Topic: Too many relays cause voltage drop!  (Read 1443 times)
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Beijing
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Hi there, sorry for my terrible English, but i do have a little problem:
I use Arduino MEGA and W5100 to control 25 relays(OMRON G5LA 5VDC). But it seems too many relays made my voltage drop down. And when voltage drop down, my W5100 doesn't work properly. I use a 220VAC-->5VDC 20A regulator, but there is about only 4.5V when I  measured. On PCB, I wired the vcc of Arduino, W5100's regulator and relay together with 5VDC input. I think my 5V regulator is good enough(expensive enough actually smiley-cry).
I have some ideas like: buy a higher voltage regulator(like 9VDC) or buy another 5V regulator for circuits except relays. But i don't actually know whether it will work out fine.
Does anyone has some ideas how to solve voltage drop down? smiley-eek
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I assume you power the relays directly from the  Mega pins.
I see your relays uses 72mA coil current.
A mega pin should not deliver more than 40 mA
So that is a first problem.
If you have all 25 relays on you need 25*72mA = 1,8A this is far more that the mega can deliver on its pins.
This a second problem.
Both problems can cause voltage drops.
Best regards
Jantje
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Quote
Does anyone has some ideas how to solve voltage drop down?

The arduno tutorial pages should have schematics showing how to control a relay using a transistor.
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i solved the problem by using isolated relays, this relays will get 5V from another power supply directly to the coil of the relay, this will lower the drop down.

the output pin will not get over the 40ma limit

i hope this will help you....
eyal.
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