8 Channel Relay Board crash

[popop]

Hi,

I'm working on a project using a 8 channel relay board bought here http://dx.com/p/8-channel-5v-relay-modu ... lue-171630
i connected the Relay board Vcc to +5 Rpi and GND to GND Rpi and I use a MCP23017 and ULN2803 to control relay input and it's -most of the time- working (i can turn on and off every relays several times). But sometimes, when i turn off a relay (by sending a command from the pi) ALL activated relays turn off. It happens more when there are more relays activated but i didn't find any rules to explain the problem....

I tried to connect the relay board to an external power supply by just connecting
- Vcc to +5v external
- GND External to GND and GND Rpi

With this configuration relays i got a brighter LEDs and relay seems to be activated more easily. However the relay still crash sometimes..

I'm wondering if i added the external supply correctly.. it's working but maybe not safe?
There are only 10 pins on this board: Vcc, GND and 8inputs. compared to the sainsmart one... I don't have any JD-VCC pin to connect my external supply as explain http://www.raspberrypi.org/phpBB3/viewt ... 99#p297099

Does someone has found similar problem with this type of card? What could be the problem?

Thanks in advance

[joan]

I have a similar board (same Songle relays, different board electronics). Mine takes 70mA from the 5V line for each active relay, so 0.56 amps if all relays are on.

If it fails it's possibly because it needs more power than can be supplied.

[Loonhaunt]

I am not sure but I think that the ability to power that many relays seperate from you 5VDC header pin # X is pretty critical to it working correctly and not eventually cooking your Pi. I have never seen the board you are using in use, so I don't know of it's integrity.

DB

[popop]

I'm not sure that it's a power problem as sometimes the relay crash with only 1 or 2 relays on..
Could it comes from raspberry command signal?Should I power the ULN2803 with a different 5V too?