i have 48 relays (6x8relays modules) form different brands and a mega connecting the 48 on parallel with a 5v 30amps psu but when making the relays on one by one , after the fourth one all the leds go on but with very low light and clicks continued to about the fith relay and no more clicks heard..... 
changed the psu to another 5v 2.5amps but same results , the mega power is usb cable in both trials so i gave up and need help
THNX
i have 48 relays (6x8relays modules) form different brands and a mega connecting the 48 on parallel with a 5v 30amps psu but when making the relays on one by one , after the fourth one all the leds go on but with very low light and clicks continued to about the fith relay and no more clicks heard.....
changed the psu to another 5v 2.5amps but same results , the mega power is usb cable in both trials so i gave up and need help
THNX
Show us a good schematic of your circuit.
Show us a good image of your wiring.
A photo can't tell what you're doing wrong. Please provide a circuit diagram, and data sheet for your relay modules.
minaamir:
i have 48 relays (6x8relays modules) form different brands and a mega connecting the 48 on parallel with a 5v 30amps psu but when making the relays on one by one , after the fourth one all the leds go on but with very low light and clicks continued to about the fith relay and no more clicks heard.....
changed the psu to another 5v 2.5amps but same results , the mega power is usb cable in both trials so i gave up and need helpTHNX
You first write you are using a 30 amp power supply. Then you tell us you get the same results with a 2.5 amp supply. Why?
When you computed the total current required by ALL the relays operating at once, what value did you get?
Paul
Please do not double post on the web site.
This is frowned at and wastes our time.
Do you have a common GND.
Paul_KD7HB:
You first write you are using a 30 amp power supply. Then you tell us you get the same results with a 2.5 amp supply. Why?When you computed the total current required by ALL the relays operating at once, what value did you get?
Paul
thnx,
i dont know why
each relay needs 20-30ma and i did not realize that at first so i used my usual psu
minaamir:
thnx,
i dont know whyeach relay needs 20-30ma and i did not realize that at first so i used my usual psu
Ok, now measure the voltage from your power supply while your program is turning on the relays. Watch the voltage go down as more relays are turned on. Eventually the voltage will be too low to operate more relays.
But, you say, the ratings of the power supply is 1.5 amps. True enough, but many imported power supplies can give the rated voltage or the rated current, but not both at the same time.
Go back to your 30 amp supply and try it again while monitoring the voltage.
Paul
larryd:
Please do not double post on the web site.This is frowned at and wastes our time.
Do you have a common GND.
First of all, sorry about duplicating the post but i did not know where to post inhigh voltage catg. or in the project guidance one so i decided to post it in both.
Second, yes i connected all the GND of the modules to the psu GND
Paul_KD7HB:
Ok, now measure the voltage from your power supply while your program is turning on the relays. Watch the voltage go down as more relays are turned on. Eventually the voltage will be too low to operate more relays.But, you say, the ratings of the power supply is 1.5 amps. True enough, but many imported power supplies can give the rated voltage or the rated current, but not both at the same time.
Go back to your 30 amp supply and try it again while monitoring the voltage.
Paul
so you think the problem is the psu not the mega ???? as many told me that the problem is in the Mega board as it can not supply all the relays with the needed current
Hi,
You have +5V, gnd and -5V.
What are you using the -5V for?
Have you got a DMM?
Is the gnd of the Maga connected to the gnd of the relay PCBs and power supplies?
If so measure the 5V at each of the relay boards and check that all of the gnds are connected together.
Are the gnds and 5V each connected in a star configuration or daisy chained from one board to the other.
Tom.. 
Hi,
Have you checked each relay PCB on its own with the other relay boards completely disconnected and out of circuit?
Some types are positive logic and some negative logic input.
Tom...
TomGeorge:
Hi,
You have +5V, gnd and -5V.What are you using the -5V for?
Have you got a DMM?
Is the gnd of the Maga connected to the gnd of the relay PCBs and power supplies?
If so measure the 5V at each of the relay boards and check that all of the gnds are connected together.
Are the gnds and 5V each connected in a star configuration or daisy chained from one board to the other.Tom..
thnx,
the -5v for some relays as it works with +5v and -5v but when i replaced -5v with GND it also works.
NO the Mega GND is not connected to anything.
shall i connect it with the psu????why??
yes all worked well alone and they are all active low
minaamir:
First of all, sorry about duplicating the post but i did not know where to post inhigh voltage catg. or in the project guidance one so i decided to post it in both.
Second, yes i connected all the GND of the modules to the psu GND
This is how a 5 volt, 8 channel PCB is recommended to be connected:
Hi.
The gnd of the Mega needs to be connected to any gnd terminals you have on the input to the relays to provide a gnd reference for the control signal.
As well as the gnd of your external 5V power supply.
What relay board needs -5V, you have me surprised.
We need to see a schematic of your project, NOT a FRITZY image.
Even if you break your schematic down to a page for each relay board but include the power supply and MEGA in each.
This will help with posting a complex wiring diagram.
Thanks.. Tom...
larryd:
This is how a 5 volt, 8 channel PCB is recommended to be connected:
but i have only one GND and one VCC no JD-VCC how can i connect it ???
Give a link to the relay board you are using.
